Copyright Michael Dean Durham. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.

ISOKINETIC SAMPLING OF AEROSOLS FROM
TANGENTIAL FLOW STREAMS

By

Michael Dean Durham

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

UNIVERSITY OF FLORIDA 1978

ACKNOWLEDGEMENTS

This research was partially supported by a grant (Grant Number R802692-01) from the Environmental Protection Agency (EPA)-, and was monitored by EPA's Project Officer Kenneth T. Knapp. I thank them both for their financial support during my graduate work.

I wish to thank Dr. Dale Lundgren and Dr. Paul Urone for the important part that they played in my education. I am especially appreciative of Dr. Lundgren for his guidance, encouragement and confidence. He has provided me with opportunities for classroom, laboratory and field experience that were far beyond what is expected of a committee chairman.

I would like to thank Mrs. Kathy Sheridan for her assistance in preparing this manuscript.

Finally, I wish to thank my parents for their advice and encouragement, and my wife Ellie for helping me through the difficult times.

ii

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS ii

LIST OF TABLES ...............................................

LIST OF FIGURES ................................................ viii

LIST OF SYMBOLS ................................................ xi

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

CHAPTER

I INTRODUCTION AND ISOKINETIC SAMPLING THEORY .............. 1

A. Introduction......................................... 1
B. Isokinetic Sampling Theory ........................... 2

II REVIEW OF THE PERTINENT LITERATURE ....................... 10

A. Summary of the Literature on Anisokinetic Sampling... 10
1. Sampling Bias Due to Unmatched Velocities......... 10 2. Sampling Bias Due to Nozzle Misalignment .......... 17
B. Summary of the Literature on Tangential Flow.......... 23
1. Causes and Characteristics of Tangential Flow ..... 23 2. Errors Induced by Tangential Flow................. 31
3. Errors Due to the S-Type Pitot Tube ............... 35
4. Methods Available for Measuring Velocity
Components in a Tangential Flow Field ............. 41
5. EPA Criteria for Sampling Cyclonic Flow ........... 43

III EXPERIMENTAL APPARATUS AND METHODS ....................... 48

A. Experimental Design.................................. 48
B. Aerosol Generation................................... 51
1. Spinning Disc Generator........................... 51
2. Ragweed Pollen.................................... 53
C. Velocity Determination ................................ 53
D. Selection of Sampling Locations...................... 57
E. Sampling Nozzles..................................... 57

iii

TABLE OF CONTENTS--continued

CHAPTER Page

F. Analysis Procedure..................................... 58
1. For Uranine Particles............................... 58
2. For Ragweed Pollen.................................. 58
G. Sampling Procedure..................................... 59
H. Tangential Flow Mapping................................ 60

IV RESULTS AND ANALYSIS....................................... 65

A. Aerosol Sampling Experiments........................... 65
1. Stokes Number...................................... 65
2. Sampling with Parallel Nozzles...................... 66
3. Analysis of Probe Wash .............................. 66
4. The Effect of Angle Misalignment on Sampling
Efficiencies....................................... 69
5. The Effect of Nozzle Misalignment and Anisokinetic
Sampling Velocity................................... 89
B. Tangential Flow Mapping 102

V SIMULATION OF AN EPA METHOD 5 EMISSION TEST IN A TANGENTIAL
FLOW STREAM ................................................. 117

VI SUMMARY AND RECOMMENDATIONS ................................ 129

A Summary ................................................ 129
B. Recommendations........................................ 134

Table Page I FLOW RATE DETERMINED AT VARIOUS MEASUREMENT LOCATIONS...... 33 II CONCENTRATION AT A POINT FOR DIFFERENT SAMPLING ANGLES..... 34 III EMISSION TEST RESULTS ...................................... 36

IV SIZES AND DESCRIPTIONS OF EXPERIMENTAL AEROSOLS ............ 52

V TABLE OF OBTAINABLE VELOCITIES IN 10 cm DUCT................ 54

VI TYPICAL VELOCITY TRAVERSE IN THE EXPERIMENTAL SAMPLING
SYSTEM ..................................................... 55

VII RESULTS OF SAMPLING WITH TWO PARALLEL NOZZLES ............... 67

VIII PERCENT OF PARTICULATE MATTER COLLECTED IN THE PROBE WASH
FOR NOZZLES PARALLEL WITH THE FLOW STREAM .................. 68

IX PERCENT OF PARTICULATE MATTER COLLECTED IN THE PROBE WASH
FOR NOZZLES AT AN ANGLE OF 60 DEGREES WITH THE FLOW STREAM. 70 X ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER FOR
30 DEGREE MISALIGNMENT ..................................... 75

XI ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER FOR
60 DEGREE MISALIGNMENT ..................................... 77

XII ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER FOR
90 DEGREE MISALIGNMENT ..................................... 80

XIII COMPARISON OF SAMPLING EFFICIENCY RESULTS WITH THOSE OF
BELYAEV AND LEVIN FOR B = 0, R = 2.3 AND R = 0.5........... 92

XIV ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER FOR
R = 2, 8 = 60............................................... 94

V

LIST OF TABLES--continued

Table Page

XV ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER
FOR R = 0.5, 6 = 600....................................... 95

XVI ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER
FOR 0 = 450, R = 2.0 AND 0.5................................ 97

XVII ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER
FOR R = 2, 6 = 300.... ..................................... 98

XVIII ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER
FOR R = 2.1, 6 = 900........................................ 101

XIX LOCATION OF SAMPLING POINTS ................................ 103

XX FIVE-HOLE PITOT TUBE MEASUREMENTS MADE AT 1 DIAMETER
DOWNSTREAM OF THE CYCLONE.................................. 106

XXI FIVE-HOLE PITOT TUBE MEASUREMENTS MADE AT 2 DIAMETERS
DOWNSTREAM OF THE CYCLONE ......... .......................... 107

XXII FIVE-HOLE PITOT TUBE MEASUREMENTS MADE AT 4 DIAMETERS
DOWNSTREAM OF THE CYCLONE .................................. 108

XXIII FIVE-HOLE PITOT TUBE MEASUREMENTS MADE AT 8 DIAMETERS
DOWNSTREAM OF THE CYCLONE .................................. 109

XXIV FIVE-HOLE PITOT TUBE MEASUREMENTS MADE AT 16 DIAMETERS
DOWNSTREAM OF THE CYCLONE .................................. 110

XXV AVERAGE CROSS SECTIONAL VALUES AS A FUNCTION OF DISTANCE
DOWNSTREAM AND FLOW RATE ................................... 112

XXVI S-TYPE PITOT TUBE MEASUREMENTS MADE AT THE 8-D SAMPLING
PORT FOR THE LOW FLOW CONDITION ............................ 118

XXVII S-TYPE PITOT TUBE MEASUREMENTS MADE AT THE 8-DSAMPLING PORT
FOR THE HIGH FLOW CONDITION ................................ 119

XXVIII MIDPOINT PARTICLE DIAMETERS FOR THE 10 PERCENT INTERVALS
OF THE MASS DISTRIBUTION MMD = 3pm a. = 2.13................ 121

vi

LIST OF TABLES--continued

Table Page

XXIX ASPIRATION COEFFICIENTS CALCULATED IN THE SIMULATION
MODEL FOR THE LOW FLOW CONDITION ........................... 124

XXX ASPIRATION COEFFICIENTS CALCULATED IN THE SIMULATION
MODEL FOR THE HIGH FLOW CONDITION .......................... 125

XXXI RESULTS OF THE CYCLONE OUTLET SIMULATION MODEL FOR THREE
CONDITIONS ................................................. 127

XXXII SUMMARY OF EQUATIONS PREDICTING PARTICLE SAMPLING BIAS..... 128

4 The effect of nozzle misalignment with flow stream ....... 7

5 Relationship between the concentration ratio and the
velocity ratio for several size particles ................ 11

6 Sampling efficiency as a function of Stokes number and
velocity ratio........................................... 16

7 Error due to misalignment of probe to flow stream......... 18

8 Sampling bias due to nozzle misalignment and anisokinetic
sampling velocity........................................ 21

9 Tangential flow induced by ducting....................... 25

10 Double vortex flow induced by ducting.................... 26

11 Velocity components in a swirling flow field............. 27

12 Cross sectional distribution of tangential velocity in a
swirling flow field...................................... 29

13 Cross sectional distribution of angular momentum in a
swirling flow field...................................... 30

14 S-type pitot tube with pitch and yaw angles defined ...... 38 15 Velocity error vs. yaw angle for an S-type pitot tube.... 39 16 Velocity error vs. pitch angle for an S-type pitot tube.. 40

viii

LIST OF FIGURES--continued

Figure Page

17a Conical version of a five-hole pitot tube................. 42

17b Fecheimer type three-hole pitot tube ..................... 42

18 Five-hole pitot tube sensitivity to yaw angle ............ 44

19 Fecheimer pitot tube sensitivity to yaw angle............ 45

20 Experimental set up...................................... 49

22 Typical velocity profile in experimental test section.... 56 23 Experimental system for measuring cross sectional flow patterns in a swirling flow stream....................... 61

24 Cyclone used in the study to generate swirling flow...... 62 25 Photograph of the 3-dimensional pitot with its traversing unit. Insert shows the location of the pressure taps.... 63 26 Sampling efficiency vs. Stokes number at 300 misalignment for R = 1 ................................................ 72

27 Sampling efficiency vs. Stokes number at 600 misalignment for R = 1 ................................................ 73

28 Sampling efficiency vs. Stokes number at 900 misalignment for R = 1 ................................................ 74

29 Stokes number at which 95% maximum error occurs vs.
misalignment angle....................................... 83

30 J' vs. adjusted Stokes number for 30, 60 and 90 degrees.. 85 31 Aspiration coefficient vs. Stokes number model prediction and experimental data for 30, 60 and 90 degrees..... 87 32 Predicted aspiration coefficient vs. Stokes number for 15, 30, 45, 60, 75 and 90 degrees........................ 88

ix

LIST OF FIGURES--continued

Figure Page

33 Comparison of experimental data with results from Belyaev and Levin .................................................. 91

34 Sampling efficiency vs. Stokes number at 600 misalignment for R = 2.0 and 0.5 ........................................ 96

35 Sampling efficiency vs. Stokes number at 450 misalignment for R = 2.0 and R = 0.5.................................... 99

36 Sampling efficiency vs. Stokes number at 300 misalignment for R = 2.0 ................................................ 100

37 Cross sectional view of a tangential flow stream locating pitch and yaw directions, sampling points, and the negative pressure region....................................... 105

38 Decay of the average angle 6 and the core area along the axis of the duct........................................... 113

39 Decay of the tangential velocity component along the axis of the duct ................................................ 114

40 Location of the negative pressure region as a function of distance downstream from the cyclone ....................... 116

41 Particle size distributions used in the simulation model... 120

x

SYMBOLS

A. area of sampler inlet
1
A.'- projected area of sampler inlet
1
A area of stream tube approaching nozzle A ratio of measured concentration to true concentration C Cunningham correction factor C. dust concentration in inlet
1
C dust concentration in flow stream

C
r concentration ratio of aerosol generating solution Dd droplet diameter D. inlet diameter D particle diameter K inertial impaction parameter K' adjusted Stokes number

2 stopping distance L undisturbed distance upstream from nozzle n constant R ratio of free stream velocity to inlet velocity s constant V axial component of stack velocity V. velocity in inlet
1

V radial component of stack velocity
r

Vo free stream velocity

xi

V tangential component of stack velocity
t
6, 8', B" functions determining whether particles will deviate from
streamlines

p particle density

- viscosity

angle of the flow stream with respect to the stack axis

6 angle of misalignment of nozzle with respect to the flow stream T particle relaxation time Ap pressure difference

xii

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

ISOKINETIC SAMPLING OF AEROSOLS FROM- TANGENTIAL FLOW STREAMS

By

Michael D. Durham

August, 1978

Chairman: Dale A. Lundgren
Major Department: Environmental Engineering Sciences

A comprehensive analysis of inertial effects in aerosol sampling was combined with a thorough study of swirling flow patterns in a stack following the exit of a cyclone in order to determine the errors involved in sampling particulate matter from a tangential flow stream. Two simultaneous samples, one isokinetic and the other anisokinetic,were taken from a 10 cm wind tunnel and compared to determine sampling bias as a function of Stokes number. Monodispersed uranine particles, 1 to 11 m in diameter, generated with a spinning disc aerosol generator, and mechanically dispersed 19.9 Im ragween pollen were used as experimental aerosols. The duct velocity was varied from 550 to 3600 cm/sec and two nozzle diameters of 0.465 and 0.683 cm were used to obtain values of Stokes numbers from 0.007 to 2.97. Experiments were performed at four angles, 0, 30, 60 and 90 degrees, to determine the errors encountered when sampling with an isokinetic sampling velocity but with the nozzle misaligned with the flow stream. The sampling bias approached a theoretical limit of (1-cos6) at a value of Stokes number between

xiii

1 and 6 depending on the angle of misalignment. It was discovered that the misalignment angle reduces the projected nozzle diameter and therefore effects the Stokes number; a correction factor as a function of angle was developed to adjust the Stokes number to account for this.

Using an equation empirically developed from these test results and using the equations of Belyaev and Levin describing anisokinetic sampling bias with zero misalignment, a mathematical model was developed and tested which predicts the sampling error when both nozzle misalignment and anisokinetic sampling velocities occur simultaneously. It was found that the sampling bias approached a maximum error 1l-Rcos6[ where R is the ratio of the free stream velocity to the sampling velocity. During the testing, it was discovered that as much as 60% of the particulate matter entering the nozzle remained in the nozzle and front half of the filter holder. Implications of this phenomenon with regard to particle sampling and analysis are discussed.

The causes and characteristics of tangential flow streams are described

as they relate to problems in aerosol sampling. The limitations of the S-type pitot tube when used in a swirling flow are discussed. A three dimensional or five-hole pitot tube was used to map cross sectional and axial flow patterns in a stack following the outlet of a cyclone. Angles as great as 70 degrees relative to the axis of the stack and a reverse flow core area were found in the stack.

Using information found in this study, a simulation model was developed to determine the errors involved when making a Method 5 analysis in a tangential flow stream. For an aerosol with a 3.0 pm 1\IMD (mass mean diameter)

xiv

and geometric standard deviation ( ) of 2.13, the predicted concentration was 10% less than the true concentration. For an aerosol with a 10.0 pm MMD and a a of 2.3, a 20% error was predicted. Flow rates determined by the S-type pitot tube were from 20 to 30% greater than the actual flow rate. Implications of these results are described and recommendations for modification of the Method 5 sampling train for use in a tangential flow stream are described.

xv

CHAPTER I
INTRODUCTION AND ISOKINETIC SAMPLING THEORY

A. Introduction

This study deals with the problems of obtaining a representative sample of particulate matter from a gas stream that does not flow parallel to the axis of the stack as in the case of swirling or tangential flow. This type of flow is commonly found in stacks and could be the source of substantial sampling error. The causes and characteristics of this particular flow pattern are described and the errors encountered in particulate concentration and emission rate determinations are thoroughly analyzed and discussed.

The analysis of sampling errors is approached from two directions in this study. One approach involves an investigation of aerosol sampling bias due to anisokinetic sampling velocities and misalignment of the nozzle with respect to the flow stream as a function of particle and flow characteristics. The second part of the study involves an accurate mapping of the flow patterns in a tangential flow system. The information obtained in the two parts of the study will be combined to simulate the errors that would be encountered when making an EPA Method 5 (1, 2) analysis in a tangential flow stream.

1

2

B. Isokinetic Sampling Theory

To obtain a representative sample of particulate matter from a moving fluid, it is necessary to sample isokinetically. Isokinetic sampling can be defined by two conditions: (3) 1) The suction or nozzle velocity, Vi, must be equal to the free stream velocity, Vo; and 2) the nozzle must be aligned parallel to the flow direction. If these conditions are satisfied the frontal area of the nozzle, A., will be equal to the area of the cross section of the flow stream entering the nozzle, Ao (see Figure 1). Thus, there will be no divergence of streamlines either away from or into the nozzle, and the particle concentration in the inlet, C., will be equal to the particle concentration in the flow stream, C .

When divergence of streamlines is produced by superisokinetic sampling, subisokinetic sampling or nozzle misalignment, there is a possibility of particle size fractionation due to the inertial properties of particles. In the case of superisokinetic sampling (see Figure 2), the sampling velocity, V., is greater than the free stream velocity, V Therefore, the area of the flow stream that is sampled, A ', will be greater than the. frontal area of the sampling nozzle, A.. All of the particles that lie in the projected area A.'
1 i
will enter into the nozzle. Particles outside this area but within A
O
will have to turn with the streamlines in order to be collected. Because of their inertia, some of the larger particles will be unable to make the turn and will not enter the sampling nozzle. Since not all of the particles in the sampled area Ao will be collected, the measured concentration will be less than the actual concentration.

33

0 o --

II -Hi rd

0

> H IIE ,

-,-t
3 H

oo 0L

4--4

00 el

Subisokinetic sampling defines the condition in which the sampling velocity is less than the free stream velocity (see Figure 3). In this situation the frontal area of the nozzle, A ', is greater than the sam1
pled area of the flow, Ao. The volume of air lying within the projected area, A.', but outside A will not be sampled and the streamlines will
1 o
diverge around the nozzle. However, some of the particles in this area, because of their inertia, will be unable to negotiate the turn with the streamlines and will be collected in the nozzle. Because some of the particles outside the sampled area A will be collected along with all
0
of the particles within Ao, the measured concentration will be greater than the actual particle concentration.

The bias due to misalignment of the nozzle with the flow stream

is similar to that caused by superisokinetic sampling. When the nozzle is at an angle to the flow stream (Figure 4), the projected area of the nozzle is reduced by a factor equal to the cosine of the angle. Even if the nozzle velocity is equal to the flow stream velocity, a reduced concentration will be obtained because some of the larger particles will be unable to make the turn into the nozzle with the streamlines. Therefore, whenever the nozzle is misaligned, the concentration collected will always be less than or equal to the actual concentration.

For all three conditions of anisokinetic sampling (superisokinetic, subisokinetic and nozzle misalignment), the magnitude of the measured concentration error will depend upon the size of the particles. More specifically it will depend upon particle inertia, which implies that the velocity and density of the particle are also important. Particle

6

U

0

- A .4

v 44 C C >O

/ 4J

.

m

j-4

I -p
00

4J ,

S)

U)

Q-H

uI N 00 I: 0

I I u

la
00 C)

o 0"

H

O 0

H
0..
a Q4

inertia affects the ability of the particle to negotiate turns with its streamline which determines the amount of error. Therefore, in all cases greater sampling errors will occur for larger particles and higher velocities.

Besides determining the direction of the sampling bias, it is

also possible to predict theoretically the minimum and maximum error for a given condition. This can be done by considering what happens when the inertia of the particles is very small (i.e., the particles can negotiate any turn that the streamlines make) and what happens when the inertia of particles is very large (i.e., the particles are unable to negotiate any turn with the streamlines). In the former case of very low inertia, it can easily be seen that since the particles are very mobile they do not leave their streamlines and therefore there will be no sampling bias. In this situation the concentration of particulate matter may be accurately obtained regardless of sampling velocity or whether the nozzle is aligned with the flow stream. Therefore, a minimum error of 0 is obtained for small inertia particles.

The maximum error that can theoretically occur in anisokinetic sampling depends on both the velocity ratio R, where R = Vo/Vi (1)

and the misalignment angle 8.

In the case of unequal velocities for very high inertia particles which are unable to negotiate any change of direction, only those particles directly in front of the projected area of the nozzle, Ai, will enter the nozzle regardless of the sampling velocity. Therefore,

9

the concentration collected by the nozzle will be equal to the number of particles entering the nozzle, AiV C divided by the volume of air sampled, A.V..
11
A.V C C V
C. 100 00 2
i A.V. V.
11 1

The ratio of the sampled concentration to the true concentration then is equal to the inverse of the velocity ratio. Therefore, the maximum sampling bias for the condition of unmatched velocities is equal to Vo/Vi or R. For example, if the sampling velocity is twice the free stream velocity, the resulting concentration will be one half the actual concentration.

For the case of a misaligned nozzle, a similar analysis is applied. For the particles with very large inertia, only those lying directly in line with the projected frontal area of the nozzle will be collected. The measured concentration would again be the number of particles collected in the nozzle, A.cosCoV o' divided by the volume of air sampled, A.V.. Therefore, the ratio of the measured to the true concentration
1 1
would be V cos9/V. or Rcos6. This represents the maximum sampling
0 1
error for anisokinetic sampling.

CHAPTER II
REVIEW OF THE PERTINENT LITERATURE

A. Summary of the Literature on Anisokinetic Sampling

1. Sampling Bias Due to Unmatched Velocities

Numerous articles have been written describing the sources and magnitude of errors when isokinetic conditions are not maintained. In one of the earlier works, Lapple and Shepherd (4) studied the trajectories of particles in a flow stream and presented a formula for estimating the order of the magnitude of errors resulting when there is a difference between the average sampling velocity and the local free stream velocity. Watson (5) examined errors in the anisokinetic sampling of spherical particles of 4 and 32 im mass mean diameter (MMD) and found the relationships shown in Figure 5. Superisokinetic sampling (sampling with nozzle velocity greater than the free stream velocity) leads to a concentration less than the actual concentration. while subisokinetic sampling has the opposite effect. Watson found that the magnitude of the error was not only a function of particle size as seen in Figure 5, but also of the velocity and the nozzle diameter. He proposed that the sampling efficiency was a function of the dimensionless particle inertial parameter K (Stokes number) defined as

TV
K = Cp V D 2/18D 0 (3) p 0op i D.

10

0
4

u H

-,

o

u )
J

CN O Srd
O O

H

2. 4-4

Sco ,-Pu

r.)

0 U \ Hic

12

where

D = particle diameter

C = Cunningham correction for slippage

p = particle density

T = p CD p/18 (4)
p p
p = viscosity of gas D. = nozzle diameter
1

The relaxation time is defined as T; it represents how quickly a particle can change directions. Watson concluded that to obtain a concentration correct within 10%, the velocity ratio R must lie between 0.86 and 1.13 for the 32 micron particles and between 0.5 and 2.0 for the 4 micron particles.

Data obtained by Dennis et al. (6) on a suspension of Cottrell precipitated fly ash, 14 m N ID, showed only a 10% negative error in calculated concentration for sampling velocities 60% greater than isokinetic. Tests run on an atmospheric dust of 0.5 mj m NID produced no detectable concentration changes even while sampling at a 400% variation from isokinetic flow, thus indicating that isokinetic sampling is relatively unimportant for fine particles. Hemeon and Haines (7) measured errors due to the anisokinetic sampling of particles in three size ranges (5-25, 80-100, and 400-500 pm) and in a range of nozzle to stack velocities of 0.2 to 2.0. They found that where the velocity ratio R ranges from 0.6 to 2.0 the extreme potential error was approximately 50%, and that deficient nozzle velocities resulted in greater errors than excessive nozzle velocities. In addition, they found that for the coarse particles, the velocity into the nozzle had no important

13

bearing on the quantity of dust collected. They suggested using the product of the nozzle area and the stack gas velocity approaching the nozzle as the gas sample volume, regardless of the velocity of the nozzle. By using this method for particles greater than 80 ym, it is possible to obtain small deviations even where departure from isokinetic velocity is quite large. Whiteleyand Reed (8) also observed that calculating the dust concentrations from the approach velocity instead of the actual sampling rate produced only slight errors when sampling anisokinetically for large particles.

Lundgren and Calvert (9) found the sampling bias or aspiration

coefficient A, to be a function of the inertial impaction parameter K and the velocity ratio R. They developed a chart which can be used to predict inlet anisokinetic sampling bias depending on both K and R. Badzioch's (10) equations defined the dependence of the efficiency upon particle inertia and the velocity ratio. In a slightly different terminology

A = Ci/C = 1 + (R-l) B(K) (5) where B(K) is a function of inertia given by

B(K) = [l-exp (-L/R)]/(L/Z) (6) k is the stopping distance or the distance a particle with initial velocity 1V will travel into a still fluid before coming to rest and
0
is defined by (11)

Z = TV (7)
0

14

L is the distance upstream from the nozzle where the flow is undisturbed by the downstream nozzle. It is a function of the nozzle diameter and is given by the equation:

L = nD. (8)
1

It was observed that n lies between 5.2 and 6.8 (10).

Flash illumination photographic techniques were used by Belyaev and Levin (12) to study particle aspiration. Photographic observations enabled them to verify Badzioch's claim that L, the undisturbed distance upstream of the nozzle, was between 5 to 6 times the diameter of the nozzle. They examined the data of previous studies on error due to anisokinetic sampling and concluded that the discrepancy between experimental data was due to the researchers failing to take into account three things: 1) particle deposition in the inlet channel of the sampling device; 2) rebound of particles from the front edge of the sampling nozzle and their subsequent aspiration into the nozzle; and 3) the shape and wall thickness of the nozzle. They also found that the sampling efficiency was a function of the inner diameter of the nozzle, Di, as well as K and R.

In a more recent article, Belyaev and Levin (13) examined the

dependence of the function B(K), in equation (4), on both the inertial impaction parameter, K, and the velocity ratio, R. Previous authors (10, 14) had concluded that 3(K) was a function of K alone, but Belyaev and Levin obtained experimental data demonstrating that for thin-walled nozzles, 3(K) was also a function of R. Equations were developed from the data for values of K between 0.18 and 6.0 and for values of R between

0.16 and 5.5

3(K,R) = 1 1/(1 +bK) (9) where

b = 2 + 0.617/R (10) Figure 6 shows a plot of equations (5), (9) and (10) for a range of velocity ratios and Stokes numbers. The most significant changes in the aspiration coefficient occur at values of K between 0 and 1. Beyond K = 1, the aspiration coefficient tends to assymptotically approach its theoretical limit of R. Beyond a Stokes number of about 6, it can be assumed that the aspiration coefficient equals R. This can be predicted both from equations (5), (9) and (10) and from theoretical considerations. Badzioch (10) and Belyaev and Levin (12) have shown that the streamlines start to diverge at approximately 6 diameters upstream of the nozzle. Therefore, a particle traveling at a velocity,Vo, will have to change directions in an amount of time equal to 6Di/Vo. If a particle cannot change direction in this amount of time, it will not be able to make the turn with the streamline. Since T represents the amount of time required for a particle to change directions, setting T = 6D /Vo represents the limiting size particle that will be able to make a turn with its streamline. Rearranging these terms it can be seen that this situation occurs when TV /D = 6 or at a Stokes number of 6.

Martone (15) further confirmed the importance considering free

stream velocity as well as particle diameter when sampling aerosols by

16

iI

n D Ln
CDCD In r- iN C O

(N o a 0 0
CJ

', C4)
O.
o

C:)

Z c 0 0

C 1)
O

0, o

(N D C)

oJ

TJJ U .

17

analyzing concentration errors obtained while sampling submicron particles, 0.8 vm NMD and 1.28 geometric standard deviation, traveling at near sonic and supersonic velocities. He obtained sample concentrations 2-3 times greater than the true concentration when the sampling velocity was 20% of the free stream velocity (R=5).

Sehmel (16) studied the isokinetic sampling of monodisperse

particles in a 2.81 inch TDduct and found that it is possible to obtain a 20% concentration bias while sampling isokinetically with a small diameter inlet probe. Results also showed that for all anisokinetic sampling velocities, the concentration ratios were not simply correlated with Stokes number.

2. Sampling Bias Due to Nozzle Misalignment

Sampling error associated with the nozzle misalignment has not been adequately evaluated in past studies because the sampled flow field was maintained or assumed constant in velocity and parallel to the duct axis. The studies that have been performed on the effect of probe misalignment do not provide enough quantitative information to understand more than just the basic nature of the problem. Results were produced through investigations by Mayhood and Langstroth, as reported by Watson (5), on the effect of misalignment on the collection efficiency of 4, 12 and 37 vm particles (see Figure 7). In a study by Glauberman (17) on the directional dependence of air samplers, it was found that a sampler head facing into the directional air stream collected the highest concentration. Although these results coincide with

18

1.0

S0.8

E-
H

0.6
z 0

12m
z 0.4

12 p m

0.2

37 lpm

0 30 60 90 120 ANGLE OF PROBE MISALIGNMENT, degrees Figure 7. Error due to misalignment of probe to flow stream [after
Mayhood and Langstroth, in Watson (5)1.

19

theoretical predictions (i.e., measured concentration is less than or equal to actual concentration and the concentration ratios decrease as the particle size and the angle are increased), the data are of little use since two important parameters, free stream velocity and nozzle diameter, are not included in the analysis.

Raynor (18) sampled particles of 0.68, 6 and 20 im diameter at wind speeds of 100, 200, 400 and 700 cm/sec with the nozzle aligned over a range of angles from 60 to 120 degrees. He then used a trigonometric function to convert equation (5) to the form

A = 1 + B(K)[(Visin6 + V cose)/(V.cos6 + Vo sine) 1] (11)

This function only serves to invert the velocity ratio between 0 and 90 degrees and does not realistically represent the physical properties of the flow stream. In fact, equation (11) becomes unity at 45 degrees regardless of what the velocity ratio or particle size is. This cannot be true since it has been shown that the concentration ratio will be less than unity and will decrease inversely proportional to the angle and particle diameter.

A more representative function can be derived in the following

manner: Consider the sampling velocity V. to be greater than the stack
1
velocity V Let A. be the cross sectional area of the nozzle of diameter
o 1
D.. The stream tube approaching the nozzle will have a cross sectional
1
area A such that
0

A V = A. V. (12)
0 0 1 1

20

If the nozzle is at an angle e to the flow stream, the projected area perpendicular to the flow is an ellipse with a major axis D., minor axis D.cos6, and area (D i cos6)/4. The projected area of the nozzle
I i
would therefore be A.cos6 (see Figure 8). It can be seen that all the
1
particles contained in the volume V A.cose will enter the nozzle. A O 1
fraction 5'(K,R,6) of the particles in the volume (A A cosB)V will leave the stream tube because of their inertia and will not enter the nozzle. Therefore, with C defining the actual concentration of the
o
particles, the measured concentration in the nozzle would be

C A.cos6V + [1-B'(K,R,e)](A -A.cos6)Vo C
C. (13) A.V.
1 1

Using equations (1) and (12), this may be simplified to

A = Ci/C = 1 + (K,R,e) (Rcos-1l) (14)

B'(K,R,8) would be a function of both the velocity ratio R and the inertial impaction parameter K as shown by Belyaev and Levin (13). However, $' will also be a function of the angle 8 because as the angle increases, the severity of the turn that the particles must make to be collected is also increased.

It can be seen that for large values of Stokes number, 8' must approach 1 for the predicted concentration ratio in equation (14) to reach the theoretical limit of Rcos6. The maximum error should theoretically occur somewhere between a Stokes number of 1 and 6 depending on the angle

8. The upper limit of K = 6 would be for an angle of 0 degrees as described earlier in this chapter. The theoretical lower limit of K = 1

21

CQ) <0

4J)

C)

-C)

C)

22

would be for an angle of 90 degrees in which case the particles would be traveling perpendicular to the nozzle. Since the nozzle has zero frontal area relative to the flow stream, any particle that is collected must make a turn into the nozzle. The amount of time that a particle has to negotiate a turn is the time it takes the particle to traverse the diameter of the nozzle, or Di/V Setting this equal to T the time it takes a particle to change directions and rearranging terms, we obtain TV /D. = 1 as the limiting situation for a particle to be able to
O 1
make a turn into a nozzle positioned at a 90 degree angle to the flow stream. For angles between 0 and 90 degrees the maximum error will occur between the limits of Stokes numbers of 1 and 6 and should be proportional to the average diameter of the frontal area of the nozzle. Fuchs (19) suggests that for small angles the sampling efficiency will be of the form

A = 1 4 sin(6K/7) (15) Laktionov (20) sampled a polydisperse oil aerosol at an angle to the flow stream of 90 degrees for three subisokinetic conditions. He used a photoelectric installation to enable him to determine the aspiration coefficients for different sized particles. From data obtained over a range of Stokes numbers from 0.003 to 0.2 he developed the following empirical equation:

0.5
A = 1 3K(Vi/Vo) 0.5 (16) This equation can be used only in the range of Stokes numbers given and for a range in velocity ratios (R) from 1.25 to 6.25.

23

A few analytical studies in this area have also been published. Davies' (14) theoretical calculations of particle trajectories in a nonviscous flow into a point sink determined the sampling accuracy to be a function of the nozzle inlet orientation and diameter, the sampling flow rate and the dust particle inertia. Vitols (21) also made theoretical estimates of errors due to anisokinetic sampling. He used a procedure combining an analog and a digital computer and considered inertia as the predominant mechanism in the collection of the particulate matter. However, the results obtained by Vitols are only for high values of Stokes numbers and are of little value for this study.

B. Summary of the Literature on Tangential Flow

Although anisokinetic sampling velocity is known to cause a

particle sampling bias or error, there are also several other sampling error-causing factors such as: duct turbulence; external force fields (e.g., centrifugal, electrical, gravitational or thermal); and probe misalignment due to tangential or circulation flow. These factors are almost always present in an industrial stack gas and cannot be assumed to be negligible. Not only do these factors cause sampling error directly but in addition, they cause particulate concentration gradients and aerosol size distribution variations to exist across the stack both in the radial and angular directions.

1. Causes and Characteristics of Tangential Flow

Tangential flow is the non-random flow in a direction other than that parallel to the duct center line direction. In an air pollution

24

control device, whenever centrifugal force is used as the primary particle collecting mechanism, tangential flow will occur. Gas flowing from the outlet of a cyclone is a classic example of tangential flow and a well recognized problem area for accurate particulate sampling. Tangential flow can also be caused by flow changes induced by ducting

(22). If the duct work introduces the gas stream into the stack tangentially, a helical flow will occur (see Figure 9). Even if the flow stream enters the center of the stack, if the ducting flow rate is within an order of magnitude of the stack flow rate, a double vortex flow pattern will occur (see Figure 10).

The swirling flow in the stack combines the characteristics of vortex motion with axial motion along the stack axis. The gas stream moves in spiral or helical paths up the stack. Since this represents a developing flow field, the swirl level decays and the velocity profiles and static pressure distributions change with axial position along the stack. Swirl level is used here to represent the axial flow or transport rate of angular momentum (23). Velocity vectors in tangential or vortex flows are composed of axial, radial and tangential or circumferential velocity components (see Figure 11). The established vortex flows are generally axisymmetric but during formation of the spiraling flow the symmetry is often distorted. The relative order of magnitude of the velocity components varies across the flow field with the possibility of each one of the components becoming dominant at particular points (24).

25

Z

CL
w I

0

-j
LL

b.

r
0

26

z

F
C)0

c~)

-C)

-C)

-C) C)
U C) 'C)

0

x

C)

0 C)

-C) C)
0
0

- 0
-I
0 C) F-

27

Vr

Vo V Vr, t Figure 11. Velocity components in a swirling flow field.

28

The two distinctly different types of flow that are possible in

a swirling flow field are known as free vortex and forced vortex flows. When the swirling component of flow is first created in the cyclone exit, the tangential profile of the induced flow approaches that of a forced vortex. As the forced vortex flow moves along the axis of the stack, momentum transfer and losses occur at the wall which cause a reduction in the tangential velocity and dissipation of angular momentum. This loss of angular momentum is due to viscous action aided by unstable flow and fluctuating components. Simultaneously, outside the laminar sublayer at the wall where inertial forces are significant, the field develops toward a state of constant angular momentum. This type of flow field with constant angular momention is classified as free vortex flow. The angular momentum and tangential velocities of the flow decay as the gas stream flows up the stack (23).

Baker and Sayre measured axial and tangential point velocity distributions in a 14.6 cm circular duct in which swirling flow was produced by fixed vanes (23). The tangential velocity profiles and angular momentum distributions are plotted in Figures 12 and 13 from measurements taken at 9, 24 and 44 diameters downstream of the origin of tangential flow. The tangential velocity (W) is made dimensionless by dividing it by the mean spatial axial velocity (Um) at a pipe cross section. These plots indicate developing flow fields, with two definite types of flow occurring: that approaching forced vortex flow in the central region of the pipe and flow approaching free vortex flow in the outer region. Further tests showed that the free vortex field

29

C)

cc
C

H

'H U) CC

CN If

U
C C)

-~

'p
C)

~ CC

C

C

-p

'H
p
'p
U)
-u

CC

0 'p
U C)
U) U) U)
C
p
U (2

LI) Z ("3 - C)
p

GO

CD

0

r

*01

'0

42
C CJ C .r -

development is due primarily to viscosity at the wall and not a function of inlet conditions, whereas the profiles in the forced vortex field are very dependent on the initial conditions at the inlet. Although no reverse flow was found in these tests, other tests showed that strong swirls may produce reversed axial velocities in the central region (23).

It should be noted that although tangential velocities and angular momentum decay along the axis of the pipe, see Figures 12 and 13, even after 44 diameter the tangential velocity is still quite significant when compared to the axial velocity. Therefore, satisfying the EPA Method 5 requirement of sampling 8 stack diameters downstream of the nearest upstream disturbances will not eliminate the effect of sampling in tangential flow.

The angle of the flow relative to the axis of the stack induced by the tangential component of velocity was as high as 60 degrees at some points in the flow. This compares well with angles found when sampling the outlets of cyclones (25). Another interesting fact about the flow described in Figures 12 and 13 is that the radial positions for the tangential components W/Um = 0 show that the vortex axis is off center by as much as 0.lr/R. This indicates that the swirling fields are not exactly axisymmetrical.

2. Errors Induced by Tangential Flow

Types of errors that would be expected to be introduced by tangential flow are nozzle misalignment, concentration gradients and invalid flow measurements. The sampling error caused by nozzle misalignment has been

32

described in the previous chapter. Concentration gradients occur because the rotational flow in the stack acts somewhat as a cyclone. The centrifugal force causes the larger particles to move toward the walls of the stack, causing higher concentrations in the outer regions.

Mason (22) ran tests at the outlet of a small industrial cyclone to determine the magnitude of these three types of errors induced by cyclonic flow. Results of flow rates determined at the different locations are presented in Table I. As indicated by the data, serious errors can result in cases of tangential flow. A maximum error of 212% occurred when the pitot tube was rotated to read a maximum velocity head. Sampling parallel to the stack wall also had a large error of almost 74%. When sampling downstream of the flow straightening vanes, however, the error was reduced to 15%.

Tests performed at the same point but with different nozzle angles produced the data in Table II. Measured dust concentration was lowest when the sampling nozzle was located at an angle of 0 degrees or parallel to the stack wall. The measured dust concentration continued to increase at 30 and 60 degrees but then decreased at 90 degrees. Equation (14) shows that when sampling at an angle, under apparent isokinetic conditions (i.e., R=I), the measured concentration will be less than the true concentration by a factor directly proportional to the cose. A maximum concentration, which would be the true concentration, will occur at e = 0, which from this data should lie at an angle between 60 and 90 degrees to the axis of the stack. This can be confirmed by

TABLE I
FLOW RATE DETERMINED AT VARIOUS MEASUREMENT LOCATIONS

Location Velocity (fps) Flow Rate (scfm) % Error

Actual Based on
Fan Performance 18 475 -Port A
(parallel) 40 826 74 Port A
(maximum Ap) 60 1,482 212 Port C
(straightened) 21 548 15

34

TABLE II
CONCENTRATION AT A POINT FOR DIFFERENT SAMPLING ANGLES Measured Concentration Nozzle Angle (grains/dscf)

0 0.243

30 0.296 60 0.332 90 0.316

35

using the data in Table I and the geometry in Figure 11 to calculate the angle #:

cos4 = Va/Vo = 13/60 (17)

This is true for = 72 degrees. Therefore, 0 = 0 when 4 = 72 degrees.

Table III gives the results of the emission tests. Sampling with the nozzle parallel to the stack wall showed an error of 53%.

Sampling at the angle of maximum velocity head reduced the error to 40%. The results cannot be compared directly to those with the parallel sampling approach because the feed rates were not the same due to equipment failure and replacement. Sampling in the straightened flow had a sampling error of 36%. It was expected that sampling at this location would give better results, but some of the particles were impacted on the straightening vanes and settled in the horizontal section of the duct, thus removing them from the flow stream.

Particle size distribution tests showed no significant effect of a concentration gradient across the traverse. This was due to the particles being too small to be affected by the centrifugal force field set up by the rotating flow.

3. Errors Due to the S-Type Pitot Tube

The errors in the measurement of velocity and subsequent calculations of flow rate in tangential flow are due primarily to the crudeness of the instruments used in source sampling. Because of the high particulate loadings that exist in source sampling, standard pitot tubes cannot be used to measure the velocity. Instead, the S-type pitot tube must be used

36

TABLE III
EMISSION TEST RESULTS

Measured Emission Actual Emission Probe Position Rate (gr/dscf) Error %

Nozzle parallel with stack wall 0.350 0.752 53 Nozzle rotated
toward maximum Ap 0.194 0.327 40 Straightened flow 0.207 0.325 36

37

since it has large diameter pressure ports that will not plug (see Figure 14). Besides the large pressure ports it has an additional advantage of producing approximately a 20% higher differential pressure than the standard pitot tube for a given velocity. However, although the S-type pitot tube will give an accurate velocity measurement, it is somewhat insensitive to the direction of the flow (25-29). Figures 15 and 16 show the velocity errors for yaw and pitch angles. Although the S-type pitot tube is very sensitive to pitch direction, the curve for yaw angle is symmetrical and somewhat flat for an angle of 45 degrees in either direction. Because of this insensitivity to direction of flow in the yaw direction, the S-type pitot tube cannot be used in a tangential flow situation to align the nozzle to the direction of the flow, or to accurately measure the velocity in a particular direction.

The velocity in a rotational flow field can be broken up into three components in the axial, radial and tangential directions (see Figure 11). The magnitude of the radial and tangential components relative to the axial component will determine the degree of error induced by the tangential flow. Neither the radial nor the tangential components of velocity affect the flow rate through the stack, but both affect the velocity measurement made by the S-type pitot tube because it lacks directional sensitivity. If the maximum velocity head were used to calculate the stack velocity, the resultant calculated flow rates and emission levels could be off by as much as a factor of 1/cos. Aligning the probe parallel to the stack will reduce but not eliminate this error because part of the radial and tangential velocity components will still be detected by the pitot tube.

38

~

+ C)

C)
-C) U) C) C)) C-)

d

-C) C-)

C-)

H

N *1-'

C)
-z
N C) 4-) N 4~)
0 0
0
N \ H
C)
C) N
C) C) N U) 4-,

C) C) 04) r-t.

39

4 0

-a 0

r-4 rCD *
4-u 0 C H0

) '..4 S c'

00
Cou o 0

r,
0
T-4

H

40

o u

t-I C7) E)

oCa

mec

.C
U0

0U

0
Oz
--'-D
4
3 I C
ct 1

a,

k~FU CL~C!I i

c.)

41

Therefore, the true flow rate cannot be determined by an S-type pitot tube in tangential flow because neither the radial velocity, Vr, the tangential velocity, Vt, the axial velocity, Va, nor the angle $ can be measured directly.

4. Methods Available for Measuring Velocity Components in a Tangential
Flow Field

Almost all of the reported measurements of velocity components in a tangential flow field have been based upon introduction of probes into the flow. Because of the sensitivity of vortex flows to the introduction of probes, the probe dimensions must be small with respect to the vortex core in order to accurately measure velocity.

Two common types of pressure probes capable of measuring velocity accurately are the 5-hole and 3-hole pitot tubes pictured in Figures 17a and b. The 5-hole or three dimensional directional pressure probe is used to measure yaw and pitch angles, and total and static pressure. Five pressure taps are drilled in a hemispherical or conical probe tip, one on the axis and at the pole of the tip, the other four spaced equidistant from the first and from each other at an angle of 30 to 50 degrees from the pole. The operation of the probe is based upon the surface pressure distribution around the probe tip. If the probe is placed in a flow field at an angle to the total mean velocity vector, then a pressure differential will be set up across these holes; the magnitude of which will depend upon the geometry of the probe tip, relative position of the holes and the magnitude and direction of the velocity vector. Each probe requires calibration of the pressure

42

r-- -0

I M

-4->
oo.
o 4
un

4 4J
00 0
(Th C 1~~~~\
'- 42o
0c

0 C)
0c

rcl)4
C)

-4
0r
c~) C)
-4
0 U 0 C

Cl.
1u
r-4

C)'C 0

C);
*j t1 )
LC.t

43

differentials between holes as a function of yaw and pitch angles. Figure 18 shows the sensitivity of a typical 5-hole pitot tube to yaw angle. Because of its sensitivity to yaw angle, it is possible to rotate the probe until the yaw pressures are equal, measure the angle of probe rotation (yaw angle) and then determine the pitch angle from the remaining pressure differentials. The probe can be used without rotation by using the complete set of calibration curves but the complexity of measurement and calculation is increased and accuracy is reduced. Velocity components can then be calculated from the measured total pressure, static pressure and yaw and pitch angle measurements.

The 3-hole pitot tube, also known as the two dimensional or Fecheimer probe, is similar to the 5-hole design except that it is unable to measure pitch angle. The probe is characterized by a central total pressure opening at the tip of the probe with two static pressure taps placed symmetrically to the side at an angle of from 20 to 50 degrees. From Figure 19 it can be seen that the probe is quite sensitive to yaw angle and can therefore be used to determine the yaw angle by rotating the probe until the pressure readings at the static taps are equal. Once this is done the total pressure is read from the central port, and the static pressure can be determined by use of a calibration chart for the particular probe. Both the 5-hole and the 3-hole pitot tubes have proven useful in determination of velocity components in tangential flow fields (25, 28, 30).

5. EPA Criteria for Sampling Cyclonic Flow

The revisions to reference methods 1-8 (2) describe a test for determination of whether cyclonic flow exists in a stack. The S-type

Figure 19. Focheimer pitot tube sensitivity to yaw angle. (28)

46

pitot tube is used to determine the angle of the flow relative to the axis of the stack by turning the pitot tube until the pressure reading at the two pressure openings is the same. If the average angle of the flow across the cross section of the stack is greater then 10 degrees,

then an alternative method of Method 5 should be used to sample the gas stream. The alternative procedures include installation of straightening vanes, calculating the total volumetric flow rate stoichiometrically, or moving to another measurement site at which the flow is acceptable.

Straightening vanes have shown the capability of reducing swirling flows;however, there are some problems inherent in their use. One is the physical limitation of placing them in an existing stack. Another is the cost in terms of energy due to the loss of velocity pressure when eliminating the tangential and radial components of velocity. Since the vortex flows are so sensitive to downstream disturbances, it is quite possible that straightening vanes might have a drastic effect on the performance of the upstream cyclonic control device which is generating the tangential flow. Because of these reasons the use of straightening vanes is unacceptable in many situations.

Calculating the volumetric flow rate stoichiometrically might

produce accurate flow rates but the values could not be used to calculate the necessary isokinetic sampling velocities and directions.

Also, studies reported here have shown that the decay of the tangential component of velocity in circular stacks is rather slow and therefore

it would be unlikely that another measurement site would solve the problem.

47

It should be noted that EPA's approach to determining whether cyclonic flow exists in a stack is correct. Other approaches such as observing the behavior of the plume after leaving the stack could lead to improper conclusions. Hanson et al (28) found that the twin-spiraling vorticies often seen leaving stacks are the result of secondary flow effects generated by the bending of the gas stream by the prevailing crosswind and do not indicate any cyclonic flow existing in the stack.

CHAPTER III
EXPERIMENTAL APPARATUS AND METHODS

A. Experimental Design

The major components of the aerosol flow system can be seen in

Figure 20. An aerosol stream generated from a spinning disc generator was fed into a mixing chamber where it was combined with dilution air. The air stream then flowed through a 10 cm diameter PVC pipe containing straightening vanes. This was followed by a straight section of clear pipe from which samples were taken. The filter holder and nozzle used as a control sample originated in a box following the straight section. A test nozzle was inserted into the duct at an angle from outside the box. A thin-plate orifice, used to monitor flow rate, followed the sampling box. A 34000 Zpm industrial blower was used to move the air through the system. The flow rate could be controlled by changing the diameter of an orifice plate. An air by-pass between the blower and the orifice plate was used as a fine adjust for the flow.

The sampling systems (see Figure 21) consisted of stainless steel, thin-walled nozzles connected to 47 mm stainless steel Gelman filter holders. Each filter assembly was connected in series to a dry gas meter and a rotameter, and driven by an airtight pump with a by-pass valve to control flow.

48

49

Cc w

-L

F~

CCD

Q,
0 C

-- I

C LJ LU

C

aa)

CDd

CC

2 c

--J 1---r
O3
CD CC~t 0 UJ C T a -

50

SSO

4J
L CD

J E

JO

<5

51

B. Aerosol Generation

1. Spinning Disc Generator

A spinning disc aerosol generator (31-33) was used to generate monodisperse aerosols from 1.0 vm NMD to 11.1 um NMD (see Table IV). Droplets were generated from a mixture of 90% uranine (a fluorescent dye) and 10% methylene blue dissolved in a solution of from 90 to 100% ethanol (95% pure) and up to 10% distilled/deionized H20. Uranine was used so that the particles could be detected by fluoremetric methods. Methylene blue was added to aid in the optical sizing of the particles. The mixture of water and ethanol allowed for a uniform evaporation of the droplets. The droplets, containing dissolved solute, evaporated to yield particles whose diameters could be calculated from the equation

0.33
DP = (Cr ) DD (18)

where

D = particle diameter, um

C = ratio of solute volume to solvent volume plus solute

volume, dimensionless

DD = original droplet diameter, um

With the disc's rotational velocity, air flows and liquid feed rate held constant the size of the droplets produced were only dependent upon the ratio of the ethanol-water mixture. Since the droplets are produced from a dynamic force balance between the centrifugal force and the surface

52

TABLE IV
SIZES AND DESCRIPTIONS OF EXPERIMENTAL AEROSOLS

Number Mean
Aerosol Generation % Droplet Diameter
Description Method Ethanol Diameter, pm Particles, pm

tension of the drop, the surface characteristics of the liquid are quite important. The surface tensions of water and ethanol at 20 degrees C are respectively 72.8 and 22.3 dynes/cm (34). The effect of this large difference can be seen in Table IV where the droplets produced were approximately 37 im for 90% ethanol and 23 im for 100% ethanol.

Before and after each test a sample of the particles was collected on a membrane filter and sized using a light microscope to take into account any slight variation in the performance of the spinning disc.

2. Ragweed Pollen

In order to obtain large Stokes numbers, ragweed pollen was mechanically dispersed by means of a rubber squeeze bulb into the inlet of the duct. The ragweed pollen had a NMD of 19.9 im.

C. Velocity Determination

The velocity at each sampling point was measured using a standard pitot tube. The flow was maintained constant during the test by controlling the pressure drop across a thin-walled orifice placed in the system (35-37). Five orifice plates with orifices ranging in diameter from 1.8 to 7.2 cm were used to obtain a range in duct velocities of 82 to 2460 cm/sec (see Table V) in the 10 cm duct. To obtain higher velocities, a 5 cm duct was used.

A typical velocity profile across the 9.6 cm clear plastic duct is presented in Table VI and plotted in Figure 22. The profile is

54

TABLE V
TABLE OF OBTAINABLE VELOCITIES IN 10 cm DUCT

Orifice Diameter Ap Range Range in Velocity
cm cm H 0 cm/sec

From Pitot Tube Readings From Orifice AP 1740 1658

56

0 o 0c

o u.

4-4,

o C
N

CD

CCd
oc o

0~ 0

NJ -4 -

57

quite flat which is typical of the turbulent flow regime. The average Reynolds number for this particular case was 1.1 x 105. The velocities at traverse points 3 and 4 were used as the velocity for determination of isokinetic sampling rate and Stokes number. The difference between the average velocity determined from the pitot traverse and the orifice plate calibration is probably due to the inability of the pitot tube to accurately measure velocity near the wall at points 1 and 6.

D. Selection of Sampling Locations

Sehmel (16) observed that non-uniform particle concentrations existed across the diameter of a cylindrical duct, and that the magnitude of the concentration gradient varied with particle size. To account for these radial variations, the two sampling points were located symmetrically about the center of the duct at a distance of 2 cm from the center. Simultaneous isokinetic samples were taken at the two points and compared. Tests were repeated for different particle sizes. No concentration differences were found to exist at the two sampling points.

E. Sampling Nozzles

Two pairs of sampling nozzles were cut from stainless steel tubing of 0.465 cm and 0.683 cm I.D. The nozzles were made approximately 15 cm long to minimize the effect of the disturbance caused by the filter holders on the flow at the entrance of the nozzles. Analysis by Smith

(38) showed that a sharp-edge probe was the most efficient design;

58

therefore, the tubing was tapered on a lathe to a fine edge. Belyaev and Levin (12) observed that the rebound of particles from the tip of the nozzle into the probe was one cause of sampling error and that for tapered nozzles, the efficiency is affected by the relative wall thickness, the relative edge thickness and the angle of taper. They concluded that if the edge thickness is less than 5% of the internal diameter and the taper is less than 15 degrees, then the variation in aspiration coefficient due to particle rebound would be less than 5%. The nozzles were designed accordingly.

F. Analysis Procedure

1. For Uranine Particles

Uranine particles were collected on Gelman type A glass fiber

filters. The filters were then placed in a 250 ml beaker. One hundred milliliters of distilled water were then pipetted into the front half of the filter holder and down through the nozzle into the beaker containing the filter. The uranine leachate concentration was then diluted and analyzed by a fluorometer (39).

2. For Ragweed Pollen

The ragweed pollen was collected on membrane filters and counted under a stereo microscope. In this part of the experiment the filters and probe were analyzed separately. The filters used for collecting the particles were 5.0 Jm type SM Millipore membrane filters. In order to count the particles under a microscope a dark background was necessary;

59

therefore, each filter was dyed with ink and a grid was drawn to aid in the counting. Before being placed in the filter holders, the filters were examined under the microscope to determine if any background count existed. After each test the filters were removed and the entire area of the filter was counted.

The pollen caught in the nozzle and filter holder was analyzed

using isopropyl alcohol and 0.45 pm pore size Millipore membrane filters with black grids. The isopropyl was first filtered several times to remove background particulate matter. Once the background was low enough, the alcohol was poured into the front half of the filter holder and through the nozzles. The solution was then sucked through the membrane filters. The filters were allowed to dry and then the entire filter area was counted under the microscope.

G. Sampling Procedure

1. A desired flow rate was obtained by selecting an orifice

plate and using the by-pass as a fine adjust.

2. The velocity was measured using a standard pitot tube.

3. A solute-solvent solution was selected for a given particle

size.

4. Particles were collected on a membrane filter and sized

using a light microscope.

5. A nozzle diameter which would allow for an isokinetic

sampling rate closest to 1 cfm was selected.

6. Isokinetic sampling rates were calculated and sampling

flow rates were adjusted accordingly.

60

7. Two simultaneous isokinetic samples were taken, one

parallel to the flow (control), and one at a specified

angle. Sampling times varied from 10 to 20 minutes.

H. Tangential Flow Mapping

The system used to map the flow pattern in a tangential flow stream is shown in Figure 23. It consists of a 34000 Zpm industrial blower, a section of 15 cm PVC pipe containing straightening vanes, a small industrial cyclone collector, followed by a 6.1 meter length of 20 cm PVC pipe. The 150 cm long cyclone, shown in Figure 24 was laid on its side so that the stack was horizontal and could be conveniently traversed at several points along its length. A change in flow through this system could be produced by supplying a restriction at the inlet to the blower.

To measure the velocity in the stack a United Sensor type DA 3dimentional directional pitot tube was used. The probe, pictured with its traversing unit in Figure 25, is .32 cm in diameter and is capable of measuring yaw and pitch angles of the fluid flow as well as total and static pressures. From the blow up of the probe tip (Figure 25) it can be seen that the head consists of 5 pressure ports. Port number 1 is the centrally located total pressure tap. On each side are two lateral pressure taps 2 and 3. When the probe is rotated by the manual traverse unit until P2 = P3, the yaw angle of flow is indicated by the traverse unit scale. When the yaw angle has been determined an additional differential pressure is measured by pressure holes located perpendicularly above and below the total pressure hole 1. Pitch angle is then determined using a calibration curve for the individual probe. The yaw angle is a

61

15 cm. 1I) Straig htenin, vanes

2.4 m
Blower

i

O

6.1 m

20cm Figure 23. Experimental system for measuring
cross sectional flow patterns in
a swirling flow stream.

62

14.7
15.2 22.9

68.6

Note: All dimensions in centimeters

68.6

Figure 24. Cyclone used in the study to generate swirling flow.

63

5 3 1

2 4

Figure 25. Photograph of the 3-dimensional pitot with its
traversing unit. Insert shows the location of
the pressure taps.
~~A

c\ ;<'
~A,'

5~- ~3 1 ~~~~1sj -'t;71 0.37

Figure~~~~k~jg 25. Phtgrp of.. th dmnsoalpto it t
tirwvrsn unt netsos hoaino
the presue tps

64

measure of the flow perpendicular to the axis of the stack and tangent to the stack walls. The pitch angle is a measure of the flow perpendicular to the axis of the stack and perpendicular to the stack walls. The axial component of the velocity can therefore be determined from the following equation:

Va = Vt cos@ (19)

where V = component of velocity flowing parallel to the axis of the stack.

Vt = total or maximum velocity measured by the pitot tube

-= cos [cos(pitch x cos(vawl
= cos [cos (pitch) x cos (yaw)]I

CHAPTER IV
RESULTS AND ANALYSIS

A. Aerosol Sampling Experiments

1. Stokes Number

Experiments were set up and run with Stokes number as the independent variable. Duct velocity, nozzle diameter and particle diameter were varied in order to produce a range of Stokes numbers from 0.007 to 2.97. The Stokes number used in the analysis of data was calculated from

Cp V D
K _- p o p (20) 18D.

where

-C0.434 D /L)
C = 1 + 2.492 L/Dp + 0.84 L/D e p (11) (21)

and

L = mean free path = 0.065 lm (11) Values for density and viscosity used in the calculations were
-4
S= 1.81 x 10 g/cm-sec (40)

p = density of uranine particles = 1.375 g/cm3 (41)

p = density of ragweed pollen = 1.1 g/cm3 (18)

65

66

2. Sampling with Parallel Nozzles

In order to determine if the concentration of particles was the same at both sampling locations, simultaneous samples were taken with both nozzles aligned parallel to the duct. Table VII shows the results of tests performed over a range of Stokes numbers from 0.022 to 1.73. The average over all of the tests showed only a 0.34% difference between the two points with a 95% confidence interval of 1.2%. The data show an increase in the range of the values as the Stokes number increases. This can be expected because a small error in probe misalignment would have a greater effect at the higher Stokes number.

3. Analysis of Probe Wash

In the analysis of the tests using ragweed pollen, the filter catch and probe wash were measured separately. This method allowed for the determination of the importance of analyzing both the filter and wash. From Table VIII it can be seen that even for a solid dry particle, analysis of the probe wash is a necessity. An average of 40% of the particles entering the nozzle was collected on the walls of the nozzle-filter holder assembly. This was only for nozzles aligned parallel to the flow stream and sampling isokinetically. Therefore, the loss of particles was due to turbulent deposition and possibly bounce off the filter, and probably not inertial impaction. For tests run with the nozzle at an angle to the flow stream, it is assumed that the loss would increase as impaction of particles on the walls became

67

0 cn 0- C0- tn

0

0 ccc

00 c cC O ,)

68

TABLE VIII
PERCENT OF PARTICULATE MATTER COLLECTED IN THE PROBE WASH
FOR NOZZLES PARALLEL WITH THE FLOW STREAM

*Numbers represent the number of ragweed pollen counted.

69

important. This can be seen from the data taken at 60 degrees (see Table IX) where an average of 54% of the particles was lost on the walls.

The probe wash for eight tests using 6.7 pm uranine particles

was also analyzed separately for comparison with the results of the ragweed pollen tests. While parallel sampling, from 15 to 34% of the total mass was collected in the nozzle and front end of the filter holder. While this was somewhat less than the amount of ragweed pollen found in the nozzle, it is substantial enough to show the importance of including the nozzle wash with the filter catch. Also because of the variation of the percent collected in the nozzle during identical tests, the probe wash cannot be accounted for by a correction factor. During further testing, it was qualitatively observed that the percent in the probe wash increased with particle size and decreased with increasing nozzle diameter.

4. The Effect of Angle Misalignment on Sampling Efficiency

The aspiration coefficient was determined by comparing the amount of particulate matter captured while sampling isokinetically with a control nozzle placed parallel and a test nozzle set at an angle to the flow stream. Tests were run at three angles, 30, 60 and 90 degrees. The results showed the theoretical predictions to be quite accurate. For all three angles the aspiration coefficient approached 1 for small Stokes numbers (K), decreased as K increased and then leveled off at a minimum of cos6 for large values of Stokes number. The most significant changes occur in the range between K = 0.01 and K = 1.0.

70

TABLE IX
PERCENT OF PARTICULATE MATTER COLLECTED IN TIlE PROBE WASH FOR NOZZLES AT AN ANGLE OF 60 DEGREES WITH THE FLOW STREAM

* Numbers represent the number of ragweed pollen counted.

71

Figures 26, 27 and 28 represent the sampling efficiency as a function of Stokes number for 30, 60 and 90 degrees respectively. The experimental data used in these plots are presented in Tables X, XI and XII. From these tables it can be seen that the variables of particle diameter and velocity and nozzle diameter were varied rather randomly. This was done to check the legitimacy of using Stokes number as the principle independent variable. From the shape of the curves in Figures 26-28, it can be seen that the aspiration coefficient is indeed a function primarily of Stokes number.

The curves for 30, 60 and 90 degrees are all similar in shape except for the values of Stokes number where they approach their theoretical limit. As the angle of misalignment increases, the more rapidly the aspiration coefficient reaches its maximum error. This can be accounted for as an apparent change in nozzle diameter, because it is the only parameter in the Stokes number that is affected by the nozzle angle to the flow stream. As described before, the nozzle diameter is important because it determines the amount of time available for the particle to change directions (approximately 6 D./V ). As the
1 O
nozzle is tilted at an angle to the flow stream, the projected frontal area and therefore the projected nozzle diameter are reduced proportional to the angle. Therefore, as the angle of misalignment increases, the time available for the particle to change direction decreases leading to increased sampling error for a given value of K. To normalize these curves for angle to the flow stream, it is necessary to define an "adjusted Stokes number" (K') which takes into account the change in projected

72

C) I I

0

II

0

C

C)

0 -~ C) CC 0 C

0
C)

-~
C o x ~
C) C) o 0
C) ~t
C)
-~
C C
U * -~ C)
o

C) 0 0 C)

U

C) CC
0

o ~~1

C

C) C) C) C) C) CC ~C C'] C) C)

C) C) C)
CC

Cv) ;u~OOD uor;~uusv

73

o
o

0
-rd

o 0 0 Oo

4

00 cb

*H E
de

0 F--i O i

/:o
O

0

0C
i "i\r

0 EC

0

0
o E
q

r-

0

GC 0 0 0 0i '-b
- 0 0F x-

74

CDI

0 0]

-fi

-~'4

0

I U C/Dj

75

0 r
oC
MU b O O 0 O0 >" 44- Cc c 00 4 -00mr m 4
ct I, 00 0 0

<0

U CC

*L too tn LO L.
O

00

4
C U

H H 4t 00 o t n r- u, 0
U

H N

0 Cr: cc LLN.
fE i N

76

00 OCC
-Ha) .0- L C *- o -IT C0014~ v cc 00 Lom

0 1 O M" C b 00 N M O N

H )

42 C)
U.l

E

0) O J cco

c

C u

77

o\0

OC

00

0 Z N 0 0 (n 0o

0 L C0 O O O n r- 0 D C 0 0 0 0 0 0 CO
-;

CO C

H 0 c0 0 L0 c co ,0 0

0 M 0 0 0 U O

S 00
SL o o cc

- 00 2 0

C)
O

Cj O

to\l

CD cc (7, r, i r CD t n m (o Nt X Ln N v, c C
r- 00 cc 00 r- r- .o

aL

E

5

o z

4-J

N
C

'0' .

-c- l ~-

79

O\O Ln n LLl L Lfn )Lra f LO t e aLn

CD 0CI 00
0 O

4-;
co

4J
O

o E 0 o
0

0- 1 ,

00 i r- c \D

00
r,. >iO o ~P

OC

0
40
Z C CO

S) 0 0 0 0 0 O O O O 0C, O
0

n N

z

CC
O ) 0 C0 co CVo Co Ln tl Co cc 11 co coI

02

Co

C) 0

0- N. C N. (N V) UN

CO
U~~~-C N NN 0- CoN N )V
-, -

81

o z < O

0

(D 0 ir 4-d

E ) C 0 4 U r H: 1

82

nozzle diameter with angle. When plotted against K', the aspiration coefficients for 30, 60 and 90 degrees should approach their theoretical minima at the same place as the curves for zero misalignment angle and anisokinetic sampling velocities (see Figure 6).

To develop the adjustment factor for Stokes number, it was necessary to plot as a function of e, the value of K where the aspiration coefficient reached a value that represented 95% of the maximum error. For example the maximum theoretical error for 60 degrees is cos(60) or

0.5. Therefore the value of K of interest is where there is (.95)(0.5) = 47.5% sampling error or an aspiration coefficient of 1 .475 = .525. For zero degrees, equations (9) and (10) were solved for R = 0.5 and 6 = 0.95 to obtain a value of K = 5.9. This velocity ratio was used because its theoretical maximum sampling error is 0.5, the same as for 60 degrees. The values for 60 and 90 degrees were obtained from Figures

27 and 28 respectively. Because of the flatness of the 30 degree curve (it varies only 16% over two and a half orders of magnitude of K), it was not possible to detect exactly when the curve reached 95% of its minimum value. Therefore no value for 30 degrees was used in this analysis.

The equation for the adjusted Stokes number determined from Figure

29 is

K' = Ke 022 (22) Using this equation it can be determined that the Stokes numbers for 30, 60 and 90 degrees must be multiplied by 1.93, 3.74 and 7.24 respectively to account for the effect of nozzle angle to the flow stream on the

83

6

o
5

4

0
c

-4

0 30 60 90

Misal ignment Angle (e) Figure 29. Stokes number at which 95% maximum error occurs
vs. misalignment angle.

84

apparent nozzle diameter. Using these correction factors it is possible to use the data to determine an expression for 8' in equation (14). Setting R = 1 and solving for 8' this equation becomes A 1
cos6

Using this expression the experimental datawere used to plot 8' as a function of the adjusted Stokes number K' (see Figure 30). From this plot, it can be observed that the data points for 30, 60 and 90 degrees all fall approximately on the same line. It should be noted that most of the scatter is due to the 30 degree data and that the amount of the scatter is somewhat deceptive. Solving equation (23) for 30 degrees, requires that the sampling bias (1-A) must be multiplied by 7.5 to normalize it with the 90 degree data. This has an effect of greatly increasing any spread in the experimental data.

To develop a model for inertial sampling bias, it was necessary

to develop an equation for the line drawn through the data in Figure 30. An equation of the form similar to that used by Belyaev and Levin was selected to fit the data.

B'(K',6) = 1 1 (24)
1 + aK'

where a and b are constants. The advantage of this equation form is that it acts similar to the theoretical expectations of the relationship (i.e., B' approaches zero for very small values of K' and approaches 1 for very large values of K').

85

I. I I

0 0*

o

U) C) C)
0

C)

-U

-U

C)

z 0 'U
0
K

K 0 -~ 0 C) K C

0

-U
U) U) C)
C U)
0 0
-p
-p
U ~0 C)
-p
C) U)

-u
C)
C)

o U)

0 C) C

<00

I -~ z

D C) D C C)

i )

Full Text

r/R
Figure 13. Cross sectional distributions of angular momentum in a swirling flow field. o

58
therefore, the tubing was tapered on a lathe to a fine edge. Belyaev
and Levin (12) observed that the rebound of particles from the tip of
the nozzle into the probe was one cause of sampling error and that for
tapered nozzles, the efficiency is affected by the relative wall thick
ness, the relative edge thickness and the angle of taper. They con
cluded that if the edge thickness is less than 5% of the internal diameter
and the taper is less than 15 degrees, then the variation in aspiration
coefficient due to particle rebound would be less than 5%. The nozzles
viere designed accordingly.
F. Analysis Procedure
1. For Uranine Particles
Uranine particles were collected on Gelman type A glass fiber
filters. The filters were then placed in a 250 ml beaker. One hundred
milliliters of distilled water were then pipetted into the front half of
the filter holder and down through the nozzle into the beaker containing
the filter. The uranine leachate concentration was then diluted and
analyzed by a fluorometer (39).
2. For Ragweed Pollen
The ragweed pollen was collected on membrane filters and counted
under a stereo microscope. In this part of the experiment the filters
and probe were analyzed separately. The filters used for collecting
the particles were 5.0 pm type SM Millipore membrane filters. In order
to count the particles under a microscope a dark background was necessary;

Adjusted Stokes Number (K')
Figure 30. 3'(K',0) vs. adjusted Stokes number for 30, 60 and 90 degrees.

Aspiration Coefficient (A)
Figure 26. Sampling efficiency vs. Stokes number at 30 misalignment for R = 1.
tsj

TABLE XX
FIVE-HOLE PITOT TUBE MEASUREMENTS
MADE AT 1 DIAMETER DOWNSTREAM OF THE CYCLONE
Point
1-D Low Flow
Total
Angles, Degrees Velocity
Pitch Yaw (j) cm/sec
Axial
Velocity
cm/sec
Tangential
Velocity
cm/sec
1
kkk
k k
kkk
kkk
kkk
kkk
2
25.5
67.9
70.1
1786
608
1655
3
17.0
77.4
78.0
1600
333
1561
4
+ + +
+ + +
+ + +
+ + +
+ + +
+ + +
5
3.0
76.0
76.0
1341
324
1301
6
21.0
60.0
62.2
1761
821
1525
7
30.0
51.0
57.0
1762
959
1369
8
32.0
48.0
55.4
1664
945
1237
1-D High Flow
Total
Axial
Tangential
Aneles. Deerees
Velocity
Velocity
Velocity
Point
Pitch
Yaw
cm/sec
cm/sec
cm/sec
1
* k
kkk
kkk
kkk
kkk
kkk
2
24.0
64.0
66.4
2782
1114
2500
3
19.0
78.5
79.1
2348
444
2301
4
+ + +
+ + +
+ + +
+ + +
+ + +
+ + +
5
3.0
74.4
74.4
1846
496
1778
6
22.0
63.8
65.8
2699
1106
2421
7
28.0
57.8
61.9
2742
1292
2320
8
31.0
54.6
60.23
2572
1277
2096
*** Point No. 1
was too
close to
the wall to
allow insertion of all five
pressure taps.
+++ Point lies inside the negative pressure section.

TO PUMPS AND GAS METERS
Figure 20.
Experimental set up.
TO BLOWER

Aspiration Coefficient (A)
1.00
0.80
0.60
0.40
0.20
0.00
O G
0.01
O
o
i u
G
Typical 95% C.I.
o
O
<&
o
o
o
o
G
J L I 1111
J I 1 I 1...1 J-l.
J 1 1111
0.
1.0
10.
Stokes Number (K)
Figure 27. Sampling efficiency vs. Stokes number at 60 misalignment for R = 1.

TABLE OF CONTENTS--continued
CHAPTER Page
F. Analysis Procedure 58
1. For Uranine Particles 58
2. For Ragweed Pollen 58
G. Sampling Procedure 59
H. Tangential Flow Mapping 60
IV RESULTS AND ANALYSIS 65
A. Aerosol Sampling Experiments 65
1. Stokes Number 65
2. Sampling with Parallel Nozzles 66
3. Analysis of Probe Wash 66
4. The Effect of Angle Misalignment on Sampling
Efficiencies 69
5. The Effect of Nozzle Misalignment and Anisokinetic
Sampling Velocity 89
B. Tangential Flow Mapping 102
V SIMULATION OF AN EPA METHOD 5 EMISSION TEST IN A TANGENTIAL
FLOW STREAM 117
VI SUMMARY AND RECOMMENDATIONS 129
A. Summary 129
B. Recommendations 134
REFERENCES 135
BIOGRAPHICAL SKETCH 139
iv

20
If the nozzle is at an angle 0 to the flow stream, the projected area
perpendicular to the flow is an ellipse with a major axis D^, minor
2
axis D^cos0, and area (D^ ttcos0)/4. The projected area of the nozzle
would therefore be A^cosG (see Figure 8). It can be seen that all the
particles contained in the volume V A.cosG will enter the nozzle. A
fraction B'(K,R,0) of the particles in the volume (A A.cos@)V will
0 10
leave the stream tube because of their inertia and will not enter the
nozzle. Therefore, with C defining the actual concentration of the
o 6
particles, the measured concentration in the nozzle would be
C A.COS0V + [1 -31(K,R,0)](A -A.cos0)V C
r 01 o L 7 J v o i J o o r,
C = (13)
A. V.
i i
Using equations (1) and (12), this may be simplified to
A = C./Co = 1 + 3'(K,R,0)(Rcose-1) (14)
B'(K,R,0) would be a function of both the velocity ratio R and the
inertial impaction parameter K as shown by Belyaev and Levin (13).
However, 3' will also be a function of the angle 0 because as the angle
increases, the severity of the turn that the particles must make to be
collected is also increased.
It can be seen that for large values of Stokes number, 6' must ap
proach 1 for the predicted concentration ratio in equation (14) to reach
the theoretical limit of Rcos0. The maximum error should theoretically
occur somewhere between a Stokes number of 1 and 6 depending on the angle
0. The upper limit of K = 6 would be for an angle of 0 degrees as des
cribed earlier in this chapter. The theoretical lower limit of K = 1

AIR FLOW
9. Tangential flow induced by ducting
FLOW PATTERN
tsJ

36
TABLE III
EMISSION TEST RESULTS
Probe Position
Measured Emission
Rate (gr/dscf)
Actual Emission
Rate (gr/dscf)
Error
Nozzle parallel
with stack wall
0.350
0.752
53
Nozzle rotated
toward maximum Ap
0.194
0.327
40
Straightened flow
0.207
0.325
36

CHAPTER IV
RESULTS AND ANALYSIS
A. Aerosol Sampling Experiments
1. Stokes Number
Experiments were set up and run with Stokes number as the independent
variable. Duct velocity, nozzle diameter and particle diameter were varied
in order to produce a range of Stokes numbers from 0.007 to 2.97. The
Stokes number used in the analysis of data was calculated from
2
18D.n
(20)
i
where
C = 1 + 2.492 L/D + 0.84 L/D e
P P
and
L = mean free path = 0.065 ym (11)
Values for density and viscosity used in the calculations were
p = 1.81 x 10 4 g/cm-sec (40)
Pp = density of uranine particles = 1.375 g/cm.0 (41)
T
p = density of ragweed pollen = 1.1 g/cm (18)
65

136
14. Davies, C. N. The Entry of Aerosols into Sampling Tubes and Heads.
Brit. J. Appl. Phys., Ser. 2, 1:921, 1970.
15. Martone, J. A. Sampling of Submicrometer Particles Suspended in Near
Sonic and Supersonic Free Jets of Air. Presented at the Annual Meeting
of the Air Pollution Control Association, Toronto, Canada, 1977.
16. Sehmel, G. Particle Sampling Bias Introduced by Anisokinetic Sampling
and Deposition within the Sampling Lines. Amer. Ind. Hyg. Assoc. J.,
31(6) : 758, 1970.
17. Glauberman, H. The Directional Dependence of Air Samplers. Amer. Ind.
Hyg. Assoc. J., 23(3):235, 1962.
18. Raynor, G. S. Variation in Entrance Efficiency of a Filter Sampler with
Air Speed, Flow Rate, Angle and Particle Size. Amer. Ind. Hyg. Assoc.
J., 31(3) :294, 1970.
19. Fuchs, N. A. Sampling of Aerosols. Atmos. Envir., 9:697, 1975.
20. Laktionov, A. G. Aspiration of an Aerosol Into a Vertical Tube from a
Flow Transverse to It. AD-760 947, Foreign Technology Division, Wright-
Patterson Air Force Base, Ohio, 1973.
21. Vitols, V. Theoretical Limits of Errors Due to Anisokinetic Sampling of
Particulate Matter. J. Air Pollut. Control Assoc., 16(2): 79, 1960.
22. Mason, K. W. Location of the Sampling Nozzle in Tangential Flow. M. S.
Thesis, University of Florida, Gainesville, Florida, 1974.
23. Baker, D. W. and C. L. Sayre. Decay of Swirling Turbulent Flow of Incom
pressible Fluids in Long Pipes. Flow: Its Measurement and Control in
Science and Industry, Volume 1, Part 1, Flow Characteristics. Instrument
Society of America, Pittsburgh, 1974, p. 301.
24. Chigier, N. A. Velocity Measurement in Vortex Flows. Flow: Its Measure
ment and Control in Science and Industry, Volume 1, Part 1, Flow Charac
teristics. Instrument Society of America, Pittsburgh, 1974, p. 399.
25. Hanson, H. A. and D. P. Saari. Effective Sampling Techniques for
Particulate Emissions from Atypical Stationary Sources. EPA-600/2-77-036,
U.S. Environmental Protection Agency, Research Triangle Park, N.C., 1977.
26. Brooks, E. F. and R. L. Williams. Process Stream Volumetric Flow Measure
ment and Gas Sample Extraction Methodology. TRW Document No. 24916-6028-
RU-00, TRW Systems Group, Redondo Beach, California, 1975.

TABLE XIV
ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER FOR R = 2, 6 = 60
Velocity
cm/sec
Particle Diameter
micrometers
Nozzle Diameter
cm
Stokes Number
Aspiration
Coefficient %
732
4.59
0.683
0.099
96.9
104.1
100.5
732
6.5
0.683
0.196
109.0
93.4
98.4
701
9.6
0.683
0.406
90.9
101.9
101.9
1402
9.6
0.683
0.812
97.6
94.0
105.0
1140
9.9
0.465
1.01
95.2
105.1
97.0

47
It should be noted that EPA's approach to determining whether
cyclonic flow exists in a stack is correct. Other approaches such
as observing the behavior of the plume after leaving the stack could
lead to improper conclusions. Hanson et al (28) found that the
twin-spiraling vorticies often seen leaving stacks are the result of
secondary flow effects generated by the bending of the gas stream by
the prevailing crosswind and do not indicate any cyclonic flow
existing in the stack.

57
quite flat which is typical of the turbulent flow regime. The average
Reynolds number for this particular case was 1.1 x lO'. The velocities
at traverse points 3 and 4 were used as the velocity for determination
of isokinetic sampling rate and Stokes number. The difference between
the average velocity determined from the pitot traverse and the orifice
plate calibration is probably due to the inability of the pitot tube to
accurately measure velocity near the wall at points 1 and 6.
D. Selection of Sampling Locations
Sehmel (16) observed that non-uniform particle concentrations
existed across the diameter of a cylindrical duct, and that the
magnitude of the concentration gradient varied with particle size.
To account for these radial variations, the two sampling points were
located symmetrically about the center of the duct at a distance of
2 cm from the center. Simultaneous isokinetic samples were taken at
the two points and compared. Tests were repeated for different
particle sizes. No concentration differences were found to exist at
the two sampling points.
E. Sampling Nozzles
Two pairs of sampling nozzles were cut from stainless steel tubing
of 0.465 cm and 0.683 cm I.D. The nozzles were made approximately 15 cm
long to minimize the effect of the disturbance caused by the filter
holders on the flow at the entrance of the nozzles. Analysis by Smith
(38) showed that a sharp-edge probe was the most efficient design;

TABLE XXIII
FIVE-HOLE PITOT TUBE MEASUREMENTS
MADE AT 8 DIAMETERS DOWNSTREAM OF THE CYCLONE
109
8-D Low Flow
Point
Angles, Degrees
Pitch Yaw cf)
Total
Velocity
cm/sec
Axial
Velocity
cm/sec
Tangential
Velocity
cm/sec
1
kkk
***
kkk
k k k
kkk
kkk
2
19.5
59.0
61.0
1414
685
1212
3
15.0
69.0
70.3
1436
484
1346
4
+ + +
+ + +
+ + +
+ + +
+ + +
+ + +
5
8.0
63.6
63.9
1396
614
1250
6
20.0
50.2
53.0
1326
798
1019
7
28.0
39.4
47.0
1289
879
818
8
29.0
38.0
46.4
1231
849
758
8-D High
Flow
Point
.Angle
Pitch
s, Degrees
Yaw cf>
Total
Velocity
cm/sec
Axial
Velocity
cm/sec
Tangential
Velocity
cm/sec
1
k k k
* *
kk-k
k kk
kkk
kkk
2
19.0
57.0
59.0
1875
966
1572
3
9.0
70.0
70.3
1881
634
1767
4
+ + +
+ + +
+ + +
+ + +
+ + +
+ + +
5
0
64.6
64.6
1743
748
1574
6
15.0
50.0
51.6
1942
1206
1488
7
21.0
43.2
47.1
1869
1272
1279
8
25.0
42.0
47.7
1795
1208
1201
*** Point No. 1 was too close to the wall to allow insertion of all five
pressure taps.
+++ Point lies inside the negative pressure section.

137
27. Grove, D. J. and W. S. Smith. Pitot Tube Errors Due to Misalignment and
Nonstreamlined Flow. Stack Sampling News, November, 1973.
28. Hanson, H. A., R. J. Davini, J. K. Morgan and A. A. Iversen. Particulate
Sampling Strategies for Large Power Plants Including Nonuniform Flow.
EPA-600/2-76-170, U. S. Environmental Protection Agency, Research Triangle
Park, N.C., 1976, 349 pp.
29. Williams, F. C. and F. R. DeJarnette. A Study on the Accuracy of Type S
Pitot Tube. EPA 600/4-77-030, U. S. Environmental Protection Agency,
Research Triangle Park, N.C., 1977.
30. Lea, J. F. and D. C. Price. Mean Velocity Measurements in Swirling Flow
in a Pipe. Flow: Its Measurement and Control in Science and Industry,
Volume 1, Part 1, Flow Characteristics. Instrument Society of America,
Pittsburgh, 1974, p. 313.
31. Green, H. L. and W. R. Lane. Particulate Clouds: Dusts, Smokes and
Mists. E. F. M. Spon. Ltd., London, 1957, p. 36.
32. Air Pollution Manual. Part II Control Equipment. Amer. Ind. Hyg.
Assoc., Detroit, 1968, p. 4.
33. Whitby, K. T., D. A. Lundgren and C. M. Peterson. Homogeneous Aerosol
Generators. J. Air and Water Poll., 9:263, 1965.
34. Perry, J. K. Chemical Engineers' Handbook, McGraw-Hill, New York, 1941.
35. Flowmeter Computation Handbook. Amer. Soc. Mech. Eng., Ne\i York, 1961.
36. Fluid Meters, Their Theory and Application. H. S. Bean, Ed., Amer. Soc.
Mech. Eng., New York, 1971.
37. Doebelin, E. 0. Measurement Systems, Application and Design. McGraw-
Hill, New York, 1975.
38. Smith, F. H. The Effects of Nozzle Design and Sampling Techniques on
Aerosol Measurements. EPA-650/2-74-070, U. S. Environmental Protection
Agency, Washington, D. C., 1974, 89 pp.
39. Manual of Fluorometric Clinical Procedures. G. K. Turner Association,
Palo Alto, California, 1971.
40. American Institute of Physics Handbook. D. E. Gray, Ed., McGraw-Hill,
New York, 1957.

Ill
checking the measurement setup, it was discovered that because of the
construction of the probe and the closeness of the first traverse
point to the opening, one of the pitch pressure points was not completely
in the flow stream. Because of this, data from traverse point number 1
are not presented with the rest of the data.
The velocity measurements at the other traverse points for both
flow rates and all five axial distances showed approximately the same
characteristics. The pitch angle increased from the core area to the
duct wall. The yaw angle and the combined angle (p decreased from the
core area to the walls. At the inlet and up to eight diameters down
stream, angles as high as 70 degrees were found near the core area of
the flow field. The total velocity, axial velocity, and the tangential
velocity all showed the same cross sectional flow pattern. The velocities
were minimum at the core, increased with radius and then slightly decreased
near the wall. These patterns are similar to those found in the swirling
flow generated with fixed vanes (23).
In order to observe the changes in the flow as a function of axial
distance from the inlet, the cross sectional averages of the angle cf>,
core area, and tangential velocity were calculated and presented in Table
XXV and plotted in Figures 38 and 39. All three parameters show a very
gradual decay of the indicators of tangential flow as was expected from
the reported tests (23). The curves have the same shape for both flow
rates.
The high core area for the measurements at 16 diameters downstream
was confirmed by repeated measurements. These values may be due to a

41
Therefore, the true flow rate cannot be determined by an S-tvpe pitot
tube in tangential flow because neither the radial velocity, V the
tangential velocity, V the axial velocity, V nor the angle cj> can
l a.
be measured directly.
4, Methods Available for Measuring Velocity Components in a Tangential
Flow Field
Almost all of the reported measurements of velocity components in
a tangential flow field have been based upon introduction of probes into
the flow. Because of the sensitivity of vortex flows to the introduction
of probes, the probe dimensions must be small with respect to the vortex
core in order to accurately measure velocity.
Two common types of pressure probes capable of measuring velocity
accurately are the 5-hole and 3-hole pitot tubes pictured in Figures 17a
and b. The 5-hole or three dimensional directional pressure probe is
used to measure yaw and pitch angles, and total and static pressure.
Five pressure taps are drilled in a hemispherical or conical probe tip,
one on the axis and at the pole of the tip, the other four spaced
equidistant from the first and from each other at an angle of 30 to 50
degrees from the pole. The operation of the probe is based upon the
surface pressure distribution around the probe tip. If the probe is
placed in a flow field at an angle to the total mean velocity vector,
then a pressure differential will be set up across these holes; the
magnitude of which will depend upon the geometry of the probe tip,
relative position of the holes and the magnitude and direction of the
velocity vector. Each probe requires calibration of the pressure

I
r/R
Figure 12. Cross sectional distribution of tangential velocity in a swirling flow field.
K)

46
pitot tube is used to determine the angle of the flow relative to the
axis of the stack by turning the pitot tube until the pressure reading
at the two pressure openings is the same. If the average angle of the
flow across the cross section of the stack is greater then 10 degrees,
then an alternative method of Method 5 should be used to sample the
gas stream. The alternative procedures include installation of
straightening vanes, calculating the total volumetric flow rate
stoichiometrically, or moving to another measurement site at which the
flow is acceptable.
Straightening vanes have shown the capability of reducing swirling
flows; however, there are some problems inherent in their use. One is
the physical limitation of placing them in an existing stack. Another
is the cost in terms of energy due to the loss of velocity pressure
when eliminating the tangential and radial components of velocity.
Since the vortex flows are so sensitive to downstream disturbances,
it is quite possible that straightening vanes might have a drastic
effect on the performance of the upstream cyclonic control device
which is generating the tangential flow. Because of these reasons the
use of straightening vanes is unacceptable in many situations.
Calculating the volumetric flow rate stoichiometrically might
produce accurate flow rates but the values could not be used to
calculate the necessary isokinetic sampling velocities and directions.
Also, studies reported here have shown that the decay of the tangential
component of velocity in circular stacks is rather slow and therefore
it would be unlikely that another measurement site would solve the problem.

I certify that I have read this study and that in ray opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
^U'nalC//U-'y\
Dale A.Lundgren, Chaijrjfsfn
Professor of Environmental
Engineering Sciences
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
LU.
t
Paul Urone
Professor of Environmental
Engineering Sciences
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
w C 1U-
\
Wayne Â£. Huber
Professor of Environmental
Engineering Sciences
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
/
L
/
<
y
[o.
/I' r . Cm
Alex E. Green
Graduate Research Professor of
Physics and Nuclear Engi
neering Sciences

TABLE XVI
ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER FOR 0 = 45, R = 2.0 and 0.5
Velocity Particle Diameter
cm/sec micrometers
Nozzle Diameter
cm
Stokes Number
Velocity
Ratio
Aspiration
Coefficient
701
9.6
0.683
0.406
0.5
67 .4
78.2
65.5
65.0
701
9.6
0.683
0.406
2.0
134.5
131.4
113.8
121 .4
to

I
Figure 8. Sampling bias due to nozzle misalignment and anisokinetic sampling velocity.

60
7. Two simultaneous isokinetic samples were taken, one
parallel to the flow (control), and one at a specified
angle. Sampling times varied from 10 to 20 minutes.
H. Tangential Flow Mapping
The system used to map the flow pattern in a tangential flow' stream
is shown in Figure 23. It consists of a 34000 Â£pm industrial blower, a
section of 15 cm PVC pipe containing straightening vanes, a small in
dustrial cyclone collector, followed by a 6.1 meter length of 20 cm PVC
pipe. The 150 cm long cyclone, shown in Figure 24 was laid on its side
so that the stack was horizontal and could be conveniently traversed at
several points along its length. A change in flow through this system
could be produced by supplying a restriction at the inlet to the blower.
To measure the velocity in the stack a United Sensor type DA 3-
dimentional directional pitot tube was used. The probe, pictured with
its traversing unit in Figure 25, is .52 cm in diameter and is capable
of measuring yaw and pitch angles of the fluid flow as well as total
and static pressures. From the blow up of the probe tip (Figure 25) it
can be seen that the head consists of 5 pressure ports. Port number 1
is the centrally located total pressure tap. On each side are two
lateral pressure taps 2 and 3. When the probe is rotated by the manual
traverse unit until P9 = P the yaw angle of flow is indicated by the
traverse unit scale. When the yaw angle has been determined an additional
differential pressure is measured by pressure holes located perpendicularly
above and below the total pressure hole 1. Pitch angle is then determined
using a calibration curve for the individual probe. The yaw angle is a

CHAPTER V
SIMULATION OF AN EPA METHOD 5 EMISSION TEST
IN A TANGENTIAL FLOW STREAM
A model has been developed and tested which describes particle
collection efficiency as a function of particle characteristics, angle
of misalignment, and velocity ratio. Together with the measurement of
velocity components in a swirling flow it is possible to analyze the
emission rate errors that would occur when performing a Method 5
analysis of the effluent stream following a cyclone.
For this simulation analysis, the volumetric flow rate and iso
kinetic sampling velocities are calculated from velocity measurements
obtained at the eight diameter sampling location using a S-type pitot
tube (see Tables XXVI and XXVII) The angle , velocity ratio, and
particle velocity are determined from velocity measurements made at
the same location using the five-hole pitot tube (see Table XXII).
The particle characteristics are obtained from particle size distribution
tests made by Mason (22) on basically the same system. From a particle
distribution with a 3.0 pm MMD and geometric standard deviation of 2.13
(see Figure 41) ten pa'rticle diameters were selected which represent
the midpoints of 10% of the mass of the aerosol (see Table XXVIII). The
density of the particles was assumed to be 2.7 g/cm The nozzle diameter
was selected using the standard criteria to be 0.635 cm (1/4 inch). In
the model it was assumed that the nozzle would be aligned parallel with
the axis of the stack, and therefore, 0 = tj).
117

Percent Less Than
99.9
Figure 41. Particle size distributions used in the simulation model.
120

7
130
The two aspects of this study, anisokinetic sampling errors and
flow measurements, were combined in a simulation model to determine the
magnitude of errors when an EPA Method 5 emission test is performed at
the exit of a cyclone.
A summary of the important results determined from this study is
as follows:
A. The flow patterns found in a stack following the exit of a
small industrial cyclone are of such a nature that it makes it extremely
difficult to obtain a representative sample with the present EPA recom
mended equipment. Angles in excess of 70 degrees relative to the stack
axis are found in some parts of the flow. Since large scale turbulence,
such as swirling flow, is inherently self-preserving in round ducts, it
decays very slowly as it moves up the stack and therefore sampling at
any location downstream of the cyclone will involve the same problems.
B. The yaw characteristics of the S-type pitot tube lead to several
types of errors when used in a tangential flow stream. Wien the angle
of yaw is less than 45 degrees, the measured velocity is greater than or
equal to the actual velocity with the maximum error being approximately
5%. Beyond 45 degrees the measured velocity drops off quite rapidly and
at an angle of 70 degrees the measured velocity is less than half the
true velocity. Because of its yaw characteristics, the S-type pitot tube
is not suitable for distinguishing the axial component of flow from the
total flow which includes the tangential component. Volumetric flow
calculations based on S-type pitot tube measurements in a swirling flow
were found to be in excess of the actual flow by as much as 309.

Aspiration Coefficient (Al
i
Stokes Number (K)
Figure 32. Predicted aspiration coefficient vs. Stokes number for 15, 30, 45, 60, 75 and 90 degrees
CO
CO

122
Using these parameters the average aspiration coefficients are
determined at each traverse point using the ten particle diameters and
equations (33) (39).
A., (1*2 ,(f>2 j K9)
A3(r3^3,K3)
1A r + 1A .+ .1A co + ..
Dp5-s Dplb-6 Dp25-6
' + 1ADp95%
(53)
1A _0 + 1A _0 + 1A_ O[ro +
Dp5% Dpl5% Dp25%
" + '1ADp95%
(34)
.
(35)
(36)
(37)
AgiRg^g^g) 1ADp5?6 + -1ADpl5% + 1ADp25;
+ 1A
Dp95%
(38)
(39)
Where A^ = total aspiration coefficient for traverse point i.
= (total velocity at i)/(sampling velocity at i).
cj> = angle of flow at point i relative to the axis of the stack.
K.,= Stokes number based on the nozzle diameter, total velocity
lk
at i, and particle diameter Dp. 0 .
K'
Dp, 0= Midpoint particle diameters each representing 10% of the
total mass.
Since the sampling velocity will determine the volume of air sampled at
each traverse point, the total aspiration coefficient for each flow rate
is determined by taking an average weighted according to sampling velocity.
V.A + V.A_
10 0
iz
V.nA^ + V.-A, + V._A_ + V.nA
i5 5
i6 6
i7 7
i8 8
V. + V., + V._ + V., + V._ + V
i2 10 i5 16 i7 18
(40)
Where (Y ) = inlet velocity at traverse point j.
Because of the missing data at point. 1 and negative pressure section at
point 4, these two traverse points were not used in the analysis.

REFERENCES
1. Standards of Performance for New Stationary Sources. Federal Register,
36(247) :24876, 1971.
2. Revision to Reference Method 1-8. Federal Register, 42(160):41754, 1977
3. Wilcox, J. D. Isokinetic Flow and Sampling of Airborne Particulates.
Artificial Stimulation of Rain. Pergamon Press, New York, 1957, p. 177.
4. Lapple, C. E. and C. G. Shepherd. Calculation of Particle Trajectories.
Ind. Eng. Chem., 32(5):605, 1940.
5. Watson, H. H. Errors Due to Anisokinetic Sampling of Aerosols. Amer.
Ind. Hyg. Assoc. Quart., 15(1): 21, 1954.
6. Dennis, R., W. R. Samples, D. M. Anderson and L. Silverman. Isokinetic
Sampling Probes. Ind. Eng. Chem., 49(2) :294, 1957.
7. Hemeon, W. C. L. and G. F. Haines, Jr. The Magnitude of Errors in
Stack Dust Sampling. Air Repair, 4(3):159, 1954.
8. Whiteley, A. B. and L. E. Reed. The Effect of Probe Shape on the
Accuracy of Sampling Flue Gases for Dust Content. J. Inst. Fuel,
32:316, 1959.
9. Lundgren, D. A. and S. Calvert. Aerosol Sampling with a Side Port
Probe. Amer. Ind. Hyg. Assoc. J., 28(3) :208, 1967.
10. Badzioch, S. Collection of Gas-Borne Dust Particles by Means of an
Aspirated Sampling Nozzle. Brit. J. Appl. Phys., 10:26, 1959.
11. Fuchs, N. A. The Mechanics of Aerosols. The Macmillan Co., New York,
1964, p. 73.
12. Belyaev, S. P. and L. M. Levin. Investigation of Aerosol Aspiration
by Photographing Particle Tracks Under Flash Illumination. J. Aerosol
Sci., 3:127, 1972.
13. Belyaev, S. P. and L. M. Levin. Techniques for Collection of Representa
tive Aerosol Samples. J. Aerosol Sci., 5:325, 1974.
135

TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS
LIST OF TABLES v
LIST OF FIGURES vi'ii
LIST OF SYMBOLS xi
ABSTRACT xiii
CHAPTER
I INTRODUCTION AND ISOKINETIC SAMPLING THEORY 1
A. Introduction 1
B. Isokinetic Sampling Theory 2
II REVIEW OF THE PERTINENT LITERATURE 10
A. Summary of the Literature on Anisokinetic Sampling... 10
1. Sampling Bias Due to Unmatched Velocities 10
2. Sampling Bias Due to Nozzle Misalignment 17
B. Summary of the Literature on Tangential Flow 23
1. Causes and Characteristics of Tangential Flow 23
2. Errors Induced by Tangential Flow 31
3. Errors Due to the S-Type Pitot Tube 35
4. Methods Available for Measuring Velocity
Components in a Tangential Flow Field 41
5. EPA Criteria for Sampling Cyclonic Flow 43
III EXPERIMENTAL APPARATUS AND METHODS 48
A. Experimental Design 48
B. Aerosol Generation 51
1. Spinning Disc Generator 51
2. Ragweed Pollen 53
C. Velocity Determination 53
D. Selection of Sampling Locations 57
E. Sampling Nozzles 57
iii

SYMBOLS
- area of sampler inlet
'- projected area of sampler inlet
Aq area of stream tube approaching nozzle
A ratio of measured concentration to true concentration
C Cunningham correction factor
C. dust concentration in inlet
i
C dust concentration in flow stream
o
C
r concentration ratio of aerosol generating solution
- droplet diameter
D. inlet diameter
i
D particle diameter
P
K inertial impaction parameter
K' adjusted Stokes number
i stopping distance
L undisturbed distance upstream from nozzle
n constant
R ratio of free stream velocity to inlet velocity
s constant
Va axial component of stack velocity
V. velocity in inlet
- radial component of stack velocity
V free stream velocity
xi

104
with the rotation of the probe. Inside the core area it was not possible
to determine the direction of flow because there was no point in the 360
degree rotation of the probe where the pressures at point 2 and 3 were
the same. The location of the core area was measured at each location
along the duct axis and recorded. During the velocity measurements, it
was observed that the flow was very sensitive to downstream disturbances.
A crosswind at the end of the pipe produced large fluctuations in the
pressure measurements.
Figure 37 shows the graphical interpretation of the pitch and yaw
components of velocity. The two radii r^ and r9 represent the distance
from the center of the duct to the outer boundary of the core region.
The area in the core region was approximated by the following equation:
A
core
2
Tr(r1
~~~2
+ r.
(32)
Tables XX-XXIV show the calculated results of the velocity measure
ments at the five axial positions. The low flow was the flow measured
when a restriction was placed at the inlet of the blower. The restriction
induced approximately a 40% decrease in the flow rate. The high flow rate
represented a volumetric flow rate of 15,500 liters per minute, and the
low flow rate was 11,260 liters per minute. The Reynolds number of the
system calculated on a basis of the average axial flow rate were 80,000
and 111,000 for the low and high flow rates respectively.
After the data were broken down, it appeared that data from point
number 1 did not agree well with the rest of the traverse points. Upon

o
Misalignment Angle (6)
Figuie 29. Stokes number at which 95% maximum error occurs
vs. misalignment angle.

TABLE XIX
LOCATION OF SAMPLING POINTS
Point % of Diameter Distance from Wall, cm
1 3.3 0.65
2 10.5 2.07
3 19.4 3.83
4 32.3 6.38
5 67.7 13.36
6 80.6 15.91
7 89.5 17.67
8 96.7 19.09
Duct Diameter = 19.74 cm

43
differentials between holes as a function of yaw and pitch angles.
Figure 18 shows the sensitivity of a typical 5-hole pitot tube to yaw
angle. Because of its sensitivity to yaw angle, it is possible to rotate
the probe until the yaw pressures are equal, measure the angle of probe
rotation (yaw angle) and then determine the pitch angle from the re
maining pressure differentials. The probe can be used without rotation
by using the complete set of calibration curves but the complexity of
measurement and calculation is increased and accuracy is reduced. Vel
ocity components can then be calculated from the measured total pressure,
static pressure and yaw and pitch angle measurements.
The 3-hole pitot tube, also known as the two dimensional or
Fecheimer probe, is similar to the 5-hole design except that it is
unable to measure pitch angle. The probe is characterized by a central
total pressure opening at the tip of the probe with two static pressure
taps placed symmetrically to the side at an angle of from 20 to 50
degrees. From Figure 19 it can be seen that the probe is quite sensitive
to yaw angle and can therefore be used to determine the yaw angle by
rotating the probe until the pressure readings at the static taps are .
equal. Once this is done the total pressure is read from the central
port, and the static pressure can be determined by use of a calibration
chart for the particular probe. Both the 5-hole and the 3-hole pitot
tubes have proven useful in determination of velocity components in
tangential flow fields (25, 28, 30).
5. EPA Criteria for Sampling Cyclonic Flow
The revisions to reference methods 1-8 (2) describe a test for
determination of whether cyclonic flow exists in a stack. The S-type

TABLE XXXI
RESULTS OF THF. CYCLONE OUTLET SIMULATION MODEL
FOR THREE CONDITIONS
Particle Size Flow Concentration, Flow Rate3, Flow Rate'3, Emission Ratea,
Distribution Condition Measured/True Measured/True Measured/True Measured/True
MMD 3 ym
ag = 2.13
Low
0.937
1.27
1.16
1.19
MMD 3 ym
ag = 2.13
High
0.906
1.28
1.17
1 .16
MMD 10 ym
og =2.3
High
0.799
1.28
1.17
1.02
a Negative velocity is not used in the calculation of average velocity,
b Negative velocity is used in the calculation of average velocity.
Emission Rate ,
Measured/True
1.09
1.06
0.93

17
analyzing concentration errors obtained while sampling submicron
particles, 0.8 ym NMD and 1.28 geometric standard deviation, traveling
at near sonic and supersonic velocities. He obtained sample con
centrations 2-3 times greater than the true concentration when the
sampling velocity was 20% of the free stream velocity (R=5).
Sehmel (16) studied the isokinetic sampling of monodisperse
particles in a 2.81 inch ID duct and found that it is possible to obtain
a 20% concentration bias while sampling isokinetically with a small
diameter inlet probe. Results also showed that for all anisokinetic
sampling velocities, the concentration ratios were not simply cor
related with Stokes number.
2, Sampling Bias Due to Nozzle Misalignment
Sampling error associated with the nozzle misalignment has not
been adequately evaluated in past studies because the sampled flow
field was maintained or assumed constant in velocity and parallel to
the duct axis. The studies that have been performed on the effect of
probe misalignment do not provide enough quantitative information to
understand more than just the basic nature of the problem. Results
were produced through investigations by Mayhood and Langstroth, as
reported by Watson (5), on the effect of misalignment on the collection
efficiency of 4, 12 and 37 ym particles (see Figure 7). In a study by
Glauberman (17) on the directional dependence of air samplers, it was
found that a sampler head facing into the directional air stream col
lected the highest concentration. Although these results coincide with

15
0.16 and 5.5
3 (K, R) = 1 1/(1 +bK) (9)
where
b = 2 + 0.617/R (10)
Figure 6 shows a plot of equations (5), (9) and (10) for a range of
velocity ratios and Stokes numbers. The most significant changes in
the aspiration coefficient occur at values of K between 0 and 1.
Beyond K = 1, the aspiration coefficient tends to assymptotically ap
proach its theoretical limit of R. Beyond a Stokes number of about
6, it can be assumed that the aspiration coefficient equals R. This
can be predicted both from equations (5), (9) and (10) and from
theoretical considerations. Badzioch (10) and Belyaev and Levin (12)
have shown that the streamlines start to diverge at approximately 6
diameters upstream of the nozzle. Therefore, a particle traveling at
a velocity, V will have to change directions in an amount of time
equal to 6D^/Vo. If a particle cannot change direction in this amount
of time, it will not be able to make the turn with the streamline.
Since t represents the amount of time required for a particle to change
directions, setting x = 6D^/Vo represents the limiting size particle
that will be able to make a turn with its streamline. Rearranging these
terms it can be seen that this situation occurs when xV /D. = 6 or at a
o 1
Stokes number of 6.
Martone (15) further confirmed the importance considering free
stream velocity as well as particle diameter when sampling aerosols by

13
bearing on the quantity of dust collected. They suggested using the
product of the nozzle area and the stack gas velocity approaching the
nozzle as the gas sample volume, regardless of the velocity of the
nozzle. By using this method for particles greater than 80 pm, it
is possible to obtain small deviations even where departure from
isokinetic velocity is quite large. Whiteley and Reed (8) also observed
that calculating the dust concentrations from the approach velocity
instead of the actual sampling rate produced only slight errors when
sampling anisokinetically for large particles.
Lundgren and Calvert (9) found the sampling bias or aspiration
coefficient A, to be a function of the inertial impaction parameter K
and the velocity ratio R. They developed a chart which can be used
to predict inlet anisokinetic sampling bias depending on both K and R.
Badzioch's (10) equations defined the dependence of the efficiency upon
particle inertia and the velocity ratio. In a slightly different
terminology
A = C./Co = 1 + (R-l) 3(10 (5)
where f3(K) is a function of inertia given by
BOO [1-exp (-L/Â£)]/(L/Â£) (6)
Â£ is the stopping distance or the distance a particle with initial
velocity V will travel into a still fluid before coming to rest and
is defined by (11)
Â£ = tVo (7)

and geometric standard deviation (a ) of 2.13, the predicted concentration
was 10% less than the true concentration. For an aerosol with a 10.0 pm HMD
and a a of 2.3, a 20% error was predicted. Flow rates determined by the
Â§
S-type pitot tube were from 20 to 30% greater than the actual flow rate.
Implications of these results are described and recommendations for modifica
tion of the Method 5 sampling train for use in a tangential flow stream are
described.
xv

TABLE XXIV
FIVE-HOLE PITOT TUBE MEASUREMENTS
MADE AT 16 DIAMETERSDOWNSTREAM OF THE CYCLONE
16-D Low Flow
Point
Angles, Degrees
Pitch Yaw (J>
Total
Velocity
cm/sec
Axial
Velocity
cm/sec
Tangential
Velocity
cm/sec
1
* k *
kkk
k k k
k k k
kkk
kkk
2
27.0
34.0
42.4
1073
729
600
3
19.0
41.0
44.5
1169
834
767
4
9.0
58.6
59.0
1014
522
865
5
+ + +
+ + +
+ + +
+ + +
+ + +
+ + +
6
13.0
63.0
63.7
929
412
828
7
17.0
50.4
52.3
1205
735
928
8
18.0
47.6
50.11
1190
763
979
16-D
High Flow
Point
Ang
Pitch
les, Degrees
Yaw (f>
Total
Velocity
cm/sec
Axial
Velocity
cm/sec
Tangential
Velocity
cm/sec
1
k k k
kk k
k k k
k k k
k k k
kkk
2
22.5
36.4
42.0
1553
1154
921
3
21.0
44.0
47.8
1653
1110
1148
4
9.0
66.0
66.3
1513
608
1382
5
+ + +
+ + +
+ + +
+ + +
+ + +
+ + +
6
12.0
61.2
61.9
1675
789
1468
7
20.0
53.4
55.9
1753
983
1407
8
19.0
49.0
51.7
1739
1078
1312
*** Point No. 1 was too close to the wall to allow insertion of all five
pressure taps.
+++ Point lies inside the negative pressure section.

TABLE XV
ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER FOR R = 0.5, 0 = 60
Velocity
cm/sec
Particle Diameter
micrometers
Nozzle Diameter
cm
Stokes Number
Aspiration
Coefficient %
732
4,
,59
0.
,683
0.
,099
77
.7
80
.7
88
.8
732
6.
,5
0,
.683
0.
.196
79
.8
72
.2
72,
. 5
701
9.
,6
0,
.683
0.
.406
68
.4
58
. 6
62
.6
1463
7.
.8
0,
.465
0,
.8 25
47
.3
49
.2
47
.8
1585
9.
,6
0,
.465
1.
.35
34
.8
39.5
42.4
Cn

TABLE XII
ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER FOR 90 DEGREE MISALIGNMENT
Velocity Particle Diameter Nozzle Diameter Aspiration
cm/sec micrometers cm Stokes Number Coefficient %
549
1.372
0.683
0.0071
95.8
96.2
93.7
98.5
97.3
1798
1.08
0.465
0.002
95.0
93.5
97.4
1798
1.37
0.465
0.034
92.9
94.5
94.0
1798
1.72
0.465
0.053
87.6
1326
2.53
0.683
0.056
88.3
86.7
83.5
83.9
1326
3.23
0.683
0.090
73.7
74.7
75.3
1676
2.87
0.465
0.132
65.0
57.0
58.6
CO
o

Sampling
points
Figure 37. Cross sectional view of a tangential flow' stream locating pitch and yaw directions,
sampling points, and the negative pressure region.
105

134
B. Recommendations
EPA recommends that if the average angle of the flow relative to
the axis of the stack is greater than 10 degrees, then EPA Method 5
should not be performed. Since the maximum error in particle sampling
has been found to be (1 Rcos0), the 10 degree requirement is unduly
restrictive and a 20 degree limitation would be more appropriate. For
a 20 degree angle, the velocity measured by the S-type pitot tube would
be approximately the same as the true velocity (i.e., R = 1). Therefore,
the maximum error would be (1 cos 20) or 6% for a very large aerosol.
When cyclonic flow does not exist in a stack, EPA recommends
either straightening the flow or moving to another location. Because
of the physical limitations of these suggestions, a better approach
would be to modify Method 5 so that it could be used in a tangential
flow stream. By replacing the S-type pitot tube with a three-hole
pitot tube, the direction of the flow could be accurately determined
for aligning the nozzle, and the velocity components could be measured
for a correct calculation of volumetric flow rate. In addition to the
three-hole pitot tube, the modification would have to include a pro
tractor to measure the flow angle, an extra manometer, and a method of
rotating the probe without rotating the entire impinger box.

CHAPTER I
INTRODUCTION AND ISOKINETIC SAMPLING THEORY
A. Introduction
This study deals with the problems of obtaining a representative
sample of particulate matter from a gas stream that does not flow
parallel to the axis of the stack as in the case of swirling or
tangential flow. This type of flow is commonly found in stacks and
could be the source of substantial sampling error. The causes and
characteristics of this particular flow pattern are described and
the errors encountered in particulate concentration and emission
rate determinations are thoroughly analyzed and discussed.
The analysis of sampling errors is approached from two directions
in this study. One approach involves an investigation of aerosol
sampling bias due to anisokinetic sampling velocities and misalignment
of the nozzle with respect to the flow stream as a function of particle
and flow characteristics. The second part of the study involves an
accurate mapping of the flow patterns in a tangential flow system.
The information obtained in the two parts of the study will be combined
to simulate the errors that would be encountered when making an EPA
Method 5 (1, 2) analysis in a tangential flow stream.
1

59
therefore, each filter was dyed with ink and a grid was drawn to aid
in the counting. Before being placed in the filter holders, the filters
were examined under the microscope to determine if any background count
existed. After each test the filters were removed and the entire area
of the filter was counted.
The pollen caught in the nozzle and filter holder was analyzed
using isopropyl alcohol and 0.45 ym pore size Millipore membrane filters
with black grids. The isopropyl was first filtered several times to
remove background particulate matter. Once the background was low enough,
the alcohol was poured into the front half of the filter holder and
through the nozzles. The solution was then sucked through the membrane
filters. The filters were allowed to dry and then the entire filter
area was counted under the microscope.
G. Sampling Procedure
1. A desired flow rate was obtained by selecting an orifice
plate and using the by-pass as a fine adjust.
2. The velocity was measured using a standard pitot tube.
3. A solute-solvent solution was selected for a given particle
size.
4. Particles were collected on a membrane filter and sized
using a light microscope.
5. A nozzle diameter which would allow for an isokinetic
sampling rate closest to 1 cfm was selected.
6. Isokinetic sampling rates were calculated and sampling
flow rates were adjusted accordingly.

8
inertia affects the ability of the particle to negotiate turns with
its streamline which determines the amount of error. Therefore, in
all cases greater sampling errors will occur for larger particles and
higher velocities.
Besides determining the direction of the sampling bias, it is
also possible to predict theoretically the minimum and maximum error
for a given condition. This can be done by considering what happens
when the inertia of the particles is very small (i.e., the particles
can negotiate any turn that the streamlines make) and what happens
when the inertia of particles is very large (i.e., the particles are
unable to negotiate any turn with the streamlines). In the former
case of very low inertia, it can easily be seen that since the particles
are very mobile they do not leave their streamlines and therefore there
will be no sampling bias. In this situation the concentration of
particulate matter may be accurately obtained regardless of sampling
velocity or whether the nozzle is aligned with the flow stream. There
fore, a minimum error of 0 is obtained for small inertia particles.
The maximum error that can theoretically occur in anisokinetic
sampling depends on both the velocity ratio R, where
R = V /V. (1)
0 1
and the misalignment angle 0.
In the case of unequal velocities for very high inertia particles
which are unable to negotiate any change of direction, only those
particles directly in front of the projected area of the nozzle, A^,
will enter the nozzle regardless of the sampling velocity. Therefore,

LIST OF FIGURES
Figure Page
1 Isokinetic sampling 3
2 Superisokinetic sampling 4
3 Subisokinetic sampling 6
4 The effect of nozzle misalignment with flow stream 7
5 Relationship between the concentration ratio and the
velocity ratio for several size particles.... 11
6 Sampling efficiency as a function of Stokes number and
velocity ratio 16
7 Error due to misalignment of probe to flow stream 18
8 Sampling bias due to nozzle misalignment and anisokinetic
sampling velocity 21
9 Tangential flow induced by ducting 25
10 Double vortex flow induced by ducting 26
11 Velocity components in a swirling flow field 27
12 Cross sectional distribution of tangential velocity in a
swirling flow field 29
13 Cross sectional distribution of angular momentum in a
swirling flow field 30
14 S-type pitot tube with pitch and yaw angles defined 38
15 Velocity error vs. yaw angle for an S-type pitot tube.... 39
16 Velocity error vs. pitch angle for an S-type pitot tube.. 40
viii

CHAPTER II
REVIEW OF THE PERTINENT LITERATURE
A. Summary of the Literature on Anisokinetic Sampling
1. Sampling Bias Due to Unmatched Velocities
Numerous articles have been written describing the sources and
magnitude of errors when isokinetic conditions are not maintained.
In one of the earlier works, Lapple and Shepherd (4) studied the
trajectories of particles in a flow stream and presented a formula
for estimating the order of the magnitude of errors resulting when
there is a difference between the average sampling velocity and the
local free stream velocity. Watson (5) examined errors in the aniso
kinetic sampling of spherical particles of 4 and 32 pm mass mean
diameter (MMD) and found the relationships shown in Figure 5. Super-
isokinetic sampling (sampling with nozzle velocity greater than the
free stream velocity) leads to a concentration less than the actual
concentration, while subisokinetic sampling has the opposite effect.
Watson found that the magnitude of the error was not only a function
of particle size as seen in Figure 5, but also of the velocity and the
nozzle diameter. He proposed that the sampling efficiency was a function
of the dimensionless particle inertial parameter K (Stokes number)
defined as
? tV
K = Cp V D VlSnD. = 2- m
pop i 'J
10

MANOMETER
FILTER
ooo
GAS
METER
J
Figure 21
BY PASS
Sampling system.
cn
O

2
B. Isokinetic Sampling Theory
To obtain a representative sample of particulate matter from a
moving fluid, it is necessary to sample isokinetically. Isokinetic
sampling can be defined by two conditions: [3) 1) The suction or
nozzle velocity, must be equal to the free stream velocity, Vq;
and 2) the nozzle must be aligned parallel to the flow direction.
If these conditions are satisfied the frontal area of the nozzle, A.,
i
will be equal to the area of the cross section of the flow stream
entering the nozzle, Aq (see Figure 1). Thus, there will be no
divergence of streamlines either away from or into the nozzle, and
the particle concentration in the inlet, C., will be equal to the
particle concentration in the flow stream, C .
o
When divergence of streamlines is produced by superisokinetic
sampling, subisokinetic sampling or nozzle misalignment, there is a
possibility of particle size fractionation due to the inertial
properties of particles. In the case of superisokinetic sampling
(see Figure 2), the sampling velocity, V., is greater than the free
stream velocity, V Therefore, the area of the flow stream that is
o
sampled, A will be greater than the. frontal area of the sampling
nozzle, A^. All of the particles that lie in the projected area A^'
will enter into the nozzle. Particles outside this area but within A
o
will have to turn with the streamlines in order to be collected. Be
cause of their inertia, some of the larger particles will be unable to
make the turn and will not enter the sampling nozzle. Since not all of
the particles in the sampled area Aq will be collected, the measured
concentration will be less than the actual concentration.

Aspiration Coefficient (A)
1.00
0.80
0.60
0.4 0
0.20
0.00
0.01
O
O
o
o
o
|j>4-Typ
ical 95% C.I
G
O
o
J I I I L
G
I I 1 1 -L l l ti QL
0. L
1.0
l I I I l I
10.0
Stokes Number (K)
Figure 28. Sampling efficiency vs. Stokes number at 90 misalignment for R = 1.

ISOKINETIC SAMPLING OF AEROSOLS FROM TANGENTIAL FLOW STREAMS By Michael Dean Durham A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE 'REQUIRE^ENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1978

PAGE 2

ACKNOWLEDGEMENTS This research was partially supported by a grant (Grant Number R802692-01) from the Environmental Protection Agency (EPA)-, and was monitored by EPA's Project Officer Kenneth T. Knapp. I thank them both for their financial support during my graduate work. I wish to thank Dr. Dale Lundgren and Dr. Paul Urone for the important part that they played in my education. I am especially appreciative of Dr. Lundgren for his guidance, encouragement and confidence. He has provided me witli opportunities for classroom, laboratory and field experience that were far beyond what is expected of a committee chairman. 1 would like to thank Mrs. Kathy Sheridan for her assistance in preparing this manuscript. Finally, I wish to thank my parents for their advice and encouragement, and my wife Ellie for helping me through the difficult times. 11

PAGE 3

TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ii LIST OF TABLES v LIST OF FIGURES viii LIST OF SYMBOLS xi ABSTRACT xiii CHAPTER I INTRODUCTION AND ISOKINETIC SAMPLING THEORY 1 A. Introduction 1 B. Isokinetic Sampling Theory 2 II REVIEW OF THE PERTINENT LITERATURE 10 A. Summary of the Literature on Anisokinetic Sampling. 10 1. Sampling Bias Due to Unmatched Velocities 10 2. Sampling Bias Due to Nozzle Misalignment 17 B. Summary of the Literature on Tangential Flow 23 1. Causes and Characteristics of Tangential Flow 23 2 Errors Induced by Tangential Flow 31 3. Errors Due to the S-Type Pitot Tube 35 4. Methods Available for Measuring Velocity Components in a Tangential Flow Field 41 5. EPA Criteria for Sampling Cyclonic Flow 43 in EXPERIMENTAL APPARATUS AND METHODS 48 A. Experimental Design 48 B. Aerosol Generation 51 1 Spinning Disc Generator 51 2. Ragweed Pollen 53 C. Velocity Determination 53 D. Selection of Sampling Locations 57 E. Sampling Nozzles 57 111

PAGE 4

TABLE OF CONTENTS --continued CHAPTER Page F. Analysis Procedure 58 1 For Uranine Particles 58 2. For Ragweed Pollen 58 G. Sampling Procedure 59 H. Tangential Flow Mapping 60 IV RESULTS AND ANALYSIS 65 A. Aerosol Sampling Experiments 65 1 Stokes Number 65 2. Sampling with Parallel Nozzles 66 3. Analysis of Probe Wash 66 4. The Effect of Angle Misalignment on Sampling Efficiencies 69 5. The Effect of Nozzle Misalignment and Anisokinetic Sampling Velocity 89 B. Tangential Flow Mapping 102 V SIMULATION OF AN EPA METHOD 5 EMISSION TEST IN A TANGENTIAL FLOW STREAjM 117 VI SUMMARY AND RECOMMENDATIONS 129 A. Summary 129 B. Recommendations 134 REFERENCES 135 BIOGRAPHICAL SKETCH 139 IV

PAGE 5

LIST OF Ty\BLES Table Page I FLOW RATE DETERMINED AT VARIOUS MEASUREMENT LOCATIONS 33 II CONCENTRATION AT A POINT FOR DIFFERENT SAMPLING ANGLES 34 III EMISSION TEST RESULTS 36 IV SIZES AND DESCRIPTIONS OF EXPERIMENTAL AEROSOLS 52 V TABLE OF OBTAINABLE VELOCITIES IN 10 cm DUCT. 54 VI TYPICAL VELOCITY TRAVERSE IN THE EXPERIMENTAL SAJ-IPLING SYSTEM 55 VII RESULTS OF SAMPLING WITH TWO PARALLEL NOZZLES 67 VIII PERCENT OF PARTICULATE MATTER COLLECTED IN THE PROBE WASH FOR NOZZLES PARALLEL WITH THE FLOW STREAM 68 IX PERCENT OF PARTICULATE MATTER COLLECTED IN THE PROBE WASH FOR NOZZLES AT AN ANGLE OF 60 DEGREES WITH THE FLOW STREAiM. 70 X ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER FOR 30 DEGREE MISALIGNMENT 75 XI ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER FOR 60 DEGREE MISALIGNMENT 77 XII ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER FOR 90 DEGREE MISALIGNMENT 80 XIII COMPARISON OF SAMPLING EFFICIENCY RESULTS WITH THOSE OF BELYAEV AND LEVIN FOR 6 = R = 2 3 AND R = 0.5 92 XIV ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER FOR R = 2, = 60 94

PAGE 6

LIST OF TABLES-continued Table Pape XV ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER FOR R = 0.5, 6 = 60 95 XVI ASPIR./\TION COEFFICIENT AS A FUNCTION OF STOKES NUMBER FOR e = 45, R = 2.0 AND 0.5 97 XVII ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER FOR R = 2, 6 = 30 98 XVIII ASPIRATION COEFFICIENT AS A FUNCTION OF STOKES NUMBER FOR R = 2.1, e = 90 101 XIX LOCATION OF SAMPLING POINTS 105 XX FIVE-HOLE PITOT TUBE MEASUREMENTS MADE AT 1 DIAMETER DOWNSTREAM OF THE CYCLONE 106 XXI FIVE-HOLE PITOT TUBE MEASUREMENTS MADE AT 2 DIAMETERS DOWNSTREAM OF THE CYCLONE 107 XXII FIVE-HOLE PITOT TUBE MEASURENffiNTS MADE AT 4 DIAMETERS DOWNSTREAM OF THE CYCLONE 108 XXIII FIVE-HOLE PITOT TUBE MEASUREMENTS MADE AT 8 DIAMETERS DOWNSTREAI'l OF THE CYCLONE 109 XXIV FIVE -HOLE PITOT TUBE MEASUREMENTS MADE AT 16 DIAMETERS DOIVNSTREAM OF THE CYCLONE 110 XXV AVERAGE CROSS SECTIONAL VALUES AS A FUNCTION OF DISTANCE DOWNSTREAM AND FLOW RATE 112 XXVI S-TYPE PITOT TUBE MEASUREMENTS MADE AT THE 8-D SAiMPLING PORT FOR THE LOW FLOW CONDITION 118 XXVII S-TYPE PITOT TUBE MEASUREMENTS MADE AT THE 8-D S.-UIPLING PORT FOR THE HIGH FLOW CONDITION 119 XXVIII MIDPOINT PARTICLE DIAMETERS FOR THE 10 PERCENT INTERVALS OF THE MASS DISTRIBUTION MMD = 3ym a = 2.13 121 VI .-S'^lÂ•^=^^S^ ...MS^L ^

PAGE 7

LIST OF TABLES--continued Table Page XXIX ASPIRATION COEFFICIENTS CALCULATED IN THE SIMULATION MODEL FOR THE LOW FLOW CONDITION 124 XXX ASPIRATION COEFFICIENTS CALCULATED IN THE SIMULATION MODEL FOR THE HIGH FLOW CONDITION 125 XXXI RESULTS OF THE CYCLONE OUTLET SIMULATION MODEL FOR THREE CONDITIONS 127 XXXII SUMMARY OF EQUATIONS PREDICTING PARTICLE SA^1PLING BIAS 128 VI 1

PAGE 8

LIST OF FIGURES Figure Page 1 Isokinetic sampling 3 2 Superisokinetic sampling 4 3 Subisokinetic sampling 6 4 The effect of nozzle misalignment with flow stream 7 5 Relationship between the concentration ratio and the velocity ratio for several size particles 11 6 Sampling efficiency as a function of Stokes number and velocity ratio 16 7 Error due to misalignment of probe to flow stream IS 8 Sampling bias due to nozzle misalignment and anisokinetic sampling velocity 21 9 Tangential flow induced by ducting 25 10 Double vortex flow induced by ducting 26 11 Velocity components in a swirling flow field 27 12 Cross sectional distribution of tangential velocity in a swirling flow field 29 13 Cross sectional distribution of angular momentum in a swirling flow field 30 14 S-type pitot tube with pitch and yaw angles defined 38 15 Velocity error vs. yaw angle for an S-type pitot tube.... 39 16 Velocity error vs. pitch angle for an S-type pitot tube.. 40 Vlll

PAGE 9

LIST OF FIGURES--continued Figure Page 17a Conical version of a five-hole pitot tube 42 17b Fecheimer type three-hole pitot tube 42 18 Five-hole pitot tube sensitivity to yaw angle 44 19 Fecheimer pitot tube sensitivity to yaw angle 45 20 Experimental set up 49 21 Sampling system 50 22 Typical velocity profile in experimental test section.... 56 23 Experimental system for measuring cross sectional flow patterns in a swirling flow stream 61 24 Cyclone used in the study to generate swirling flow 62 25 Photograph of the 3-dimensional pitot with its traversing unit. Insert shows the location of the pressure taps.... 63 26 Sampling efficiency vs. Stokes number at 30 misalignment for R = 1 72 27 Sampling efficiency vs. Stokes number at 60 misalignment for R = 1 73 28 Sampling efficiency vs. Stokes number at 90 misalignment for R = 1 74 29 Stokes number at which 95% maximum error occurs vs. misalignment angle 83 30 6' vs. adjusted Stokes number for 30, 60 and 90 degrees.. 85 31 Aspiration coefficient vs. Stokes number model prediction and experimental data for 30, 60 and 90 degrees 87 32 Predicted aspiration coefficient vs. Stokes number for 15, 30, 45, 60, 75 and 90 degrees 88 IX

PAGE 10

LIST OF FIGURES--continued Figure Page 33 Comparison of experimental data with results from Belyaev and Levin 91 34 Sampling efficiency vs. Stokes number at 60 misalignment for R = 2.0 and 0.5 96 35 Sampling efficiency vs, Stokes number at 45 misalignment for I^ = 2.0 and R = 0.5 99 36 Sampling efficiency vs. Stokes number at 30 misalignment for U = 2.0 100 37 Cross sectional view of a tangential flow stream locating pitch and yaw directions, sampling points, and the negative pressure region 105 38 Decay of the average angle 9 and the core area along the axis of the duct 113 39 Decay of the tangential velocity component along the axis of the duct 114 40 Location of the negative pressure region as a function of distance downstream from the cyclone 116 41 Particle size distributions used in the simulation model... 120 ^! W^ ^t^rTJ^U^^*"*Â— T'^-t-*.'** i."* '^ i *'"'*-i**I-Vt'*'*

PAGE 11

SYMBOLS A. area of sampler inlet A 'projected area of sampler inlet A^ area of stream tube approaching nozzle A ratio of measured concentration to true concentration C Cunningham correction factor C. dust concentration in inlet Cq dust concentration in flow stream C r concentration ratio of aerosol generating solution D, droplet diameter D. inlet diameter 'S 1 D particle diameter K inertial impaction parameter K' adjusted Stokes number i stopping distance L undisturbed distance upstream from nozzle n constant R ratio of free stream velocity to inlet velocity s constant V axial component of stack velocity V velocity in inlet ^r ~ radial component of stack velocity V^ free stream velocity XI

PAGE 12

V^ tangential component of stack velocity &, 3', 6" functions determining whether particles will deviate from streamlines P particle density n viscosity ^ angle of the flow stream with respect to the stack axis e angle of misalignment of nozzle with respect to the flow stream T particle relaxation time Ap pressure difference Xll

PAGE 13

Abstract of Dissertation Presented to the Graduate Council of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy ISOKINETIC SAMPLING OF AEROSOLS FROM TANGENTIAL FLOW STREAMS By Michael D. Durham August, 1978 Chairman: Dale A. Lundgren Major Department: Environmental Engineering Sciences A comprehensive analysis of inertial effects in aerosol sampling was combined with a thorough study of swirling flow patterns in a stack following the exit of a cyclone in order to determine the errors involved in sampling particulate matter from a tangential flow stream. Two simultaneous samples, one isokinetic and the other anisokinetic were taken from a 10 cm wind tunnel and compared to determine sam.pl ing bias as a function of Stokes number. Monodispersed uranine particles, 1 to 11 pm in diameter, generated with a spinning disc aerosol generator, and mechanically dispersed 19.9 pm ragween pollen were used as experimental aerosols. The duct velocity was varied from 550 to 3600 cm/sec and two nozzle diameters of 0.465 and 0.6S3 cm were used to obtain values of Stokes numbers from 0.007 to 2.97. Experiments were performed at four angles, 0, 30, 60 and 90 degrees, to determine the errors encountered when sampling with an isokinetic sampling velocity but with the nozzle misaligned with the flow stream. The sampling bias approached a theoretical limit of (l-cosG) at a value of Stokes number between Xlll Â•(4=*Â— M *=-<^ti-:-a Wi

PAGE 14

1 and 6 depending on the angle of misalignment. It was discovered that the misalignment angle reduces the projected nozzle diameter and therefore effects the Stokes number; a correction factor as a function of angle was developed to adjust the Stokes number to account for this. Using an equation empirically developed from these test results and using the equations of Belyaev and Levin describing anisokinetic sampling bias with zero misalignment, a mathematical model was developed and tested which predicts the sampling error when both nozzle misalignment and anisokinetic sampling velocities occur simultaneously. It was found that the sampling bias approached a maximum error |l-Rcos0| where R is the ratio of the free stream velocity to the sampling velocity. During the testing, it was discovered that as much as 60% of the particulate matter entering the nozzle remained in the nozzle and front half of the filter holder. Implications of this phenomenon with regard to particle sampling and analysis are discussed The causes and characteristics of tangential flow streams are described as they relate to problems in aerosol sampling. The limitations of the S-type pitot tube when used in a swirling flow are discussed. A three dimensional or five-hole pitot tube was used to map cross sectional and axial flow patterns in a stack following the outlet of a cyclone. Angles as great as 70 degrees relative to the axis of the stack and a reverse flow core area were found in the stack. Using information found in this study, a simulation model was developed to determine the errors involved when making a Method 5 analysis in a tangential flow stream. For an aerosol with a 3.0 ym MMD (mass mean diameter) XIV

PAGE 15

and geometric standard deviation (o ) of 2.13, the predicted concentration was 10-5 less than the true concentration. For an aerosol with a 10.0 ym ^C^1D and a a of 2.3, a 20% error was predicted. Flow rates determined by the S-type pitot tube were from 20 to 30-5 greater than the actual flow rate. Implications of these results are described and recommendations for modification of the Method 5 sampling train for use in a tangential flow stream are described. XV Â• Â•is^m^'-'itix^i^

PAGE 16

CHAPTER I INTRODUCTION AND ISOKINETIC SAMPLING THEORY A. Introduction This study deals with the problems of obtaining a representative sample of particulate matter from a gas stream that does not flow parallel to the axis of the stack as in the case of swirling or tangential flow. This type of flow is commonly found in stacks and could be the source of substantial sampling error. The causes and characteristics of this particular flow pattern are described and the errors encountered in particulate concentration and emission rate determinations are thoroughly analyzed and discussed. The analysis of sampling errors is approached from two directions in this study. One approach involves an investigation of aerosol sampling bias due to anisokinetic sampling velocities and misalignment of the nozzle with respect to the flow stream as a function of particle and flow characteristics. The second part of the study involves an accurate mapping of the flow patterns in a tangential flow system. The information obtained in the two parts of the study will be combined to simulate the errors that would be encountered when making an EPA Method 5 (1, 2) analysis in a tangential flow stream. fc-,i^.MfinH'jt-^'r

PAGE 17

B. isokinetic S ampling Theory To obtain a representative sample of particulate matter from a moving fluid, it is necessary to sample isokinetically Isokinetic sampling can be defined by two conditions: [3} 1) The suction or nozzle velocity, V., must be equal to the free stream velocity, V ; 1 o and 2) the nozzle must be aligned parallel to the flow direction. If these conditions are satisfied the frontal area of the nozzle, A 1 will be equal to the area of the cross section of the flow stream entering the nozzle, A^ (see Figure 1). Thus, there will be no divergence of streamlines either away from or into the nozzle, and the particle concentration in the inlet, C, will be equal to the particle concentration in the flow stream, C o When divergence of streamlines is produced by superisokinetic sampling, subisokinetic sampling or nozzle misalignment, there is a possibility of particle size fractionation due to the inertial properties of particles. In the case of superisokinetic sampling [see Figure 2), the sampling velocity, V., is greater than the free stream velocity, V^ Therefore, the area of the flow stream that is sampled, A^ will be greater than the, frontal area of the sampling nozzle, A All of the particles that lie in the projected area A.' will enter into the nozzle. Particles outside this area but within A o will have to turn with the streamlines in order to be collected. Because of their inertia, some of the larger particles will be unable to make the turn and will not enter the sampling nozzle. Since not all of the particles in the sampled area A will be collected, the measured concentration will be less than the actual concentration.

PAGE 18

u u II Â•r > > -H > H Cu B rd M u -H -U OJ c o H 0) tn Â•H Em

PAGE 19

t > o u vl Â•H u V > > Â•H 1/; o H 3 W IN 3 Â•H. -~^S>*^0 -i-, Jfc-r 1 JÂ— >, |fc*->fcd| |( *-p^l^J

PAGE 20

Subisokinetic sampling defines the condition in which the sampling velocity is less than the free stream velocity (see Figure 5) In this situation the frontal area of the nozzle. A.', is greater than the sampled area of the flow, A^ The volume of air lying within the projected area, A^ but outside A will not be sampled and the streamlines will diverge around the nozzle. However, some of the particles in this area, because of their inertia, will be unable to negotiate the turn with the streamlines and will be collected in the nozzle. Because some of the particles outside the sampled area A will be collected along with all o '^ of the particles within A the measured concentration will be greater than the actual particle concentration. The bias due to misalignment of the nozzle with the flow stream is similar to that caused by superisokinetic sampling. When the nozzle is at an angle to the flow stream (Figure 4), the projected area of the nozzle is reduced by a factor equal to the cosine of the angle. Even if the nozzle velocity is equal to the flow stream velocity, a reduced concentration will be obtained because some of the larger particles will be unable to make the turn into the nozzle with the streamlines. Therefore, whenever the nozzle is misaligned, the concentration collected will always be less than or equal to the actual concentration. For all three conditions of anisokinetic sampling (superisokinetic, subisokinetic and nozzle misalignment] the magnitude of the measured concentration error will depend upon the size of the particles. More specifically it will depend upon particle inertia, which implies that the velocity and density of the particle are also important. Particle ^^i'k4-nnicnTJkl'*.~M>t'WlatirCiaF^f:UlII' t

PAGE 21

u u o > V > c Â•H rH i u r-( M P! Â•H O H to

PAGE 22

5-1 y o -H :5 -U c d) g c t7> Â•H rH N N O a 4-1 p u E^ CD U &> Â•H a,

PAGE 23

inertia affects the ability of the particle to negotiate turns with its streamline which determines the amount of error. Therefore, in all cases greater sampling errors will occur for larger particles and higher velocities. Besides determining the direction of the sampling bias, it is also possible to predict theoretically the minimum and maximum error for a given condition. This can be done by considering what happens when the inertia of the particles is very small (i.e., the particles can negotiate any turn that the streamlines make] and what happens when the inertia of particles is very large (i.e., the particles are unable to negotiate any turn with the streamlines) In the former case of very low inertia, it can easily be seen that since the particles are very mobile they do not leave their streamlines and therefore there will be no sampling bias. In this situation the concentration of particulate matter may be accurately obtained regardless of sampling velocity or whether the nozzle is aligned with the flow stream. Therefore, a minimum error of is obtained for small inertia particles. The maximum error that can theoretically occur in anisokinetic sampling depends on both the velocity ratio R, where f^ = \/\ CD and the misalignment angle 9. In the case of unequal velocities for very high inertia particles which are unable to negotiate any change of direction, only those particles directly in front of the projected area of the nozzle, A i' will enter the nozzle regardless of the sampling velocity. Therefore,

PAGE 24

the concentration collected by the nozzle will be equal to the number of particles entering the nozzle, A.V C divided bv the volume of 1 o o air sampled, A.V. 1 1 A.V C C V r10 o o ^i = -icvr = T(2) 11 1 The ratio of the sampled concentration to the true concentration then is equal to the inverse of the velocity ratio. Therefore, the maximum sampling bias for the condition of unmatched velocities is equal to V^/V^ or R. For example, if the sampling velocity is twice the free stream velocity, the resulting concentration will be one half the actual concentration. For the case of a misaligned nozzle, a similar analysis is applied. For the particles with very large inertia, only those lying directly in line with the projected frontal area of the nozzle will be collected. The measured concentration would again be the number of particles collected in the nozzle, A^cosBC^V^, divided by the volume of air sampled, A^V^. Therefore, the ratio of the measured to the true concentration would be V^cose/V^ or RcosB. This represents the maximum sampling error for anisokinetic sampling.

PAGE 25

CHAPTER II REVIEW OF THE PERTINENT LITERATURE A^__SummaÂ£)^^f^^ on Anisokinet ic Sampling j^. Sampling Bia s Due to Unmatched Velocities Numerous articles have been written describing the sources and magnitude of errors when isokinetic conditions are not maintained. In one of the earlier works, Lapple and Shepherd (4) studied the trajectories of particles in a flow stream and presented a formula for estimating the order of the magnitude of errors resulting when there is a difference between the average sampling velocity and the local free stream velocity. Watson (5) examined errors in the anisokinetic sampling of spherical particles of 4 and 32 ym mass mean diameter (MMD) and found the relationships shown in Figure 5. Superisokinetic sampling (sampling with nozzle velocity greater than the free stream velocity) leads to a concentration less than the actual concentration, while subisokinetic sampling has the opposite effect. Watson found that the magnitude of the error was not only a function of particle size as seen in Figure 5, but also of the velocity and the nozzle diameter. He proposed that the sampling efficiency was a function of the dimensionless particle inertial parameter K (Stokes number) defined as tV K = Cp V D -^/ISpD. = Â— ^ ,,, P o p 1 D. C3) 10

PAGE 26

11 H o H >^ t^ H U o > s C) u H \ H Â•H j' u R 23 W o n H 2: R O u Cm c o w (D -P 4-1 S: -0 B C O m !-l 4-1 O 'Â— r-( -P m rJ (U H -P 4J W rO fd ^^ CL -P C 0) QJ N o 0) x: -p m 5^ O c 0) -p y-i 0) X3 o -H Â•H rd x; J-j W C >, O -P H -H -P U rd O -H H CD dJ P^ > tn Â•H P4

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12 where D = particle diameter C Cunningham correction for slippage p = particle density T = p CD -/18n P P ^ C4} P = viscosity of gas D^ = nozzle diameter The relaxation time is defined as r; it represents how quickly a particle can change directions. Watson concluded that to obtain a concentration correct within 10%. the velocity ratio R must lie between 0.86 and 1.13 for the 32 micron particles and between 0.5 and 2.0 for the 4 micron particles. Data obtained by Dennis et al (6] on a suspension of Cottrell precipitated fly ash. 14 |^i MMD, showed only a 10% negative error in calculated concentration for sampling velocities 60% greater than isc kinetic. Tests run on an atmospheric dust of 0.5 ym MMD produced no detectable concentration changes even while sampling at a 400% variatic from isokinetic flow, thus indicating that isokinetic sampling is relatively unimportant for fine particles. Hemeon and Haines (7) measured errors due to the anisokinetic sampling of particles in three size ranges (5-25, 80-100, and 400-500 ym) and in a range of nozzle to stack velocities of 0.2 to 2.0. They found that where the velocity ratio R ranges from 0.6 to 2.0 the extreme potential error was approximately 50%, and that deficient nozzle velocities resulted m greater errors than excessive nozzle velocities. In addition, they found that for the coarse particles, the velocity into the nozzle had no important 30Lon

PAGE 28

bearing on the quantity of dust collected. They suggested using the product of the nozzle area and the stack gas velocity approaching the nozzle as the gas sample volume, regardless of the velocity of the nozzle. By using this method for particles greater than 80 ym, it is possible to obtain small deviations even where departure from isokinetic velocity is quite large. HTHteleyand Reed (8) also observed that calculating the dust concentrations from the approach velocity instead of the actual sampling rate produced only slight errors when sampling anisokinetically for large particles. Lundgren and Calvert (9) found the sampling bias or aspiration coefficient A, to be a function of the inertial impaction parameter K and the velocity ratio R. They developed a chart which can be used to predict inlet anisokinetic sampling bias depending on both K and R. Badzioch's CIO) equations defined the dependence of the efficiency upon particle inertia and the velocity ratio. In a slightly different terminology C5) (6} A = C./C^ = 1 (R-i) g^K) where g(K) is a function of inertia given by 3CK) = [1-exp C-L/Â£)]/(L/Â£) Z is the stopping distance or the distance a particle with initial velocity V^ will travel into a still fluid before coming to rest and is defined by [11] Â£ = TV .7. o (7)

PAGE 29

14 L is the distance upstream from the nozzle where the flow is undisturbed by the do^stream nozzle. It is a function of the nozzle diameter and is given by the equation: L = nD. ^g^ It was observed that n lies between 5.2 and 6.8 (10). Flash illumination photographic techniques were used by Belyaev and Levin (12) to study particle aspiration. Photographic observations enabled them to verify Badzioch's claim that L, the undisturbed distance upstream of the nozzle, was between 5 to 6 times the diameter of the nozzle. They examined the data of previous studies on error due to anisokinetic sampling and concluded that the discrepancy between experimental data was due to the researchers failing to take into account three things: 1) particle deposition in the inlet channel of the sampling device; 2) rebound of particles from the front edge of the sampling nozzle and their subsequent aspiration into the nozzle.; and 3) the shape and wall thickness of the nozzle. They also found that the sampling efficiency was a function of the inner diameter of the nozzle, D., as well as K and R. In a more recent article, Belyaev and Levin (13) examined the dependence of the function 6CK), in equation (4), on both the inertial impaction parameter. K, and the velocity ratio, R. Previous authors (10, 14) had concluded that 6(K) was a function of K alone, but Belyaev and Levin obtained experimental data demonstrating that for thin-walled nozzles, B(K) was also a function of R. Equations were developed from the data for values of K between O.IS and 6.0 and for values of R betv tween

PAGE 30

15 0.16 and 5.5 3(K,R) = 1 1/(1 +bK3 (9) where b = 2 + 0.617/R (10) Figure 6 shows a plot of equations (5) (9) and (10] for a range of velocity ratios and Stokes numbers. The most significant changes in the aspiration coefficient occur at values of K between and 1. Beyond K = 1, the aspiration coefficient tends to assymptotically approach its theoretical limit of R. Beyond a Stokes number of about 6, it can be assumed that the aspiration coefficient equals R. This can be predicted both from equations (5) (9) and (10) and from theoretical considerations. Badzioch (10) and Belyaev and Levin (12) have shown that the streamlines start to diverge at approximately 6 diameters upstream of the nozzle. Therefore, a particle traveling at a velocity, V will have to change directions in an amount of time equal to 6D-/V If a particle cannot change direction in this amount of time, it will not be able to make the turn with the streamline. Since T represents the amount of time required for a particle to change directions, setting t = 6D./V represents the limiting size particle 10^ c 1 that will be able to make a turn with its streamline. Rearranging these o o terms it can be seen that this situation occurs when tV /D. = 6 or at a o 1 Stokes number of 6. Martone (15) further confirmed the importance considering free stream velocity as well as particle diameter when sampling aerosols by

PAGE 31

16 H o o o o LO o o n o o

PAGE 32

17 analyzing concentration errors obtained while sampling submicron particles, 0.8 m NMD and 1.28 geometric standard deviation, travel.-n. at near sonic and supersonic velocities. He obtained sample concentrations 2-3 times greater than the true concentration when the sampling velocity was 205Â„ of the free stream velocity CR=5) Sehmel (16) studied the isokinetic sampling of monodisperse particles in a 2.81 inch IDduct and found that it is possible to obtain a 20% concentration bias while sampling isokinetically with a small diameter inlet probe. Results also showed that for all anisokinetic sampling velocities, the concentration ratios were not simply correlated with Stokes number. ^-^Â— ^^^^^2liilg_Ji^.lJHie toN Misali gnment Sampling error associated with the nozzle misalignment has not been adequately evaluated in past studies because the sampled flow field was maintained or assumed constant in velocity and parallel to the duct axis. The studies that have been performed on the effect of probe misalignment do not provide enough quantitative information to understand more than just the basi.c nature of the problem. Results were produced through investigations by Mayhood and Langstroth, as reported by IVatson (5), on the effect of misalignment on the collectxor efficiency of 4, 12 and 37 ym particles (see Figure 7). In a study by Glauberman (17) on the directional dependence of air samplers, it was found that a sampler head facing xnto the directional air stream collected the highest concentration. Although these results coincide with

PAGE 33

*ru < IX o u 12 ym 30 60 90 120 ANGLE OF PROBE MISALIGNMENT, degrees Figure 7. Error due to misalignment of probe to flow stream faft Mayhood and Langstroth, in Watson (5]]. er

PAGE 34

19 theoretical predictions [i.e., measured concentration is less than or equal to actual concentration and the concentration ratios decrease as the particle size and the angle are increased), the data are of little use since two important parameters, free stream velocity and nozzle diameter, are not included in the analysis. Raynor (18) sampled particles of 0.68, 6 and 20 ym diameter at wind speeds of 100, 200, 400 and 700 cm/sec with the nozzle aligned over a range of angles from 60 to 120 degrees. He then used a trigonometric function to convert equation (5) to the form A = 1 + BCK)[(V.sin0 + V cos0)/ (V. cos0 + V sinG) 1] (11) This function only serves to invert the velocity ratio between and 90 degrees and does not realistically represent the physical properties of the flow stream. In fact, equation (11) becomes unity at 45 degrees regardless of what the velocity ratio or particle size is. This cannot be true since it has been shown that the concentration ratio will be less than unity and will decrease inversely proportional to the angle and particle diameter. A more representative function can be derived in the following manner: Consider the sampling velocity V. to be greater than the stack velocity V^. Let A^ be the cross sectional area of the nozzle of diameter D^. The stream tube approaching the nozzle will have a cross sectional area A such that o A V = A. V. (^7^ 11 '-^^J i-(l,_*l i'"rliil^l.t.ll-

PAGE 35

20 If the nozzle is at an angle 9 to the flow streaip,, the projected area perpendicular to the flow is an ellipse with a major axis D., minor axis D.COS0, and area (D. "^cose)/4 The projected area of the nozzle would therefore be A.cos0 (see Figure 8). It can be seen that all the particles contained in the volume V^A.cosG will enter the nozzle. A fraction 8'CK,R,9} of the particles in the volume (A A.cosGlV will o 1 ^ o leave the stream tube because of their inertia and will not enter the nozzle. Therefore, with C^ defining the actual concentration of the particles, the measured concentration in the nozzle would be C A coseV + [l-3'(K,R,e3](A -A.cos0)V C C. = -5-i .JLÂ— 1 o o ,^^_ 1 ~ Â— Â— (1^) A.V. 1 1 Using equations (1) and (12), this may be simplified to A = C^/C^ = 1 + 3'(K,R,e)(Rcos0-l) (14) 6'(K,R,0) would be a function of both the velocity ratio R and the inertial impaction parameter K as shown by Belyaev and Levin (13). However, 3' will also be a function of the angle because as the angle increases, the severity of the turn that the particles must make to be collected is also increased. It can be seen that for large values of Stokes number, 6' must approach 1 for the predicted concentration ratio in equation (14) to reach the theoretical limit of RcosO. The maximum error should theoretically occur somewhere between a Stokes number of 1 and 6 depending on the angle a. The upper limit of K 6 would be for an angle of degrees as described earlier in this chapter. The theoretical lower limit of K = 1 1 1 miatim^ m^ nt^czmaai^uUii:.^^^^

PAGE 36

21 >s o o > Pi m +-> 0) c r-< O Â•H c nj Â•n (=; Â• H 1Â— I cd i/i Â•H e CD IÂ— I N N O c Â•H CO 0)

PAGE 37

22 would be for an angle oÂ£ 90 degrees in which case the particles would be traveling perpendicular to the nozzle. Since the nozzle has zero frontal area relative to the flow stream, any particle that is collected must make a turn into the nozzle. The amount of time that a particle has to negotiate a turn is the time it takes the particle to traverse the diameter of the nozzle, or D^/V Setting this equal to T the time it takes a particle to change directions and rearranging terms, we obtain tV^/D^ = 1 as the limiting situation for a particle to be able to make a turn into a nozzle positioned at a 90 degree angle to the flow stream. For angles between and 90 degrees the maximum error will occur between the limits of Stokes numbers of 1 and 6 and should be proportional to the average diameter of the frontal area of the nozzle. Fuchs [19) suggests that for small angles the sampling efficiency will be of the form A = 1 4 sinCGK/TT) (15) Laktionov (20) sampled a polydisperse oil aerosol at an angle to the flow stream of 90 degrees for three subisokinetic conditions. He used a photoelectric installation to enable him to determine the aspiration coefficients for different sized particles. From data obtained over a range of Stokes numbers from 0.003 to 0.2 he developed the following empirical equation: ^ .,.[v./v )'^ A = 1 jK^ i' 0-' (16) This equation can be used only in the range of Stokes numbers given and for a range in velocity ratios (R) from 1.25 to 6.25.

PAGE 38

23 A few analytical studies in this area have also been published. Davies' (14) theoretical calculations of particle trajectories in a nonviscous flow into a point sink determined the sampling accuracy to be a function of the nozzle inlet orientation and diameter, the sampling flow rate and the dust particle inertia. Vitols (21) also made theoretical estimates of errors due to anisokinetic sampling. He used a procedure combining an analog and a digital computer and considered inertia as the predominant mechanism in the collection of the particulate matter. However, the results obtained by Vitols are only for high values of Stokes numbers and are of little value for this study. B. Summary of the Literature on Tangential Fl ow Although anisokinetic sampling velocity is known to cause a particle sampling bias or error, there are also several other sampling error-causing factors such as: duct turbulence; external force fields (e.g., centrifugal, electrical, gravitational or thermal); and probe misalignment due to tangential or circulation flow. These factors are almost always present in an industrial stack gas and cannot be assumed to be negligible. Not only do these factors cause sampling error directly but in addition, they cause particulate concentration gradients and aerosol size distribution variations to exist across the stack both in the radial and angular directions. 1. Causes and Characteristics_ of Tangential Fl oiv an Tangential flow is the non-random flow in a direction other th that parallel to the duct center line direction. In an air pollution

PAGE 39

24 control device, whenever centrifugal force is used as the primary particle collecting mechanism, tangential flow will occur. Gas flowing from the outlet of a cyclone is a classic example of tangential flow and a well recognized problem area for accurate particulate sampling. Tangential flow can also be caused by flow changes induced by ducting (22). If the duct work introduces the gas stream into the stack tangentially, a helical flow will occur (see Figure 9). Even if the flow stream enters the center of the stack, if the ducting flow rate is within an order of magnitude of the stack flow rate, a double vortex flow pattern will occur (see Figure 10) The swirling flow in the stack combines the characteristics of vortex motion with axial motion along the stack axis. The gas stream moves in spiral or helical paths up the stack. Since this represents a developing flow field, the swirl level decays and the velocity profiles and static pressure distributions change with axial position along the stack. Swirl level is used here to represent the axial flow or transport rate of angular momentum (23) Velocity vectors in tangential or vortex flows are composed of axial, radial and tangential or circumferential velocity components (see Figure 11). The established vortex flows are generally axisymmetric but during formation of the spiraling flow the symmetry is often distorted. The relative order of magnitude of the velocity components varies across the flow field with the possibLlity of each one of the components becoming dominant at particular points (24) -^Wii^^diir^

PAGE 40

25 < a. o c Â•H +J o U 3 C >H s o i-i H +J faO C CD H

PAGE 41

26 m < I tc +-> o 3 T3 X o c Â•H o X u o > 3 a o M M 3 Â•H

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27 Figure 11. Velocity components in a swirling flow field.

PAGE 43

28 The two distinctly different types of flow that are possible in a swirling flow field are knovm as free vortex and forced vortex flows. When the swirling component of flow is first created in the cyclone exit, the tangential profile of the induced flow approaches that of a forced vortex. As the forced vortex flow moves along the axis of the stack, momentum transfer and losses occur at the wall which cause a reduction in the tangential velocity and dissipation of angular momentum. This loss of angular momentum is due to viscous action aided by unstable flow and fluctuating components. Simultaneously, outside the laminar sublayer at the wall where inertial forces are significant, the field develops toward a state of constant angular momentum. This type of flow field with constant angular momention is classified as free vortex flow. The angular momentum and tangential velocities of the flow decay as the gas stream flows up the stack (23) Baker and Sayre measured axial and tangential point velocity distributions in a 14.6 cm circular duct in which swirling flow was produced by fixed vanes (23) The tangential velocity profiles and angular momentum distributions are plotted in Figures 12 and 13 from measurements taken at 9, 24 and 44 diameters downstream of the origin of tangential flow. The tangential velocity (W) is made dimensionless by dividing it by the mean spatial axial velocity (U^) at a pipe cross section. These plots indicate developing flow fields, with two definite types of flow occurring: that approaching forced vortex flow in the central region of the pipe and flow approaching free vortex flow in the outer region. Further tests showed that the free vortex field

PAGE 44

29 rH CD Â•H Mh a o .-( m O o > Â• H )-> c M C c P o PJ o H' U P Â•rt 13 R O Â•H +J O d) U3 tn o u So H

PAGE 45

30 1 i 1 1 1 rÂ— 1 f 1 \ -1\ r-i \ II Â• / 11 X X \ \ \ \ -' \\ \ \ ^ \ \ \ \ \ \ Â— \ 1 1 : 1 1 ( 1 I 1 / i O LT; o H 3: o IÂ— I G 'A B Â•H I P i E P O o !-> 3 ,o Â•H Â•p Â• H PI o Â•H +J u m m m O U a ci. 5j

PAGE 46

development is due primarily to viscosity at the wall and not a function of inlet conditions, whereas the profiles in the forced vortex field are very dependent on the initial conditions at the inlet. Although no reverse flow was found in these tests, other tests showed that strong swirls may produce reversed axial velocities in the central region (25) It should be noted that although tangential velocities and angular momentum decay along the axis of the pipe, see Figures 12 and 13, even after 44 diameter the tangential velocity is still quite significant when compared to the axial velocity. Therefore, satisfying the EPA Method 5 requirement of sampling 8 stack diameters downstream of the nearest upstream disturbances will not eliminate the effect of sampling in tangential flow. The angle of the flow relative to the axis of the stack induced by the tangential component of velocity was as high as 60 degrees at some points in the flow. This compares well with angles found when sampling the outlets of cyclones (25) Another interesting fact about the flow described in Figures 12 and 13 is that the radial positions for the tangential components W/U = show that the vortex axis is off center by as much as O.lr/R. This indicates that the swirling fields are not exactly axis^-mmetrical 2. Errors Induced by Tangential Flow Types of errors that would be expected to be introduced by tangential flow are nozzle misalignment, concentration gradients and invalid flow measurements. The sampling error caused by nozzle misalignment lias been

PAGE 47

32 described in the previous chapter. Concentration gradients occur because the rotational flow in the stack acts somewhat as a cyclone. The centrifugal force causes the larger particles to move toward the walls of the stack, causing higher concentrations in the outer regions. Mason (22] ran tests at the outlet of a small industrial cyclone to determine the magnitude of these three types of errors induced by cyclonic flow. Results of flow rates determined at the different locations are presented in Table I. As indicated by the data, serious errors can result in cases of tangential flow. A maximum error of 212', occurred when the pitot tube was rotated to read a maximum velocity head. Sampling parallel to the stack wall also had a large error of almost 74-6. When sampling downstream of the flow straightening vanes, however, the error was reduced to 15%. Tests performed at the same point but with different nozzle angles produced the data in Table 11. Measured dust concentration was lowest when the sampling nozzle was located at an angle of degrees or parallel to the stack wall. The measured dust concentration continued to increase at 30 and 60 degrees but then decreased at 90 degrees. Equation (14) shoivs that when sampling at an angle, under apparent isokinetic conditions (i.e., R=l) the measured concentration will be less than the true concentration by a factor directly proportional to the cos9. A maximum concentration, which would be the true concentration, will occur at = 0, which from this data should lie at an angle between 60 and 90 degrees to the axis of the stack. This can be confirmed by vsss>"i^S^L^i^^fi^^s^ 2i''\'i.*.^r>^.^

PAGE 48

TABLE I FLOW RATE DETERMINED AT VARIOUS MEASURENENT LOCATIONS Location VelocjLty_j;fp_sJ__ Flow Rate (scfm) % Error Actual Based on Fan Performance Port A (parallel) Port A (maximum Ap) Port C (straightened) 18 40 60 21 475 826 1,482 548 74 212 15

PAGE 49

34 TABLE II CONCENTRATION AT A POINT FOR DIFFERENT SAMPLING ANGLES Nozzle Angle 30 60 90 easured Concentration (grains/dscf) 243 296 332 316 n ,..44
PAGE 50

35 using the data in Table I and the geometry in Figure 11 to calculate the angle cj): cos(|) = V /V = 18/60 (17) This is true for ^ 12 degrees. Therefore, 9 = when (}) = 72 degrees. :| Table III gives the results of the emission tests. Sampling with I il the nozzle parallel to the stack wall showed an error of 53%. I j Sampling at the angle of maximum velocity head reduced the error to 40-<;. The results cannot be compared directly to those with the parallel sampling approach because the feed rates were not the same due to equipment failure and replacement. Sampling in the straightened flow had a sampling error of 36%. It was expected that sampling at this location would give better results, but some of the particles were impacted on the straightening vanes and settled in the horizontal section of the duct, thus removing them from the flow stream. Particle size distribution tests showed no significant effect of a concentration gradient across the traverse. This was due to the particles being too small to be affected by the centrifugal force field set up by the rotating flow. 5. Errors Due to t he S-Type Pitot Tube The errors in the measurement of velocity and subsequent calculations of flow rate in tangential flow are due primarily to the crudenoss of the instruments used in source sampling. Because of the high particulate loadings that exist in source sampling, standard pitot tubes cannot be used to measure the velocity. Instead, the S-type pitot tube must be used

PAGE 51

TABLE III EMISSION TEST RESULTS Probe Position Measured Emission Rate (gr/dscf) Actual Emission Rate (gr/dscf) Error % Nozzle parallel with stack wall Nozzle rotated toward maximum Ap Straightened flow 0.350 0.194 0.207 0.752 53 0.327 40 0.325 36

PAGE 52

37 since it has large diameter pressure ports that will not plug (see Figure 14) Besides the large pressure ports it has an additional advantage of producing approximately a 20% higher differential pressure than the standard pitot tube for a given velocity. However, although the S-type pitot tube will give an accurate velocity measurement, it is somewhat insensitive to the direction of the flow (25-29) Figures 15 and 16 show the velocity errors for yaw and pitch angles. Although the S-type pitot tube is very sensitive to pitch direction, the curve for yaw angle is symmetrical and somewhat flat for an angle of 45 degrees in either direction. Because of this insensitivity to direction of flow in the yaw direction, the S-type pitot tube cannot be used in a tangential flow situation to align the nozzle to the direction of the flow, or to accurately measure the velocity in a particular direction. The velocity in a rotational flow field can be broken up into three components in the axial, radial and tangential directions (see Figure 11). The magnitude of the radial and tangential components relative to the axial component will determine the degree of error induced by the tangential flow. Neither the radial nor the tangential components of velocity affect the flow rate through the stack, but both affect the velocity measurement made by the S-type pitot tube because it lacks directional sensitivity. If the maximum velocity head were used to calculate the stack velocity, the resultant calculated flow rates and emission levels could be off by as much as a factor of l/cos(J). Aligning the probe parallel to the stack will reduce but not eliminate this error because part of the radial and tangential velocity components will still be detected by the pitot tube.

PAGE 53

38 Â•i-r 4-i in I Â— f c p o o 1:1I

PAGE 54

39 00 o D Â•H Cc o 1*^ c Â£ > o u H U o a; > U no

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40 a u CD '71 E E o 1 Â— I to O) o O > P <-J =>,= c Â•H o CD () (N CJ o 1 fH OJ CU o o (M Â• 3 o ID C w c c3 c a u +-> Â•w > O U u o X .Â—J u o o KO 3

PAGE 56

41 L Therefore, the true flow rate cannot be determined by an S-type pitot tube in tangential flow because neither the radial velocitv, V the tangential velocity, V the axial velocity, V nor the angle c^ can be measured directly. ii-JMlH^^^A^i^ilable^Jo^^ in a Tangential Flow Field ~^"" "~ ~ Â— -^_ ^^ Â— Almost all of the reported measurements of velocity components in a tangential flow field have been based upon introduction of probes into the flow. Because of the sensitivity of vortex flows to the introduction of probes, the probe dimensions must be small with respect to the vortex core in order to accurately measure velocity. Two common types of pressure probes capable of measuring velocity accurately are the 5-hole and 5-holc pitot tubes pictured in Figures 17a and b. The 5-hole or three dimensional directional pressure probe is used to measure yaw and pitch angles, and total and static pressure. Five pressure taps are drilled in a hemispherical or conical probe tip, one on the axis and at the pole of the tip, the other four spaced equidistant from the first and from each other at an angle of 30 to 50 degrees from the pole. The operation of the probe is based upon the surface pressure distribution around the probe tip. If the probe is placed in a flow field at an angle to the total mean velocity vector, then a pressure differential will be set up across these holes; the magnitude of which will depend upon the geometry of the probe tip, relative position of the holes and the magnitude and direction of the velocity vector. Each probe requires calibration of the pressure

PAGE 57

42 _J o O CD > O e o H m > (J H c o u u M ^Â•^^-Tl**-
PAGE 58

45 differentials betvveen holes as a function of yaw and pitch angles. Figure IS shows the sensitivity of a typical 5-hole pitot tube to yaw angle. Because of its sensitivity to yaw angle, it is possible to rotate the probe until the yaw pressures are equal, measure the angle of probe rotation (yaw angle) and then determine the pitch angle from the remaining pressure differentials. The probe can be used without rotation by using the complete set of calibration curves but the complexity of measurement and calculation is increased and accuracy is reduced. Velocity components can then be calculated from the measured total pressure, static pressure and yaw and pitch angle measurements. The 3-hole pitot tube, also known as the two dimensional or Fecheimer probe, is similar to the 5-hole design except that it is unable to measure pitch angle. The probe is characterized by a central total pressure opening at the tip of the probe with two static pressure taps placed s>imiietrically to the side at an angle of from 20 to 50 degrees. From Figure 19 it can be seen that the probe is quite sensitive to yaw angle and can therefore be used to determine the yaw angle by rotating the probe until the pressure readings at the static taps are equal. Once this is done the total pressure is read from the central port, and the static pressure can be determined by use of a calibration chart for the particular probe. Both the 5-hole and the 3-hole pitot tubes have proven useful in determination of velocity components in tangential flow fields (25, 28, 30). 5. EPA Criteria for Sampling _Cyc lonic Fl ow The revisions to reference methods 1-8 (2) describe a test for determination of whether cyclonic flow exists in a stack. The S-type sMitim**r-,mf.i

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44 Figure 18. ('ive-holc pi pitot tube sensitivity to yaw angle. (281

46 pitot tube is used to determine the angle of the flow relative to the axis of the stack by turning the pitot tube until the pressure reading at the two pressure openings is the same. If the average angle of the flow across the cross section of the stack is greater then 10 degrees, then an alternative method of Method 5 should be used to sample the gas stream. The alternative procedures include installation of straightening vanes, calculating the total volumetric flow rate stoichiometrically, or moving to another measurement site at which the flow is acceptable. Straightening vanes have shown the capability of reducing swirling flows; however, there are some problems inherent in their use. One is the physical limitation of placing them in an existing stack. Another is the cost in terms of energy due to the loss of velocity pressure when eliminating the tangential and radial components of velocity. Since the vortex flows are so sensitive to downstream disturbances, it is quite possible that straightening vanes might have a drastic effect on the performance of the upstream cyclonic control device which is generating the tangential flow. Because of these reasons the use of straightening vanes is unacceptable in many situations. Calculating the volumetric flow rate stoichiometrically might produce accurate flow rates but the values could not be used to calculate the necessary isokinetic sampling velocities and directions. Also, studies reported here have shown that the decay of the tangential component of velocity in circular stacks is rather slow and therefore it would be unlikely that another measurement site would solve the problem.

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47 It should be noted that EPA's approach to determining whctlier cyclonic flow exists in a stack is correct. Other approaches such as observing the behavior of the plume after leaving the stack could lead to improper conclusions. Hanson et al (28} found that the twin-spiraling vorticies often seen leaving stacks are the result of secondary flow effects generated by the bending of the gas stream by the prevailing crosswind and do not indicate any cyclonic flow existing in the stack.

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CHAPTER III EXPERIMENTAL APPARATUS AND METHODS A. Experimental Design The major components of the aerosol flow system can be seen in Figure 20. An aerosol stream generated from a spinning disc generator was fed into a mixing chamber where it was combined with dilution air. The air stream then flowed through a 10 cm diameter PVC pipe containing straightening vanes. This was followed by a straight section of clear pipe from which samples were taken. The filter holder and nozzle used as a control sample originated in a box following the straight section. A test nozzle was inserted into the duct at an angle from outside the box. A thin-plate orifice, used to monitor flow rate, followed the sampling box. A 34000 Â£pm industrial blower was used to move the air through the system. The flow rate could be controlled by changing the diameter of an orifice plate. An air by-pass between the blower and the orifice plate was used as a fine adjust for the flow. The sampling systems (see Figure 21] consisted of stainless steel, thin-walled nozzles connected to 47 mm stainless steel Gelman filter holders. Each filter assembly was connected in series to a dry gas meter and a rotameter, and driven by an airtight pump with a by-pass valve to control flow. 48

PAGE 64

49 CO en LU Q_ CD or: CD 1 tÂ— CD LU Qi ^i: LU LlJ
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50 , d Â•H H g 0) 3 Â•rH &4

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:e 51 B^ Aeroso l Generation 1_^ Sj^in ning Disc Generator A spinning disc aerosol generator (51-33) was used to generate monodisperse aerosols from 1.0 ym NMD to 11.1 ym NMD [see Table IV). Droplets were generated from a mixture of 90% uranine (a fluorescent dye) and 10?6 methylene blue dissolved in a solution of from 90 to 100% ethanol (95% pure) and up to 10% distil led/deionized H^O. Uranine was used so that the particles could be detected by fluoremetric methods. Methylene blue was added to aid in the optical sizing of the particles. The mixture of water and ethanol allowed for a uniform evaporation of the droplets. The droplets, containing dissolved solute, evaporated to yield particles whose diameters could be calculated from the equation % = ^^'-''^ % (IB) where D = particle diameter, ym C^ = ratio of solute volume to solvent volume plus solute volume, dimensionless Dp = original droplet diameter, ym With the disc's rotational velocity, air flows and liquid feed rate held constant the size of the droplets produced were only dependent upon the ratio of the ethanol -water mixture. Since the droplets are produced from a dynamic force balance between the centrifugal force and the surface

55 tension of the drop, the surface characteristics of the liquid are quite important. The surface tensions of water and ethanol at 20 degrees C are respectively 72.8 and 22.3 dynes/cm (34). The effect of this large difference can be seen in Table IV where the droplets produced were approximately 37 ym for 90% ethanol and 23 ym for 100% ethanol Before and after each test a sample of the particles was collected on a membrane filter and sized using a light microscope to take into account any slight variation in the performance of the spinning disc. 2. Ragweed Pollen In order to obtain large Stokes numbers, ragweed pollen was mechanically dispersed by means of a rubber squeeze bulb into the inlet of the duct. The ragweed pollen had a NMD of 19.9 ym. C. Velocity Determination The velocity at each sampling point was measured using a standard pitot tube. The flow was maintained constant during the test by controlling the pressure drop across a thin-walled orifice placed in the system (35-37). Five orifice plates with orifices ranging in diameter from 1.8 to 7.2 cm were used to obtain a range in duct velocities of 82 to 2460 cm/sec (see Table V) in the 10 cm duct. To obtain higher velocities, a 5 cm duct was used. A typical velocity profile across the 9 6 cm clear plastic duct is presented in Table VI and plotted in Figure 22. The profile is (m'-: lllllir"-.ill*"**= w^ *-"^.M

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54 TABLE V TABLE OF OBTAINABLE VELOCITIES IN 10 cm DUCT Orii -ice Diameter Ap Range Ran ge in Velocity cm cm H^b 5.6 21.6 cm/ sec 1 795 82 162 2.539 5.3 21.8 162 326 5.5 89 4.2 22.9 304 670 5.080 4.1 22.6 582 1371 7.182 2.2 14.5 945 2460

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55 TABLE VI TYPICAL VELOCITY TRAVERSE IN THE EXPERIMENTAL SMIPLING SYSTEM (9.58 cm I.D. Duct) Point d/D AP Hor cm 11^ izontal V, cm/sec AP, cm Vert ical V cm/ sec 1 0.044 1.27 1454 1.57 161S 2 146 1.83 1743 2.11 1871 3 0.296 2.03 1S3S 2. OS 1859 4 0.704 2.13 1884 2.11 1871 5 854 1.88 1768 1.98 1813 6 0.956 1.47 1564 1.52 1591 Average Velocities [cm/sec) From Pitot Tube Readings From Orifice AP 1740 1658

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56 O ID Â•H CD M-< rÂ— 1 O Â•H ^-1 t+J p o J-l pÂ— J CL, rt p rH c ri o o N l-J +-> f-l u o (D iz: > O Q m \o 3 CO c o Â•H p u 0) 'Jl 'O Â•l-l 'Jl o 0) c e Â•H a X Â•H 4-^ o Â• t-l Â•H a o TÂ— t > rt o Â• H ^4 (D 3 Â•H tl. o o c o o rj (N rÂ—4

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57 quite flat which is typical of the turbulent flow regime. The average Reynolds number for this particular case was 1.1 x 10 The velocities at traverse points 3 and 4 were used as the velocity for determination of isokinetic sampling rate and Stokes number. The difference between the average velocity determined from the pitot traverse and the orifice plate calibration is probably due to the inability of the pitot tube to accurately measure velocity near the wall at points 1 and 6. D. Selection of Sampling Locations Sehmel (16) observed that non-uniform particle concentrations existed across the diameter of a cylindrical duct, and that the magnitude of the concentration gradient varied with particle size. To account for these radial variations, the two sampling points were located symmetrically about the center of the duct at a distance of 2 cm from the center. Simultaneous isokinetic samples were taken at the two points and compared. Tests were repeated for different particle sizes. No concentration differences were found to exist at the two sampling points. E. Sampling Nozzles Two pairs of sampling nozzles were cut from stainless steel tubing of 0.465 cm and 0.683 cm l.D. The nozzles were made approximately 15 cm long to minimize the effect of the disturbance caused by the filter holders on the flow at the entrance of the nozzles. Analysis by Smith (38) showed that a sharp-edge probe was the most efficient design; it!:*A4-.*^it*Â— iC-ii^-t -NS-Ui i.rr:;w

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58 therefore, the tubing was tapered on a lathe to a fine edge. Belyaev and Levin (12) observed that the rebound of particles from the tip of the nozzle into the probe was one cause of sampling error and that for tapered nozzles, the efficiency is affected by the relative wall thickness, the relative edge thickness and the angle of taper. They concluded that if the edge thickness is less than 5% of the internal diameter and the taper is less than 15 degrees, then the variation in aspiration coefficient due to particle rebound would be less than 5%. The nozzles were designed accordingly. F. Analysis Procedu re 1. For Uranine Particles Uranine particles were collected on Gelman type A glass fiber filters. The filters were then placed in a 250 ml beaker. One hundred milliliters of distilled water were then pipetted into the front half of the filter holder and down through the nozzle into the beaker containing the filter. The uranine leachate concentration was then diluted and analyzed by a fluorometer (39) 2. For Ragweed Pollen The ragweed pollen was collected on membrane filters and counted under a stereo microscope. In this part of the experiment the filters and probe were analyzed separately. The filters used for collecting the particles were 5.0 pm type SM Millipore membrane filters. In order to count the particles under a microscope a dark background was necessary; M-**^. Vf lDliM'1Ui-t>|c<''^kMM

PAGE 74

59 therefore, each filter was dyed with ink and a grid was drawn to aid in the counting. Before being placed in the filter holders, the filters were examined under the microscope to determine if any background count existed. After each test the filters were removed and the entire area of the filter was counted. The pollen caught in the nozzle and filter holder was analyzed using isopropyl alcohol and 0.45 ym pore size Millipore membrane filters with black grids. The isopropyl was first filtered several times to remove background particulate matter. Once the background was low enough, the alcohol was poured into the front half of the filter holder and through the nozzles. The solution was then sucked through the membrane filters. The filters were allowed to dry and then the entire filter area was counted under the microscope. G. Sampling Proc edure 1. A desired flow rate was obtained by selecting an orifice plate and using the by-pass as a fine adjust. 2. The velocity was measured using a standard pitot tube. 3. A solute-solvent solution was selected for a given particle size. 4. Particles were collected on a membrane filter and sized using a light microscope. 5. A nozzle diameter which would allow for an isokinetic sampling rate closest to 1 cfm was selected. 6. Isokinetic sampling rates were calculated and sampling flow rates were adjusted accordincrly "Â•-id WrTTi ;>Â•(Â•.-Â• Â• I

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60 7. Two simultaneous isokinetic samples were taken, one parallel to the flow (control), and one at a specified angle. Sampling times i^aried from 10 to 20 minutes. H. Tangential Flow Mapping The system used to map the flow pattern in a tangential flow stream is shown in Figure 25. It consists of a 54000 Â£pm industrial blower, a section of 15 cm PVC pipe containing straightening vanes, a small industrial cyclone collector, followed by a 6.1 meter length of 20 cm PVC pipe. The 150 cm long cyclone, shown in Figure 24 was laid on its side so that the stack was horizontal and could be conveniently traversed at several points along its length. A change in flow through this system could be produced by supplying a restriction at the inlet to the blower. To measure the velocity in the stack a United Sensor type DA 5dimentional directional pitot tube was used. The probe, pictured with its traversing unit in Figure 25, is .32 cm in diameter and is capable of measuring yaw and pitch angles of the fluid flow as well as total and static pressures. From the blow up of the probe tip (Figure 25) it can be seen that the head consists of 5 pressure ports. Port number 1 is the centrally located total pressure tap. On each side are two lateral pressure taps 2 and 3. When the probe is rotated by the manual traverse unit until P., = P,, the yaw angle of flow is indicated by the traverse unit scale. When the yaw angle has been determined an additional differential pressure is measured by pressure holes located perpendicularly above and below the total pressure hole 1. Pitch angle is then determined using a calibration curve for the individual probe. The yaw angle is a

PAGE 76

61 ]5 cm. ID Straightening van cs .4 m Â— Slower 6.1 m Figure 23. Experimental system for measuring cro.^s sectional flow patterns in a swirling flow stream. 3 V) re o -> !Ocm I Ti^i^s-**-?' n*w-

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62 k-22.f 0Â— > 1 T T Note: All dimensions in centimeters lI_j^J 17.1 14.7 Figure 24. Cyclone used in the study to generate swirling fl ow.

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63 3 1 2 4 Figure 25. Photograph of the 5-dimcns Lonal pitot with its traversing unit. Insert shows the location of the pressure taps.

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64 measure oÂ£ the flow perpendicular to the axis of the stack and tangent to the stack walls. The pitch angle is a measure of the flow perpendicular to the axis of the stack and perpendicular to the stack walls. The axial component of the velocity can therefore be determined from the following equation: V^ = V^ coscj) (19) where V = component of velocity flowing parallel to tlie axis of the stack, a V = total or maximum velocity measured by the pitot tube (j) = cos [cos (pitch) X cos (yaw)]

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CHAPTER IV RESULTS AND ANALYSIS A. Ae rosol Sampling Experiments 1. Stokes Number Experiments were set up and run with Stokes number as the independent variable. Duct velocity, nozzle diameter and particle diameter were varied in order to produce a range of Stokes numbers from 0.007 to 2.97. The Stokes number used in the analysis of data was calculated from Cp V D 1 where -fn 4^4 n /LI C = 1 + 2.492 L/D + 0.84 L/D e p' ^ (11) (21) p p and L = mean free path = 0.065 pm (11) Values for density and viscosity used in the calculations were n = 1.81 X 10""^ g/cm-sec (40) p = density of uranine particles = 1.375 g/cm." (41) p = density of ragweed pollen = 1.1 g/cm (18) 65

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66 2 Sampl J^ng with Parallel N ozzles In order to determine if the concentration of particles was the same at both sampling locations, simultaneous samples were taken with both nozzles aligned parallel to the duct. Table VII shows the results of tests performed over a range of Stokes numbers from 0.022 to 1.75. The average over all of the tests showed only a 0.34% difference between the two points with a 95% confidence interval of 1.2%. The data show an increase in the range of the values as the Stokes number increases. This can be expected because a small error in probe misalignment would have a greater effect at the higher Stokes number. 5. Analysis of Probe Wa sh In the analysis of the tests using ragweed pollen, the filter catch and probe wash were measured separately. This method allowed for the determination of the importance of analyzing both the filter and wash. From Table VIII it can be seen that even for a solid dry particle, analysis of the probe wash is a necessity. An average of 40% of the particles entering the nozzle was collected on the walls of the nozzle-filter holder assembly. This was only for nozzles aligned parallel to the flow stream and sampling isokinetically Therefore, the loss of particles was due to turbulent deposition and possibly bounce off the filter, and probably not inertial impaction. For tests run with the nozzle at an angle to the flow stream, it is assumed that the loss would increase as impaction of particles on the walls became

PAGE 82

67 o o c CM Lo t^ cni K) en vO vo t-~lyi vio CTi CM CNJ K) C C O rÂ— I ^M r-H I + + I + I + O CxJ r^ O! K) O O O rH K^, CM CO C to 1 + + + 1 1 + 1 1 + + + 1 1 w I CD '^ o PI V31 o LO tn o f) LO M o o fo > ^ hJ I Â— I < +-> 0) N N O 2 LTl Ln LT, LTl Ln CO o vD ^ \D CO "^ Â•^ ^ Â•5t ^o O H to
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TABLE VIII PERCENT OF PARTICULATE MATTER COLLECTED IN THE PROBE WASH FOR NOZZLES PARALLEL WITH THE FLOW STREAM 68 Probe W ash* 511 196 161 366 407 377 265 415 351 220 442 Filter" Totar 497 1008 218 414 250 411 721 1087 697 1104 669 1046 464 729 647 1062 522 873 240 460 614 1036 -6 in Wash 51 47 39 34 37 36: 36 39 40 15 41 ''Numbers represent the number of ragweed pollen counted.

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69 important. This can be seen from the data taken at 60 degrees (see Table IX) where an average of 54% of the particles was lost on the walls The probe wash for eight tests using 6.7 ym uranine particles was also analyzed separately for comparison with the results of the ragweed pollen tests. While parallel sampling, from 15 to 34% of the total mass was collected in the nozzle and front end of the filter holder. While this was somewhat less than the amount of ragweed pollen found in the nozzle, it is substantial enough to show the importance of including the nozzle wash with the filter catch. Also because of the variation of the percent collected in the nozzle during identical tests, the probe wash cannot be accounted for by a correction factor. During further testing, it was qualitatively observed that the percent in the probe wash increased with particle size and decreased with increasing nozzle diameter. 4. The Effect of Angle Misalignmen t on Sampli ng Efficiency The aspiration coefficient was determined by comparing the amount of particulate matter captured while sampling isokinetically with a control nozzle placed parallel and a test nozzle set at an angle to the flow stream. Tests were run at three angles, .30, 60 and 90 degrees. The results showed the theoretical predictions to be quite accurate. For all three angles the aspiration coefficient approached 1 for small Stokes numbers (K) decreased as K increased and then leveled off at a minimum of cos8 for large values of Stokes number. The most significant changes occur in the range between K = 0.01 and K = 1.0.

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70 TABLE IX PERCENT OF PARTICULATE MATTER COLLECTED IN THE PROBE WASH FOR NOZZLES AT AN ANGLE OF 60 DEGREES WITH THE FLOW STRE/\iM Probe Wash* Filter* Total* % in Wash 348 211 559 62.0 161 138 299 54.0 288 333 621 46.4 Numbers represent the number of ragweed pollen counted.

PAGE 86

71 Figures 26, 27 and 28 represent the sampling efficiency as a function of Stokes number for 30, 60 and 90 degrees respectively. The experimental data used in these plots are presented in Tables X, XI and XII. From these tables it can be seen that the variables of particle diameter and velocity and nozzle diameter were varied rather randomly. This was done to check the legitimacy of using Stokes number as the principle independent variable. From the shape of the curves in Figures 26-28, it can be seen that the aspiration coefficient is indeed a function primarily of Stokes number. The curves for 30, 60 and 90 degrees are all similar in shape except for the values of Stokes number where they approach their theoretical limit. As the angle of misalignment increases, the more rapidly the aspiration coefficient reaches its maximum error. This can be accounted for as an apparent change in nozzle diameter, because it is the only parameter in the Stokes number that is affected by the nozzle angle to the flow stream. As described before, the nozzle diameter is important because it determines the amount of time available for the particle to change directions (approximately 6 D./V ). As the nozzle is tilted at an angle to the flow stream, the projected frontal area and therefore the projected nozzle diameter are reduced proportional to the angle. Therefore, as the angle of misalignment increases, the time available for the particle to change direction decreases leading to increased sampling error for a given value of K. To normalize these curves for angle to the flow stream, it is necessary to define an "adjusted Stokes number" (K') which takes into account the change in projected

PAGE 87

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PAGE 88

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76 c +-> o c Â•H o; \D rt O o tn c ^ -^ G^i LT, CTl 00 00 i-H LO +J -H rt a t'"/ cn o vC r-r-g vC t^j ^C rj r-i I-^ \0 ^D CM f-< -H C^. CO c cn M cn cc c-. CC CTl C-, cc CO CO CTl Â•H Â— Ci E -vD ^JD CO \D o ^ ^ O ^ X CD m i-H N O O o O iJ N ca O < IZ. H ^ cu +-> o; m f=: r~t c^ (J Â•H Â•p CD a.} '-' CD c t-H P o CJ H 1 Â— : P ^ fn rt a. fo o CO cn M CJ H CD 1 > /) rj ^^ 1 Â— < ^ a) CJ > vD O tn c-M

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77 o Â•H o t-n r-U~; O-j O -=3^ CO o tn uo r^ 1 Â— 1 CM LO CJ LO ^'^ C r-. c C^J Z~^ +J H J2t rt U I Â— [ Â•^ O CO LT) CTl ^ ^ m ^o r\i o 1 Â— 1 rj a~i CO 1 Â— 1 Ol O .-H bO to [Â•T] rH Â•H o CT; C7~* Cn CT) CTl a-. CTl a-, CTl C7-. en CD G^* OO CO CO CO en C-, CO 00 gr Â•ri 4-1 (-H IS Ph M-J C3 w (D M < C ^' u < CO l-H 's:' 'd*' Â•W m Pi fn 5J3 O w o o g o Â£ r\) o o CN) O so (/i O o o o IÂ— 1 1Â— 1 Di a; Â• O ^ o o o o o d fe o 4-1 w W tu fn t-J M CD X C P H CD K en e c^i CS [t Â•H IjO LO Kl < o Q E vD \D 00 to ^ '^ o s O o ^H o o c Â— 1 ISI H Nl u o S z. D' IX < to <; r^ H 0) 2 +J Â•w. CD ;/) i-( ^ rH o 5 G tÂ— 1 Â•H P p^ o to ft c: o N^ LO w CD 5 t o TÂ—^ ^ 1 Â— ( rÂ— 1 (M u U Â•H CJ H ,2 +-1 c: O 'H M cd H Cl. < ..Di 1Â— 1 O. W < X M CJ H CD CJ C/l O ^^ CD > u on CO Vi2 LO m \0 vO ^ -* CO LO IÂ— I I-O CO C7) 00 CM to t-O o 00 t^ en 'Â•O r--

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PAGE 95

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PAGE 97

nozzle diameter with angle. Wien plotted against K', the aspiration coefficients for 30, 60 and 90 degrees should approach their tlieoretical minima at the same place as the curves for zero misalignment angle and anisokinetic sampling velocities (see Figure 6) To develop the adjustment factor for Stokes number, it was necessary to plot as a function of 0, the value of K where the aspiration coefficient reached a value that represented 95% of the maximum error. For example the maximum theoretical error for 60 degrees is cos (60) or 0.5. Therefore the value of K of interest is where there is (.95) (0.5) = 47.5% sampling error or an aspiration coefficient of 1 .475 = .525. For zero degrees, equations (9) and (10) were solved for R = 0.5 and 6 = 0.95 to obtain a value of K = 5.9. This velocity ratio was used because its theoretical maximum sampling error is 0.5, the same as for 60 degrees. The values for 60 and 90 degrees were obtained from Figures 27 and 28 respectively. Because of the flatness of the 30 degree curve (it varies only 16% over two and a half orders of magnitude of K) it was not possible to detect exactly when the curve reached 95% of its minimum value. Therefore no value for 30 degrees was used in this analysis. The equation for the adjusted Stokes number determined from Figure 29 is ,. 0.0226 K' = Ke (22) Using this equation it can be determined that the Stokes numbers for 30, 60 and 90 degrees must be multiplied by 1.93, 3.74 and 7.24 respectively to account for the effect of nozzle angle to the flow stream on the

PAGE 98

83 X o lT, r> O a. o 00 4 IÂ— 30 60 Misalignment Anemic (6) 90 Figure 29. Stokes number at which 95% maximum error occurs vs. misalignment angle.

PAGE 99

84 apparent nozzle diameter. Using these correction factors it is possible to use the data to determine an expression for 3' in equation (14). Setting R = 1 and solving for B' this equation becomes 6'(K'3=4q^ (25) Using this expression the experimental data were used to plot B' as a function of the adjusted Stokes number K' (see Figure 30) From this plot, it can be observed that the data points for 30, 60 and 90 degrees all fall approximately on the same line. It should be noted that most of the scatter is due to the 30 degree data and that the amount of the scatter is somewhat deceptive. Solving equation (23) for 30 degrees, requires that the sampling bias (1-A) must be multiplied by 7.5 to normalize it with the 90 degree data. This has an effect of greatly increasing any spread in the experimental data. To develop a model for inertial sampling bias, it was necessary to develop an equation for the line drawn through the data in Figure 30. An equation of the form similar to that used by Belyaev and Levin was selected to fit the data. 3'(K',0) = 1 ^Â—^ (24) 1 + aK' where a and b are constants. The advantage of this equation form is that it acts similar to the theoretical expectations of the relationship (i.e., 3' approaches zero for very small values of K' and approaches 1 for very large values of K').

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85 c o Â•H u H O: o Â•s. c t-J 'JO o t/5 O cn C o o to o /3 l/l CD c 'a Â•rÂ—i >
PAGE 101

86 While attempting to determine the constants a and b, it was found that the form of the equation had to be altered somewhat to allow g' to approach 1 at a faster rate for values of K' greater than 4.0. The following is tlic final form of the equation selected. B'(K',e) = 1 ---iÂ— ^ C25) 1 + ak' e The constants were determined through trial and error to be 0.55 and 0.25 for a and b respectively. Therefore, the final equation to describe the sampling efficiency due to nozzle misalignment as a function of Stokes number becomes for R = 1: A = 1 + (cose 1) 3' CK',e) [26) where CK',e) = 1 _Â„_i._^_^ (27) 1 + 0..S5 K'e and Â„ 0.0226 K' = Ke (22) Thc;5c equations are solved for 30, 60 and 90 degrees and plotted against Stokes number in Figure 31. It can be seen from the graph that the equations fit the data within experimental accuracy. Figure 32 is a plot of the sampling efficiency for angles between and 90 degrees in 15 degree increments

PAGE 102

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PAGE 103

88 0. E 3 O at) o t3 C cS m o o to ui U o ^^ u o t/5 o CO > c 4) Â•ri U H ,MH W
PAGE 104

89 5_^__Th_e_jffect of Nozzle Misalignme nt ar idJ\m^Â£okJÂ£iayx__Sa^^ Velocity To complete the analysis of anisokinetic sampling, it is necessary to know what is the combined effect of both a nozzle misalignment and a sampling velocity differing from the free stream velocity. The theoretical model predicts that the sampling efficiency will be in the form A = 1 + (Rcose 133" (28) where 3"= f[3(K,R) 3'[K',e}] (29) Since the reduction of projected nozzle diameter due to nozzle misalignment will effect the time available for a particle to change directions when sampling at an anisokinetic velocity, the adjusted Stokes number K' should also be used in the equation for 3 as well as 3'. Another modification that must be made in the model involves correcting for the fact that 3(K',R) does not equal 1 when R = 1. B(K',R=l) = l-^-^43j^^ C30) To account for this 3'(K',e) must be divided by 3(K',R = 1) so that equations (28) Â£).nd (29) are valid at R = 1. The model to be tested now becomes A = 1 + (RcosO 1) 3(K',R) |11^1^51__ (31) At first there appears to be an obvious flaw in the model in that the aspiration coefficient equals 1 whenever R = l/cos0 regardless of the :Â£%(A.i._ak

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90 Stokes number. An example of this is when R = 2 and = 60 degrees. This phenomenum can be explained as follows. Since the projected frontal area of the nozzle is one half the actual area when 9 = 60 degrees, in order to sample isokinetically such that there is no divergence of streamlines into the nozzle, the sample velocitymust be one half of the free stream velocity or R = 2. Therefore, the condition of R = l/cos6 defines the condition for obtaining a representative sample when the nozzle is misaligned with the flow stream. Since the sampling methodologies used to determine 3(K,R) and 3'CK,9) were substantially different [photographic observation vs. comparative sampling), it was necessary to see if the two methods gave comparable results before the model could be tested. Four sets of tests were run with two parallel nozzles; the control nozzle sampled isokinetically and the test nozzle sampled anisokinetically Tests were performed at two Stokes numbers (K = 0.154 and K = 0.70) and at t\TO velocity ratios (R = 2.3 and R ^ 0.51). The aspiration coefficients obtained by comparing the two measured concentrations are presented in Figure 33 and Table XIII. The data obtained lie within the experimental bounds of the lines produced from Belyaev and Levin's data [Equations (5), (9) and (10)]. Since the two methods give comparable results, experiments were run to test the model. A control nozzle was placed parallel to the flow stream and the sampling velocity was set to be isokinetic. The test nozzle was inserted at an angle from outside the duct and the sampling velocity was set to be either one half or two times the free

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92 i?o o ci oi vo rvo t^ r-. CO oi a-, CO bn t-n to a n~i -^ u~! [> \o -^ ^ CD a a-: CO en r~s > rv X i Â— t 1 Â— I 1 Â— 1 1 Â— 1 1 Â— ^ r-H Â— 1 o c o o o o o > m P > < w S3 O OJ Â• LO O o X II H Q l-H KH 12: HH 2: < f Â— I X W to H Â• PJ J rM i-J Ha CTj II < U^ irIX P^ u o 2: m II 1Â— 1 U CD M (X o z w o o w h-l a: < T3 0) CO P f= U O Â•H -H -a +-> CD cvi pj -Â— D E ^ O ^Â— Â•H o U -r-i O 4-> I -H Cj 1/) f^ N C) M O n 2 u o o o CO CM to d o LO LO O O Â•* ^ \a vO r^ t--. o --0 lO o -It LO ao p ,Â— re 'M -i

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stream velocity. Tests were run for a range of Stokes numbers from 0.1 to 1. This range was selected because this was expected to be the area where the greatest change in aspiration coefficient occurred. The data obtained for R = 2 and R =0.5 for a 60 degree misalignment are presented in Tables XIV and XV. Thesedata are plotted and compared with the model's prediction in Figure 34. The aspiration coefficient does indeed appear to be unity when R = l/cos6 as in the case of R = 2 and 6 = 60 degrees. The data for R = 0.5, 9 = 60 degrees appear to approach tlieir theoretical limit of Rcose [0.25) at approximately a value of Stokes number of 2 to 5. This is near the location that the aspiration coefficient for 9 = 60 degrees, R = 1 approaches its theoretical limit. This further confirms the necessity of using an adjusted Stokes number when the probe is misaligned with the flow stream. To further test the model, experiments were run at 45 degrees (R = 2.0 and R = 0.5} and at 30 degrees (R = 2.0). Thesedata presented in Tables XVI and XVII are plotted in Figures 35 and 36 also show good agreement with the prediction model When tests were run at 9 = 90 degrees, R = 2.1 and K = 0.195 (see Table XVIII), an average aspiration coefficient of only 1.5-6 was obtained. The value predicted for equation (31) for these conditions is 49%. It appears that the model falls apart at 90 degrees for R ^ 1. This is due to the fact that when 6 = 90 degrees there is zero projected frontal area of the nozzle. This means that subisokinetic sampling could in no way produce an increase in concentration as it does when particles lie in front of the projected nozzle area. Because of this it is necessary to put the condition 9 < 90 degrees on equation (31)

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o o 96 3 3 h^ >4 U m O o c o [V3 luaiorjjsoD uo laBatdsv o o EN O Â§ e Â•H E o Q SO a) P o +-> w in > o Â•H o H :^ j^ Â— Â— Â— "w^v*-i h ^ ". i pg-