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Development of an Ohmic Thawing Apparatus for Accurate Measurement of Electrical Resistance


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D EV EL O PM EN T O F A N O H M IC TH A W IN G A PP A R A TU S F O R A C C U R A TE ME A S URE ME NT OF ELE CT RI CA L RES I S T A NCE By R A N D Y A L L EN C L EM EN TS A DIS SE RTA T ION PRE SE NTE D TO T HE GRA DUA T E SCHOO L OF T HE UNI VERSI T Y OF F L OR IDA IN P A RTI A L F UL F ILL M E NT OF T HE RE QUIREMENT S F OR T HE DE GR E E OF DOC T OR OF PHI L OSOPHY UNIVE RSIT Y OF F L OR IDA 2006

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Co py ri gh t 2006 by R a n d y A l l e n C l e m e n ts

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T o my w ife T a mmy a n d my s o n s K yle a n d A u s t in

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iv A C K N O W L ED G M EN TS M a ny i nd i vi d u a l s t ha t ha ve m a d e t hi s w o r k p o s s i bl e T he r e a r e m o r e t ha n c a n be r e a s o n a b ly l is t e d b u t I w o u ld lik e t o e x t e n d s p e c ia l t h a n k s t o D r M u r a t O B a la b a n fo r h is e n c o u r a g e me n t s u p p o r t a n d g u id a n c e in c o mp le t in g t h is w o r k I a m in d e b t e d t o my g r a d u a t e c o mmi t t e e fo r t h e ir p a t ie n c e a n d p e r s is t e n c e I a ls o w is h t o t h a n k D r R a n d o lf H ook f or h i s f r i e n d s h i p h e l p a n d e n g a g i n g c on v e r s a ti on s on th i s r e s e a r c h C om p l e ti on of t hi s w o r k w o u l d no t ha ve be e n p o s s i bl e w i t ho u t t he s u p p o r t o f m y f a m i l y t hr o u g ho u t t he p roce s s

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v TA B L E O F C O N TEN TS page A C K N O W L E D G M E N T S .............................................. iv L I S T O F T A B L E S .................................................. v iii L I S T O F F I G U R E S................................................... ix L I S T O F O B J E C T S .................................................. xi A B S T R A C T ....................................................... x iii C H A PTER 1 I N T R O D U C T I O N ................................................. 1 2 L I T E R A T U R E R E V I E W ............................................ 3 T r a d i t i o n a l H e a t i n g ................................................. 3 V o l u m e t r i c H e a t i n g ................................................ 4 M i c r o w a v e ................................................... 4 O h m i c ...................................................... 5 H i s t o r i c a l O v e r v i e w o f O h m i c H e a t i n g .................................. 5 O h m i c T h a w i n g ................................................... 9 3 M A T E R I A L S A N D M E T H O D S ..................................... 13 P h y s i c a l T e s t S a m p l e .............................................. 13 G e l T y p e ................................................... 13 S a m p l e C e l l ................................................. 14 C y l i n d r i c a l h o u s i n g ........................................ 14 I n t e r i o r i n s u l a t i o n .......................................... 15 E x t e r i o r i n s u l a t i o n ......................................... 16 E l e c t r o d e s ............................................... 16 E n d c a p s ................................................ 17 P r o b e s .................................................. 18 C e l l H o l d e r ................................................. 20 T e m p e r a t u r e C o n t r o l C h a m b e r ................................... 21 P o w e r S u p p l y ................................................ 22

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vi C o n t r o l ................................................. 22 M a n u a l c o n t r o l ........................................... 23 A u t o m a t e d c o n t r o l ......................................... 23 A l t e r n a t i v e d i r e c t c u r r e n t .................................... 23 L e a d s a n d p l u g s ........................................... 24 D a t a C o l l e c t i o n H a rd w a re a n d Sof t w a re . . . . . . . . . . . . . . . . 24 D a t a A c q u i s i t i o n C a r d ......................................... 24 I n t e r f a c i n g ............................................... 24 B a c k p l a n e ............................................... 25 S i g n a l C o n d i t i o n i n g ........................................... 25 S i g n a l C o n d i t i o n i n g H o u s i n g .................................... 26 D a t a L o g g i n g D i g i t a l M u l t i m e t e r ................................. 27 S o f t w a r e ................................................... 28 D a t a c o l l e c t i o n ............................................ 28 D a t a v i s u a l i z a t i o n ......................................... 29 E q u i p m e n t C a r t .................................................. 29 A p p a r a t u s C o n s t r u c t i o n ............................................ 31 P r o b e C o n s t r u c t i o n ........................................... 31 D e s i g n .................................................. 31 A s s e m b l y ................................................ 32 S a m p l e C e l l C o n s t r u c t i o n ....................................... 34 D e s i g n .................................................. 34 A s s e m b l y ................................................ 36 S a m p l e C e l l H o l d e r C o n s t r u c t i o n ................................. 39 D e s i g n .................................................. 39 A s s e m b l y ................................................ 39 S i g n a l C on d i ti on i n g H ou s i n g C on s tr u c ti on . . . . . . . . . . . . . 41 D e s i g n .................................................. 41 A s s e m b l y ................................................ 41 A p p a r a t u s W i r i n g ............................................. 42 P o w e r .................................................. 43 M e t e r s .................................................. 46 B a c k p l a n e ............................................... 47 S c r e w t e r m i n a l p a n e l ....................................... 48 E x p e r i m e n t a l M e t h o d s ............................................. 49 D a t a C o l l e c t i o n .............................................. 50 L a p t o p c o m p u t e r .......................................... 50 D a t a l o g g i n g d i g i t a l m u l t i m e t e r ............................... 51 L a b o r a t o r y n o t e b o o k ....................................... 52 T e m p e r a t u r e P r o b e C a l i b r a t i o n ................................... 52 G e l P r e p a r a t i o n .............................................. 54 G e l D e n s i t y D e t e r m i n a t i o n ...................................... 55 F r e e z i n g .................................................... 56 E n v i r o n m e n t C h a r a c t e r i z a t i o n ................................... 58 C o n t i n u o u s R u n n i n g ....................................... 58

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v ii C y c l i n g ................................................. 59 T h e r m a l D a m p i n g ......................................... 59 A u t o m a t i c P o w e r C o n t r o l M e t h o d ................................ 60 R e l a y s e t u p .............................................. 60 P o w e r c o n t r o l v a l i d a t i o n .................................... 61 R e s i s t a n c e M e a s u r e m e n t ....................................... 62 U n f r o z e n s a m p l e .......................................... 62 F r o z e n s a m p l e ............................................ 64 O h m i c T h a w i n g .............................................. 66 4 R E S U L T S A N D D I S C U S S I O N ...................................... 69 D a t a C o l l e c t i o n ................................................... 69 T e m p e r a t u r e C a l i b r a t i o n ............................................ 70 T h e o r e t i c a l .................................................. 70 E x p e r i m e n t a l ................................................ 72 E x p e r i m e n t a l G e l ................................................. 81 T o t a l M a s s P e r c e n t ........................................... 81 D e n s i t y .................................................... 81 F r e e z i n g .................................................... 82 E n v i r o n m e n t a l C h a r a c t e r i z a t i o n ...................................... 84 A u t o m a t i c P o w e r C o n t r o l V a l i d a t i o n .................................. 87 R e s i s t a n c e M e a s u r e m e n t ............................................ 88 U n f r o z e n G e l ................................................ 88 F r o z e n G e l .................................................. 96 C o m b i n e d T e m p e r a t u r e R a n g e s ................................. 100 O h m i c T h a w i n g ................................................. 101 E r r o r A n a l y s i s ................................................... 109 T e m p e r a t u r e ............................................... 109 R e s i s t a n c e ................................................. 111 5 CO NC L USI ONS A ND R E CO M M E NDA T IONS . . . . . . . . . . . . 117 A PP EN D IX A A L T E R N A T E N E U M A N N S S O L U T I O N ............................ 119 B T E M P E R A T U R E E R R O R ......................................... 123 C R E S I S T I V I T Y E R R O R ........................................... 124 R E F E R E N C E S ..................................................... 127 B I O G R A P H I C A L S K E T C H ........................................... 131

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v iii L IS T O F TA B L ES T ab l e page 4 1 C a l i b r a t i o n O f f s e t V a l u e s ........................................... 75 4 2 P e r c e n t o f T o t a l M a s s o f G e la t in in G e l. . . . . . . . . . . . . . . . . 81 4 3 G e l D e n s i t y ..................................................... 82

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ix L IS T O F F IG U R ES F i gures pa ge 3 1 C y l i n d r i c a l H o u s i n g ............................................... 15 3 2 S k e t c h o f P V C C e l l ............................................... 16 3 3 E l e c t r o d e S k e t c h a n d P i c t u r e ........................................ 17 3 4 P r o b e S k e t c h .................................................... 19 3 5 P r o b e A s s e m b l y B e n c h R a i l ......................................... 2 0 3 6 S a m p l e C e l l H o l d e r ............................................... 21 3 7 H o u s i n g ......................................................... 27 3 8 B o x A r r a n g e m e n t ................................................ 30 3 9 S h e l l W i t h P o r t s ................................................. 37 3 -1 0 Sa m p l e H o l d e r P i c t u re F ron t a n d Si d e V i e w s . . . . . . . . . . . . . . 40 3 1 1 D e t a i l e d S a m p l e P o w e r W i r i n g ..................................... 45 312 P r o b e P o si t i o n s an d Na m i n g Co n v en t i o n s. . . . . . . . . . . . . . . 53 3 1 3 R e l a y s ........................................................ 61 3 1 4 A d d i t i o n a l F i b e r g l a s s I n s u l a t i o n ..................................... 65 4 1 C a l i b r a t i o n S e t u p F e a t u r e s .......................................... 73 4 2 P r o b e C a l i b r a t i o n D a t a ............................................ 74 4 3 C a l i b r a t i o n W a r m i n g D a t a .......................................... 76 4 4 C a l i b r a t i o n N o i s e .................................................79

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x 4 5 N o i s e U n d e r H i g h V o l t a g e ......................................... 80 4 6 T e m p e r a t u r e C y c l i n g .............................................. 85 47. Cy cl i n g an d A dj acen t P r o b e T em per at ur e Di f f er en ces. ..................... 87 4-8. Sam pl e an d E n v i ro n m en t al W arm i n g. .................................. 88 49. Un f r o zen Gel T em per at ur e, Vo l t age and Cur r en t P l o t s. . . . . . . . . . . 90 410 Un f r o zen Gel T em per at ur e, Vo l t age and Cur r en t P l o t s. . . . . . . . . . 91 4 1 1 U n f r o z e n G e l R e s i s t a n c e .......................................... 92 4-12. Un f ro zen Gel Re s i s t i v i t y an d M ax i m um T em perat ure Di f f eren ce. . . . . . . 93 4-13. Un f ro zen Gel Re s i s t i v i t y Be f o re an d A f t er F reezi n g. . . . . . . . . . . . 94 4 1 4 U n f r oz e n R e s i s ti v i ty w i th C u b i c P ol y n om i a l F i t. ........................ 95 415 F r o zen Gel T em per at ur e, Vo l t age and Cur r en t P l o t s. .................... 97 4 1 6 F r o z e n G e l s R e s i s t a n c e ........................................... 98 4-17. F ro zen Re s i s t i v i t y an d M ax i m um T em perat ure Di f f eren ce. . . . . . . . . .99 4 1 8 F r oz e n R e s i s ti v i ty w i th C u b i c P ol y n om i a l F i t. . . . . . . . . . . . . . 100 419 Un f r o zen an d Fro zen Resi st i v i t y Cub i c F i t s. . . . . . . . . . . . . . 101 4-20. Oh m i c Th awi n g Vo l t age a n d Curren t Dat a. . . . . . . . . . . . . . 103 4 2 1 O h m i c T e m p e r a t u r e D a t a ........................................ 105 4-22. Oh m i c Tem perat ure an d Curren t Dat a. . . . . . . . . . . . . . . . 106 4-23. Oh m i c A pparen t Re s i s t i v i t y an d M ax i m um T em perat ure Di f f eren ce. . . . . 109 4 2 4 P o w e r A p p l i e d .................................................. 110 4 2 5 F r o z e n R e s i s t i v i t y E r r o r .......................................... 113 4-26. F ro zen Re s i s t i v i t y E rr o r an d M ax i m um T em perat ure Di f f eren ce. . . . . . 114 4 2 7 U n f r o z e n R e s i s t i v i t y E r r o r ........................................ 115

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xi L IS T O F O B J EC TS Ob j ect s page 3 1 P V C C e l l j p g .................................................... 15 3 2 S a m p l e C e l l j p g ................................................... 16 3 3 E l e c t r o d e S k e t c h j p g ............................................... 17 3 4 P r o b e j p g ....................................................... 19 3 5 P r o b e B e n c h j ................................................... 20 3 6 S a m p l e H o l d e r j p g ................................................. 21 3 7 T o w e r L a p t o p j p g ................................................ 27 3 7 D e t a i l e d P o w e r C i r c u i t 2 L a b e l s j p g ..................................... 45 4 1 C a l 3 8 5 x 1 1 j p g .................................................. 74 4 2 C a l 6 8 5 x 1 1 j p g .................................................. 76 4 3 C a l N o i s e 3 j p g ...................................................79 4 4 H i g h V o l t a g e N o i s e j p g ............................................. 80 4 5 C y c l i n g A l l M a r 2 2 j p g .............................................. 85 4 6 C y c 1 5 1 3 D i f f A l l j p g ...............................................87 4 7 W a r m i n g A l l j ................................................... 88 4 8 U F R e s i s t T V C 1 j p g .............................................. 90 4 9 U F R e s i s t T V C 2 j p g .............................................. 91 4 1 0 U F R e s i s t A l l J P G ................................................ 92

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x ii 4 1 1 U F R e s i s t y M T D i f f A l l j p g ......................................... 93 4-12. UF _Re s i s t y _M T Di f f _A l l _Sep10. j pg . . . . . . . . . . . . . . . . . 94 4 1 3 U F R e s i s t y A l l w F i t j p ........................................... 95 4 1 4 F r o z e n R e s i s t T V C j p g ........................................... 97 4 1 5 F r o z e n R e s i s t A l l j p g............................................. 98 4-16. F ro zen _Re s i s t y _M T Di f f 21-10. j pg . . . . . . . . . . . . . . . . . 99 4 1 7 F r o z e n R e s i s t y A l l w F i t j p g ....................................... 100 4 1 8 R e s i s t y F i t s B o t h j p g .............................................. 101 4 1 9 O h m i c V C j p g .................................................. 103 4 2 0 O h m i c T e m p B o t h j p g ............................................ 105 4 2 1 O h m i c C u r r e n t T e m p B o t h j p g ...................................... 106 4 2 2 O h m i c R e s i s t y A v e T e m p M T D j p g ................................... 109 4 2 3 O h m i c P o w e r A p p C u m u j p g ........................................ 110 4 2 4 E r r o r P e r c F r o z R e s i s t y B o t h j p g ..................................... 113 4 2 5 E r r o r P e r c F r o z M T D R e s i s t y j p g ..................................... 114 4 2 6 E r r o r P e r c U n f r o z R e s i s t y A l l j p g ..................................... 115

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x iii A b s tr a c t of D i s s e r ta ti on P r e s e n te d to th e G r a d u a te S c h ool o f t he U ni ve r s i t y o f Fl o r i d a i n P a r t i a l Fu l f i l l m e nt o f t he R e q u i r e m e nt s f o r t he D e g r e e o f D o c t o r o f P hi l o s o p hy D EV EL O PM EN T O F A N O H M IC TH A W IN G A PP A R A TU S F O R A C C U R A TE ME A S URE ME NT OF ELE CT RI CA L RES I S T A NCE By R a n d y A l l e n C l e m e n ts M ay 2006 Ch ai r: M urat O. Bal ab an D e p a r t m e nt : Ag r i c u l t u r a l a nd B i o l o g i c a l E ng i ne e r i ng H e a t i ng o c c u r s w he n a n e l e c t r i c a l c u r r e nt i s p a s s e d t hr o u g h a n o bj e c t T he a m o u nt o f he a t g e ne r a t e d i n t he o bj e c t i s d e p e nd e nt o n t he e l e c t r i c a l r e s i s t a nc e o f t he ob j e c t. T h i s f or m of h e a ti n g i s c om m on l y r e f e r r e d to a s oh m i c h e a ti n g T h e a p p l i c a ti on of t h is h e a t t o a fr o z e n o b je c t t o c h a n g e t h e ma t e r ia l p h a s e fr o m fr o z e n t o u n fr o z e n is o h mic t h awi n g. T h e el ect ri cal resi s t an ce o f a f o o d i s h eav i l y i n f l uen ced b y t em perat ure. F o o ds u n d e r g o in g t h a w in g c o mmo n ly e x h ib it t w o o r d e r s o f ma g n it u d e d e c r e a s e in t h e ir r e s is t a n c e A c c u r a t e k n o w le d g e o f t h e e le c t r ic a l r e s is t a n c e is v it a l t o p r a c t ic a l o h mic a p p l i c a t i o n s i n f o o d p roce s s i n g T hi s r e s e a r c h p r e s e nt s t he d e ve l o p m e nt o f a n a p p a r a t u s f o r m e a s u r i ng t he e l e c tr i c a l r e s i s ta n c e of a f ood i te m i n b oth i ts f r oz e n a n d u n f r oz e n s ta te s A m od e l f ood s u b s ta n c e w a s u s e d to i l l u s tr a te th e c a p a b i l i ti e s of th e a p p a r a tu s T h e m od e l f ood

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x iv s ub s t an ce us ed i n t h i s rese arch was a gel at i n gel T h e el ect ri cal resi s t an ce o f t h e gel was m e a s u re d i n b o t h t h e f roze n a n d u n f roze n s t a t e Th e re s i s t a n c e d a t a f o r t h e g e l w e re c o nve r t e d t o r e s i s t i vi t y d a t a T he r e s i s t i vi t y d a t a f o r t he f r o z e n g e l w e r e f i t t e d w i t h a cub i c po l y n o m i al (y = -35. 9628 x + 162.3497 x 526. 1101 x + 67.9648) wh ere y was 32 t he r e s i s t i vi t y i n o hm m e t e r s a nd x w a s t he t e m p e r a t u r e i n d e g r e e s C e l s i u s w hi l e t he f roze n re s i s t i v i t y d a t a w e re f i t t e d w i t h (y = -0 .0 0 0 4 x + 0 .0 2 7 0 x 1 .0 9 6 0 x + 3 1 .3 9 3 9 ). 32 T h e f i t s gen erat ed R v al ues o f 0. 9977 an d 0. 9953, respe ct i v el y T h e erro rs as s o ci at ed 2 w i t h t h e d a t a a n d t h e f i t s w e re d i s c u s s e d a n d p re s e n t e d It w a s s h o w n t h a t t e m p e ra t u re m e a s u r e m e n t e r r or w a s a n i m p or ta n t a s p e c t i n th e a c c u r a c y of th e r e s i s ti v i ty d a ta cal cul at ed. T h i s r e s e a r c h p r od u c e d a u s e f u l a p p a r a tu s f or m e a s u r i n g a n i m p or ta n t f ood pro pert y i n t h e appl i cat i o n o f o h m i c t h awi n g. T h e res earch al s o pro v i ded n ew da t a i n an a r e a w h e r e v e r y l i ttl e p u b l i s h e d d a ta e x i s ts T h i s d a ta w i l l p r ov e u s e f u l to th e f ood en gi n eeri n g co m m un i t y f o r b o t h f ut ure co m parat i v e an d m o del i n g purpo s es i n t h e f urt h er d e v e lo p me n t o f o h mic h e a t in g t e c h n o lo g y.

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1 CHA P T E R 1 INT RO DUC T ION L ow te m p e r a tu r e s tor a g e of f ood m a te r i a l s i s a c om m on m e th od of f ood p re s e rv a t i o n Th e l o w t e m p e ra t u re s u s e d a re o f t e n i n t h e f roze n ra n g e o f a f o o d p rodu c t T he s e t e m p e r a t u r e s r e d u c e t he a c t i vi t y o f m i c r o o r g a ni s m s a nd e nz y m e s ( B a i r d a nd G r e s s g o t t 1 9 7 8 ) As a r e s u l t t he f r e e z i ng o f f o o d s ha s be e n e xt e ns i ve l y s t u d i e d C l e l a nd a n d E a r l e ( 1 9 8 4 ) r e p or te d th a t th e p u b l i s h e d w or k d on e w i th j u s t f r e e z i n g ti m e p r e d i c ti on m e t ho d s ha s hu nd r e d s o f c o nt r i bu t o r s P r e d i c t i o n o f f r e e z i ng p he no m e no n i s i m p o r t a nt b e c a u s e t h e d e s i g n o f c o m m e rc i a l p roce s s e s w i t h o u t t h i s k n o w l e d g e l e a v e s o n l y l a b o ra t o ry a n d p i l ot s c a l e e x p e r i m e n ts to m a k e d e s i g n d e c i s i on s T h e s e a r e n ot e l i m i n a te d w i th predi ct i v e ab i l i t i es b ut can b e reduce d f o r t o a m i n i m um f o r co s t s av i n gs (Hel dm an 1983) a nd o p t i m i z a t i o n o f p r o c e s s d e s i g n. F o r t h e purpo s e o f m o del i n g f reezi n g, Si n gh (1994) repo rt ed t h at t h ere are s ev eral key pro pert i es o f f o o ds t h at m us t b e t aken i n t o co n s i derat i o n He l i s t ed am o n g t h es e key p rope rt i e s : d e n s i t y t h e rm a l c o n d u c t i v i t y e n t h a l p y s p e c i f i c h e a t a n d t h e rm a l d i f f u s i v i t y S i n g h a l s o r e p or te d th a t th e r e h a v e b e e n s e v e r a l m a j or r e v i e w s of r e p or te d d a ta on p u b l i s h e d l i te r a tu r e f or s om e of th e s e p r op e r ti e s a s w e l l a s a c om p u te r i z e d d a ta b a s e f or t h e pub l i s h ed dat a t h at h e dev el o ped i n 1993. A l l o f t h e wo rk o n f reezi n g h as h el ped c om m e r c i a l f r e e z i n g b e c om e a r e l a ti v e l y e f f i c i e n t a n d r e a s on a b l y u n d e r s tood p r oc e s s f or t h e f o o d i n d u s t ry

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2 H e n d ri c k s a n d o t h e rs (1 9 8 8 ) re p o rt e d t h a t i n t h e p a s t f re e z i n g h a s b e e n m o re i m po rt an t t h an t h awi n g, b ut due t o great er quan t i t i es o f f ro zen f o o d recei v i n g f urt h er p r o c e s s i ng by m a nu f a c t u r e r s t ha w i ng w a s g a i ni ng m o r e i nd u s t r i a l i nt e r e s t T ha w i ng o perat i o n s are n o t s i m pl y i n v erse f reezi n g o perat i o n s T h awi n g o f f ro zen f o o ds b ri n gs s ev eral un i que pro b l em s t h at f reezi n g do es n o t ex h i b i t It al s o h as ph y s i cal m et h o ds t h at h av e n o f r eezi n g co r o l l ar y T h i s re sear ch ex am i n ed o n e o f t h o se m et h o ds. O h m i c th a w i n g u s e s th e e l e c tr i c a l r e s i s ta n c e of a f r oz e n f oo d p r od u c t to v o l um et ri cal l y gen erat e t h e h eat requi red f o r t h awi n g wi t h i n t h e f o o d pro duct i t s el f as an e l e c t r i c a l c u r r e nt i s p a s s e d t hr o u g h t he f o o d p r o d u c t T he e l e c t r i c a l r e s i s t a nc e o f t he f ro zen f o o d pro duct i s addi t i o n al kn o wl edge n o t requi red b y a f reezi n g pro ces s A di rect r e s u l t o f t hi s i nc l u d e d ve r y l i t t l e p u bl i s he d d a t a o n a k e y p r o p e r t y ne e d e d f o r p r e d i c t i ve mo d e lin g o f o h mic t h a w in g T h is r e s e a r c h d e v e lo p e d a n e x p e r ime n t a l a p p a r a t u s c a p a b le o f m e a s u r i ng t hi s k e y p r o p e r t y f o r a g e l i n bo t h t he f r o z e n a nd u nf r o z e n s t a t e s T he apparat us dev el o ped wa s al s o capa b l e o f perf o rm i n g o h m i c t h awi n g. In t h i s s eco n d m o de i t can gat h er dat a s i m ul t an eo us l y f o r t i m e, t em perat ure an d resi s t an ce t h at wo ul d b e us ef ul f o r m o d e l v e ri f i c a t i o n o f p re d i c t i v e m e t h o d s t o b e d e v e l o p e d f o r oh m i c t h a w i n g

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3 CHA P T E R 2 L ITER A TU R E R EV IEW T r adi tiona l He ating T r a d i ti on a l m e th od s of h e a ti n g f oo d p r od u c ts i n v ol v e a p p l y i n g th e r m a l e n e r g y to t h e s urf ace o f t h e pro duct T h e t h erm al en ergy i s del i v ered t o t h e s urf ace b y di rect e x p os u r e to a th e r m a l l y r a d i a ti v e s ou r c e or b y d i r e c t c on ta c t w i th a f l u i d g a s or s ol i d of hi g he r t e m p e r a t u r e T he s e he a t d e l i ve r y m e t ho d s a c c o u nt f o r r a d i a t i ve c o nve c t i ve a nd c o nd u c t i ve bo u nd a r y c o nd i t i o ns a t t he f o o d s u r f a c e O nc e t he e ne r g y i s a p p l i e d t he s urf ace t em perat ure wi l l ri s e an d h eat wi l l b egi n t o f l o w i n t o t h e pro duct T h e en ergy t r a ns f e r no w w i l l be g o ve r ne d by t he r m a l c o nd u c t i o n. T he he a t f l o w c a n be d e s c r i be d by t h e f o l l o wi n g d i f f e ren t i a l e qu a t i o n : I n t hi s e q u a t i o n k i s t her m a l c o nd u c t i vi t y ; T i s t e m p e r a t u r e ; r is t h e p o s it io n v e c t o r ; t is p t i m e D i s d e n s i ty ; C i s s p e c i f i c h e a t. T h i s e q u a ti on i n d i c a te s th e l i m i ts of th e r a te of t e mp e r a t u r e c h a n g e in t h e fo o d p r o d u c t T h e t h e r ma l c o n d u c t iv it y, d e n s it y, a n d s p e c ific h e a t i n e q u a ti on ( 1 1 ) a r e p r op e r ti e s i n h e r e n t to a g i v e n f ood p r od u c t. O n e m e th od of i nd u c i ng hi g h r a t e s o f t e m p e r a t u r e c ha ng e i s by u s i ng ve r y hi g h t e m p e r a t u r e s a t t he s urf ace Sur f ace t em perat ures f o r f o o d pro duct s are l i m i t ed b y t h erm al s en s i t i v i t y f o o ds h a v e i n th e i r s tr u c tu r a l a n d or g a n ol e p ti c p r op e r ti e s A n oth e r m e th od i s to r e d u c e th e p a th f o r co n duct i o n h eat t ran s f er. T h i s can b e ac h i ev ed b y f o rci n g t h e f o o d pro duct t o h av e a s h a p e t h a t p r e s e n t s a v e r y s h o r t c o n d u c t io n p a t h T h is c a n b e a v ia b le o p t io n fo r c e r t a in l i qu i d f o o d p r o du ct s, b ut gen er al l y n o t f o r so l i d f o o d p r o du ct s.(1-1)

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4 Vo l um e tr ic He ating V o l u m e t r i c he a t i ng d o e s no t s u f f e r t he s a m e l i m i t a t i o ns a s t r a d i t i o na l he a t i ng m e t ho d s Wi t h vo l u m e t r i c he a t i ng t he he a t s o u r c e i s i nt e r na l t o t he f o o d p r o d u c t T he en t i re v o l um e o f t h e f o o d i s s t i m ul at ed b y an ex t ern al en ergy s o urce t o pro duce h eat i n t ern al l y T h e ex t ern al en ergy can b e del i v ered b y el ect ro m agn et i c wa v es T h es e i n cl ude h ig h fr e q u e n c y w a v e s mic r o w a v e s a n d r a d io w a v e s T h e s e e le c t r o ma g n e t ic w a v e s w o u ld al s o i n cl ude f requen ci es at wh i ch el ect ri ci t y i s co m m erci al l y t ran s m i t t ed an d ev en di rect e l e c tr i c a l c u r r e n t. M icr owave M i c r ow a v e h e a ti n g h a s r e c e i v e d th e m os t s tu d y a n d a p p l i c a ti on i n r e l a ti on to h e a ti n g f ood p r od u c ts M i c r ow a v e h e a ti n g r e q u i r e s n o d i r e c t c on ta c t w i th th e f ood p rodu c t b u t d o e s re q u i re t h e f o o d p rodu c t t o b e e n c l o s e d s o t h e m i c rowa v e s a re co n t ai n ed f o r h um an s af et y T h e us e o f m i cro wav es i s l i m i t ed b y h o w t h ey are ab s o rb ed b y t h e f o o d m at eri al T h e dept h o f pen et rat i o n i s l i m i t ed f o r m i cro wav es an d wat er can pref eren t i al l y ab s o rb t h em T h e pref eren t i al ab s o rpt i o n b y wat er h as b een t h o ugh t t o b e a ma jo r c a u s e fo r lo c a liz e d o v e r h e a t in g ( L i a n d S u n 2 0 0 2 ) L o c a liz e d o v e r h e a t in g is r e f e r r e d t o a s r u na w a y he a t i ng I t i s c a l l e d r u na w a y he a t i ng be c a u s e i t ha s a c a s c a d i ng e ffe c t T h e a b s o r p t io n p r o p e r t ie s t e n d t o in c r e a s e a s t h e t e mp e r a t u r e r is e s a n d a s a r e s u lt ev en m o re en ergy i s ab s o rb ed b y t h e l o cal i zed a rea. T h i s t h en l eads t o a great er t e m p e r a t u r e r i s e a nd a bs o r p t i o n p r o p e r t i e s be c o m i ng e ve n m o r e f a vo r a bl e d r i vi ng t he lo c a l h e a t in g p r o c e s s o u t o f c o n t r o l t o fo o d d a ma g in g t e mp e r a t u r e s C o n t r o l o f t h is p h e n om e n on w h e n d r i v e n b y m i c r ow a v e s i s v e r y d i f f i c u l t.

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5 Ohm ic O hm i c he a t i ng u nl i k e m i c r o w a ve r e q u i r e s s o m e t y p e o f d i r e c t c o nt a c t w i t h t he f o o d p r o d u c t O hm i c he a t i ng u s e s e l e c t r i c a l e ne r g y t o d r i ve t he vo l u m e t r i c he a t i ng p roce s s In o h m i c h e a t i n g t h e f o o d p rodu c t a c t s a s a re s i s t o r i n a n e l e c t ri c a l c i rc u i t A vo l t a g e i s a p p l i e d a c r o s s t he f o o d p r o d u c t a nd a c u r r e nt f l o w s T hi s c a n be d e s c r i be d by Oh m s l aw. E quat i o n 1-2 l i s t s Oh m s l aw. (12) I n t h is e q u a t io n V is v o lt a g e ; I is c u r r e n t ; a n d R is e le c t r ic a l r e s is t a n c e T r u e v o lu me t r ic h eat i n g o ccurs as t h e curren t f l o ws t h ro ugh t h e f o o d pro duct Si n ce n earl y al l t h e en ergy go es i n t o t h e f o o d as h eat f ro m t h i s pro ces s o h m i c h eat i n g i s m o re ef f i ci en t t h an m i c rowa v e ( d e A l w i s a n d F ry e r, 1 9 9 0 c ; L i a n d Su n 2 0 0 2 ). His tor ic al Ove r vie w o f Ohm ic He ating T h e a p p l i c a ti on of oh m i c h e a ti n g to f ood d a te s b a c k m or e th a n 1 0 0 y e a r s O n e of t h e e a r lie s t u s e s c it e d in t h e lit e r a t u r e w a s c r e d it e d t o F o w le r in 1 8 8 2 fo r a d e v ic e t h a t h e ld m eat o r f i s h i n a b o x wi t h a s al t s o l ut i o n co n t ai n i n g el ect ro des (de A l wi s an d F ry er, 1990c; Hal den an d o t h ers, 1990) Ot h er f o o d pro duct s al s o s aw e arl y wo rk acco rdi n g t o de A lw is a n d F r ye r ( 1 9 9 0 c ) s u c h a s liq u id s in 1 8 9 7 in c a n s t e r ili z a t io n in 1 9 0 0 a n d mil k p a s t e u r i z a t i o n i n 1 9 1 4 T he a u t ho r s a l s o m e nt i o ne d o t he r e a r l y f i r s t s r e p o r t e d i n t he l i t erat ure suc h as b l an ch i n g o f po t at o es i n 1951 b y Sch ade. T h i s was t h e s am e y ear t h at th e a u th or s c i te d T a n a k a a n d T a n a k a a s h a v i n g s h a r e d w or k on a tte m p ti n g th e th a w i n g of f r o z e n m e a t c hu nk s w i t h l i t t l e s u c c e s s O hm i c he a t i ng s a w i nt e r e s t i n t he e a r l y ha l f o f t he 2 0 c e nt u r y bu t o nl y s a w o ne br i e f c o m m e r c i a l s u c c e s s w i t h m i l k p a s t e u r i z a t i o n. I n t he th

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6 op i n i on of d e A l w i s a n d F r y e r ( 1 9 9 0 c ) th e p r ob l e m s w e r e p r i m a r i l y r e l a te d to l a c k of sui t ab l e el ect r o de m at er i al s an d co n t r o l sy st em s. I nt e r e s t i n p o s s i bl e c o m m e r c i a l a p p l i c a t i o ns o f o hm i c he a t i ng c o nt i nu e d i nt o t he 1 9 7 0 's T he U k r a ni a n M e a t a nd D a i r y I nd u s t r i e s I ns t i t u t e w a s r e p o r t e d i n 1 9 7 2 t o ha ve dev el o ped an ex peri m en t al as ept i c l i n e f o r m an uf act uri n g s ki n l es s f ran kf urt ers us i n g a co m b i n ed o h m i c an d co n v en t i o n al pro ces s b y Ruc h ko v s ki an d o t h ers, acco rdi n g t o de A l w i s a n d F ry e r (1 9 9 0 c ). A c o m m e rc i a l b l a n c h i n g p roce s s re q u i re d b y p o t a t o e s b e f o re d e e p fr ying w a s a ls o r e p o r t e d b y E le c t r o fo o d A B a n d c a lle d t h e O S C O p r o c e s s ( d e A lw is a nd Fr y e r 1 9 9 0 c ) S u c c e s s f u l s t u d y o f bl a nc hi ng c o r n o n t he c o b w a s r e p o r t e d by M iz r a h i a n d o t h e r s ( 1 9 7 5 ) H e r e p o r t e d t h e c o mp le t e in a c t iv a t io n o f p e r o x id a s e in o n ly 3 m i n ut es wi t h an o h m i c pro ces s wh i l e t h e co n v en t i o n al pro ces s o f us i n g b o i l i n g wat er wo ul d t ake 1 7 m i n ut es. Oh m i c h eat i n g us ed f o r b aki n g was repo rt ed t o reduce pro ces s t i m es b y ab o ut 6 0 % w h e n c o m p a re d t o c o n v e n t i o n a l m e t h o d s i n 1 9 8 5 a n d 1 9 8 6 Th e s e re p o rt s w e re c r e d i t e d t o D a ni l e s k o by d e Al w i s a nd Fr y e r ( 1 9 9 0 c ) T he l a t e 1 9 8 0 's m a r k e d t he b e g i n n i n g of a w i d e s p r e a d i n te r e s t i n i n v e s ti g a ti n g oh m i c h e a ti n g T h e p r i m a r y c a ta l y s t f or t h i s wo ul d b e wo rk do n e b y t h e UK E l ect ri ci t y Co un ci l Re s earch Ce n t re. A pro ces s was d e v e lo p e d fo r u s in g o h mic h e a t in g in c o n t in u o u s s t e r ili z a t io n o f p a r t ic u la t e fo o d s T h is p r o c e s s w a s lic e n s e d t o A P V B a k e r w h o d e v e lo p e d it in t o a c o mme r c ia l s ys t e m ( d e A lw is a n d F ry e r, 1 9 9 0 c ). F ol l ow i n g th i s c om m e r c i a l p r oc e s s d e v e l op m e n t, th e r e h a s b e e n a g r e a t d e a l of r e s e a r c h i nt o o hm i c he a t i ng T he bu l k o f t he r e s e a r c h ha s be e n c e nt e r e d a r o u nd t he h e a t i n g o f p a rt i c u l a t e f o o d s Th e re s e a rc h h a s b e e n c a rri e d o u t i n s e v e ra l i m p o rt a n t w a y s

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7 Th e p roce s s h a s b e e n e x p e ri m e n t a l l y m o d e l e d a n d e x a m i n e d i n a s t a t i c o h m i c c e l l w h e re t h e part i cul at e i s s t at i o n ary E arl y wo rk i n t h i s area i n cl uded t h at o f de A l wi s an d F ry er (1990a, 1990b ) an d Z h an g an d F ry er ( 1993) at t h e Un i v ersi t y o f Ca m b ri dge i n t h e Un i t ed K i n gdo m Ot h er earl y wo rk i n cl uded t h at o f Sas t ry an d Pal an i appan (1992a, 1992b ) at t he O hi o S t a t e U ni ve r s i t y T he u s e f u l ne s s o f s t u d y i ng a s t a t i c c e l l r e l a t e d t o t he c o n t i n u o u s p roce s s w a s f u rt h e r i l l u s t ra t e d b y l a t e r w o rk s o f K h a l a f a n d Sa s t ry (1 9 9 6 ). T hi s a r e a o f r e s e a r c h c o nt i nu e d t hr o u g h t he 1 9 9 0 's a s i l l u s t r a t e d w i t h w o r k by D a vi e s a nd o t h e rs (1 9 9 9 ), a s w e l l a s w o rk b y F u a n d H s i e h (1 9 9 9 ). Th e m o s t re c e n t p u b l i s h e d w o rk re l a t e d t o u s i n g s t a t i c c e l l s h a v e b e e n b y Y e a n d o t h e rs (2 0 0 3 ) a n d Z a re i f a rd a n d o t h e rs (2 0 0 3 ). T h e wo rk wi t h s t at i c ce l l s rel at i n g t o pro ces s i n g f o o d part i cul at e h as b een a c c o m p a n i e d b y w o rk w i t h c o n t i n u o u s f l o w Ea rl y re s e a rc h w a s u n d e rt a k e n b y Sa s t ry (1992) as wel l as Z h an g an d F ry er ( 1994). T h e wo rk co n t i n ued t h ro ugh t h e 1990' s as i l l u s tr a te d w i th f u r th e r w or k b y K h a l a f a n d S a s tr y ( 1 9 9 6 ) T h e c om p l e x i ti e s of f l ow c a u s e d ma n y p r o b le ms w it h t h e e a r ly w o r k s a n d ma n y s imp lify in g a s s u mp t io n s t yp ic a lly ha d t o be u nd e r t a k e n. T he g a i ns i n u nd e r s t a nd i ng f r o m e a r l y w o r k a nd t he w o r k d o ne wi t h s t at i c ce l l s wh en co upl ed wi t h t h e s t eep de cl i n e i n co m put i n g co s t h as l ed t o great er r e s e a r c h i n te r e s t i n th e c on ti n u ou s f l ow p r oc e s s W or k s i n c e 2 0 0 0 i n c l u d e s th a t of Be n ab derr ah m an e an d Pai n (2000) E l i o t -Go dreaux an d o t h ers (2001a, 2001b ), T ucker a n d o t h e rs (2 0 0 2 ), a n d A y a d i a n d o t h e rs (2 0 0 4 ). T h e st at i c an d co n t i n uo us f l o w r esear ch i n spi r ed b y t h e A P V Baker pr o cess al so creat ed o t h er areas o f o h m i c res earch Oh m i c h eat i n g o f a part i cl e i n a l i qui d creat es an e n h a n c e d d i f f u s i on e f f e c t f r om th e p a r ti c l e to th e l i q u i d S om e e a r l y p u b l i s h e d w or k on

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8 t hi s w a s by S t a p l e y a nd o t he r s ( 1 9 9 5 ) a nd I m a i a nd o t he r s ( 1 9 9 5 ) Fu r t he r r e s e a r c h i n t he a r e a w ou l d c on s i d e r h ow th i s p h e n om e n on a f f e c ts h ot a i r d r y i n g r a te s a n d j u i c e y i e l d s of cert ai n f o o ds (Li m a an d Sas t ry 1999). F urt h er wo rk i n dry i n g rat es an d ex t ract i o n y i el ds ha s c o nt i nu e d a s r e p o r t e d by Wa ng a nd S a s t r y ( 2 0 0 2 ) Z ho ng a nd L i m a ( 2 0 0 3 ) a nd L akkakul a an d o t h ers (2004). T h es e o h m i c h eat i n g appl i cat i o n s h av e n o t h erm al an al o g, s i n ce t h e ef f ect s are due t o t h e el ect ri c f i el d appl i ed an d n o t o n l y t h e h eat gen erat ed. T h e m o s t i m po rt an t f o o d pro pert y wh en appl y i n g o h m i c h eat i n g i s t h e el ect ri cal r esi st an ce o f t h e f o o d p r o du ct Bef o r e t h e co m m er ci al i zat i o n o f t h e A P V Baker pr o cess l i ttl e d a ta e x i s te d on th e e l e c tr i c a l r e s i s ta n c e v a l u e s of f ood s or th e i n v e r s e v a l u e of c on d u c ta n c e T h e r e s e a r c h r e l a te d to s ta ti c a n d c on ti n u ou s c e l l s w ou l d g i v e r i s e to re s e a rc h s p e c i f i c a l l y t o d e t e rm i n e e l e c t ri c a l c o n d u c t i v i t y v a l u e s f o r c e rt a i n f o o d p rodu c t s T he f i r s t p u bl i s he d w o r k i n t he a r e a i s H a l d e n a nd o t he r s ( 1 9 9 0 ) w hi c h w a s f o l l o w e d by P a l a ni a p p a n a nd S a s t r y ( 1 9 9 1 a 1 9 9 1 b) L a t e r w o r k w o u l d be d o ne w i t h p a c i f i c w hi t i ng s u ri m i p a s t e (Y o n g s a w a t d i g u l a n d o t h e rs 1 9 9 5 ) a n d s t a rc h g e l s (W a n g a n d Sa s t ry 1 9 9 7 ). W o rk i n t h i s area h as co n t i n ued as repo rt ed b y F u an d L i n (2003) wh o al s o h as m ade m eas urem en t s o n a v ari et y o f m eat s v eget ab l es an d f rui t s Ca s t ro an d o t h ers (2004) repo rt ed o n co n duct i v i t y v al ues f o r st rawb err y pro duct s wh i l e Sh i rsat an d o t h ers (2004) r e p or te d on c on d u c ti v i ty v a l u e s f or c u ts of p or k T h e m os t r e c e n t r e p or ti n g of c o n d u c t iv it y v a lu e s w e r e r e la t e d t o t ylo s e ( s o d iu m c a r b o x y me t h yl c e llu lo s e ) w h ic h is u s e d a s a f o o d a n a l o g f o r m o d e l i n g l e a n b e e f (Ic i e r a n d Il i c a l i 2 0 0 5 ). O h m i c h e a t i n g c a n b e a p p l i e d t o t h a w i n g o f f o o d p rodu c t s Th e re h a s b e e n v e ry l i t t l e r e s e a r c h r e l a t e d t o o hm i c t ha w i ng ( L i a nd S u n, 2 0 0 2 ) Ac c o r d i ng t o d e Al w i s a nd F ry er ( 1990c), Ra o an d M at h en i n 1974 repo rt ed us i n g o h m i c t h awi n g f o r f ro zen b l o cks

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9 o f p r a w n s fo r q u ic k q u a lit y c h e c k s S e g a r s a n d K a s a lis w e r e r e p o r t e d t o h a v e u s e d o h mic t h awi n g an d h eat i n g o f preco o ked f ro zen cas s ero l e i t em s (Nav eh an d o t h ers, 1983; de A lw is a n d F r ye r 1 9 9 0 c ) N a v e h a n d o t h e r s ( 1 9 8 3 ) p r o p o s e d a me t h o d a p p lyi n g o h mic t h awi n g t o f ro zen m eat ch un ks T h e m et h o d di d n o t h av e di rect co n t act wi t h t h e m eat b ut i n s t ead us ed a c arr i er f l ui d t h at co n t act ed b o t h t h e m eat an d t h e el ect ro des Si m i l ar re s e a rc h w a s c re d i t e d t o Y u n a n d o t h e rs i n 1 9 9 8 b y L i a n d Su n (2 0 0 2 ). At t he U ni ve r s i t y o f Fl o r i d a i n 1 9 9 3 p r e l i m i na r y w o r k o n t he t e c hni c a l a nd e c on om i c f e a s i b i l i ty of a p p l y i n g oh m i c th a w i n g to f r oz e n s h r i m p w a s d on e b y H e n d e r s on ( 1 9 9 3 ) T he p o s i t i ve f i nd i ng s l e d t o t he f u r t he r w o r k w i t h f r o z e n s hr i m p bl o c k s T he e l e c t r i c a l c o nd u c t i vi t y o f f r o z e n s hr i m p a nd f l o u nd e r w e r e r e p o r t e d by L u z u r i a g a a nd Ba l ab an (1996) T h es e v al ues were un i que b eca us e o f h o w l i t t l e dat a h as b een pub l i s h ed o n fr o z e n fo o d s A p r o t o t yp e a u t o ma t e d o h mic t h a w in g u n it w a s d e s ig n e d a n d t e s t e d in 1 9 9 4 ( R o be r t s 1 9 9 4 ; R o be r t s a nd o t he r s 1 9 9 8 ) T he w o r k s u c c e s s f u l l y d e m o ns t r a t e d t he t e c h n o lo g y o f t h a w in g fr o z e n s h r imp b lo c k s w it h o h mic h e a t in g a n d a u t o ma t e d c o n t r o l. Ohm ic T haw ing T h awi n g o f f o o d pro duct s ref ers t o t h e s peci f i c ch an ge o f s t at e o f t h e wa t er i n t h e pro duct f ro m a f ro zen s t at e t o un f ro zen s t at e. T h e h eat i n g requi red i s gen eral l y s eparat ed i n to s e n s i b l e a n d l a te n t h e a t. T h e s e n s i b l e h e a t i s th e h e a t a c tu a l l y a s s oc i a te d w i th t e m p e r a t u r e c ha ng e a nd t he l a t e nt he a t i s a s s o c i a t e d w i t h o nl y t he c ha ng e o f p ha s e T he l a te n t h e a t of f oo d p r od u c ts i s h i g h b e c a u s e of th e i r h i g h w a te r c on te n t. T h a w i n g of f ood p r od u c ts p r e s e n ts s e v e r a l p r ob l e m s T h e th e r m a l c on d u c ti v i ty of f o o d pro duct s i s depen den t o n t em perat ure. No rm al l y t h ei r t h erm al co n duct i v i t y i s h i gh w h e n f r oz e n T h i s i s n ot s u r p r i s i n g s i n c e m os t f oo d p r od u c ts h a v e a h i g h w a te r c on te n t,

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10 an d wat er h as a l o wer t h erm al co n duct i v i t y t h an i ce. E v eri n gt o n (1971) repo rt ed t h at regardi n g t h e t h erm al co n duct i v i t y f o r f i s h m us cl e t h e f ro zen co n duct i v i t y was t h ree t i m es t h at o f t h e un f ro zen co n duct i v i t y T h i s m ean s t h at a f o o d pro duct t h at un dergo es c o n v e n t io n a l t h a w in g w h e r e h e a t is a p p lie d t o t h e s u r fa c e w ill d e v e lo p w h a t is e s s e n t ia lly a l ay er o f i n sul at i o n T h e h eat r equ i r ed t o t h aw t h e cen t er o f t h e pr o du ct m ust pass t h roug h t h e i n s u l a t i n g o r t h a w e d l a y e r b e f o re re a c h i n g a n u n t h a w e d i n n e r l a y e r of p rodu c t T h i s caus es s i gn i f i can t pro b l em s i n t ry i n g t o rapi dl y t h aw a f o o d pro duct b y co n v en t i o n al h e a t ing me t h o d s T h is p r o b le m i s fu r t h e r c o mp o u n d e d b y t h e fa c t t h e s p e c if ic h e a t o f a f r oz e n f ood p r od u c t w i l l b e l ow e r th a n th e u n f r oz e n p r od u c t. T h e u n f r oz e n i n s u l a ti on l a y e r t he n w i l l no t o nl y c o nd u c t he a t m o r e s l o w l y bu t r e q u i r e s m o r e e ne r g y t o r a i s e t he t e m p e ra t u re i n t h i s l a y e r. R a p i d th a w i n g h a s b e e n of i n te r e s t b e c a u s e u n c on tr ol l e d s l ow th a w i n g c a n n e g a te t h e h i gh qual i t y o f a f o o d pro duct ach i ev ed b y co n t ro l l ed rapi d f reezi n g an d co l d s t o rage ( E ve r i ng t o n, 1 9 7 1 ; N a ve h, 1 9 8 3 ; d e Al w i s a nd Fr y e r 1 9 9 0 c ) I n o r d e r t o i nc r e a s e t he h eat t r an sf er at t h e sur f ace o f t h e f r o zen pr o du ct wat er h as b een co m m o n l y used as a w o rk i n g f l u i d t o t h a w m e a t s f i s h e g g a s w e l l a s o t h e r f o o d s t u f f s (Ev e ri n g t o n 1 9 7 1 ). W at er can l eac h s o l ub l e co n s t i t uen t s f ro m t h e f o o d pro duct (Jas o n an d San ders, 1962; E ve r i ng t o n 1 9 7 1 ; R o be r t s 1 9 9 8 ) T he w a t e r u s e d be c o m e s a w a s t e s t r e a m t ha t m u s t be deal t wi t h o f t en at co s t t o t h e pro ces s o r ( Hen derso n 1993). W at er use d i n di rect co n t act wi t h a f o o d p r o du ct m ust b e po t ab l e. T h i s can al so b e a b ur den t o a pr o cesso r du e t o co st a n d o r lim it e d a v a ila b ili t y ( R o b e r t s 1 9 9 8 ) T h e w a t e r t e mp e r a t u r e h a s b e e n c o mmo n ly i n th e r a n g e of 1 8 to 2 1 C ( 6 5 to 7 0 F ) ( E v e r i n g ton 1 9 7 1 ) T h i s c a n l e a d to th e e x te r i or of

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11 t he f o o d p r o d u c t be i ng he a t e d i nt o a r a ng e t ha t m i c r o bi a l g r o w t h i s a p r o bl e m be f o r e t he pro duct can b e co m pl et el y t h awe d o r pr o ces s ed. V o lu me t r ic h e a t in g me t h o d s o ffe r s o lu t io n s t o t h a w in g p r o b le ms V o lu me t r ic h e a t i n g d o e s n o t re q u i re l a rg e a m o u n t s o f w a t e r. It does n o t ra i s e t h e s u rf a c e t e m p e ra t u re o f t he f o o d p r o d u c t t o u nd e s i r a bl e l e ve l s T hi s f o r m o f he a t i ng i s m o r e r a p i d be c a u s e t he f o o d pro duct s t h erm al co n duct i v i t y i s n o t co n t ro l l i n g t h e t h awi n g rat e. T h e e l e c tr i c a l r e s i s ta n c e of th e f ood p r od u c t i s th e c on tr ol l i n g f ood p r op e r ty f or o h mic t h a w in g T h is p r o p e r t y a ls o h a s a d e p e n d e n c e o n t e mp e r a t u r e I t c h a n g e s g r e a t ly as t h e f o o d pro duct go es f ro m t h e f ro zen t o un f ro zen s t at e f o r a f o o d pro duct F ro zen f i s h m u s c l e w a s s r e p or te d to h a v e a s p e c i f i c r e s i s ta n c e th a t c h a n g e s b y s e v e r a l or d e r s of m a g n i tu d e b y J a s on i n d e A l w i s a n d F r y e r ( 1 9 9 0 c ) A s i m i l a r f i n d i n g i s r e p or te d f or s h r i m p ( L u z u r i a g a a n d B a l a b a n 1 9 9 6 ) T h e d r a s ti c c h a n g e i n th i s c on tr ol l i n g p r op e r ty l e a d s t o r u na w a y he a t i ng i n a f a s hi o n ve r y s i m i l a r t o m i c r o w a ve r u na w a y he a t i ng O ne di f f eren ce w i t h o h m i c wo ul d b e t h at t h e run awa y h eat i n g wo ul d n o t b e a ph en o m en o n t h at co ul d b e s uppo rt ed i n a s i n gl e po cket s urr o un ded b y f ro zen m at eri al It wo ul d requi re a p a th of u n f r oz e n m a te r i a l or l ow r e s i s ta n c e m a te r i a l f r om on e c on d u c ti n g e l e c tr od e to a n o t h e r. E l e c t r i c a l r e s i s t a nc e o f a f o o d p r o d u c t i s no t t y p i c a l l y m e a s u r e d d i r e c t l y T he r e s is t a n c e is n o r ma lly c a lc u la t e d fr o m k n o w le d g e o f t h e v o lt a g e a n d c u r r e n t I n a s imp le ci rcui t t h at co n t ai n s o n l y a res i s t o r i f t h e v o l t age a n d curr en t are m eas ured t h e res i s t an ce c a n b e c a l c u l a te d f r om O h m s L a w p r e s e n te d e a r l i e r A n i m p or ta n t p r op e r ty of a r e s i s tor i s t ha t i t s va l u e i s m a i nl y d e t e r m i ne d by i t s p hy s i c a l d i m e ns i o ns a nd t he r e s i s t i vi t y o f t he m a t e r i a l o f w hi c h i t i s c o m p o s e d ( P e e bl e s a nd G i u m a 1 9 9 1 ) T he r e s i s t a nc e m e a s u r e d by

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12 a n y e x p e r i m e n ta l s e t u p w ou l d b e s p e c i f i c to th a t e x p e r i m e n ta l s e t u p a n d th e f ood pro duct s ph y s i cal di m en s i o n s T h e res i s t i v i t y h as b ro ader appl i cat i o n as i t can b e appl i ed t o f i n d t h e res i s t an ce o f t h e s am e f o o d pro duct wi t h di f f eren t di m en s i o n s T h e res i s t an ce e R fo r a r e s is t o r o f c o n s t a n t c r o s s s e c t io n a l a r e a A le n g t h L a n d r e s is t iv it y D is w r it t e n in e q u a t i o n 1 -3 (P e e b l e s a n d G i u m a 1 9 9 1 ). (13) I t i s e a s y t o d e t e r m i ne f r o m t he e q u a t i o n t ha t i f r e s i s t a nc e i s i n o hm s l e ng t h i n m e t e r s a nd area i n m et ers s quared, t h en resi s t i v i t y wi l l h av e un i t s o f o h m m et er. In an ex peri m en t al s et u p th a t i s m e a s u r i n g b oth th e v ol ta g e a n d c u r r e n t s i m u l ta n e ou s l y i t i s a l s o v e r y e a s y to cal cul at e t h e po wer t h at i s appl i ed. T h e po wer wi l l s i m pl y b e t h e pro duct o f t h e v o l t age a n d th e c u r r e n t.

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13 CHA P T E R 3 M A T E RIA L S A ND M E T HODS T hi s r e s e a r c h ha s be e n c o ns i d e r e d i n t w o m a j o r a r e a s T he f i r s t a r e a w a s t he p h y s i c a l te s t s a m p l e u n d e r c on s i d e r a ti on a n d th e s e c on d a r e a w a s r e l a te d to d a ta c ol l e c ti on fr o m t h e t e s t s a mp le I t e ms r e la t e d t o t h e p h ys ic a l t e s t s a mp le in c lu d e d t h e s a mp le it s e lf a n d ob j e c ts i n d i r e c t c on ta c t w i th th e s a m p l e T h i s a l s o i n c l u d e d a n y th i n g th a t w a s u s e d to c on tr ol th e p h y s i c a l s ta te of th e s a m p l e T h e s e c on d a r e a w a s i n c l u s i v e of a l l d a ta c o l l e c t i o n h a rd w a re a n d s o f t w a re u s e d In a d d i t i o n t o t h e t w o m a j o r a re a s t h e re w a s a t h i rd m i n or a r e a r e l a te d to th e p h y s i c a l m ou n ti n g a n d i n te r c on n e c ti n g of th e f i r s t tw o. Se v e ra l d i s t i n c t m e t h o d s w e re u s e d i n t h i s re s e a rc h Pr e l i m i n a ry m e t h o d s w e re co n s i dered t o en co m pas s t h e pro cedures f o r gen erat i n g t h e m at eri al s T h es e i n cl uded co n s t ruct i o n an d as s em b l y t ech n i ques f o r cust o m m at eri al s as wel l as o v eral l s y s t em des i gn a nd a s s e m bl y M e t ho d s a l s o c o m p r i s e d t he o p e r a t i o na l va l i d a t i o ns c ha r a c t e r i s t i c s a nd c a l i b ra t i o n n e e d e d b y t h e e x p e ri m e n t a l a p p a ra t u s b e f o re i t s u s e T h e e x p e r ime n t a l u s e o f t h e a p p a r a t u s w a s a ls o c o n s id e r e d a me t h o d t o p ic T h is i n cl ud ed t h e act ual pr o cedu r es used i n dat a co l l ect i o n r edu ct i o n an d v i sual i zat i o n T h ese v a ri e d a c c o rd i n g t o t h e p u rp o s e o f t h e e x p e ri m e n t t h a t w a s p re f o rm e d b y t h e a p p a ra t u s Ph y si c a l Te st S a mp le Ge l T ype Th e p h y s i c a l t e s t s a m p l e c o n s i d e re d i n t h i s s t u d y w a s a s i m p l e f o o d g e l S p e c i f i c a l l y i t w a s a u nf l a vo r e d g e l a t i n g e l T he g e l a t i n w a s m a nu f a c t u r e d by t he Kno x

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14 C o m p a n y (P a rs i p p a n y N J ), w h i c h w a s a u n i t o f N a b i s c o In c o rp o ra t e d Th e i r s t a n d a rd ret ai l b o x packa ge o f 28 gram s (o n e o un ce) s ub di v i ded i n t o f o ur i n di v i dual un h y drat ed p a c k a g e s w a s p r o c u r e d l o c a l l y T he a ve r a g e d e ns i t y o f t he hy d r a t e d g e l a t i n g e l u s e d i n t he rese arch was 1. 02 g/cm T h e av erage pe rcen t rat i o o f t h e un h y drat ed pro duct t o wat er 3 a d d e d w a s 6 6 % I n th e u n f r oz e n s ta te i t w a s tr a n s p a r e n t w i th s om e s l i g h t y e l l ow c o l o ri n g In t h e f roze n s t a t e i t w a s o n l y p a rt i a l l y t ra n s l u c e n t S a mp le C e ll T h e g e l d u r i n g th e e x p e r i m e n t w a s c on ta i n e d i n a s a m p l e c e l l I t c on s i s te d of s ev eral part s T h e m aj o r co m po n en t was t h e ri gi d po l y v i n y l ch l o ri de (PVC) cy l i n dri cal h ou s i n g th r e a d e d f or e n d c a p s on b oth e n d s I n s u l a ti on l a y e r s e x i s te d on b oth th e i n te r i or an d ex t eri o r r adi al s urf ace s as wel l as o n b o t h o f t h e el ect ro de ex t eri o rs. T h e el ect ro des w e r e a l s o c o ns i d e r e d p a r t o f t he s a m p l e c e l l s i nc e t he y f o r m e d t he a xi a l bo u nd a r i e s f o r t he gel T em perat ure pr o b es i n t h e s am pl e we re l i kewi s e co n s i dered a pa rt o f t h e ce l l s i n ce t h e y w e r e e s s e n t ia lly fix e d in p la c e o n c e t h e g e l w a s fo r me d in t h e s a mp le c e ll. Cy l indr ic al hous ing T h i s h o usi n g ( F i gu r e 31) co n si st ed o f 76 2 m m ( 3") sch edu l e40 P VC pi pe f i t t i n gs, Ch arl o t t e Pi pe an d F o un dry Co m pan y (Ch arl o t t e, NC) part n um b ers PVC 101 an d PVC 105 ( h ttp : / / c h a r l otte p i p e c om ) B oth e n d s w e r e th r e a d e d on th e i n te r i or w i th a s m oo th w a l l e d t r a ns i t i o n be t w e e n t he t hr e a d e d a r e a s T he s m o o t h w a l l e d t r a ns i t i o n t o t he th r e a d i n g w a s s e p a r a te d b y a n i n te r i or s h ou l d e r T h e s m ooth w a l l e d or c e n tr a l r e g i on of t h e h o u s i n g h a d a n a x i a l l i n e o f 3 h o l e s o n e a c h s i d e o f a d i a m e t e r of t h e h o u s i n g t h a t w e re e q u a l l y s p a c e d o ve r t ha t r e g i o n. T hi s p l a c e d t he c e nt e r s e t a t t he c e nt e r o f t he a xi a l he i g ht o f t h e s m o o t h regi o n wi t h t h e o t h er t wo s et s h al v i n g t h e rem ai n i n g h al f h ei gh t s A s ket ch o f t h es e f eat ures c an b e s een i n F i gure 32.

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15 I nt er ior insul ati on T h e i n sul at i o n o n t h e r adi al i n t er i o r o f t h e cel l was P er m aS eal b y P er m a R P r od u c ts I n c or p or a te d ( J oh n s on C i ty T N ) T h i s i n s u l a ti on w a s a c l os e d c e l l i n s u l a ti on n o r ma lly u s e d in c o n s t r u c t io n fo r c r e a t in g a s ill s e a l. I t c a me in a s t a n d a r d 6 3 5 mm x 1 3 9 7 m m x 1 5 2 4 m ( 1 / 4 x 5 5 x 5 0 ) w h i te r ol l I t w a s s i z e d to f i t th e g e l c ol u m n h e i g h t of t h e s m o o t h ed wa l l ed po rt i o n o f t h e cy l i n dri cal h o us i n g. A s t an dard ut i l i t y kn i f e wa s us ed fo r t h e s iz in g T h is in s u la t io n w a s r e s ili e n t t o b e in g c o mp r e s s e d d u e t o it s c lo s e d c e ll n a t u re w i t h re l a t i v e l y l a rg e a i r p o c k e t s F i gure 31. Cy l i n dri cal Ho us i n g. O b j e c t 3 -1 PV C C e l l .j p g (2 .59 MB).

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16 Ex ter ior insul ati on T h e i n s ul at i o n o n t h e radi al ex t eri o r o f t h e ce l l was Great St uf f b y Do w C h em i cal C o m p a n y (M i d l a n d M I). I t w a s a n e x p a n d i n g f o a m s e a l a n t s o l d i n a p re s s u ri z e d c a n T hi s i ns u l a t e d t he r a d i a l e xt e r i o r i n t he r e g i o n o f t he s m o o t h t r a ns i t i o n be t w e e n t he th r e a d e d r e g i on s of th e c y l i n d r i c a l h ou s i n g I t a l s o s e a l e d th e c l os e tol e r a n c e p a s s a g e s f or t h e p r o b e s t h a t c a me in t h r o u g h t h e r a d ia l e x t e r io r o f t h e c e ll. El ectr odes A ci rcul ar st ai n l es s s t eel el ect ro de res t ed o n eac h i n t eri o r sh o ul der t h at s eparat ed t h e s mo o t h in t e r io r fr o m t h e t h r e a d e d in t e r io r T h e e le c t r o d e s w e r e a p p r o x ima t e ly 3 2 mm F ig u r e 3 2 S k e t c h o f P V C C e ll. O b j e c t 3 -2 Sa m p l e C e l l .j p g (4 3 K B ).

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17 ( 1 / 8 ) t h ic k E a c h h a d a 1 0 2 4 1 2 7 mm ( ) s t a in le s s b o lt w e ld e d t o t h e b a c k s id e T h is b o l t al o n g wi t h t wo n ut s an d t wo was h ers, f o rm ed t h e el ect ri cal i n put co n n ect o r f o r each el ect r o de. T h e f r o n t si de o f t h e el ect r o de w h i ch co n t act ed t h e sam pl e h ad a sur f ace f i n i sh c on s i s te n t w i th r a n d om or b i ta l s a n d i n g w i th a f i n e e m e r y c l oth F i g u r e 3 3 i s a s k e tc h of t h e e l e c t rode a n d a p i c t u re o f t h e g e l c o n t a c t i n g s u rf a c e E nd c aps T h ree s eparat e m at eri al s were us ed i n s eri es t o f o rm t h e en d caps f o r t h e cy l i n dri cal h o us i n g. T h e f i rst m at eri al i n di rect co n t act wi t h t h e el ect ro de wa s 19 m m (3/ 4") t h i ck f o a m e d p o l y s t y re n e i n s u l a t i o n Th e n e x t l a y e r w a s a 3 m m (1 /8 ) t h i c k 3 p l y w o o d d i s k C o n t a c t in g t h e d is k la ye r w a s a s t a n d a r d t h r e a d e d p lu g T h e p lu g w a s fille d w it h t h e s a me i n s ul at i n g m at eri al as t h e i n t eri o r o f t h e ce l l T h i s pro v i ded an d ef f ect i v e f i l l f o r t h e pl ug t h at al l o wed t h e po wer co n duct o r t o pas s t h ro ugh t h i s s ect i o n T h e en d o f t h e pl ug was d r i l l e d t o a l l o w p a s s a g e o f t he e l e c t r i c a l c o nne c t i o n. F i gure 33. E l ect ro de Sket ch an d Pi ct ure. O b j e c t 3 -3 El e c t rode Sk e t c h .j p g (2 1 1 KB).

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18 P r obes Th e t e m p e ra t u re p rob e s w e re c u s t o m m a d e f o r t h e e x p e ri m e n t Th e y w e re es s en t i al l y t y pe T t h erm o co upl es T h e un i quen es s o f t h e pro b es was i n t h e f act t h at t h ey w e r e t w o s e p a r a t e t he r m o c o u p l e s bo nd e d t o g e t he r a nd e l e c t r i c a l l y i s o l a t e d f r o m o ne a n oth e r T h i s a l l ow e d f or tw o s e p a r a te te m p e r a tu r e m e a s u r e m e n ts to b e ta k e n f or e s s e n t i a l l y o n e g e o m e t ri c p o s i t i o n i n s i d e t h e s a m p l e T h e pr o b e h as b een b r o ken i n t o t h e f o l l o wi n g co m po n en t s. T h e f i r st was a Om egat i t e 200 ce ram i c i n s ul at o r ( Om ega En gi n eeri n g, In c., St am f o rd, CT, m o del nu m be r T R M 1 6 4 1 1 6 6 ) t ha t m a d e u p t he r i g i d e l e c t r i c a l l y i ns u l a t i ng p o r t i o n. T he i ns u l a t o r w a s a c y l i nd r i c a l t u be s ha p e a nd ha d t w o r o u nd c ha nne l s t ha t p r o t e c t e d a nd el ect ri cal l y i s o l at ed t h e t h erm o co upl e wi res. T h e di am et er o f t h e t ub e wa s 1. 5 m m (1/ 16 i n ) w h i l e th e c h a n n e l d i a m e te r s w e r e 0 4 m m ( 1 / 6 4 i n ) T h e p u b l i s h e d a p p r ox i m a te t h e rm a l c o n d u c t i v i t y w a s 0 .7 1 2 W /m K (1 .3 3 3 B TU /h r f t F ). T h e s e c on d p a r t of th e p r ob e w a s th e a c tu a l th e r m oc ou p l e j u n c ti on s E a c h j u n c ti on co n s i s t ed o f t h e t wo t h erm o co upl e wi res, o n e a 0.254 m m co pper an d t h e o t h er a 0. 254 m m co n s t an t an (Om ega En gi n eeri n g, In c. par t n um b ers SPCP-010 an d SPCC-010 respe ct i v el y ), wo un d t o get h er an d s o l dered. T h e s o l der an d wi re co m b i n at i o n co n f o rm ed t o t h e c e r a mic in s u la t o r s e x t e r io r d ia me t e r T h is a c t e d a s a n e n d c a p o n t h e c e r a mic i n s ul at o r. A s ket ch o f t h e pro b e wa s m ade i n F i gure 34. T h e th i r d p a r t of th e p r ob e w a s th e e l e c tr i c a l i n s u l a ti on f or th e e x p os e d p or ti on of t h e t h erm o co upl es T h e el ect ri cal i n s ul at i o n was a Qui ckTi t e s uper gl ue b y L o ct i t e (A v o n OH ). It was a cy an o acry l at e t y pe adh es i v e. Cy an o acry l at es h av e an el ect ri cal re s i s t i v i t y o f g re a t e r t h a n 1 0 O h m m m a n d a d i e l e c t ri c s t re n g t h o f 2 5 k i l o v o l t s p e r m m 15

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19 T he i ns u l a t o r be i ng a n a d he s i ve a l l o w e d i t t o s e r ve a s e c o nd r o l e a s t he bo nd i ng a g e nt b e t w e e n t h e p r o b e t ip s o r e n d c a p s T h e s e p r o b e t ip s w e r e a ls o b o n d e d t o t h e c e r a mic i n s u l a t o r w i t h t h i s m a t e ri a l T h e l a s t p h y s i c a l p a r t of th e p r ob e w a s th e j u n c ti on s th a t c on n e c te d th e tr a n s m i s s i on l e a d s O m e g a p a r t n u m b e r S M P W T m i n i a tu r e c on n e c tor s w e r e u s e d T h e f e m a l e p or ti on o f t h e t wo b l aded co pp er co n st an t an co n n ect o r s wer e used o n t h e pr o b e en d o f t h ese j u n c ti on s T h e tw o p i e c e d e s i g n of th e f e m a l e p or ti on a l l ow e d i t to b e a tta c h e d d i r e c tl y to eac h en d o f t h e pro b e b y cl am pi n g o v er t h e ce ram i c i n s ul at o r po rt i o n o f t h e pro b e. Fi g u r e 3 4 P r o be S k e t c h. Ob j ect 34. P r o b e. j pg ( 90 KB)

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20 T h e p r ob e s w e r e a l s o c on s i d e r e d to i n c l u d e th e i r a s s e m b l y b e n c h T h i s w a s c u s tom m a d e t o m a n u f a c t u re t h e p rob e s Th e b e n c h ra i l w a s a n a n g l e d p i e c e o f a l u m i n u m F i g u re 3-5 h as a s ket ch o f t h e as s em b l y b en ch rai l T h e b en ch h ad an o pen s ect i o n i n i t s cen t er a l l o w i ng f o r a d he s i ve s t o be a p p l i e d t o t he t he r m o c o u p l e e nd s T he r a i l w a s f a s t e ne d by t wo s crews t o a pai r o f s m al l wo o d b l o cks cut at 45 an gl es T h es e we re t h e b en ch f o un dat i o n s an d l i f t ed t h e rai l f o r cen t er acc es s Sm al l s pri n g l o aded c l am ps were ut i l i zed t o b i n d t h e p rob e p o rt i o n s o n t o t h e ra i l i n t e ri o r c o rn e r. Cel l Hol der T h e te s t c e l l h a d a c u s tom h ol d e r to m a k e i t e a s i e r to b e m ov e d a n d p r ote c te d i ts t h e rm o c o u p l e l e a d s d u ri n g m o v e m e n t A d i a g ra m o f t h e c e l l h o l d e r c a n b e s e e n i n F i g u re 3 6 I t w a s c o ns t r u c t e d o f w o o d T he ho l d e r ha d s p e c i f i c f e a t u r e s t ha t a s s i s t e d i n t he ex peri m en t s T h e t o p h an dl e al l o wed t h e h o l der t o b e ea s i l y gri pped wh en t h e s am pl e wa s b e in g mo v e d fr o m t h e t e mp e r a t u r e c o n t r o l c h a mb e r T h e s id e s h a d t h r e e h o le s b o r e d in t h e m t o p rov i d e f o r s t re s s re l i e f t o t h e t h e rm o c o u p l e s w h e n t h e s a m p l e w a s b e i n g m o v e d T h e s h o rt l egs were ut i l i zed t o al l o w t h e s am pl e h o l der t o rest o n i t s s i de, wh en a gel was b e in g p o u r e d T h e la r g e o p e n in g b e t w e e n t h e t e s t c e ll a n d t h e h a n d le a llo w e d t h e s a mp le t o b e cl am ped duri n g f reezi n g. A 304. 8 m m (12") Craf t s m an C s t y l e s crew cl am p was us ed Figure 3-5. Probe Assembly Bench Rail. Object 3-5. ProbeBench.jpg (3 7 KB).

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21 o n t h e ce l l f o r cl am pi n g purpo s es T h e cl am p was co n s i dered a pa rt o f t h e ce l l h o l der ev en t h o u g h i t w a s o n l y a p p l i e d d u ri n g t h e f re e z i n g p h a s e o f t h e e x p e ri m e n t s Te m per atu r e Contr ol Cham ber T he t e m p e r a t u r e c o nt r o l c ha m be r w a s a s m a l l c he s t t y p e f r e e z e r m a nu f a c t u r e d by Gen eral E l ect ri c (Lo ui s v i l l e, K Y). It s m o del n um b er was F CM 5DM A W H. I t h ad s ev eral f eat ures t h at were v ery b en ef i ci al t o t h e ex peri m en t al n eeds T h e f i rst f eat ure was an a d j u s t a bl e t he r m o s t a t a nd i nc l u d e d a c o nt i nu o u s r u n m o d e s w i t c h. T hi s a l l o w e d t he t e mp e r a t u r e t o b e c yc le d o n d iffe r e n t r a n g e s o r s imp ly be t a k e n t o t h e e q u ip me n t a l li mit an d h el d. T h e f ro n t o f t h e f reeze r al s o h ad a drai n po rt al at t h e b o t t o m cen t er. T h i s act ed Figure 3-6. Sample Cell Holder. Object 3-6. SampleHolder.jpg (120 KB).

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22 as a po wer l ead a cce s s po i n t duri n g ex peri m en t at i o n T h e i n t eri o r o f t h e f reeze r was l i n ed w it h a lu min u m. T h e g a s k e t s e a lin g t h e t o p w a s v e r y fle x ib le a n d a p p r o x ima t e ly 1 2 5 mm ( 1 / 2 ) t hi c k a nd 2 5 m m ( 1 ) w i d e T he f l e xi bi l i t y o f t he g a s k e t a l l o w e d f o r t he t h e r mo c o u p le t r a n s mis s io n le a d s t o b e r o u t e d in t o t h e t o p o f t h e fr e e z e r b e t w e e n t h is g a s k e t a n d t h e lid T h e t h ic k n e s s le t t h e fr e e z e r ma in t a in it s t o p s e a l e v e n w it h t h e le a d s in p l a c e Th e c h a m b e r a l s o h a d e n o u g h roo m f o r t h e rm a l d a m p e rs Th e t h e rm a l d a m p e rs were t wo o n e gal l o n j ugs o f di s t i l l ed wa t er. T h es e t wo gal l o n s wh en f ro zen act ed as d a m p e r s t o r a p i d t e m p e r a t u r e c ha ng e s i n t he c ha m be r T hi s a l l o w e d f o r ve r y s l o w w a r m i ng w h e n th e f r e e z e r w a s s h u t of f T h e y a l s o h a d th e a d d e d b e n e f i t of d a m p i n g th e c y c l i n g of t em perat ure wh en t h e f reeze r i s run n i n g i n a cy cl i n g m o de. Po w e r S u p p ly T he p r i m a r y p o w e r s u p p l y u s e d w a s m a d e by S T AC O E ne r g y P r o d u c t s ( D a y t o n, OH) t y pe 6020C T -2S T h i s s uppl y ut i l i zed 220 v o l t A C i n put t o pro v i de v ari ab l e o ut put f ro m 0 t o 500 v o l t s A C. T h e po wer suppl y f o r ex peri m en t al purpo s es was al s o co n s i dered t o i n cl ude o t h er f ace t s o f pro v i di n g po wer t o t h e t es t cel l T h es e i n cl uded co n t ro l o f po wer t h ro ugh v o l t age a dj us t m en t an d curr en t l i m i t i n g. T h e l eads an d pl ugi n s requi red t o del i v er th e p ow e r to t h e te s t c e l l e l e c tr od e s a s w e l l a s a l te r n a ti v e D C p ow e r a r r a n g e m e n ts p o s s ib le w e r e o t h e r it e ms g r o u p e d w it h t h e p o w e r s u p p ly. Cont r ol Co n t ro l o f appl i ed po wer t o t h e s am pl e ce l l h ad t wo l ay ers. T h e f i rst l ay er was m an ual l y co n t ro l l ed b y t h e o perat o r o f t h e po wer suppl y T h e s eco n d l ay er was an aut o m at ed l ay er Bo t h t y pes o f co n t r o l wer e used a n y t i m e po wer was app l i ed t o t h e t est c e l l

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23 M anual contr ol T h e f i rst l ay er was t h e m an ual b reaker sw i t ch t o t h e po wer suppl y i t s el f t h at co n t ro l ed t h e 220 v o l t i n put t o t h e s uppl y s y s t em T h e o ut put o f t h e po wer suppl y al s o h ad a m a nu a l br e a k e r s w i t c h. T he s e m a nu a l c o nt r o l s w e r e c o m bi ne d t o g i ve i nd e p e nd e nt o no f f co n t ro l f o r b o t h t h e i n put t o t h e s uppl y an d i t s v ari ab l e o ut put v o l t age. T h e v o l t age o ut put l ev el was s et wi t h a m an ual ro t ary di al t h at adj us t ed t h e v o l t age o ut put f ro m 01 0 0 % of t h e s u p p l y s v o l t a g e ra n g e Aut om ated cont r ol Th e a u t o m a t e d c o n t rol w a s a p p l i e d t o t h e c u rre n t o u t p u t o f t h e p o w e r s u p p l y A C r o mp t o n me t e r w it h t w o o p t io n a l a t t a c h me n t s w a s t h e fir s t p a r t o f t h is c o n t r o l. T h is m e t e r c o n t i n u o u s l y m o n i t o re d t h e c u rre n t l e v e l a n d c u t s i t o f f a b o v e a s p e c i f i e d ra n g e It ach i ev ed t h i s b y co n t ro l l i n g t h e s uppl y v o l t age t o an o t h er r el ay b et t er sui t ed f o r t h e h i gh v ol ta g e s u s e d i n th e e x p e r i m e n t. T h i s p r i m a r y r e l a y w a s a C r y d om D 4 8 1 2 b y C r y d om El e c t ron i c s (S a n D i e g o C A ). T h e a u tom a te d c on tr ol a l s o i n c l u d e d a s e p a r a te te s t i n s tr u m e n t c on s tr u c te d to s h ow t ha t t he c o nt r o l w o r k e d c o r r e c t l y T hi s i ns t r u m e nt w a s a s i m p l e l i g ht f i xt u r e w i r e d t o be p lu g c o mp a t ib le w it h t h e s ys t e m o u t p u t p lu g T h e lig h t p r o d u c e d b y t h e r e s is t a n c e b u lb g iv e s v is u a l v e r if ic a t io n t h a t t h e ma n u a l a n d a u t o ma t e d c o n t r o ls w e r e o p e r a t in g c o r r e c t ly. Al ter nativ e dir e c t cur r e nt T he p o w e r s e t u p w a s f l e xi bl e I t a l l o w e d f o r a n a l t e r na t i ve D C s o u r c e t o be i n s ert ed i n t o t h e ci rui t T h i s s o urce h ad o n l y m an ual co n t ro l o f t h e v o l t age. T h e po wer s u p p ly fo r t h e D C s o u r c e w s a L B K t yp e 3 3 7 1 C b y L B K E le c t r o n ic s T h is s u p p ly c o u ld p r ov i d e D C v ol ta g e s u p to t h e 1 2 0 0 v ol t r a n g e b u t w a s l i m i te d to 6 0 m A ou tp u t c u r r e n t.

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24 Le ads and pl ugs Se v e ra l l e a d s a n d p l u g s w e re u s e d i n t h e i n t e rc o n n e c t i n g o f p o w e r. Th e p ri m a ry p l u g s f o r c a r r y i ng c u r r e nt t o t he t e s t s a m p l e w e r e t hr e e bl a d e d p l u g s a nd r e c e p t a c l e s T he po wer suppl y s i de we re al l recept acl es f o r saf et y T h e l ead t o t h e t es t cel l el ect ro des h ad a c o m p a t i b l e m a l e p l u g o n o n e e n d a n d i n s u l a t e d ri n g t o n g u e t e rm i n a l s o n t h e o t h e r. Th e re w a s a l s o a s p e c i a l l e a d t ha t w a s e s s e nt i a l l y a d o u bl e e nd e d m a l e p l u g T hi s l e a d w a s t he b r i d g e f or th e A C p ow e r to t h e te s t l e a d s T h i s b r i d g e w h e n r e m ov e d a l l ow e d a D C l e a d to be i ns e r t e d i nt o t he p l u g T he D C l e a d ha d a c o m p a t i bl e m a l e p l u g o n o ne e nd a nd ba na na pl ugs o n t h e o t h er f o r co n n ect i n g t h e DC s o urce. D a t a C o lle c t i o n H a rd w a re a n d S o ft w a re To u l t i m a t e l y g a t h e r u s e f u l i n f o rm a t i o n s e v e ra l d i f f e re n t f o rm s o f d a t a w e re c ol l e c te d T h e s e d a ta ty p e s w e r e c ol l e c te d b y tw o s e p a r a te i n s tr u m e n ts e a c h w i th s u p p o r t i ng ha r d w a r e a nd s o f t w a r e T he s e s u p p o r t i ng p a r t s a s s i s t e d i n s i g na l r o u t i ng a nd c o nd i t i o ni ng a s w e l l a s d a t a r e d u c t i o n a nd vi s u a l i z a t i o n. D a t a A c q u i s i t i o n C a rd T h e dat a ac qui s i t i o n card us ed i n t h i s i n v es t i gat i o n was a K ei t h l ey E l ect ro n i cs ( C l e ve l a nd O hi o ) P C I 3 1 0 7 T hi s w a s a 1 6 bi t 1 6 c ha nne l P C I c a r d I t w a s ho u s e d i n a To s h i b a d o c k i n g s t a t i o n V p l u s m o d e l n u m b e r P A 2 7 1 0 U Th i s d o c k i n g s t a t i o n w a s w h e re t h e To s h i b a Tecra 8000, m o del n um b er PA T 80A U l apt o p co n n ect s T h e l apt o p s erv ed a s a c on tr ol l i n g i n te r f a c e to t h e d a ta a c q u i s i ti on c a r d a s w e l l a s a s tor a g e m e d i u m f or d a ta c o l l e c t e d b y t h e c a rd I nter f ac ing T he Ke i t hl e y c a r d u s e d a 3 6 p i n D s t y l e c o nne c t o r t o t he e xt e r na l s i g na l s t o be s a m p l e d A K e i th l e y m od e l C A B 1 2 8 4 5 c a b l e i n te r f a c e d th e c on n e c tor T h e oth e r e n d of

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25 t h e ca b l e i n t erf ace d wi t h a K ei t h l ey m o del ST A 36 s crew t erm i n al pan el T h e s crew t e rm i n a l p a n e l t h e n c o u l d b e c o n n e c t e d t o s i m p l e w i ri n g t h a t re q u i re d n o s p e c i a l c o n n e c t o rs f o r i n t erf aci n g. T h e wi ri n g co n n ect ed t o t h e s crew t erm i n al was a s t an dard 28 gauge r ib b o n w ir e T h e o p p o s it e e n d o f t h e r ib b o n w ir e h a d a 2 6 p in fe ma le c o n n e c t o r T h is co n n ect o r i n t erf ace d wi t h t h e I/O pl ugs o n s i gn al co n di t i o n i n g b ackpl an e. B ack pl ane T h e b ackpl an e wa s an A n al o g Dev i ces In co rpo rat ed (A DI) (No rwo o d, M A ) m o del 5B01 ( h ttp : / / w w w a n a l og c om ). T h i s b ackpl an e wa s des i gn ed t o h o us e pl ug-i n s i gn al c o nd i t i o ni ng m o d u l e s I t a l s o w a s u s e d a s a n i nt e r f a c e f o r e xt e r na l s i g na l l e a d s T he b a c k p l a n e h a d s c re w t e rm i n a l i n p u t s o n e a c h o f i t s 1 6 d a t a l i n e s w h i c h s e rv e d t h i s p u rp o s e T h es e l i n es wen t t h ro ugh an A DI si gn al co n di t i o n i n g m o dul e o r di rect l y t o o n e o f t h e t wo 2 6 p i n I/ O c o n n e c t o rs o n t h e b a c k p l a n e Sig nal Co nditio ning A l l o f t h e raw dat a s i gn al s were co n di t i o n ed b ef o re b ei n g s am pl ed b y t h e K ei t h l ey c a rd Th e re w e re t h re e t y p e s o f c o n d i t i o n i n g u s e d O n e t y p e w a s u s e d f o r t e m p e ra t u re pro b es T h e o t h er t wo were us ed f o r v o l t age da t a. A DI 5B37-T -03 si gn al co n di t i o n i n g m o dul es pro v i ded t h e t em perat ure si gn al c o n d it io n in g T h e s e mo d u le s w e r e s p e c ific fo r T t yp e t h e r mo c o u p le s T h e y w e r e o p t ic a lly is o la t ing a n d p r o v id e d a li n e a r iz e d o u t p u t fr o m 0 5 v o lt s fo r t h e ir t e mp e r a t u r e r a n g e o f 1 0 0 t o + 4 0 0 C V o l t a g e d a t a w e re m o re c h a l l e n g i n g t o c o n d i t i o n f o r re a d i n g b y t h e K e i t h l e y c a rd T he r a ng e o f i nt e r e s t i n t hi s i nve s t i g a t i o n w a s f r o m 0 5 0 0 vo l t s T hi s w a s f a r be y o nd t he c a r d r a n g e o f 0 t o 1 0 v o lt s A C r o mp t o n 2 6 2 3 0 d ig it a l p a n e l me t e r w a s u s e d t o s a mp le t h e raw s i gn al an d gav e a v i s ual di s pl ay o f t h e readi n g. T h e C ro m pt o n m et er h ad an

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26 o pt i o n al b ackpa ck at t ach ed t h at pro v i ded a c o n t i n uo us an al o g curr en t o ut put T h i s o ut put was l i n earl y rel at ed t o an adj us t ab l e i n put ran ge. T he a na l o g o u t p u t s i g na l w a s a s e l e c t a bl e c u r r e nt r a ng e I n t hi s i nve s t i g a t i o n t he i nd u s t r y s t a nd a r d 4 2 0 m A c u r r e nt o u t p u t w a s u s e d T hi s c u r r e nt s i g na l t he n m u s t be co n v ert ed t o a v o l t age s i gn al t h at t h e K ei t h l ey card co ul d reco gn i ze. T h i s co n v ersi o n was ha nd l e d by u s i ng a p r e c i s i o n r e s i s t o r T he r e s i s t o r w a s a 2 5 0 o hm r e s i s t o r m a d e by P r e c is io n R e s is t o r C o I n c ( L a r g o F lo r id a ) w it h a s t a t e d t o le r a n c e o f 0 0 1 p e r c e n t T h is r e s i s t o r w a s c o nne c t e d t o t he s c r e w t e r m i na l s o f t he AD I ba c k p l a ne w he r e t he c u r r e nt s ig n a l w a s c o n n e c t e d T h e a r r a n g e me n t r e n d e r e d a 1 5 v o lt s ig n a l. Sig nal Co nditio ning Hou s ing T h e s ig n a l c o n d it io n in g e q u ip me n t a n d c o n n e c t io n s w e r e h o u s e d t o g e t h e r T h is h o us i n g was a co n v ert ed t o wer st y l e co m put er cas e. T h e ca s e h ad an ex t ern al po wer s w i t c h w h i c h t u rn e d o n a n d o f f b o t h o f t h e C rom p t o n m e t e rs u s e d i n t h i s i n v e s t i g a t i o n T h e C r om p ton m e te r s w e r e s e c u r e l y m ou n te d i n th e f or m e r e x te r n a l d r i v e b a y a r e a f or c l e a r vi e w i ng D i r e c t l y be l o w t he m e t e r s s t i l l i n t he f o r m e r e xt e r na l d r i ve ba y a r e a t he Ke i t hl e y s c r e w t e r m i na l w a s m o u nt e d O nl y i t s c a bl e c o nne c t o r w a s vi s i bl e f r o m t he ou ts i d e F i g u r e 3 7 s h ow s th e h ou s i n g a n d d oc k i n g l a p top T h e A D I b a c k p l a n e w a s n ot v i s i b l e f ro m t h e o ut s i de. I t was m o un t ed i n t ern al l y an d po s i t i o n ed l i ke a m o t h erb o ard. T h e h o us i n g h ad f i v e b as i c po i n t s o f acc es s us ed i n t h i s i n v es t i gat i o n T h e f i rst was t h e K ei t h l ey s crew t erm i n al co n n ect o r. T h e o t h er f o ur were o n t h e b ack o f t h e ca s e. T h ree used a 1 9 m m ( 3/ 4") di am et er co n n ect o r t o pr o v i de a p o r t al i n t o t h e case. On e o f t h ese th r e e c a r r i e d th e e x p e r i m e n ta l p ow e r l e a d i n to a n d ou t of a C r om p ton m e te r I t w a s n ot s h i e l d e d o u t s i d e t h e c a s e o n l y i n s i d e It ra n i t s i n t e ri o r route i n s i d e a 1 9 m m (3 /4 ) f l e x i b l e tu b u l a r m e ta l s h i e l d i n g T h e p ow e r l e a d f or th e m e te r s w a s r u n w i th s h i e l d i n g on

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27 th e i n te r i or b u t n ot th e e x te r i or T h e th e r m oc ou p l e l e a d s on th e oth e r h a n d w e r e n ot sh i el ded i n si de t h e case, b ut wer e sh i el ded o n t h e ex t er i o r F l ex i b l e t ub ul ar 19 m m ( 3/ 4") m et al s h i el di n g was us ed. T h e t h i rd l i n e co m i n g i n t o t h e rear o f t h e ca s e wa s s h i el ded ca b l i n g. It h ad f o ur l e a d s O ne p a i r c a r r i e d t he vo l t a g e s i g na l t o be s a m p l e d f r o m t he AC p o w e r s u p p l y T he o t h e r p a ir o f le a d s c a r r ie d t h e c o n t r o l s ig n a l fo r t h e C r yd o m r e la y u s e d fo r a u t o ma t ic c o n t r o l o f p o w e r t o t h e t h a w in g s ys t e m. Data Logging Digit al M ul ti m eter Ano t he r d e vi c e u s e d t o c o l l e c t d a t a w a s a d a t a l o g g i ng d i g i t a l m u l t i m e t e r An Ex t e c h (W a l t h a m M A ) m o d e l M L 7 2 0 w a s u s e d It c o u l d s t o re u p t o 4 3 ,0 0 0 d a t a p o i n t s It f e a t u re d a n i n f ra re d c o m m u n i c a t i o n p o rt w h i c h c o u l b e l i n k e d t o a PC v i a t h e s e ri a l p o rt T h i s al l o wed t h e dat a t o b e t ran s m i t t ed af t er t h e ac t ual dat a co l l ect i o n pro ces s h ad en ded, an d s t o red o n a perm an en t b as i s el s ewh ere. F i gure 37. Ho us i n g. O b j e c t 3 -7 To w e r-L a p t o p .j p g (349 KB).

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28 S o ft w a re T h e r e w e r e th r e e s i g n i f i c a n t w a y s i n w h i c h s of tw a r e w a s u ti l i z e d i n th i s i n v e s ti g a ti on r e l a te d to d a ta I t w a s u s e d to m a n i p u l a te c on tr ol a n d ob s e r v e th e d a ta c ol l e c ti on p r oc e s s A f te r d a ta c ol l e c ti on s of tw a r e w a s u s e d to r e d u c e a n d c om b i n e th e d a ta a n d i ts f i n al us e wa s f o r dat a v i s ual i zat i o n T h e f i rst t wo repr es en t ed m ai n l y cus t o m pro gram m i n g, wh i l e t h e t h i rd r el i ed o n co m m erci al l y av ai l ab l e graph i cs s o f t ware. Data col l ection A cus t o m wri t t en Vi s ual Ba s i c 6 (Mi cro s o f t Re dm o n d, W as h i n gt o n ) pr o gram was us ed t o co n t ro l t h e dat a ac qui s i t i o n card. It ut i l i zed a DL L dri v er i n t erf ace kn o wn as D r iv e r L in x p r o v id e d b y Ke it h le y. T h e V is u a l B a s ic p r o g r a m a ls o c o n v e r t e d t h e r a w b it d a t a i nt o m e a ni ng f u l u ni t s o f m e a s u r e I t w a s r e s p o ns i bl e f o r s a vi ng a l l d a t a p o i nt s i n a c o m m a d e l i m i t e d t e xt f i l e T he p r o g r a m c o nt r o l l e d t he d a t a c o l l e c t i o n, m a ni p u l a t e d t he d a t a a n d s a v e d i t w h i l e t h e u s e r s a w t h e d a t a i n re a l t i m e a s i t w a s c o l l e c t e d Ano t he r s o f t w a r e p r o g r a m w a s u s e d t o c o l l e c t t he a l t e r na t i ng c u r r e nt d a t a f r o m t he d a t a l o g g i ng m u l t i m e t e r T hi s p r o g r a m w a s c a l l e d B s 8 1 5 x D a t a L o g g i ng S y s t e m T he s o f t ware wa s pro v i ded b y E x t ech wi t h t h e m ul t i m et er. T h e pro gram was us ed t o deco de t he d a t a t r a ns m i s s i o n f r o m t he d a t a l o g g i ng d i g i t a l m u l t i m e t e r I t c o u l d a l s o d i s p l a y t he d a ta a n d s a v e th e d a ta i n a s ta n d a r d c om m a d e l i m i te d te x t f or m a t or a p r op r i e ta r y f or m a t. O t he r c u s t o m w r i t t e n V i s u a l B a s i c p r o g r a m s a s s i s t e d i n c o m bi ni ng a nd r e d u c i ng t he d a t a O n e p rogra m m e rg e d t h e t w o s e p a ra t e d a t a f i l e s c o n t a i n i n g v o l t a g e a n d t e m p e ra t u re i n th e f i r s t, a n d c u r r e n t d a ta i n th e s e c on d T h i s p r og r a m c r e a te d a th i r d s y n c h r on i z e d d a ta f i l e t h at was f urt h er m an i pul at ed. T h es e f urt h er m an i pul at i o n s s uch as resi s t an ce c a lc u la t io n s w e r e p r e fo r me d b y a n o t h e r c u s t o m V is u a l B a s ic p r o g r a m.

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29 Data visual iz ati on T h e pri m ary s o f t ware us ed i n t h i s i n v es t i gat i o n f o r t h e v i s ual i zat i o n o f dat a wa s A x um 6. 0 b y M at h So f t E n gi n eeri n g & E ducat i o n In c. ( Ca m b ri dge, MA ). A x um was us ed i n pref eren ce t o a s preads h eet s uch as E x cel b y M i cro s o f t o r Quat ro Pr o b y Co rel Co rp. (Ot t awa ONT, Ca n ada). T h e i n ab i l i t y o f ei t h er t o deal wi t h l arge dat a s et s f o r gr aph i n g, was t h e pri m ary reas o n f o r pr ef eren ce gi v en t o a dedi cat ed graph i n g pro gram A x um was capa b l e o f eas i l y graph i n g dat a s et s o f m o re t h an 175, 000 po i n t s T h i s s i ze da t a s et was c o m m o n i n t hi s i nve s t i g a t i o n. E q u i p me n t C a rt Fo r e a s e o f u s e i n i nve s t i g a t i o n, s e ve r a l k e y c o m p o ne nt s w e r e m o u nt e d o n a n e q u i p m e nt c a r t. T h e c a r t w a s th e s a m e c a r t d e s c r i b e d i n R ob e r ts ( 1 9 9 4 ) I t w a s c u s tom m a d e f or t h a t w o r k I t r e t a in e d it s g e n e r a l fo r m, b u t w a s mo d ifie d t o fit t h e n e e d s o f t h is i n v e s ti g a ti on A s i n th e or i g i n a l f or m th e c a r t h a d th e A C p ow e r s u p p l y m ou n te d u n d e r i ts t o p s u r f a c e B o t h o f t he m a nu a l c i r c u i t br e a k e r s w e r e i nt a c t a nd l e f t p o s i t i o ne d a s i n t he o ri gi n al s et up. T h e m o di f i cat i o n s st ar t ed o n t h e t o p sur f ace. T h e si gn al co n di t i o n i n g h o usi n g wa s m ou n te d th e r e I t w a s s e c u r e l y f a s te n e d b y s i x s c r e w s a n d w a s h e r s A v e r ti c a l p l y w ood sur f ace f r o m t h e o r i gi n al desi gn was used t o m o un t t h e pl ug s n eeded t o co n n ect t h e t est c e l l T he C r y d o m r e l a y w a s m o u nt e d i ns i d e a p l u g bo x he r e Fe m a l e ba na na j a c k s f o r t he D a t a lo g g in g d ig it a l mu lt ime t e r w e r e a ls o lo c a t e d in a s e p a r a t e p lu g b o x fa s t e n e d t o t h is s u r f a c e Ano t he r p l u g bo x ha d a f e m a l e s u b D m i ni 9 p i n c o nne c t o r u s e d f o r c o nne c t i ng t he vo l t a g e s a m p l i ng l e a d s a nd t he c o nt r o l s i g na l f o r t he C r y d o m r e l a y A p i c t u r e o f t he l ay o ut can b e s een i n F i gure 38.

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30 O n l y o n e o f t h e f o l d d o w n s h e l v e s o f t h e c a rt w a s u t i l i z e d d u ri n g t h i s re s e a rc h T h i s s h el f pro v i de a w o rki n g s pace wh ere t h e do cki n g s t at i o n f o r t h e l apt o p an d o t h er m i s c e l l a n e o u s i t e m s u s e d d u ri n g e x p e ri m e n t s w e re p l a c e d Th e d a t a a c q u i s i t i o n c a rd h o us ed i n t h e do cki n g s t at i o n co ul d t h en b e co n n ect ed b y t h e 0.5 m dat a ca b l e t o t h e s i gn al co n di t i o n i n g h o us i n g. T h i s al s o pl ace d t h e l apt o p at a co n v en i en t h ei gh t i n wh i ch t o v i ew a nd c o nt r o l t he p r o c e s s e s d u r i ng d a t a c o l l e c t i o n. Figure 3-8. Box Arrangement.

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31 Appar atu s Constr ucti on T h e co n s t ruct i o n o f t h e appa rat us was b ro ken i n t o t h e ph y s i cal el em en t s t h at m ake up e ach po rt i o n o f t h e appa rat us E ach el em en t h ad a n um b er o f co n s t rai n t s o r ch aract eri s t i cs t h at h ad t o b e adh ered t o i n o rder t o m eet t h e n eeds o f t h e ex peri m en t al wo rk. T h es e des i gn co n s i derat i o n s were an es s en t i al part o f t h e co n s t ruct i o n i n addi t i o n t o t h e ac t ual co n s t ruct i o n m et h o ds us ed. P r obe Constr ucti on Des ign T he t e m p e r a t u r e p r o be d e s i g n r e f l e c t e d t he s p e c i f i c ne e d s o f t he e xp e r i m e nt I n t he e x p e ri m e n t s t h e p rob e h a d t o re m a i n s t a t i o n a ry w h e n i t w a s i n c o n t a c t w i t h a l i q u i d It a l s o h a d t o m a i n t a i n i t s p o s i t i o n d u ri n g p h a s e c h a n g e re l a t e d e x p a n s i o n o r c o n t ra c t i o n T hi s l e d t o s e l e c t i ng a r i g i d p r o be I f t he s e ns o r e nd o f t he p r o be w e r e p l a c e d i ns i d e t he s a m p l e t he s e ns o r a r e a a t t he t i p w o u l d ha ve ha d o nl y o ne s u p p o r t p o i nt T he p r o be ne e d e d t o be s u p p o r t e d a t bo t h e nd s f o r g r e a t e r s t a bi l i t y a nd a c c u r a c y i n p l a c e m e nt T he s u p p o r t p r o bl e m w a s s o l ve d by a d d i ng a no t he r l i ne a r s e c t i o n t o t he p r o be T hi s g a ve t he c o m p l e t e d p r o be t w o f i xe d s u p p o r t p o i nt s a s i t s p a nne d t he d i a m e t e r o f t he t e s t c e l l T he n e w lin e a r s e c t io n a ls o h a d t h e o p p o r t u n it y t o b e c o me a s e c o n d s e n s o r h o ld e r fo r t h e s a me l o c a t i o n. T he l i ne a r d e s i g n a l s o a i d e d i n d e t e r m i ni ng l o c a t i o n o f t e m p e r a t u r e s e ns o r o n t he p r o be i n t he s a m p l e T hi s d e s i g n a l l o w e d f o r t w o i nd e p e nd e nt s e ns o r s t o g a t he r d a t a a t t he s a m e g e o m e t ri c l o c a t i o n i n t h e s a m p l e c e l l T h e pr o b es wer e at t i m es ex po sed t o el ect r i c f i el ds o n t h e o r der o f 50 0 v o l t s. T h us, t h e pro b es h ad t o b e el ect ri cal l y n o n -co n duct i v e. By s el ect i n g a ri gi d ceram i c wi t h t wo roun d c h a n n e l s i n i t b a re t h e rm o c o u p l e w i re s c o u l d b e u s e d i n s i d e t h e p rob e Th e s e b a re

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32 w i re s h e l p e d t o k e e p t h e t o t a l d i a m e t e r of t h e p rob e s m a l l Th e s m a l l e r t h e p rob e d i a m e t e r, t h e l es s h eat co ul d f l o w t o o r f ro m t h e ex t ern al en v i ro n m en t t h ro ugh t h e pro b e wh i ch co ul d h av e ac t ed as a f i n T h e ch o i ce o f a gl as s ceram i c t h at h ad a l o w t h erm al co n duct i v i t y as s i s t ed i n reduci n g t h i s f i n n i n g ef f ect F i n n i n g b y t h e t h erm o co upl e l eads t h em s el v es was addres s ed b y us i n g s m al l t h erm o co upl e wi res i n t h e pro b es s i n ce t h e m et al o f t h e w ir e h a d a la r g e t h e r ma l c o n d u c t iv it y. A ss e mb ly T h e f i rst s t ep i n co n s t ruct i n g t h e pro b es was t o b reak t h e ce ram i c i n s ul at o r i n t o t wo s ect i o n s T h e i n s ul at o r cam e i n a s t an dard 152 m m (6") l en gt h T h e l en gt h was s co red at o n e o f t wo po si t i o n s dependi n g o n wh er e t h e pr o b e was i n t en ded t o b e used. I f used as a c e n te r p r ob e th e c e n te r of th e i n s u l a tor w a s s c or e d a n d b r ok e n I f on th e h a n d i t w a s to b e us ed as a t o p o r b o t t o m pro b e t h e s co re i s m ade o f f cen t er. T h i s s co re l o cat i o n ref l ect ed t he a p p r o xi m a t e ha l f r a d i u s l e ng t h f o r t he s a m p l e B y ha vi ng d i f f e r e nt l e ng t hs e a c h p r o be ha d a p p r o xi m a t e l y t he s a m e l e ng t h t ha t p r o t r u d e d f r o m t he s a m p l e c e l l f r o m e a c h d i f f e r e nt lo c a t io n t h a t a p r o b e o c c u p ie d T h e b r e a k s w e r e s a n d e d a s n e e d e d t o h a v e a r e a s o n a b ly f l at en d. T h e n e x t s t e p w a s t o in s e r t t h e t h e r mo c o u p le w ir e s in t o t h e c h a n n e ls o f t h e c e r a mic i ns u l a t o r T he c l e a r a nc e w a s l o w a nd c a r e w a s e xe r c i s e d no t t o be nd t he ba r e l e a d s T he l eads were t h en b e t wi s t ed t o get h er at t h e en d wh ere t h e b reak was i n i t i at ed. T h e l eads were s o l dered t o get h er af t er t wi s t i n g. T h i s gav e a s o l i d pro b e t i p f o rm ed f ro m t h e s o l der a n d th e r m oc ou p l e l e a d s T h e s h a p e of th e ti p a t th i s p oi n t of c on s tr u c ti on w a s s i m i l a r to a te a r d r op w i th a f l a t b ott om T h e te a r d r op s h a p e w a s m a c h i n e d b y f i l i n g a n d s a n d i n g to co n f o rm t o t h e ex t eri o r di am et er o f t h e ce ram i c i n s ul at o r. F urt h er m ach i n i n g o f t h e ax i al

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33 di r ect i o n t h en f l at t en ed t h e t i p an d r edu ced t h e ax i al h ei gh t T h e f i n al f o r m o f t h i s t i p wa s a d i s k a t t he p r o be e nd o r a n e nd c a p t o t he p a r t i a l p r o be l e ng t h. A t th i s p oi n t i n th e p r ob e c on s tr u c ti on a s p e c i a l c on s tr u c ti on b e n c h w a s u s e d to f i n i s h th e p r ob e a s s e m b l y T h e c u s tom c on s tr u c ti on b e n c h w a s s p e c i f i c a l l y d e s i g n e d to a l l ow th e p r ob e s e c ti on s to b e a s s e m b l e d i n a s tr a i g h t l i n e T h e s i m p l e g e om e tr i c r e l a ti on t ha t a l i ne i s f o r m e d i f t w o p l a ne s i nt e r s e c t w a s u s e d T he be nc h c r e a t e d a l i ne by u t i l i z i ng t he t w o p e r p e nd i c u l a r p l a ne s o f t he r a i l o n t he be nc h. T he r a i l o f t he be nc h w a s w he r e t he p r o b e le n g t h s w e r e p la c e d c o n t a c t in g b o t h p la n e s s imu lt a n e o u s ly. T h u s t h e p r o b e s lie p a ra l l e l t o t h e i n t e rs e c t i o n o f t w o p l a n e s w h i c h w a s a s t ra i g h t l i n e b y d e f i n i t i o n O n c e a p r ob e w a s i n p os i ti on on th e r a i l th e e n d c a p s c ou l d b e g l u e d f i r s t to cer am i c i n sul at o r an d t h en t o o n e an o t h er T h e b en ch r ai l h ad an o pen sl o t t o al l o w access t o t he j u nc t i o n be t w e e n t he e nd c a p s T hi s s l o t k e p t t he a d he s i ve f r o m c o nt a c t i ng t he be nc h a nd bo nd i ng t he p r o be t o i t T he s ha l l o w l i p o f t he r a i l a l l o w e d s i m p l e c l i p s t o be a p p l i e d to t h e p r ob e T h e s e c l i p s s e r v e d tw o p u r p os e s F i r s t, th e y h e l d th e p r ob e ti g h tl y to bo t h o f t he i nt e r s e c t i ng p l a ne s o f t he r a i l e nf o r c i ng t he s t r a i g ht l i ne c o nd i t i o n. S e c o nd t he cl i ps h el d t h e pro b e s o i t co ul d n o t m o v e duri n g t h e curi n g pro ces s o r dur i n g l at er appl i cat i o n o f t h e adh es i v e. T h e a d h e s i v e u s e d to b on d th e e n d c a p s to on e a n oth e r w a s th e e l e c tr i c a l i n s u l a tor be t w e e n t he t w o s e p a r a t e t he r m o c o u p l e e nd c a p s T hi s e l e c t r i c a l i s o l a t i o n w a s ve r i f i e d by ch ecki n g wi t h a di gi t al m ul t i m et er f o r co n t i n ui t y b et wee n t h e l eads t h at pro t rude f ro m eac h e nd o f t he p r o be Af t e r i s o l a t i o n w a s ve r i f i e d a l a y e r o f a d he s i ve w a s a p p l i e d o n t he e x p os e d s u r f a c e of th e tw o b on d e d e n d c a p s T h i s l a y e r a c te d a s th e e l e c tr i c a l i n s u l a ti on fo r t h e e x p o s e d r a d ia l s e c t io n o f t h e t h e r mo c o u p le s T h e b e n c h w a s a g a in in s t r u me n t a l in

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34 ho l d i ng t he p r o be d u r i ng t hi s a p p l i c a t i o n, a nd a l l o w e d t he l a y e r t o be a p p l i e d a r o u nd t he e nt i r e c i r c u m f e r e nc e i n o ne a p p l i c a t i o n. T h e p r ob e s w e r e th e n a s tr a i g h t l i n e d ou b l e s e n s or d e v i c e s w i th l oos e w i r e l e a d s on b o t h en ds T o en h an ce c o n n ect i v i t y o f t h e pro b es t o dat a ac qui s i t i o n l eads t h e l o o s e wi res o n o n e en d were co n n ect ed t o t h e m al e en d o f a t wo b l aded c o n n ect o r. T h e t wo pi ece O me g a c o n n e c t o r p h ys ic a lly c la mp e d o v e r t h e e n d o f t h e c e r a mic w h e r e it c o u ld b e e a s ily c on n e c te d to i ts f e m a l e c ou n te r p a r t on th e d a ta a c q u i s i ti on l e a d T h e f i n a l m a l e c on n e c tor c o u ld n o t b e p u t in p la c e u n t il t h e p r o b e w a s in p o s it io n in t h e s a mp le c e ll. Sam pl e Ce l l Constr ucti on Des ign T he p r o c e s s o f d e s i g ni ng t he s a m p l e c e l l i nvo l ve d i d e nt i f y i ng t he m o s t i m p o r t a nt c on s tr a i n ts r e l a te d to t h e r e s e a r c h a n d th e n f i n d i n g w a y s to s a ti s f y th e m T h e c e l l h a d to b e ab l e t o pro v i de t h e s t ruct ural ri gi di t y f o r h o l di n g t h e pro b es i n a f i x ed po s i t i o n It act ed a s a f o r m t o s ha p e t he l i q u i d g e l d u r i ng i t s p ha s e c ha ng e f r o m l i q u i d t o s o l i d I n a d d i t i o n, i t h ad t o b e ab l e t o pro t ect t h e pro b es duri n g t h e v o l um e ch an ge t h at t h e gel un dergo es w h e n b e i n g f roze n Th e c e l l e l i m i n a t e d a l t e rn a t e e l e c t ri c a l p a t h s a roun d t h e s a m p l e i t h e l d It n eede d a geo m et ri c s h ape t h at co ul d b e reduce d di m en s i o n al l y f ro m a t h ree di m en s i o n al s t ruct ure t o a t wo di m en s i o n al s h ape f o r si m pl er n um eri cal m o del s T h e o v eral l des i gn re q u i re d a m i n i m u m o f m a c h i n i n g w i t h p re f e re n c e g i v e n t o re a d i l y a v a i l a b l e p a rt s T he f i r s t t a s k i n t he d e s i g n w a s s e l e c t i ng t he g e o m e t r i c s ha p e a nd m a t e r i a l o f t he s a m p l e c e l l Th i s s h a p e w a s a l s o t h e s o l i d s h a p e o f t h e g e l A s i m p l e c y l i n d e r w a s u s e d T he c y l i nd e r p r o vi d e s a t hr e e d i m e ns i o na l s ha p e t ha t c o u l d be r e d u c e d t o t w o d i m e ns i o ns d u e t o i t s a x i s y m e t ri c n a t u re Th i s s h a p e i s c o m m o n i n p i p i n g a n d t h u s re a d i l y a v a i l a b l e

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35 P V C p ip in g w a s r e a d ily a v a ila b le a s a c o n s t r u c t io n ma t e r ia l, a n d h a d t h e a d d it io n a l b e n e fit of a v e r y h i g h e l e c tr i c a l r e s i s ta n c e I n s ta n d a r d s c h e d u l e 4 0 f or m i t w a s v e r y r i g i d f or s h o rt s pan s an d was eas i l y m ach i n ed. T he c e l l w a s c l o s e d o n bo t h e nd s by t he e l e c t r o d e s w hi c h d i r e c t l y c o nt a c t e d t he gel T h i s co n f i gurat i o n creat ed a f i x ed v o l um e ca v i t y f o r t h e gel b o un ded b y t h e el ect ro des o n t h e en ds Un f o rt un at el y t h e gel un derwen t ex pan s i o n duri n g f reezi n g o n t h e s am e o rder as t h at o f wat er dur i n g f reezi n g o r r o ugh l y t en percen t an d a ri gi d cav i t y wo ul d h av e b een c r a c k e d o r b r o k e n A d d it io n a lly a n y r ig id p r o b e t h a t e n t e r e d t h e c a v it y r a d ia lly w o u ld h av e b een s h eared i f ex pan s i o n was al l o wed i n t h e ax i al di rect i o n T h e des i gn ch al l en ge was t h en b ro ken i n t o 2 part s f i rst t o m ai n t ai n t h e un f ro zen geo m et ry an d s eco n d t o pro t ect t h e i n ser t ed t em per at ur e pr o b es. O ne p a r t o f t he d e s i g n s o l u t i o n w a s t o m a k e s u r e t he e l e c t r o d e s c o u l d be c o n s t r a in e d fr o m mo v in g d u r in g t h e p h a s e c h a n g e e x p a n s io n T h is t h e n d ic t a t e d t h e s a mp le m u s t u n d e rg o e x p a n s i o n o n l y i n t h e ra d i a l d i re c t i o n Si n c e t h e PV C w a s ri g i d a c o mp r e s s ib le la ye r w a s a d d e d t o it s in t e r io r t h a t a llo w e d fo r r a d ia l g e l e x p a n s io n T h is m a i nt a i ne d t he ba s i c g e o m e t r y o f a c y l i nd e r k e e p i ng t he o r i g i na l he i g ht i nt a c t a nd c ha ng i ng on l y th e d i a m e te r of th e s a m p l e I t a l s o p r ote c te d th e p r ob e s e n te r i n g r a d i a l l y f r om e n c o u n t e ri n g a n y a x i a l s h e a ri n g d u ri n g t h e p h a s e c h a n g e e x p a n s i o n T h e l as t co n s t rai n t s t h at were s at i s f i ed we re n o t as ch al l en gi n g. T h ey i n cl uded acc o un t i n g f o r h o w t h e gel wi l l b e po ured i n t o t h e ca v i t y T h i s requi red a l i qui d t i gh t s eal o n t h e ax i al b o t t o m an d radi al s urf ace s T h e ce l l was dri l l ed f o r t h e pro b es an d el ect ri cal le a d s t o a llo w t h e ir e n t r y.

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36 A ss e mb ly T h e f i rst ph as e i n as s em b l y was t o creat e t h e b as i c PVC pl as t i c s h el l T h e s h el l was m a d e f r o m t w o s t a nd a r d 7 6 m m ( 3 ) P V C f i t t i ng s T he f i r s t w a s a f e m a l e d r a i n, w a s t e a nd v en t (DW V) f i t t i n g. T h i s f i t t i n g was f em al e t h readed f o r a st an dard 76 m m (3") t h readed p l u g t ha t t r a ns i t i o ns t o a f e m a l e s l i p j o i nt T he s e c o nd f i t t i ng w a s a 7 6 m m ( 3 ) m a l e D WV a d a p t e r T h is fit t in g h a d a ma le s lip s id e t h a t t r a n s it io n s t o a fe ma le t h r e a d T h e t w o s lip j o i n t s w e re g l u e d t o g e t h e r w i t h a s t a n d a rd PV C g l u e T h e s h el l was t h en m o di f i ed t o acc o m m o dat e t h e t em perat ure pr o b es T h e ce n t er h e ig h t fo r t h e s mo o t h s e c t io n w a s d r ill e d w it h a n 2 4 1 mm ( 0 0 9 5 ) d ia me t e r b it perpen di cul ar an d i n l i n e wi t h t h e ax i s o f t h e cy l i n der. T h e cy l i n der was t h en ro t at ed 180 an d t h e s eco n d cen t er h o l e dri l l ed. T h e s am e pro cedure wa s us ed t o dri l l t h e t wo quart er h ei g h t s. T h e t h r ee co l l i n ea r p o i n t s o n ea ch si d e d ef i n ed d i am et er s t h at cr o ss t h e c y l i n d er s s m o o t h s e c t i o n a t i t s a x i a l 1 /4 h e i g h t 1 /2 h e i g h t a n d 3 /4 h e i g h t In o rd e r t o i n s u re accur acy o f t h e pl acem en t o f t h e h o l es, t h ese m o di f i cat i o n s wh er e pr ef o r m ed b y a m ach i n i st o n a m i l l i n g m ach i n e. T h e s h e ll h a d t w o k e y fe a t u r e s n o w c o mp le t e d T h e s h e ll c o u ld h o ld r ig id p r o b e s in p l a c e a t p r e s c r i b e d h e i g h t l oc a ti on s I t a l s o h a d a n a tu r a l s h ou l d e r a t th e tr a n s i ti on f r om t hr e a d e d t o s m o o t h a t e a c h e nd T he s e s ho u l d e r s a c t e d a s t he d e f i ni ng s t o p s f o r t he e l e c t rode s Th e h e i g h t o f t h e e x p e ri m e n t a l c y l i n d e r w a s n o w f i x e d F i g u re 3 -9 i s a p i c t u re o f t h e fin is h e d s h e ll. Th e e l e c t rode s h a d t o b e h e l d i n p l a c e Tw o s e p a ra t e c o m p re s s i o n m e t h o d s w e re c o n s t r u c t e d fo r t h is p u r p o s e T h e fir s t u s e d s t a n d a r d ma le t h r e a d e d 7 6 2 mm ( 3 ) d r a in pl ugs T h es e pl ugs co ul d b e s crewed i n t o t h e en ds o f t h e s h el l By us i n g a s pace r, t h e pl ug

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37 c o u l d a p p l y a n a xi a l f o r c e t o t he e l e c t r o d e T hi s c o nf i g u r a t i o n a l l o w e d e a c h e l e c t r o d e t o be i n depen den t l y h el d i n pl ace T wo s pace rs were us ed i n t h e res earch T h e f i rst was a s i m pl e 51 m m (2") P VC s l i p c o u p l i n g t h a t f i t t e d i n s i d e t h e t h re a d e d a re a Th e s e c o n d s p a c e r w a s c u s t o m m a d e It u s e d o n e i n c h t h i c k p o l y s t re n e f o a m t o c o n t a c t t h e e l e c t rode a c ros s i t s c o m p l e t e s u rf a c e T h e f o am i n s ul at i o n was s pl i t i n t o t wo s em i -ci rcl es f o r eas y pl ace m en t an d rem o v al It h ad a c e nt r a l ho l e j u s t l a r g e e no u g h t o a l l o w t he e l e c t r i c a l c o nne c t i o n t o p a s s t hr o u g h. T he f o a m r e q u i r e d a s t i f f s u r f a c e t o a p p l y a r e l a t i ve l y e ve n l o a d f r o m t he e nd p l u g t o t he el ect ro de b en eat h t h e f o am A 76 m m (3") di am et er pl y wo o d ci rcl e wa s f i t t ed t o co n s t ruct Figure 3-9. Shell With Ports.

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38 t h e r i gi d sur f ace b et ween t h e en d p l ug an d f o am T h e wo o d ci r cl e was sawed o n a r adi us, a nd t he c e nt e r d r i l l e d t o a l l o w f o r p a s s a g e o f a n e l e c t r i c a l l e a d t o t he e l e c t r o d e T he t h readed pl ugs were m o di f i ed f o r t h e el ect ri cal l ead a l s o T h ey h ad a h o l e dri l l ed i n t h e ax i al c e n t e r t h a t w a s a p p rox i m a t e l y 1 0 m m (3 /8 ) a l l o w i n g p a s s a g e o f t h e e l e c t ri c a l c o n n e c t o r. T he s e c o nd m e t ho d u s e d a 3 0 5 m m ( 1 2 ) c a s t i r o n s c r e w s t y l e C c l a m p a nd s t an dard 19 m m (3/ 4") co pper sl i p co upl i n gs T h e co upl i n gs act ed as a s pace rs t o pro t ect t he e l e c t r o d e e l e c t r i c a l c o nne c t o r s w he n t he a xi a l l o a d w a s a p p l i e d by t he c l a m p T he seco n d m et h o d al l o wed t h e cl am pi n g f o r ce t o b e ex t er n al i zed f r o m t h e sh el l I t al so a l l ow e d th e e l e c tr od e s to b e v i e w e d w h i l e i n th e c l a m p e d s ta te H ow e v e r i t d i d n ot a l l ow f o r t h e cl am pi n g o f o n l y o n e el ect ro de l i ke t h e drai n pl ug m et h o d. T h e def i n ed cy l i n der i n s i de t h e s h el l co ul d b e f i t t ed wi t h t h e i n t eri o r i n s ul at i o n at a n y ti m e a f te r th e s h e l l c on s tr u c ti on w a s c om p l e te T h e i n s u l a ti on w a s c u t w i th a u ti l i ty kn i f e t o di m en s i o n s o f 254 m m (10") b y 49. 21 m m (1 15/ 16"). T h i s was s l i gh t l y o v ersi zed in b o t h t h e d ime n s io n s o f le n g t h a n d w id t h T h e e x t r a le n g t h h e lp e d t h e in s u la t io n fo r m a ti g h t j oi n t to e a c h c u t e n d a s th e i n s u l a ti on h a d to c om p r e s s s l i g h tl y to f i t i n th e i n te r i or ci rcum f eren ce s h el l T h e ex t ra h ei gh t di d t h e s am e f o r t h e b o t t o m s urf ace t h at co n t act ed t h e el ect ro de. T h e e x te r i or i n s u l a ti on w a s n ot p l a c e d on th e s a m p l e c e l l u n ti l i t w a s s e c u r e on i ts h o l der. T h e t em perat ure pr o b es were i n pl ace at t h i s t i m e. T h e ex pan di n g f o am was s p r a ye d o n t o t h e a r e a c o r r e s p o n d in g t o t h e c e n t r a l s mo o t h in t e r io r a r e a t h a t e v e n t u a lly c o nt a i ne d t he s a m p l e i n t he c e l l I t w a s a l l o w e d t o e xp a nd i n p l a c e a nd s e a l a r o u nd t he p r o b e s T h e fo a m r e q u ir e d e ig h t h o u r s t o c u r e a n d b e c o me s t if f.

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39 Sam pl e Ce l l Hol der Constr ucti on Des ign S e v e r a l r e q u ir e me n t s a n d c o n d it io n s w e r e id e n t ifie d t h a t p la ye d a r o le in t h e s a mp le c e ll h o ld e r d e s ig n T h e s a mp le c e ll w a s n o t s e lf s t a n d in g I t r e q u ir e d a s t a n d t h a t c o u ld h ol d i t i n a f i x e d p os i ti on T h e r e q u i r e d f i x e d p os i ti on s w e r e s a m p l e c e l l a x i s h or i z on ta l or ax i s v ert i cal T h e ce l l h o l der was ab l e t o t ran s i t i o n f ro m o n e po s i t i o n t o t h e o t h er wi t h o ut r e q u ir in g t h e s a mp le c e ll t o b e r e mo v e d T h e s a mp le c e ll h o ld e r r e s t r a in e d t h e s a mp le c e ll a s i t m o ve d t o a nd f r o m t he t e m p e r a t u r e c o nt r o l l e d c ha m be r I t w a s d e s i r a bl e f o r i t t o be e a s i l y g r i p p e d d u r i ng t he s e t r a ns i t i o ns T he ho l d e r p r o t e c t e d t he p r o be s f r o m be nd i ng s tr e s s e s a t a l l ti m e s f r om th e th e r m oc ou p l e l e a d s th a t c on n e c te d to th e d a ta c ol l e c ti on h o u s i n g A ss e mb ly Th e c e l l h o l d e r w a s c o n s t ru c t e d o f w o o d Th e l a y o u t c a n b e s e e n i n F i g u re 3 -6 Fi r s t t he ba s e w a s c u t o u t o f 5 0 m m x 1 5 2 m m ( 2 x6 ) s p r u c e T he n, t he c a r r i a g e p o r t i o ns were cut f ro m 50 m m x 101 m m (2"x 4") s pruce. T h e ca rr i age po rt i o n s were t h en p o s it io n e d c e n t e r e d w it h r e s p e c t t o t h e lo n g e d g e o f t h e b a s e T h e s p a c e b e t w e e n t h e ir in s id e e d g e s w a s s e t t o e q u a l t w o r a d ia l r id g e s o n t h e e x t e r io r o f t h e s a mp le c e ll. T h is creat ed t wo s t o ps prev en t i n g t h e ce l l f ro m s l i di n g i n i t s ax i al di rect i o n T h e ca rr i age p o rt i o n s w e re t h e n f a s t e n e d t o t h e b a s e b y d ry w a l l t y p e w o o d s c re w s Th e u p ri g h t s w e re cut f r o m 50 m m x 10 1 m m ( 2"x 4") spr uce. T h e up r i gh t was t h en cen t er ed o n t h e b ase s ho r t s i d e w i t h i t s e nd f l u s h w i t h t he ba s e bo t t o m I t w a s a t t a c he d i n t hi s p o s i t i o n t o t he b ase wi t h t h e sam e t y pe scr ews. T h e h an dl e was cut f r o m 19 m m x 38 m m ( 3/ 4"x 11/ 2")

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40 s p r u c e I t w a s c e n t e r e d o n t o p o f t h e u p r ig h t fl u s h w it h t h e e d g e s a n d a t t a c h e d b y a dry wal l t y pe s crew o n eac h en d. T he s a m p l e c e l l w a s t he n p l a c e d i n t he c a r r i a g e t o d e t e r m i ne t he he i g ht o f t he p rob e s Th i s h e i g h t w a s t h e n m a rk e d a n d d ri l l e d w i t h i d e n t i c a l s p a c i n g t o t h e s a m p l e c e l l T h e ce l l h o l der t h en h ad i n t egral t h erm o co upl e l ead h o l es T h es e 38 m m deep h o l es al l o wed t h e t h er m o co up l e l eads t o app r o ach t h e sam pl e cel l i n a l i n ear f ash i o n T h ey al so p r e v e n te d th e l e a d s f r om a p p l y i n g a n y b e n d i n g s tr e s s on th e p r ob e s d u r i n g m ov e m e n t of th e h ol d e r w h e n th e c e l l w a s i n p l a c e A p i c tu r e of th e c e l l h ol d e r a t th i s p oi n t of c o n s t ru c t i o n w a s t a k e n (F i g u re 3 -1 0 ). T h e l a s t p a r ts to b e a s s e m b l e d w e r e th e h or i z on ta l l e g s T h e l e g s w e r e c u t f r om c r a f t s ti c k s T h e l e n g th s w e r e a d j u s te d to a l l ow th e h ol d e r to s i t l e v e l w i th c l e a r a n c e f or t h e s am pl e ce l l i n t h e h o ri zo n t al po s i t i o n E ach l eg wa s cl earan ce dri l l ed f o r t h e s crew t h at at t ach ed i t A dry wal l s crew wi t h an addi t i o n al f l at s t eel was h er was us ed t o at t ach eac h l e g i nt o i t s p o s i t i o n. Figure 3-10. Sample Holder Picture, Front and Side Views.

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41 Sign al Condit ionin g Housing Constr ucti on Des ign T he d e s i g n o f t he s i g na l c o nd i t i o ni ng ho u s i ng a d d r e s s e d s e ve r a l i s s u e s Fi r s t t he ho u s i ng a c t e d a s a n e l e c t r i c a l s hi e l d f o r t he s i g na l c o nd i t i o ni ng e q u i p m e nt T he ho u s i ng was eas y t o acc es s It al s o pro v i ded a c o n v en i en t m an n er f o r v i ewi n g t h e C ro m pt o n m et er di s pl ay s E as y acc es s t o an ex t ern al po wer sw i t ch f o r t h e s am e m et ers wa s al s o des i red, s i n ce t h ey requi red st an dard 110/120v i n put t o o perat e. Ov eral l h o us i n g s i ze w as i m pact ed by t he ne e d t o p r o vi d e a d e q u a t e r o o m f o r m o u nt i ng t he ba c k p l a ne a nd s i g na l c o nd i t i o ni ng m od u l e s on th e i n te r i or R e a d i l y a v a i l a b l e p a r ts a n d s u p p l i e s w e r e g i v e n p r e f e r e n c e to m i n i m i ze c o s t Co n s t ruct i o n t ech n i ques t h at requi red o n l y s i m pl e h an d t o o l s were gi v en p r e fe r e n c e a s w e ll. A ss e mb ly T h e f i rst part o f co n s t ruct i o n was s el ect i n g a s ui t ab l e m at ch f o r t h e gen eral ph y s i cal ch aract eri s t i cs t h e h o us i n g f ul f i l l ed. A t o wer st y l e co m put er cas e wa s s el ect ed. I t pro v i ded t he r e q u i r e d r o o m s hi e l d i ng a nd e a s e o f a c c e s s T he c a s e w a s t he n m o d i f i e d f o r t he s p e c i f i c ne e d s o f t he e q u i p m e nt i t ho u s e d T he i nt e r i o r o f t he c a s e w a s c l e a ne d o u t l e a vi ng o n ly t h e d r iv e b a y s u b s t r u c t u r e a n d t h e c o mp u t e r p o w e r s w it c h T h e t o p t w o d r iv e b a ys was us ed t o m o un t t h e C ro m pt o n m et ers. By b ei n g m o un t i n g cl o s e t o t h e t o p o f t h e ca s e, th e y w e r e e a s y to v i e w T h e e x te r i or c ov e r s f or th e d r i v e b a y s w e r e r e m ov e d m a k i n g r oom f o r t he m e t e r s T he o p e ni ng w a s t he n c l o s e d d o w n i n he i g ht w i t h m e t a l t o m a t c h t he m o u nt i ng c a s e s o f t he C r o m p t o n m e t e r s T he e xp o s e d a r e a t ha t w a s p r r e vi o u s l y c l o s e d by m e t a l w a s no w t a p e d o ve r w i t h a l u m i nu m t a p e t o i m p r o ve t he e xt e r i o r a p p e a r a nc e T he m e t e rs w e re t h e n a t t a c h e d t o t h e c a s e v i a t h e i r m o u n t i n g c a s e s

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42 Th e K e i t h l e y s c re w t e rm i n a l w a s m o u n t e d t o t h e b o t t o m o f t h e d ri v e b a y s e c t i o n It was ph y s i cal l y pl ace d o n t h e i n s i de o f t h e ca s e. T wo 25 m m (1") sel f -t appi n g s h eet m et al s c r e w s w e r e u s e d t o s e c u r e it in p la c e T h e s e s c r e w s p e n e t r a t e d t h e b o t t o m o f t h e 1 3 3 mm ( 5 1 / 4 ) d r i v e b a y s T h i s s c r e w c on n e c ti on to th e d r i v e b a y b ottom h e l d th e c on n e c ti on p o i nt t o l i nk t he d a t a a c q u i s i t i o n t r a ns m i s s i o n c a bl e r i g i d e no u g h t o w i t hs t a nd l o c k i ng a nd un l o cki n g t h e co n n ect o r. T h i s pro t ect ed t h e i n t eri o r co n n ect i o n m ade a cro s s t h e s crew t e r m i na l f r o m d a m a g e t ha t m o ve m e nt c o u l d c a u s e A d r i ve ba y c o ve r w a s m o d i f i e d by m a k i ng a s q u a r e c u t o u t T he c u t o u t m a t c he d t he s i z e o f t he c o nne c t o r f o r c o nne c t i ng t he s c re w t e rm i n a l t o i t s t ra n s m i s s i o n c a b l e Th e d ri v e c o v e r w a s t h e n i n s t a l l e d N e x t t h e A D I b a c k p l a n e w a s m o u n t e d t o t h e c o m p u t e r c a s e s i d i n g w h e re p r e v io u s ly t h e mo t h e r b o a r d a n d e x p a n s io n c a r d s h a d r e s id e d I n o r d e r t o e a s ily a c c o mmo d a t e t h e fix e d mo u n t in g p o in t s o f t h e b a c k p la n e a 5 0 8 mm x 2 0 3 mm x 1 6 mm (20"x 8"x 5/8") pi ece o f pl y wo o d was m o un t ed di rect l y t o t h e i n t eri o r cas e wa l l t o pro v i de a m o un t i n g pl at f o rm T h i s pl y wo o d was po s i t i o n ed an d m o un t ed wi t h dry wal l t y pe s crews th r ou g h e x i s ti n g h ol e s i n th e i n te r i or c a s e w a l l T h e b a c k p l a n e w a s th e n p os i ti on e d on p l y w oo d w i th ou t r e g a r d to t h e i n te r i or c a s e w a l l d e s i g n w h i c h h a d i n s u f f i c i e n t h e i g h t to a c c o m m o d a t e a l l t he m o u nt i ng p o i nt s o f t he ba c k p l a ne T he ba c k p l a ne w a s s e c u r e d t o t he p lyw o o d b y s e v e n d r yw a ll s c r e w s t h a t r a n t h r o u g h it s in t e g r a t e d s t a n d o ffs t h a t w e r e in d i re c t c o n t a c t w i t h t h e p l y w o o d p l a t f o rm App ar atus Wir ing Cus t o m wi ri n g o f t h e appa rat us was an i n t egral part o f t h e des i gn W i ri n g was ne c e s s a r y f o r s e ve r a l r e a s o ns I t a c t e d a s a c o nd u i t f o r p o w e r t o be d e l i ve r e d t o t he a p p a ra t u s a n d i t w a s n e e d e d t o d e l i v e r t h e p o w e r t o t h e s a m p l e t h roug h a c u s t o m c i rc u i t

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43 T he w i r i ng a l s o s e r ve d t o c a r r y s i g na l s f o r c o nt r o l a nd d a t a s a m p l i ng p u r p o s e s T he b ackpl an e ut i l i zed a l s o h ad a c ert ai n am o un t o f cus t o m wi ri n g t o acc o m m o dat e t h e n eeds o f t h e a p p a ra t u s a n d c o n n e c t i n g i t t o t h e d a t a a c q u i s i t i o n c a rd P ower T h e C ro m pt o n m et ers n eede d a 120 v o l t A C po wer suppl y T h i s l i n e wa s ro ut ed f r o m s o u r c e t o t he ba c k o f t he s i g na l c o nd i t i o ni ng ho u s i ng a nd u p o n t r a ns i t i o n t o t he i n t eri o r, i t was cas ed i n an el ect ri cal l y i n s ul at i n g s h i el di n g. It ran f ro m t h ere t o t h e po wer s w i t c h o f t h e c o m p u t e r c a s e w h i c h h a d b e e n re w i re d t o s e rv i c e t h e C rom p t o n m e t e rs Be t wee n t h e po wer sw i t ch an d eac h Cro m pt o n m et er was an i n l i n e repl ace ab l e f us e h o l der w i t h a o ne a m p f u s e Wi t h t hi s w i r i ng s e t u p a n e a s y t o a c c e s s p o w e r s w i t c h o n t he e xt e r i o r o f t he ho u s i ng w a s a va i l a bl e f o r t u r ni ng o n a nd o f f t he C r o m p t o n m e t e r s a nd t he s uppl y t o eac h m et er was i n depen den t l y f us e pro t ect ed. A 1 2 0 vo l t p o w e r ba r w i t h a n o n/ o f f s w i t c h w a s a t t a c he d t o o ne l e g o f t he e q u ip me n t c a r t T h is a llo w e d t h e c a r t t o h a v e a s in g le p o in t c o n n e c t io n fo r u p t o s ix s t a n d a rd 1 2 0 v o l t p l u g s Th e C rom p t o n m e t e rs a s w e l l a s t h e l a p t o p c o m p u t e r w e re c o nne c t e d he r e D e vi c e s u s e d w i t h t he l a p t o p s u c h a s e xt e r na l d r i ve s c o u l d a l s o be c o n n e c t e d t o t h e p o w e r b a r D ir e c t c u r r e n t fo r e x p e r ime n t in g w a s p o w e r e d fr o m t h is l o cat i o n T h e po wer b ar i t s el f h ad a m et er l o n g co rd f o r co n n ect i n g t o an ex t ern al e x te n s i on c or d th a t r ou te s th e p ow e r f r om a s ta n d a r d 1 2 0 v ol t ou tl e t. A h i g h e r v o l t a g e s u p p l y w a s n e e d e d b y t h e e x p e ri m e n t a l s a m p l e p o w e r s u p p l y It r e q u ir e d a 2 4 0 v o lt s o u r c e T h is w a s c o n n e c t e d w it h a s t a n d a r d p lu g a t t h e e n d o f a f l ex i b l e l ead t h at was appro x i m at el y 3 m et ers l o n g. T h e l ead ran t o a IT -E en cl o s ed swi t ch m ade by S i em en s (c at al o g n um b er CNF R22 2) T h i s gen er al du t y swi t ch was a

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44 p lu g fu s e t yp e I t h a d a n e x t e r n a l li ft le v e r a n d in t e g r a t e d lig h t T h is g a v e t h e s a mp le s u p p l y a c on v e n i e n t p r ote c te d on of f s w i tc h th a t i n d i c a te d v i s u a l l y w h e n p ow e r w a s on to t h e po wer suppl y F ro m t h e en cl o s ure swi t ch t h e wi ri n g was ro ut ed i n s i de a f l ex i b l e m et al s h ie ld ing t o t h e p o w e r s u p p ly it s e lf T h e wi ri n g t o del i v er po wer t o t h e s am pl e i s s h o wn i n F i gure 311. T h i s di agram s ho w s t he i m p o r t a nt f e a t u r e s o f ho w t he p o w e r w a s r o u t e d f r o m s u p p l y t o s a m p l e T he l eads f o r po wer ex i t ed t h e s uppl y i n f l ex i b l e m et al s h i el di n g an d en t ered a Square D ( P a la t in e I L ) h e a v y d u t y s a fe t y s w it c h ( c a t a lo g n u mb e r H 3 6 1 N ) T h is 6 0 0 V A C 3 0 a mp s w i t c h ha d a n e xt e r na l l e ve r a r m f o r a c t u a t i o n f r o m t he o p e n t o c l o s e d p o s i t i o n. T he po wer l eads were t h en ro ut ed f ro m t h e b o t t o m o f t h i s s wi t ch en cl o s ure. Th e l e a d s w e re c o n n e c t e d t o t w o s e p a ra t e m e t a l o u t l e t b o x e s m o u n t e d t o p l y w o o d T he p hy s i c a l l a y o u t o f t he bo xe s i s i nd i c a t e d i n Fi g u r e 3 8 T he t o p bo x p r o vi d e d t he c o n n e c t i o n p o i n t f o r t h e C rom p t o n m e t e r t h a t a c t e d a s a n a m m e t e r a n d c u rre n t c o n t rol l e r. T h i s l ead t h en ex i t ed b eh i n d t h e pl y wo o d an d was ro ut ed i n t o t h e ce n t er b o x wh ere a Cry do m D4812 s o l i d s t at e rel ay was m o un t ed. T h i s b o x h ad a s o l i d f ace s i n ce t h e po wer di d n o t n eed t o en t er o r ex i t t h e f ace o f t h e b o x T h e l ead t h en ex i t ed t h e m o un t s i de o f t h e b o x a n d w a s rout e d t o t h e b o t t o m b o x Th e b o t t o m b o x m a d e u s e o f t h e s a m e s t a n d a rd fe ma le p lu g T h is w a s w h e r e t h e o t h e r le a d fr o m t h e S q u a r e D s w it c h w a s r o u t e d d ir e c t ly, an d en t ered f ro m t h e m o un t s i de. T h i s pl ug n o w h ad b o t h po wer l eads co n n ect ed an d was capa b l e o f po wer suppl y In o rder t o f aci l i t at e t h e ea s y an d s af e co n n ect i o n o f t h e ex t ern al d a ta l og g i n g m u l ti m e te r a n d th e C r om p ton m e te r m e a s u r i n g v ol ta g e a n oth e r s e r i e s of t h ree b o x es were m o un t ed t o t h e pl y wo o d as prese n t ed i n F i gure 38. T h e b o t t o m b o x h ad th e s a m e ty p e f e m a l e p l u g a s th e s u p p l y T h i s a c te d a s a n i n p u t p oi n t. A c u s tom m a l e to

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45 m a l e c on n e c tor j u m p e r w a s c on s tr u c te d to r ou te th e p ow e r ou t of th e l ow e s t r i g h t b ox i n to t h e l o w e s t l e f t b o x Th e l e a d s t h e n e x i t e d t h i s b o x f rom i t s m o u n t s i d e T he l e a d s e nt e r e d t he t o p l e f t bo x f r o m t he m o u nt s i d e be hi nd t he p l y w o o d O ne was co n n ect ed di rect l y t o t h e f em al e co n n ect o r see n o n t h e b o x s f ace wh i l e t h e o t h er was co n n ect ed t o a s t an dard f em al e b an an a j ack a t t h e t o p s i de o f t h e b o x T h e b an an a j ack was o n e o f a pai r o f f em al e j acks o n t h e t o p o f t h e b o x T h e o t h er o f t h e pai r was c o n n e c t e d t o t h e f e m a l e c o n n e c t o r on t h e f ron t o f t h e b o x Th i s g a v e s a f e s t a n d a rd co n n ect i o n s f o r t h e dat a l o ggi n g m ul t i m et er v i a a m al e t o m al e b an an a pl ug j um per t h at w a s u s e d t o rout e o n e l e g o f t h e p o w e r l e a d s t h roug h t h e m u l t i m e t e r. T he t o p l e f t bo x a c t e d a s t he i nt e r f a c e t o t he e xp e r i m e nt a l s a m p l e l e a d s T he s a m p l e l e a d s w e r e a p p r ox i m a te l y tw o m e te r s i n l e n g th O n e e n d h a d a m a l e c on n e c tor c o m p a t i bl e w i t h t he f e m a l e c o nne c t o r o n t he o u t p u t bo x m o u nt e d t o t he p l y w o o d i n t he Figure 3-11. Detailed Sample Power Wiring. Object 3-8. DetailedPowerCircuit.jpg (58 KB).

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46 u p p e r l e f t p o s i t i o n o n t he e xp e r i m e nt c a r t T he o t he r e nd s o f t he l e a d s ha d i ns u l a t e d r i ng t o n g u e t e rm i n a l s Th e s e w e re p l a c e d o n t h e e l e c t rode s a n d s e c u re d t o t h e b o l t c o n n e c t o rs T h e r i n g ton g u e te r m i n a l s w e r e s m a l l e n ou g h to b e r ou te d d i r e c tl y th r ou g h th e b ottom d ra i n p o rt o f t h e t e m p e ra t u re c o n t rol u n i t M e t e rs T h e t wo Cro m pt o n m et ers h ad addi t i o n al wi ri n g b es i des wh at was al ready p r e s e nt e d O ne m e t e r w a s c o nf i g u r e d t o r e a d t he vo l t a g e s u p p l i e d t o t he s a m p l e T he s ig n a l w a s s a mp le d b e fo r e it w e n t t h r o u g h t h e d a t a lo g g in g mu lt ime t e r A s u b D min i 9 p in co n n ect o r was us ed t o act as an eas y pl ugi n co n n ect i o n T h i s 9 pi n co n n ect o r h ad f o ur a c t iv e c o n n e c t io n s t w o t o c a r r y t h e v o lt a g e s ig n a l t o a C r o mp t o n me t e r a n d t w o t o c a r r y a c o n t rol s i g n a l f rom t h e o t h e r C rom p t o n m e t e r. T h i s f em al e s i de o f t h i s co n n ect o r was m o un t ed i n t h e ce n t er l ef t b o x (see F i gure 38 ) T h e f ou r l e a d s e x i te d th e s i d e of th i s b ox T h r e e l e a d s tw o f or c on tr ol a n d on e f or v o l t age s am pl i n g, wen t t o t h e ce n t er r i gh t b o x an d en t ered t h ro ugh i t s s i de. Here t h ey c on n e c te d to t h e C r y d om r e l a y T h e tw o th a t c om p l e te d a f i v e v ol t c i r c u i t c on n e c te d to t h e co n t ro l t erm i n al s o n t h e rel ay an d t h e t h i rd l ead w as co n n ect ed o n t h e v o l t age o ut put s i d e o f t he r e l a y T he f o u r t h l e a d e nt e r e d t he bo t t o m r i g ht bo x a nd w a s c o nne c t e d t o t he f e m a l e o u t p u t c o nne c t o r w he r e t he o t he r l e g o f t he e xp e r i m e nt a l s u p p l y a t t a c he d T he l eads wer e cl am ped o n ex i t an d en t r y f r o m t h e b o x es t o pr ev en t st r ai n o n t h e co n n ect i o n s. T h e l e a d s w e r e c a r r i e d u p to th e s i g n a l c on d i ti on i n g h ou s i n g v i a a c u s tom c o n s t ru c t e d l e a d O n e e n d o f t h e l e a d h a d t h e m a t i n g m a l e s u b D 9 p i n m i n i c o n n e c t o r. T he o t he r e nd o f t he l e a d w a s s t r i p p e d w i r e s t ha t w e r e c o nne c t e d d i r e c t l y t o t he a p p r o p r i a t e c o nne c t i o n p o i nt s o n t he C r o m p t o n m e t e r s T he l e a d i t s e l f w a s 3 2 AWG

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47 s hi e l d e d w i r e t y p e w i t h f o u r c o nd u c t o r s I t r a n d i r e c t l y i nt o t he s i g na l c o nd i t i o ni ng ho u s i ng v ia a c lo s e t o le r a n c e e x is t in g h o le T h e w ir e s w e r e le ft s h ie ld e d in s id e t h e h o u s in g u n t il ve r y c l o s e t o t he c o nne c t i o n p o i nt s o n t he C r o m p t o n m e t e r s T he l e a d w a s c l a m p e d ne xt to th e i n te r i or of th e h ou s i n g to p r e v e n t s tr a i n on th e i n te r i or c on n e c ti on s f r om th e e x te r i or po rt i o n o f t h e l ead. T h e C ro m pt o n m et er r es po n s i b l e f o r cur ren t co n t ro l was o ut f i t t ed wi t h a dual rel ay po d (262RL Y). T h i s po d h ad t wo ch an ge o v er rel ay s wi t h a co m m o n wi per. T h e rel ay c on tr ol e d a f i v e v ol t s i g n a l p r ov i d e d b y th e d a ta a c q u i s i ti on c a r d T h e w i r i n g c on n e c ti on to t h e r e la ys c a me fr o m t h e s c r e w t e r min a l p a n e l w h ic h in t e r fa c e d t h e d a t a a c q u is it io n c a b le co n n ect ed t o t h e dat a ac qui s i t i o n card. Back pl ane T h e A DI b ackpl an e pl an e h ad t wo ro l es an d wi ri n g s peci f i c f o r each F i rst i t act ed as t h e i n t erf aci n g po i n t f o r t h e s i x t h erm o co upl e l eads co n n ect ed t o i n di v i dual ch an n el s c r e w te r m i n a l c on n e c tor s on th e b a c k p l a n e T h e n u m b e r 2 a n d n u m b e r 3 c on n e c tor s of e a c h s e t w e r e u s e d o n c ha nne l p o s i t i o ns 5 7 9 1 1 1 3 1 5 N o f u r t he r o n bo a r d w i r i ng w a s n e e d e d f or th e s e c h a n n e l s T h e y r ou te d th r ou g h th e A D I c on d i ti on i n g m od u l e a n d to t h e pi n o ut co n n ect o r o f t h e b ackpl an e. T h e s e c on d r ol e th e b a c k p l a n e w a s to a c t a s a n i n te r f a c i n g p oi n t f or th e a n a l og o ut put o f t h e C ro m pt o n m et ers. T h e C ro m pt o n m et er o ut put was a s cal ed curren t an d was c on v e r te d to a s c a l e d v ol ta g e s i g n a l O n e 2 5 0 oh m p r e c i s i on r e s i s tor w a s p l a c e d c l os e to t he nu m be r 2 a nd nu m be r 3 s c r e w c o nne c t o r o n c ha nne l 1 a nd o n c ha nne l 3 o f t he b a c k p l a n e r e s p e c ti v e l y T h e r e s i s tor w a s p h y s i c a l l y c on n e c te d to e a c h of th e a n a l og c u rre n t o u t p u t l e a d s t o c o m p l e t e t h e c u rre n t c i rc u i t Th e c o n n e c t i o n w a s m a d e w i t h a w i re

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48 tw i s t ty p e c on n e c tor E a c h j u n c ti on h a d a n e x tr a l e a d w i r e a l s o a tta c h e d th a t w a s r ou te d to o n e o f t h e s crew t erm i n al s E ach t wi s t o n co n n ect o r t h us h ad t h ree wi res i t co n n ect ed, wi t h t h e l as t o n e b ei n g t h e v o l t age s am pl i n g l ead. Bo t h t h e l ead t o t h e m et er an d t h e s crew t e r m i na l w e r e 1 8 AWG i ns u l a t e d c o p p e r l e a d s T hi s c o nf i g u r a t i o n p l a c e d t he s a m p l i ng l eads o n eac h en d o f t h e preci s i o n resi s t o r f o r v o l t age s am pl i n g. Si n ce n o A DI m o dul e wa s i n p l a c e o n t he ba c k p l a ne f o r c ha nne l s 1 a nd 3 d i r e c t j u m p e r s w e r e i ns t a l l e d t o r o u t e t he s i g na l a c r o s s t he m o d u l e p l u g i nt e r f a c e T he j u m p e r s w e r e m a d e f r o m 1 8 AWG w i r e a nd f i t t h e b o ard f em al e pi n co n n ect o rs des i gn ed f o r 0. 0965 m m (0. 038") pi n s T h e s i gn al was t h e n rout e d b y t h e b a c k p l a n e t o t h e b a c k p l a n e p i n o u t c o n n e c t o r. T h e b ackpl an e h ad n o ex t ern al co n n ect i o n s t o t h e i n di v i dual i n put s crew t erm i n al c on n e c tor s of c h a n n e l s 0 2 4 6 8 1 0 1 2 a n d 1 4 T h e s e c h a n n e l s w e r e e a c h g r ou n d e d to t h e b ackpl an e. T h e gro un di n g co n n ect i o n was m ade o n eac h ch an n el wh ere an A DI c o nd i t i o ni ng m o d u l e w a s p l a c e d A j u m p e r w a s i ns t a l l e d o n e a c h t o a c c o m p l i s h t hi s T he ju mp e r w a s a g a in 1 8 A W G w ir e c o n n e c t e d t o t h e a p p r o p r ia t e fe ma le p in c o n n e c t o r s T h is p r ov i d e d a g r ou n d e d c h a n n e l b e tw e e n e a c h of th e e i g h t c h a n n e l s th a t w e r e r e a d b y th e d a ta acqui s i t i o n card. Scr ew ter m inal panel T he ba c k p l a ne p i n c o nne c t o r ha d o nl y 2 6 p i ns a nd w a s no t p i n c o m p a t i bl e w i t h t he Ke i t hl e y d a t a a c q u i s i t i o n c a r d T he Ke i t hl e y s c r e w t e r m i na l p a ne l a c t e d a s t he w i r i ng i nt e r f a c e be t w e e n t he d a t a a c q u i s i t i o n c a r d a nd t he ba c k p l a ne T he s c r e w t e r m i na l f r o nt h a d a n i n te g r a l c on n e c tor s p e c i f i c f or th e K e i th l e y d a ta a q u i s i ti on c a b l e T h i s c on n e c tor lo c k e d t h e d a t a a c q u is it io n c a b le in t o p la c e p r e v e n t in g a c c id e n t a l d is c o n n e c t io n o f t h e c a b le f ro m t h e s crew t erm i n al T h e o t h er en d o f t h e s crew t erm i n al pan el al l o wed f o r a sc rew

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49 c l a m p c o nne c t i o n t o e a c h o f t he 3 6 d i s c r e e t l i ne s t ha t c o m e vi a c o nne c t i ng c a bl e f r o m t he Ke i t hl e y d a t a a c q u i s i t i o n c a r d T he s e s c r e w t e r m i na l s w e r e u s e d t o i nt e r f a c e t o t he b ackpl an e. T he w i r i ng be t w e e n t he ba c k p l a ne a nd t he s c r e w t e r m i na l w a s c u s t o m m a d e by t he f ol l ow i n g p r oc e s s A s e c ti on of 4 0 c on d u c tor h a r d d r i v e c a b l i n g ( 2 8 A W G f l a t r i b b on c a bl e ) w a s r e d u c e d t o 2 6 l i ne s A 2 6 p i n c l a m p o n f e m a l e c o nne c t o r w a s a t t a c he d t o t he f l a t r i bbo n c a bl e T he o t he r e nd o f t he r i bbo n c o nd u c t o r w a s s t r i p p e d s e p a r a t i ng t he i n di v i dual co n duct o rs. T h e i n di v i dual l eads were t h en m at ch ed t o t h e appro pri at e s crew t e rm i n a l f o r i n p u t t o t h e K e i t h l e y d a t a a c q u i s i t i o n c a rd T he s c r e w t e r m i na l a l s o a c t e d a s t he c o nne c t i o n p o i nt f o r a p a i r o f 1 8 AWG co n duct o rs. T h es e we re co n n ect ed t o t h e s crew t erm i n al s t h at carri ed a f i v e v o l t DC s ou r c e f r om th e d a ta a c q u i s i ti on c a r d T h e s e l e a d s w e r e th e n c on n e c te d v i a w i r e n u ts to 2 m o r e 1 8 AWG c o nd u c t o r s p r o vi d i ng a w i r i ng s p l i t O ne s i d e o f t he s p l i t w e nt t o t he ba c k p l a ne t o p o w e r t he AD I s i g na l c o nd i t i o ni ng m o d u l e s m o u nt e d o n t he ba c k p l a ne T he i n t erf ace f o r t h e l ead o n t h e b ackpl an e wa s a s crew t erm i n al o n t h e b ackpl an e. T h e o t h er ha l ve s o f t he s p l i t s r o u t e d p o w e r t o t he C r y d o m s a m p l e p o w e r r e l a y As p r e s e nt e d i n t he prev i o us s ect i o n t h es e l eads were co n n ect ed t o t h e co n t ro l rel ay o n t h e C ro m pt o n m et er th a t w a s m e a s u r i n g c u r r e n t. E x pe r im e ntal M e thods I n t he c o u r s e o f d e ve l o p i ng t he a p p a r a t u s s e ve r a l e xp e r i m e nt a l i nve s t i g a t i o ns u t i l i z i ng va r i o u s t e c hni q u e s w e r e p e r f o r m e d T he m e t ho d s o f d a t a c o l l e c t i o n w i l l f i r s t be di s cus s ed, as t h ey were rel ev an t t o al l ex peri m en t s un dert aken T h en t h e ex peri m en t al cal i b rat i o n o f t h e t em perat ure pr o b es i s prese n t ed. T h i s i s f o l l o wed b y t h e m et h o d o f gel

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50 p r e p a r a ti on u s e d a n d th e m e th od of d e te r m i n i n g th e g e l d e n s i ty E x p e r i m e n ts f ol l ow w i th s o m e v e ry s i m p l e g e l f re e z i n g t ri a l s t h a t l a t e r h e l p e d t o f u rt h e r re f i n e d e s i g n d e c i s i o n s T he y a l s o p r o vi d e d i nf o r m a t i o n t ha t he l p e d t o c ha r a c t e r i z e c e r t a i n c o m p o ne nt s o f t he ex peri m en t al apparat us an d t h e gel us ed i n t h e res earch Ot h er ex peri m en t s were des i gn ed t o v a l i d a t e c e rt a i n o p e ra t i o n a l p roce d u re s o f t h e e q u i p m e n t W i th th e k n ow l e d g e g a i n e d th r ou g h a l l th e i n i ti a l e x p e r i m e n ts th e f i n a l e x p e r i m e n ts were des i gn ed. T h e f i n al ex peri m en t s i n cl uded m eas uri n g t h e el ect ri cal resi s t an ce o f t h e gel a n d m a k i n g c o n t i n u o u s m e a s u re m e n t s o n a g e l a s i t w a s s u b j e c t e d t o o h m i c t h a w i n g Data Col l ection D a ta c ol l e c ti on oc c u r r e d a t s e v e r a l l oc a ti on s s i m u l ta n e ou s l y T h e p r i m a r y l oc a ti on was at t h e l apt o p wh ere t h e v o l t age a n d t em perat ure dat a we re co l l ect ed duri n g an e xp e r i m e nt T he s e c o nd a r y l o c a t i o ns i nc l u d e d t he d a t a l o g g i ng d i g i t a l m u l t i m e t e r T he f i n a l l o c a t i o n w a s t h e l a b o ra t o ry n o t e b o o k w h e re o b s e rv a t i o n a l i n f o rm a t i o n w a s re c o rd e d T h es e m et h o ds o f co l l ect i n g dat a are f urt h er det ai l ed b el o w. Laptop com put er Th e l a p t o p w a s ru n n i n g a c u s t o m V i s u a l B a s i c p rogra m t h a t u t i l i z e s t h e s o f t w a re p ol l i n g c a p a b i l i ti e s of th e K e i th l e y d a ta a c q u i s i ti on c a r d T h e p r og r a m u ti l i z e d u s e r i n p u t to s t a r t t he p r o c e s s O nc e t he p r o c e s s w a s s t a r t e d t he l a p t o p s i nt e r na l c l o c k w a s u s e d a s t he tr i g g e r T h e p r og r a m a l l ow e d th e u s e r to s e t h ow m a n y d a ta p oi n ts on a s i n g l e c ol l e c ti on c ha nne l w e r e a ve r a g e d p e r s e c o nd by t he p r o g r a m T he p r o g r a m t he n s c a nne d t he ch an n el s f o r t h e s et n um b er o f s wee ps eac h s eco n d. T h e raw dat a po i n t s were av eraged a n d co n v ert ed t o m ean i n gf ul un i t s T h e raw d a t a w e re i n b i t s re p re s e n t i n g a z e ro t o f i v e v o l t s i g n a l m e a s u re d b y t h e a c q u i s i t i o n c a rd

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51 T h i s s i g n a l w a s c on d i ti on e d p r e v i ou s to a c q u i s i ti on T h e s i g n a l c on d i ti on i n g c om p on e n ts s c a l e d a nd l i ne a r i z e d i t T he c o nve r t e d a nd no w m e a ni ng f u l d a t a w e r e t he n w r i t t e n t o t he ha r d d r i ve w i t h a t i m e s t a m p t ha t t he p r o g r a m r e a d f r o m t he l a p t o p c l o c k a t t he be g i nni ng o f t he p o l l i ng s e q u e nc e T he p r o g r a m t he n w a i t e d f o r t he ne xt s e c o nd t o r e g i s t e r o n t he l apt o p cl o ck t o i n i t i at e an o t h er co l l ect i o n T h i s pro ces s co n t i n ued un t i l t h e us er pr o m pt ed th e p r og r a m to s top T h e n u m b e r of p oi n ts a v e r a g e d p e r s e c on d on a l l e x p e r i m e n ts p r e fo r me d w e r e 1 0 0 T h e o n e e x c e p t io n w a s in it ia l r u n s w it h t h e p r o g r a m. T h e s e i n i ti a l r u n s w e r e e x e c u te d w i th v a r i ou s n u m b e r s of s w e e p s ov e r th e d a ta a c q u i s i ti on c h a n n e l s T h e p u r p os e of th e s e i n i ti a l d a ta r u n s w e r e to v a l i d a te th e op e r a ti on o f t he p r o g r a m a nd r e f i ne t he i nt e r f a c e I t a l s o a i d e d i n f i nd i ng t he l i m i t o f ho w m a ny s c a ns each seco n d t h e car d, l apt o p an d so f t war e co m b i n at i o n co ul d b e ex pect ed t o ex ecut e. By ma k in g r u n s w it h in c r e a s in g n u mb e r s o f p o in t s t o b e a v e r a g e d a n d o b s e r v in g t h e t ime s t a m p s t he m a xi m u m nu m be r o f s c a ns p e r s e c o nd w a s d e t e r m i ne d T he s e o bs e r va t i o ns a d d i t i o na l l y i nd i c a t e d a n a p p r o xi m a t e t i m e p e r s c a n. Data l ogging d igit al m ul ti m eter T h e dat a co l l ect ed wi t h t h e l o ggi n g di gi t al m ul t i m et er i n v o l v ed a m ul t i -st ep p roce s s Th e i n i t i a l s t e p w a s t o s e t t h e d i g i t a l m u l t i m e t e r t o t h e p rope rt y t o b e m e a s u re d T he r o t a r y d i a l o n t he d i g i t a l m u l t i m e t e r w a s u s e d f o r t hi s s t e p T he s e c o nd s t e p o f t he pro ces s was s et t i n g t h e dat a s can n i n g rat e f o r t h e di gi t al m ul t i m et er. T h i s was a c c o m p l i s he d t hr o u g h i t s i nt e g r a l bu t t o n a nd r e a d o u t i nt e r f a c e s T he r a t e u s e d w a s o ne readi n g per se co n d. T h i s rat e wa s us ed o n al l ex peri m en t s ut i l i zi n g t h e dat a l o ggi n g di gi t al m u l t i m e t e r. N e x t t h e d i g i t a l m u l t i m e t e r w a s t ri g g e re d b y b u t t o n i n t e rf a c e t o s t a rt

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52 a c q u i r i n g d a ta I t c on ti n u e d to c ol l e c t d a ta s e q u e n ti a l l y ti l l th e u s e r p r om p te d i t to s top or i t re a c h e d 4 3 ,0 0 0 d a t a p o i n t s t h e m a x i m u m s t o ra g e c a p a c i t y f o r t h e m e t e r. T he d a t a c o l l e c t e d r e s i d e d i n t he i nt e r na l m e m o r y o f t he d i g i t a l m u l t i m e t e r a nd n eede d t ran s f err i n g t o a co m put er. T h e t ran s f er was po s s i b l e b y us i n g t h e di gi t al m ul t i m et er s IR po rt A s peci al cab l e co n n ect ed t h e IR po rt t o a co m put er st an dard RS232 s eri al po rt A s o f t ware pro gram wri t t en b y t h e di gi t al m ul t i m et er m an uf act urer t h en i n te r p r e te d th e i n c om i n g s i g n a l to th e c om p u te r s s e r i a l p or t a n d tr a n s l a te d i t to a m ean i n gf ul dat a s t ream T h e m an uf act urer s pro gram was ut i l i zed b eca us e t h e t ran s m i t t ed d a t a s t r e a m w a s no ns t a nd a r d f o r a R S 2 3 2 s e r i a l c o nne c t i o n. T he d a t a c a p t u r e d by t he pro gram were s av ed i n s ev eral f o rm at s i n cl udi n g o n e pro pri et ary t o t h e s o f t ware an d a s i m pl e co m m a del i m i t ed f o rm T h e co m m a del i m i t ed f o rm s equen t i al l y n um b ered t h e dat a, w hi c h e f f e c t i ve l y g a ve a t i m e s t a m p i n s e c o nd s r e f e r e nc e d t o t he s t a r t o f t he e xp e r i m e nt wi t h t h e ch o s en dat a co l l ect i o n rat e. Labor ator y not ebook T h e l a b or a tor y n ote b ook w a s i m p or ta n t f or k e e p i n g tr a c k of d a ta th a t w e r e n ot b e i n g c o l l e c t e d e l e c t ron i c a l l y Th e s e o b s e rv a t i o n s w e re re c o rd e d b y p e n i n a s t a n d a rd f o rm at ut i l i zi n g t h e gui del i n es o f K an are (1985) It al s o act ed as a reco rder o f al l m et h o ds em pl o y ed and i m po r t an t o b ser v at i o n s dur i n g ex per i m en t s. Te m per atu r e P r obe Cal ibr ati on T h e te m p e r a tu r e p r ob e s r e q u i r e d c a l i b r a ti n g to a s s u r e th e d e s i r e d d e g r e e of a c c u ra c y Th e e x p e ri m e n t a l c a l i b ra t i o n u t i l i z e d t h e p h a s e c h a n g e t e m p e ra t u re o f w a t e r. A s i m p l e e xp e r i m e nt d e s i g n t ha t c o nt i nu o u s l y m o ni t o r e d t he t e m p e r a t u r e o f w a t e r a s t he w a t e r w a s c o o l e d t o i t s p h a s e c h a n g e t e m p e ra t u re w a s u t i l i z e d

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53 I n t h is e x p e r ime n t t h e s a mp le c e ll w a s a s s e mb le d w it h t h e b o t t o m e le c t r o d e in p l a c e T h e e l e c tr od e w a s s e a te d on th e b ottom s h ou l d e r of th e s a m p l e c e l l A c oa ti n g of pet ro l eum j el l y was appl i ed t o t h e s h o ul der v i a a 5m l h y po derm i c s y ri n ge. T h i s en s ured a w a t e r t i g ht s e a l o n t he bo t t o m s u r f a c e be t w e e n s a m p l e c e l l s ho u l d e r a nd e l e c t r o d e T he e l e c t rode w a s h e l d i n p l a c e w i t h a n e n d c a p s p a c e r c o m b i n a t i o n T h e t e mp e r a t u r e p r o b e s w e r e in s e r t e d T h e o r d e r o f t h e p r o b e s w it h t h e ir re s p e c t i v e d a t a n a m e s a re i n d i c a t e d i n F i g u re 3 -1 2 Th i s a rra n g e m e n t a n d n a m i n g w e re c o ns i s t e nt f o r a l l e xp e r i m e nt s Af t e r i ns e r t i o n, t he e xt e r i o r c l e a r a nc e a r e a be t w e e n t he pro b e an d t h e ce l l were s eal ed wi t h pet ro l eum j el l y T h e s am e 5 m l h y po derm i c s y ri n ge w a s u s e d t o d e liv e r t h e p e t r o le u m je lly t o t h e d e s ir e d r e g io n T h e p r o b e w a s n o w in po s i t i o n s o t h at t h e s eco n d s et o f co n n ect o rs co ul d b e at t ach ed. T h e s am pl e ce l l h o l der was prepared f o r r ece i v i n g t h e s am pl e ce l l b y ro ut i n g t h e t h erm o co upl e t ran s m i s s i o n l eads t h roug h i t s e x t e ri o r. Th e l e a d p a i rs w e re t h e n c o n n e c t e d t o t h e i r re s p e c t i v e c o n n e c t o rs Th e s a m p l e c e l l w a s t h e n s e c u re d i n t h e s a m p l e c e l l h o l d e r, a n d t h e c o n n e c t o rs w e re at t ach ed f ro m pro b e en d t o t ran s m i s s i o n l ead e n d. Figure 3-12. Probe Positions and Naming Conventions.

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54 T h e c e ll h o ld e r w a s mo v e d t o t h e t e mp e r a t u r e c o n t r o l c h a mb e r T h e c e ll w a s in a n a x is v ert i cal po s i t i o n wi t h i t s t o p o pen T h e t em perat ure dat a co l l ect i o n was s t art ed. Dei o n i zed w a t e r w a s a d d e d t o t h e c e l l Th e c o n t rol c h a m b e r w a s c l o s e d a n d t h e w a t e r b e g a n t o c o o l T he t e m p e r a t u r e w a s m o ni t o r e d At p ha s e c ha ng e t he t e m p e r a t u r e r e m a i ne d c o ns t a nt T he c e ll w a s r e mo v e d fr o m t h e c h a mb e r a t t h is p o in t a n d a llo w e d t o w a r m. T h e d a ta c ol l e c ti on p r oc e s s w a s s top p e d T h e c ol l e c te d d a ta w e r e c op i e d to a co m pact di sk. T h e dat a wer e pl o t t ed t o det er m i n e wh i ch r egi o n r epr esen t ed t h e ph ase ch an ge t em per at ur e f o r wat er T h e t em per at ur e r eadi n gs t h en o f f set t o t h e act ual ph ase c h a n g e t e m p e ra t u re Gel P r epar ati on T h e me t h o d o f p r e p a r in g t h e fo o d g e l fo r e a c h e x p e r ime n t w a s c o n s is t e n t fo r a ll ex peri m en t s wh ere t h e gel was pl ace d i n t h e s am pl e ce l l T h e f i rst s t ep i n prepari n g t h e gel w a s t o w e i g h t w o o f t h e re t a i l e n v e l o p e s o n a l a b o ra t o ry b a l a n c e (O h a u s m o d e l G T4 1 0 ). T h e w e i g h ts w e r e th e n r e c or d e d i n th e l a b or a tor y n ote b oo k A 2 5 0 m L b e a k e r w a s u s e d to h o l d appro x i m at el y 150 m L o f dei o n i zed w at er o n a h o t pl at e. A 400 m L b eake r was us ed t o h o l d an o t h er 125 m L o f di o n i zed w at er t h at was n o t h eat ed. T h e 125 m L o f wat er was m e a s u re d w i t h a 1 0 0 m L g ra d u a t e d c y l i n d e r. T h e gel en v el o pes were o pen ed, an d t h e po wder po ured i n t o t h e b eake r t h at c on ta i n e d th e 1 2 5 m L of r oo m te m p e r a tu r e d e i on i z e d w a te r T h e g e l p ow d e r w a s l e f t to a b s o r b t h e w a t e r fo r a p p r o x ima t e ly t w o min u t e s A t t h e e n d o f t h e t w o min u t e s 1 0 0 mL o f al m o s t b o i l i n g h o t wat er f ro m t h e 250 m L b eake r was m eas ured wi t h a graduat ed c y l i nd e r a nd a d d e d t o t he g e l T he m i xt u r e w a s s t i r r e d w i t h a s t a i nl e s s s t e e l s p a t u l a a nd

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55 pl ace d o n an el ect ri c h o t pl at e. T h e s t i rr i n g was co n t i n ued t i l l al l gran ul es were di s s o l v ed, w h i c h o c c u rre d i n a p p rox i m a t e l y o n e m i n u t e T h e b eake r was t aken b y b are h an d f ro m t h e h o t pl at e. T h e s o l ut i o n was t h en p ou r e d i n to t h e s a m p l e c e l l to t h e d e s i r e d f i l l l e v e l A s e p a r a te 3 0 m L b e a k e r w a s u s e d to c o lle c t t h e r e ma in in g s o lu t io n T h is a d d it io n a l s a mp le o f t h e g e l w a s c o v e r e d b y P a r a film M . T h e s am pl e wa s us ed l at er t o det erm i n e t h e den s i t y o f t h e gel T h e l i qui ds t h en s o l i d i f i e d a t r o o m t e m p e r a t u r e T he l a s t s t e p s w e i g he d t he e m p t y g e l e nve l o p e s a nd reco rded t h e we i gh t s i n t h e l ab o rat o ry n o t eb o o k. Gel Dens it y Deter m inat ion T h e m e th od f or d e te r m i n i n g th e g e l d e n s i ty u ti l i z e d a Q u a n ta c h r om e I n s tr u m e n ts ( B o y nt o n B e a c h, FL ) m u l t i p y c no m e t e r a nd a l a bo r a t o r y s c a l e T he f i r s t s t e p i n u t i l i z i ng t he mu lt ip yc n o me t e r w a s t o v e r ify i t s c a lib r a t io n T h e s ma ll s a mp le c e ll a n d t w o s ma ll cal i b rat i o n b al l s were us ed. T h e v o l um es o f t h e ca l i b rat i o n b al l s were kn o wn T h ree repeat ed m eas ures we re m ade us i n g t h e i n s t rum en t T h e m eas urem en t s were t h en c o m p a r e d w i t h t he k no w n va l u e T hi s p r o c e d u r e i ns u r e d t ha t t he o p e r a t o r o f t he i n s t ru m e n t w a s u s i n g i t c o rre c t l y T he m u l t i p y c no m e t e r w a s r e a d y t o d e t e r m i ne a c c u r a t e vo l u m e s f o r s a m p l e s o f t he g e l T he g e l s a m p l e f r o m t he 3 0 m L be a k e r w a s u nc o ve r e d a nd c u t w i t h a c o r i ng t o o l T he c o re w a s w e i g h e d o n t h e l a b o ra t o ry s c a l e a n d t h e w e i g h t re c o rd e d i n t h e l a b o ra t o ry no t e bo o k T he c o r e w a s p l a c e d i n t he s m a l l s a m p l e c e l l o f t he m u l t i p y c no m e t e r T he v o l u m e m e a s u re m e n t b y t h e m u l t i p y c n o m e t e r w a s re p e a t e d s i x t i m e s f o r e a c h c o re s a m p l e Th re e c o re s a m p l e s w e re t a k e n f rom e a c h g e l s a m p l e e x a m i n e d

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56 T he d e ns i t y w a s c a l c u l a t e d f r o m t he w e i g ht m e a s u r e d by t he l a bo r a t o r y s c a l e a nd t he vo l u m e c a l c u l a t e d f r o m t he p r e s s u r e m e a s u r e m e nt s m a d e by t he m u l t i p y c no m e t e r T he p re s s u re m e a s u re m e n t s w e re t ra n s f e rre d f rom t h e l a b o ra t o ry n o t e b o o k t o a s p re a d s h e e t T h e v ol u m e c a l c u l a ti on s u s i n g th e p r e s s u r e m e a s u r e m e n t w e r e d on e i n th e s p r e a d s h e e t to s p e e d u p t he r e p e t i t i ve c a l c u l a t i o ns U l t i m a t e l y t he d e ns i t y c a l c u l a t i o ns w e r e m a d e i n t he s p r e a d s h e e t a s w e l l H a v i n g a l l th e c a l c u l a ti on i n a s p r e a d s h e e t f or m a t a l l ow e d c om p a r i s on o f t h e dat a f r o m di f f er en t gel sam pl es. F r e e z ing E x p e r ime n t s in g e l fr e e z in g h e lp e d t o c h a r a c t e r iz e t h e c h a n g e s t h e g e l u n d e r w e n t in t h e s o l i d-so l i d (un f ro zen t o f ro zen ) ph as e t ran s i t i o n T h e f i rst b as i c ex peri m en t was an o b s e rv a t i o n e x p e ri m e n t G e l w a s m i x e d a n d p o u re d t o f o rm a n i n c h t h i c k s l a b i n a b e a k e r. T h e gel was t h en al l o wed t o t ran s i t i o n f ro m l i qui d t o s o l i d. T h e t o p o f t h e b eake r was c ov e r e d w i th P a r a f i l m s l ow i n g w a te r e x c h a n g e w i th th e s u r r ou n d i n g a tm os p h e r e T h e top s u r f a c e o f t he g e l w a s u nc o ns t r a i ne d T he g e l w a s p l a c e d i n a f r e e z e r a nd f r o z e n. T he f r o zen gel was r em o v ed f r o m t h e f r eezer an d o b ser v at i o n s re co r ded o n sh ape. T h ese o b ser v at i o n s di scussed i n Ch apt er 4, l ead t o t h e n ex t i t er at i o n o f t h e f r eezi n g ex per i m en t s. T h e n ex t i t erat i o n was po uri n g a gel i n t o t h e s am pl e ce l l wi t h o ut t h e i n t ern al i n s u l a t i o n In t h i s e x p e ri m e n t t h e g e l t o p s u rf a c e w a s p o u re d e v e n w i t h t h e u p p e r s h o u l d e r, a n d c o v e re d b y t h e t o p e l e c t rode Th e t o p e l e c t rode w a s i n c o n t a c t w i t h t h e l i q u i d g e l T h e el ect ro de wa s n o t co n s t rai n ed o t h er t h an t h e s h o ul der i t rest ed o n T h i s s h o ul der kept t he e l e c t r o d e f r o m i ni t i a l l y s i nk i ng i nt o t he g e l T he g e l w a s r e f r i g e r a t e d t o s p e e d u p t he l i q u i d t o s o l i d p h a s e t ra n s i t i o n O n c e c o n g e a l e d t h e g e l w a s p l a c e d i n a f re e z e r a n d f roze n T h e s am pl e wa s rem o v ed an d o b s erv at i o n s reco rded.

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57 Wi t h t he o bs e r va t i o ns o f t he p r e vi o u s e xp e r i m e nt s f o r g u i d a nc e a ne w e xp e r i m e nt was des i gn ed. T h e s am pl e ce l l was f i t t ed wi t h i n t eri o r i n s ul at i o n T h e gel was po ured i n s i de wh at was t h e s eco n d i t erat i o n cel l wi t h i n t eri o r i n s ul at i o n an d t h e el ect ro de pl ace d o n t h e t o p g e l s u r fa c e T h e g e l w a s r e fr ig e r a t e d t o c o n g e a l. T h e o n ly va r ia t io n a t t h is p o i nt w a s t he ne w i nt e r i o r i ns u l a t i o n. A f t er co n geal i n g t h e ce l l was rem o v ed f ro m ref ri gerat i o n T h e co n s t rai n i n g en d cap o n t h e b o t t o m o f t h e ce l l was rem o v ed. T h e C -cl am p an d co pper spa cers were po s i t i o n ed to c on s tr a i n th e e l e c tr od e s i n a n a x i a l m a n n e r T h e c l a m p e d c e l l w a s p l a c e d i n a f r e e z e r to u n d e r g o th e s ol i d to s ol i d p h a s e tr a n s i ti on A f te r th e g e l w a s f r oz e n i t w a s r e m ov e d f r om t h e f re e z e r. Th e c l a m p w a s re m o v e d t o e x p o s e t h e e l e c t rode s Th e e l e c t rode s w e re w a rm e d b y t a p w a t e r t o f a c i l i t a t e t h e i r re l e a s e f rom t h e f roze n g e l A n i n e rt i a l m e t h o d w a s u s e d t o e x t ra c t t h e f roze n s a m p l e f rom t h e s a m p l e c e l l In t hi s m e t ho d t he c e l l w a s r a i s e d a bo ve t he l a bo r a t o r y be nc h t o p a nd d r o p p e d t o i t T he f ro zen gel an d i n s ul at i o n t h en s l i d i n t h e ax i al di rect i o n o f t h e ce l l On ce s l i ppage h as o c c u r r e d t he g e l a nd i ns u l a t i o n e a s i l y p u s he d i n t he a xi a l d i r e c t i o n f o r r e m o va l f r o m t he s am pl e ce l l On ce t h e gel was rem o v ed t h e i n s ul at i o n can b e pul l ed aw ay f ro m t h e radi al s u r fa c e o f t h e fr o z e n g e l. Ob ser v at i o n s wer e r eco r ded wh en t h e el ect r o des wer e r em o v ed. T h ese o b s erv at i o n s pri m ari l y reco rd t h e s urf ace co n di t i o n s M o re o b s erv at i o n s were reco rded a f t e r t he i ns u l a t i o n w a s r e m o ve d f r o m t he s a m p l e T hi s s e t o f o bs e r va t i o ns r e c o r d e d t he c o n d i t i o n o f t h e ra d i a l e d g e a n d o v e ra l l g e o m e t ry o f t h e s a m p l e M o re o b s e rv a t i o n s w e re t a k e n a s t he s a m p l e w a s a l l o w e d t o m a k e t he s o l i d t o s o l i d p ha s e t r a ns i t i o n ba c k t o t he un f ro zen s t at e. T h e o b s erv at i o n al em ph as i s was t h e o v eral l geo m et ri c s h ape.

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58 A v a r ia t io n o f t h is fin a l fr e e z in g e x p e r ime n t w a s p r e fo r me d w it h a s e t o f s a mp le p r o b e s in p la c e T h e p r ima r y d iffe r e n c e in t h is v a r ia t io n w a s s a mp le p r o b e s p o s it io n e d in t h e l i qui d gel b ef o re i t i s s et T h e gel s am pl e n o w rese m b l ed t h e ac t ual s et up t h at was u t ili z e d fo r t r a c k in g t h e t e mp e r a t u r e o f t h e g e l s a mp le U p o n r e mo v a l fr o m t h e s a mp le c e ll b y t h e in e r t ia l me t h o d t h e p r o b e s w e r e s h e a r e d a t t h e c e ll w a ll i n t e r fa c e T h e d e s ig n o f t h is ex peri m en t al l o wed f o r f urt h er o b s erv at i o n al v al i dat i o n o f t h e f reezi n g geo m et ry as wel l as t h e ef f ect o f t h e so l i d t o so l i d p h ase ch an ge o n i n ser t ed p r o b es. Envir onm ent Ch ar acter iz ati on T he e nvi r o nm e nt a l c o nt r o l c ha m be r i nt e r a c t e d w i t h t he s a m p l e T he i nt e r a c t i o ns w e r e c h a r a c te r i z e d to h e l p d e s i g n a n d c on tr ol e x p e r i m e n ts S e v e r a l m e th od s w e r e u s e d to g a i n i ns i g ht i nt o ho w i t i m p a c t e d t he s a m p l e t e m p e r a t u r e a nd t he c a p a bi l i t i e s o f t he c h a m b e r. Co ntinuo us Run ning T h e co n t ro l ch am b er co ul d b e o perat ed i n a co n t i n uo us m o de. T h i s m o de t urn ed o n t h e un i t s co m press o r an d l ef t i t i n t h e run n i n g s t at e un t i l i t was m an ual l y s wi t ch ed b ack t o a t e m p e r a t u r e c y c l i ng s t a t e T hi s a l l o w e d t he m i ni m u m p o s s i bl e t e m p e r a t u r e o f t he c o nt r o l c ha m be r t o be d e t e r m i ne d T he m e t ho d e m p l o y e d w a s t o s e t t he c ha m be r i nt o t he c o n t in u o u s r u n s t a t e a n d mo n it o r it s t e mp e r a t u r e T h e c h a mb e r w a s a llo w e d t o s t a y in t h is s t a t e f o r a t l e a s t 1 2 ho u r s T he t e m p e r a t u r e i ns i d e t he c ha m be r w a s m o ni t o r e d a nd r e c o r d e d W h e n t h is me t h o d w a s u s e d w it h a g e l s a mp le t h e fr e e z in g o f t h e s a mp le o ccurred i n t h e m i n i m um t i m e al l o wab l e b y t h e equi pm en t T h i s h el ped t o pro v i de co n si st en t f r eezi n g o f di f f er en t gel sam pl es.

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59 Cy c l ing T he c ha m be r w a s a l s o o p e r a t e d i n a m o r e s t a nd a r d f a s hi o n. T hi s w a s a c y c l i ng m o de t h at aut o m at i cal l y t urn ed o n t h e co m press o r wh en a h i gh t em perat ure se t po i n t was cro s s ed t he n a u t o m a t i c a l l y s hu t s o f f t he c o m p r e s s o r w he n t he l o w t e m p e r a t u r e s e t p o i nt was reach ed. T h e ch am b er di d n o t h av e a prec i s e m an n er f o r sel ect i n g t h e upper an d l o wer s et po i n t s It ut i l i zed a m an ual ro t ary co n t ro l wi t h n um b eri n g f o r sel ect i n g f ro m a ran ge p r e d e te r m i n e d b y th e m a n u f a c tu r e r T h e n u m b e r i n g of th e s c a l e g a v e r e f e r e n c e p oi n ts f r om th e l ow e s t c y c l i n g te m p e r a tu r e s to th e h i g h e s t c y c l i n g te m p e r a tu r e s a n d h a d n o u n i ts of m eas ure. T h e m et h o d f o r det erm i n i n g t h e i m pact o f cy cl i n g o n t h e gel s am pl e o f i n t eres t was s t rai gh t f o rward. T h e t em perat ure o f t h e f ro zen gel s am pl e wa s m o n i t o red dur i n g an e xt e nd e d t i m e u p t o 7 ho u r s T he s e t e m p e r a t u r e s w e r e g r a p he d T he c y c l i ng na t u r e o f t he c h a m b e r b e c a m e v i s i b l e Th e p rom i n e n t f e a t u re s s u c h a s m a g n i t u d e o f s a m p l e t e m p e ra t u re c ha ng e a nd f r e q u e nc y o f t he c ha ng e s w e r e e xt r a c t e d T he m e t ho d u s e d f o r e va l u a t i ng t he c y c l i n g a l s o y i e l d e d i n f o rm a t i o n a b o u t p rob e f i n n i n g d i s c u s s e d i n c h a p t e r 4 T he r m al Da m ping T h e f i n a l c h a r a c te r i s ti c i n te r a c ti on b e tw e e n th e c h a m b e r a n d s a m p l e th a t n e e d e d to b e u n d e r s t o o d w a s h o w t h e s a mp le w a r ms u p w h e n t h e c h a mb e r is n o lo n g e r a c t iv e ly run n i n g i n ei t h er m o de. T h e m et h o d f o r gai n i n g t h i s i n f o rm at i o n was t o t rack a f ro zen gel s a m p l e s te m p e r a tu r e w h e n th e c h a m b e r w a s tu r n e d of f T h i s p r oc e d u r e w a s u s e d to d e t e rm i n e h o w ra p i d l y t h e s a m p l e w a rm e d A s e c o n d it e r a t io n in v o lv e d in c r e a s in g t h e t h e r ma l ma s s in s id e t h e c h a mb e r I n t h is e x p e r ime n t a l s e t u p 7 5 L ( 2 g a llo n s ) o f d is t ill e d w a t e r in s t a n d a r d 3 7 5 L ( 1 g a llo n ) p la s t ic

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60 mil k s t yle ju g s w e r e fr o z e n in a s e p a r a t e fr e e z e r T h e fr o z e n w a t e r ju g s w e r e t h e n p la c e d in th e c h a m b e r a l on g w i th th e s a m p l e T h e f r e e z e r w a s th e n s h u t of f a n d th e te m p e r a tu r e of th e s a m p l e tr a c k e d T h i s i n c r e a s e d th e r m a l m a s s a c te d a s a th e r m a l d a m p e r T h e d a ta graph ed an d t h e i m pact o f t h e t h erm al dam pi n g det erm i n ed. Aut om ati c P ower Cont r ol M ethod Re l ay s e t up A s i ng l e r e l a y o p t i o n p a c k f o r t he C r o m p t o n M e t e r w a s u s e d f o r c o nt r o l l i ng t he m ax i m um curr en t appl i ed t o a s am pl e duri n g o h m i c t h awi n g. T h e rel ay pack w as t wo r e l a y s t ha t u t i l i z e d a s i ng l e w i p e r ( S e e Fi g u r e 3 1 3 ) T he r e l a y s w e r e u s e d i n s e r i e s T he i n c o m i n g l e a d c a rri e d t h e 5 v o l t c o n t rol s i g n a l t h a t a t t a c h e d t o c o n n e c t i o n 1 i n F i g u re 3 -1 3 T h e ou tg oi n g l e a d to t h e C r y d om r e l a y a tta c h e d to c on n e c ti on 5 T h e f i r s t r e l a y w a s s e t to b e a l o w al arm an d t h e s eco n d rel ay was s et t o b e a h i gh al arm T h e f i rst rel ay h ad a 5 seco n d d el ay an d t h e seco n d h ad n o del ay T h e r el ay s al so h ad u ser def i n ed h y st er i si s. Th e l o w l e v e l a l a rm w a s s e t a t a 0 .0 5 a m p s a n d t h e h i g h l e v e l a l a rm w a s s e t t o 0 .4 a mp s T h e h ys t e r is is le v e l o n t h e lo w a la r m w a s s e t t o c o in c id e w it h t h e h ig h le v e l a la r m, a nd t he hi g h l e ve l a l a r m hy s t e r i s i s w a s s e t t o c o i nc i d e w i t h t he l o w l e ve l a l a r m Whe n t he m e t e r w a s t u r ne d o n a nd no p o w e r i s be i ng t r a ns m i t t e d t he l o w l e ve l a l a r m w a s a c t i ve a nd c l o s e d t he f i r s t r e l a y a nd i t s t a y e d i n t hi s s t a t e u nt i l i t s hy s t e r i s i s va l u e w a s r e a c he d T he s eco n d rel ay was al ready cl o s ed an d s t ay ed cl o s ed un t i l t h e h i gh l ev el al arm v al ue wa s e xc e e d e d P o w e r c o u l d t he n be a p p l i e d a nd w he n t he hi g h l e ve l a l a r m w a s t r i p p e d t he co n t ro l s i gn al ci rcui t was b ro ken T h e v o l t age v al ue dro pped wi t h b o t h rel ay s i n an o pen p os i ti on u n ti l th e s e c on d r e l a y r e s e t a t i ts h y s te r i s i s p oi n t.

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61 T h e l o w l ev el al arm was act i v at ed al s o b ut i t h ad a 5 s eco n d del ay b ef o re i t ch an ged s t at e. T h e d e l a y f r om a n ov e r c u r r e n t s h u t d ow n to t h e a p p l y i n g p ow e r a l l ow e d th e op e r a tor to a d ju s t t h e v o lt a g e t o a lo w e r v a lu e T h is c u r r e n t lim it a t io n p r e v e n t e d t h e p o w e r s u p p ly f ro m del i v eri n g un des i rab l e l ev el s o f po wer t o t h e s am pl e. P ower contr ol val idat ion T he r e l a y c o nf i g u r a t i o n w a s ve r i f i e d p r i o r t o t he o hm i c e xp e r i m e nt r u ns by t he f o l l o w i ng m e t ho d An i nc a nd e s c e nt e l e c t r i c l i g ht bu l b w a s m a d e w i r e c o m p a t i bl e w i t h t he e xp e r i m e nt a l a p p a r a t u s o u t p u t T hi s a l l o w e d t he vo l t a g e s u p p l i e d t o t he l i g ht bu l b t o be v ari ed, wh i ch i n t urn l ed t o t h e curren t s uppl i ed t o t h e b ul b b ei n g v ari ed. T h e l i gh t was s u p p lie d a c u r r e n t t h a t w a s le s s t h a n t h e h ig h a la r m s t a t e T h e c u r r e n t w a s in c r e a s e d u n t il i t t ri ps t h e h i gh al arm an d s h ut s o f f t h e o ut put T h e res ul t was v i s i b l e b o t h o n m et er r eadi n gs f r o m t he C r o m p t o n m e t e r a nd no l i g ht be i ng e m i t t e d f r o m t he bu l b. Af t e r a f i ve s e c o nd d e l a y th e s y s te m on c e a g a i n s u p p l i e d p ow e r to t h e l i g h t b u l b a n d w a s v e r i f i e d b y b oth m e t e r r e a d i ng a nd l i g ht e m i s s i o n. T he s y s t e m t he n i m m e d i a t e l y s hu t d o w n, be c a u s e t he v o l t age w as n o t adj us t ed t o a l o wer v al ue. Dur i n g t h e n ex t f i v e s eco n d del ay t h e v o l t age w a s r e d u c e d a nd p o w e r d i d no t s hu t d o w n. Figure 3-13. Relays.

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62 Re s is tanc e M e as ur e m e nt T h e e x p e r i m e n ta l d e te r m i n a ti on of th e s a m p l e r e s i s ta n c e e m p l oy e d tw o m e th od s b oth us ed t h e s am e equi pm en t T h e di f f eren ce i n resi s t an ce pro pert y m agn i t udes requi red a di f f eren t appro ach depen di n g o n t h e ph y s i cal s t at e o f t h e s am pl e. T h e f i rst m et h o d was u s e d w it h t h e s a mp le in a n u n fr o z e n s t a t e T h e s e c o n d me t h o d w a s u s e d w it h t h e s a mp le in a f ro zen s t at e. U n froze n sa mp le T h e f i rst s t ep wa s t o prepare a gel as di s cus s ed prev i o us l y J us t b ef o re t h e gel was p o u r e d i nt o t he i ns t r u m e nt e d s a m p l e c e l l t he d a t a a c q u i s i t i o n w a s s t a r t e d a nd r e c o r d e d t he t e m p e ra t u re h i s t o ry o f t h e l i q u i d g e l a s i t c o o l s a n d b e c a m e a s o l i d a t roo m t e m p e ra t u re A f t e r t h e g e l w a s p o u re d t h e s e c o n d e l e c t rode w a s p u t i n t o p l a c e o n t h e t o p o f t h e s a m p l e A s m a l l a m o u nt o f l i q u i d s a m p l e f o r m e d a be a d be t w e e n t he s a m p l e c e l l e d g e a nd t he e le c t r o d e T h e n t h e t o p o f t h e e le c t r o d e w a s c o v e r e d w it h a t h in la ye r o f g e l. T h is p r e v e n t e d a n y d e h yd r a t io n fr o m o c c u r r in g t o t h e g e l lo c a t e d b e t w e e n t h e e le c t r o d e s w h ile t h e s am pl e co n geal ed. O nc e t he g e l w a s s e t t he t o p e l e c t r o d e w a s a t t a c he d t o t he p o w e r l e a d a nd t he e nd c a p p u t i n p l a c e p r e v e n ti n g th e e l e c tr od e f r om p u l l i n g a w a y f r om th e s a m p l e T h e b ottom en d cap w as rem o v ed al l o wi n g t h e b o t t o m el ect ro de t o b e co n n ect ed t o t h e o t h er po wer l e a d T he i ns t r u m e nt e d s a m p l e w i t h p o w e r l e a d s c o nne c t e d w a s p l a c e d i nt o t he en v i ro n m en t al co n t ro l ch am b er. T h e s am pl e wa s ready f o r t h erm al co n di t i o n i n g. T h e ch am b er was t urn ed o n an d t wo j ugs o f i ce i n t ro duced. T h i s was v ery s i m i l ar t o t h e m et h o d o f t h erm al dam pi n g. T h e ai r t em perat ure o f t h e ch am b er was m o n i t o red wi t h an ex t ern al t em perat ure m eas uri n g dev i ce. On e dev i ce w as t h e m ul t i m et er wh i ch h as

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63 t yp e K t h e r mo c o u p le d ir e c t in p u t fo r t e mp e r a t u r e mo n it o r in g W h e n it w a s n o t a v a ila b le du e t o co l l ect i n g cu r r en t dat a, a si m pl e i n ex pen si v e t h er m i st o r pr o b e was used. T h ese pro b es were n o t cal i b rat ed. T h ey s h o wed go o d agreem en t b et wee n eac h o t h er wh en ref eren ced t o t h e t h erm o co upl e pro b es Ca l i b rat i o n was n o t requi red si n ce h i gh acc uracy w a s n o t n e c e s s a ry i n m o n i t o ri n g t h e a i r t e m p e ra t u re s Th e c h a m b e r w a s i n i t i a l l y c o o l e d t o s l i g h t l y b e l o w f re e z i n g a n d t h e n t u rn e d o f f T he t e m p e r a t u r e o f t he s a m p l e m o ni t o r e d T he m a nu a l c y c l i ng o f t he t e m p e r a t u r e i n t he c h a m b e r w a s c o n t i n u e d b ri n g i n g t h e s a m p l e s l o w l y c l o s e t o f re e z i n g O n c e t h e t e m p e ra t u re w a s i n t he d e s i r e d r a ng e t he n d a t a c o l l e c t i o n f o r d e t e r m i ni ng r e s i s t a nc e be g a n. T h e po wer suppl y was s et t o a predet erm i n ed v al ue, wi t h t h e f i n al m an ual s wi t ch l e f t op e n T h e m u l ti m e te r a n d d a ta a c q u i s i ti on s of tw a r e w e r e s ta r te d T h e p ow e r w a s n ow s w it c h e d o n a n d t h e t e mp e r a t u r e r e a d ing s fo r t h e s a mp le mo n it o r e d T h e p o w e r w a s le ft o n f o r a p p r o xi m a t e l y 3 0 s e c o nd s t he n s w i t c he d o f f T he s a m p l e w a s o hm i c a l l y he a t e d by t he a p p l i c a t i o n o f t he p o w e r a nd i t s t e m p e r a t u r e r o s e o n t he o r d e r o f 0 5 C d u r i ng t he p o w e r a p p lic a t io n T h e p o w e r w a s t h e n s w it c h e d o ff fo r a p p r o x ima t e ly 3 0 s e c o n d s T h is a l l o w e d f o r i nt e r na l t he r m a l r e l a xa t i o n o f t he s a m p l e T hi s c y c l i ng w a s c o nt i nu e d u nt i l t he t em per at ur e di f f er en ce b et ween pr o b e l o cat i o n s was o n t h e o r der o f 0. 2 C. O nc e t he r u n f i ni s he d t he d a t a w e r e d o w nl o a d e d f r o m t he m u l t i m e t e r T he ch am b er was t h en t h erm al l y co n di t i o n ed t o a n ew t em perat ure. T h e n ew t em perat ure was c ho s e n t o o ve r l a p a p o r t i o n o f a p r e vi o u s r u n. T hi s p r o vi d e d m u l t i p l e d a t a p o i nt s a t t he s a me t e mp e r a t u r e T h e g e n e r a l d a t a c o lle c t io n p r o c e d u r e o f t h is me t h o d w a s r e p e a t e d u n t il t h e t em perat ure r an ge o f i n t eres t was adequa t el y co v ered.

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64 T h e res i s t an ce w as cal cul at ed f ro m t h e co l l ect ed dat a. T h e dat a we re f i rst reduced b y a c u s tom p r og r a m th a t d e te c te d th e e d g e s of e a c h c u r r e n t c y c l e a n d a l i g n e d th a t w i th t he e d g e o f e a c h vo l t a g e c y c l e T he c o m bi ne d d a t a ha d t he m a t c he d vo l t a g e a nd c u r r e nt v al ues wh i ch i n di cat ed t h e res i s t an ce. T h e av erage t em perat ure v ersus resi s t an ce w as graph ed an d f i t t ed wi t h a po l y n o m i al T h e graph i n g an d f i t t i n g were do n e wi t h t h e A x um s o f t ware. A t h i rd o rder po l y n o m i al was ch o s en wi t h t h e i n v erse o f t h e m ax i m um t e mp e r a t u r e d iffe r e n c e b e t w e e n p r o b e s u s e d a s a w e ig h t fo r e a c h p o in t T h is g a v e s lig h t ly m o r e wei gh t t o po i n t s t h at sh o w cl o ser t em per at ur e agr eem en t b et ween al l t h r ee l o cat i o n s. Fro z e n sa mp le T h e f ro zen s am pl e we n t t h ro ugh t h e s am e gel preparat i o n as t h e un f ro zen A f t er t he u nf r o z e n s t a t e m e a s u r e m e nt s w e r e f i ni s he d t he s a m p l e w a s r e m o ve d f r o m t he en v i ro n m en t al co n t ro l ch am b er f o r f reezi n g preparat i o n s T h e en d caps were f i rst rem o v ed s o th e e l e c tr od e c on n e c ti on s c ou l d b e a c c e s s e d T h e n th e e l e c tr od e s w e r e d i s c on n e c te d to al l o w cl am pi n g f o r f reezi n g. T h e l ay er o f ex ces s gel was rem o v ed f ro m t h e t o p el ect ro de d u ri n g t h i s p roce s s T h e s m pl e wa s ready t o b e f ro zen af t er cl am pi n g. T h e un f ro zen s am pl e wa s pl ace d i n t h e e n v i ron m e n t a l c o n t rol c h a m b e r s e t t o c o n t i n u o u s ru n m o d e Th e s a m p l e t e m p e ra t u re was m o n i t o red b y t h e dat a ac qui s i t i o n s y s t em wh i ch co l l ect ed t h e s am pl e ph as e ch an ge i nf o r m a t i o n. T he c ha m be r w a s t u r ne d o f f w he n t he s a m p l e ha d r e a c he d t he l i m i t i ng t em per at ur e o f t h e ch am b er app r o x i m at el y 35 C. T h e f ro zen s am pl e wa s rem o v ed an d prepared f o r dat a co l l ect i o n i n t h e f ro zen s t at e. T h e f i rst s t ep wa s t o reco n n ect t h e el ect ro des t o t h e po wer suppl y an d put ax i al i n s u l a ti on a n d e n d c a p s i n p l a c e T h e e x te r i or of th e s a m p l e h ol d e r w a s c ov e r e d w i th

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65 addi t i o n al l ay ers o f f i b ergl as s i n s ul at i o n T h i s was h el d i n pl ace b y m es h f i b ergl as s t ape ( Fi g u r e 3 1 4 ) T he ne w c o nf i g u r a t i o n w a s p l a c e d ba c k i nt o t he f r e e z e r C y c l i ng a nd w a r m i ng d a t a w e r e t a k e n f o r t he ne w c o nf i g u r a t i o n. D u e t o t h e e x t r e me ly hig h e le c t r ic a l r e s is t a n c e o f t h e fr o z e n s a mp le it w a s t h e r ma lly c o nd i t i o ne d be f o r e r e s i s t a nc e m e a s u r e m e nt s T hi s t i m e t he c o nd i t i o ni ng w a s t o w a r m t he f r o z e n s a m p l e t o a r a ng e o f i nt e r e s t t ha t w a s s t i l l be l o w f r e e z i ng T he t he r m a l d a m p i ng m e t h o d d i s c u s s e d p re v i o u s l y w a s u t i l i z e d t o b ri n g t h e s a m p l e t e m p e ra t u re c l o s e t o -5 C T h i s was t h e st ar t i n g p o i n t i n t h e f r o zen st at e f o r t h e el ect r i cal r esi st an ce v al ues. T h e h ig h r e s is t a n c e o f t h e fr o z e n s t a t e a llo w e d t h e d a t a t o b e c o lle c t e d a s a s in g le c o n t in u o u s s t r e a m. T h e w a r min g o f t h e s a mp le in t h is c a s e w a s n o t d r iv e n b y t h e o h mic po rt i o n o f h eat i n g s i n ce t h e t o t al po wer appl i ed wa s v ery l o w. T o m ai n t ai n t h i s ef f ect as th e te m p e r a tu r e w a r m e d th e v ol ta g e w a s r e d u c e d on e ti m e d u r i n g th e c ol l e c ti on W i th c l o s e m o ni t o r i ng o f t he t e m p e r a t u r e r i s e o f t he s a m p l e a nd p r e vi o u s k no w l e d g e o f t he Figure 3-14. Additional Fiberglass Insulation.

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66 warm i n g, i t was po s s i b l e t o t ake da t a v ery cl o s e t o 0 C w i t h o ut cro s s i n g t h e ph as e ch an ge b o u n d a ry o f t h e s a m p l e g e l Th e d a t a c o l l e c t i o n w a s s t o p p e d a t a p p rox i m a t e l y -0 .2 C T h e p r oc e s s of c oo l i n g th e s a m p l e w a s r e p e a te d to s e t u p f or a n oth e r d a ta co l l ect i o n run T h e dat a co l l ect ed f ro m t h es e run s were an al y zed m uch t h e s am e wa y as t he u nf r o z e n d a t a A c u s t o m p r o g r a m d i d e d g e d e t e c t i o n t o a s s u r e a l i g nm e nt o f t he v o l t age a n d curr en t dat a po i n t s t aken wi t h t h e t wo di f f eren t i n s t rum en t s T h e co m b i n ed dat a wer e t h en used t o cal cul at e t h e r esi st an ce v al ues. Th e t ra n s f o rm e d d a t a w e re t h e n g ra p h e d a n d f i t t e d w i t h A x u m s o f t w a re A g a i n a t hi r d o r d e r p o l y no m i a l w a s s u s e d w i t h t he s a m e t y p e w e i g ht i ng f a c t o r s T he w e i g ht i ng f act o r was us ed f o r co n s i s t en cy b et wee n t h e t wo s et s T h e t em perat ure spread b et wee n p r o be s f o r t he u nf r o z e n s t a t e e xp e r i m e nt s w e r e m u c h m o r e t ha n t ha t f o r t he f r o z e n. T he s p r e a d on th e f r oz e n s ta te e x p e r i m e n ts w e r e a t or b e l ow a p p r ox i m a te l y 0 1 C or l e s s w i th t h e m aj o r i t y o f t h e dat a sh o wi n g a spr ead m o r e o n t h e o r der o f 0. 05 C. Ohm ic T haw ing T he f i na l e xp e r i m e nt a l m e t ho d i nvo l ve d c o l l e c t i ng d a t a d u r i ng a n o hm i c t ha w i ng p r o c e s s T he s a m p l e a t t hi s p o i nt ha s a l r e a d y u nd e r g o ne r e s i s t a nc e m e a s u r e m e nt s i n t he u n f roze n a n d t h e f roze n s t a t e s Th e g e l p re p a ra t i o n a n d d e t a i l s o f t h o s e m e a s u re m e n t s a re di s cus s ed i n prev i o us s ect i o n s A t t h e en d o f t h e f ro zen resi s t an ce m eas urem en t s t h e gel w a s s ti l l f r oz e n i n th e c h a m b e r w h i c h w a s i n a c y c l i n g m od e T h e f i r s t s te p w a s to t he r m a l l y c o nd i t i o n t he s a m p l e t o t he d e s i r e d t e m p e r a t u r e r a ng e t o s t a r t t he p r o c e s s T he a i r t e m p e ra t u re w a s a l s o m o n i t o re d t o b ri n g i t c l o s e t o t h e s a m p l e t e m p e ra t u re j u s t b e f o re po wer was appl i ed t o t h e s am pl e.

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67 T he a u t o m a t i c p o w e r c o nt r o l w a s c o nf i g u r e d t o s w i t c h t he s y s t e m o f f i f t he c u r r e nt r o s e a b o v e 0 4 a mp s T h e p o w e r s u p p ly w a s s e t t o it s ma x imu m o u t p u t a p p r o x ima t e ly 4 9 0 v o lt s A C T h e d a t a lo g g in g mu lt ime t e r w a s c o n n e c t e d a n d s e t o n t h e mil lia mp s c a le in a l te r n a ti n g c u r r e n t m od e T h i s a l l ow e d th e c u r r e n t to b e r e a d i n i ti a l l y i n h u n d r e d s of m i l l i a m p s o n t he f o u r d i g i t d i s p l a y w i t h a u t o m a t i c s w i t c h o ve r t o m i l l i a m p s o nc e t he readi n g ex cee ded 50 m i l l i am ps T h e f requen cy f o r t h e l o ggi n g o n t h e m ul t i m et er was s et at o n e H e rt z Th e d a t a a c q u i s i t i o n w a s i n i t i a t e d s i m u l t a n e o u s l y w i t h t h e s o f t w a re c o n t rol l e d c a rd a n d ma n u a lly c o n t r o lle d d a t a lo g g in g mu lt ime t e r T h e s ys t e m w a s r e a d y t o b e g in o h mic h e a t i n g Th e p o w e r s w i t c h c l o s e d t o a p p l y p o w e r t o t h e s a m p l e Th e s a m p l e t e m p e ra t u re m o n i t o re d o n t h e s c re e n a s i t w a s re c o rd e d N o t e s w e re m a i n t a i n e d i n t h e l a b o ra t o ry n o t e b o o k o n t h e a p p rox i m a t e c h a m b e r t e m p e ra t u re T h e s y s t em was al l o wed t o run un t i l t h e s am pl e h as a 0.5 C di f f eren ce b et wee n t em perat ure m eas uri n g po i n t s i n t h e gel T h e po wer was m an ual l y t urn ed o f f T h e s y s t em was al l o wed t o t h erm al l y rel ax b ef o re po wer was appl i ed aga i n T h e po wer was appl i ed a s e c o n d t ime t o a p p r o x ima t e ly t h e s a me t e mp e r a t u r e d iffe r e n c e a n d t u r n e d o ff. T h e s a mp le w a s a llo w e d t o r e la x a g a in ju s t b e lo w t h e p h a s e t r a n s it io n p o in t N o t e a t t h is p o in t a ll te m p e r a tu r e s w e r e r e a d i n g b e l ow th e s a m p l e p h a s e tr a n s i ti on p oi n t. T h e sam pl e was t h en po wer ed t h r o ug h t h e ph ase t r an si t i o n F o l l o wi n g t h e ph ase t ra n s i t i o n t h e a u t o m a t i c p o w e r c o n t rol t o o k o v e r, s h u t t i n g o f f t h e p o w e r a n d a m a n u a l t u rn o f f appl i ed t h at co n t ro l l ed t h e po wer o f f t i m e. T h e appl i ed v o l t age w as adj us t ed t o reduce t h e po wer suppl i ed t o h eat t h e s am pl e. T h e s am pl e wa s t aken f ro m t h e en v i ro n m en t al ch am b er o n ce i t was t h ro ugh t h e ph as e t ran s i t i o n T h i s f urt h er en h an ced t h e i n s ul at ed

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68 bo u nd a r y c o nd i t i o ns s i nc e t he s a m p l e w a s w a r m e r t ha n t he e nvi r o nm e nt a l c ha m be r a nd w a s c lo s in g in o n a mb ie n t r o o m t e mp e r a t u r e T h e s a mp le w a s fu r t h e r h e a t e d t o s lig h t ly ab o v e am b i en t ro o m co n di t i o n s f o l l o wi n g t h e s am e cy cl i n g o f l i m i t ed po wer an d v o l t age a d j u s t m e n t s Th e d a t a a c q u i s i t i o n s w e re s t o p p e d Th e d a t a l o g g i n g d i g i t a l m u l t i m e t e r d a t a w e re do wn l o aded. T h e s am pl e wa s pl ace d b ack i n t h e en v i ro n m en t al co n t ro l ch am b er. It was s t i l l a s o l i d gel at t h i s po i n t T h e s am pl e wa s ready t o h av e an o t h er r o un d o f t h erm al c o nd i t i o ni ng T he c o nd i t i o ni ng p r e p a r e d t he s a m p l e f o r u nf r o z e n r e s i s t a nc e m e a s u r e m e nt a s eco n d t i m e. A f t er a s eco n d s et o f un f ro zen dat a wa s acqui red, t h e s am pl e wa s ready f o r ph y s i cal ex am i n at i o n T h e o ut er l ay er o f f i b ergl as s i n s ul at i o n was rem o v ed f i rst T h en t h e en d caps a n d a s s o c i a t e d i n s u l a t i o n w e re re m o v e d s o t h e e l e c t rode c o n n e c t i o n s c o u l d b e t a k e n a p a rt T h e el ect ro des were t h en rem o v ed f ro m b o t h en ds o f t h e s am pl e f o r ph o t o graph i n g. No t es w e r e m a d e i n t he l a bo r a t o r y no t e bo o k o n t he p hy s i c a l o bs e r va t i o ns a bo u t t he g e l a nd t he e l e c t rode s c o n t a c t i n g i t Th e c o l l e c t e d d a t a w e re re a d y f o r c o n s o l i d a t i o n a n d re d u c t i o n Sof t w a re a g a i n a s s i s t e d i n f u rt h e r a n a l y s i s Th e re s u l t s w e re t h e n g ra p h i c a l l y d i s p l a y e d

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69 CHA P T E R 4 RESULTS A ND DISCUSSI ON T h i s rese arch y i el ded m an y resul t s T h ey were gro uped wi t h t h e s am e s t ruct ure as t h e M a t e ri a l s a n d M e t h o d s c h a p t e r. Data Col l ection T h ere were t wo dat a co l l ect i o n ex peri m en t s wi t h resul t s o f i n t eres t T h e f i rst was d e t e rm i n i n g a n a c c e p t a b l e ra t e f o r t e m p e ra t u re p o l l i n g a n d c h a ra c t e ri z i n g t h e d a t a T hr o u g h p r o g r e s s i ve l y i nc r e a s i ng t he p o l l i ng r a t e i t w a s d e t e r m i ne d t ha t t he ha r d w a r e a nd s o f t ware co m b i n at i o n h ad an upper l i m i t o f appro x i m at el y 500 Hert z f o r l o o pi n g t h e 16 ch an n el s A b o v e t h i s l ev el i t was n o t ed t h at t h e dat a t aken n o l o n ger h ad s equen t i al s eco n ds as t h e t i m e s t am p. F ro m s i m pl e di v i s i o n i t was deduce d, t h at t h e l o o p rat e wa s o n t h e o rder o f 0. 002 s e c o nd s S i nc e a l l e xp e r i m e nt s w e r e r u n by a ve r a g i ng 1 0 0 l o o p s e a c h d a t a p o i nt r e p r e s e nt e d a t i m e s l i c e o f a p p r o xi m a t e l y 0 2 s e c o nd s l o ng Ano t he r w a y o f d e s c r i bi ng t he po l l i n g rat e wa s t o l o o k at t h e n um b er o f dat a po i n t s t h at were co l l ect ed b as ed o n eac h l o o p. T h ere were 16 po i n t s co l l ect ed f o r each l o o p. T h i s m ean t t h at t h e s y s t em co l l ect ed 1 6 0 0 p oi n ts w h e n i t p ol l e d 1 0 0 l oo p s T h e s e w e r e th e n r e d u c e d to 1 6 a v e r a g e d p oi n ts b e f or e r e c or d i n g T h e a d v a n ta g e of l ook i n g a t th e n u m b e r of d a ta p oi n ts on a s i n g l e l oop w a s t hi s g a ve s o m e i ns i g ht t o c o l l e c t i o n t i m e c a p a bi l i t y o f a s i ng l e d a t a p o i nt by t he h a rd w a re s o f t w a re c o m b i n a t i o n A s i n g l e d a t a p o i n t t o o k o n t h e o rd e r of 1 .2 5 x 1 0 s -4 F urt h er, i t was o b s erv ed t h at t h e t i m e b et wee n co n s ecut i v e po i n t s o n t h e s am e ch an n el w e r e e q u a l t o t he l o o p t i m e o f 0 0 0 2 s e c o nd s w he n 1 6 c ha nne l s w e r e s c a nne d a s w a s t he c a s e i n a l l o f t hi s r e s e a r c h.

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70 T h e 16 ch an n el s b ei n g s am pl ed we re o rder ed s peci f i cal l y t o i n cl ude a gro un ded c h a n n e l b e t w e e n e a c h d a t a c h a n n e l o f in t e r e s t S in c e s o ft w a r e p o lli n g w a s b e in g u s e d in a ll c a s e s t hi s g a ve vo l t a g e va l u e s o f t he ba c k p l a ne g r o u nd T he a d va nt a g e o f t he c on f i g u r a ti on w a s i n c r e a ti n g a m or e f l e x i b l e d a ta c ol l e c ti on d e v i c e T h e K e i th l e y d a ta acqui s i t i o n b o ard h ad a D M A (di rect m em o ry acc es s ) m o de t h at al l o wed s i gn i f i can t l y f as t er acqui s i t i o n s i n wh i ch t h e s et t l i n g t i m e b et wee n readi n gs co ul d b e en h an ced b y ref eren ci n g a gro un d b ef o re eac h m eas urem en t T h e dat a co l l ect i o n rat e b as ed o n a per po i n t b as i s t h en co ul d b e pus h ed t o t h e b o ard l i m i t o r 100, 000 kHz. Th e d a t a c o l l e c t i o n s o f t w a re ra n u n d e r W i n d o w s 9 8 a n d e x h i b i t e d o n e l i m i t a t i o n It be g a n t o s t a l l a f t e r t a k i ng a l a r g e nu m be r o f a ve r a g e d p o i nt s T he s y s t e m s ho w e d s l o w i ng m arked b y l o n ger t h an o n e s eco n d i n t erv al s b et wee n av eraged po i n t s T h i s s l o wi n g was n ot a n i s s u e i n th e r e s e a r c h b e c a u s e of th e h i g h n u m b e r of p oi n ts th a t h a d to b e ta k e n to s ee t h e ph en o m en o n It was ex h i b i t ed wh en t h e n um b er o f l o o ped av erages ex cee ded a p p rox i m a t e l y 2 5 ,0 0 0 Th i s t ra n s l a t e d t o a l m o s t s e v e n h o u rs o f c o n t i n u o u s d a t a t a k i n g A l l p h y s i c a l p h e n o m e n a o f i n t e re s t i n t h e e x p e ri m e n t s t o o k a s h o rt e r p e ri o d t o c a p t u re T h e c a u s e f or th e e v e n tu a l s l ow d ow n w a s n ot d e te r m i n e d a s i t h a d n o p r a c ti c a l i m p a c t on t h e re s e a rc h Te m per atu r e Cal ibr ati on Theor etical I n a n y t e mp e r a t u r e me a s u r in g in s t r u me n t t h e g r e a t e s t a c c u r a c y is a c h ie v e d b y mu lt ip o i nt c a l i br a t i o n. I n t hi s r e s e a r c h a s i ng l e t e m p e r a t u r e r e f e r e nc e p o i nt w a s u s e d T he t he o r e t i c a l j u s t i f i c a t i o n f o r a s i ng l e p o i nt be i ng e no u g h f o r o u r p u r p o s e s w a s t w o f o l d T he

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71 f i r s t w a s th e m e th od of te m p e r a tu r e m e a s u r e m e n t u s e d a n d th e s e c on d w a s th e r a n g e of t e m p e ra t u re s m e a s u re d In t h i s rese arch t h e t em perat ure pr o b es were t h erm o co upl es T h es e t h erm o co upl es were n o t read di rect l y i n s t ead a co n di t i o n ed o ut put s i gn al was read. T h ei r o ut put s i gn al w a s c on d i ti on e d b y th e A D I s i g n a l c on d i ti on i n g m od u l e s T h e m od u l e s w e r e d e s i g n e d to s p e c i f i c a l l y c o nd i t i o n f o r T t y p e t he r m o c o u p l e s T he m a nu f a c t u r e r s s p e c i f i c a t i o ns f o r t he m od u l e s a c c u r a c y w e r e d e p e n d e n t on s e v e r a l f a c tor s T h e f i r s t w a s th e s p a n of t em perat ure r an ge f o r t h e m o dul e s des i gn T h e n ex t was a v o l t age s i gn al readi n g acc uracy al o n g wi t h t h e ac curacy o f a co l d j un ct i o n co m pen s at i o n s en s o r f o r each ch an n el W h en t h e erro rs were e v al uat ed an d t h e s quare ro o t o f t h e s um o f t h ei r squares t aken t h e o rder o f m a g ni t u d e o f t he e r r o r w a s 0 5 C T hi s r e p r e s e nt e d t he a c c u r a c y e xp e c t a t i o n w i t h no f urt h er cal i b rat i o n appl i ed. By ref eren ci n g a kn o wn t em perat ure t h e ac curacy was i m p r o ve d I t w a s no t e d f r o m t he s i ng l e p o i nt va l u e s p r e s e nt e d l a t e r t ha t i nd e e d t he m o d u l e s re q u i re d a n o f f s e t o f l e s s t h a n t h e m a n u f a c t u re r s e rror ra n g e T he m a i n i s s u e w a s t he no nl i ne a r i t y o f t he o u t p u t w hi c h w a s l i ne a r i z e d by t he s i g na l c o nd i t i o ni ng m o d u l e T he no nl i ne a r i t y o f t he m o d u l e a c c o r d i ng t o t he m a n u f a c tu r e r s s p e c i f i c a ti on s w a s + / 0 0 2 % of th e r a n g e T h e r a n g e d u r i n g e x p e r i m e n ts ne ve r e xc e e d e d 5 0 C f r o m t he c a l i br a t e d p o i nt T he no nl i ne a r i t y w a s t he n e xp e c t e d t o be o n t he o r d e r o f 0 0 1 C T hi s c o u p l e d w i t h t he f a c t t ha t t he r a ng e o f i nt e r e s t i n t he r e s e a r c h w a s r e l a ti v e l y s m a l l i n d i c a te d th a t a s i n g l e c a l i b r a ti on p oi n t c l os e to th e m i d d l e of t h e ran ge wa s s uf f i ci en t t o ex pect acc uracy m o re o n t h e o rder o f t h e n o n l i n eari t y T h i s was c ou p l e d w i th th e r e s ol u ti on of th e d e v i c e r e a d i n g th e m od u l e a n d th e a p p a r e n t l e v e l s of

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72 n o i s e i n t h e s y s t e m w h i c h y i e l d e d a f i n a l o rd e r of m a g n i t u d e e x p e c t e d f o r t h e t e m p e ra t u re m easur em en t er r o r s. Th e c a l i b ra t i o n o f t h e t e m p e ra t u re s e n s o rs u t i l i z e d a c l a s s i c t h e o re t i c a l p rob l e m T h e pro b l em i s co m m o n l y ref err ed t o as t h e St eph an Pr o b l em It i s a s i m pl e h o m o gen eo us p h a s e c h a n g e fr o m li q u id t o s o lid A s o lu t io n t o t h is o n e d ime n s io n a l p r o b le m is g iv e n in C a r s l a w a nd J a e g e r ( 1 9 5 9 ) T he s o l u t i o n i s r e f e r r e d t o a s t he N e u m a n s o l u t i o n f o r t he s e m i -i n f i n i t e p rob l e m Th e p rob l e m m a i n t a i n s t h e i n i t i a l s u rf a c e a t x = 0 t o b e a t z e ro t e m p e r a t u r e T he r e s t o f t he bo d y i s i ni t i a l l y a t a c o ns t a nt t e m p e r a t u r e a bo ve t he s u bs t a nc e s m e l t i ng p o i nt T he s o l u t i o n t o t hi s o ne d i m e ns i o na l p r o bl e m i s a r r i ve d a t by m a k i ng a n a s s u m p t i o n t ha t t he p o s i t i o n o f t he p ha s e c ha ng e s u r f a c e i s p r o p o r t i o na l t o t he s quare ro o t o f t i m e. T h e aut h o rs arb i t rar i l y ch o s e a f o rm t h at i n cl udes t h e t h erm al d iffu s iv it y o f t h e s o lid p h a s e T h e s o lu t io n c a n b e s h o w n t o b e e q u iv a le n t t o t h e s a me a s s u m p t i o n u s i ng t he t he r m a l d i f f u s i vi t y o f t he l i q u i d p ha s e A d e r i va t i o n o f t hi s s e c o nd f o r m o f t he s o l u t i o n c a n be f o u nd i n Ap p e nd i x A. Th e t h e o re t i c a l p rob l e m t h e n i n h e re n t l y i s a c o n d u c t i o n h e a t t ra n s f e r p rob l e m It a l l ow s f or d i f f e r e n t th e r m a l p r op e r ti e s i n e a c h of th e tw o p h a s e s I t a s s u m e s th e d e n s i ty of b o t h p h a s e s t o b e t h e s a m e w i t h n o v o l u m e c h a n g e s a c c o u n t e d f o r. Ex per im ental Th e e x p e ri m e n t a l p rob l e m f o r c a l i b ra t i o n l o o k e d v e ry s i m i l a r t o t h e t h e o re t i c a l T he i m p o r t a nt f e a t u r e s w e r e s ho w n i n Fi g u r e 4 1 T hi s u nd e r i d e a l c o nd i t i o ns w a s a o ne d i m e ns i o na l he a t t r a ns f e r s e t u p I t w a s r e c o g ni z e d t ha t t he d a t a c o l l e c t e d w i t h t he e x p e r i m e n ta l a p p a r a tu s r e f l e c te d s e v e r a l f e a tu r e s th a t th e th e or e ti c a l s ol u ti on d i d n ot ex h i b i t T h e f i rst was t h at t h e ph y s i cal pro pert i es were f un ct i o n s o f t em perat ure as wel l as

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73 ph as e. T h e ex peri m en t al s et up al s o o n l y appro x i m at ed t h e i deal b o un dary co n di t i o n s t h at w e r e r e p r e s e nt e d by t he t he o r e t i c a l p r o bl e m T he u p p e r s u r f a c e i n r e a l i t y ha s s o m e t hi ng o t he r t ha n a c o ns t a nt t e m p e r a t u r e bo u nd a r y c o nd i t i o n t ha t d r o ve t he he a t t r a ns f e r T he d i f f e r e nc e s i ni t i a l l y l o o k e d r e l a t i ve l y m i no r bu t d u e t o w a t e r s u ni q u e p r o p e r t i e s t he t he o r e t i c a l s o l u t i o n ha d no c o m p a r a t i ve va l u e t o a c t u a l d a t a t a k e n f o r c a l i br a t i ng t he sen so r s. T h e in fo r ma t iv e p a r t o f a c a lib r a t io n r u n a t fi r s t a p p e a r e d t o s e e k o n ly a t e m p e ra t u re p l a t e a u A v i s i b l e p l a t e a u i n d i c a t e d c o n s t a n t t e m p e ra t u re w h e n i n f a c t t h e re w a s e ne r g y t r a ns f e r o c c u r r i ng i n t he f o r m o f c o o l i ng T hi s t he n y i e l d e d a r e f e r e nc e p o i nt fo r t h e p h a s e c h a n g e t e mp e r a t u r e o f t h e liq u id in t h e s a mp le c e ll. T h e a c t u a l d a t a fr o m a cal i b rat i o n run were pl o t t ed i n F i gure 42. It was i m m edi at el y s t ri ki n g t h at t h ere was a m uch m o re co m pl i cat ed s y s t em i n pl ay t h a n a s imp le c o n d u c t io n p r o b le m e x p la in e d T h e in it ia l p a r t o f t h e g r a p h s h o w e d t h a t a ll t e m p e r a t u r e s w e r e t r a c k i ng o ne a no t he r ve r y c l o s e l y T hi s w a s e xp l a i ne d by t he c o nve c t i ve m i xi ng t ha t w o u l d ha ve be e n d r i ve n by a p r o c e s s w he r e t he l i q u i d u p p e r s u r f a c e u p o n Figure 4-1. Calibration Setup Features.

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74 co o l i n g b eco m es m o r e dens e an d si n ks do wn W at er s m ax i m um den si t y was at 4 C, so t h e co n v ect i v e pr o cess was n o t m ai n t ai n ed al l t h e way t o t h e f r eezi n g p o i n t at 0 C T h e graph cl earl y s h o wed t h at i n t h e area o f 4 C a n o t h er ph y s i cal ph en o m en o n was o ccurri n g. T h e i n t eres t i n g po i n t h ere was t h at o n e co ul d act ual l y s ee t h e ex pect ed tr a n s i ti on f r om a c on v e c ti on d r i v e n p r oc e s s to a c on d u c ti on d r i v e n p r oc e s s T h e c ool top l a y e r b e c a m e th e l e s s d e n s e l a y e r n o l on g e r s i n k i n g a n d c a u s i n g th e n a tu r a l c on v e c ti on to o c c u r T hi s c o o l l a y e r t he n r e s t e d i n p l a c e a nd t he r m a l s t r a t i f i c a t i o n be g a n w he n t he p r i m a r y h e a t tr a n s f e r m od e w a s c on d u c ti on D u r i n g th e e n ti r e ty of th e r e s e a r c h e n d e a v or s e v e ra l s i m i l a r c a l i b ra t i o n e x p e ri m e n t s w e re c a rri e d o u t a n d c o n s i s t e n t o b s e rv a t i o n s w e re m ade o n each o f t h e r un s. F i gure 42. Pr o b e C al i b rat i o n Dat a. O b j e c t 4 -1 C a l 3 8 5 x 1 1 .j p g (1 74 KB).

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75 Th e d a t a c a p t u re d b y t h e e x p e ri m e n t a l s o s h o w e d a n o t h e r e x p e c t e d p h e n o m e n o n S u b c ool i n g of th e l i q u i d w a s a l s o a p p a r e n t. T h i s w a s y e t a n oth e r p h y s i c a l p h e n om e n on t h a t t h e s i m p l e t h e o re t i c a l m o d e l c o u l d n o t a c c o u n t f o r, b u t o n e w a s e x p e c t e d t o o c c u r. F o l l o wi n g t h e s ub co o l i n g o n t h e graph t h ere was a pl at eau w h ere ph as e t ran s i t i o n was t ry i n g t o i n i t i a t e Th i s a re a w a s w h e re t h e o f f s e t n u m b e rs f o r c a l i b ra t i o n w e re c o l l e c t e d A s h o rt s pan o f t h e dat a wa s l i n earl y regr es s ed an d y i el ded a s l o pe t o v eri f y t h at i t was v i rt ual l y h o ri zo n t al A n av erage v al ue t h en was us ed t o cal i b rat e ea ch s en s o r. T h e v al ues arr i v ed at f o r t h ree ca l i b rat i o n run s are l i s t ed i n T ab l e 4-1. T ab l e 41. Cal i b r at i o n Of f set Val ues. Cal i b r at i o n Of f set Val ues ( C ) T h e r m oc ou p l e P r ob e D e s i g n a ti on Ca l i b rat i o n Run # Ch an 5 Ch an 7 Ch an 9 Ch an 11 Ch an 13 Ch an 15 1 0. 248 0. 319 0. 246 0. 209 0. 472 0. 258 2 0. 259 0. 329 0. 260 0. 211 0. 464 0. 272 3 0. 263 0. 341 0. 260 0. 216 0. 471 0. 288 A v erage Va l ues 0. 257 0. 330 0. 255 0. 212 0. 469 0. 273 Fi g u r e 4 3 p l o t t e d d a t a c o l l e c t e d w hi l e t he w a t e r s a m p l e w a r m e d u p T he t i m e c o u nt w a s r e s t a r t e d a t z e r o w h e n t h e s a mp le w a s r e mo v e d fr o m t h e t e mp e r a t u r e c o n t r o l ch am b er. It was i n t eres t i n g t o n o t e h o w t h e wa rm i n g wat er sh o wed a ph y s i cal ph en o m en o n aro un d s am e 4 C po i n t T h i s t i m e i t appea red as i f t h e wa rm i n g was i n i t i at ed f ro m t h e b o t t o m s i n ce i t was t h e l o wes t s en s o rs t h at were s h o wi n g t h e wa rm er t e m p e r a t u r e s i ni t i a l l y u p o n l e a vi ng t he p l a t e a u a r e a T hi s c o u l d ha ve be e n r e l a t e d t o t he l a c k o f a p e r f e c t l y i ns u l a t e d bo u nd a r y c o nd i t i o n a p p l i e d a t t he bo t t o m C o u p l e d w i t h t he f a c t th a t on th e c oo l i n g s i d e th e b ott om s l i g h tl y l e d w h e n c on v e c ti v e m od e w a s d om i n a n t,

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76 t h e d a t a s e e me d t o in d ic a t e t h a t t h e b o t t o m in s u la t e d c o n d it io n w a s in d e e d s lig h t ly i m p e r f e c t T he i ns u l a t e d c o nd i t i o n p r o ba bl y w a s no t t he m a i n c a u s e f o r t he l e a d i ng o f t he b ottom s e t i n te m p e r a tu r e c h a n g e I n b oth c a s e s th e r e w ou l d h a v e b e e n c on v e c ti on f av o ri n g t h e b o t t o m b ei n g co l der i n t h e f i rst cas e, an d warm er i n t h i s s eco n d cas e. W h en v i ewi n g t h e wa rm i n g i t h as t o b e rem em b ered t h at t h e wa rm er t em perat ure b el o w 4 C w as a c t u a l l y t he m o r e d e ns e w a t e r a nd w a s e xp e c t e d t o be f o u nd a t t he bo t t o m I t w a s r e l e va nt t o n o t e t h at i n b o t h cas es t h e i n i t i al part o f t h e dat a ref l ect ed co n di t i o n s s uppo rt i n g n at ural c o nve c t i o n, w hi l e a f t e r c r o s s i ng t he 4 C m a r k bo t h t e nd e d t o s u p p o r t c o nd u c t i o n a nd s t ra t i f i c a t i o n i n t h e t e m p e ra t u re p rof i l e s Figure 4-3. Calibration Warming Data. Object 4-2. Cal6_85x11.jpg (15 7 KB).

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77 O t he r f a c t o r s c o u l d ha ve be e n a l s o i nf l u e nc i ng t he t e m p e r a t u r e r e s p o ns e o f t he s y s t e m Th e ra d i a l i n s u l a t e d b o u n d a ry c o n d i t i o n c o u l d h a v e b e e n p l a y i n g a rol e If t h e re w a s he a t l e a k a g e t hr o u g h t hi s s u r f a c e i t w o u l d ha ve be e n e nha nc i ng t o t he e f f e c t s o f t he co n v ect i v e h eat t ran s f er o f t h e s y s t em duri n g peri o ds wh en n at ural co n v ect i o n was f av o red i n t h e s y s t em T h e en ergy l ev el o f t h e wa t er as ref l ect ed t h ro ugh t h e t em perat ure r eadi n gs a t d i f f e r e nt d e p t hs w he n a l l s e ns o r s w e r e a t t he p ha s e c ha ng e t e m p e r a t u r e w o u l d no t ha ve b e e n e x p e c t e d t o b e e q u a l. T h is w a s d u e t o t h e fa c t t h e e n e r g y w a s b e in g e x t r a c t e d ma in ly f ro m t h e wa t er s t o p s urf ace Si n ce t h e t o p s urf ace was as s um ed t o h av e a l o wer en ergy le v e l, t h a t ma y h a v e a ls o in d ic a t e d t h e lo w e s t le v e l o f w a t e r w o u ld h a v e b e e n mo r e g r e a t ly i m p a c te d b y i m p e r f e c ti on of th e r a d i a l c on d i ti on a l on g w i th a n y i m p e r f e c ti on i n th e b ottom bo u nd a r y c o nd i t i o n. U l ti m a te l y w h e n th e w a te r r e a c h e d i ts m a x i m u m d e n s i ty th e top d r i v e n c on d u c ti on pr o cess t o o k o v er T h er m al st r at i f i cat i o n ex h i b i t ed w as ex pect ed as t h e war m er l ess den se w a te r w a s on th e top a n d th e h e a t d e l i v e r e d p r i m a r i l y a l s o on th e top T h e s tr a ti f i c a ti on f rom t h e t o p t o m i d d l e w a s g re a t e r t h a n w h a t w a s o b s e rv e d f rom t h e m i d d l e t o t h e b o t t o m Th i s l e n d e d s u p p o rt t o t h e i n s u l a t e d b o u n d a ry c o n d i t i o n s h a v i n g b e e n v i o l a t e d s l i g h t l y T he w a r m e r w a t e r p r o d u c e d a t t he s i d e o r bo t t o m w o u l d ha ve i m p a c t e d t he l o w e r a nd upper r eadi n gs t h e m o s t T h e l o wes t an d h i gh es t po s i t i o n s i n t h e wa t er wo ul d h av e b een e x p e c t e d t o h a v e t h e ir t e mp e r a t u r e s s lig h t ly hig h e r T h e c e n t e r lo c a t e d a t t h e r a d ia l o r ig in w o u l d n o t h a v e b e e n e x p e c t e d t o re f l e c t a n y b re a k d o w n o f t h e i n s u l a t e d b o u n d a ry co n di t i o n s un l es s t h o s e b reak do wn s were o f a l arge m agn i t ude rel at i v e t o t h e t o p h eat f l ux a p p l i e d B a s e d o n t he i ns u l a t i o ns u s e d o n t he s i d i ng a nd t he bo t t o m t hi s w a s w ha t o ne w o u ld in t u it iv e ly ha v e e x p e c t e d a s w e ll.

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78 T he c a l i br a t i o n d a t a y i e l d e d m o r e i nf o r m a t i o n t ha n j u s t a n o f f s e t va l u e f o r t he s en s o rs. I t al s o gav e i n s i gh t i n t o h o w co m pl ex a real St eph an pro b l em co ul d b e i n v o l v i n g a c om p l e x f l u i d s u c h a s w a te r T h e d a ta a l s o i m p l i e d th a t i f w a te r w a s c oo l e d to i ts m a xi m u m d e ns i t y f i r s t t he r e w o u l d p r o ba bl y ha ve be e n a m u c h be t t e r a p p r o xi m a t i o n t o t he t h e o re t i c a l s i n c e t h e rm a l s t ra t i f i c a t i o n w o u l d h a v e m a d e t h e p ri m a ry m o d e o f h e a t t ra n s f e r co n du ct i o n F ur t h er m o r e, t h e an al o go us t h awi n g p r o b l em wo ul d h av e r un i n t o di f f i cul t i es, i f t he t ha w i ng w a s i ni t i a t e d f r o m t he t o p s i nc e o nc e a l a y e r w a s f o r m e d o ve r t he i c e t he warm es t upperm o s t l ay er wo ul d i n i t i al l y h av e b een m o re den s e an d i n i t i at ed n at ural c o n v e c t i o n u n t i l i t re a c h e d m a x i m u m d e n s i t y t e m p e ra t u re f o r w a t e r. Th e c a l i b ra t i o n d a t a g a v e a f i rs t l o o k a t t h e a p p a re n t n o i s e i n t h e t e m p e ra t u re m easur em en t s. F i gu r e 44 t o o k sl i ces o f t h e un cal i b r at ed d at a i n t h e r egi o n o f t h e ph ase c h a n g e te m p e r a tu r e T h e g r a p h s r e p r e s e n te d i s oth e r m a l s l i c e s of ti m e te m p e r a tu r e d a ta fr o m t h r e e d iffe r e n t c a lib r a t io n e x p e r ime n t s T h e s p r e a d o f t h e d a t a o n in d iv id u a l c h a n n e ls ( C h a n 5 C h a n 1 5 ) w a s n ot a ttr i b u ta b l e to c h a n g e s i n te m p e r a tu r e a n d w e r e c or r e l a te d to n o is e in t h e s ys t e m. T h e fi g u r e s h o w e d t h a t t h e d a t a lo o k e d t o b e b o u n d e d b y r o u g h ly + / 0 0 4 C T hi s r e p r e s e nt e d a n a p p a r e nt no i s e f o r t he s y s t e m w hi l e i t w a s no t u nd e r g o i ng o h m i c h e a t i n g It was i m po rt an t t o l o o k at a s l i ce o f dat a wh i l e t h e s en s o rs were i n t h e h i gh v o l t age f i el d co n di t i o n s t h at were m o re r epres en t at i v e o f o h m i c co n di t i o n s F i gure 45 pl o t t ed a ti m e s l i c e w h e n th e a p p l i e d e l e c tr i c f i e l d w a s a p p r ox i m a te l y 5 0 0 v ol ts A C I t a p p e a r e d to s h o w t h a t t h e s p re a d a t t ri b u t a b l e t o n o i s e w a s o n t h e s a m e o rd e r of m a g n i t u d e a s b e f o re T h i s t i m e t h o ugh t h ere was n o t t h e l ux ury o f l o o ki n g at an i s o t h erm al t i m e s l i ce.

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79 T h e l o w n o i s e l ev el ex h i b i t ed b y t h es e t h erm o co upl e s en s o rs was at t ri b ut ed t o s ev eral f act o rs. Fi rst care wa s t aken t o pro perl y s h i el d t h e t ran s m i s s i o n po rt i o n s o f t h e t h erm o co upl es wh i ch h el ped prev en t i n t rusi o n o f s t ray el ect ri cal s i gn al s T h e A DI m o dul es h ad b ui l t i n n o i s e s uppress i o n o pt i m i zed f o r 60 h ert z s i gn al s T h e t h erm o co upl es in t h e h ig h v o lt a g e fie ld a r e a w e r e d e s ig n e d t o b e p e r p e n d ic u la r t o t h e a p p lie d v o lt a g e fie ld t o reduce i n duced v o l t ages f ro m t h e appl i ed al t ern at i n g f i el d. E ach dat a po i n t was an a v e ra g e o f 1 0 0 p o i n t s w h i c h f u rt h e r a i d e d i n re d u c i n g t h e n o i s e i n t h e re a d i n g s Figure 4-4. Calibration Noise. Object 4-3. CalNoise3.jpg (1000 KB).

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80 T he t e m p e r a t u r e d a t a w e r e c o l l e c t e d by t he Ke i t hl e y d a t a a c q u i s i t i o n bo a r d i n t he f o rm o f a l i n eari zed v o l t age t h at h ad b een s cal ed f ro m 0 t o 5 VDC It h ad b een n o t ed t h at t hi s w a s a l s o i nhe r e nt l y a p a r t o f t he t e m p e r a t u r e e r r o r s i nc e t he bo a r d c o nve r t e d t he a n a lo g s ig n a l t o a d ig it a l o n e T h e K e it h le y b o a r d w a s a 1 6 b it b o a r d a n d t h e r e fo r e c o u ld re s o l v e t h e s i g n a l t o 2 o r 6 5 ,5 3 6 p a rt s Th i s y i e l d e d a v o l t s p e r b i t o f roug h l y 7 6 .3 x 1 0 16 -6 T h e l i n eari zed C/V w as o b t ai n ed b y di v i di n g t h e ran ge o f t h e A DI m o dul e b y i t s l i n eari zed o ut put ran ge. T h e l i n eari zed C/V t h en was 100. T h e pro duct o f t h e l as t t wo quan t i t i es y i el ded t h e C/b i t t h at t h e ca rd was rea di n g. Ca rr y i n g o ut t h e ca l cul at i o n t h i s v al ue wa s d e te r m i n e d to h a v e b e e n 7 6 2 x 1 0 C / b i t. -3 T h e n o i se an d co n v er si o n t o a di gi t al si gn al ev en wh en co m b i n ed l i n ear l y wer e l ess t ha n ha l f o f t he no nl i ne a r i t y o f t he m o d u l e w hi c h w a s 0 1 C B a s e d o n t he s e nu m be r s t he c a l i br a t e d s e ns o r s w e r e j u d g e d t o be o f a c c e p t a bl e a c c u r a c y f o r t hi s r e s e a r c h. Figure 4-5. Noise Under High Voltage. Object 4-4. HighVoltageNoise.jpg (233 KB).

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81 Ex per im ental Gel T otal M as s P e r c e nt T he g e l u s e d i n t he e xp e r i m e nt w a s p r e p a r e d i n a c o ns i s t e nt m a nne r e a c h t i m e T he ma s s p e r c e n t o f fiv e s e p a r a t e r u n s in v o lv in g t h e g e l w e r e r e c o r d e d in T a b le 4 2 I t c o u ld b e s e e n th a t th e r e ta i l p a c k a g e s h a d a s m a l l a m ou n t of v a r i a ti on S i n c e th e w a te r u s e d to hy d r a t e t he g e l w a s k e p t c o ns t a nt t hi s va r i a t i o n u l t i m a t e l y l e d t o s l i g ht va r i a t i o ns i n t he m ass per cen t o f t h e di f f er en t gel s. T h e gel s f el l i n t o a r an ge o f 6. 1 +/ 0. 2% t o t al m ass. T a b le 4 2 P e r c e n t o f T o t a l M a s s o f G e la t in in G e l. Percen t o f T o t al M as s o f Gel at i n i n Gel F u ll P a c k e t s E mp t y P a c k e t s N e t G e la t in W a t e r G e la t in S am pl e Mass ( Gr am s) ( Gr am s) ( m L) ( P er cen t o f T o t al Mass ) 1 16. 630 1. 544 15. 086 225 6. 71 2 16. 700 1. 543 15. 157 225 6. 74 3 16. 380 1. 527 14. 853 225 6. 60 4 16. 056 1. 607 14. 449 225 6. 42 5 16. 314 1. 540 14. 774 225 6. 57 A v erage: 6.61 D e ns it y Th e a v e ra g e d e n s i t y f o r t h re e s e p a ra t e g e l p re p a ra t i o n s w a s re c o rd e d i n Ta b l e 4 -3 Th e s e v a l u e s w e re t h e a v e ra g e v a l u e s o f t h re e c o re s a m p l e s f rom e a c h g e l p re p a ra t i o n E a c h o f t h e c o r e s a mp le s w e r e me a s u r e d b y t h e mu lt ip yc n o me t e r a t o t a l o f 5 t ime s T h is t r a n s la t e d t o 1 5 t o t a l m e a s u r e me n t s fo r e a c h a v e r a g e w h ic h c o n s is t e d o f 5 r e p e t it io n s o f 3 d i f f e r e nt c o r e s a m p l e s f o r e a c h o f t he g e l s a m p l e s T he d e ns i t i e s f o r a l l s a m p l e s w e r e i n t he ra n g e o f 1 .0 2 + /0 .0 1 g /c m Th e d a t a re s u l t s w e re c o n s i s t e n t b e t w e e n g e l p re p a ra t i o n s 3 T he y a l s o c o m p a r e d w e l l t o t he d e ns i t y o f w a t e r w hi c h m a d e u p a l m o s t 9 4 % o f t he g e l o n a t o t al m ass b asi s.

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82 T a b le 4 3 G e l D e n s it y. G e l D e n s i ty M e a s u r e d D e n s i ty St andard Dev i ati on Sam pl e Gram s /cm 3 1 1. 014 003 2 1. 024 003 3 1. 019 004 A v erage: 1.020 F r e e z ing Th e f re e z i n g e x p e ri m e n t s w e re s t a rt e d w i t h a v e ry s i m p l e c o n c e p t a n d b e c a m e m o re ref i n ed. T h e ref i n em en t s b et wee n i t erat i o n s were due t o t h e o b s erv at i o n s f ro m eac h p r e vi o u s e xp e r i m e nt T he f r e e z i ng e xp e r i m e nt s a r e d i s c u s s e d i n t he o r d e r o f t he i r i t e r a t i ve c ha ng e s w hi c h m i r r o r s t he p r e s e nt a t i o n o r d e r i n t he M a t e r i a l s a nd M e t ho d s s e c t i o n. T he f i r s t m o s t ba s i c f r e e z i ng e xp e r i m e nt y i e l d e d s o m e ve r y i m p o r t a nt q u a l i t a t i ve resul t s T h e un co n s t rai n ed t o p s urf ace o f t h e s am pl es di d n o t rem ai n pl an ar. T h e s urf ace was o b s erv ed t o f ract ure an d ro s e un ev en l y T h i s was un acc ept ab l e f o r appl y i n g a f l at el ect ro de, as w el l as n o t ex h i b i t i n g an i deal geo m et ry T h e t ran s l ucen ce o f t h e gel was d e c r e a s e d in t h e fr o z e n s t a t e a s w e ll. B a s e d on th e s e ob s e r v a ti on s a n e x p e r i m e n t w a s d e s i g n e d to tr y to c on tr ol th e top s u rf a c e f l a t n e s s w h i l e f re e z i n g Th e t o p g e l s u rf a c e w a s s e t w i t h t h e e l e c t rode i n p l a c e F ro m t h i s co n f i gurat i o n t h e f reezi n g was i n i t i at ed f ro m t h e t o p s urf ace o f t h e gel T h e h o pe w a s t h a t t h is w o u ld h a v e a d d r e s s e d t h e s u r fa c e fla t n e s s a n d t h e g e o me t r y is s u e s T h e g e l in t hi s c a s e w a s a l l o w e d t o r i s e i n t he a xi a l d i r e c t i o n. T he o bs e r va t i o n w he n t he e xp e r i m e nt was carri ed o ut was t h at wh i l e t h e el ect ro de m i gh t rem ai n i n co n t act t h e geo m et ry h ad s i g ni f i c a nt l y c ha ng e d f r o m t he u nf r o z e n i ni t i a l g e o m e t r y T he t o p a nd bo t t o m p l a ne s o f t he s a mp le w h ic h s t a r t e d o u t p a r a lle l w e r e n o lo n g e r p a r a lle l b y a s ig n ific a n t a n d v is ib le

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83 am o un t It was ev en n o t ed i n s o m e ca s es t h e el ect ro de di d n o t s t ay i n co m pl et e co n t act w i t h t h e u p p e r s u rf a c e o f t h e g e l Th e e x p a n s i o n i n t h e a x i a l d i re c t i o n w a s n o t i d e a l f o r ri g i d p rob e s t h a t w e re e nt e r i ng r a d i a l l y i nt o t he s a m p l e I f o nl y o ne p r o be a t t he c e nt e r w a s u s e d t he i s s u e m i g ht ha ve be e n a d d r e s s e d by a l l o w i ng bo t h t he t o p a nd bo t t o m p l a ne s t o ha ve m o ve d d u r i ng f r e e z i ng A p r o be i n a c e nt r a l p l a ne w o u l d no t ha ve be e n e xp e c t e d t o m o ve a xi a l l y T he go al was t o m ake m ul t i po i n t m eas urem en t s an d t h eref o re ax i al ex pan s i o n was deem ed un acc ept ab l e. Th e n e x t i t e ra t i o n o f f re e z i n g e x p e ri m e n t s p rov i d e d s e v e ra l i m p o rt a n t s o l u t i o n s T h e i n i t i al co n cept was t o al l o w t h e sam pl e t o ex pan d i n t h e r adi al di r ect i o n o n l y T h i s m ean t t h at t h e t o p an d b o t t o m pl an es were co n s t rai n ed t o b e f l at an d paral l el T h e kn o wn v o l um e o f t h e s am pl e ce l l gav e an es t i m at e o f h o w m uch ex t ra v o l um e wa s n eede d b as ed on th e e x p a n s i on th a t w a te r u n d e r g oe s d u r i n g f r e e z i n g A s u i ta b l e c om p r e s s i b l e m a te r i a l of an appro pri at e t h i ckn es s was ch o s en t o l i n e t h e i n s i de o f t h e s am pl e ce l l T h i s decrea s ed t h e s am pl e ce l l v o l um e an d al l o wed f o r r adi al ex pan s i o n T h e ri gi d o ut er sh el l o n l y s aw ve r y m i no r p r e s s u r e a p p l i e d f r o m t he c o m p r e s s e d l i ni ng T he e l e c t r o d e i nt e r f a c e s w i t h t he gel s urf ace s were ex pect ed t o s t ay i n co m pl et e co n t act wi t h t h i s arr an gem en t T h e pro b es were n o t ex pect ed t o s ee a n y s h eari n g s t ress as t h e gel m o v em en t was i n t h e pro b e ax i al d i r e c t i o n. T he f i r s t r u ns o f t hi s ne w c o nf i g u r a t i o n w e r e m a d e w i t h no p r o be s i ns t a l l e d T he i n i t i al o b s erv at i o n s af t er f reezi n g were t h at t h e el ect ro des m ai n t ai n ed t h ei r par al l el p os i ti on s T h e f r oz e n g e l w h e n e x tr a c te d f r om th e s a m p l e c e l l h ol d e r a n d u n w r a p p e d f r om t he i nt e r i o r i ns u l a t i o n ( t he c o m p r e s s i bl e m a t e r i a l ) s ho w e d c l o s e a d he r e nc e t o t he s o u g ht

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84 a f te r f i n a l f r oz e n g e om e tr y T h e r a d i a l e x te r i or h a d s om e s l i g h t te x tu r i n g w h e r e i t co n f o rm ed t o t h e i n s ul at i o n duri n g t h e gel s et t i n g ph as e. W h en t h e el ect ro de wa s rem o v ed, i t w a s no t e d t o ha ve m a i nt a i ne d c o nt a c t w i t h t he g e l T hi s w a s e xp e c t e d be c a u s e t he e l e c t r o d e w a s i ni t i a l l y s e t i nt o t he l i q u i d be f o r e i t c o ng e a l e d O t he r i m p o r t a nt o bs e r va t i o ns w e r e m a d e a b ou t th e g e l a t th i s p oi n t. T h e tr a n s i ti on b a c k to u n f r oz e n g e l p r oc e e d e d w i th v er y l i t t l e wat er l o ss f r o m t h e sam pl e. T h e sam pl e app ear ed t o r et ur n t o i t s i n i t i al st at e as a g e l w i t h o n l y v e ry m i n o r v i s i b l e d e f e c t s a f t e r a f re e z e a n d t h a w c y c l e T h e n ex t i t erat i o n pl ace d pro b es i n a s am pl e, an d s ub j ect ed t h e s am pl e t o a f reeze t h aw c y cl e. T h e ex peri m en t ul t i m at el y s acri f i ced t h e pro b es t h at were i n s t al l ed. A f t er f r e e z i ng t he o nl y w a y t o r e m o ve t he f r o z e n g e l i nt a c t w a s by s he a r i ng t he p r o be s a t t he r i g i d w a l l of th e s a m p l e h ol d e r T h e p r ob e s w e r e th e n ob s e r v e d f r om th e e n d v i e w w i th bo t h o f t he e l e c t r o d e s r e m o ve d Wi t h t he s a m p l e r e m o ve d f r o m t he s a m p l e ho l d e r a nd t he i ns u l a t i o n r e m o ve d t he p r o be s w e r e o bs e r ve d f r o m t he r a d i a l d i r e c t i o n o f t he s a m p l e T he pro b es h ad m ai n t ai n ed t h ei r po s i t i o n s i n t h e s am pl e. Envir onm ental Char acter iz ati on T h e en v i ro n m en t al ch am b er use d i n t h e ex peri m en t s h ad s ev eral o f i t s f eat ures ch aract eri zed. T h e f i rst was t h e m i n i m um m ai n t ai n ab l e t em perat ure. By s et t i n g t h e s y s t em t o a co n t i n uo us run m o de o v ern i gh t an d m eas uri n g t h e t em perat ures i n s i de, i t was d e t e r min e d t h a t t h e s ys t e m w a s c a p a b le o f c o o lin g t o a p p r o x ima t e ly 3 3 C T h is t e mp e r a t u r e w a s mu c h lo w e r t h a n r e q u ir e d fo r o u r p u r p o s e s b u t ma d e t h e s ys t e m c a p a b le o f a g re a t e r ra n g e o f a p p l i c a t i o n s f o r f u t u re i n v e s t i g a t i o n s Th e s y s t e m w a s n o rm a l l y o p e ra t e d i n a c y c l i n g m o d e D a t a f o r c y c l i n g w e re c a p t u r e d i nt e r m i t t e nt l y d u r i ng t he e xp e r i m e nt a l i nve s t i g a t i o ns O ne s e t o f r e p r e s e nt a t i ve

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85 d a t a w e r e p l o t t e d i n Fi g u r e 4 6 T hi s d a t a s ho w e d ho w t he i nt e r na l t e m p e r a t u r e f o r t he s a mp le g e l t yp ic a lly v a r ie d a n d a p p r o x ima t e ly ho w t h e a ir t e mp e r a t u r e v a r ie d T h e s a mp le i n t h i s dat a wa s i n ex act l y t h e s am e ph y s i cal s et up as t h e o h m i c ex peri m en t s di s cus s ed l a t e r Al l t hr e e l a y e r s o f i ns u l a t i o n w e r e i n p l a c e o n t he s a m p l e ho l d e r T he d a t a f o r t he f reeze r ai r t em perat ures we re co l l ect ed wi t h t h e di gi t al m ul t i m et er an d a m an uf act urer s u p p l i e d t y p e K t he r m o c o u p l e w hi c h ha d a m u c h l o w e r t e m p e r a t u r e r e s o l u t i o n t ha n t he sam pl e pr o b es. T h e graph s o f F i gure 46 s h o wed t h e rel ev an t ch aract eri s t i cs o f cy cl i n g. T h e graph l a be l e d T e m p e r a t u r e C y c l i ng O ne g a ve a vi s u a l c o m p a r i s o n o f t he t w o d i f f e r e nt t e mp e r a t u r e c yc le s I t w a s in t e r e s t in g t o n o t e t h a t w h ile t h e a ir t e mp e r a t u r e t yp ic a lly F i gure 46. T em perat ure Cy cl i n g. O b j e c t 4 -5 C y c l i n g A l l M a r2 2 .j p g (1 4 7 1 K B ).

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86 va r i e d a bo u t 7 C o ve r o ne c y c l e t he g e l t e m p e r a t u r e o nl y va r i e d a bo u t 0 1 C T he f o l l o w i n g g ra p h u t i l i z e d a s e c o n d Y a x i s w h i c h a l l o w e d t h e g e l t e m p e ra t u re s t o b e m o re c l o s e l y o bs e r ve d T he g r a p h l a be l e d T e m p e r a t u r e O ne C y c l e c o nt a i ne d a p p r o xi m a t e l y o ne c yc le o f d a t a fo r t h e g e l, w h ile t h e la s t g r a p h in t h e fig u r e h a d t h e v a lle y s e c t io n o f t h is s i n gl e cy cl e. T h e dat a f o r t h e ai r t em perat ure were reso l v ed i n 1 C s t eps b ut t h e cy cl i n g c ha r a c t e r i s t i c s w e r e s t i l l o bvi o u s T he d a t a w e r e ve r y u s e f u l a s i t g a ve a n i d e a o f ho w t he s a mp le r e s p o n d e d t o e x t e r n a l c h a n g e s in t e mp e r a t u r e A n o t h e r p ie c e o f d yn a mic i n f o rm at i o n was o b s erv ed i n t h e Tem perat ure On e C y cl e graph T h e t em perat ure pr o b es d i d no t s e e m t o s ho w a ny s i g ni f i c a nt f i nni ng o f e xt e r na l he a t w i t hi n t he r a ng e o f t he c y c l i ng t em perat ures. I f f i n n i n g were s i gn i f i can t t h e pro b es wi t h t h e l eas t pen et rat i o n (F i gure 312) i n t o t h e s am pl e wo ul d h av e l ed i n b o t h t h e co o l i n g an d h eat i n g. T h e o b s erv at i o n m ade th ou g h w a s th e p r ob e s tr a c k e d v e r y c l os e l y e v e n w i th th e r e v e r s a l d u r i n g c y c l i n g f r om h eat i n g t o co o l i n g. T h e di f f eren ces b et wee n a pro b e pai r were gr aph ed an d n o t ren ds a p p e a re d (F i g u re 4 -7 ). T he t e m p e r a t u r e r a ng e o f i nt e r e s t f o r t he g e l w a s w a r m e r t ha n t he c y c l i ng t e m p e r a t u r e o f t he e nvi r o nm e nt a l c o nt r o l u ni t T he t e m p e r a t u r e o f t he s a m p l e ha d t o be r a i s e d Af t e r t he i ns t a l l a t i o n o f t he r m a l d a m p e r s t he t e m p e r a t u r e c ha ng e i n t he a i r a nd t he s a m p l e i ns i d e t he u ni t w e r e t r a c k e d T he c o nf i g u r a t i o n w a s a g a i n j u s t a s i t w a s i n t he a c t u a l o hm i c t ha w i ng e xp e r i m e nt s w i t h a l l i ns u l a t i o n i n p l a c e Fi g u r e 4 8 s ho w s ho w t he s am pl e an d t h e ch am b er i n t eri o r ai r co n di t i o n s v ari ed af t er t h e un i t was t urn ed o f f A f t er a n in it ia l p e r io d t h e a ir t e mp e r a t u r e a n d s a mp le t e mp e r a t u r e h a d a p p r o x ima t e ly t h e s a me s l o pe. W h en we regres s ed t h e l i n ear s ect i o n t h e s l o pe t h ere was det erm i n ed t o b e 4.856 x

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87 10 C/s T h i s was appro x i m at el y 0. 029 C pe r m i n ut e o r 1. 748 C/h r. T h e t em perat ure -4 di f f er en ce b et ween sam pl e an d ai r was r o ug h l y 7 C. Aut om ati c P ower Cont r ol Val idat ion T h e aut o m at i c po wer co n t ro l v al i dat i o n ex peri m en t v eri f i ed t h at t h e s y s t em co ul d a u t o m a t i c a l l y s hu t d o w n t he p o w e r t o p r e ve nt t o o m u c h c u r r e nt f r o m be i ng s u p p l i e d t o t he s am pl e. A n i n t eres t i n g o b s erv at i o n was capt ured dur i n g t h e ex peri m en t T h e s et up us ed an i n can des cen t resi s t an ce l i gh t b ul b t o pro v i de t h e res i s t an ce. T h e upper al arm was s et ba s e d o n t he w a t t a g e o f t he bu l b r a t e d f o r 1 2 0 V AC Whe n t he c i r c u i t w a s c l o s e d w i t h t he vo l t a g e s e t a t t he u p p e r e nd o f t hi s w a t t a g e bu t be l o w w he r e i t s ho u l d ha ve t r i g g e r e d t he hi g h a l a r m t he a l a r m w a s t r i p p e d T hi s w a s d u e t o a n i ni t i a l s p i k e i n t he c u r r e nt w he n t he Figure 4-7. Cycling and Adjacent Probe Temperature Differences. Object 4-6. Cyc15-13DiffAll.jpg (985 KB).

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88 c i r c u i t c l o s e d T he s p i k e w a s vi s i bl e o n t he m e t e r d i s p l a y a l s o O nc e t he bu l b w a s o n a nd t h e f i l a m e n t h o t t h e v o l t a g e w a s a d j u s t e d u p t o t h e s a m e l e v e l w i t h o u t t ri p p i n g t h e a l a rm T h i s w a s n ot s u r p r i s i n g a s th e r e s i s ta n c e of c ol d f i l a m e n t w a s d i f f e r e n t th a n th a t of a h ot o n e. T h i s un pl an n ed f acet o f t h e ex per i m en t gav e a f ur t h er i n si gh t i n h o w t h e r el ay s re a c t e d t o a v e ry f a s t ra m p e d c u rre n t i n p u t Re s is tanc e M e as ur e m e nt Unf r oz en Gel On e o f t h e pri m ary f un ct i o n s o f t h e ex peri m en t al apparat us was t o m ake e l ect ri cal r e s i s ta n c e m e a s u r e m e n ts T h e s e v a l u e s w e r e th e r e s u l t of c om b i n i n g th e d a ta f r om b oth dat a co l l ect i o n dev i ces t h at were an i n t egral part o f t h e appa rat us A s am pl e o f i n i t i al F i gure 48. Sam pl e an d E n v i ro n m en t al W arm i n g. O b j e c t 4 -7 W a rm i n g A l l .j p g (7 19 KB).

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89 vo l t a g e d a t a f o r t he u nf r o z e n g e l a t i n w e r e p l o t t e d i n Fi g u r e 4 9 a nd Fi g u r e 4 1 0 T he vo l t a g e a p p l i e d l o o k e d ve r y m u c h l i k e a s q u a r e w a ve T hi s w a s a r e s u l t o f t he c y c l i ng p a tte r n c h os e n f or th e e x p e r i m e n t. D u r i n g th e d e te r m i n a ti on of r e s i s ta n c e a s a f u n c ti on of t e mp e r a t u r e ma n y s a mp le s o f d a t a lik e t h e s e w e r e c o lle c t e d F ig u r e 4 9 in d ic a t e d t h a t t h is s a mp le w a s t a k e n o v e r r o u g h ly a 2 5 C r a n g e T h e r a n g e s o f e a c h s a mp le v a r ie d s lig h t ly bu t w e r e g e ne r a l l y o ve r a 2 5 t o 6 C s p a n. T he r a ng e s s a m p l e d ha d o ve r l a p a nd g a ve repeat ed t em perat ure po i n t s f o r t h e f i n al det erm i n at i o n o f t h e res i s t an ce v ersus t em perat ure. T he c u r r e nt d a t a p l o t f o r e a c h s a m p l e s e t o f d a t a w a s p l o t t e d i n Fi g u r e 4 9 a nd Fi g u r e 4 1 0 be l o w t he vo l t a g e a nd t e m p e r a t u r e d a t a p l o t s B o t h f i g u r e s i nd i c a t e d t he vo l t a g e w a s m a i nt a i ne d a t a r o u g hl y c o ns t a nt va l u e w hi l e t he c u r r e nt i nc r e a s e d T he t r a p e z o i d a l s ha p e t he c u r r e nt a s s u m e d w a s a d i r e c t r e s u l t o f t he r e c t a ng u l a r s ha p e o f t he vo l t a g e i np u t T hi s w a s e xp e c t e d s i nc e t he t e m p e r a t u r e o f t he g e l w a s c ha ng i ng d u r i ng t he appl i cat i o n o f t h e v o l t age. T h e f i gures a l s o i l l us t rat ed t h e t em perat ure ch an ges i n eac h v o l t a g e p o w e r on c y c l e Th e re g i o n s w i t h t h e v o l t a g e p o w e r of f s h o w e d s l i g h t t e m p e ra t u re d e c r e a s e s T hi s r e p r e s e nt e d t he t he r m a l r e l a xa t i o n o c c u r r i ng i n t he s y s t e m T he t e m p e ra t u re d rop w a s l e s s w h e n t h e 6 e n d t e m p e ra t u re s o f a p o w e r on c y c l e w e re m o re t i g h t l y g roup e d It was o b s erv ed t h at ev en wi t h a rel at i v el y l o w l ev el o f v o l t age a ppl i ed t h ere was o hm i c he a t i ng t ha t o c c u r r e d i n t he u nf r o z e n g e l T he t e m p e r a t u r e d i s t r i bu t i o n w i t hi n t he g e l s ta r te d ou t r e l a ti v e l y u n i f or m T h e oh m i c h e a ti n g c a u s e d th e te m p e r a tu r e d i s tr i b u ti on t o va r y i n t he s a m p l e Fo r c a l c u l a t i o n p u r p o s e s t he a ve r a g e t e m p e r a t u r e o f a l l 6 o f t he t em perat ure se n s o rs were us ed.

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90 Figure 4-9. Unfrozen Gel Temperature, Voltage and Current Plots. Object 4-8. UF-Resist-TVC1.jpg (323 KB).

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91 Figure 4-10. Unfrozen Gel Temperature, Voltage and Current Plots. Object 4-9. UF-Resist-TVC2.jpg (381 KB).

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92 T h e r e a s on s f or ta k i n g th e d a ta i n a c y c l i n g f a s h i on w e r e i l l u s tr a te d f r om th e p oi n ts a l r e a d y g i ve n. I f t he c o m p l e t e s y s t e m o f g e l a nd a l l bo u nd a r y c o nd i t i o ns w e r e p e r f e c t t he gel wo ul d h av e h eat ed un i f o rm l y T h e s y s t em t h o ugh was a real s y s t em an d h ad a ge l t h at was n o t perf ect l y h o m o gen o us o r per f ect l y i s o t h erm al t h eref o re t h e gel ex h i b i t ed t em per at ur e i n cr eases t h at wer e n o t en t i r el y un i f o r m A speci f i cat i o n was set o n h o w cl o se t o i s o t h erm al t h e s am pl e i n i t i al l y appea red t o s t art a cy cl e an d t h e m ax i m um s pread be t w e e n s e ns o r s t ha t w o u l d no t be e xc e e d e d T hi s u l t i m a t e l y a l l o w e d t he e r r o r t o be es t i m at ed. A re p re s e n t a t i v e p l o t o f a l l t h e u n f roze n re s i s t a n c e m e a s u re m e n t s w a s m a d e F i g u re 4 1 1 T he a ve r a g e t e m p e r a t u r e va l u e s o n t hi s p l o t a s w e l l a s o t he r p l o t s r e p r e s e nt e d t he Figure 4-11. Unfrozen Gel Resistance. Object 4-10. UF_ResistAll.JPG (114 KB).

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93 a v e ra g e o f a l l 6 t e m p e ra t u re re a d i n g s t a k e n f o r a s i n g l e p o i n t Th e re s i s t a n c e d a t a w e re t r a ns f o r m e d t o r e s i s t i vi t y d a t a f o r t he g e l by u s e o f t he c o ns i s t e nt g e o m e t r i c s ha p e T he r e s i s t i vi t y a p p e a r e d a s s c a l e d r e s i s t a nc e va l u e s T he r e s i s t a nc e va l u e s w e r e s c a l e d by t he a re a o f t h e s a m p l e d i v i d e d b y t h e h e i g h t Th e n u m e ri c a l v a l u e f o r t h i s w a s 6 9 .8 2 x 1 0 m -3 T h e dat a we re pl o t t ed i n t erm s o f resi s t i v i t y s ee F i gure 412. In F i gure 412 t h e m ax i m um t em perat ure di f f eren ce (M T D) i s pl o t t ed s i m u l t a ne o u s l y w i t h t he r e s i s t i vi t y T he m a xi m u m t e m p e r a t u r e d i f f e r e nc e r e p r e s e nt e d t he l a r g e s t d i f f e r e nc e be t w e e n a ny 1 o f t he 6 a ve r a g e d r e a d i ng s a nd t he a ve r a g e va l u e T he c h a n n e l th a t s u s ta i n e d th e h i g h e s t te m p e r a tu r e w a s a l s o i d e n ti f i e d a n d r e c or d e d T h e p l ot Figure 4-12. Unfrozen Gel Resistivity and Maximum Temperature Difference. Object 4-11. UF_Resisty_MTDiffAll.jpg (235 KB).

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94 s ho w e d t ha t t he u p p e r bo u nd t o t he t e m p e r a t u r e s p r e a d w a s 0 2 5 C Whi l e t hi s w a s t he upper b o un d, t h e b ul k o f t h e dat a we re co l l ect ed at a l ev el b el o w 0.15 C m ax i m um di f f eren ce. By us e o f t h i s m et h o d f o r co l l ect i n g an d reduci n g t h e dat a, t h e av erage te m p e r a tu r e h a d m e a n i n g w i th r e s p e c t to e r r or a s s oc i a te d w i th th e m e a s u r e m e n t of t em perat ure at a po i n t b y t h e s y s t em It al s o l et t h e i s o t h erm al n at ure o f t h e gel b e def i n ed an d v eri f i ed wh i l e t h e s y s t em was m eas uri n g t h e el ect ri cal resi s t an ce. Th e d a t a o n t h e u n f roze n g e l w e re c o l l e c t e d a t t w o d i s t i n c t e x p e ri m e n t a l p h a s e s T h e f i rst dat a s et was t aken b ef o re t h e gel was f ro zen T h e s eco n d dat a s et was t aken af t er t h e gel h ad b een f ro zen an d s ub j ect ed t o o h m i c t h awi n g. In F i gure 413 t h e t wo s et s o f t h e Figure 4-13. Unfrozen Gel Resistivity Before and After Freezing. Object 4-12. UF_Resisty_MTDiff_All_Sep10.jpg (226 KB).

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95 resi s t an ce da t a we re se parat ed an d i n di cat ed. F o r eas i er v i s ual i n s pect i o n t h e graph h ad o n l y ev ery t en t h dat a po i n t o f eac h s et pl o t t ed. Dat a b ef o re f reezi n g were o v er a s m al l er t e m p e r a t u r e r a ng e t ha n t ha t t a k e n a f t e r t he t ha w i ng T hi s w a s d o ne t o be c o ns e r va t i ve i ni t i a l l y a nd a vo i d e d d r i vi ng t he g e l ba c k t o a l i q u i d s t a t e T he a g r e e m e nt be t w e e n t he b ef o re an d af t er dat a we re v ery go o d. It i n di cat ed t h at f ro m an el ect ri cal resi s t an ce s t a n d p o i n t t h e g e l w a s v i rt u a l l y u n c h a n g e d b y a f re e z e /th a w c y c l e Fi g u r e 4 1 4 s ho w s a l l t he u nf r o z e n r e s i s t a nc e d a t a r e d u c e d t o e ve r y t e nt h p o i nt a nd a po l y n o m i al f i t t ed t o t h e dat a. A t h i rd o rder po l y n o m i al wo rked n i cel y t o f i t t h e un f ro zen r e s is t a n c e me a s u r e me n t s w it h a n R v a lu e o f 0 9 9 7 7 T h e e q u a t io n fo r t h e p o lyno mia l is 2 g i v e n b e l o w a s e q u a t i o n 4 -1 w h e re y i s re s i s t i v i t y (oh m m e t e rs ) a n d x i s t e m p e ra t u re ( C ). (41) Figure 4-14. Unfrozen Resistivity with Cubic Polynomial Fit. Object 4-13. UF-Resisty-All-wFit.jpg (121 KB).

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96 I t w a s d e r i ve d by f i t t i ng a l l t he d a t a p o i nt s i n Axu m a nd u s i ng a w e i g ht i ng f a c t o r o f t he i n v erse o f t h e m ax i m um t em perat ure di f f eren ce. T h e i n cl us i o n o f t h e we i gh t i n g f act o r was des i gn ed t o f av o r po i n t s o n wh i ch t h ere was l es s v ari at i o n i n t h e gel t em perat ure. F r oz en Gel T h e m eas urem en t o f resi s t an ce f o r t h e f ro zen s am pl e wa s v ery s i m i l ar t o t h e un f ro zen f r om a p r oc e d u r a l s ta n d p oi n t. T h e m a i n d i f f e r e n c e w a s th a t l on g e r c on ti n u ou s b l oc k s of dat a we re po s s i b l e, b eca us e t h e o h m i c h eat i n g was l es s F i gure 415 ref l ect ed t h e v o l t age appl i ed duri n g dat a co l l ect i o n f o r t h i s run It was n o t ed t h at t h i s was a co m pl et e run o v er t h e t e mp e r a t u r e r a n g e o f in t e r e s t a p p r o x ima t e ly 5 C t o 0 C T h e r a n g e w a s s lig h t ly l a r g e r th a n 5 C T h e te m p e r a tu r e p r of i l e s h ow e d th e e f f e c ts of oh m i c h e a ti n g T h e d r op in v o lt a g e t o a lo w e r le v e l c le a r ly c h a n g e d t h e r a t e t h e t e mp e r a t u r e w a s r is in g in t h e s a mp le co rr es po n di n g t o t h e o h m i c h eat i n g. It was n o t ed t h at t h i s co l l ect i o n was o v er a t wo h o ur p e r i o d w hi l e a s a m p l e r u n p r e s e nt e d f o r t he u nf r o z e n g e l w a s m u c h s ho r t e r B o t h t he f r o z e n a nd u nf r o z e n r u ns c o ve r e d a p p r o xi m a t e l y t he s a m e a m o u nt o f t e m p e r a t u r e r i s e T he di f f eren ce i n t h e m agn i t udes o f t h e v o l t ages appl i ed we re apparen t T h e i n i t i al v o l t age a p p l i e d to t h e f r oz e n g e l w a s r ou g h l y th r e e ti m e s th e m a g n i tu d e of th e v ol ta g e a p p l i e d to t h e u n f roze n g e l Th e c u rre n t m e a s u re d d u ri n g t h e ru n w a s p l o t t e d i n t h e b o t t o m p l o t o f F i g u re 4 -1 5 T hi s w a s a s i ng l e c o nt i nu o u s s t r e a m o f d a t a T he c u r va t u r e o f t he d a t a s u g g e s t e d t ha t t he r e s i s t a nc e w a s c ha ng i ng q u i t e r a p i d l y a nd t he r e s i s t a nc e w a s no t l i ne a r l y r e l a t e d t o t he t em perat ure. T h e v o l t age s t ep do wn po i n t was cl earl y v i s i b l e f ro m t h e v i ew o f v o l t age d a t a o n t he g r a p hs T he c u r r e nt d r o p a t t hi s p o i nt w a s i m m e d i a t e l y f o l l o w e d by t he c u r r e nt i nc r e a s i ng a g a i n.

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97 Figure 4-15. Frozen Gel Temperature, Voltage and Current Plots. Object 4-14. Frozen-Resist-TVC.jpg (273 KB).

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98 F i g u re 4 -1 6 h a d f roze n re s i s t a n c e d a t a f o r 2 g e l s a n d 2 d a t a ru n s f o r e a c h o f t h e g e l s T he s e c o nd g e l f i r s t d a t a r u n w a s t he s a m e d a t a s e t t ha t w a s u s e d i n Fi g u r e 4 1 5 T he s eco n d gel was repr es en t ed i n t h e un f ro zen m eas urem en t s prese n t ed prev i o us l y T h i s was a ls o t h e g e l s ys t e m u s e d in t h e o h mic e x p e r ime n t T h e r e s is t a n c e p lo t w a s in c lu d e d a g a in f o r c o n s i s t e n t p re s e n t a t i o n a n d g a v e a f e e l f o r t h e re s i s t a n c e v a l u e s t h a t w e re m e a s u re d T h ese r esi st an ce v al ues l i ke t h e un f r o zen gel v al ues co ul d b e co n v er t ed t o r esi st i v i t y v al ues. A re s i s t i v i t y p l o t f o r t h e s a m e s e t o f d a t a u s e d i n F i g u re 4 -1 5 w a s m a d e s e e F i g u re 4 1 7 T hi s g r a p h s i m u l t a ne o u s l y p l o t t e d t he m a xi m u m t e m p e r a t u r e d i f f e r e nc e s T he m a xi m u m t e m p e r a t u r e d i f f e r e nc e s i n t he f i g u r e g a ve i ns i g ht a s t o ho w t he g e l w a s r e a c t i ng t o t h e p r o c e s s I t in d ic a t e d t h a t t h e t e mp e r a t u r e s p r e a d b e fo r e t h e r u n s t a r t e d w a s s lig h t ly h i gh er t h an duri n g part o f t h e dat a ac qui s i t i o n T h i s ph en o m en o n was eas i l y ex pl ai n ed F i gure 416. F ro zen Gel s Re s i s t an ce. O b j e c t 4 -1 5 F roze n -R e s i s t -A l l .j p g (1 30 KB).

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99 w h e n w h e n t a k e n i n c o n s i d e ra t i o n w i t h h o w t h e s a m p l e a rri v e d a t t h e i n i t i a l s t a rt t e m p e ra t u re Th e s a m p l e h a d t o w a rm f rom t h e c y c l i n g t e m p e ra t u re t o t h i s ra n g e Th e re wo ul d h av e b een a m i n o r gr adi en t i n t h e s am pl e duri n g t h i s warm i n g. T h e s am pl e wa s t h en s u bj e c t e d t o ve r y m i no r w a r m i ng d u e t o o hm i c he a t i ng O ne e xp e c t e d t o s e e t he g r a d i e nt t h at was causi n g t h e war m i n g t o ev en t ual l y r ev er se as t h e gel st ar t ed at so m e po i n t t o l o se h eat i n s t ead o f gai n i n g i t f ro m t h e en v i ro n m en t T h e t em perat ure di f f eren ce da t a v al ues w e nt d o w n a g a i n w he n t he vo l t a g e w a s r e d u c e d T hi s c o r r e s p o nd e d t o t he o hm i c he a t i ng b e i n g re d u c e d Th e t e m p e ra t u re d i f f e re n c e s b e t w e e n p rob e s w e re v e ry m i n o r f o r t h i s e n t i re r un wi t h t h e b ul k o f t h e dat a b el o w a m ax i m um t em per at ur e di f f er en ce o f 0. 05 C. T h e 4 f r oz e n r e s i s ti v i ty d a ta s e ts w e r e p l ott e d i n F i g u r e 4 1 8 T h e r e s i s ti v i ty d a ta h ad a t h i rd o rder po l y n o m i al f i t t ed t o i t T h e f i t t ed po l y n o m i al i s l i s t ed as equat i o n 4-2, w h e re y i s re s i s t i v i t y (oh m m e t e rs ) a n d x i s t e m p e ra t u re ( C ). Figure 4-17. Frozen Resistivity and Maximum Temperature Difference. Object 4-16. Frozen_Resisty_MTDiff21-10.jpg (221 KB).

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100 I t w a s a r r i ve d a t i n t he s a m e m a nne r a s t he p o l y no m i a l f o r t he u nf r o z e n r e s i s t i vi t y d a t a a nd ma d e u s e o f t h e s a me fo r m o f w e ig h t in g c o e ffic ie n t s U s e t h e w e ig h t in g c o e ffic ie n t s in t h is cas e pro v i ded co n s i s t en cy i n an al y s i s s i n ce t h e t em perat ure spread f ro m t h e av erage t em perat ure was v ery s m al l f o r al l o f t h e dat a. T h e R f o r t h e f i t was 0. 9953. 2 Com bin ed Te m per atu r e Ranges T h e res i s t i v i t y m eas ured f o r t h e s am pl e gel i s prese n t ed f o r b o t h s o l i d ph as es u n f roze n a n d f roze n Th e s e p h a s e s re p re s e n t t w o n o n o v e rl a p p i n g t e m p e ra t u re ra n g e s A t h i r d o r der po l y n o m i al can adeq uat el y r ef l ect t h e n at ur e o f dat a i n each o f t h o se t em perat ure r an ges It i s n o t ed t h o ugh t h at t h ey are n o t t h e s am e po l y n o m i al F i gure 419 (42) Figure 4-18. Frozen Resistivity with Cubic Polynomial Fit. Object 4-17. Frozen-Resisty-All-wFit.jpg (124 KB).

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101 p r e s e n ts th e tw o f i ts a p p l i e d to t h e d a ta on a s i n g l e p l ot. W i th a s i n g l e s c a l e a p p l i e d to b o t h s et s o f dat a, t h e di f f eren ce i n m agn i t ude b et wee n t h e res i s t i v i t y i n eac h ph as e wa s g r a p hi c a l l y e vi d e nt T hi s g a ve a c l e a r p i c t u r e o f w ha t w a s e xp e c t e d t o ha p p e n t o t he e le c t r ic a l r e s is t iv it y o f fin it e v o lu me s w it h in t h e g e l a s t h e y u n d e r w e n t t r a n s it io n b o t h in t em perat ure an d ph as e duri n g t h awi n g. Ohm ic T haw ing T h e oh m i c th a w i n g d a ta i s p r e s e n te d i n s i m i l a r or d e r a s th e r e s i s ta n c e d a ta to e mp h a s iz e t h e s imila r it ie s a n d d if fe r e n c e s b e t w e e n t h e t w o t yp e s o f d a t a I t w a s p r e v io u s ly n o t e d t h a t t h e re s i s t a n c e d a t a c o l l e c t i o n ru n s i n v o l v e d o h m i c h e a t i n g o f t h e g e l s a m p l e Figure 4-19. Unfrozen and Frozen Resistivity Cubic Fits. Object 4-18. ResistyFitsBoth.jpg (105 KB).

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102 T h e o h m i c t h awi n g dat a ac t ual l y capt ured i n f o rm at i o n o n t h e s o l i d t o s o l i d ph as e ch an ge t ha t w a s o c c u r r i ng i n t he g e l T he t e m p e r a t u r e r a ng e w a s r o u g hl y t he f u l l s p a n o f a l l t he r e s i s t a nc e d a t a a nd i nc l u d e d t he g a p a r e a w he r e t he p ha s e c ha ng e o c c u r r e d t ha t no resi s t an ce da t a ex i s t ed. T h e v ol ta g e a p p l i c a ti on d u r i n g th e e x p e r i m e n t w a s p l otte d i n F i g u r e 4 2 0 on th e top p l ot. T h e v ol ta g e w a s b a s i c a l l y a s te p i n p u t w i th v a r i ou s a m ou n ts of ti m e b e tw e e n i ts a p p l i c a t i o n. T he s t e p na t u r e o f t he i np u t w a s a r e s u l t o f t he s w i t c hi ng u s e d t o c o nt r o l t he po wer appl i cat i o n T h e f i rst po wer appl i cat i o n cy cl e wa s appl i ed an d t h e s am pl e al l o wed t o t h erm al l y rel ax s o t h at t h e t em perat ures we re m o re un i f o rm T h e s am e pro cedure wa s fo llo w e d fo r t h e s e c o n d p o w e r a p p lic a t io n c yc le B o t h o f t h e s e c yc le s w e r e ma n u a lly co n t ro l l ed b y t h e o perat o r. T h e t h i rd po wer appl i cat i o n cy cl e wa s di f f eren t It was s t o p p e d by t he c u r r e nt l i m i t i ng c o nt r o l s y s t e m o f t he a p p a r a t u s D u r i ng t he f i ve s e c o nd w i n d o w o f t h e a u t o m a t i c s h u t d o w n t h e v o l t a g e w a s m a n u a l l y a d j u s t e d b y t h e o p e ra t o r. T h e s ys t e m a u t o ma t ic a lly s t a r t e d t h e n e x t c yc le a t t h e e n d o f t h e p r o g r a mme d d e la y. T h is w a s c a r r i e d ou t 2 m or e ti m e s a s i n d i c a te d b y th e g r a p h T h e s h u t d ow n w a s th e n m a n u a l to al l o w f o r t h erm al rel ax at i o n s i m i l ar t o t h e i n i t i al po wer o f f cy cl es T h e n ex t s ect i o n s h o wed t he a p p l i e d vo l t a g e ha d be e n a d j u s t e d a nd t he p o w e r c o nt r o l w a s i ni t i a t e d by t he a u t o m a t i c bu t o ve r r i d d e n by m a nu a l c o nt r o l T he s y s t e m s hu t d o w n a u t o m a t i c a l l y a nd t he ci rcui t was m an ual l y o pen ed t o al l o w f o r m o re t h erm al rel ax at i o n an d was m an ual l y cl o s ed agai n t o i n i t i at e an o t h er cy cl e. T h e curren t dat a f o r t h e o h m i c ex peri m en t were pl o t t ed i n F i gure 420 o n t h e l o wer p l o t T he c u r r e nt d a t a c l e a r l y i nd i c a t e d w he r e a u t o m a t i c s hu t o f f w a s u s e d E a c h c u r r e nt peak a t 0. 4 am ps repr es en t ed o n e o f t h es e ca s es T h e pea ks b el o w t h i s l ev el repr es en t ed

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103 Figure 4-20. Ohmic Thawing Voltage and Current Data. Object 4-19. OhmicVC.jpg (225 KB).

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104 m a n u a l p ow e r s h u t of f T h e p l ot of th e c u r r e n t d a ta i n d i c a te d p e r i od s of th e r m a l r e l a x a ti on wi t h pl at eau a reas h av i n g a ze ro v al ue. T h e f ul l y aut o m at ed po wer o f f t o po wer o n cy cl es w e r e i d e n ti f i a b l e b y th e s te e p d r op a n d r i s e 5 s e c on d s l a te r T h e ti m e s c a l e of th e p l ot m a k e s t hi s a p p e a r a s t ho u g h i t w a s a l m o s t i m m e d i a t e T he no nl i ne a r na t u r e o f t he r e s i s t a nc e va l u e s w a s ve r y c l e a r f r o m t he s ha p e o f t he c u r r e nt d a t a w he n vi e w i ng t he c or r e s p on d i n g v ol ta g e d a ta T h e c u r v a tu r e of th e c u r r e n t d a ta d u r i n g a p p l i c a ti on w a s q u i te a c o nt r a s t t o t he vo l t a g e d a t a w hi c h w e r e ve r y f l a t d u r i ng a p p l i c a t i o n. I n Fi g u r e 4 2 1 t he t e m p e r a t u r e d a t a f o r t he o hm i c e xp e r i m e nt w e r e p r e s e nt e d i n 2 pl o t s T h e t o p pl o t i n t h i s f i gure r epres en t ed a s h o rt peri o d j us t b ef o re t h e po wer was a p p l i e d I t w a s e s s e nt i a l l y t he i ni t i a l t e m p e r a t u r e c o nd i t i o n o f t he g e l s a m p l e T he t e m p e ra t u re d a t a p l o t t e d i n d i c a t e d t h e s a m p l e w e re b a s i c a l l y i s o t h e rm a l w i t h a t e m p e ra t u re spr ead o f app r o x i m at el y pl us o r m i n us 0. 05 C. T h e c o mp le t e t e mp e r a t u r e d a t a c o lle t e d fo r t h e o h mic e x p e r ime n t w e r e p lo t t e d in t h e lo w e r p lo t o f F ig u r e 4 2 1 T h is r a n g e c o v e r e d d a t a fr o m t h e p lo t a b o v e it t o a p o in t in t i m e we l l af t er t h e l as t po wer appl i cat i o n was en ded. I t was s een t h at t h e gel di d n o t h eat in a p e r fe c t ly u n ifo r m ma n n e r T h e t e mp e r a t u r e d a t a a s it r e la t e d t o p h a s e s o f t h e s a mp le were ea s i er t o i n t erpr et wi t h t h e addi t i o n o f t h e curren t dat a. T w o a d d i t i o na l p l o t s o f t he t e m p e r a t u r e d a t a w e r e p l o t t e d i n Fi g u r e 4 2 2 T he u p p e r p l o t w a s a l l o f t he t e m p e r a t u r e d a t a w i t h t he c u r r e nt d a t a T he ne w p l o t a l l o w e d t he regi o n b ef o re ph as e ch an ge t o b e ea s i l y i den t i f i ed f ro m t h e t em perat ure dat a. T h i s was wh ere t h e i n i t i al m an ual l y co n t ro l l ed po wer cy cl es were. T h e regi o n wh ere ph as e ch an ge w a s o c c u rri n g c o u l d t h e n b e i d e n t i f i e d a s a re a s w h e re a u t o m a t i c c o n t rol o f t h e p o w e r

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105 Figure 4-21. Ohmic Temperature Data. Object 4-20. OhmicTempBoth.jpg (418 KB).

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106 Figure 4-22. Ohmic Temperature and Current Data. Object 4-21. OhmicCurrentTempBoth.jpg (417 KB).

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107 appl i cat i o n was b ei n g us ed f ro m l o o ki n g at t h e curren t dat a. T h e f i n al regi o n wi t h po wer c y c l e s a f t e r t h e p h a s e c h a n g e c o u l d a l s o t h e n b e e a s i l y i d e n t i f i e d I t w a s e vi d e nt t ha t be f o r e p ha s e c ha ng e m u c h l e s s c u r r e nt w a s be i ng d e l i ve r e d t o t he s a m p l e f o r h e a t i n g j u s t a s w a s e x p e c t e d f rom t h e k n o w n re s i s t i v i t y d a t a o f t h e s a m p l e g e l T h e cur r en t app l i ed f o r ph ase ch an ge and b ey o n d wa s m uch gr eat er an d i n al l b ut o n e case w a s c o nt r o l l e d by t he a u t o m a t i c c u t o f f va l u e T he t e m p e r a t u r e s p r e a d s be t w e e n d i f f e r e nt g e o m e t r i c p o s i t i o ns i n t he s a m p l e w e r e r e l a t i ve l y s m a l l i n t he f r o z e n r e g i o n e ve n d u r i ng h eat i n g. T h es e s preads b egan t o i n creas e s i gn i f i can t l y wh en t h e s am pl e b egan t o ch an ge ph as e. T h e p h a s e c h a n g e r e g i on w a s s h ow n i n th e l ow e r p l ot of F i g u r e 4 2 2 T h i s p l ot s h o wed m o re det ai l o f t h e ph as e ch an ge regi o n It s t art ed at t h e en d o f t h e s eco n d t h erm al re l a x a t i o n re g i o n a n d s p a n n e d t o o n e c y c l e p a s t a l l t e m p e ra t u re d a t a o v e r t h e p h a s e c h a n g e T h e c u r r e n t i n c r e a s e ov e r th e f i r s t s p a n of a v e r y s m a l l c h a n g e i n d i c a te d th a t s om e p or ti on o f t h e s a mp le w a s u n d e r g o in g p h a s e t r a n s it io n T h e r is e in c u r r e n t if n o t c o n t r o lle d w o u ld h av e l ed t o run awa y h eat i n g at t h at po i n t T h e t em perat ure r eadi n gs appea red t o co n v erge f or a b r i e f p e r i od w i th th e v ol ta g e r e d u c e d T h e n e x t p ow e r c y c l e e n d e d a s on e p a i r of s e n s o rs (C h a n 5 a n d C h a n 7 ) s t a rt e d t o s h o w a t e m p e ra t u re ri s e T he d a t a i l l u s t r a t e d ho w t he t e m p e r a t u r e s f r o m a f i ni t e s e t o f p o i nt s w o u l d no t ha ve b een s uf f i ci en t t o det ect t h e i n i t i at i o n o f ph as e ch an ge i n t h e s am pl e. T h e curren t dat a gav e a n e a r ly i n d ic a t io n t h a t s o me w h e r e in t h e s a mp le t h e g e l w a s u n d e r g o in g a la r g e c h a n g e in i t s resi s t i v i t y v al ue. T h e t em perat ure dat a f ro m t h e ph as e ch an ge regi o n s h o wed o t h er i nt e r e s t i ng p o i nt s w i t h r e s p e c t t o g e o m e t r i c p o s i t i o ns o f t he s e ns o r s T w o s e ns o r s a t t he s am e po s i t i o n di v erged i n readi n gs o n ce t h e t em perat ure was ab o v e t h e ph as e ch an ge

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108 t e m p e r a t u r e I t w a s i nt e r e s t i ng t o no t e t ha t t he hi g he s t r e a d i ng s c o ns i s t e nt l y c a m e f r o m t he s am e s i de o f t h e s am pl e. T h e m o s t pro b ab l e ex pl an at i o n was t h at t h e s en s o rs were s eei n g a f i n n i n g e f f e c t on th e p r ob e i ts e l f i n s i d e th e g e l f r om a h e a te d r e g i on A l oc a l i z e d v ol u m e of t h e g e l t h a t w a s e x p e r ie n c in g r u n a w a y h e a t in g w o u ld h a v e b e e n mu c h h ig h e r in t em perat ure t h an o t h er v o l um es o f t h e gel T h i s h o t v o l um e co ul d h av e f i n n ed h eat t hr o u g h t he p r o be bo d y t o t he t e m p e r a t u r e p r o be t i p T he i m p a c t o n a s i ng l e e nd o f t he p r o be w o u l d ha ve be e n r e l a t e d t o t he p o s i t i o n o f t he hi g he r t e m p e r a t u r e vo l u m e t o t he p r o be s e c t i o n. T he p r o be a r r a ng e m e nt l e f t ve r y l i t t l e c ha nc e t ha t t hi s e f f e c t c o u l d ha ve imp a c t e d b o t h e n d s o f t h e p r o b e s e t e q u a lly T h is p o in t ill u s t r a t e d t h e d iffic u lt y in e s ta b l i s h i n g v a l i d i ty of a s i n g l e p r ob e te m p e r a tu r e m e a s u r e m e n t i n a s ol i d th a t w a s n ot i s o t he r m a l w he r e t he r e w o u l d ha ve be e n no s e c o nd p r o be t o s ho w t he p he no m e no n. A p l ot o f th e m a x i m u m te m p e r a tu r e d i f f e r e n c e s a n d g e l s a m p l e a p p a r e n t r e s i s ti v i ty f o r av erage ge l t em perat ures we re m ade i n F i gure 423, an d co n t rast ed t em perat ure spread f o r a n o h m i c d a t a e x p e ri m e n t c o m p a re d t o a n e x p e ri m e n t d e s i g n e d t o m e a s u re re s i s t i v i t y It was cl ear t h at v ery l i t t l e o f t h i s dat a co ul d b e us ed t o get t h e res i s t i v i t y at a gi v en t e m p e r a t u r e d u e t o t he t e m p e r a t u r e d i f f e r e nc e s w i t hi n t he g e l s a m p l e T he va l u e o f t he d a t a w e re i n a l re a d y k n o w i n g t h e re s i s t i v i t y t h e n t h e o re t i c a l l y a t e m p e ra t u re ra n g e f o r a s am pl e co ul d b e s et wi t h a t em perat ure di s t ri b ut i o n t h at wo ul d creat e t h e s am e t o t al resi s t i v i t y T h e o v erl aps i n dat a we re a resul t o f t h erm al rel ax at i o n wh ere t h e av erage t em perat ure wen t do wn wh i l e po wer was n o t s uppl i ed. T he a p p a r e nt p o w e r s u p p l i e d t o t he s a m p l e d u r i ng t he o hm i c t ha w i ng e xp e r i m e nt w a s p l o t t e d i n Fi g u r e 4 2 4 T he g r a p h ha d bo t h t he i ns t a nt a ne o u s a nd t he c u m u l a t i ve am o un t s uppl i ed. T h e cum ul at i v e wa s arr i v ed at b y s um m i n g t h e i n di v i dual av erage

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109 apparen t po wer appl i cat i o n m eas urem en t s T h e av erage wa s t h e s um o f t h e prev i o us s eco n d pl us t h e curren t s eco n d di v i ded b y 2. T h i s was an es t i m at e t h at as s um ed t h e i n put w a s c on s ta n t ov e r th e on e s e c on d i n te r v a l th a t th e a v e r a g e m e a s u r e m e n t r e p r e s e n te d W i th t he t i m e i nt e r va l be i ng s m a l l ( 1 s e c o nd ) t hi s p r o vi d e d a g o o d e s t i m a t e T he u ni t s f o r t he cum ul at i v e po wer was VA s eco n ds T h e f i n al v al ue f o r t h e cum ul at i v e po wer was 79140 VA s eco n ds T h e h i gh es t i n s t an t an eo us i n put o ccured duri n g ph as e ch an ge. E r r or Ana l ys is T e mp e ra t u re T he t e m p e r a t u r e e r r o r w a s d e p e nd e nt o n s e ve r a l f a c t o r s a s m e nt i o ne d i n t he cal i b rat i o n s ect i o n T h e m ai n err o r so urces o f co n cern were t h e dat a ac qui s i t i o n s y s t em F i gure 423. Oh m i c A pparen t Re s i s t i v i t y an d M ax i m um T em perat ure Di f f eren ce. O b j e c t 4 -2 2 O h m i c R e s i s t y A v e Te m p M TD .j p g (1 58 KB).

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110 reso l ut i o n s i gn al co n di t i o n i n g err o r an d l ev el o f n o i s e. T h es e pri m ary s o urces pro v i ded a u s e fu l e s t ima t e o f t h e t e mp e r a t u r e me a s u r e me n t e r r o r e x p e c t e d fr o m t h e c a lib r a t e d s ys t e m. T h e r eso l ut i o n o f t h e dat a acqu i si t i o n sy st em was cal cul at ed t o b e 76 3 x 10 C -3 p e r bi t T he s i g na l c o nd i t i o ni ng e r r o r ha d a l r e a d y be e n e s t i m a t e d a t t he l i ne a r i t y o f t he s i gn al co n di t i o n i n g m o dul e wh i ch was 0. 01 C T h e n o i s e wa s es t i m at ed f ro m l o o ki n g at dat a t h at were ex pect ed t o b e i s o t h erm al wi t h respe ct t o t i m e an d h ad l i t t l e s l o pe, t h en no t i ng t he r a ng e o f va l u e s T he no i s e o n t hi s ba s i s a p p e a r e d t o be r o u g hl y 0 0 4 C T he a s s u mp t io n w a s ma d e t h a t t h e s e e r r o r s w e r e in d e p e n d e n t a n d t h e n t h e y c o u ld b e a d d e d in q u a d r a tu r e to g e t a f i n a l v a l u e T h i s y i e l d e d a f i n a l e s ti m a te on th e te m p e r a tu r e e r r or of app r o x i m at el y 0. 04 2 C. T h e b r eak d o wn o f t h e cal cul at i o n s wer e pl aced i n A pp en di x B. Figure 4-24. Power Applied. Object 4-23. OhmicPowerAppCumu.jpg (132 KB).

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111 Res istance T h e r e s is t a n c e e r r o r in c lu d e d a g r e a t e r n u mb e r o f me a s u r e d q u a n t it ie s ma k in g it m o r e c o m p l e x. I t w a s d e p e nd e nt o n t he e r r o r a s s o c i a t e d w i t h bo t h t he vo l t a g e a nd c u r r e nt m e a s u r e m e nt s T o a d d r e s s t he r e s i s t a nc e m e a s u r e m e nt e r r o r a t a s p e c i f i c t e m p e r a t u r e t he te m p e r a tu r e e r r or w a s a l s o b e ta k e n i n to a c c ou n t to a v oi d g i v i n g a r a n g e f or b oth t em perat ure an d resi s t an ce. T h ey were co upl ed t h ro ugh t h e t h i rd o rder po l y n o m i al f i t t ed t o t h e res i s t an ce v ersus t em perat ure dat a. T h e us ef ul n es s o f b ei n g ab l e t o f i t t h e res i s t an ce v e r s u s te m p e r a tu r e d a ta w i th a p ol y n om i a l w a s th e n a p p a r e n t. T h e po l y n o m i al was us ed t o es t ab l i s h t h ro ugh i t s deri v at i v e, t h e s l o pe at a gi v en av erage t em perat ure dat a po i n t T h e s l o pe wa s t h en i n Oh m s / C. T h i s s l o pe wa s m u l t i p l i e d by t he a ve r a g e t e m p e r a t u r e e r r o r t o p r o vi d e t he t e m p e r a t u r e e r r o r i m p a c t o n t he readi n g o f t h e res i s t an ce. T h e av erage t em perat ure err o r acco un t ed f o r t h e f act t h at t h e gel w a s n ot e x p e c te d to h a v e b e e n c om p l e te l y i s oth e r m a l T h e a v e r a g e te m p e r a tu r e e r r or took t h e m ax i m um t em perat ure di f f eren ce a n d t h e t em perat ure m eas urem en t err o r t h en c o m bi ne s t he va l u e s by a d d i ng t he m i n q u a d r a t u r e T he o r i g i na l e r r o r s a s s o c i a t e d w i t h t he m e a s u re m e n t a n d c a l c u l a t i o n o f t h e re s i s t a n c e w e re t h e n a d d e d t o t h i s v a l u e i n q u a d ra t u re t o gi v e an es t i m at e o f t h e res i s t an ce e rr o r at a gi v en t em perat ure. T h e t em perat ure was a s s u m e d t o be e xa c t no w s i nc e a l l t he e r r o r a s s o c i a t e d w i t h i t ha d be e n p l a c e d i nt o t he v a l u e o f t h e re s i s t a n c e e rror. T h e r e s i s ti v i ty e r r or w a s n ot s i m p l y a s c a l e d r e s i s ta n c e e r r or T h e p r ob l e m f or r esi st i v i t y i n v o l v ed t h e f act t h at t h e l en gt h o f t h e sam pl e was m easur ed, an d t h e cr o ss s ect i o n al area wa s cal cul at ed f ro m a di am et er m eas urem en t T h i s i n t ro duced a n o t h er s o u r c e o f e r r o r t h a t w a s a c c o u n t e d fo r w h e n r e s is t iv it y e r r o r w a s e x a min e d T h e e r r o r in

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112 resi s t i v i t y as i t rel at ed t o t em perat ure err o r was h an dl ed i n t h e s am e m an n er as prese n t ed f o r r es i s t an ce e rr o r as i t rel at ed t o t em perat ure err o r. A n ex am pl e ca l cul at i o n was m ade a n d inc lu d e d in A p p e n d ix C T h e a p p e n d ix w a s g e n e r a t e d a s a M a t h c a d ( M a t h S o ft E n g ine e r ing a n d E d u c a t io n I n c C a mbr id g e M a s s a c h u s e t t s ) s h e e t t h a t w a s s e t u p t o v e r if y cal cul at i o n s carri ed o ut t o t ran s f o rm t h e dat a al ready i n A x um t o b e graph ed. T h e res ul t s o f t h e erro r an al y s i s were graph ed. A f i t t ed curv e wi t h t h e f ro zen r e s i s t i vi t y o n t he f i r s t y a xi s w a s p l o t t e d i n t he t o p p l o t o f Fi g u r e 4 2 5 T he p e r c e nt re s i s t i v i t y e rror w a s p l a c e d o n t h e s e c o n d y -a x i s T he t o t a l p e r c e nt r e s i s t i vi t y e r r o r w a s i nc l u s i ve o f t he t e m p e r a t u r e m e a s u r e m e nt e rror, w h i l e t h e re s i s t i v i t y e rror h a d o n l y t h e re s i s t i v i t y e rror w i t h o u t t h e t e m p e ra t u re m e a s u r e m e nt e r r o r i nc l u d e d T he t o t a l t he o r e t i c a l p e r c e nt e r r o r i nc r e a s e d a s t he t e m p e r a t u r e i nc r e a s e d T he s c a l e o f t he g r a p h m a d e t he d a t a l o o k a s i f i t w e r e be c o m i ng c l os e r to t h e f i t a n d l e s s s p r e a d ou t. T h e l ow e r p l ot o f F i g u r e 4 2 5 w a s th e s a m e d a ta on a n e w s c a l e z oo m e d to appro x i m at el y t h e l as t 1. 5 C o f dat a. On t h i s s cal e t h e s pread f ro m t h e t h i rd o rder p ol y n om i a l w a s e a s i l y s e e n T h e i m p or ta n c e of i n c l u d i n g a te m p e r a tu r e m e a s u r e m e n t e r r or i n t h e t o t al err o r was e as i l y v eri f i ed f ro m t h i s pl o t T h e res i s t i v i t y err o r was n o t l arge en o ugh t o acc o un t f o r t h e s pread o f v al ues f o un d ex peri m en t al l y T h e t o t al err o r gav e a r e a l i s t i c va l u e t ha t a c c o u nt e d f o r t he s p r e a d f o u nd e xp e r i m e nt a l l y T he hi g he r t he t e m p e r a t u r e i n t hi s s p a n t he m o r e d o m i na nt t he e r r o r d u e t o t e m p e r a t u r e e r r o r be c a m e a nd t he l a r g e r t he t o t a l e r r o r T he r e s i s t i vi t y e r r o r a l o ne w o u l d ha ve l e d o ne t o be l i e ve t he o ppo s i t e.

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113 Figure 4-25. Frozen Resistivity Error. Object 4-24. ErrorPercFrozResistyBoth.jpg (576 KB).

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114 T h e m ax i m um t em perat ure di f f eren ce s ro l e i n t h e t o t al resi s t i v i t y err o r was a l s o i l l us t rat ed graph i cal l y A pl o t o f t h e m ax i m um t em perat ure di f f eren ces an d t h e t o t al err o r were m ade i n F i gure 426. T h e s h ape o f t h e t o t al err o r was v ery s i m i l ar t o t h at o f t h e m ax i m um te m p e r a tu r e d i f f e r e n c e A r i s e i n th e m a x i m u m te m p e r a tu r e d i f f e r e n c e v a l u e l e d to a s u b s t a n t i a l ri s e i n t h e t o t a l e rror. Th e u n f roze n re s i s t i v i t y d a t a w e re p l o t t e d i n F i g u re 4 -2 7 Th e p l o t i n t h i s f i g u re was s i m i l ar t o t h e upper pl o t i n F i gure 425. T h e s cal e v al ues f o r each o f t h e ax es were a co n t rast i n g f eat ure o f t h i s pl o t T h i s was ex pect ed f o r t h e res i s t i v i t y v al ues b ut carri ed o ve r t o t he e r r o r va l u e s a s w e l l T he t o t a l p e r c e nt e r r o r w a s ve r y c l o s e t o be i ng c o ns t a nt a roun d 3 .3 p e rc e n t It d i d n o t v a ry m o re t h a n o n e t e n t h o f o n e p e rc e n t f rom t h i s v a l u e T h e f ro zen dat a ex h i b i t ed a m uch wi der r an ge o f t o t al percen t err o r. It i n cl uded v al ues t h at w e r e a l m os t 1 0 ti m e s th a t a m ou n t. Figure 4-26. Frozen Resistivity Error and Maximum Temperature Difference. Object 4-25. ErrorPercFrozMTDResisty.jpg (417 KB).

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115 co n t rast i n g f eat ure o f t h i s pl o t T h i s was ex pect ed f o r t h e res i s t i v i t y v al ues b ut carri ed o ve r t o t he e r r o r va l u e s a s w e l l T he t o t a l p e r c e nt e r r o r w a s ve r y c l o s e t o be i ng c o ns t a nt a roun d 3 .3 p e rc e n t It d i d n o t v a ry m o re t h a n o n e t e n t h o f o n e p e rc e n t f rom t h i s v a l u e T h e f ro zen dat a ex h i b i t ed a m uch wi der r an ge o f t o t al percen t err o r. It i n cl uded v al ues t h at w e r e a l m os t 1 0 ti m e s th a t a m ou n t. T he u nf r o z e n r e s i s t i vi t y m e a s u r e m e nt w a s l e s s s e ns i t i ve t o t e m p e r a t u r e e r r o r T he resi s t i v i t y err o r wi t h o ut co m pen s at i n g f o r t h e t em perat ure err o r was v ery cl o s e t o t h e t o t al v a lu e a s w a s in d ic a t e d in F ig u r e 4 2 7 T h e ma x imu m t e mp e r a t u r e d iffe r e n c e s p r e s e n t e d in Fi g u r e 4 1 2 s ho w e d t ha t i n c o nt r a s t t o t he f r o z e n d a t a t hi s d a t a ha d l a r g e r d i f f e r e nc e s T he m ax i m um di f f eren ces f o r t h e un f ro zen dat a we re m o re t h an t wi ce a s l arge as t h e f ro zen d a ta T h e l ow e r s e n s i ti v i ty of th e u n f r oz e n m e a s u r e m e n ts w a s r e l a te d to th e s l ow e r r a te of F i g u re 4 -2 7 U n f roze n R e s i s t i v i t y Error. O b j e c t 4 -2 6 ErrorPe rc U n f rozR e s i s t y A l l .j p g (1 85 KB).

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116 ch an ge o f t h e r esi st i v i t y i n t h e un f r o zen st at e. T h e r at e o f ch an ge f o r t h e f r o zen r an ge w as m u c h g re a t e r w h e n c o n t ra s t e d t o t h e u n f roze n a n d m a g n i f i e d a n y t e m p e ra t u re e rror. F i g u r e 4 1 9 v i s u a l l y v e r i f i e d th e l a s t p oi n t.

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117 CHA P T E R 5 CO NC L USI ONS A ND R E CO M M E NDA T IONS T h e r e s e a r c h w a s s u c c e s s f u l i n d e s i g n i n g a n d c on s tr u c ti n g a n a p p a r a tu s c a p a b l e of ma k in g a c c u r a t e me a s u r e me n t s n e e d e d fo r d e t e r min in g t h e e le c t r ic a l r e s is t iv it y o f a g e l in bo t h t he u nf r o z e n a nd f r o z e n s t a t e s T he s y s t e m d e s i g n w a s c a p a bl e o f c o nt i nu o u s l y t a k i ng d a t a o n a f r o z e n g e l a s i t u nd e r w e nt o hm i c t ha w i ng T he r e s e a r c h a l s o va l i d a t e d t he i m p o r t a nc e o f k no w i ng a p p r o xi m a t e l y ho w i s o t he r m a l a g e l w a s i n t e r m s o f r e p o r t i ng t he t he o r e t i c a l e r r o r T he d a t a c o l l e c t e d o n u nf r o z e n g e l r e s i s t i vi t y d i d no t i nd i c a t e t ha t t he f r eezi n g o r t h e t h awi n g p r o cesses i m pact ed t h e gel el ect r i cal pr o per t i es. C a l i b r a ti on of th e e x p e r i m e n ta l a p p a r a tu s p r e s e n te d d a ta th a t w a s i d e n ti f i e d w i th d i f f e r e nt m e t ho d s o f he a t t r a ns f e r C o nd u c t i o n a nd c o nve c t i o n w e r e bo t h p r e s e nt i n t he cal i b rat i o n ex peri m en t T h e dat a i n di cat ed t h at as s um i n g co n duct i o n f ro m t h e t o p s urf ace f o r t he c l a s s i c S t e p ha n p r o bl e m o f w a t e r f r e e z i ng w a s p r o ba bl y r e a s o na bl e u p t o t he ma x imu m d e n s it y t e mp e r a t u r e o f w a t e r T h e c a lib r a t io n d a t a c a r r ie d fu r t h e r imp lic a t io n s in t h e r ev er se pr o cess, t h awi n g, t h at co n v ect i o n wo ul d h av e pl ay ed a r o l e ear l y i n t h e pr o cess u p to th e m a x i m u m d e n s i ty te m p e r a tu r e b u t a f te r th a t p oi n t c on d u c ti on f r om th e top s urf ace do m i n at ed. Duri n g t h e o perat i o n f urt h er ch al l en ges o f m aki n g m eas urem en t s o n a gel s y s t em u n d e r g o in g p h a s e c h a n g e w e r e id e n t ifie d I n t e r n a l fin n in g o f h e a t b y t h e p r o b e s c o u ld i m p a c t th e te m p e r a tu r e m e a s u r e m e n ts T h e p l a n a r p r ob e a r r a n g e m e n t w a s u n a b l e to d i s t i ng u i s h be t w e e n s y m m e t r i c g e o m e t r i c he a t s o u r c e l o c a t i o ns o n o p p o s i t e s i d e s o f t he

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118 p l a n e of th e p r ob e s S i n g l e te m p e r a tu r e l oc a ti on s w e r e u n l i k e l y to c a p tu r e th e i n i ti a ti on of p ha s e c ha ng e T he i ni t i a t i o n o f p ha s e c ha ng e c o u l d o c c u r a ny w he r e r a nd o m l y i n t he s am pl e an d t h e ev en t wo ul d o n l y b e ev i den t wh en a pro b e l o cat i o n was t h erm al l y i m pact ed b y t h e e v e n t T h e p h ys ic a l s iz e o f t h e p r o b e c o mp a r e d t o t h e s a mp le ma d e it h ig h ly un l i kel y t h at t h e pro b e wa s l o cat ed ex act l y wh ere ph as e ch an ge i n i t i at ed. T h ere were s ev eral reco m m en dat i o n s f o r f urt h er r es earch T h e ex peri m en t al apparat us co ul d un dergo a s eco n d des i gn i t erat i o n T h e pro b e di am et ers c o ul d b e reduce d t o h el p m i n i m i ze i n t ern al f i n n i n g. T h e pro b e geo m et ri c l ay o ut co ul d b e ch an ged s o t h at e a c h p r ob e w ou l d e n te r a t 6 0 a n g l e s to on e a n oth e r T h i s w ou l d d i v i d e th e g e l i n to 6 s e c t o r s a nd y i e l d m o r e g e o m e t r i c i nf o r m a t i o n o n l o c a t i o ns o f he a t s o u r c e s O hm i c t ha w i ng e x p e r ime n t s c o u ld b e d e s ig n e d w it h g e ls t h a t h a v e s o lid in c lu s io n s o f s imp le g e o me t r ic n at ure o f an o t h er gel o r f o o d m at eri al wi t h di f f eren t el ect ri cal pro pert i es T h e ex peri m en t al d a t a g a i ne d f r o m t hi s r e s e a r c h a nd f u r t he r r e s e a r c h i n t he a r e a s ho u l d be u s e d f o r va l i d a t i ng n um er i cal m o del s o f t h e o h m i c t h awi n g p r o cess.

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Temperature in liquid phase v2Temperature in solid phase v1Melting point temperature T1Latent heat of fusion L Thermal conductivity of the liquid K2Thermal conductivity of the solid K1Specific heat of the liquid c2Specific heat of the solid c1Numerical constants AB Density of liquid and solid phases Numerical constant Thermal diffusivity of the liquid 2Thermal diffusivity of solid 1 This sheet created with Mathcad 2001 provides a derivation of the equation assuming the front location has the form of X2 2t 1 2 = insead of assuming X2 1t 1 2 = as in Carslaw & Jaeger (1959). The symbols are consistent with those in the original derivation. ALTERNATE NEUMANN'S SOLUTION APPENDIX A 119

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120 K1x Aerf x 2 1t 1 2 d d K2x VBerfc x 2t 1 2 d d L t 2 2t 1 2 d d = K1x v1 d d K2x v2 d d L t X d d = 1 2 X 2t = X2 2t 1 2 = B VT1 erfc X 2 2t 1 2 = A T1erf X 2 1t 1 2 = Aerf X 2 1t 1 2 VBerf X 2t 1 2 = T1= Phase Surface boundary condition xXt () = When v1v2= T1= v2VBerf x 2t 1 2 = v1Aerf x 2 1t 1 2 = erfcx ()1erfx () 2 expx2 = x erfx () d d erf1 ()0.843 Position of the phase change front X Position x Initial Temperature of liquid phase V

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121 K1A exp 1 4 x21t 1t 2K2 B exp x2 2t 2t L 2t 2 = Substitute in for A and B K1T1erf 1 2 X 1t exp 1 4 x21t 1t + ... K2 VT1erfc 1 2 X 2t exp 1 4 x22t 2t L 2t 2 = Recognizing the terms, and rewriting. 1 2 X 2t = 21 4 X22t = K1T1erf 21 exp 2 21 1t K2VT1erfc exp 22t L 2t 2 = Dividing by T1 and multiplying by square root of K11 erf 21 exp 2 21 1t K2VT1erfc exp 2T12t L T12t 21 2 =

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122 Dividing through by K2, getting ready to recognize the c2 K1K2 1 erf 21 exp 2 21 1t VT1erfc exp 2T12t L K2 T12t 21 2 = Utilizing 2K2 c2 = and mutiplying by 2t K1K2 exp 2 21 erf 21 21 VT1erfc exp 2 12 T1 L c2 T1 1 2 = Now you have a form for the from assuming X2 2t 1 2 = instead of X2 1t 1 2 = as in Carslaw & Jaeger (1959).

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Expected Error in Degrees Celsius C .0120.0076320.042 0.042Summation of the Errors in Quadrature Yields Expected Error in Degrees Celsius Level of noise from data based on observation of Calibration and other data, roughly 5 bits C 0.04 Level of Noise Range of Interest is less than 50 therefore less than 1/10 of total nonliearity or 0.01 Nonlinearity of the Conditioning Module C 5000.00020.1Linearity of the Signal Conditioning Module (Total Range of Module) Signal Conditioning Error Resolution in Degrees Celsius per Bit 10076.2951067.63103 Degrees Celsius per linearized Volt output C/V 500 5 100Volts per Bit 5V2161 76.295106V 21665.536103 Data Acquisition Resolution Components of that error: Data Acquisiton Resolution Signal Conditioning Error Level of Noise Error in Temperature Measurement ERROR IN TEMPERATURE MEASUREMENT APPENDIX B 123

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4 500 This would be the scaled voltage error, before converting back to Voltage applied to sa m The value can be converted by dividing by the original scaling factor, where the original volt range of the Crompton meter was converted to a effective 4 volt range by current ou t 11.2106 A 250 225103 20 mA2 2.844103 V Since V=IR, need to look at dV = I VR d dR VI d d which will be done in quadrature. Accuracy of Current output (Manufacturer Specification 0.07% of Span) 16mA0.0007 1.12105 A High side output 20mA250 5V Low side output 4mA250 1V Accuracy of the Precision Resistor 250 0.0001 0.025 Span of output pod 204 ()mA0.016A Voltage Measurement by Crompton Meter Converted to Current by Output Pod. Current Converted to Voltage by DAC Reading Voltage across Precision Resistor. First Examine the Voltage Measurement Error Resistance433.553 Resistance Voltage Current Data Value Current0.1566A Data Value Voltage67.89447V Resistivity error with no temperature error RESISTIVITY ERROR APPENDIX C 124

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125 Assumes Diameter error equal to the Length Error, which implies Radius error would be the same. Area_Error2 Radius .5 mm Area3.421103 m2 Area Radius2 Radius of the sample cell Radius33mm Length_Error.5mm Length of the sample cell Length49mm Ohms_Percent_Error0.649 Ohms_Percent_Error Ohms_Error Resistance 100 Ohms_Error2.813 Ohms_Error Voltage Current2 Current_Error 21 Current Voltage_Error 2 Renaming the Error to a variable Current_Error600106 A Low Range 60106 A High Range 600106 A Manufacturer Specification of 0.6%+3d this leads to 2 values, determined by theRange that the DMM is reading 50.0mA0.0006 0.03mA 6105 A Current Read by Extech DMM Examine the Current Error Renaming the Error to a variable Voltage_Error355.536625103 V Accuracy of Voltage, which can be considered as Measure of Error 2.844293103 V 4 500 0.356V

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126 Resistivity_UnknownResistivity_Error2SlopeTemperature_Unknown ()2 Slope335.9628 Temperature2 2162.3497 Temperature 526.1101 Apply the slope at the given temperature for the data point by taking the derivative of th e cubic polynomial that was fitted at that point, and multiply by the temperature unknown Temperature_UnknownTemperature_accuracy2Max_Temperature_Diff2 From Data at each Point C Max_Temperature_Diff0.10 From Temperature Error Analysis C Temperature_accuracy0.042 Temperature Contribution Resistivity_Percent_Error3.263 Resistivity_Percent_Error Resistivity_Error Resistivity 100 Resistivity_Error0.988 m Resistivity_ErrorOE ()2AE ()2 LE ()2 LE ResistanceArea Length2 Length_Error AE Resistance Length Area_Error OE Area Length Ohms_Error Take the derivative for the Resistivity and add the parts in quadrature. For presentation a substitution will be made for the each part. Resistivity30.271 m ResistivityResistance Area Length

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127 R EF ER EN C ES A ya d i M A L e u lie t J C C h o p a r d F B e r t h o u M L e b o u c h 2 0 0 4 C o n t in u o u s O h mic H e a t i ng U ni t U nd e r Whe y P r o t e i n Fo u l i ng I nno va t i ve Fo o d S c i e nc e a nd E m e r g i ng T ech n o l o gi es 5: 465473. Ba i rd D, Gress go t t H. 1978. T h erm o dy n am i cs o f F o o d F reezi n g. Paper No 78-6544. W i nt e r Me e t i ng Am e r i c a n S o c i e t y o f Agr i c u l t u r a l E ng i nee r i ng ; 1 9 7 8 D e c 1 8 2 0 ; Ch i cago IL. Mi ch i gan : A m eri can So ci et y o f A gri cul t ural E n gi n eers 11 p. B e na bd e r r a hm a ne L J P a i n J P 2 0 0 0 T he r m a l B e ha vi o r o f a S o l i d / L i q u i d M i xt u r e i n a Oh m i c He at i n g St eri l i zer S l i p Ph as e M o del Ch em i cal E n gi n eeri n g Sci en ce. 55: 1371-1384. Ca rsl aw, HS, J aege r, J C. 1959. Co n duct i o n o f Hea t i n So l i ds Seco n d E di t i o n New Yo rk: Ox f o rd Un i v ersi t y Pr es s In c. 510 p. C a s tr o I T e i x e i r a J A S a l e n g k e S S a s tr y S K V i n c e n te A A 2 0 0 4 O h m i c H e a ti n g of S t r a w b e r r y P r o d u c t s : E le c t r ic a l C o n d u c t iv it y M e a s u r e me n t s a n d A s c o r b ic A c id Degradat i o n K i n et i cs In n o v at i v e F o o d Sci en ce a n d E m ergi n g T ech n o l o gi es 5: 2736. Cl el an d A C, E arl e R L 1984. A s s es s m en t o f F reezi n g T i m e Predi ct i o n M et h o ds J o urn al o f F o o d Sci en ce 49: 1034-1042. D a v i e s L J K e m p M R F r y e r P J 1 9 9 9 T h e G e om e tr y of S h a d ow s : E f f e c ts of In h o m o gen ei t i es i n E l ect ri cal F i el d Pr o ces s i n g. J o urn al o f F o o d E n gi n eeri n g 40: 245258. d e Al w i s AAP Fr y e r P J 1 9 9 0 a A Fi ni t e E l e m e nt Ana l y s i s o f H e a t G e ne r a t i o n a nd T ran s f er Duri n g Oh m i c He at i n g o f F o o d. Ch em i cal E n gi n eeri n g Sci en ce 45 (6): 15471559. d e A lw is A A P F r ye r P J 1 9 9 0 b O p e r a b ili t y o f t h e O h mic H e a t in g P r o c e s s : E le c t r ic a l Co n duct i v i t y E f f ect s J o urn al o f F o o d E n gi n eeri n g 15: 2148. d e A l w i s A A P F r y e r P J 1 9 9 0 c T h e U s e of D i r e c t R e s i s ta n c e H e a ti n g i n th e F ood In dus t ry J o urn al o f F o o d E n gi n eeri n g. 11: 327. E lio t G o d r e a u x S C F a ir h u r s t P G G o u lli e u x A P a in J P 2 0 0 1 a P a s s a g e T ime Di s t ri b ut i o n s o f Cub es an d Sph eri cal Part i cl es i n an Oh m i c He at i n g Pi l o t Pl an t J o urn al o f F o o d E n gi n eeri n g 47: 1122.

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128 E l i o t G o d r e a u x S C Fa i r hu r s t P G G o u l l i e u x A, P a i n J P 2 0 0 1 b. P r o c e s s i ng a nd Sab i l i s at i o n o f Ca ul i f l o wer b y Oh m i c He at i n g T ech n o l o gy In n o v at i v e F o o d Sci en ce an d E m ergi n g T ech n o l o gi es 2: 279287. E v eri n gt o n DW 1971. T h awi n g o f F ro zen F o o ds t uf f s Ch em i s t ry an d In dus t ry 27: 973979. Fu WR H s i e h C C 1 9 9 9 S i m u l a t i o n a nd V e r i f i c a t i o n o f T w o D i m e ns i o na l O hm i c H e a t i ng i n St at i c Sy s t em J o urn al o f F o o d Sci en ce 64 (6): 946949. F u W R L in E L 2 0 0 3 A p p lic a t io n o f A C I mp e d e n c e S p e c t r o s c o p y An a lys is fo r S o lid Fo o d s AS AE Annu a l I nt e r na t i o na l M e e t i ng P a p e r # 0 3 6 1 4 5 R i vi e r a H o t e l a nd Co n v en t i o n Ce n t er La s Vega s Nev ada U SA 27-30 Jul y 2003. A SA E St J o s eph M i ch i gan 15 p. H a l d e n K d e A l w i s A A P F r y e r P J 1 9 9 0 C h a n g e s i n th e E l e c tr i c a l C on d u c ti v i ty of F o o ds Duri n g Oh m i c He at i n g. In t ern at i o n al J o urn al o f F o o d Sci en ce a n d T ech n o l o gy 25: 925. H e ld ma n D R 1 9 8 3 F a c t o r s I n flu e n c in g F o o d F r e e z in g R a t e s F o o d T e c h n o lo g y Ap r il: 103-109. H e nd e r s o n J T 1 9 9 3 O hm i c T ha w i ng o f Fr o z e n S hr i m p : P r e l i m i na r y T e c hni c a l a nd Ec o n o m i c F e a s i b i l i t y M a s t e r s Th e s i s U n i v e rs i t y o f F l o ri d a H e n d ri c k s M V a n G e n e c h t e n K To b b a c k P. 1 9 8 8 Tra n s m i s s i o n L i n e M a t ri x (TL M ) M o d e l s f o r P r e d i c t i ng Fr e e z i ng a nd T ha w i ng T i m e s o f Fo o d s P r o c e e d i ng s o f t he In t ern at i o n al Sy m po s i um o n Pr o gress i n F o o d Pr es erv at i o n Pr o ces s es : Vo l um e 1 Oral Pr e s e n t a t i o n s 1 9 8 8 A p ri l 1 2 -1 4 B ru s s e l s B e l g i u m C ER IA p 8 1 -9 9 Ic i e r F Il i c a l i C 2 0 0 5 Th e U s e o f Ty l o s e a s a F o o d A n a l o g i n O h m i c H e a t i n g Stud i e s J o urn al o f F o o d E n gi n eeri n g 69: 6777. I m ai T Uem ur a K I sh i da N Yo sh i zaki S Nug uch i A 19 95 Oh m i c Heat i n g o f Japan ese Whi t e R a d i s h R haphanus s ativus L I nt e r na t i o na l J o u r na l o f Fo o d S c i e nc e a nd T ech n o l o gy 30: 461472. J as o n A S, San ders HR 1962. Di el ect ri c Th awi n g o f F i s h I. E x peri m en t s wi t h F ro zen Herri n gs F o o d T ech n o l o gy 101-106. K an are, HM 1985. W ri t i n g t h e L ab o rat o ry No t eb o o k. W as h i n gt o n D.C. A m eri can Ch em i cal So ci et y 150 p.

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129 K h a l a f W S a s tr y S K 1 9 9 6 E f f e c t of F l u i d V i s c os i ty on th e O h m i c H e a ti n g R a te s of So l i d-Li qui d M i x t ures. Jo urn al o f F o o d E n gi n eeri n g 27: 145158. L a k k a k u la N R L ima M W a lk e r T 2 0 0 4 R ic e B r a n S t a b ili z a t io n a n d R ic e B r a n O il E x t ract i o n Us i n g Oh m i c He at i n g. Bi o reso urce Tech n o l o gy 92: 157161. L i B Su n D W 2 0 0 2 N o v e l M e t h o d s f o r R a p i d F re e z i n g a n d Th a w i n g o f F o o d s a Re v i ew. Jo urn al o f F o o d E n gi n eeri n g. 54: 175182. L i m a M S a s t r y S K. 1 9 9 9 T he E f f e c t s o f O hm i c H e a t i ng Fr e q u e nc y o n H o t Ai r D r y i ng Ra t e an d J ui ce Y i el d. J o urn al o f F o o d E n gi n eeri n g 41: 115119. L u z u r i a g a D A, B a l a ba n M O 1 9 9 6 E l e c t r i c a l C o nd u c t i vi t y o f Fr o z e n S hr i m p a nd F l ou n d e r a t D i f f e r e n t T e m p e r a tu r e s a n d V ol ta g e L e v e l s J ou r n a l of A q u a ti c F ood Pr o duct T ech n o l o gy 5(3) :4163. M i z ra h i S, K o p e l m a n IJ Pe rl m a n J 1 9 7 5 B l a n c h i n g b y El e c t ro-c o n d u c t i v e H e a t i n g J o urn al o f F o o d T ech n o l o gy 10: 281288. N a v e h D K o p e l M a n IJ M i z ra h i S. 1 9 8 3 El e c t rocon d u c t i v e Th a w i n g b y L i q u i d C o n t a c t J o urn al o f F o o d T ech n o l o gy 18: 171176. Pal an i appan S, Sas t ry SK 1991a. E l ect ri cal Co n duct i v i t i es o f Sel ect ed J ui ces : I n f l uen ces of T e m p e r a tu r e S ol i d s C on te n t, A p p l i e d V ol ta g e a n d P a r ti c l e S i z e J ou r n a l of F ood Pr o ces s E n gi n eeri n g 14: 247260. Pal an i appan S, Sas t ry SK 1991b E l ect ri cal Co n duct i v i t i es o f Sel ect ed So l i d F o o ds Duri n g Oh m i c He at i n g. J o urn al o f F o o d Pr o ces s E n gi n eeri n g 14: 221236. Peeb l es Z P, Gi um a TA 1991. Pr i n ci pl es o f E l ect ri cal E n gi n eeri n g. New Y o rk: M cGrawHi l l In c. 757 p. R o b e r t s J S 1 9 9 4 D e s ig n a n d T e s t in g o f a P r o t o t yp e A u t o ma t e d O h mic T h a w in g U n it [t h es i s ]. F l o ri da. Un i v ersi t y o f F l o ri da. 256 p. R o b e r t s J S B a la b a n M O Z im me r ma n R L u z u r ia g a D 1 9 9 8 D e s ig n a n d T e s t ing o f a Pr o t o t y p e A u t o m a t e d O h m i c Th a w i n g U n i t C o m p u t e rs a n d El e c t ron i c s i n A g ri c u l t u re 19: 211222. S a s tr y S K 1 9 9 2 A M od e l f or H e a ti n g O f L i q u i d P a r ti c l e M i x tu r e s i n a C on ti n u os F l ow Oh m i c He at er. J o urn al o f F o o d Pr o ces s E n gi n eeri n g 15: 263278. S a s t r y S K, P a l a ni a p p a n S 1 9 9 2 a I nf l u e nc e o f P a r t i c l e O r i e nt a t i o n o n t he E f f e c t i ve E l e c tr i c a l R e s i s ta n c e a n d O h m i c H e a ti n g R a te of a L i q u i d P a r ti c l e M i x tu r e J ou r n a l of Pr o ces s E n gi n eeri n g 15: 213227.

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BROKEN_LINK
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Permanent Link: http://ufdc.ufl.edu/UFE0013034/00001

Material Information

Title: Development of an Ohmic Thawing Apparatus for Accurate Measurement of Electrical Resistance
Physical Description: Mixed Material
Copyright Date: 2008

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Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0013034:00001

Permanent Link: http://ufdc.ufl.edu/UFE0013034/00001

Material Information

Title: Development of an Ohmic Thawing Apparatus for Accurate Measurement of Electrical Resistance
Physical Description: Mixed Material
Copyright Date: 2008

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0013034:00001


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DEVELOPMENT OF AN OHMIC THAWING APPARATUS FOR ACCURATE
MEASUREMENT OF ELECTRICAL RESISTANCE















By

RANDY ALLEN CLEMENTS


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA


2006






























Copyright 2006

by

Randy Allen Clements



































To my wife Tammy and my sons Kyle and Austin
















ACKNOWLEDGMENTS

Many individuals that have made this work possible. There are more than can be

reasonably listed, but I would like to extend special thanks to Dr. Murat O. Balaban for his

encouragement, support and guidance in completing this work. I am indebted to my

graduate committee for their patience and persistence. I also wish to thank Dr. Randolf

Hook for his friendship, help and engaging conversations on this research. Completion of

this work would not have been possible without the support of my family throughout the

process.


















TABLE OF CONTENTS


page


ACKNOWLEDGMENTS .......... ................... iv


LISTOFTABLES ......... ........... ......... viii


LIST OF FIGURES .............. ......... ........... ix


LISTOFOBJECTS ......... ........... ......... xi


ABSTRACT .......... ................... xiii


CHAPTER


1 INTRODUCTION .......... .................. .. 1


2 LITERATURE REVIEW .............. ........... ...... 3


Traditional Heating ............... ......... .......... 3
Volumetric Heating .............. ......... .......... 4
Microwave .............. ......... ........... 4
Ohmic ........,, ..... .... ,,, .........,, 5
Historical Overview of Ohmic Heating ... . ., .. . 5
Ohmic Thawing .........,,, .....,,,........., 9


3 MATERIALS AND METHODS .........,, ..........,,, 13


PhysicalTestSample ......... .................... 13
GelType .......... ................... 13
SampleCell .......... ................... 14
Cylindrical housing . ......... .... .. .. .. 14
Interior insulation ............. ............ .... 15
Exterior insulation ............... ................. 16
Electrodes .......... .................... 16
Endcaps .......... .................... 17
Probes ............... .............. ...., 18
CellHolder ............ .................. 20

Temperature ControlChamber .............. ............. 21
Power Supply .............. .......... ......... 22












Control ............... ......... ........... 22
Manual control .............. ..... .......... ...23
Automated control .............. ................. 23
Alternative direct current ........ .. .. .. .. .. 23
Leads andplugs ............... .................. 24
Data Collection Hardware and Software . .... .. .. .. .. 24
DataAcquisitionCard .......... ................... 24
Interfacing ............... ..... .......... .....24
Backplane ............... .................... 25
SignalConditioning .......... .......... ......... 25
Signal Conditioning Housing ......... .. .. ... .. .. 26
DataLogging DigitalMultimeter ............... ............ 27
Software ......... .................... 28
Data collection .............. ........... ...... 28
Data visualization .............. ................. 29

Equipment Cart .............. .............. ...., 29
Apparatus Construction . . ..., . 31
Probe Construction . ......... .. .. .. 31

Design ............... ......... ........... 31
Assembly ............. ......... .......... 32
Sample Cell Construction.........., ........, 34
Design ....., .........,,, .........,.34
Assembly..........,, ......,, .......... 36

Sample Cell Holder Construction ... .. ., . . 39
Design ....., .........,,, .........,.39
Assembly.......... ......,, .......... 39
Signal Conditioning Housing Construction . . . .. 41
Design ....., .........,,, .........,.41
Assembly ............. ......... .......... 41

Apparatus Wiring..........,,, ......,,,....... 42
Power ....., .........,,, .........,.43
Meters .............. .............. ...., 46

Backplane ............... .................... 47
Screw terminalpanel ........... ................ 48
Experimental Methods ............... ..... .......... ....49
DataCollection .......... ................... 50

Laptop computer ............... ............ .... 50
Datalogging digitalmultimeter .............. .........., 51
Laboratory notebook ............... ................ 52

Temperature Probe Calibration ........ .. .. ... .. .. 52
GelPreparation .......... ................... 54
Gel Density Determination ......... .. .. .. . .. 55
Freezing .......... ..... .......... ........... 56
Environment Characterization ......... .. .... .. .. 58
Continuous Running .............. ................ 58












Cycling ......... .................. .. 59
Thermal Damping .............. ..... .......... ..59
Automatic Power Control Method . ..... ... .. . .. 60

Relay set up ............... .......... ........ 60
Power controlvalidation ............... ... .......... 61
Resistance Measurement ......... .. ... .. .. 62
Unfrozen sample ............... ............ .... 62
Frozen sample ............... ........... ...... 64
OhmicThawing .......... .......... ......... 66


4 RESULTS AND DISCUSSION.........., ..........,,, 69


Data Collection..........,,, .....,,, ........., 69

Temperature Calibration . . ..., . 70
Theoretical .. ..., .........,,, ........., 70

Experimental .......... ................... 72
Experimental Gel .. ..., ........., ........... 81
TotalMassPercent ......... ........... ......... 81
Density ......... .................... 81
Freezing ................ .......... ......... 82
Environmental Characterization ......... .. .... .. .. .. 84
Automatic Power Control Validation . ...... ...... .. . .. 87
Resistance Measurement .............. ........... ...... 88
Unfrozen Gel ............... ......... .......... 88
Frozen Gel ......... ............... ........., 96
Combined Temperature Ranges . ...... ..... .. . .. 100
OhmicThawing ......... .......... .......... 101
Error Analysis..........,,, .....,,, ........., 109
Temperature ......... .................... 109
Resistance .......... .................. 111


5 CONCLUSIONS AND RECOMMENDATIONS . . . 117


APPENDIX


A ALTERNATE NEUMANN'S SOLUTION . . .. .. .. .. .. 119


B TEMPERATURE ERROR .............. ................. 123


C RESISTIVITY ERROR ............... .................. 124


REFERENCES .......... .................... 127


BIOGRAPHICAL SKETCH ............... .................. 131


















LIST OF TABLES


Table gg

4-1. Calibration Offset Values. ......... . ... .. .75


4-2. Percent of Total Mass of Gelatin inGel. . ..... .. .. .. .. 81


4-3. GelDensity. .............. ............... ........82



















LIST OF FIGURES


Figures pg


3-1. CylindricalHousing. .............. ..... .......... .....15


3-2. SketchofPVC Cell. .........,,, .....,,,......... 16


3-3. Electrode Sketch and Picture. ......... .. ..... . .. 17


3-4. Probe Sketch ............... ......... ............ 19


3-5. Probe Assembly Bench Rail. ......... .. ... .. .. 20


3-6. Sample CellHolder. .............. .................... 21


3-7. Housing ............... ......... .............. 27


3-8. Box Arrangement. .............. ......... .......... 30


3-9. Shell With Ports. .............. ......... .......... 37


3-10. Sample Holder Picture Front and Side Views. .. .. .. . .. .. .. .. 40


3-11. Detailed Sample Power Wiring. .......... .. .. .. .. .. .. 45


3-12. Probe Positions and Naming Conventions. . . .. .. .. .. 53


3-13. Relays. .............. ......... .............. 61


3-14. Additional Fiberglass Insulation. ......... .. ...... .. . .. 65


4-1. Calibration Setup Features ............... ............ .... 73


4-2. Probe Calibration Data. ......... . .. .. .. 74


4-3. CalibrationWarming Data. .............. ............ .... 76


4-4. CalibrationNoise ............... .......... ..........79











4-5. Noise Under High Voltage. ......... .. ... .. .. 80


4-6. Temperature Cycling. ......... . . .. .. 85


4-7. Cycling and Adjacent Probe Temperature Differences. .. .. .. .. .. .. .. .. 87


4-8. Sample and Environmental Warming. . .... .. .. .. .. 88


4-9. Unfrozen Gel Temperature, Voltage and Current Plots. .. .. .. .. .. .. . 90


4-10. Unfrozen Gel Temperature, Voltage and Current Plots. .. .. .. .. .. . 91


4-11. Unfrozen Gel Resistance. ........ .. .. .. .. .92


4-12. Unfrozen Gel Resistivity and Maximum Temperature Difference. . . 93


4-13. Unfrozen Gel Resistivity Before and After Freezing. .. .. .. . .... ... 94


4-14. Unfrozen Resistivity with Cubic Polynomial Fit. ... .. .. . .. .. .. 95


4-15. Frozen Gel Temperature, Voltage and Current Plots. . . .. 97


4-16. Frozen Gels Resistance. . . .,,, .. . 98


4-17. Frozen Resistivity and Maximum Temperature Difference. .. .. .. .. . 99


4-18. Frozen Resistivity with Cubic Polynomial Fit. .. .. .. .. .. .. .. 100


4-19. Unfrozen and Frozen Resistivity Cubic Fits. ... . . .. .. .. 101


4-20. Ohmic Thawing Voltage and Current Data. ... .. .. .. .. .. .. 103


4-21. Ohmic Temperature Data. . . .,,, .. ... 105


4-22. Ohmic Temperature and Current Data. ... . .. .. . 106


4-23. Ohmic Apparent Resistivity and Maximum Temperature Difference. .. .. .. .. 109


4-24. Power Applied. ........,,, ......,, .......... 110


4-25. Frozen Resistivity Error. .. . .,,, .... .. 113


4-26. Frozen Resistivity Error and Maximum Temperature Difference. .. . 114


4-27. Unfrozen Resistivity Error. ........ .. .. .. .. . 115




















LIST OF OBJECTS


objects


3-1. PVC_Cell.jpg .......... ....


3-2. SanipleCell.jpg .......... ....


3-3. ElectrodeSketch.jpg .. .. . .


3-4.Probe.jpg ............... .


3-5. Probe]Bench.j .....


3-6. SampleHolder.jpg .......... ...


3-7. Tower-Laptop.jpg . . .


3-7. DetailedPowerCircuit2Labels.jpg .. .


4-1. Cad3_85xll.jpg ......... ....


4-2. Cad6_85xll.jpg ......... ....


4-3. Caloise3.jpg ......... ,,


4-4. HighVoltageNoise.jpg .. .. .. .


4-5. CyclingAltyher22.jpg ......... .


4-6. Cycl5-13DiffAll.jpg .......... ..


4-7. Wannhyptll.j .....


4-8. UF-Resist-TVC1.jpg .. . .


4-9. UF-Resist-TVC2.jpg .. . .


4-10. UF ResistAll.JPG .......... .


page


............... ............ 15


........................... 16


............. ... .. .. 17


........................... 19


........................... 20


............... .............21


............. .. .. .. .27


. ......... ... .. .. .. .45


........................... 74


........................... 76


...........................79


.. .. .. 80


... ... .. 85


...........................87


........................... 88


............. ... .. .. 90


............. ... .. .. 91


........................... 92











4-11. UF_Resisty_MTDiffAll.jpg .......... . .. . .. .93


4-12. UF_Resisty_MTDiff AllSepl0.jpg . ...... .. ... .. .. .94


4-13. UF-Resisty-All-wFit~jp ......... . ... .. .. 95


4-14. Frozen-Resist-TVC~jpg ......... . ... .. .. 97


4-15. Frozen-Resist-All~jpg ......... . ... .. .. 98


4-16. Frozen_~Resisty_MTDifm21-10.jpg ........ .. ... .. .. 99


4-17. Frozen-Resisty-All-wFit .jpg ......... .. .. .. . .. 100


4-18. ResistyFitsBoth.jpg ............... .......... ........ 101


4-19. OhmicVC.jpg ............... .............. ...., 103


4-20. OhmicTempBoth.jpg ........ . ... . .. .. 105


4-21. O~hmicCurrentTempBoth.jpg ........ .. .. .. .. .. 106


4-22. OhmicResistyAvieTemnpMTD .jpg ........ .. ..... .. . .. 109


4-23. OhmicPowerAp~pCumu.jpg .......... .. .. ... . .. 110


4 -24 ErrorP ercFro zResistyBo0th.jp g ......... .. ...... .. . .. 11 3


4 -2 5. ErrorP ercFro zMTDResisty.jp g ......... .. ...... .. . .. 114


4-26. ErrorPercUnfrozResistyAll.jpg ......... .. ...... .. . .. 115

















Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

DEVELOPMENT OF AN OHMIC THAWING APPARATUS FOR ACCURATE
MEASUREMENT OF ELECTRICAL RESISTANCE

By

Randy Allen Clements

May 2006


Chair: Murat O. Balaban
Department: Agricultural and Biological Engineering

Heating occurs when an electrical current is passed through an object. The

amount of heat generated in the object is dependent on the electrical resistance of the

object. This form of heating is commonly referred to as ohmic heating. The application of

this heat to a frozen object to change the material phase from frozen to unfrozen is ohmic

thawing. The electrical resistance of a food is heavily influenced by temperature. Foods

undergoing thawing commonly exhibit two orders of magnitude decrease in their

resistance. Accurate knowledge of the electrical resistance is vital to practical ohmic

applications in food processing.

This research presents the development of an apparatus for measuring the

electrical resistance of a food item in both its frozen and unfrozen states. A model food

substance was used to illustrate the capabilities of the apparatus. The model food









substance used in this research was a gelatin gel. The electrical resistance of the gel was

measured in both the frozen and unfrozen state. The resistance data for the gel were

converted to resistivity data. The resistivity data for the frozen gel were fitted with a

cubic polynomial (y = -35.9628 x3 + 162.3497 x2 526.1101 x + 67.9648), where y was

the resistivity in ohm-meters and x was the temperature in degrees Celsius, while the

frozen resistivity data were fitted with (y = -0.0004 x3 + 0.0270 x2 1.0960 x + 31.3939).

The fits generated R2 values of0.9977 and 0.9953, respectively. The errors associated

with the data and the fits were discussed and presented. It was shown that temperature

measurement error was an important aspect in the accuracy of the resistivity data

calculated.

This research produced a useful apparatus for measuring an important food

property in the application of ohmic thawing. The research also provided new data in an

area where very little published data exists. This data will prove useful to the food

engineering community for both future comparative and modeling purposes in the further

development of ohmic heating technology.















CHAPTER 1
INTRODUCTION

Low temperature storage of food materials is a common method of food

preservation. The low temperatures used are often in the frozen range of a food product.

These temperatures reduce the activity of microorganisms and enzymes (Baird and

Gressgott 1978). As a result the freezing of foods has been extensively studied. Cleland

and Earle (1984) reported that the published work done with just freezing time prediction

methods has hundreds of contributors. Prediction of freezing phenomenon is important

because the design of commercial processes without this knowledge leaves only laboratory

and pilot scale experiments to make design decisions. These are not eliminated with

predictive abilities, but can be reduced for to a minimum for cost savings (Heldman 1983)

and optimization of process design.

For the purpose of modeling freezing, Singh (1994) reported that there are several

key properties of foods that must be taken into consideration. He listed among these key

properties: density, thermal conductivity, enthalpy, specific heat, and thermal diffusivity.

Singh also reported that there have been several major reviews of reported data on

published literature for some of these properties, as well as a computerized data base for

the published data that he developed in 1993. All of the work on freezing has helped

commercial freezing become a relatively efficient and reasonably understood process for

the food industry.









Hendricks and others (1988) reported that in the past freezing has been more

important than thawing, but due to greater quantities of frozen food receiving further

processing by manufacturers, thawing was gaining more industrial interest. Thawing

operations are not simply inverse freezing operations. Thawing of frozen foods brings

several unique problems that freezing does not exhibit. It also has physical methods that

have no freezing corollary. This research examined one of those methods.

Ohmic thawing uses the electrical resistance of a frozen food product to

volumetrically generate the heat required for thawing within the food product itself, as an

electrical current is passed through the food product. The electrical resistance of the

frozen food product is additional knowledge not required by a freezing process. A direct

result of this included very little published data on a key property needed for predictive

modeling of ohmic thawing. This research developed an experimental apparatus capable

of measuring this key property for a gel in both the frozen and unfrozen states. The

apparatus developed was also capable of performing ohmic thawing. In this second mode

it can gather data simultaneously for time, temperature and resistance that would be useful

for model verif ication of predictive methods to be developed for ohmic thawing.













CHAPTER 2
LITERATURE REVIEW

Traditional Heating

Traditional methods of heating food products involve applying thermal energy to

the surface of the product. The thermal energy is delivered to the surface by direct

exposure to a thermally radiative source or by direct contact with a fluid, gas or solid of

higher temperature. These heat delivery methods account for radiative, convective and

conductive boundary conditions at the food surface. Once the energy is applied the

surface temperature will rise and heat will begin to flow into the product. The energy

transfer now will be governed by thermal conduction. The heat flow can be described by

the following differential equation:

dT (r; t-)
V -k V T(r, t) =p Cp dt (1-1)

In this equation k is thermal conductivity; T is temperature; r is the position vector; t is

time, p is density; C, is specific heat. This equation indicates the limits of the rate of

temperature change in the food product. The thermal conductivity, density, and specific

heat in equation (1-1) are properties mnherent to a given food product. One method of

inducing high rates of temperature change is by using very high temperatures at the

surface. Surface temperatures for food products are limited by thermal sensitivity foods

have in their structural and organoleptic properties. Another method is to reduce the path

for conduction heat transfer. This can be achieved by forcing the food product to have a

shape that presents a very short conduction path. This can be a viable option for certain

liquid food products, but generally not for solid food products.









Volumetric Heating

Volumetric heating does not suffer the same limitations as traditional heating

methods. With volumetric heating the heat source is internal to the food product. The

entire volume of the food is stimulated by an external energy source to produce heat

internally. The external energy can be delivered by electromagnetic waves. These include

high frequency waves, microwaves, and radio waves. These electromagnetic waves would

also include frequencies at which electricity is commercially transmitted and even direct

electrical current.

Microwave

Microwave heating has received the most study and application in relation to

heating food products. Microwave heating requires no direct contact with the food

product, but does require the food product to be enclosed so the microwaves are

contained for human safety. The use of microwaves is limited by how they are absorbed

by the food material. The depth of penetration is limited for microwaves, and water can

preferentially absorb them. The preferential absorption by water has been thought to be a

major cause for localized overheating (Li and Sun, 2002). Localized overheating is

referred to as runaway heating. It is called runaway heating because it has a cascading

effect. The absorption properties tend to increase as the temperature rises, and as a result

even more energy is absorbed by the localized area. This then leads to a greater

temperature rise and absorption properties becoming even more favorable, driving the

local heating process out of control to food damaging temperatures. Control of this

phenomenon when driven by microwaves is very difficult.









Ohmic

Ohmic heating, unlike microwave, requires some type of direct contact with the

food product. Ohmic heating uses electrical energy to drive the volumetric heating

process. In ohmic heating the food product acts as a resistor in an electrical circuit. A

voltage is applied across the food product and a current flows. This can be described by

Ohm's law. Equation 1-2 lists Ohm's law.

V~ = IR (1-2)

In this equation V is voltage; I is current; and R is electrical resistance. True volumetric

heating occurs as the current flows through the food product. Since nearly all the energy

goes into the food as heat from this process, ohmic heating is more efficient than

microwave ( de Alwis and Fryer, 1990c; Li and Sun, 2002).

Historical Overview of Ohmic Heating

The application of ohmic heating to food dates back more than 100 years. One of

the earliest uses cited in the literature was credited to Fowler in 1882 for a device that held

meat or fish in a box with a salt solution containing electrodes (de Alwis and Fryer, 1990c;

Halden and others, 1990). Other food products also saw early work according to de

Alwis and Fryer (1990c), such as liquids in 1897, in can sterilization in 1900 and milk

pasteurization in 1914. The authors also mentioned other early firsts reported in the

literature such as blanching of potatoes in 1951 by Schade. This was the same year that

the authors cited Tanaka and Tanaka as having shared work on attempting the thawing of

frozen meat chunks with little success. Ohmic heating saw interest in the early half of the

20th century, but only saw one brief commercial success with milk pasteurization. In the









opinion of de Alwis and Fryer (1990c) the problems were primarily related to lack of

suitable electrode materials and control systems.

Interest in possible commercial applications of ohmic heating continued into the

1970's. The Ukranian Meat and Dairy Industries Institute was reported in 1972 to have

developed an experimental aseptic line for manufacturing skinless frankfurters using a

combined ohmic and conventional process by Ruchkovski and others, according to de

Alwis and Fryer (1990c). A commercial blanching process required by potatoes before

deep frying was also reported by Electro-food AB and called the OSCO process (de Alwis

and Fryer, 1990c). Successful study of blanching corn on the cob was reported by

Mizrahi and others (1975). He reported the complete inactivation of peroxidase in only 3

minutes with an ohmic process, while the conventional process of using boiling water

would take 17 minutes.

Ohmic heating used for baking was reported to reduce process times by about

60% when compared to conventional methods in 1985 and 1986. These reports were

credited to Danilesko by de Alwis and Fryer (1990c). The late 1980's marked the

beginning of a widespread interest in investigating ohmic heating. The primary catalyst for

this would be work done by the UK Electricity Council Research Centre. A process was

developed for using ohmic heating in continuous sterilization of particulate foods. This

process was licensed to APV Baker who developed it into a commercial system (de Alwis

and Fryer, 1990c).

Following this commercial process development, there has been a great deal of

research into ohmic heating. The bulk of the research has been centered around the

heating of particulate foods. The research has been carried out in several important ways.









The process has been experimentally modeled and examined in a static ohmic cell where

the particulate is stationary. Early work in this area included that of de Alwis and Fryer

(1990a, 1990b) and Zhang and Fryer (1993) at the University of Cambridge in the United

Kingdom. Other early work included that of Sastry and Palaniappan (1992a, 1992b) at

the Ohio State University. The usefulness of studying a static cell related to the

continuous process was further illustrated by later works of Khalaf and Sastry (1996).

This area of research continued through the 1990's as illustrated with work by Davies and

others (1999), as well as work by Fu and Hsieh (1999). The most recent published work

related to using static cells have been by Ye and others (2003) and Zareifard and others

(2003).

The work with static cells relating to processing food particulate has been

accompanied by work with continuous flow. Early research was undertaken by Sastry

(1992) as well as Zhang and Fryer (1994). The work continued through the 1990's as

illustrated with further work by Khalaf and Sastry (1996). The complexities of flow

caused many problems with the early works and many simplifying assumptions typically

had to be undertaken. The gains in understanding from early work and the work done

with static cells, when coupled with the steep decline in computing cost, has led to greater

research interest in the continuous flow process. Work since 2000 includes that of

Benabderrahmane and Pain (2000), Eliot-God~reaux and others (2001a, 2001b), Tucker

and others (2002), and Ayadi and others (2004).

The static and continuous flow research inspired by the APV Baker process also

created other areas of ohmic research. Ohmic heating of a particle in a liquid creates an

enhanced diffusion effect from the particle to the liquid. Some early published work on









this was by Stapley and others (1995) and Imai and others (1995). Further research in the

area would consider how this phenomenon affects hot air drying rates and juice yields of

certain foods (Lima and Sastry, 1999). Further work in drying rates and extraction yields

has continued as reported by Wang and Sastry (2002), Zhong and Lima (2003), and

Lakkakula and others (2004). These ohmic heating applications have no thermal analog,

since the effects are due to the electric field applied and not only the heat generated.

The most important food property when applying ohmic heating is the electrical

resistance of the food product. Before the commercialization of the APV Baker process

little data existed on the electrical resistance values of foods or the inverse value of

conductance. The research related to static and continuous cells would give rise to

research specifically to determine electrical conductivity values for certain food products.

The first published work in the area is Halden and others (1990), which was followed by

Palaniappan and Sastry (1991a, 1991b). Later work would be done with pacific whiting

surimi paste (Yongsawatdigul and others, 1995) and starch gels (Wang and Sastry, 1997).

Work in this area has continued as reported by Fu and Lin (2003) who also has made

measurements on a variety of meats, vegetables, and fruits. Castro and others (2004)

reported on conductivity values for strawberry products, while Shirsat and others (2004)

reported on conductivity values for cuts of pork. The most recent reporting of

conductivity values were related to tylose (sodium carboxy methyl cellulose), which is

used as a food analog for modeling lean beef (Icier and Ilicali, 2005).

Ohmic heating can be applied to thawing of food products. There has been very

little research related to ohmic thawing (Li and Sun, 2002). According to de Alwis and

Fryer (1990c), Rao and Mathen in 1974 reported using ohmic thawing for frozen blocks









of prawns for quick quality checks. Segars and Kasalis were reported to have used ohmic

thawing and heating of precooked frozen casserole items (Naveh and others, 1983; de

Alwis and Fryer, 1990c). Naveh and others (1983) proposed a method applying ohmic

thawing to frozen meat chunks. The method did not have direct contact with the meat but

instead used a carrier fluid that contacted both the meat and the electrodes. Similar

research was credited to Yun and others in 1998 by Li and Sun (2002).

At the University of Florida in 1993 preliminary work on the technical and

economic feasibility of applying ohmic thawing to frozen shrimp was done by Henderson

(1993). The positive findings led to the further work with frozen shrimp blocks. The

electrical conductivity of frozen shrimp and flounder were reported by Luzuriaga and

Balaban (1996). These values were unique because of how little data has been published

on frozen foods. A prototype automated ohmic thawing unit was designed and tested in

1994 (Roberts, 1994; Roberts and others, 1998). The work successfully demonstrated the

technology of thawing frozen shrimp blocks with ohmic heating and automated control.

Ohmic Thawing

Thawing of food products refers to the specific change of state of the water in the

product from a frozen state to unfrozen state. The heating required is generally separated

into sensible and latent heat. The sensible heat is the heat actually associated with

temperature change, and the latent heat is associated with only the change of phase. The

latent heat of food products is high because of their high water content.

Thawing of food products presents several problems. The thermal conductivity of

food products is dependent on temperature. Normally their thermal conductivity is high

when frozen. This is not surprising since most food products have a high water content,









and water has a lower thermal conductivity than ice. Everington (1971) reported that

regarding the thermal conductivity for fish muscle the frozen conductivity was three times

that of the unfrozen conductivity. This means that a food product that undergoes

conventional thawing, where heat is applied to the surface, will develop what is essentially

a layer of insulation. The heat required to thaw the center of the product must pass

through the insulating or thawed layer before reaching an unthawed inner layer of product.

This causes significant problems in trying to rapidly thaw a food product by conventional

heating methods. This problem is further compounded by the fact the specific heat of a

frozen food product will be lower than the unfrozen product. The unfrozen insulation

layer then will not only conduct heat more slowly, but requires more energy to raise the

temperature in this layer.

Rapid thawing has been of interest because uncontrolled slow thawing can negate

the high quality of a food product achieved by controlled rapid freezing and cold storage

(Everington, 1971; Naveh, 1983; de Alwis and Fryer, 1990c). In order to increase the

heat transfer at the surface of the frozen product, water has been commonly used as a

working fluid to thaw meats, fish, egg as well as other food stuffs (Everington, 1971).

Water can leach soluble constituents from the food product (Jason and Sanders, 1962;

Everington 1971; Roberts, 1998). The water used becomes a waste stream that must be

dealt with often at cost to the processor (Henderson, 1993). Water used in direct contact

with a food product must be potable. This can also be a burden to a processor due to cost

and or limited availability (Roberts, 1998). The water temperature has been commonly in

the range of 18 to 21 oC (65 to 70 OF) (Everington, 1971). This can lead to the exterior of









the food product being heated into a range that microbial growth is a problem before the

product can be completely thawed or processed.

Volumetric heating methods offer solutions to thawing problems. Volumetric

heating does not require large amounts of water. It does not raise the surface temperature

of the food product to undesirable levels. This form of heating is more rapid because the

food product's thermal conductivity is not controlling the thawing rate.

The electrical resistance of the food product is the controlling food property for

ohmic thawing. This property also has a dependence on temperature. It changes greatly

as the food product goes from the frozen to unfrozen state for a food product. Frozen

fish muscle wass reported to have a specific resistance that changes by several orders of

magnitude by Jason in de Alwis and Fryer (1990c). A similar finding is reported for

shrimp (Luzuriaga and Balaban, 1996). The drastic change in this controlling property

leads to runaway heating in a fashion very similar to microwave runaway heating. One

difference with ohmic would be that the runaway heating would not be a phenomenon that

could be supported in a single pocket surrounded by frozen material. It would require a

path of unfrozen material or low resistance material from one conducting electrode to

another.

Electrical resistance of a food product is not typically measured directly. The

resistance is normally calculated from knowledge of the voltage and current. In a simple

circuit that contains only a resistor if the voltage and current are measured the resistance

can be calculated from Ohm's Law presented earlier. An important property of a resistor

is that its value is mainly determined by its physical dimensions and the resistivity of the

material of which it is composed (Peebles and Giuma, 1991). The resistance measured by









any experimental set up would be specific to that experimental set up and the food

product's physical dimensions. The resistivity has broader application as it can be applied

to find the resistance of the same food product with different dimensions. The resistance

R for a resistor of constant cross sectional area A, length L, and resistivity pe is written in

equation 1-3 (Peebles and Giuma, 1991).

p eL
R -(1-3)

It is easy to determine from the equation that if resistance is in ohms, length in meters and

area in meters squared, then resistivity will have units of ohm meter. In an experimental set

up that is measuring both the voltage and current simultaneously, it is also very easy to

calculate the power that is applied. The power will simply be the product of the voltage

and the current.














CHAPTER 3
MATERIALS AND METHODS

This research has been considered in two major areas. The first area was the

physical test sample under consideration, and the second area was related to data collection

from the test sample. Items related to the physical test sample included the sample itself

and objects in direct contact with the sample. This also included anything that was used to

control the physical state of the sample. The second area was inclusive of all data

collection hardware and software used. In addition to the two major areas there was a third

minor area related to the physical mounting and interconnecting of the first two.

Several distinct methods were used in this research. Preliminary methods were

considered to encompass the procedures for generating the materials. These included

construction and assembly techniques for custom materials, as well as overall system design

and assembly. Methods also comprised the operational validations, characteristics and

calibration needed by the experimental apparatus before its use.

The experimental use of the apparatus was also considered a method topic. This

included the actual procedures used in data collection, reduction, and visualization. These

varied according to the purpose of the experiment that was preformed by the apparatus.

Physical Test Sample

Gel Type

The physical test sample considered in this study was a simple food gel.

Specifically, it was a unflavored gelatin gel. The gelatin was manufactured by the Knox@









Company (Parsippany, NJ), which was a unit of Nabisco Incorporated. Their standard

retail box package of 28 grams (one ounce) subdivided into four individual unhydrated

packages was procured locally. The average density of the hydrated gelatin gel used in the

research was 1.02 g/cm3. The average percent ratio of the unhydrated product to water

added was 6.6 %. In the unfrozen state it was transparent with some slight yellow

coloring. In the frozen state it was only partially translucent.

Sample Cell

The gel during the experiment was contained in a sample cell. It consisted of

several parts. The major component was the rigid polyvinyl chloride (PVC) cylindrical

housing threaded for end caps on both ends. Insulation layers existed on both the interior

and exterior radial surfaces, as well as on both of the electrode exteriors. The electrodes

were also considered part of the sample cell, since they formed the axial boundaries for the

gel. Temperature probes in the sample were likewise considered a part of the cell, since

they were essentially fixed in place once the gel was formed in the sample cell.

Cylindrical housing

This housing (Figure 3-1) consisted of76.2 mm (3") schedule-40 PVC pipe fittings,

Charlotte Pipe and Foundry Company (Charlotte, NC) part numbers PVC 101 and PVC

105 (http:.//charlottepipe. comn). Both ends were threaded on the interior, with a smooth

walled transition between the threaded areas. The smooth walled transition to the

threading was separated by an interior shoulder. The smooth walled or central region of

the housing had an axial line of 3 holes on each side of a diameter of the housing, that were

equally spaced over that region. This placed the center set at the center of the axial height

of the smooth region with the other two sets halving the remaining half heights. A sketch

of these features can be seen in Figure 3-2.









































Figure 3-1. Cylindrical Housing.
Object 3-1. PVC_Cell.jpg (2.59 MB).

Interior insulation

The insulation on the radial interior of the cell was PermaSealTM by Perma "R"

Products Incorporated (Johnson City, TN ). This insulation was a closed cell insulation

normally used in construction for creating a sill seal. It came in a standard 6.35 mm x

139.7 mm x 15.24 m (1/4"x5.5"x50') white roll. It was sized to fit the gel column height of

the smoothed walled portion of the cylindrical housing. A standard utility knife was used

for the sizing. This insulation was resilient to being compressed, due to its closed cell

nature with relatively large air pockets.


































Top Viewc Side View




Figure 3-2. Sketch of PVC Cell.
Object 3-2. SampleCell.jpg (43 KB).

Exterior insulation

The insulation on the radial exterior of the cell was Great StuffM by Dow Chemical

Company (Midland, MI). It was an expanding foam sealant sold in a pressurized can.

This insulated the radial exterior in the region of the smooth transition between the

threaded regions of the cylindrical housing. It also sealed the close tolerance passages for

the probes that came in through the radial exterior of the cell.

Electrodes

A circular stainless steel electrode rested on each interior shoulder that separated

the smooth interior from the threaded interior. The electrodes were approximately 3.2 mm










(1/8") thick. Each had a 10-24 12.7 mm (V/2") Stainless bolt welded to the backside. This

bolt along with two nuts and two washers, formed the electrical input connector for each

electrode. The front side of the electrode which contacted the sample had a surface finish

consistent with random orbital sanding with a fine emery cloth. Figure 3-3 is a sketch of

the electrode and a picture of the gel contacting surface.

8 Smm
47mm






S081 2 mm










Figure 3-3. Electrode Sketch and Picture.
Object 3-3. ElectrodeSketch.jpg (211 KB).

End caps

Three separate materials were used in series to form the end caps for the cylindrical

housing. The first material in direct contact with the electrode was 19 mm (3/4") thick

foamed polystyrene insulation. The next layer was a 3 mm (1/8") thick 3 ply wood disk.

Contacting the disk layer was a standard threaded plug. The plug was filled with the same

insulating material as the interior of the cell. This provided and effective fill for the plug

that allowed the power conductor to pass through this section. The end of the plug was

drilled to allow passage of the electrical connection.









Probes

The temperature probes were custom made for the experiment. They were

essentially type T thermocouples. The uniqueness of the probes was in the fact that they

were two separate thermocouples bonded together and electrically isolated from one

another. This allowed for two separate temperature measurements to be taken for

essentially one geometric position inside the sample.

The probe has been broken into the following components. The first was a

Omegatite@ 200 ceramic insulator (Omega Engineering, Inc., Stamford, CT, model

number TRM-164116-6) that made up the rigid electrically insulating portion. The

insulator was a cylindrical tube shape, and had two round channels that protected and

electrically isolated the thermocouple wires. The diameter of the tube was 1.5 mm (1/16

in.),while the channel diameters were 0.4 mm (1/64 in.). The published approximate

thermal conductivity was 0.712 W/m K (1.333 BTU/hr it oF).

The second part of the probe was the actual thermocouple junctions. Each junction

consisted of the two thermocouple wires, one a 0.254 mm copper and the other a 0.254

mm constantan (Omega Engineering, Inc. part numbers SPCP-010 and SPCC-010

respectively), wound together and soldered. The solder and wire combination conformed

to the ceramic insulator's exterior diameter. This acted as an end cap on the ceramic

insulator. A sketch of the probe was made in Figure 3-4.

The third part of the probe was the electrical insulation for the exposed portion of

the thermo couples. The electrical insulation was a QuickTite@ super glue by Loctite@

(Avon, OH ). It was a cyanoacrylate type adhesive. Cyanoacrylates have an electrical

resistivity of greater than 10'" Ohm mm, and a dielectric strength of 25 kilovolts per mm.









Probe Length


Probe Tips (Junction)


End View


O O


Figure 3-4. Probe Sketch.
Object 3-4. Probe.jpg (90 KB)

The insulator being an adhesive allowed it to serve a second role as the bonding agent

between the probe tips or end caps. These probe tips were also bonded to the ceramic

insulator with this material.

The last physical part of the probe was the junctions that connected the transmission

leads. Omega part number SMPW-T miniature connectors were used. The female portion

of the two bladed copper-constantan connectors were used on the probe end of these

junctions. The two piece design of the female portion allowed it to be attached directly to

each end of the probe by clamping over the ceramic insulator portion of the probe.


10 X Magnification







20

The probes were also considered to include their assembly bench. This was custom

made to manufacture the probes. The bench rail was an angled piece of aluminum. Figure

3-5 has a sketch of the assembly bench rail. The bench had an open section in its center

allowing for adhesives to be applied to the thermocouple ends. The rail was fastened by

two screws to a pair of small wood blocks cut at 450 angles. These were the bench

foundations and lifted the rail for center access. Small spring loaded clamps were utilized

to bind the probe portions onto the rail interior corner.

Cell Holder

The test cell had a custom holder to make it easier to be moved, and protected its

thermocouple leads during movement. A diagram of the cell holder can be seen in Figure

3-6. It was constructed of wood. The holder had specific features that assisted in the

experiments. The top handle allowed the holder to be easily gripped when the sample was

being moved from the temperature control chamber. The sides had three holes bored in

them to provide for stress relief to the thermocouples when the sample was being moved.

The short legs were utilized to allow the sample holder to rest on its side, when a gel was

being poured. The large opening between the test cell and the handle allowed the sample

to be clamped during freezing. A 304.8 mm (12") Craftsman C style screw clamp was used


3.1 mmlm

08.3~- mm, 08. mm .1m
33.8 mm



21. mm 31 m

Figure 3-5. Probe Assembly Bench Rail.
Object 3-5. ProbeBench~jpg (37 KB).


















To-p View
Front View Side View


Figure 3-6. Sample Cell Holder.
Object 3-6. SampleHolder.jpg (120 KB).

on the cell for clamping purposes. The clamp was considered a part of the cell holder even

though it was only applied during the freezing phase of the experiments.

Temperature Control Chamber

The temperature control chamber was a small chest type freezer, manufactured by

General Electric (Louisville, KY). Its model number was FCM5DMA WH. It had several

features that were very beneficial to the experimental needs. The first feature was an

adjustable thermostat and included a continuous run mode switch. This allowed the

temperature to be cycled on different ranges or simply be taken to the equipmental limit

and held. The front of the freezer also had a drain portal at the bottom center. This acted









as a power lead access point during experimentation. The interior of the freezer was lined

with aluminum. The gasket sealing the top was very flexible and approximately 12.5 mm

(1/2") thick, and 25 mm (1") wide. The flexibility of the gasket allowed for the

thermocouple transmission leads to be routed into the top of the freezer between this

gasket and the lid. The thickness let the freezer maintain its top seal even with the leads in

place.

The chamber also had enough room for thermal dampers. The thermal dampers

were two, one gallon jugs of distilled water. These two gallons when frozen acted as

dampers to rapid temperature changes in the chamber. This allowed for very slow warming

when the freezer was shut off. They also had the added benefit of damping the cycling of

temperature when the freezer is running in a cycling mode.

Power Supply

The primary power supply used was made by STACO Energy Products (Dayton,

OH) type 6020CT-2S. This supply utilized 220 volt AC input to provide variable output

from 0 to 500 volts AC. The power supply for experimental purposes was also considered

to include other facets of providing power to the test cell. These included control of power

through voltage adjustment and current limiting. The leads and plugins required to deliver

the power to the test cell electrodes, as well as, alternative DC power arrangements

possible were other items grouped with the power supply.

Control

Control of applied power to the sample cell had two layers. The first layer was

manually controlled by the operator of the power supply. The second layer was an

automated layer. Both types of control were used any time power was applied to the test

cell.









Manual control

The first layer was the manual breaker switch to the power supply itself that

controled the 220 volt input to the supply system. The output of the power supply also had

a manual breaker switch. These manual controls were combined to give independent on-

off control for both the input to the supply and its variable output voltage. The voltage

output level was set with a manual rotary dial that adjusted the voltage output from 0-

100% of the supply's voltage range.

Automated control

The automated control was applied to the current output of the power supply. A

Crompton meter with two optional attachments was the first part of this control. This

meter continuously monitored the current level and cuts it off above a specified range. It

achieved this by controlling the supply voltage to another relay better suited for the high

voltages used in the experiment. This primary relay was a Crydom D4812 by Crydom

Electronics (San Diego, CA).

The automated control also included a separate test instrument constructed to show

that the control worked correctly. This instrument was a simple light fixture wired to be

plug compatible with the system output plug. The light produced by the resistance bulb

gives visual verification that the manual and automated controls were operating correctly.

Alternative direct current

The power set up was flexible. It allowed for an alternative DC source to be

inserted into the ciruit. This source had only manual control of the voltage. The power

supply for the DC source ws a LBK type 3371C by LBK Electronics. This supply could

provide DC voltages up to the 1200 volt range, but was limited to 60 mA output current.









Leads and plugs

Several leads and plugs were used in the interconnecting of power. The primary

plugs for carrying current to the test sample were three bladed plugs and receptacles. The

power supply side were all receptacles for safety. The lead to the test cell electrodes had a

compatible male plug on one end and insulated ring tongue terminals on the other. There

was also a special lead that was essentially a double ended male plug. This lead was the

bridge for the AC power to the test leads. This bridge when removed allowed a DC lead to

be inserted into the plug. The DC lead had a compatible male plug on one end and banana

plugs on the other for connecting the DC source.

Data Collection Hardware and Software

To ultimately gather useful information, several different forms of data were

collected. These data types were collected by two separate instruments, each with

supporting hardware and software. These supporting parts assisted in signal routing and

conditioning, as well as data reduction and visualization.

Data Acquisition Card

The data acquisition card used in this investigation was a Keithley Electronics

(Cleveland, Ohio) PCI 3107. This was a 16 bit 16 channel PCI card. It was housed in a

Toshiba docking station V plus model number PA2710U. This docking station was where

the Toshiba TecraTM 8000, model number PAT80AU laptop connects. The laptop served

as a controlling interface to the data acquisition card, as well as a storage medium for data

collected by the card.

Interfacing

The Keithley card used a 36 pin D style connector to the external signals to be

sampled. A Keithley model CAB-1284-.5 cable interfaced the connector. The other end of









the cable interfaced with a Keithley model STA36 screw terminal panel. The screw

terminal panel then could be connected to simple wiring that required no special connectors

for interfacing. The wiring connected to the screw terminal was a standard 28 gauge

ribbon wire. The opposite end of the ribbon wire had a 26 pin female connector. This

connector interfaced with the I/O plugs on signal conditioning backplane.

Backplane

The backplane was an Analog Devices Incorporated (ADI) (Norwood, MA) model

5B01 (http://www.analog. comn). This backplane was designed to house plug-in signal

conditioning modules. It also was used as an interface for external signal leads. The

backplane had screw terminal inputs on each of its 16 data lines, which served this purpose.

These lines went through an ADI signal conditioning module or directly to one of the two

26 pin I/O connectors on the backplane.

Signal Conditioning

All of the raw data signals were conditioned before being sampled by the Keithley

card. There were three types of conditioning used. One type was used for temperature

probes. The other two were used for voltage data.

ADI 5B37-T-03 signal conditioning modules provided the temperature signal

conditioning. These modules were specific for T type thermocouples. They were optically

isolating and provided a linearized output from 0-5 volts for their temperature range of -

1000 to +4000 C.

Voltage data were more challenging to condition for reading by the Keithley card.

The range of interest in this investigation was from 0-500 volts. This was far beyond the

card range of 0 to 10 volts. A Crompton 262-30 digital panel meter was used to sample

the raw signal, and gave a visual display of the reading. The Crompton meter had an







26

optional backpack attached that provided a continuous analog current output. This output

was linearly related to an adjustable input range.

The analog output signal was a selectable current range. In this investigation the

industry standard 4-20 mA current output was used. This current signal then must be

converted to a voltage signal that the Keithley card could recognize. This conversion was

handled by using a precision resistor. The resistor was a 250 ohm resistor made by

Precision Resistor Co., Inc. (Largo, Florida) with a stated tolerance of 0.01 percent. This

resistor was connected to the screw terminals of the ADI backplane, where the current

signal was connected. The arrangement rendered a 1-5 volt signal.

Signal Conditioning Housing

The signal conditioning equipment and connections were housed together. This

housing was a converted tower style computer case. The case had an external power

switch, which turned on and off both of the Crompton meters used in this investigation.

The Crompton meters were securely mounted in the former external drive bay area for

clear viewing. Directly below the meters, still in the former external drive bay area, the

Keithley screw terminal was mounted. Only its cable connector was visible from the

outside. Figure 3-7 shows the housing and docking laptop. The ADI backplane was not

visible from the outside. It was mounted internally and positioned like a motherboard.

The housing had five basic points of access used in this investigation. The first was

the Keithley screw terminal connector. The other four were on the back of the case. Three

used a 19 mm (3/4") diameter connector to provide a portal into the case. One of these

three carried the experimental power lead into and out of a Crompton meter. It was not

shielded outside the case, only inside. It ran its interior route inside a 19 mm (3/4")

flexible tubular metal shielding. The power lead for the meters was run with shielding on









the interior, but not the exterior. The thermocouple leads on the other hand were not

shielded inside the case, but were shielded on the exterior. Flexible tubular 19 mm (3/4")

metal shielding was used.

The third line coming into the rear of the case was shielded cabling. It had four

leads. One pair carried the voltage signal to be sampled from the AC power supply. The

other pair of leads carried the control signal for the Crydom relay used for automatic

control of power to the thawing system.

Data Logging Digital Multimeter

Another device used to collect data was a data logging digital multimeter. An

Extech (Waltham, MA) model ML720 was used. It could store up to 43,000 data points.

It featured an infrared communication port, which coul be linked to a PC via the serial port.

This allowed the data to be transmitted after the actual data collection process had ended,

and stored on a permanent basis, elsewhere.























Figure 3-7. Housing.
Object 3-7. Tower-Laptop.jpg (349 KB).









Software

There were three significant ways in which software was utilized in this investigation

related to data. It was used to manipulate, control, and observe the data collection

process. After data collection, software was used to reduce and combine the data, and its

final use was for data visualization. The first two represented mainly custom programming,

while the third relied on commercially available graphics software.

Data collection

A custom written Visual Basic 6 (Microsoft, Redmond, Washington) program was

used to control the data acquisition card. It utilized a DLL driver interface known as

Driver Linx provided by Keithley. The Visual Basic program also converted the raw bit

data into meaningful units of measure. It was responsible for saving all data points in a

comma delimited text file. The program controlled the data collection, manipulated the

data and saved it, while the user saw the data in real time as it was collected.

Another software program was used to collect the alternating current data from the

data logging multimeter. This program was called Bs81-5x Data Logging System. The

software was provided by Extech with the multimeter. The program was used to decode

the data transmission from the data logging digital multimeter. It could also display the

data, and save the data in a standard comma delimited text format or a proprietary format.

Other custom written Visual Basic programs assisted in combining and reducing the

data. One program merged the two separate data files containing voltage and temperature

in the first, and current data in the second. This program created a third synchronized data

file that was further manipulated. These further manipulations, such as resistance

calculations, were preformed by another custom Visual Basic program.









Data visualization

The primary software used in this investigation for the visualization of data was

Axum 6.0 by MathSoft Engineering & Education, Inc. (Cambridge, MA). Axum was used

in preference to a spreadsheet such as Excel by Microsoft or Quatro Pro by Corel Corp.

(Ottawa, ONT, Canada). The inability of either to deal with large data sets for graphing,

was the primary reason for preference given to a dedicated graphing program. Axum was

capable of easily graphing data sets of more than 175,000 points. This size data set was

common in this investigation.

Equipment Cart

For ease of use in investigation, several key components were mounted on an equipment

cart. The cart was the same cart described in Roberts (1994). It was custom made for

that work. It retained its general form, but was modified to fit the needs of this

investigation. As in the original form the cart had the AC power supply mounted under its

top surface. Both of the manual circuit breakers were intact and left positioned as in the

original set up.

The modifications started on the top surface. The signal conditioning housing was

mounted there. It was securely fastened by six screws and washers. A vertical plywood

surface from the original design was used to mount the plugs needed to connect the test

cell. The Crydom relay was mounted inside a plug box here. Female banana jacks for the

Data logging digital multimeter were also located in a separate plug box fastened to this

surface. Another plug box had a female sub D mini 9 pin connector used for connecting

the voltage sampling leads, and the control signal for the Crydom relay. A picture of the

layout can be seen in Figure 3-8.















































Figure 3-8. Box Arrangement.

Only one of the fold down shelves of the cart was utilized during this research.

This shelf provide a working space where the docking station for the laptop and other

miscellaneous items used during experiments were placed. The data acquisition card

housed in the docking station could then be connected by the 0.5 m data cable to the signal

conditioning housing. This also placed the laptop at a convenient height in which to view

and control the processes during data collection.









Apparatus Construction

The construction of the apparatus was broken into the physical elements that make up each

portion of the apparatus. Each element had a number of constraints or characteristics that

had to be adhered to in order to meet the needs of the experimental work. These design

considerations were an essential part of the construction in addition to the actual

construction methods used.

Probe Construction

Design

The temperature probe design reflected the specific needs of the experiment. In the

experiments, the probe had to remain stationary when it was in contact with a liquid. It

also had to maintain its position during phase change related expansion or contraction.

This led to selecting a rigid probe. If the sensor end of the probe were placed inside the

sample, the sensor area at the tip would have had only one support point. The probe

needed to be supported at both ends for greater stability and accuracy in placement. The

support problem was solved by adding another linear section to the probe. This gave the

completed probe two fixed support points as it spanned the diameter of the test cell. The

new linear section also had the opportunity to become a second sensor holder for the same

location. The linear design also aided in determining location of temperature sensor on the

probe in the sample. This design allowed for two independent sensors to gather data at the

same geometric location in the sample cell.

The probes were at times exposed to electric fields on the order of500 volts. Thus,

the probes had to be electrically non-conductive. By selecting a rigid ceramic with two

round channels in it, bare thermocouple wires could be used inside the probe. These bare









wires helped to keep the total diameter of the probe small. The smaller the probe diameter,

the less heat could flow to or from the external environment through the probe which

could have acted as a fmn. The choice of a glass ceramic that had a low thermal

conductivity assisted in reducing this finning effect. Finning by the thermocouple leads

themselves was addressed by using small thermocouple wires in the probes, since the metal

of the wire had a large thermal conductivity.

Assembly

The first step in constructing the probes was to break the ceramic insulator into two

sections. The insulator came in a standard 152 mm (6") length. The length was scored at

one of two positions depending on where the probe was intended to be used. If used as a

center probe, the center of the insulator was scored and broken. If on the hand, it was to

be used as a top or bottom probe the score is made off center. This score location reflected

the approximate half radius length for the sample. By having different lengths, each probe

had approximately the same length that protruded from the sample cell from each different

location that a probe occupied. The breaks were sanded as needed to have a reasonably

flat end.

The next step was to insert the thermocouple wires into the channels of the ceramic

insulator. The clearance was low and care was exercised not to bend the bare leads. The

leads were then be twisted together at the end where the break was initiated. The leads

were soldered together after twisting. This gave a solid probe tip formed from the solder

and thermocouple leads. The shape of the tip at this point of construction was similar to a

tear drop with a flat bottom. The tear drop shape was machined by filing and sanding to

conform to the exterior diameter of the ceramic insulator. Further machining of the axial









direction then flattened the tip and reduced the axial height. The fmnal form of this tip was a

disk at the probe end, or an end cap to the partial probe length.

At this point in the probe construction a special construction bench was used to

finish the probe assembly. The custom construction bench was specifically designed to

allow the probe sections to be assembled in a straight line. The simple geometric relation

that a line is formed if two planes intersect was used. The bench created a line by utilizing

the two perpendicular planes of the rail on the bench. The rail of the bench was where the

probe lengths were placed contacting both planes simultaneously. Thus, the probes lie

parallel to the intersection of two planes, which was a straight line by definition.

Once a probe was in position on the rail, the end caps could be glued, first to

ceramic insulator and then to one another. The bench rail had an open slot to allow access

to the junction between the end caps. This slot kept the adhesive from contacting the

bench and bonding the probe to it. The shallow lip of the rail allowed simple clips to be

applied to the probe. These clips served two purposes. First, they held the probe tightly to

both of the intersecting planes of the rail enforcing the straight line condition. Second, the

clips held the probe so it could not move during the curing process or during later

application of the adhesive.

The adhesive used to bond the end caps to one another was the electrical insulator

between the two separate thermocouple end caps. This electrical isolation was verified by

checking with a digital multimeter for continuity between the leads that protrude from each

end of the probe. After isolation was verified, a layer of adhesive was applied on the

exposed surface of the two bonded end caps. This layer acted as the electrical insulation

for the exposed radial section of the thermocouples. The bench was again instrumental in









holding the probe during this application, and allowed the layer to be applied around the

entire circumference in one application.

The probes were then a straight line double sensor devices with loose wire leads on

both ends. To enhance connectivity of the probes to data acquisition leads, the loose wires

on one end were connected to the male end of a two bladed connector. The two piece

Omega connector physically clamped over the end of the ceramic, where it could be easily

connected to its female counterpart on the data acquisition lead. The fmnal male connector

could not be put in place until the probe was in position in the sample cell.

Sample Cell Construction

Design

The process of designing the sample cell involved identifying the most important

constraints related to the research, and then finding ways to satisfy them. The cell had to

be able to provide the structural rigidity for holding the probes in a fixed position. It acted

as a form, to shape the liquid gel during its phase change from liquid to solid. In addition,

it had to be able to protect the probes during the volume change that the gel undergoes

when being frozen. The cell eliminated alternate electrical paths around the sample it held.

It needed a geometric shape that could be reduced dimensionally from a three dimensional

structure to a two dimensional shape for simpler numerical models. The overall design

required a minimum of machining, with preference given to readily available parts.

The first task in the design was selecting the geometric shape and material of the

sample cell. This shape was also the solid shape of the gel. A simple cylinder was used.

The cylinder provides a three dimensional shape that could be reduced to two dimensions

due to its axisymetric nature. This shape is common in piping, and thus readily available.









PVC piping was readily available as a construction material, and had the additional benefit

of a very high electrical resistance. In standard schedule 40 form, it was very rigid for

short spans, and was easily machined.

The cell was closed on both ends by the electrodes, which directly contacted the

gel. This configuration created a Ex~ed volume cavity for the gel bounded by the electrodes

on the ends. Unfortunately, the gel underwent expansion during freezing on the same order

as that of water during freezing or roughly ten percent, and a rigid cavity would have been

cracked or broken. Additionally, any rigid probe that entered the cavity radially, would

have been sheared if expansion was allowed in the axial direction. The design challenge

was then broken into 2 parts, first to maintain the unfrozen geometry and second to protect

the inserted temperature probes.

One part of the design solution was to make sure the electrodes could be

constrained from moving during the phase change expansion. This then dictated the sample

must undergo expansion only in the radial direction. Since the PVC was rigid, a

compressible layer was added to its interior that allowed for radial gel expansion. This

maintained the basic geometry of a cylinder keeping the original height intact and changing

only the diameter of the sample. It also protected the probes entering radially from

encountering any axial shearing during the phase change expansion.

The last constraints that were satisfied were not as challenging. They included

accounting for how the gel will be poured into the cavity. This required a liquid tight seal

on the axial bottom and radial surfaces. The cell was drilled for the probes and electrical

leads to allow their entry.









Assembly

The first phase in assembly was to create the basic PVC plastic shell. The shell was

made from two standard 76 mm (3") PVC fittings. The first was a female drain, waste and

vent (DWV) fitting. This fitting was female threaded for a standard 76 mm (3") threaded

plug that transitions to a female slip joint. The second fitting was a 76 mm (3") male DWV

adapter. This fitting had a male slip side that transitions to a female thread. The two slip

joints were glued together with a standard PVC glue.

The shell was then modified to accommodate the temperature probes. The center

height for the smooth section was drilled with an 2.41 mm (0.095") diameter bit

perpendicular and in line with the axis of the cylinder. The cylinder was then rotated 1800

and the second center hole drilled. The same procedure was used to drill the two quarter

heights. The three collinear points on each side defined diameters that cross the cylinder's

smooth section at it's axial 1/4 height, 1/2 height, and 3/4 height. In order to insure

accuracy of the placement of the holes, these modifications where preformed by a machinist

on a milling machine.

The shell had two key features now completed. The shell could hold rigid probes in

place at prescribed height locations. It also had a natural shoulder at the transition from

threaded to smooth at each end. These shoulders acted as the defining stops for the

electrodes. The height of the experimental cylinder was now fixed. Figure 3-9 is a picture

ofthe finished shell.

The electrodes had to be held in place. Two separate compression methods were

constructed for this purpose. The first used standard male threaded 76.2 mm (3") drain

plugs. These plugs could be screwed into the ends of the shell. By using a spacer, the plug









could apply an axial force to the electrode. This configuration allowed each electrode to be

independently held in place

Two spacers were used in the research. The first was a simple 51 mm (2") PVC

slip coupling that fitted inside the threaded area. The second spacer was custom made. It

used one inch thick polystrene foam to contact the electrode across its complete surface.

The foam insulation was split into two semi-circles for easy placement and removal. It had

a central hole just large enough to allow the electrical connection to pass through. The

foam required a stiff surface to apply a relatively even load from the end plug to the

electrode beneath the foam. A 76 mm (3") diameter plywood circle was fitted to construct


Figure 3-9. Shell With Ports.









the rigid surface between the end plug and foam. The wood circle was sawed on a radius,

and the center drilled to allow for passage of an electrical lead to the electrode. The

threaded plugs were modified for the electrical lead also. They had a hole drilled in the axial

center that was approximately 10 mm (3/8") allowing passage of the electrical connector.

The second method used a 305 mm (12") cast iron screw style C clamp, and

standard 19 mm (3/4") copper slip couplings. The couplings acted as a spacers to protect

the electrode electrical connectors, when the axial load was applied by the clamp. The

second method allowed the clamping force to be externalized from the shell. It also

allowed the electrodes to be viewed while in the clamped state. However, it did not allow

for the clamping of only one electrode like the drain plug method.

The defined cylinder inside the shell could be fitted with the interior insulation at

any time after the shell construction was complete. The insulation was cut with a utility

knife to dimensions of 254 mm (10") by 49.21 mm (1 15/16"). This was slightly oversized

in both the dimensions of length and width. The extra length helped the insulation form a

tight joint to each cut end as the insulation had to compress slightly to fit in the interior

circumference shell. The extra height did the same for the bottom surface that contacted

the electrode.

The exterior insulation was not placed on the sample cell until it was secure on its

holder. The temperature probes were in place at this time. The expanding foam was

sprayed onto the area corresponding to the central smooth interior area that eventually

contained the sample in the cell. It was allowed to expand in place and seal around the

probes. The foam required eight hours to cure and become stiff.









Sample Cell Holder Construction

Design

Several requirements and conditions were identified that played a role in the sample

cell holder design. The sample cell was not self standing. It required a stand that could

hold it in a fixed position. The required fixed positions were sample cell axis horizontal, or

axis vertical. The cell holder was able to transition from one position to the other without

requiring the sample cell to be removed. The sample cell holder restrained the sample cell

as it moved to and from the temperature controlled chamber. It was desirable for it to be

easily gripped during these transitions. The holder protected the probes from bending

stresses at all times from the thermocouple leads that connected to the data collection

housing.

Assembly

The cell holder was constructed of wood. The layout can be seen in Figure 3-6.

First, the base was cut out of 50 mm x 152 mm (2"x6") spruce. Then, the carriage portions

were cut from 50 mm x 101 mm (2"x4") spruce. The carriage portions were then

positioned centered with respect to the long edge of the base. The space between their

inside edges was set to equal two radial ridges on the exterior of the sample cell. This

created two stops preventing the cell from sliding in its axial direction. The carriage

portions were then fastened to the base by drywall type wood screws. The uprights were

cut from 50 mm x 101 mm (2"x4") spruce. The upright was then centered on the base

short side with its end flush with the base bottom. It was attached in this position to the

base with the same type screws. The handle was cut from 19 mm x 38 mm (3/4"xl-1/2")









spruce. It was centered on top of the upright, flush with the edges, and attached by a

drywall type screw on each end.

The sample cell was then placed in the carriage to determine the height of the

probes. This height was then marked and drilled with identical spacing to the sample cell.

The cell holder then had integral thermocouple lead holes. These 38 mm deep holes

allowed the thermocouple leads to approach the sample cell in a linear fashion. They also

prevented the leads from applying any bending stress on the probes during movement of

the holder when the cell was in place. A picture of the cell holder at this point of

construction was taken (Figure 3-10).

The last parts to be assembled were the horizontal legs. The legs were cut from

craft sticks. The lengths were adjusted to allow the holder to sit level with clearance for

the sample cell, in the horizontal position. Each leg was clearance drilled for the screw that

attached it. A drywall screw with an additional flat steel washer was used to attach each

leg into its position.


Figure 3-10. Sample Holder Picture, Front and Side Views.










Signal Conditioning Housing Construction

Design

The design of the signal conditioning housing addressed several issues. First the

housing acted as an electrical shield for the signal conditioning equipment. The housing

was easy to access. It also provided a convenient manner for viewing the Crompton meter

displays. Easy access to an external power switch for the same meters was also desired,

since they required standard 110/120v input to operate. Overall housing size was impacted

by the need to provide adequate room for mounting the backplane and signal conditioning

modules on the interior. Readily available parts and supplies were given preference to

minimize cost. Construction techniques that required only simple hand tools were given

preference as well.

Assembly

The first part of construction was selecting a suitable match for the general physical

characteristics the housing fulfilled. A tower style computer case was selected. It provided

the required room, shielding, and ease of access. The case was then modified for the

specific needs of the equipment it housed. The interior of the case was cleaned out leaving

only the drive bay substructure and the computer power switch. The top two drive bays

was used to mount the Crompton meters. By being mounting close to the top of the case,

they were easy to view. The exterior covers for the drive bays were removed making room

for the meters. The opening was then closed down in height with metal to match the

mounting cases of the Crompton meters. The exposed area that was previously closed by

metal was now taped over with aluminum tape to improve the exterior appearance. The

meters were then attached to the case via their mounting cases.







42

The Keithley screw terminal was mounted to the bottom of the drive bay section. It

was physically placed on the inside of the case. Two 25 mm (1") self-tapping sheet metal

screws were used to secure it in place. These screws penetrated the bottom of the 133 mm

(5-1/4") drive bays. This screw connection to the drive bay bottom held the connection

point to link the data acquisition transmission cable rigid enough to withstand locking and

unlocking the connector. This protected the interior connection made across the screw

terminal from damage that movement could cause. A drive bay cover was modified by

making a square cut out. The cut out matched the size of the connector for connecting the

screw terminal to its transmission cable. The drive cover was then installed.

Next the ADI backplane was mounted to the computer case siding, where

previously the motherboard and expansion cards had resided. In order to easily

accommodate the fixed mounting points of the backplane, a 508 mm x 203 mm xl6 mm

(20"x8"x5/8") piece of plywood was mounted directly to the interior case wall to provide a

mounting platform. This plywood was positioned and mounted with drywall type screws

through existing holes in the interior case wall. The backplane was then positioned on

plywood without regard to the interior case wall design, which had insufficient height to

accommodate all the mounting points of the backplane. The backplane was secured to the

plywood by seven drywall screws that ran through its integrated standoffs that were in

direct contact with the plywood platform.

Apparatus Wiring

Custom wiring of the apparatus was an integral part of the design. Wiring was

necessary for several reasons. It acted as a conduit for power to be delivered to the

apparatus, and it was needed to deliver the power to the sample through a custom circuit.









The wiring also served to carry signals for control and data sampling purposes. The

backplane utilized also had a certain amount of custom wiring to accommodate the needs

of the apparatus and connecting it to the data acquisition card.

Power

The Crompton meters needed a 120 volt AC power supply. This line was routed

from source to the back of the signal conditioning housing, and upon transition to the

interior, it was cased in an electrically insulating shielding. It ran from there to the power

switch of the computer case, which had been rewired to service the Crompton meters.

Between the power switch and each Crompton meter was an inline replaceable fuse holder

with a one amp fuse. With this wiring set up, an easy to access power switch on the

exterior of the housing was available for turning on and off the Crompton meters, and the

supply to each meter was independently fuse protected.

A 120 volt power bar with an on/off switch was attached to one leg of the

equipment cart. This allowed the cart to have a single point connection for up to six

standard 120 volt plugs. The Crompton meters as well as the laptop computer were

connected here. Devices used with the laptop such as external drives could also be

connected to the power bar. Direct current for experimenting was powered from this

location. The power bar itself had a meter long cord for connecting to an external

extension cord that routes the power from a standard 120 volt outlet.

A higher voltage supply was needed by the experimental sample power supply. It

required a 240 volt source. This was connected with a standard plug at the end of a

flexible lead that was approximately 3 meters long. The lead ran to a I-T-E enclosed

switch made by Siemens (catalog number CNFR-222). This general duty switch was a










plug fuse type. It had an external lift lever and integrated light. This gave the sample

supply a convenient protected on-off switch that indicated visually when power was on to

the power supply. From the enclosure switch the wiring was routed inside a flexible metal

shielding to the power supply itself.

The wiring to deliver power to the sample is shown in Figure 3-11. This diagram

shows the important features of how the power was routed from supply to sample. The

leads for power exited the supply in flexible metal shielding and entered a Square D

(Palatine, IL) heavy duty safety switch (catalog number H-361-N). This 600 VAC 30 amp

switch had an external lever arm for actuation from the open to closed position. The

power leads were then routed from the bottom of this switch enclosure.

The leads were connected to two separate metal outlet boxes mounted to plywood.

The physical layout of the boxes is indicated in Figure 3-8. The top box provided the

connection point for the Crompton meter that acted as an ammeter and current controller.

This lead then exited behind the plywood and was routed into the center box where a

Crydom D4812 solid state relay was mounted. This box had a solid face since the power

did not need to enter or exit the face of the box. The lead then exited the mount side of the

box and was routed to the bottom box. The bottom box made use of the same standard

female plug. This was where the other lead from the Square D switch was routed directly,

and entered from the mount side. This plug now had both power leads connected and was

capable of power supply. In order to facilitate the easy and safe connection of the external

data logging multimeter and the Crompton meter measuring voltage, another series of

three boxes were mounted to the plywood as presented in Figure 3-8. The bottom box had

the same type female plug as the supply. This acted as an input point. A custom male to











Data Loggingl Voltage Current
i311IDMM Panel Meter Panel Meter


Banana
Jumpers



Powver Sourc








U U Cstom umperSafety Switch




Figure 3-11. Detailed Sample Power Wiring.
Object 3-8. DetailedPowerCircuit.jpg (58 KB).

male connector jumper was constructed to route the power out of the lowest right box into

the lowest left box. The leads then exited this box from its mount side.

The leads entered the top left box from the mount side behind the plywood. One

was connected directly to the female connector seen on the box's face, while the other was

connected to a standard female banana jack at the top side of the box. The banana jack

was one of a pair of female jacks on the top of the box. The other of the pair was

connected to the female connector on the front of the box. This gave safe standard

connections for the data logging multimeter via a male to male banana plug jumper that

was used to route one leg of the power leads through the multimeter.

The top left box acted as the interface to the experimental sample leads. The

sample leads were approximately two meters in length. One end had a male connector

compatible with the female connector on the output box mounted to the plywood in the










upper left position on the experiment cart. The other ends of the leads had insulated ring

tongue terminals. These were placed on the electrodes and secured to the bolt connectors.

The ring tongue terminals were small enough to be routed directly through the bottom

drain port of the temperature control unit.

Meters

The two Crompton meters had additional wiring besides what was already

presented. One meter was configured to read the voltage supplied to the sample. The

signal was sampled before it went through the data logging multimeter. A sub D mini 9 pin

connector was used to act as an easy plugin connection. This 9 pin connector had four

active connections, two to carry the voltage signal to a Crompton meter and two to carry a

control signal from the other Crompton meter.

This female side of this connector was mounted in the center left box (see Figure 3-

8). The four leads exited the side of this box. Three leads, two for control and one for

voltage sampling, went to the center right box and entered through its side. Here they

connected to the Crydom relay. The two that completed a Hyve volt circuit connected to

the control terminals on the relay, and the third lead was connected on the voltage output

side of the relay. The fourth lead entered the bottom right box and was connected to the

female output connector where the other leg of the experimental supply attached. The

leads were clamped on exit and entry from the boxes to prevent strain on the connections.

The leads were carried up to the signal conditioning housing via a custom

constructed lead. One end of the lead had the mating male sub D 9 pin mini connector.

The other end of the lead was stripped wires that were connected directly to the

appropriate connection points on the Crompton meters. The lead itself was 32 AWG







47

shielded wire type with four conductors. It ran directly into the signal conditioning housing

via a close tolerance existing hole. The wires were left shielded inside the housing until

very close to the connection points on the Crompton meters. The lead was clamped next

to the interior of the housing to prevent strain on the interior connections from the exterior

portion of the lead.

The Crompton meter responsible for current control was outfitted with a dual relay

pod (262-RLY). This pod had two "change over" relays with a common wiper. The relay

controled a five volt signal provided by the data acquisition card. The wiring connection to

the relays came from the screw terminal panel which interfaced the data acquisition cable

connected to the data acquisition card.

Backplane

The ADI backplane plane had two roles, and wiring specific for each. First, it acted

as the interfacing point for the six thermocouple leads connected to individual channel

screw terminal connectors on the backplane. The number 2 and number 3 connectors of

each set were used on channel positions 5, 7, 9, 11, 13, 15. No further on board wiring

was needed for these channels. They routed through the ADI conditioning module and to

the pin out connector of the backplane.

The second role the backplane was to act as an interfacing point for the analog

output of the Crompton meters. The Crompton meter output was a scaled current and was

converted to a scaled voltage signal. One 250 ohm precision resistor was placed close to

the number 2 and number 3 screw connector on channel 1 and on channel 3 of the

backplane, respectively. The resistor was physically connected to each of the analog

current output leads to complete the current circuit. The connection was made with a wire









twist type connector. Each junction had an extra lead wire also attached that was routed to

one of the screw terminals. Each twist on connector thus had three wires it connected,

with the last one being the voltage sampling lead. Both the lead to the meter and the screw

terminal were 18 AWG insulated copper leads. This configuration placed the sampling

leads on each end of the precision resistor for voltage sampling. Since no ADI module was

in place on the backplane for channels 1 and 3, direct jumpers were installed to route the

signal across the module plug interface. The jumpers were made from 18 AWG wire, and

fit the board female pin connectors designed for 0.0965 mm (0.038") pins. The signal was

then routed by the backplane to the backplane pinout connector.

The backplane had no external connections to the individual input screw terminal

connectors of channels 0, 2, 4, 6, 8, 10, 12, and 14. These channels were each grounded to

the backplane. The grounding connection was made on each channel where an ADI

conditioning module was placed. A jumper was installed on each to accomplish this. The

jumper was again 18 AWG wire connected to the appropriate female pin connectors. This

provided a grounded channel between each of the eight channels that were read by the data

acquisition card.

Screw terminal panel

The backplane pin connector had only 26 pins, and was not pin compatible with the

Keithley data acquisition card. The Keithley screw terminal panel acted as the wiring

interface between the data acquisition card and the backplane. The screw terminal front

had an integral connector specific for the Keithley data acquisition cable. This connector

locked the data acquisition cable into place preventing accidental disconnection of the cable

from the screw terminal. The other end of the screw terminal panel allowed for a screw







49

clamp connection to each of the 36 discreet lines that come via connecting cable from the

Keithley data acquisition card. These screw terminals were used to interface to the

backplane.

The wiring between the backplane and the screw terminal was custom made by the

following process. A section of 40 conductor hard drive cabling (28 AWG flat ribbon

cable) was reduced to 26 lines. A 26 pin clamp on female connector was attached to the

flat ribbon cable. The other end of the ribbon conductor was stripped, separating the

individual conductors. The individual leads were then matched to the appropriate screw

terminal for input to the Keithley data acquisition card.

The screw terminal also acted as the connection point for a pair of 18 AWG

conductors. These were connected to the screw terminals that carried a five volt DC

source from the data acquisition card. These leads were then connected via wire nuts to 2

more 18 AWG conductors providing a wiring split. One side of the split went to the

backplane to power the ADI signal conditioning modules mounted on the backplane. The

interface for the lead on the backplane was a screw terminal on the backplane. The other

halves of the splits routed power to the Crydom sample power relay. As presented in the

previous section, these leads were connected to the control relay on the Crompton meter

that was measuring current.

Experimental Methods

In the course of developing the apparatus several experimental investigations

utilizing various techniques were performed. The methods of data collection will first be

discussed, as they were relevant to all experiments undertaken. Then, the experimental

calibration of the temperature probes is presented. This is followed by the method of gel










preparation used, and the method of determining the gel density. Experiments follow with

some very simple gel freezing trials that later helped to further refmne design decisions.

They also provided information that helped to characterize certain components of the

experimental apparatus and the gel used in the research. Other experiments were designed

to validate certain operational procedures of the equipment.

With the knowledge gained through all the initial experiments, the fmnal experiments

were designed. The fmnal experiments included measuring the electrical resistance of the gel

and making continuous measurements on a gel as it was subjected to ohmic thawing.

Data Collection

Data collection occurred at several locations simultaneously. The primary location

was at the laptop where the voltage and temperature data were collected during an

experiment. The secondary locations included the data logging digital multimeter. The

fmnal location was the laboratory notebook where observational information was recorded.

These methods of collecting data are further detailed below.

Laptop computer

The laptop was running a custom Visual Basic program that utilizes the software

polling capabilities of the Keithley data acquisition card. The program utilized user input to

start the process. Once the process was started the laptop's internal clock was used as the

trigger. The program allowed the user to set how many data points on a single collection

channel were averaged per second by the program. The program then scanned the

channels for the set number of sweeps each second.

The raw data points were averaged and converted to meaningful units. The raw

data were in bits representing a zero to five volt signal measured by the acquisition card.









This signal was conditioned previous to acquisition. The signal conditioning components

scaled and linearized it. The converted and now meaningful data were then written to the

hard drive with a time stamp that the program read from the laptop clock at the beginning

of the polling sequence. The program then waited for the next second to register on the

laptop clock to initiate another collection. This process continued until the user prompted

the program to stop. The number of points averaged per second on all experiments

preformed were 100. The one exception was initial runs with the program.

These initial runs were executed with various numbers of sweeps over the data

acquisition channels. The purpose of these initial data runs were to validate the operation

of the program and refmne the interface. It also aided in finding the limit of how many scans

each second the card, laptop and software combination could be expected to execute. By

making runs with increasing numbers of points to be averaged and observing the time

stamps, the maximum number of scans per second was determined. These observations

additionally indicated an approximate time per scan.

Data logging digital multimeter

The data collected with the logging digital multimeter involved a multi-step

process. The initial step was to set the digital multimeter to the property to be measured.

The rotary dial on the digital multimeter was used for this step. The second step of the

process was setting the data scanning rate for the digital multimeter. This was

accomplished through its integral button and readout interfaces. The rate used was one

reading per second. This rate was used on all experiments utilizing the data logging digital

multimeter. Next, the digital multimeter was triggered by button interface to start










acquiring data. It continued to collect data sequentially till the user prompted it to stop or

it reached 43,000 data points, the maximum storage capacity for the meter.

The data collected resided in the internal memory of the digital multimeter, and

needed transferring to a computer. The transfer was possible by using the digital

multimeter's IR port. A special cable connected the IR port to a computer standard RS232

serial port. A software program written by the digital multimeter manufacturer then

interpreted the incoming signal to the computer's serial port and translated it to a

meaningful data stream. The manufacturer's program was utilized because the transmitted

data stream was non-standard for a RS232 serial connection. The data captured by the

program were saved in several formats including one proprietary to the software and a

simple comma delimited form. The comma delimited form sequentially numbered the data,

which effectively gave a time stamp in seconds referenced to the start of the experiment

with the chosen data collection rate.

Laboratory notebook

The laboratory notebook was important for keeping track of data that were not

being collected electronically. These observations were recorded by pen in a standard

format utilizing the guidelines of Kanare (1985). It also acted as a recorder of all methods

employed and important observations during experiments.

Temperature Probe Calibration

The temperature probes required calibrating to assure the desired degree of

accuracy. The experimental calibration utilized the phase change temperature of water. A

simple experiment design that continuously monitored the temperature of water, as the

water was cooled to its phase change temperature was utilized.









In this experiment the sample cell was assembled with the bottom electrode in

place. The electrode was seated on the bottom shoulder of the sample cell. A coating of

petroleum jelly was applied to the shoulder via a 5ml hypodermic syringe. This ensured a

water tight seal on the bottom surface between sample cell shoulder and electrode. The

electrode was held in place with an end cap spacer combination.

The temperature probes were inserted. The order of the probes with their

respective data names are indicated in Figure 3-12. This arrangement and naming were

consistent for all experiments. After insertion, the exterior clearance area between the

probe and the cell were sealed with petroleum jelly. The same 5 ml hypodermic syringe

was used to deliver the petroleum jelly to the desired region. The probe was now in

position so that the second set of connectors could be attached. The sample cell holder

was prepared for receiving the sample cell by routing the thermocouple transmission leads

through its exterior. The lead pairs were then connected to their respective connectors.

The sample cell was then secured in the sample cell holder, and the connectors were

attached from probe end to transmission lead end.

Sample Top


Chanll3 Chanl5


Chan9 Chanl1


Chan5 Chan7



Sample Bottom


Figure 3-12. Probe Positions and Naming Conventions.









The cell holder was moved to the temperature control chamber. The cell was in an axis

vertical position with its top open. The temperature data collection was started. Deionized

water was added to the cell. The control chamber was closed and the water began to cool.

The temperature was monitored. At phase change the temperature remained constant. The

cell was removed from the chamber at this point and allowed to warm.

The data collection process was stopped. The collected data were copied to a

compact disk. The data were plotted to determine which region represented the phase

change temperature for water. The temperature readings then offset to the actual phase

change temperature.

Gel Preparation

The method of preparing the food gel for each experiment was consistent for all

experiments where the gel was placed in the sample cell. The first step in preparing the gel

was to weigh two of the retail envelopes on a laboratory balance (Ohaus model GT410).

The weights were then recorded in the laboratory notebook. A 250 mL beaker was used to

hold approximately 150 mL of deionized water on a hot plate. A 400 mL beaker was used

to hold another 125 mL of dionized water that was not heated. The 125 mL of water was

measured with a 100 mL graduated cylinder.

The gel envelopes were opened, and the powder poured into the beaker that

contained the 125 mL of room temperature deionized water. The gel powder was left to

absorb the water for approximately two minutes. At the end of the two minutes, 100 mL

of almost boiling hot water from the 250 mL beaker was measured with a graduated

cylinder and added to the gel. The mixture was stirred with a stainless steel spatula, and










placed on an electric hotplate. The stirring was continued till all granules were dissolved,

which occurred in approximately one minute.

The beaker was taken by bare hand from the hot plate. The solution was then

poured into the sample cell to the desired fill level. A separate 30 mL beaker was used to

collect the remaining solution. This additional sample of the gel was covered by Parafilm@

"M". The sample was used later to determine the density of the gel. The liquids then

solidified at room temperature. The last steps weighed the empty gel envelopes and

recorded the weights in the laboratory notebook.

Gel Density Determination

The method for determining the gel density utilized a Quantachrome Instruments

(Boynton Beach, FL) multipycnometer and a laboratory scale. The first step in utilizing the

multipycnometer was to verify its calibration. The small sample cell and two small

calibration balls were used. The volumes of the calibration balls were known. Three

repeated measures were made using the instrument. The measurements were then

compared with the known value. This procedure insured that the operator of the

instrument was using it correctly.

The multipycnometer was ready to determine accurate volumes for samples of the

gel. The gel sample from the 30 mL beaker was uncovered and cut with a coring tool. The

core was weighed on the laboratory scale and the weight recorded in the laboratory

notebook. The core was placed in the small sample cell of the multipycnometer. The

volume measurement by the multipycnometer was repeated six times for each core sample.

Three core samples were taken from each gel sample examined.









The density was calculated from the weight measured by the laboratory scale, and

the volume calculated from the pressure measurements made by the multipycnometer. The

pressure measurements were transferred from the laboratory notebook to a spreadsheet.

The volume calculations using the pressure measurement were done in the spreadsheet to

speed up the repetitive calculations. Ultimately the density calculations were made in the

spreadsheet as well. Having all the calculation in a spreadsheet format allowed comparison

of the data from different gel samples.

Freezing

Experiments in gel freezing helped to characterize the changes the gel underwent in

the solid-solid (unfrozen to frozen) phase transition. The first basic experiment was an

observation experiment. Gel was mixed and poured to form an inch thick slab in a beaker.

The gel was then allowed to transition from liquid to solid. The top of the beaker was

covered with Parafilm slowing water exchange with the surrounding atmosphere. The top

surface of the gel was unconstrained. The gel was placed in a freezer and frozen. The

frozen gel was removed from the freezer and observations recorded on shape. These

observations discussed in Chapter 4, lead to the next iteration of the freezing experiments.

The next iteration was pouring a gel into the sample cell without the internal

insulation. In this experiment the gel top surface was poured even with the upper shoulder,

and covered by the top electrode. The top electrode was in contact with the liquid gel.

The electrode was not constrained other than the shoulder it rested on. This shoulder kept

the electrode from initially sinking into the gel. The gel was refrigerated to speed up the

liquid to solid phase transition. Once congealed the gel was placed in a freezer and frozen.

The sample was removed and observations recorded.









With the observations of the previous experiments for guidance, a new experiment

was designed. The sample cell was fitted with interior insulation. The gel was poured

inside what was the second iteration cell with interior insulation, and the electrode placed

on the top gel surface. The gel was refrigerated to congeal. The only variation at this

point was the new interior insulation.

After congealing the cell was removed from refrigeration. The constraining end cap

on the bottom of the cell was removed. The C-clamp and copper spacers were positioned

to constrain the electrodes in an axial manner. The clamped cell was placed in a freezer to

undergo the solid to solid phase transition. After the gel was frozen, it was removed from

the freezer. The clamp was removed to expose the electrodes. The electrodes were

warmed by tap water to facilitate their release from the frozen gel.

An inertial method was used to extract the frozen sample from the sample cell. In

this method the cell was raised above the laboratory bench top and dropped to it. The

frozen gel and insulation then slid in the axial direction of the cell. Once slippage has

occurred, the gel and insulation easily pushed in the axial direction for removal from the

sample cell. Once the gel was removed the insulation can be pulled away from the radial

surface of the frozen gel.

Observations were recorded, when the electrodes were removed. These

observations primarily record the surface conditions. More observations were recorded

after the insulation was removed from the sample. This set of observations recorded the

condition of the radial edge and overall geometry of the sample. More observations were

taken as the sample was allowed to make the solid to solid phase transition back to the

unfrozen state. The observational emphasis was the overall geometric shape.









A variation of this fmnal freezing experiment was preformed with a set of sample

probes in place. The primary difference in this variation was sample probes positioned in

the liquid gel before it is set. The gel sample now resembled the actual set up that was

utilized for tracking the temperature of the gel sample. Upon removal from the sample cell

by the inertial method, the probes were sheared at the cell wall interface. The design of this

experiment allowed for further observational validation of the freezing geometry, as well as

the effect of the solid to solid phase change on inserted probes.

Environment Characterization

The environmental control chamber interacted with the sample. The interactions

were characterized to help design and control experiments. Several methods were used to

gain insight into how it impacted the sample temperature, and the capabilities of the

chamber.

Continuous Running

The control chamber could be operated in a continuous mode. This mode turned

on the unit's compressor and left it in the running state until it was manually switched back

to a temperature cycling state. This allowed the minimum possible temperature of the

control chamber to be determined. The method employed was to set the chamber into the

continuous run state and monitor its temperature. The chamber was allowed to stay in this

state for at least 12 hours. The temperature inside the chamber was monitored and

recorded. When this method was used with a gel sample, the freezing of the sample

occurred in the minimum time allowable by the equipment. This helped to provide

consistent freezing of different gel samples.










Cycling

The chamber was also operated in a more standard fashion. This was a cycling

mode that automatically turned on the compressor when a high temperature set point was

crossed, then automatically shuts off the compressor when the low temperature set point

was reached. The chamber did not have a precise manner for selecting the upper and lower

set points. It utilized a manual rotary control with numbering for selecting from a range

predetermined by the manufacturer. The numbering of the scale gave reference points from

the lowest cycling temperatures to the highest cycling temperatures and had no units of

measure.

The method for determining the impact of cycling on the gel sample of interest was

straight forward. The temperature of the frozen gel sample was monitored during an

extended time up to 7 hours. These temperatures were graphed. The cycling nature of the

chamber became visible. The prominent features such as magnitude of sample temperature

change and frequency of the changes were extracted. The method used for evaluating the

cycling, also yielded information about probe finning discussed in chapter 4.

Thermal Damping

The final characteristic interaction between the chamber and sample that needed to

be understood was how the sample warms up when the chamber is no longer actively

running in either mode. The method for gaining this information was to track a frozen gel

sample's temperature when the chamber was turned off. This procedure was used to

determine how rapidly the sample warmed.

A second iteration involved increasing the thermal mass inside the chamber. In this

experimental set up 7.5 L (2 gallons) of distilled water in standard 3.75 L (1 gallon) plastic









milk style jugs were frozen in a separate freezer. The frozen water jugs were then placed in

the chamber along with the sample. The freezer was then shut off and the temperature of

the sample tracked. This increased thermal mass acted as a thermal damper. The data

graphed and the impact of the thermal damping determined.

Automatic Power Control Method

Relay set up

A single relay option pack for the Crompton Meter was used for controlling the

maximum current applied to a sample during ohmic thawing. The relay pack was two

relays that utilized a single wiper (See Figure 3-13). The relays were used in series. The

incoming lead carried the 5 volt control signal that attached to connection 1 in Figure 3-13.

The outgoing lead to the Crydom relay attached to connection 5. The first relay was set to

be a low alarm, and the second relay was set to be a high alarm. The first relay had a 5

second delay, and the second had no delay. The relays also had user defined hysterisis.

The low level alarm was set at a 0.05 amps, and the high level alarm was set to 0.4

amps. The hysterisis level on the low alarm was set to coincide with the high level alarm,

and the high level alarm hysterisis was set to coincide with the low level alarm. When the

meter was turned on and no power is being transmitted, the low level alarm was active and

closed the first relay, and it stayed in this state until its hysterisis value was reached. The

second relay was already closed and stayed closed until the high level alarm value was

exceeded. Power could then be applied, and when the high level alarm was tripped the

control signal circuit was broken. The voltage value dropped with both relays in an open

position until the second relay reset at its hysterisis point.










NO = Normally Open
NC = Normally Closed
= lead connector




1 2 34 5



Figure 3-13. Relays.

The low level alarm was activated also, but it had a 5 second delay before it changed state.

The delay from an over current shut down to the applying power allowed the operator to

adjust the voltage to a lower value. This current limitation prevented the power supply

from delivering undesirable levels of power to the sample.

Power control validation

The relay configuration was verified prior to the ohmic experiment runs by the

following method. An incandescent electric light bulb was made wire compatible with the

experimental apparatus output. This allowed the voltage supplied to the light bulb to be

varied, which in turn led to the current supplied to the bulb being varied. The light was

supplied a current that was less than the high alarm state. The current was increased until it

trips the high alarm and shuts off the output. The result was visible both on meter readings

from the Crompton meter and no light being emitted from the bulb. After a five second

delay the system once again supplied power to the light bulb and was verified by both

meter reading and light emission. The system then immediately shut down, because the

voltage was not adjusted to a lower value. During the next five second delay the voltage

was reduced and power did not shut down.









Resistance Measurement

The experimental determination of the sample resistance employed two methods both

used the same equipment. The difference in resistance property magnitudes required a

different approach depending on the physical state of the sample. The first method was

used with the sample in an unfrozen state. The second method was used with the sample in

a frozen state.

Unfrozen sample

The first step was to prepare a gel as discussed previously. Just before the gel was

poured into the instrumented sample cell the data acquisition was started and recorded the

temperature history of the liquid gel as it cools and became a solid at room temperature.

After the gel was poured the second electrode was put into place on the top of the sample.

A small amount of liquid sample formed a bead between the sample cell edge and the

electrode. Then the top of the electrode was covered with a thin layer of gel. This

prevented any dehydration from occurring to the gel located between the electrodes, while

the sample congealed.

Once the gel was set, the top electrode was attached to the power lead and the end

cap put in place preventing the electrode from pulling away from the sample. The bottom

end cap was removed allowing the bottom electrode to be connected to the other power

lead. The instrumented sample with power leads connected was placed into the

environmental control chamber. The sample was ready for thermal conditioning.

The chamber was turned on and two jugs of ice introduced. This was very similar

to the method of thermal damping. The air temperature of the chamber was monitored

with an external temperature measuring device. One device was the multimeter which has










type K thermocouple direct input for temperature monitoring. When it was not available

due to collecting current data, a simple inexpensive thermistor probe was used. These

probes were not calibrated. They showed good agreement between each other when

referenced to the thermocouple probes. Calibration was not required since high accuracy

was not necessary in monitoring the air temperatures.

The chamber was initially cooled to slightly below freezing and then turned off.

The temperature of the sample monitored. The manual cycling of the temperature in the

chamber was continued bringing the sample slowly close to freezing. Once the temperature

was in the desired range then data collection for determining resistance began.

The power supply was set to a predetermined value, with the fmnal manual switch

left open. The multimeter and data acquisition software were started. The power was now

switched on and the temperature readings for the sample monitored. The power was left

on for approximately 30 seconds then switched off. The sample was ohmically heated by

the application of the power, and its temperature rose on the order of 0.50 C during the

power application. The power was then switched off for approximately 30 seconds. This

allowed for internal thermal relaxation of the sample. This cycling was continued until the

temperature difference between probe locations was on the order of 0.20 C.

Once the run finished, the data were downloaded from the multimeter. The

chamber was then thermally conditioned to a new temperature. The new temperature was

chosen to overlap a portion of a previous run. This provided multiple data points at the

same temperature. The general data collection procedure of this method was repeated until

the temperature range of interest was adequately covered.









The resistance was calculated from the collected data. The data were first reduced

by a custom program that detected the edges of each current cycle, and aligned that with

the edge of each voltage cycle. The combined data had the matched voltage and current

values which indicated the resistance. The average temperature versus resistance was

graphed and fitted with a polynomial. The graphing and fitting were done with the Axum

software. A third order polynomial was chosen, with the inverse of the maximum

temperature difference between probes used as a weight for each point. This gave slightly

more weight to points that show closer temperature agreement between all three locations.

Frozen sample

The frozen sample went through the same gel preparation as the unfrozen. After

the unfrozen state measurements were finished, the sample was removed from the

environmental control chamber for freezing preparations. The end caps were first removed

so the electrode connections could be accessed. Then, the electrodes were disconnected to

allow clamping for freezing. The layer of excess gel was removed from the top electrode

during this process.

The simple was ready to be frozen after clamping. The unfrozen sample was placed

in the environmental control chamber set to continuous run mode. The sample temperature

was monitored by the data acquisition system which collected the sample phase change

information. The chamber was turned off when the sample had reached the limiting

temperature of the chamber, approximately -350 C.

The frozen sample was removed and prepared for data collection in the frozen

state. The first step was to reconnect the electrodes to the power supply, and put axial

insulation and end caps in place. The exterior of the sample holder was covered with









additional layers of fiberglass insulation. This was held in place by mesh fiberglass tape

(Figure 3-14). The new configuration was placed back into the freezer. Cycling and

warming data were taken for the new configuration.

Due to the extremely high electrical resistance of the frozen sample it was thermally

conditioned before resistance measurements. This time the conditioning was to warm the

frozen sample to a range of interest that was still below freezing. The thermal damping

method discussed previously was utilized to bring the sample temperature close to -50 C.

This was the starting point in the frozen state for the electrical resistance values.

The high resistance of the frozen state allowed the data to be collected as a single

continuous stream. The warming of the sample in this case was not driven by the ohmic

portion of heating since the total power applied was very low. To maintain this effect as

the temperature warmed, the voltage was reduced one time during the collection. With

close monitoring of the temperature rise of the sample and previous knowledge of the


Figure 3-14. Additional Fiberglass Insulation.









warming, it was possible to take data very close to 00 C without crossing the phase change

boundary of the sample gel. The data collection was stopped at approximately -0.20 C.

The process of cooling the sample was repeated to set up for another data

collection run. The data collected from these runs were analyzed much the same way as

the unfrozen data. A custom program did edge detection to assure alignment of the

voltage and current data points taken with the two different instruments. The combined

data were then used to calculate the resistance values.

The transformed data were then graphed and fitted with Axum software. Again, a

third order polynomial wass used with the same type weighting factors. The weighting

factor was used for consistency between the two sets. The temperature spread between

probes for the unfrozen state experiments were much more than that for the frozen. The

spread on the frozen state experiments were at or below approximately 0.10" C or less, with

the majority of the data showing a spread more on the order of 0.050 C.

Ohmic Thawing

The final experimental method involved collecting data during an ohmic thawing

process. The sample at this point has already undergone resistance measurements in the

unfrozen and the frozen states. The gel preparation and details of those measurements are

discussed in previous sections. At the end of the frozen resistance measurements, the gel

was still frozen in the chamber which was in a cycling mode. The first step was to

thermally condition the sample to the desired temperature range to start the process. The

air temperature was also monitored to bring it close to the sample temperature just before

power was applied to the sample.









The automatic power control was configured to switch the system off if the current

rose above 0.4 amps. The power supply was set to its maximum output, approximately

490 volts AC. The data logging multimeter was connected and set on the milliamp scale in

alternating current mode. This allowed the current to be read initially in hundreds of

milliamps on the four digit display with automatic switch over to milliamps once the

reading exceeded 50 milliamps. The frequency for the logging on the multimeter was set at

one Hertz.

The data acquisition was initiated simultaneously with the software controlled card

and manually controlled data logging multimeter. The system was ready to begin ohmic

heating. The power switch closed to apply power to the sample. The sample temperature

monitored on the screen as it was recorded. Notes were maintained in the laboratory

notebook on the approximate chamber temperature.

The system was allowed to run until the sample has a 0.50 C difference between

temperature measuring points in the gel. The power was manually turned off. The system

was allowed to thermally relax before power was applied again. The power was applied a

second time to approximately the same temperature difference and turned off. The sample

was allowed to relax again just below the phase transition point. Note at this point all

temperatures were reading below the sample phase transition point.

The sample was then powered through the phase transition. Following the phase

transition the automatic power control took over, shutting off the power and a manual tumn

off applied that controlled the power off time. The applied voltage was adjusted to reduce

the power supplied to heat the sample. The sample was taken from the environmental

chamber once it was through the phase transition. This further enhanced the insulated









boundary conditions, since the sample was warmer than the environmental chamber and

was closing in on ambient room temperature. The sample was further heated to slightly

above ambient room conditions following the same cycling of limited power and voltage

adjustments.

The data acquisitions were stopped. The data logging digital multimeter data were

downloaded. The sample was placed back in the environmental control chamber. It was

still a solid gel at this point. The sample was ready to have another round of thermal

conditioning. The conditioning prepared the sample for unfrozen resistance measurement

a second time.

After a second set of unfrozen data was acquired, the sample was ready for physical

examination. The outer layer of fiberglass insulation was removed first. Then the end caps

and associated insulation were removed, so the electrode connections could be taken apart.

The electrodes were then removed from both ends of the sample for photographing. Notes

were made in the laboratory notebook on the physical observations about the gel and the

electrodes contacting it. The collected data were ready for consolidation and reduction.

Software again assisted in further analysis. The results were then graphically displayed.












CHAPTER 4
RESULTS AND DISCUSSION

This research yielded many results. They were grouped with the same structure as

the Materials and Methods chapter.

Data Collection

There were two data collection experiments with results of interest. The first was

determining an acceptable rate for temperature polling and characterizing the data.

Through progressively increasing the polling rate, it was determined that the hardware and

software combination had an upper limit of approximately 500 Hertz for looping the 16

channels. Above this level it was noted that the data taken no longer had sequential

seconds as the time stamp.

From simple division it was deduced, that the loop rate was on the order of 0.002

seconds. Since all experiments were run by averaging 100 loops, each data point

represented a time slice of approximately 0.2 seconds long. Another way of describing the

polling rate was to look at the number of data points that were collected based on each

loop. There were 16 points collected for each loop. This meant that the system collected

1600 points when it polled 100 loops. These were then reduced to 16 averaged points

before recording. The advantage of looking at the number of data points on a single loop

was this gave some insight to collection time capability of a single data point by the

hardware software combination. A single data point took on the order of 1.25 x 10-4 S.

Further, it was observed that the time between consecutive points on the same channel

were equal to the loop time of 0.002 seconds, when 16 channels were scanned, as was the

case in all of this research.










The 16 channels being sampled were ordered specifically to include a grounded

channel between each data channel of interest. Since software polling was being used in all

cases, this gave voltage values of the backplane ground. The advantage of the

configuration was in creating a more flexible data collection device. The Keithley data

acquisition board had a DMA (direct memory access) mode that allowed significantly faster

acquisitions in which the settling time between readings could be enhanced by referencing a

ground before each measurement. The data collection rate based on a per point basis then

could be pushed to the board limit or 100,000 kHz.

The data collection software ran under Windows 98 and exhibited one limitation. It

began to stall after taking a large number of averaged points. The system showed slowing

marked by longer than one second intervals between averaged points. This slowing was

not an issue in the research, because of the high number of points that had to be taken to

see the phenomenon. It was exhibited when the number of looped averages exceeded

approximately 25,000. This translated to almost seven hours of continuous data taking.

All physical phenomena of interest in the experiments took a shorter period to capture.

The cause for the eventual slow down was not determined, as it had no practical impact on

the research.

Temperature Calibration

Theoretical

In any temperature measuring instrument the greatest accuracy is achieved by multi-

point calibration. In this research a single temperature reference point was used. The

theoretical justification for a single point being enough for our purposes was two fold. The









first was the method of temperature measurement used, and the second was the range of

temperatures measured.

In this research the temperature probes were thermocouples. These thermocouples

were not read directly, instead a conditioned output signal was read. Their output signal

was conditioned by the ADI signal conditioning modules. The modules were designed to

specifically condition for T-type thermocouples. The manufacturer's specifications for the

module's accuracy were dependent on several factors. The first was the span of

temperature range for the module's design. The next was a voltage signal reading accuracy

along with the accuracy of a cold junction compensation sensor for each channel. When

the errors were evaluated and the square root of the sum of their squares taken, the order

of magnitude of the error was 0.5 oC. This represented the accuracy expectation with no

further calibration applied. By referencing a known temperature the accuracy was

improved. It was noted from the single point values presented later, that indeed the

modules required an offset of less than the manufacturer's error range.

The main issue was the nonlinearity of the output, which was linearized by the

signal conditioning module. The nonlinearity of the module according to the

manufacturer's specifications was +/- 0.02% of the range. The range during experiments

never exceeded 50 oC from the calibrated point. The nonlinearity was then expected to be

on the order of 0.01 oC. This coupled with the fact that the range of interest in the

research was relatively small, indicated that a single calibration point close to the middle of

the range was sufficient to expect accuracy more on the order of the nonlinearity. This was

coupled with the resolution of the device reading the module and the apparent levels of










noise in the system which yielded a fmnal order of magnitude expected for the temperature

measurement errors.

The calibration of the temperature sensors utilized a classic theoretical problem.

The problem is commonly referred to as the Stephan Problem. It is a simple homogeneous

phase change from liquid to solid. A solution to this one dimensional problem is given in

Carslaw and Jaeger (1959). The solution is referred to as the Neuman solution for the

semi-infmnite problem. The problem maintains the initial surface at x=0 to be at zero

temperature. The rest of the body is initially at a constant temperature above the

substance's melting point. The solution to this one dimensional problem is arrived at by

making an assumption that the position of the phase change surface is proportional to the

square root of time. The authors arbitrarily chose a form that includes the thermal

diffusivity of the solid phase. The solution can be shown to be equivalent to the same

assumption using the thermal diffusivity of the liquid phase. A derivation of this second

form of the solution can be found in Appendix A.

The theoretical problem then inherently is a conduction heat transfer problem. It

allows for different thermal properties in each of the two phases. It assumes the density of

both phases to be the same with no volume changes accounted for.

Experimental

The experimental problem for calibration looked very similar to the theoretical.

The important features were shown in Figure 4-1. This, under ideal conditions, was a one

dimensional heat transfer set up. It was recognized that the data collected with the

experimental apparatus reflected several features that the theoretical solution did not

exhibit. The first was that the physical properties were functions of temperature as well as













Important Features

1. Insulated InstrumentedSample Cell
1 2. Water Fill Covering All Probes
3. Open Top
4. Placed in Enviromental Control Chamber







Figure 4-1. Calibration Setup Features.

phase. The experimental set up also only approximated the ideal boundary conditions that

were represented by the theoretical problem. The upper surface in reality has something

other than a constant temperature boundary condition that drove the heat transfer. The

differences initially looked relatively minor, but due to water's unique properties the

theoretical solution had no comparative value to actual data taken for calibrating the

sensors.

The informative part of a calibration run at first appeared to seek only a

temperature plateau. A visible plateau indicated constant temperature, when in fact there

was energy transfer occurring in the form of cooling. This then yielded a reference point

for the phase change temperature of the liquid in the sample cell. The actual data from a

calibration run were plotted in Figure 4-2.

It was immediately striking that there was a much more complicated system in play

than a simple conduction problem explained. The initial part of the graph showed that all

temperatures were tracking one another very closely. This was explained by the convective

mixing that would have been driven by a process where the liquid upper surface upon







74



Probe Calibration Data











--- ChanS
Chan7
E Chan9
S21 -- Chanl1
--- Chanl3
Chanl5




1000 2000 3000 4000 5000
Elasped Time (Seconds)


Figure 4-2. Probe Calibration Data.
Object 4-1. Cal3_85xll.jpg (174 KB).

cooling becomes more dense and sinks down. Water's maximum density was at 4 OC, so

the convective process was not maintained all the way to the freezing point at 0 OC .

The graph clearly showed that in the area of 4 oC another physical phenomenon was

occurring. The interesting point here was that one could actually see the expected

transition from a convection driven process to a conduction driven process. The cool top

layer became the less dense layer, no longer sinking and causing the natural convection to

occur. This cool layer then rested in place and thermal stratification began when the

primary heat transfer mode was conduction. During the entirety of the research endeavor

several similar calibration experiments were carried out and consistent observations were

made on each of the runs.










The data captured by the experiment also showed another expected phenomenon.

Sub-cooling of the liquid was also apparent. This was yet another physical phenomenon

that the simple theoretical model could not account for, but one was expected to occur.

Following the sub cooling on the graph, there was a plateau where phase transition was

trying to initiate. This area was where the offset numbers for calibration were collected. A

short span of the data was linearly regressed and yielded a slope to verify that it was

virtually horizontal. An average value then was used to calibrate each sensor. The values

arrived at for three calibration runs are listed in Table 4-1.

Table 4-1. Calibration Offset Values.


Calibration Offset Values (oC)

Thermocouple Probe Designation

Calibration Run # Chan5 Chan7 Chan9 Chanl 1 Chanl3 Chanl5

1 0.248 0.319 0.246 0.209 0.472 0.258

2 0.259 0.329 0.260 0.211 0.464 0.272

3 0.263 0.341 0.260 0.216 0.471 0.288

Average Values 0.257 0.330 0.255 0.212 0.469 0.273

Figure 4-3 plotted data collected while the water sample warmed up. The time count

was restarted at zero, when the sample was removed from the temperature control

chamber. It was interesting to note how the warming water showed a physical

phenomenon around same 4 oC point. This time it appeared as if the warming was initiated

from the bottom, since it was the lowest sensors that were showing the warmer

temperatures initially upon leaving the plateau area. This could have been related to the

lack of a perfectly insulated boundary condition applied at the bottom. Coupled with the

fact that on the cooling side the bottom slightly led when convective mode was dominant,




















Can




6 -~ Chan9
Chan11
6- Chanl3

6) 4 -- Cal
2-*




1,000 6,000 11 0001 16,1:000
Elasped Time (Scconds)


Figure 4-3. Calibration Warming Data.
Object 4-2. Cal6_85xll.jpg (157 KB).

the data seemed to indicate that the bottom insulated condition was indeed slightly

imperfect. The insulated condition probably was not the main cause for the leading of the

bottom set in temperature change. In both cases there would have been convection

favoring the bottom being colder in the first case, and warmer in this second case. When

viewing the warming it has to be remembered that the warmer temperature below 4 oC was

actually the more dense water and was expected to be found at the bottom. It was relevant

to note that in both cases the initial part of the data reflected conditions supporting natural

convection, while after crossing the 4 oC mark both tended to support conduction and

stratification in the temperature profiles.









Other factors could have been also influencing the temperature response of the

system. The radial insulated boundary condition could have been playing a role. If there

was heat leakage through this surface, it would have been enhancing to the effects of the

convective heat transfer of the system during periods when natural convection was favored

in the system. The energy level of the water as reflected through the temperature readings

at different depths when all sensors were at the phase change temperature would not have

been expected to be equal. This was due to the fact the energy was being extracted mainly

from the water's top surface. Since the top surface was assumed to have a lower energy

level, that may have also indicated the lowest level of water would have been more greatly

impacted by imperfection of the radial condition, along with any imperfection in the bottom

boundary condition.

Ultimately, when the water reached its maximum density the top driven conduction

process took over. Thermal stratification exhibited was expected as the warmer less dense

water was on the top, and the heat delivered primarily also on the top. The stratification

from the top to middle was greater than what was observed from the middle to the bottom.

This lended support to the insulated boundary conditions having been violated slightly.

The warmer water produced at the side or bottom would have impacted the lower and

upper readings the most. The lowest and highest positions in the water would have been

expected to have their temperatures slightly higher. The center located at the radial origin

would not have been expected to reflect any breakdown of the insulated boundary

conditions unless those break downs were ofa large magnitude relative to the top heat flux

applied. Based on the insulations used on the siding and the bottom this was what one

would intuitively have expected as well.









The calibration data yielded more information than just an offset value for the

sensors. It also gave insight into how complex a real Stephan problem could be involving a

complex fluid such as water. The data also implied that if water was cooled to its

maximum density first there would probably have been a much better approximation to the

theoretical, since thermal stratification would have made the primary mode of heat transfer

conduction. Furthermore, the analogous thawing problem would have run into difficulties,

if the thawing was initiated from the top since once a layer was formed over the ice, the

warmest uppermost layer would initially have been more dense and initiated natural

convection until it reached maximum density temperature for water.

The calibration data gave a first look at the apparent noise in the temperature

measurements. Figure 4-4 took slices of the uncalibrated data in the region of the phase

change temperature. The graphs represented isothermal slices of time temperature data

from three different calibration experiments. The spread of the data on individual channels

(Chan5 Chanl5) was not attributable to changes in temperature and were correlated to

noise in the system. The figure showed that the data looked to be bounded by roughly

+/- 0.04 oC. This represented an apparent noise for the system while it was not undergoing

ohmic heating.

It was important to look at a slice of data while the sensors were in the high voltage

field conditions that were more representative ofohmic conditions. Figure 4-5 plotted a

time slice, when the applied electric field was approximately 500 volts AC. It appeared to

show that the spread attributable to noise was on the same order of magnitude as before.

This time though there was not the luxury of looking at an isothermal time slice.











Calibration One Noise





~04







4,000 4 050 4,100 4 150 4 200
Data Point
06 Cha 06 Ch5
Calibration Two Noise C"7 Calibration Three Noise "






S021 .,A~o

01s
540 55 50 50 50 ,00 400 410 5 ,0
Dat Pon DaaPon

Figre4-. CliraionNose
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average of00points which firher aied pen intn reucn stha eecta noseigna the redigs












4 60 _I Noise Under High Voltage


-4 65-





-4 75 -

0i -4 80-


-4 85 Ca 1


-4 90
60 70 80 90 100 110 120
Time (Seconds)


Figure 4-5. Noise Under High Voltage.
Object 4-4. HighVoltageNoise.jpg (233 KB).

The temperature data were collected by the Keithley data acquisition board in the

form of a linearized voltage that had been scaled from 0 to 5 VDC. It had been noted that

this was also inherently a part of the temperature error since the board converted the

analog signal to a digital one. The Keithley board was a 16 bit board, and therefore could

resolve the signal to 216 Or 65,536 parts. This yielded a volts per bit of roughly 76.3x1 0-6

The linearized oC/V was obtained by dividing the range of the ADI module by its linearized

output range. The linearized oC/V then was 100. The product of the last two quantities

yielded the oC/bit that the card was reading. Carrying out the calculation, this value was

determined to have been 7.62x10-3 OC/bit.

The noise and conversion to a digital signal even when combined linearly were less

than half of the nonlinearity of the module which was 0. 1 oC. Based on these numbers the

calibrated sensors were judged to be of acceptable accuracy for this research.










Experimental Gel

Total Mass Percent

The gel used in the experiment was prepared in a consistent manner each time. The

mass percent of five separate runs involving the gel were recorded in Table 4-2. It could

be seen that the retail packages had a small amount of variation. Since the water used to

hydrate the gel was kept constant, this variation ultimately led to slight variations in the

mass percent of the different gels. The gels fell into a range of 6.1 +/- 0.2% total mass.

Table 4-2. Percent of Total Mass of Gelatin in Gel.

Percent of Total Mass of Gelatin in Gel

Full Packets Empty Packets Net Gelatin Water Gelatin
Samle Mass (Grams) Grams) mL) Percent of Total Mass)
1 16.630 1.544 15.086 225 6.71
2 16.700 1.543 15.157 225 6.74
3 16.380 1.527 14.853 225 6.60
4 16.056 1.607 14.449 225 6.42
5 16.314 1.540 14.774 225 6.57
Aveae: 6.61

Density

The average density for three separate gel preparations was recorded in Table 4-3.

These values were the average values of three core samples from each gel preparation.

Each of the core samples were measured by the multipycnometer a total of 5 times. This

translated to 15 total measurements for each average which consisted of 5 repetitions of 3

different core samples for each of the gel samples. The densities for all samples were in the

range of 1.02 +/- 0.01 g/cm The data results were consistent between gel preparations.

They also compared well to the density of water which made up almost 94% of the gel on a

total mass basis.










Table 4-3. Gel Density.

Gel Density
Measured Density Standard Deviation
Samle Grams/cm3
1 1.014 .003
2 1.024 .003
3 1.019 .004
Aveae: 1.020

Freezing

The freezing experiments were started with a very simple concept and became more

refmned. The refmnements between iterations were due to the observations from each

previous experiment. The freezing experiments are discussed in the order of their iterative

changes, which mirrors the presentation order in the Materials and Methods section.

The first most basic freezing experiment yielded some very important qualitative

results. The unconstrained top surface of the samples did not remain planar. The surface

was observed to fracture and rose unevenly. This was unacceptable for applying a flat

electrode, as well as not exhibiting an ideal geometry. The translucence of the gel was

decreased in the frozen state as well.

Based on these observations an experiment was designed to try to control the top

surface flatness while freezing. The top gel surface was set with the electrode in place.

From this configuration the freezing was initiated from the top surface of the gel. The hope

was that this would have addressed the surface flatness and the geometry issues. The gel in

this case was allowed to rise in the axial direction. The observation when the experiment

was carried out was that while the electrode might remain in contact the geometry had

significantly changed from the unfrozen initial geometry. The top and bottom planes of the

sample which started out parallel were no longer parallel by a significant and visible









amount. It was even noted in some cases the electrode did not stay in complete contact

with the upper surface of the gel.

The expansion in the axial direction was not ideal for rigid probes that were

entering radially into the sample. If only one probe at the center was used the issue might

have been addressed by allowing both the top and bottom planes to have moved during

freezing. A probe in a central plane would not have been expected to move axially. The

goal was to make multipoint measurements, and therefore axial expansion was deemed

unacceptable.

The next iteration of freezing experiments provided several important solutions.

The initial concept was to allow the sample to expand in the radial direction only. This

meant that the top and bottom planes were constrained to be flat and parallel. The known

volume of the sample cell gave an estimate of how much extra volume was needed based

on the expansion that water undergoes during freezing. A suitable compressible material of

an appropriate thickness was chosen to line the inside of the sample cell. This decreased

the sample cell volume and allowed for radial expansion. The rigid outer shell only saw

very minor pressure applied from the compressed lining. The electrode interfaces with the

gel surfaces were expected to stay in complete contact with this arrangement. The probes

were not expected to see any shearing stress as the gel movement was in the probe axial

direction.

The first runs of this new configuration were made with no probes installed. The

initial observations after freezing were that the electrodes maintained their parallel

positions. The frozen gel when extracted from the sample cell holder and unwrapped from

the interior insulation (the compressible material), showed close adherence to the sought









after final frozen geometry. The radial exterior had some slight texturing, where it

conformed to the insulation during the gel setting phase. When the electrode was removed,

it was noted to have maintained contact with the gel. This was expected because the

electrode was initially set into the liquid before it congealed. Other important observations

were made about the gel at this point. The transition back to unfrozen gel proceeded with

very little water loss from the sample. The sample appeared to return to its initial state as a

gel with only very minor visible defects after a freeze and thaw cycle.

The next iteration placed probes in a sample, and subjected the sample to a freeze

thaw cycle. The experiment ultimately sacrificed the probes that were installed. After

freezing, the only way to remove the frozen gel intact was by shearing the probes at the

rigid wall of the sample holder. The probes were then observed from the end view with

both of the electrodes removed. With the sample removed from the sample holder and the

insulation removed, the probes were observed from the radial direction of the sample. The

probes had maintained their positions in the sample.

Environmental Characterization

The environmental chamber used in the experiments had several of its features

characterized. The first was the minimum maintainable temperature. By setting the system

to a continuous run mode overnight and measuring the temperatures inside, it was

determined that the system was capable of cooling to approximately -33 Co. This

temperature was much lower than required for our purposes, but made the system capable

of a greater range of applications for future investigations.

The system was normally operated in a cycling mode. Data for cycling were

captured intermittently during the experimental investigations. One set of representative







































































ture One Cycle 1644-




u,



Chn7 e
hn
ha1



Chnl3 1654-


0 3000 6,000 9,000 12.000 15,000 18,000 21,000
Elasped Time (Seconds)


data were plotted in Figure 4-6. This data showed how the internal temperature for the



sample gel typically varied and approximately how the air temperature varied. The sample


in this data was in exactly the same physical set up as the ohmic experiments discussed


later. All three layers of insulation were in place on the sample holder. The data for the


freezer air temperatures were collected with the digital multimeter and a manufacturer



supplied type K thermocouple which had a much lower temperature resolution than the


sample probes.


The graphs of Figure 4-6 showed the relevant characteristics of cycling. The graph


labeled Temperature Cycling One gave a visual comparison of the two different



temperature cycles. It was interesting to note that while the air temperature typically


0 3,000


6.000 9000 12,000 15,000 18000 21,000
Elapsed Time (Seconds)


1641

1643

9 1645

S16 47

S1649

S1651

1653

1655


Temperature Valley of One Cycle -_ Chan7





I? .~ II Can





,I r



6,550 6,570 6.590 66810 66830 6,650
Elasped Time (Seconds)


Elasped Time (Seconds)


Figure 4-6. Temperature Cycling.

Object 4-5. CyclingAl~lar22.jpg (1471 KB).


Temperature Cycling One --C in
--- Chanl3
Chan1


Temperature Cycling Two


16 30

S1635




16 55





1665









varied about 7 oC over one cycle the gel temperature only varied about 0.1 oC. The

following graph utilized a second Y axis which allowed the gel temperatures to be more

closely observed. The graph labeled Temperature One Cycle contained approximately one

cycle of data for the gel, while the last graph in the figure had the valley section of this

single cycle.

The data for the air temperature were resolved in 1 oC steps, but the cycling

characteristics were still obvious. The data were very useful, as it gave an idea of how the

sample responded to external changes in temperature. Another piece of dynamic

information was observed in the Temperature One Cycle graph. The temperature probes

did not seem to show any significant finning of external heat within the range of the cycling

temperatures. Iffinning were significant, the probes with the least penetration (Figure 3-

12) into the sample would have led in both the cooling and heating. The observation made

though was the probes tracked very closely even with the reversal during cycling from

heating to cooling. The differences between a probe pair were graphed and no trends

appeared (Figure 4-7).

The temperature range of interest for the gel was warmer than the cycling

temperature of the environmental control unit. The temperature of the sample had to be

raised. After the installation of thermal dampers, the temperature change in the air and the

sample inside the unit were tracked. The configuration was again just as it was in the

actual ohmic thawing experiments with all insulation in place. Figure 4-8 shows how the

sample and the chamber interior air conditions varied after the unit was turned off. After

an initial period, the air temperature and sample temperature had approximately the same

slope. When we regressed the linear section, the slope there was determined to be 4.856 x