<%BANNER%>

Computational Fluid Dynamics Analysis of the Effects of Rodent Activities in Ventilated Cages


PAGE 1

COMPUTATIONAL FLUID DYNAMICS ANALYSIS OF THE EFFECTS OF RODENT ACTIVITIES IN VENTILATED CAGES By JATIN LAMBA A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2005

PAGE 2

Copyright 2005 by Jatin Lamba

PAGE 3

This document is dedicated to my family for their unwavering support

PAGE 4

ACKNOWLEDGMENTS I would first like to thank my advisor, Dr. H. A. Ingley. Dr. Ingley shared his knowledge with me and always motivated me to do better. I would also like to thank Dr. S. A. Sherif and Dr. J. Chung for acting as my committee members and for the time and support they provided. I would also like to thank my friends especially, Ashutosh Pandey and Rohit Sharma. Above all I would like to express my gratitude to my parents and brothers for their unwavering support and blessings. iv

PAGE 5

TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES............................................................................................................vii LIST OF FIGURES.........................................................................................................viii NOMENCLATURE.........................................................................................................xii ABSTRACT.......................................................................................................................xv CHAPTER 1 INTRODUCTION........................................................................................................1 2 LITERATURE REVIEW.............................................................................................5 3 APPROACH...............................................................................................................20 4 RESULTS AND DISCUSSION.................................................................................26 5 SUMMARY AND CONCLUSIONS.........................................................................53 6 RECOMMENDATIONS............................................................................................56 APPENDIX A MESH CAGE PROFILES..........................................................................................57 B CONTOURS OF DIFFERENT SPECIES..................................................................59 C CALCULATIONS FOR POWER CONSUMPTION AND SAVINGS....................80 D CALCULATIONS FOR VERIFICATION OF MASS FLOW RATE......................82 E CASES THAT DID NOT WORK..............................................................................84 F GOVERNING EQUATIONS.....................................................................................86 v

PAGE 6

LIST OF REFERENCES...................................................................................................88 BIOGRAPHICAL SKETCH.............................................................................................90 vi

PAGE 7

LIST OF TABLES Table page 2-1 Effect of cage ventilation and frequency of cage changes on microenvironment......9 2.2 Response time needed for CO 2 concentrations to reach above 3%..........................11 2-3 Ammonia concentrations in IVC2S & IVC1 for negative pressure.........................13 2-4 Ammonia concentrations in IVC2S & IVC1 for positive pressure..........................14 2-5 Comparisons of CO 2 and NH 3, concentrations........................................................19 2-6 Results of CO 2 and NH 3, concentrations.................................................................19 3-1 Model definitions.....................................................................................................24 3-2 Discretization scheme..............................................................................................25 3-3 Variable definitions..................................................................................................25 4-1 Results from CFD simulations.................................................................................49 4-2 CO 2 and NH 3 concentrations Vs. ACPH for center of cage case.............................49 4-3 Comparison of NH 3 concentrations for different cases at 60 ACPH.......................51 4-4 Comparisons of NH 3 concentrations against results reported by Pandey (2005) at 100 ACPH................................................................................................................51 4-5 Comparisons of NH 3 concentrations against results reported by Pandey (2005) at 60 ACPH..................................................................................................................52 vii

PAGE 8

LIST OF FIGURES Figure page 2-1 Effect of 1% and 3% CO 2 on mice preference...........................................................6 2-2 Effect of airspeeds on mice preference......................................................................7 2-3 Effect of air change rates on preference of mice........................................................8 2-4 Cage microenvironment...........................................................................................10 2-5 CO 2 concentrations in different types of sealed filter top cages..............................11 2-6 Schematic diagram of Hasegawa apparatus.............................................................15 2-7 CO 2 concentrations in FVMIS cages.......................................................................16 2-8 Geometry of Allentown cage...................................................................................17 2-9 Contours of CO 2 for corner bottom at 100 ACPH...................................................18 2-10 Contours of CO 2 for whole bottom at 100 ACPH....................................................18 3-1 Mice positioned at the outer walls of the cage.........................................................22 3-2 Mice positioned along the y axis..............................................................................22 3-3 Mice positioned at the center of the cage.................................................................23 3-4 Meshing scheme used in the LM case......................................................................24 4-1 Outside wall case......................................................................................................27 4-2 Center of cage case...................................................................................................27 4-3 Four mice case..........................................................................................................28 4-4 Velocity profiles for center of cage at 100 ACPH...................................................29 4-5 Contours of mole fraction of CO 2 for center of cage (100 ACPH)..........................30 4-6 Contours of mole fraction of NH 3 for center of cage (100 ACPH)..........................31 viii

PAGE 9

4-7 Top view of contours of mole fraction of NH 3 for center of cage (100 ACPH)......31 4-8 Velocity profiles for four mice at 60 ACPH............................................................32 4-9 Contours of mole fraction of CO 2 for four mice (60 ACPH)...................................33 4-10 Contours of mole fraction of NH 3 for four mice (60 ACPH)...................................33 4-11 Top view of contours of mole fraction of NH3 for four mice (60 ACPH)..............34 4-12 Velocity profiles for outside wall at 60 ACPH........................................................35 4-13 Contours of mole fraction of CO 2 for outside wall (60 ACPH)...............................36 4-14 Contours of mole fraction of NH 3 for outside wall (60 ACPH)...............................36 4-15 Top view of contours of mole fraction of NH 3 for outside wall (60 ACPH)...........37 4-16 Velocity profiles for center of cage case at 20 ACPH.............................................38 4-17 Contours of mole fraction CO 2 for center of cage (20 ACPH)................................39 4-18 Contours of mole fraction of NH 3 for center of cage (20 ACPH)............................40 4-19 Top view of contours of mole fraction of NH 3 for center of cage (20 ACPH)........40 4-20 Velocity profiles for outside wall at 40 ACPH........................................................41 4-21 Contours of mole fraction of CO 2 for outside wall (40 ACPH)...............................42 4-22 Contours of mole fraction of NH 3 for outside wall (40 ACPH)...............................42 4-23 Top view of contours of mole fraction of NH 3 for outside wall (40 ACPH)...........43 4-24 Velocity profiles for center of cage at 60 ACPH.....................................................44 4-25 Contours of mole fraction of CO 2 for center of cage (60 ACPH)............................45 4-26 Contours of mole fraction of NH 3 for center of cage (60 ACPH)............................45 4-27 Top view of contours of mole fraction of NH 3 for center of cage (60 ACPH)........46 4-28 Velocity profiles for center of cage case at 40 ACPH.............................................47 4-29 Contours of mole fraction of CO 2 for center of cage case (40 ACPH)....................47 4-30 Contours of mole fraction of NH 3 for center of cage case (40 ACPH)....................48 4-31 Top view of contours of mole fraction of NH 3 for center of cage case (40 ACPH)......................................................................................................................48 ix

PAGE 10

4-32 CO 2 concentrations Vs. ACPH.................................................................................50 4-33 NH 3 concentrations Vs. ACPH................................................................................50 A-1 Mesh used for CC case.............................................................................................57 A-2 Mesh used for OW case...........................................................................................58 B-1 Contours of CO 2 for CC in X-Y-Z plane (100 ACPH)............................................59 B-2 Contours of CO 2 for CC in X-Y plane (100 ACPH)................................................60 B-3 Contours of CO 2 for CC in Z-X plane (100 ACPH)................................................60 B-4 Contours of NH 3 for CC in X-Y-Z plane (100 ACPH)............................................61 B-5 Contours of NH 3 for CC in X-Y plane (100 ACPH)................................................61 B-6 Contours of NH 3 for CC in Z-X plane (100 ACPH)................................................62 B-7 Contours of CO 2 for LM in X-Y plane (60 ACPH).................................................62 B-8 Contours of CO 2 for LM in X-Y-Z plane (60 ACPH).............................................63 B-9 Contours of CO 2 for LM in Z-X plane (60 ACPH)..................................................63 B-10 Contours of NH 3 for LM in X-Y plane (60 ACPH).................................................64 B-11 Contours of NH 3 for LM in X-Y-Z plane (60 ACPH).............................................64 B-12 Contours of NH 3 for LM in Z-X plane (60 ACPH).................................................65 B-13 Contours of CO 2 for OW in X-Y-Z plane (60 ACPH).............................................65 B-14 Contours of CO 2 for OW in X-Y plane (60 ACPH)................................................66 B-15 Contours of CO 2 for OW in Z-X plane (60 ACPH).................................................66 B-16 Contours of NH 3 for OW in X-Y plane (60 ACPH)................................................67 B-17 Contours of NH 3 for OW in Z-X plane (60 ACPH).................................................67 B-18 Contours of NH 3 for OW in X-Y-Z plane (60 ACPH)............................................68 B-19 Contours of CO 2 for CC in X-Y plane (20 ACPH)..................................................68 B-20 Contours of CO 2 for CC in X-Y-Z plane (20 ACPH)..............................................69 B-21 Contours of CO 2 for CC in Z-X plane (20 ACPH)..................................................69 x

PAGE 11

B-22 Contours of NH 3 for CC in X-Y plane (20 ACPH)..................................................70 B-23 Contours of NH 3 for CC in X-Y-Z plane (20 ACPH)..............................................70 B-24 Contours of NH 3 for CC in Z-X plane (20 ACPH)..................................................71 B-25 Contours of CO 2 for OW in X-Y-Z plane (40 ACPH).............................................71 B-26 Contours of CO 2 for OW in Z-X plane (40 ACPH).................................................72 B-27 Contours of CO 2 for OW in X-Y plane (40 ACPH)................................................72 B-28 Contours of NH 3 for OW in X-Y-Z plane (40 ACPH)............................................73 B-29 Contours of NH 3 for OW in Z-X plane (40 ACPH).................................................73 B-30 Contours of NH 3 for OW in X-Y plane (40 ACPH)................................................74 B-31 Contours of CO 2 for CC in X-Y plane (60 ACPH)..................................................74 B-32 Contours of CO 2 for CC in Z-X plane (60 ACPH)..................................................75 B-33 Contours of NH 3 for CC in X-Y plane (60 ACPH)..................................................75 B-34 Contours of NH 3 for CC in X-Y-Z plane (60 ACPH)..............................................76 B-35 Contours of NH 3 for CC in Z-X plane (60 ACPH)..................................................76 B-36 Contours of CO 2 for CC in X-Y plane (40 ACPH)..................................................77 B-37 Contours of CO 2 for CC in X-Y-Z plane (40 ACPH)..............................................77 B-38 Contours of CO 2 for CC in Z-X plane (40 ACPH)..................................................78 B-39 Contours of NH 3 for CC in X-Y plane (40 ACPH)..................................................78 B-40 Contours of NH 3 for CC in X-Y-Z plane (40 ACPH)..............................................79 B-41 Contours of NH 3 for CC in Z-X plane (40 ACPH)..................................................79 E-1 Single mouse in Ydirection....................................................................................84 E-2 Two mice in the center of cage in Xdirection........................................................84 E-3 Four mice in the center of cage in Ydirection........................................................85 E-4 Four mice in the center of cage in Xdirection........................................................85 xi

PAGE 12

NOMENCLATURE CFD Computational Fluid Dynamics ACPH Air Changes per hour CO 2 Carbon dioxide NH 3 Ammonia W Weight of each mouse V Volume of each mouse d Diameter of each mouse L Length of each mouse OW Outside wall case LM Four mice case CC Center cage case Q 1 Flow rate in feet 3 per minute for 100 ACPH Q 2 Flow rate in feet 3 per minute for 60 ACPH Q 3 Flow rate in feet 3 per minute for 40 ACPH Q 4 Flow rate in feet 3 per minute for 20 ACPH P 1 Power at 100 ACPH for 140 cages P 2 Power at 60 ACPH for 140 cages P 3 Power at 40 ACPH for 140 cages P 4 Power at 20 ACPH for 140 cages P 5 Power at 30 ACPH for 140 cages xii

PAGE 13

S 1 Savings per year at 60 ACPH S 2 Savings per year at 40 ACPH S 3 Savings per year at 20 ACPH S 4 Savings per year at 30 ACPH K Turbulent kinetic energy v Velocity M Number of elements in the system N Number of species div Divergence Greek Dissipation rate Viscosity Density of each mouse ij Shear Stress ig Body force in the i th coordinates ij Krockner delta Empirical constants 1c Empirical constants 2c Empirical constants ijJ Mass molecular flux of species i in j th direction iD Diffusion Coefficient iZ Mass fraction of i th element xiii

PAGE 14

iY Mass fraction of species T Turbulent exchange coefficient ij Number of kilograms of element i in a kilogram of species j iw Mass rate of creation of species i xiv

PAGE 15

Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science COMPUTATIONAL FLUID DYNAMICS ANALYSIS OF THE EFFECTS OF RODENT ACTIVITIES IN VENTILATED CAGES By Jatin Lamba December 2005 Chair: Herbert Ingley Major Department: Mechanical and Aerospace Engineering The purpose of this study was to perform a computational fluid dynamics analysis to study the effects of rodent activities on selected air quality indicators (e.g., carbon dioxide, ammonia and humidity) in a ventilated rodent cage. The individually ventilated cage system is the most widely used method for rodent housing. Various studies have been performed to develop the optimum ventilation performance in the ventilated rodent cage. These studies have included variables such as ventilation rates, the structure of the cage and various other parameters as they affect the microenvironment variables of temperature, relative humidity, ammonia and carbon dioxide. The Guide for Care and Use of Laboratory Animals, The Institute of Laboratory Animal Resources and the American Society of Heating Refrigerating and Air Conditioning Engineers Applications and Fundamentals Handbook provide guidelines for these microenvironment variables. Computational fluid dynamics (CFD) was used for analyzing the rodent cage environment. A conventional Allentown rodent cage PC7115RT was used for the CFD xv

PAGE 16

modeling. Various locations in the cage were analyzed in the GAMBIT software. The rodents were modeled as half cylinders generally representing the size of rodents for the analyses. The cylinders were then treated as sources of carbon dioxide. FLUENT software was used to determine the effects of these sources on the microenvironment of the cage. The results for 100 and 60 ACPH agreed with the previously published experimental and CFD results. The prevailing concentrations of CO 2 and NH 3 for the case with two mice positioned near the inlet nozzle of the cage were 970 ppm and 6 ppm respectively at 100 ACPH and 4300 ppm and 27 ppm respectively at 20 ACPH. The average concentrations of CO 2 and NH 3 for the case with four mice positioned along the y-axis were 1350 ppm and 9 ppm respectively at 60 ACPH. The most prevalent concentrations of CO 2 and NH 3 for the case with two mice bodies positioned at the outer walls opposite to each other away from the nozzle were 1000 ppm and 11 ppm respectively at 60 ACPH. The CO 2 and NH 3 concentrations increased with a decrease in air change rates. From the plots it could be seen that 30 ACPH is an optimum air change rate in terms of acceptable cage environment conditions and savings as compared to 100 ACPH. With further CFD studies it may be possible to produce a design that could effectively ventilate rodent cages. xvi

PAGE 17

CHAPTER 1 INTRODUCTION At present the use of rodents as research subjects is playing an extremely significant role in medical research. Laboratory mice have been a major component of medical research since the 1880s.The microenvironment as defined by the levels of carbon dioxide, ammonia, temperature, and humidity must be maintained properly for research and the well being of the animals. In order to provide proper care for the animals, criteria for the needs of the animals are required (Institute of Laboratory Animal Resources, 1996). As there is no specified acceptable CO 2 concentration for mice so assuming acceptable CO 2 concentrations for humans that is 5000 ppm as a standard. The acceptable NH 3 concentration specified by the guide for ventilated cages is 25 ppm. Guidelines for experiments with rodents are provided by the Guide for Care and Use of Laboratory Animals, the Institute of Laboratory Animal Resources and the American Society of Heating Refrigerating and Air Conditioning Engineers Applications and Fundamentals Handbooks. The guide recognizes computational fluid dynamics as a technique for studying the optimum performance of ventilated cages. The two major types of rodent caging systems in use today are static and ventilated cages. The static cages with filter tops have been known to provide a protective barrier for rodents and thereby reduce the transcage coupling of microenvironment contaminants. Studies have shown these cages effectively reduce cross-contamination by particulate materials. However studies have also shown that the use of filter top cages can 1

PAGE 18

2 cause large accumulations of carbon dioxide, ammonia and relative humidity which have adverse effects on the health of rodents and thereby, their performance in medical studies. Ventilated cages help in reducing the high levels of carbon dioxide, ammonia and humidity in the cages. This technology has led to a significant increase in the use of ventilated cages as a method of housing research mice. Various designs are being utilized to provide ventilation to rodent cages. The basic difference between them is in the way the air is introduced into the cages. Air can be supplied directly by a portable blower and filter through a coupling attached to the cage. The top of the cage and the base of the cage can be used to provide air to the cage. Automatic watering may be combined with the system if air is provided at the base of the cage. Automatic watering saves labor (White, 2001). An indirect method of supplying air is by using individually mounted rack blowers. The blower supplies air at high velocity over the filter on the cage, which pushes the air through the filter into the cage. This method reduces the chance of contamination that may be caused due to inadequate disinfection of cage couplings used in ventilation. Filters should be changed regularly as the length of use affects the resistance provided by the cage, which can affect the ventilation efficiency (A Guide to Research Rodent Housing). Captured exhaust is another method of providing air to ventilated system. Air can be pulled directly into the cage through a filtered cage connection. A vacuum port above the filter top can also be used to pull in exhaust air. The port is not directly connected to the exhaust of the cage and it does not capture all the exhaust air from the cage. This

PAGE 19

3 method provides reduction in heat load, and moisture (A Guide to Research Rodent Housing). Pandey (2005) conducted a computational fluid dynamics analysis of ventilated cages. A conventional Allentown cage PC 7115RT was used for the study. The cage was analyzed for two different air change rates for carbon dioxide, ammonia, relative humidity, and temperature. The corners of the cages were selected as latrine areas and were also considered as sources of carbon dioxide due to mice respiration. For the second case the whole bottom of the cage was selected as a source of carbon dioxide, ammonia, and relative humidity. However, mice bodies were not included in the geometry and the bottom of the cage was taken as a source of carbon dioxide, ammonia, heat, and humidity for one case. The geometry of a conventional Allentown rodent cage PC 7115RT was also used in the current study. Computational fluid dynamics was used to construct the cage and determine the flow of air in the cage. FLUENT 6.2.16 and Gambit 2.2.30 provided the computational software for these analyses. Gambit was used to construct the geometry of cage and also to specify the rodent position. The geometry was then analyzed in FLUENT for the concentration distribution of microenvironment variables like carbon dioxide, and ammonia. In the current study cylinders generally representing the size of the rodents simulated mice bodies. The cylinders were treated as source of carbon dioxide. Different positions of mice and latrines were then analyzed. A study of the effects of rodent activity on microenvironment variables in the ventilated cages could help in improving the performance of these cages.

PAGE 20

4 Three different locations were analyzed for the study. For the first case two mice were located in the center of the cage near the inlet nozzle. This case was analyzed for 20, 40, 60, and 100 ACPH. The mice bodies were positioned next to each other to reduce the complexity of the model. This case was analyzed for 40 and 60 ACPH. Two mice were positioned opposite to each other along the outer wall of the cage for the second case. For the third case two half cylinders were positioned a small distance away from the center of the cage. The two half cylinders were double the length of the other mice bodies analyzed in the study. The two half cylinders represented four mice present in the cage. This case was analyzed for 60 ACPH.

PAGE 21

CHAPTER 2 LITERATURE REVIEW This chapter reviews literature relevant to the microenvironment parameters such as carbon dioxide, ammonia, temperature, and relative humidity for ventilated rodent cages. Krohn et al. (2003B) studied the effect of the presence of CO 2 in rodent cages. The presence of CO 2 on heart rate and blood pressure of the mice was studied by considering concentrations of 1%, 3% and 5% of CO 2 in the air in the cages Figure: 2.1 (Krohn et al., 2003B) shows the effects of CO 2 on mice. The figure shows the distribution of dwelling time of mice at day and night in ventilated cages and in cages with 1% and 3% concentrations of CO 2 It can be seen that for the case of 1% CO 2 there is very little difference between the dwelling times of mice in ventilated and ones with fixed concentration of CO 2 However, for the case of 3% CO 2 the mice prefer ventilated cages. The study showed that rodents were not affected at levels up to 3% CO 2 but were affected significantly at concentrations of CO 2 above 3% in the air. In another study, Krohn et al. (2003A) analyzed the effect of air speed in ventilated cages. The study was conducted for air speeds less than 0.2 m/s and greater than 0.5 m/s and how these air speeds affect the performance of rats. Figure 2-2 (Krohn et al., 2003A) shows the distribution of dwelling time of mice in ventilated cages in comparison to low air speeds and high air speeds. It can be seen that the mice prefer to stay in cages with high air velocity than lower air velocity. 5

PAGE 22

6 Figure 2-1. Effect of 1% and 3% CO 2 on mice preference (Krohn et al., 2003B) The effect of 50, 80 and 120 air changes on rats was also analyzed by Krohn et al (2003A). It can be seen from Figure 2-3 (Krohn et al., 2003A) that mice prefer to dwell in cages with an 80 ACPH over cages with ACPH 50 and 120 respectively. The dwelling time of mice in cages with 120 ACPH is greater than that of cages with ACPH of 50. Thus preferred ACPH in cages lays around 80 ACPH.

PAGE 23

7 Figure 2-2. Effect of airspeeds on mice preference (Krohn et al., 2003A)

PAGE 24

8 Figure 2-3. Effect of air change rates on preference of mice (Krohn et al., 2003A)

PAGE 25

9 Reeb et al. (2001) studied the health of mice and the microenvironment of cages for bed changing frequencies of 7, 14 and 21 days, for ventilation rates of 30, 60 and 100 air changes per hour. The concentrations of ammonia, CO 2 and relative humidity and temperature changes were analyzed over a period of 4 months. Three mice each were housed in all the cages. Maxi-Miser PIV cages were used for the study. Table: 2.1 (Reeb et al., 2001) show the effect of ventilation rates and the frequency of cage changes on the microenvironment of the cage. It can be seen that the concentration of ammonia decreases with the decrease in the frequency of cage changes. However, the concentration of ammonia was lower at higher ventilation rates. The relative humidity of the air in the cages did not vary significantly with either the change in ventilation rates or the frequency of cage changes. The concentration of CO 2 increased with the decrease in the frequency of cage changes. Figure 2.4 (Reeb et al., 2001) shows the effect of air change rates on ammonia and relative humidity based on the results from Table 2-1. Table 2-1. Effect of cage ventilation and frequency of cage changes on microenvironment (Reeb et al., 2001)

PAGE 26

10 Figure 2-4. Cage microenvironment (Reeb et al., 2001) Krohn and Hansen (2002) conducted a study to estimate the time required for CO 2 concentrations to reach 3% of the cage volume. CO 2 levels were measured over time in different types of individually ventilated cages when no ventilation was provided to the cages. Seven different types of commercially available cages were used for the study. A standard mouse per air volume ratio of 20 gram/liter was reached by providing a number of 8-10 month old rats. Table: 2.2 (Krohn and Hansen 2002) shows the response time

PAGE 27

11 required for CO 2 concentrations to exceed the 3% concentration in different cages. Figure: 2.5 (Krohn and Hansen. 2002) graphically represent the change in CO 2 concentration in different types of cages over a period of time. It can be seen that for standard static filter top, US filter top, and ventirack type of cages, the concentration of CO 2 never exceeded 3% of the total cage volume. Table 2.2. Response time needed for CO 2 concentrations to reach above 3% (Krohn and Hansen, 2002) Figure 2-5. CO 2 concentrations in different types of sealed filter top cages (Krohn and Hansen, 2002) Smith et al. (2004) compared different types of bedding and the effect of these types of bedding on selected micro environmental parameters such as ammonia, carbon

PAGE 28

12 dioxide, relative humidity, and temperature. Results were compared for Nestpaks and loose bedding. C57BL/6J mice and NOD/Ltd mice were used for the study. The results showed that the effect on temperature and relative humidity by bedding type were minimal. The type of bedding significantly affected ammonia concentrations. The cages with hardwood bedding had lower concentrations of ammonia. The study also showed that ventilated cages have significantly lower ammonia concentrations. Hoglund and Renstrom. (2001) conducted a study to measure the concentrations of ammonia in two different types of individually ventilated cages. BioZone VentiRack, IVC1, and Techniplast SealSafe, IVC2S were the two types of ventilated systems used for the study. The systems were analyzed for negative and positive pressure in the cages for a period of 10 days. Table: 2.3 (Hoglund and Renstrom. 2001) shows the ammonia concentration for negative pressure in both type cages. Table: 2.4 (Hoglund and Renstrom. 2001) shows the ammonia concentration for positive pressure in both types of cages. At the end of 10 days the results showed the ammonia concentration to be lower than 10 ppm in both types of cages. The ammonia concentration was found to be higher in cases where urine had accumulated in the cages. Memarzedah et al. (2004) conducted a study to compare the environment in static and ventilated cages for different velocities and ventilation designs. The different types of cages used were ventilated cages with exhaust air forced through filters, ventilated cages with forced air inlets and a static cage. The results showed that ventilated cages had higher air velocities, lower relative humidity and lower carbon dioxide and ammonia concentrations.

PAGE 29

13 Table 2-3. Ammonia concentrations in IVC2S & IVC1 for negative pressure (Hoglund and Renstrom. 2001)

PAGE 30

14 Table 2-4. Ammonia concentrations in IVC2S & IVC1 for positive pressure (Hoglund and Renstrom. 2001)

PAGE 31

15 Hasegawa et al. (1997) analyzed the relationship between carbon dioxide concentrations, oxygen and air change rate in forced-air-ventilated micro-isolation systems (FVMIS). Three 8-week-old Wistar strain male rats were used for the study. Figure: 2.6 (Hasegawa et al., 1997) shows the apparatus used for the study. Figure 2-6. Schematic diagram of Hasegawa apparatus (Hasegawa et al., 1997) Air change rates were varied from 10 ACPH to 120 ACPH and temperature, relative humidity, CO 2 and O 2 were analyzed in the cages. It was noted that with an increase in air change rates, CO 2 concentrations decreased significantly. As no standard

PAGE 32

16 CO 2 concentration in microenvironment of laboratory animals was specified, 5000 ppm was considered as a standard for the study. The air change rate required to maintain the level of CO 2 similar to conventional housing that is less than 5000 ppm (parts per million) was 60 ACPH. Figure: 2.7 (Hasegawa et al., 1997) shows the CO 2 concentration in FVMIS cages at different air changes per hour Figure 2-7. CO 2 concentrations in FVMIS cages (Hasegawa et al., 1997) Pandey (2005) conducted computational fluid dynamics analyses of ventilated cages. Air velocity profiles and concentration distributions for carbon dioxide, ammonia, and water vapor were obtained from the study. A conventional Allentown cage PC 7115RT was analyzed by Pandey. The cage was assumed to house 5 ICR mice. However, the actual mouse geometry was not simulated. The bottom of cage was assumed as a source of carbon dioxide, ammonia, and water vapor in one case, and in the other case small areas at the corners of the cage were considered sources of carbon dioxide, ammonia, and water vapor for second case. The height of cage was reduced by 1 to

PAGE 33

17 compensate for the bedding. The cage geometry was constructed using GAMBIT software. Figure: 2.8 (Pandey, 2005) shows the geometry of the Allentown cage. Figure 2-8. Geometry of Allentown cage (Pandey, 2005) The analyses show that the higher concentrations of CO 2 and NH 3 were towards the opposite corners of the inlet nozzle for both the cases. Figure 2-9: (Pandey, 2005) shows the contours of CO 2 for the corner bottom case. Figure 2-10: (Pandey, 2005) shows the contours of CO 2 for the whole bottom case.

PAGE 34

18 Figure 2-9. Contours of CO 2 for corner bottom at 100 ACPH (Pandey, 2005) Figure 2-10. Contours of CO 2 for whole bottom at 100 ACPH (Pandey, 2005)

PAGE 35

19 The analyses were carried out for 60 and 100 air changes per hour. The results were validated with the study conducted by Heurkamp et al. (1994). Table: 2.5 (Pandey, 2005) shows validated results. Table: 2.6 (Pandey, 2005) shows the concentrations of ammonia, and carbon dioxide, for 60 ACPH and 100 ACPH for both whole bottom and corner bottom cases. Table 2-5. Comparisons of CO 2 and NH 3, concentrations Species WB (100 ACPH) CB (100 ACPH) Huerkamp, M.J., Lehner, N.D.M., (1994) at 112 ACPH NH 3 8.5 ppm 6.5 ppm 6 ppm CO 2 1190 ppm 1020 ppm 1050 ppm (Pandey, 2005) Table 2-6. Results of CO 2 and NH 3, concentrations Species WB (100 ACPH) WB (60 ACPH) CB (100 ACPH) CB (60 ACPH) NH 3 8.5 ppm 14.3 ppm 6.5 ppm 13 ppm CO 2 1190 ppm 2160 ppm 1020 ppm 1920 ppm WB= Whole Bottom Case, CB= Corner Bottom (Pandey, 2005) The study conducted by Pandey (2005) is most pertinent to the current study. The current study is an extension of Pandeys work.

PAGE 36

CHAPTER 3 APPROACH The mice in a rodent cage are sources of sensible and latent heat, water vapor and carbon dioxide. The fecal matter produced by mice, acts as a source of ammonia and moisture. The concentrations of ammonia, and carbon dioxide were analyzed in the ventilated cage to study the effects of rodent activities on the cage microenvironment. To study the cage environment for mice, parameters like the geometry of the cage, bedding, number of mice, and position of the mice must be modeled. Modeling of the physical properties such as flow profiles and concentration distribution inside the cage microenvironment was carried out using FLUENT software. A conventional Allentown PC 7115RT was used as a model for the study. The cage geometry was modeled using GAMBIT software. For this study, it was assumed that ICR mice, weighing 30 grams, were present in the cage. The mouse body was modeled as a cylinder. The size of this cylinder was calculated based on the following assumptions Density of mouse () = 1 gm/cm 3 Weight of mouse (W) = 30 gm The volume of each mouse is equal to V= W/ = 30 cm 3 3-1 The diameter (d) of each mouse was assumed to be 2.54 cm (1 inch). The length of each mouse (L) is thus equal to L = V4d = 2.5 inches 3-2 20

PAGE 37

21 The type of cage bedding in the current analysis was assumed to be a typical corncob bedding of one inch depth. Corncob bedding is porous in nature and is known to reduce the concentration of ammonia. However the bedding offers resistance to the momentum of the fluid. To model the bedding in the cage, the height of the cage was reduced by one inch. To reduce the complexity of the analysis, the mice bodies were assumed to be stationary. To further reduce the complexity of the model, mice were modeled as half cylinders. The mouse body was considered to be a source of CO 2 with CO 2 coming out uniformly from the half cylinder. In one case the mice were positioned parallel to the length of the cage. For the second case, they were positioned perpendicular to the length of the cage. Figure 3-1 shows the two cylinders positioned along the x-axis at the outer walls of the cage and away from the inlet air nozzle. Figure 3-2 shows the two cylinders positioned along the y-axis. The cylinders in this case are twice the length of one mouse. This is the geometry that was used to model four mice in the cage. Figure 3-3 shows the two cylinders along the x-axis near the center if the cage and also near the inlet nozzle. It is noted that mice select specific corners for their latrines. Latrines, being a major source of ammonia, carbon dioxide and moisture, had to be considered in the model. The four corners of the cage were assumed to be the areas of the latrines. The ammonia and CO 2 concentration from the latrines were assumed to be independent of the number of mice present in the cage. Assuming 16 ppm of ammonia to be present in the condition of steady state the mass flow rate of ammonia was back calculated. The mass flow rate used for ammonia is 4e-06 kilogram per second and mass flow rate of CO 2 1.7e-05 kilogram per second.

PAGE 38

22 Air at 75F and 50% RH was supplied to the cage through the inlet nozzles at 20, 40, 60, and 100 ACPH. Figure 3-1. Mice positioned at the outer walls of the cage Figure 3-2. Mice positioned along the y-axis

PAGE 39

23 Figure 3-3. Mice positioned at the center of the cage The geometry was then meshed in the GAMBIT software. The top part of the cage was meshed with a structured mesh of size 0.15 inches. The lower part of the cage was also meshed with a structured mesh of size 0.1 inches. The lower geometry that included the mice bodies was meshed with an unstructured mesh of size 0.1 inches. This was because the geometry was too complex to be meshed by a structured mesh. The portion of the cage with the nozzle was meshed with a size .05-inch mesh as the size of nozzle is 0.15 inch and the smaller mesh gave better results. The figures showing mesh schemes used in other cages are provided in appendix A.

PAGE 40

24 Top Part of Cage Lower Part of Cage Figure 3-4. Meshing scheme used in the LM case The geometry was then analyzed in FLUENT. First order upwind is used for this case as flow is aligned with the grid. The relaxation factors are used to control the iterations of the model. By setting a lower value the model remains more stable. The following settings were used in FLUENT. Table 3-1. Model definitions Model Type Settings Space 3D Time Steady Viscous Standard k-epsilon turbulence model Wall treatment Standard Wall Functions Heat Transfer Enabled Solidification and Melting Disabled Radiation None Species Transport Non reacting

PAGE 41

25 Table 3-2. Discretization scheme Variable Scheme Pressure Standard Pressure-Velocity Coupling Simple Momentum First Order Upwind Turbulence Kinetic Energy First Order Upwind Turbulence Dissipation Rate First Order Upwind CO 2 First Order Upwind NH 3 First Order Upwind Air First Order Upwind Energy First Order Upwind H 2 O First Order Upwind Table 3-3. Variable definitions Variable Relaxation Factor Pressure 0.2 Density 0.5 Body Forces 0.5 Momentum 0.40000001 Turbulence Kinetic Energy 0.5 Turbulence Dissipation Rate 0.5 Turbulent Viscosity 0.5 CO 2 0.5 NH 3 0.5 Air 0.5 Energy 0.5 H 2 O 0.5

PAGE 42

CHAPTER 4 RESULTS AND DISCUSSION The purpose of this study was to study the effects of rodent activities on cage microenvironments. Computational fluid dynamic methods were used to find and plot the concentrations within the cage and also the flow profiles in the cage. The simulated mice bodies were positioned in various parts of the cage using GAMBIT software and the effect of mice positions on the microenvironment was then analyzed using the FLUENT software. Each mouse body was considered to be a source of CO 2. Three different mouse positions were analyzed in the study. In the first case two mouse bodies were positioned at the outer wall of the cage. The outer wall case was referred to with an abbreviation OW. Figure 4-1 shows the OW case. In the second case, two mouse bodies were positioned along the center of the cage near the inlet nozzle of the cage, referred to with an abbreviation CC. Figure 4-2 shows the CC case. For the third case, two longer cylinders were positioned along the y-axis, referred to with an abbreviation LM. Four mice bodies were simulated in the cage by doubling the length of the cylinders in the cage. Figure 4-3 shows the LM case. As there is no specified acceptable CO 2 concentration for mice so assuming acceptable CO 2 concentrations for humans that is 5000 ppm as a standard. The acceptable NH 3 concentration specified by the guide for ventilated cages is 25 ppm. 26

PAGE 43

27 Figure 4-1. Outside wall case Figure 4-2. Center of cage case

PAGE 44

28 Figure 4-3. Four mice case The CC case was analyzed for an air change rate of 100 ACPH. For 100 ACPH the velocity of inlet air was 8.57 m/s. The NH 3 mass flow rate was 4e-06 kg/s, and the CO 2 mass flow rate was 1.7e-05 kg/s. Figure 4-4 shows the air velocity profiles for this case. As expected, the profiles show that more circulation of air takes place near the nozzle of the cage. A slight bump could be seen in the velocity profile due to the presence of a mouse body at the center of the cage. The air velocity in the vicinity of the mouse was 1.02 meters per second. Assuming a comfortable air velocity of a mouse to be equal to that for a human (0.15 m/s.25 m/s), it can be seen that the air velocity is much higher than the acceptable level and can be concluded that the mouse would not stay at that

PAGE 45

29 position for very long and move away towards the corner of the cage where the air velocity would be less. Figure 4-5 shows the contours for the CO 2 concentration in the cage at 100 ACPH. It can be seen from the figure that the CO 2 concentration near the mice bodies is less than in other areas of the cage. This is because in this case the mice are positioned near the inlet nozzle and the high air velocity forces the CO 2 to the back side of the mouse and also the air exchange rate causes the concentration to be less near the mouse body. The concentration that was most prevalent in the cage was assumed to be the average concentration of CO 2 and NH 3 in the cage. Figure 4-4. Velocity profiles for center of cage at 100 ACPH

PAGE 46

30 Figure 4-5. Contours of mole fraction of CO 2 for center of cage (100 ACPH) The concentration of CO 2 in the cage was found to be 970 ppm. Figure 4-6 shows the contours for mole fractions of NH 3 The NH 3 present within the cage is 6 ppm. It can also be seen that the concentration of NH 3 near the mouse body is very low, again because the mouse body is a source of CO 2 and not ammonia, and also because the air is flowing directly on the mouse body. Figure 4-7 shows the contours of mole fraction of NH 3 viewed from the top of the mouse cage. The four corner areas defined as latrines are visible in this figure. The latrines show an NH 3 concentration of 25 ppm, which decreases as we move away from the corners and the NH 3 mixes with the air coming in the cage.

PAGE 47

31 Figure 4-6. Contours of mole fraction of NH 3 for center of cage (100 ACPH) Figure 4-7. Top view of contours of mole fraction of NH 3 for center of cage (100 ACPH)

PAGE 48

32 The LM case was run for 60 ACPH. For 60 ACPH the velocity of inlet air was 5.143 m/s. The NH 3 mass flow rate was 4e-06 kg/s, and the CO 2 mass flow rate was 1.7e-05 kg/s. Figure 4-8 shows the velocity profiles for the LM case at 60 ACPH. It can be seen that airflow is concentrated near the inlet nozzle of the cage. The air velocity in the vicinity of the mouse was 0.60 meters per second, which is higher than acceptable comfortable level of 0.15 m/s-0.25 m/s. Again it can be concluded that the mice would not stay at that position for very long and would move away towards the corner of the cage where the air velocity would be less. Figure 4-9 shows the contours of mole fraction of CO 2 concentrations in the cage. It can be seen from the figure that CO 2 concentrations are highest in the vicinity of the mouse body since mice are the major sources of CO 2 in the cage. The concentration is much lower near the nozzle of the cage as the fresh air is flowing into the cage. The CO 2 concentration in the cage is about 1350ppm. Figure 4-10 shows the contours of mole fraction of NH 3 in the cage. The concentration of NH 3 is less near the mouse body as the mouse is not a source of ammonia in the cage and also near the inlet as the air is flowing in to the cage. The NH3 concentration in the cage is 9 ppm. Figure 4-8. Velocity profiles for four mice at 60 ACPH

PAGE 49

33 Figure 4-9. Contours of mole fraction of CO 2 for four mice (60 ACPH) Figure 4-10. Contours of mole fraction of NH 3 for four mice (60 ACPH)

PAGE 50

34 Figure 4-11. Top view of contours of mole fraction of NH3 for four mice (60 ACPH) Figure 4-11 shows the top view of the mole fraction of NH 3 for the LM case. It can be seen that in the vicinity of the latrines ammonia concentrations are about 25 ppm, which decreases with the increase in the distance from the corners. The OW case was run for 60 ACPH. For 60 ACPH the velocity of inlet air was 5.143 m/s. The NH 3 mass flow rate was 4e-06 kg/s, and the CO 2 mass flow rate was 1.7e-05 kg/s. Figure 4-12 shows the velocity profiles in the cage. The airflow is concentrated near the inlet to the cage. A slight bump can be seen near the outer walls of the cage away from the nozzle, which shows the presence of a mice body at that location in the cage. The air velocity in the vicinity of the mouse was 0.275 meters per second, which is slightly higher than acceptable comfortable level of 0.15 m/s-0.25 m/s. It can be concluded that the mice would not stay at that position for very long and move away towards the corner of the cage where the air velocity is less. Figure 4-13 shows the

PAGE 51

35 contours of CO 2 concentration in the cage at 60 ACPH. The concentration of CO 2 is highest near the mouse body. It can also be seen that the higher CO 2 concentration is more towards the back end of the mouse body. This is because the air coming from the nozzle impinges on the front side of the mice and forces the CO 2 in that direction. The air hits the mouse body and passes above the body, not causing much effect on the CO 2 coming out from the back end of the body. The CO2 concentration in the cage is 1000 ppm. Figure 4-14 shows the mole fraction of concentration of NH 3 in the cage. The NH3 concentration within the cage is about 11 ppm. The NH 3 concentration is lowest near the mouse as it is not a source of ammonia. Figure 4-15 shows the top view of the contours of mole fraction of NH 3 concentration in the cage. The ammonia concentration is high at the corners of the cage. Figure 4-12. Velocity profiles for outside wall at 60 ACPH

PAGE 52

36 Figure 4-13. Contours of mole fraction of CO 2 for outside wall (60 ACPH) Figure 4-14. Contours of mole fraction of NH 3 for outside wall (60 ACPH)

PAGE 53

37 Figure 4-15. Top view of contours of mole fraction of NH 3 for outside wall (60 ACPH) The CC case was also run at 20 ACPH. For 20 ACPH the velocity of inlet air was 1.71 m/s. The NH 3 mass flow rate was 4e-06 kg/s, and the CO 2 mass flow rate was 1.7e-05 kg/s. Figure 4-16 shows the velocity profile for this case. The velocity profile is similar to all the other cages with more airflow near the nozzle and less away from the nozzle. A slight bump can also be seen near the nozzle showing the presence of a mice body at that location in the cage. The air velocity in the vicinity of the mouse was 0.182 meters per second, which is within the acceptable comfortable level of 0.15 m/s-0.25 m/s. It can be concluded that the mouse could stay at almost any position in the cage, as the air velocity is not very high.

PAGE 54

38 Figure 4-16. Velocity profiles for center of cage case at 20 ACPH Figure 4-17 shows the contours of mole fraction of CO 2 concentration in the cage at 20 ACPH. It can be seen that the concentration is low at the front end of the mouse body because it is positioned very near to the inlet nozzle and the fresh air coming in from the inlet reduces the concentration of CO 2 in that area. A small area can be seen just to the back of the mouse body where a large concentration of CO 2 exists. This is because the air is not in direct contact with the mouse body in that area. The CO 2 concentration in the cage is 4300 ppm. It can be seen that CO 2 concentration is very high; this is because of a lower air change rate of 20 air changes per hour.

PAGE 55

39 Figure 4-17. Contours of mole fraction CO 2 for center of cage (20 ACPH) Figure 4-18 shows the contours of mole fraction of NH 3 in the CC case at 20 ACPH. The concentration of NH 3 near the mouse body is less, as the mouse body is not a source of ammonia. Figure 4-19 shows the top view of the contours of NH 3 concentration in the CC case at 20 ACPH. It can be seen that the latrines show the highest concentration of ammonia. The center of the cage experiences low concentrations of ammonia, as the airflow is high within that region. The concentration of ammonia decreases away from the corners of the cage. The NH 3 concentration in the cage is about 27 ppm. This high concentration is due to lower air change rate of 20 air changes per hour.

PAGE 56

40 Figure 4-18. Contours of mole fraction of NH 3 for center of cage (20 ACPH) Figure 4-19. Top view of contours of mole fraction of NH 3 for center of cage (20 ACPH)

PAGE 57

41 The OW case was also run for 40 ACPH. For 40 ACPH the velocity of inlet air was 3.42 m/s. The NH 3 mass flow rate was 4e-06 kg/s, and the CO 2 mass flow rate was 1.7e-05 kg/s. Figure 4-20 shows the velocity profile for OW at 40 ACPH. It can be seen that the velocity is concentrated more towards the inlet nozzle. A bump can be seen showing the presence of a mouse body in the cage. The air velocity in the vicinity of the mouse was 0.158 meters per second, which is within the acceptable comfortable level of 0.15 m/s-0.25 m/s. It can be concluded that the mouse could stay at that position and be comfortable. Figure 4-21 shows the contours of mole fraction of CO 2 concentration for OW at 40 ACPH. The concentration of CO 2 is higher near the latrines. The CO 2 concentration in the cage is 2200 ppm. Figure 4-20. Velocity profiles for outside wall at 40 ACPH

PAGE 58

42 Figure 4-21. Contours of mole fraction of CO 2 for outside wall (40 ACPH) Figure 4-22. Contours of mole fraction of NH 3 for outside wall (40 ACPH)

PAGE 59

43 Figure 4-23. Top view of contours of mole fraction of NH 3 for outside wall (40 ACPH) Figure 4-22 shows the contours of mole fraction of NH 3 concentration for the OW case at 40 ACPH. Figure 4-23 shows the top view of the contours of the NH 3 concentration for OW case at 40 ACPH. The ammonia concentration is higher at the corners and less near the mouse body. The NH3 concentration in the cage is 22 ppm. Figure 4-24 shows the velocity profile for the CC case at 60 ACPH. For 60 ACPH the velocity of inlet air was 5.143 m/s. The NH 3 mass flow rate was 4e-06 kg/s, and the CO 2 mass flow rate was 1.7e-05 kg/s. As expected the velocity is concentrated near the inlet nozzle. The air velocity in the vicinity of the mouse was 0.678 meters per second, which is higher than acceptable comfortable level of 0.15 m/s-0.25 m/s. It can be concluded that the mouse would not stay at that position for very long and move away

PAGE 60

44 towards the corner of the cage where the air velocity would be lesser. Figure 4-25 shows the contours of mole fraction of CO 2 concentrations for this case. The highest concentration is in the vicinity of the mouse body. The concentration of CO 2 in the cage is 1100 ppm. Figure 4-26 shows the mole fraction of NH 3 concentrations for this case. Figure 4-27 shows the top view of mole fraction of ammonia for this case. The highest concentration of ammonia is in the vicinity of the latrines. The concentration of ammonia in the cage is approximately 10 ppm. Figure 4-24. Velocity profiles for center of cage at 60 ACPH

PAGE 61

45 Figure 4-25. Contours of mole fraction of CO 2 for center of cage (60 ACPH) Figure 4-26. Contours of mole fraction of NH 3 for center of cage (60 ACPH)

PAGE 62

46 Figure 4-27. Top view of contours of mole fraction of NH 3 for center of cage (60 ACPH) Figure 4-28 shows the velocity profiles for the CC case at 40 ACPH. For 40 ACPH the velocity of inlet air was 3.42 m/s. The NH 3 mass flow rate was 4e-06 kg/s, and the CO 2 mass flow rate was 1.7e-05 kg/s. As expected the velocity is concentrated near the inlet nozzle. The air velocity in the vicinity of the mouse was 0.376 meters per second, which is higher than acceptable comfortable level of 0.15 m/s-0.25 m/s. It can be concluded that the mouse would not stay at that position for very long and move away towards the corner of the cage where the air velocity would be lesser. Figure 4-29 shows the contours of mole fraction of CO 2 concentration at 40 ACPH. The concentration of CO 2 in the cage is 2000 ppm. Figure 4-30 shows the contours of mole fraction of NH 3 concentrations for this case. Figure 4-31 shows the top view of the contours of NH 3 concentrations for this case. The highest ammonia concentration is in the vicinity of the latrines. The concentration of ammonia in the cage is approximately 18 ppm.

PAGE 63

47 Figure 4-28. Velocity profiles for center of cage case at 40 ACPH Figure 4-29. Contours of mole fraction of CO 2 for center of cage case (40 ACPH)

PAGE 64

48 Figure 4-30. Contours of mole fraction of NH 3 for center of cage case (40 ACPH) Figure 4-31. Top view of contours of mole fraction of NH 3 for center of cage case (40 ACPH)

PAGE 65

49 Table 4-1 shows the CO 2 and NH 3 concentrations for all the results obtained from the CFD simulations. The concentration represented by the most prevalent color present in the cage is taken as the average concentration of the cage. Table 4-1. Results from CFD simulations Species CC 100 ACPH LM 60 ACPH OW 60 ACPH CC 60 ACPH OW 40 ACPH CC 40 ACPH CC 20 ACPH No. of Mice 2 4 2 2 2 2 2 CO 2 970 ppm 1350 ppm 1000 ppm 1100 ppm 2100 ppm 2000 ppm 4300 ppm NH 3 6 ppm 9 ppm 11 ppm 10 ppm 20 ppm 18 ppm 27 ppm As the CC case was analyzed for several levels of ACPH a comparison of ACPH effects can be made for this case. Table 4-2 shows this comparison for the CC case. Table 4-2. CO 2 and NH 3 concentrations Vs. ACPH for center of cage case ACPH Species 100 ACPH 60 ACPH 40 ACPH 20 ACPH Number of Mice 2 2 2 2 CO 2 970 ppm 1100 ppm 2000 ppm 4300 ppm NH 3 6 ppm 10 ppm 18 ppm 27 ppm Figure 4-32 shows the variation of CO 2 concentrations with increase in ACPH. It can be seen from the figure that CO 2 concentration increases with decrease in ACPH. The highest concentration of CO 2 is 4300 ppm at 20 ACPH. At 3000 ppm the ACPH comes about 30 ACPH. Figure 4-33 shows the variation of NH 3 with increase in ACPH. The highest concentration of NH 3 is 27 ppm at 20 ACPH, which is higher than the 25 ppm prescribed by the guide. An ACPH rate of 25 results in amid concentration of 28 ppm. 25-30 ACPH seems to be a logical choice to maintain acceptable levels of CO 2 and NH 3 in the cage.

PAGE 66

50 CO2 Concentrations Vs ACPH for CC case4300200011009700500100015002000250030003500400045005000204060100ACPHCO2 concentrations (ppm) Figure 4-32. CO 2 concentrations Vs. ACPH NH3 Concentrations Vs ACPH for CC case2718106051015202530204060100ACPHNH3 Concentrations (ppm) Figure 4-33. NH 3 concentrations Vs. ACPH

PAGE 67

51 Three cases were run for 60 ACPH, CC, LM and OW. As four mice are considered for the LM case, the CO 2 concentrations cannot be compared. Since it was assumed that ammonia concentrations are independent of the number of mice bodies, the ammonia concentration for all the three cases at 60 ACPH can be compared. Table 4-3 shows the comparison of NH 3 concentrations for three cases at 60 ACPH. It can be seen from the table that concentrations are very similar. Table 4-3. Comparison of NH 3 concentrations for different cases at 60 ACPH 60 ACPH Species CC OW LM NH 3 10 ppm 11 ppm 9 ppm The CO 2 concentrations for CC and OW can be compared for 60 ACPH. The CO 2 concentration for CC at 60 ACPH is 1000 ppm and 1100 ppm for OW at 60 ACPH. The CO 2 concentrations are almost equal. Pandey (2005) carried out similar analysis on Allentown cages for five mice but without considering mice bodies in the geometry. As the ammonia in the cage is independent of the number of mice in the cage, the results for ammonia for the current study can be compared with the results of the analysis carried out by Pandey. Table 4-4 shows the comparison of results at 100 ACPH. Table 4-5 shows the comparison of results at 60 ACPH. The results show a good agreement with results reported by Pandey Table 4-4. Comparisons of NH 3 concentrations against results reported by Pandey (2005) at 100 ACPH Species Center of Cage (100 ACPH) Pandey (2005) Corner Bottom (100 ACPH) NH 3 6 ppm 6.5 ppm

PAGE 68

52 Table 4-5. Comparisons of NH 3 concentrations against results reported by Pandey (2005) at 60 ACPH Species Center of Cage (60 ACPH) Four Mice (60 ACPH) Outside Wall (60 ACPH) Pandey (2005) Corner Bottom (60 ACPH) NH 3 10 ppm 9 ppm 11 ppm 13 ppm As the flow rate of air decreases from 100 to 60 to 40 to 20 ACPH the ventilation from power consumed is less and savings are more. The savings by using lower air change rates as compared to 100 ACPH are shown below. The calculations are for savings and power consumed are provided in Appendix C. P 1 is the power of fan at 100 ACPH. Savings for 60 ACPH is 79% which comes out to S 1 = $549.4P 1 per year Savings for 40 ACPH is 93.7% which comes out to S 2 = $656.6P1 per year Savings for 30 ACPH is 97.3% which comes out to S 4 = $681.9P 1 per year Savings for 20 ACPH is 99.3% which comes out to S 3 = $695.9P 1 per year At 30 ACPH the savings are 97.3% of money used at 100 ACPH. The mass flow rate for CO 2 used in the study can also be verified by the calculations shown in Appendix D. It can be seen that at 20 and 40 ACPH the percent error is very less 3% and 6% respectively. The error for 100 ACPH is 18%, this is due to the fact that most prevalent concentration was assumed as the CO 2 leaving the cage is lower, and there are areas in the cage where the concentration of CO 2 is much higher than the prevalent concentration. At 60 ACPH the error is highest 38%, this is again due the prevalent CO 2 is very less and there are areas near the mice and latrines where CO 2 concentration is much higher than prevalent concentration.

PAGE 69

CHAPTER 5 SUMMARY AND CONCLUSIONS The purpose of this study was to perform a computational fluid dynamic analysis to study the effect of rodent activity on ventilated cages. The air velocity profiles and concentrations of ammonia, carbon dioxide were developed for each cage configuration. The concentrations were calculated at 20, 40, 60, and 100 ACPH. Stationary mice bodies were simulated in the cage. Different positions were analyzed for the mice bodies. An Allentown rodent cage PC 7115RT was used for the study. Three different mice positions were considered for the study. The concentration that was most prevalent in the cage was assumed to be the average concentration of CO 2 and NH 3 in the cage. Two mice were positioned at the outer wall of the cage, away from the inlet nozzle, referred to with an abbreviation OW. This case was analyzed for 40, and 60 ACPH. The results CO 2 concentration was 1000 ppm for 60 ACPH and 2100 ppm for 40 ACPH. The NH 3 concentration was 11 ppm for 60 ACPH and 20 ppm for 40 ACPH. For the second case two mice bodies were positioned near the center of the cage and close to the inlet nozzle, referred to with an abbreviation CC. This case was run for 20, 40, 60, and 100 ACPH. The resulting CO 2 and NH 3 concentrations were 970 ppm and 6 ppm respectively for 100 ACPH, 4300 ppm and 27 ppm respectively for 20 ACPH, 1100 ppm and 10 ppm respectively for 60 ACPH, and 200 ppm and 18 ppm respectively for 40 ACPH. 53

PAGE 70

54 Two mice bodies were positioned near the center of the cage along y-axis of the cage, referred to with an abbreviation LM. The lengths of the cylinders were doubled to simulate four mice. This case was analyzed for 60 ACPH. The average CO 2 and NH 3 concentrations were 1350 ppm and 9 ppm respectively at 60 ACPH. The following conclusions are based on the results obtained from the simulations 1. The ammonia concentrations for all the models at 100 and 60 ACPH agreed with the results reported by Pandey (2005) for ammonia. 2. As the ventilation rate was decreased from 100 ACPH to 20 ACPH, the average concentration of carbon dioxide increased from 970 ppm to 4300 ppm, and the average ammonia concentrations increased from 6 ppm to 27 ppm in the cage. 3. The concentration of carbon dioxide also increased with an increase in the number of mice as expected. 4. The size of the cylinder would also have an effect on the CO 2 concentrations in the cage. The bigger the mouse more CO 2 it produces. 5. The concentrations of ammonia and carbon dioxide were much less in the vicinity of the inlet nozzle due to the fresh air introduced by the nozzle. 6. The area of the mouse body that comes in direct contact with the air indicates a lower concentration of CO 2 than the area, which is not in contact with the direct airflow. 7. In the CC case for 100 ACPH, the mice body is placed near the inlet nozzle and shows a lower concentration of CO 2 near the mice body. The air hits the mouse body with a volumetric flow rate of 1.27e-07 m 3 /s, and the CO 2 concentration in that area is 695 ppm, which increases to 850 ppm moving away from that area. In the LM case for 60 ACPH, in the area where the flow hits directly, the CO 2 concentration is 700

PAGE 71

55 ppm and increases to 1450 ppm moving away from the nozzle. In the OW case, for 60 ACPH the CO 2 concentration at the area of direct contact with the air is 838 ppm, which is higher than the other two cases as the mouse body is further away from the nozzle. The CO 2 concentration on the rest of the mouse body is 1390 ppm and decreases with the increase in distance from the body. 8. It can be seen that by introducing mice bodies in the cage and by positioning mice at different locations, affects the overall performance of the cage ventilation system. It can be seen that the mouse position has an effect on the concentration of CO 2 in that area. An increase was also seen in the concentration of CO 2 for the same air change rates when the numbers of mice were increased in the cage. 9. At 100, and 60 ACPH the air velocity was much higher in the cage than the assumed acceptable levels. At 40 ACPH the air velocity was higher near the inlet nozzle but was within the acceptable level away from the nozzle. At 20 ACPH the air velocity level was within the comfortable level throughout the cage. 10. As the flow rate of air decreases from 100 ACPH the power consumed by the fan also decreases, and the savings increase. The savings compared to 100 ACPH are a. 79% for 60 ACPH b. 93.7% for 40 ACPH c. 97.3% for 30 ACPH d. 99.3% for 20 ACPH. With further CFD studies it may be possible to produce a design that could effectively ventilate rodent cages in the 20-30 ACPH range, which could result in significant energy savings over current practices.

PAGE 72

CHAPTER 6 RECOMMENDATIONS 1. A model to analyze the urea and water reactions in the cage should be investigated. This model can simulate ammonia as it is produced due to composition of urea in real cages. 2. Improve the model for the mouse geometry. The mouse body can be simulated as a full cylinder for better airflow analysis in the cage. Other locations for mouse and latrines can also be analyzed. 3. The mouse body can also be simulated to be a source of heat and water vapor in the cage. This should be added to the model. 4. As it was seen that NH 3 concentrations exceeded the acceptable level of 25ppm for 20 ACPH, simulations should be run for other ACPH to optimize around the acceptable NH 3 concentrations. 5. Redesign the inlet nozzle and model the effects with CFD. Ammonia and carbon dioxide concentrations should be analyzed for two inlet nozzles opposite to each other and air being injected at a lower ACPH. By using a lower air change rate the savings also increase. The savings are within the range of 90-99% of power being consumed at 100 ACPH. 6. Conduct experiments to validate the CFD model. Both live and simulated mice should be used for the study. 56

PAGE 73

57 APPENDIX A MESH CAGE PROFILES This appendix includes the plot showing the type of mesh used in the cage. Figure A-1 shows the type of mesh used in the CC cage. The top and sides of the cage are meshed with 0.15 inch structured mesh. The inside volumes are meshed with 0.1 inch structured mesh. The nozzle area is meshed with an unstructured mesh of 0.05 inch, this is because the nozzle size is very small. 0.15 inch structured mesh .05 inch unstructured mesh 0.1 inch structured mesh Figure A-1. Mesh used for CC case

PAGE 74

58 0.15 inch structured 0.1 inch structured mesh 0.1 inch unstructured mesh 0.05 inch unstructured mesh Figure A-2. Mesh used for OW case Figure A-2 shows the mesh used for OW cage. The top and sides are meshed with a structured mesh on size 0.15 inches. The inside volumes is divided into two parts as it was not possible to mesh the whole volume with a structured mess. The upper part of the volume is meshed with 0.1 inch structured mesh. The lower part is meshed with 0.1 inch unstructured mesh. The part with nozzle is meshed with 0.05 inch unstructured mesh as the size of nozzle is very small.

PAGE 75

APPENDIX B CONTOURS OF DIFFERENT SPECIES This appendix includes the plots of contours of carbon dioxide and ammonia for CC case at 100 ACPH, and LM and OW cases for 60 ACPH Figure B-1. Contours of CO 2 for CC in X-Y-Z plane (100 ACPH) 59

PAGE 76

60 Figure B-2. Contours of CO 2 for CC in X-Y plane (100 ACPH) Figure B-3. Contours of CO 2 for CC in Z-X plane (100 ACPH)

PAGE 77

61 Figure B-4. Contours of NH 3 for CC in X-Y-Z plane (100 ACPH) Figure B-5. Contours of NH 3 for CC in X-Y plane (100 ACPH)

PAGE 78

62 Figure B-6. Contours of NH 3 for CC in Z-X plane (100 ACPH) Figure B-7. Contours of CO 2 for LM in X-Y plane (60 ACPH)

PAGE 79

63 Figure B-8. Contours of CO 2 for LM in X-Y-Z plane (60 ACPH) Figure B-9. Contours of CO 2 for LM in Z-X plane (60 ACPH)

PAGE 80

64 Figure B-10. Contours of NH 3 for LM in X-Y plane (60 ACPH) Figure B-11. Contours of NH 3 for LM in X-Y-Z plane (60 ACPH)

PAGE 81

65 Figure B-12. Contours of NH 3 for LM in Z-X plane (60 ACPH) Figure B-13. Contours of CO 2 for OW in X-Y-Z plane (60 ACPH)

PAGE 82

66 Figure B-14. Contours of CO 2 for OW in X-Y plane (60 ACPH) Figure B-15. Contours of CO 2 for OW in Z-X plane (60 ACPH)

PAGE 83

67 Figure B-16. Contours of NH 3 for OW in X-Y plane (60 ACPH) Figure B-17. Contours of NH 3 for OW in Z-X plane (60 ACPH)

PAGE 84

68 Figure B-18. Contours of NH 3 for OW in X-Y-Z plane (60 ACPH) Figure B-19. Contours of CO 2 for CC in X-Y plane (20 ACPH)

PAGE 85

69 Figure B-20. Contours of CO 2 for CC in X-Y-Z plane (20 ACPH) Figure B-21. Contours of CO 2 for CC in Z-X plane (20 ACPH)

PAGE 86

70 Figure B-22. Contours of NH 3 for CC in X-Y plane (20 ACPH) Figure B-23. Contours of NH 3 for CC in X-Y-Z plane (20 ACPH)

PAGE 87

71 Figure B-24. Contours of NH 3 for CC in Z-X plane (20 ACPH) Figure B-25. Contours of CO 2 for OW in X-Y-Z plane (40 ACPH)

PAGE 88

72 Figure B-26. Contours of CO 2 for OW in Z-X plane (40 ACPH) Figure B-27. Contours of CO 2 for OW in X-Y plane (40 ACPH)

PAGE 89

73 Figure B-28. Contours of NH 3 for OW in X-Y-Z plane (40 ACPH) Figure B-29. Contours of NH 3 for OW in Z-X plane (40 ACPH)

PAGE 90

74 Figure B-30. Contours of NH 3 for OW in X-Y plane (40 ACPH) Figure B-31. Contours of CO 2 for CC in X-Y plane (60 ACPH)

PAGE 91

75 Figure B-32. Contours of CO 2 for CC in Z-X plane (60 ACPH) Figure B-33. Contours of NH 3 for CC in X-Y plane (60 ACPH)

PAGE 92

76 Figure B-34. Contours of NH 3 for CC in X-Y-Z plane (60 ACPH) Figure B-35. Contours of NH 3 for CC in Z-X plane (60 ACPH)

PAGE 93

77 Figure B-36. Contours of CO 2 for CC in X-Y plane (40 ACPH) Figure B-37. Contours of CO 2 for CC in X-Y-Z plane (40 ACPH)

PAGE 94

78 Figure B-38. Contours of CO 2 for CC in Z-X plane (40 ACPH) Figure B-39. Contours of NH 3 for CC in X-Y plane (40 ACPH)

PAGE 95

79 Figure B-40. Contours of NH 3 for CC in X-Y-Z plane (40 ACPH) Figure B-41. Contours of NH 3 for CC in Z-X plane (40 ACPH)

PAGE 96

APPENDIX C CALCULATIONS FOR POWER CONSUMPTION AND SAVINGS As the flow rate of air decreases from 100 to 60 to 40 to 20 ACPH the power consumed by the ventilation fan also decreases. As typical ventilated rack contains 140 cages, so the change in power consumed for 140 cages can be estimated: The mass flow rate in cubic feet per minute for 100 ACPH Q 1 = 0.460079 ft 3 /min Q 1 for 140 cages= 64.411 ft 3 /min The power at 100 ACPH is P 1 The volume flow rate in cubic feet per minute for 60 ACPH Q 2 = 0.276047 ft 3 /min Q 2 for 140 cages= 38.647 ft 3 /min The power at 60 ACPH is P 2 Savings at 60 ACPH is S 1 The volume flow rate in cubic feet per minute for 40 ACPH Q 3 = 0.184032 ft 3 /min Q 3 for 140 cages= 25.764 ft 3 /min The power at 40 ACPH is P 3 Savings at 40 ACPH is S 2 The volume flow rate in cubic feet per minute for 20 ACPH Q 4 = 0.092016 ft 3 /min Q 4 for 140 cages= 12.882 ft 3 /min The power at 20 ACPH is P 4 Savings at 20 ACPH is S 3 The volume flow rate in cubic feet per minute for 30 ACPH Q 4 = 0.138024 ft 3 /min Q 5 for 140 cages= 19.323 ft 3 /min 80

PAGE 97

81 The power at 30 ACPH is P 5 Savings at 30 ACPH is S 4 As air change rate is reduced from 100 to 60 ACPH based on the fan law the change in power consumed can be calculated: P 1 /P 2 = (Q 1 /Q 2 ) 3 We get P 2 = .216P 1 Similarly P 3 = 0.063P 1 P 4 = 0.007P 1 P5= 0.027P1 The savings that can be obtained per year by reducing the airflow rate from 100 ACPH to 20 ACPH can be calculated: S 3 = (P 1 -0.007P 1 ) S 3 = 0.993P 1 Assuming $0.08 per kilowatt-hour, savings per year can be calculated: S 3 = 24*365*.993P 1 *0.08 S 3 = $695.9P 1 per year Similarly S 1 = $549.4P 1 S 2 = $656.6P 1 S4= $681.9P1

PAGE 98

APPENDIX D CALCULATIONS FOR VERIFICATION OF MASS FLOW RATE For 100 ACPH for Center of Cage case The most prevalent CO 2 concentration in the cage is in the range of 850-970 ppm. Assuming the CO 2 coming out of the cage to be C o = 970 ppm The volumetric flow rate is F= 0.000217 cubic meters per second Concentration of CO 2 entering the cage C i = 350 ppm C o -C i = 970-350= 620 ppm For 620 ppm the mass flow rate = 620*.000217*44*/(1000000*22.4) = 2.632e-07 kg/s. Actual mass flow rate= 3.58e-07 kg/s. Using this mass flow rate and back calculating CO 2 in the cage: C o -C i = 3.58e-07*22.4*1000000/(.000217*44)= 840 ppm C o = 840+350= 1190 ppm % Error in amount of CO 2 leaving the cage= (1190-970)*100/1190= 18.5% It can be seen that the amount of CO 2 assumed to be leaving the cage is less than amount of CO 2 that should actually leave the cage. This error is due to the fact that the most prevalent concentration is used for the calculation. There are some areas in the cage near the latrines where CO 2 concentration is more than the assumed concentration. For 60 ACPH for Center of Cage case The most prevalent CO 2 concentration in the cage is in the range of 980-1130 ppm. Assuming the most prevalent CO 2 concentration in the cage C o = 1130 ppm The volumetric flow rate is F= 0.00013 cubic meters per second Concentration of CO 2 entering the cage C i = 350 ppm C o -C i = 1130-350= 780 ppm For 780 ppm the mass flow rate= 780*.00013*44*/(1000000*22.4)= 2.00e-07 kg/s. Actual mass flow rate= 3.58e-07 kg/s. Using this mass flow rate and back calculating CO 2 in the cage: C o -C i = 3.58e-07*22.4*1000000/(.00013*44)= 1400 ppm C o = 1400+350= 1750 ppm % Error in amount of CO 2 leaving the cage= (1750-1130)*100/1750= 35.5% It can be seen that the amount of CO 2 assumed to be leaving the cage is less than amount of CO 2 that should actually leave the cage. This error is due to the fact that the most prevalent concentration is used for the calculation. There are some areas in the cage near the latrines where CO 2 concentration is more than the assumed concentration. For 40 ACPH for Center of Cage case The most prevalent CO 2 concentration in the cage is in the range of 1920-2300 ppm. Assuming the most prevalent CO 2 concentration in the cage C o = 2300 ppm The volumetric flow rate is F= 0.0000869 cubic meters per second Concentration of CO 2 entering the cage C i = 350 ppm 82

PAGE 99

83 Co-C i = 2300-350= 1950 ppm For 1950 ppm the mass flow rate= 1950*.0000869*44*/(1000000*22.4)= 3.32e-07 kg/s. Actual mass flow rate used for the analysis was 3.58e-07 kg/s. Using this mass flow rate and back calculating CO 2 in the cage: C o -C i = 3.58e-07*22.4*1000000/(.0000869*44)= 2098 ppm C o = 2098+350= 2448 ppm % Error in amount of CO 2 leaving the cage= (2448-2300)*100/2448= 6.0% The error in this case is 6%, which is very small as compared to errors at 100 and 60 ACPH. The CO 2 concentrations agree with the concentration calculated using the mass flow rate of CO 2 used for the simulation. For 20 ACPH for Center of Cage case The most prevalent CO 2 concentration in the cage is in the range of 3500-4400 ppm. Assuming the most prevalent CO 2 concentration in the cage Co= 4400 ppm The volumetric flow rate is F= 0.0000434 cubic meters per second Concentration of CO 2 entering the cage C i = 350 ppm C o C i = 4400-350= 4050 ppm For 4050 ppm the mass flow rate= 4050*.0000434*44*/(1000000*22.4)= 3.427e-07 kg/s. Actual mass flow rate= 3.58e-07 kg/s. Using this mass flow rate and back calculating CO 2 in the cage: C o -C i = 3.58e-07*22.4*1000000/(.0000434*44)= 4200 ppm C o = 4200+350= 4550 ppm % Error in amount of CO 2 leaving the cage= (4550-4400)*100/4550= 3.0% The error in this case is 3%, which is very small as compared to errors at 100 and 60 ACPH. The CO 2 concentrations agree with the concentration calculated using the mass flow rate of CO 2 used for the simulation.

PAGE 100

APPENDIX E CASES THAT DID NOT WORK Figure E-1. Single mouse in Ydirection Figure E-2. Two mice in the center of cage in Xdirection 84

PAGE 101

85 Figure E-3. Four mice in the center of cage in Ydirection Figure E-4. Four mice in the center of cage in Xdirection

PAGE 102

APPENDIX F GOVERNING EQUATIONS The species concentrations at various points are determined by solving the mass, momentum and energy equations numerically (Turbulent Reacting Flows, by P.A. Libby, F.A. Williams). The Mass Conservation equation is given as, 0)(kkvxt F-1 The momentum conservation equation is given as, iikkiikkigxxpvvxvt )()( F-2 Where is given by ig 3iigg F-3 The shear stress ij in the equation is expressed as, )32(ijkkijjiijxvxvxv F-4 The conservation of species equation is given as, iikkikkiwJxYvxYt)()( F-5 From Ficks Law, the turbulent flow mass diffusion equation is given by jiiijxYDJ F-6 Nowis given by iZ NjjijiYZ1 F-7 11MiiZ F-8 As the chemical elements are conserved, we have for each element 86

PAGE 103

87 01jNjijw F-9 Thus the conservation equation for elements is given by NikililkikkixYDxZvxZt1)()( F-10 If then DDi kikikkixZDxZvxZt )()( F-11 Turbulent flow was considered for the numerical analysis of the model and kmethod was used to solve the model. The following transport equations are used in the kmodel (FLUENT Inc., 2005) kTkc~ ~ 2 F-12 jjtktkEiEigradkdivkUdivx2])[()( F-13 2212])[()(CEECgraddivUdivxijijttk F-14

PAGE 104

LIST OF REFERENCES Fluent Incorporated, 2005. Fluent 6.2 Documentation, Lebanon, NH. Hasegawa, Masakazu, Kurabayashi, Yuzuru, Ishii, Toshinori, Yoshida, Kazuya, Uebayashu, Nobukazu, Sato, Norimitsu, Kurosawa, Tsutomu, 1997. Intra-Cage Air Change Rate on Forced-Air-Ventilated Micro-Isolation System-Environment within Cages: Carbon Dioxide and Oxygen Concentration, Experimental Animal Sciences, Vol 46(4), 251-257. Hoglund, A.U., Renstrom, A., 2001. Evaluation of Individually Ventilated Cage Systems for Laboratory Rodents: Cage Environment and Animal Health Aspects, Animals, Vol 35, 51-57. Institute of Laboratory Animal Resources, 1996. Guide for the Care and Use of Laboratory Animals, National Academy Press, Washington, DC. Krohn, Thomas C., Hansen, Axel K., 2002. Carbon Dioxide Concentrations in Unventilated IVC Cages, Laboratory Animals, Vol 36, 209-212. Krohn, Thomas C., Hansen, Axel K., Dragsted, Nils, 2003A. The Impact of Cage Ventilation on Rats Housed in IVC Systems, Laboratory Animals, Vol 37, 85-93. Krohn, Thomas C., Hansen, Axel K., Dragsted, Nils, 2003B. The Impact of Low Levels of Carbon Dioxide on Rats, Laboratory Animals, Vol 37, 94-99. Libby, P.A., Williams, F.A., 1993. Turbulent Reacting Flows, Academic Press, San Diego, CA. Memarzadeh, F., Harisson, P. C., Riskowski, G. L., Henze, T., 2004. Comparison of Environment and Mice in Static and Mechanically Ventilated Isolator Cages with Different Air Velocities and Ventilation Designs, Contemporary Topics in Lab Animal Science, Vol 43(1), 14-20. Pandey, A., 2005. Computational Fluid Dynamics Study of Ventilated Cages for Laboratory Animals, Masters Thesis, University of Florida, Gainesville, FL. Reeb, C. K., Paigen, B., Beamer, W. G., Bronson, R. T., Churchill, G. A., Schweitzer, I. B., Myers, D. D., 2001. The Impact of Reduced Frequency of Cage Changes on the Health of Mice Housed in Ventilated Cages, Laboratory Animals, Vol 35, 58-73. 88

PAGE 105

89 Smith, E., Stockwell, J.D., Schweitzer, I., Langley, S.H., Smith, A. L., 2004. Evaluation of Cage Micro-Environment of Mice Housed on Various Types of Bedding Materials, Contemporary Topics in Lab Animal Science, Vol 43(4), 12-7. White, W.J., 2001. A Guide to Research Rodent Housing, http://www.criver.com/research_models_and_services/research_models/rm_td_biosecurity_housing.pdf accessed Gainesville, August 2005.

PAGE 106

BIOGRAPHICAL SKETCH Jatin Lamba was born on June 9 th 1980, in Faridabad, Haryana, India. He completed his high school from Faridabad. He started his bachelors in engineering in Bharati Vidyapeeth College of Engineering in Pune, Maharashtra, India. However he transferred to Pittsburg State University after two years of engineering and then graduated from Pittsburg State in May 2003. He then enrolled in the University of Florida in the fall of 2003 to pursue his masters in mechanical engineering. 90


Permanent Link: http://ufdc.ufl.edu/UFE0013269/00001

Material Information

Title: Computational Fluid Dynamics Analysis of the Effects of Rodent Activities in Ventilated Cages
Physical Description: Mixed Material
Copyright Date: 2008

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0013269:00001

Permanent Link: http://ufdc.ufl.edu/UFE0013269/00001

Material Information

Title: Computational Fluid Dynamics Analysis of the Effects of Rodent Activities in Ventilated Cages
Physical Description: Mixed Material
Copyright Date: 2008

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0013269:00001


This item has the following downloads:


Full Text












COMPUTATIONAL FLUID DYNAMICS ANALYSIS OF THE EFFECTS OF
RODENT ACTIVITIES IN VENTILATED CAGES

















By

JATIN LAMBA


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA


2005

































Copyright 2005

by

Jatin Lamba

































This document is dedicated to my family for their unwavering support















ACKNOWLEDGMENTS

I would first like to thank my advisor, Dr. H. A. Ingley. Dr. Ingley shared his

knowledge with me and always motivated me to do better. I would also like to thank Dr.

S. A. Sherif and Dr. J. Chung for acting as my committee members and for the time and

support they provided.

I would also like to thank my friends especially, Ashutosh Pandey and Rohit

Sharma.

Above all I would like to express my gratitude to my parents and brothers for their

unwavering support and blessings.
















TABLE OF CONTENTS

page

A C K N O W L E D G M E N T S ................................................................................................. iv

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

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

N O M E N C L A T U R E ......................................................................................................... x ii

A B S T R A C T ......... .................................. ................................................x v

CHAPTER

1 IN TR O D U C TIO N ......................................................................... .... .. ........

2 LITER A TU R E R EV IEW ............................................................... ...................... 5

3 A P P R O A C H .....................................................................................................2 0

4 RESULTS AND DISCUSSION............................................ ........................... 26

5 SUMMARY AND CONCLUSIONS.......................................................................53

6 RECOMMENDATIONS .............................................................. ...............56

APPENDIX

A MESH CAGE PROFILES .......................................................... ...............57

B CONTOURS OF DIFFERENT SPECIES......................................... ....................59

C CALCULATIONS FOR POWER CONSUMPTION AND SAVINGS.................... 80

D CALCULATIONS FOR VERIFICATION OF MASS FLOW RATE ......................82

E CA SE S TH A T D ID N O T W ORK ..................................................... ....................84

F GOVERNING EQUATIONS.........................................................................86





v









L IST O F R E F E R E N C E S ........................................................................ .. ....................88

B IO G R A PH IC A L SK E TCH ...................................................................... ..................90
















LIST OF TABLES

Table p

2-1 Effect of cage ventilation and frequency of cage changes on microenvironment ......9

2.2 Response time needed for CO2 concentrations to reach above 3% ..........................11

2-3 Ammonia concentrations in IVC2S & IVC1 for negative pressure.........................13

2-4 Ammonia concentrations in IVC2S & IVC1 for positive pressure..........................14

2-5 Comparisons of C02, and NH3, concentrations................................... ............... 19

2-6 Results of CO2, and NH3, concentrations...... .................................19

3-1 M odel definitions ......................... ......... .. .. ..... ............... 24

3-2 D iscretization scheme e ..................................................................... ...................25

3-3 Variable definitions ................... ............. .... .... .... .. .......... 25

4-1 R results from CFD sim ulations ........................................ ........................... 49

4-2 CO2 and NH3 concentrations Vs. ACPH for center of cage case..........................49

4-3 Comparison of NH3 concentrations for different cases at 60 ACPH.................... 51

4-4 Comparisons of NH3 concentrations against results reported by Pandey (2005) at
100 ACPH ............... ................. ............ ............... .......... 51

4-5 Comparisons of NH3 concentrations against results reported by Pandey (2005) at
6 0 A C P H ............................................................................ 52
















LIST OF FIGURES

Figure page

2-1 Effect of 1% and 3% CO2 on mice preference ......................................................6

2-2 Effect of airspeeds on m ice preference ........................................... .....................7

2-3 Effect of air change rates on preference of mice .....................................................8

2-4 C age m icroenvironm ent ......... ................. ..................................... ......................10

2-5 CO2 concentrations in different types of sealed filter top cages ............. ..............11

2-6 Schematic diagram of Hasegawa apparatus.....................................................15

2-7 CO2 concentrations in FVM IS cages ............................................ ............... 16

2-8 Geom etry of Allentown cage ..... ......... .................................. ....................17

2-9 Contours of CO2 for corer bottom at 100 ACPH ................................................18

2-10 Contours of CO2 for whole bottom at 100 ACPH........................................... 18

3-1 Mice positioned at the outer walls of the cage ....................................................22

3-2 M ice positioned along the y axis........................................ .......................... 22

3-3 M ice positioned at the center of the cage......................................... .................. 23

3-4 Meshing scheme used in the LM case ............ ............................................. 24

4-1 O outside w all case .................. ................................ .. .. ........ .............. 27

4-2 Center of cage case............... .................... ................ .. 27

4-3 Four mice case ................................................................... ........ 28

4-4 Velocity profiles for center of cage at 100 ACPH ...............................................29

4-5 Contours of mole fraction of CO2 for center of cage (100 ACPH)..........................30

4-6 Contours of mole fraction of NH3 for center of cage (100 ACPH)..........................31









4-7 Top view of contours of mole fraction of NH3 for center of cage (100 ACPH)...... 31

4-8 Velocity profiles for four m ice at 60 ACPH ........................................ ................32

4-9 Contours of mole fraction of CO2 for four mice (60 ACPH)..............................33

4-10 Contours of mole fraction of NH3 for four mice (60 ACPH) ..............................33

4-11 Top view of contours of mole fraction of NH3 for four mice (60 ACPH) ..............34

4-12 Velocity profiles for outside wall at 60 ACPH .............. ............ .....................35

4-13 Contours of mole fraction of CO2 for outside wall (60 ACPH)..............................36

4-14 Contours of mole fraction of NH3 for outside wall (60 ACPH)..............................36

4-15 Top view of contours of mole fraction of NH3 for outside wall (60 ACPH)...........37

4-16 Velocity profiles for center of cage case at 20 ACPH .......................................38

4-17 Contours of mole fraction CO2 for center of cage (20 ACPH) ................................39

4-18 Contours of mole fraction of NH3 for center of cage (20 ACPH)............................40

4-19 Top view of contours of mole fraction of NH3 for center of cage (20 ACPH)........40

4-20 Velocity profiles for outside wall at 40 ACPH ................................ ............... 41

4-21 Contours of mole fraction of CO2 for outside wall (40 ACPH)............................42

4-22 Contours of mole fraction of NH3 for outside wall (40 ACPH).............................42

4-23 Top view of contours of mole fraction of NH3 for outside wall (40 ACPH)...........43

4-24 Velocity profiles for center of cage at 60 ACPH ..........................................44

4-25 Contours of mole fraction of CO2 for center of cage (60 ACPH)............................45

4-26 Contours of mole fraction of NH3 for center of cage (60 ACPH)............................45

4-27 Top view of contours of mole fraction of NH3 for center of cage (60 ACPH)........46

4-28 Velocity profiles for center of cage case at 40 ACPH ..........................................47

4-29 Contours of mole fraction of CO2 for center of cage case (40 ACPH)....................47

4-30 Contours of mole fraction of NH3 for center of cage case (40 ACPH)....................48

4-31 Top view of contours of mole fraction of NH3 for center of cage case (40
A C P H ) ..........................................................................................4 8









4-32 CO 2 concentrations V s. A CPH .......................................... ........................... 50

4-33 N H 3 concentrations V s. A CPH ........................................... ......................... 50

A M esh u sed for C C case............................................................................. ..... .......57

A -2 M esh u sed for O W case ........................................ .............................................58

B-l Contours of CO2 for CC in X-Y-Z plane (100 ACPH)................. ... ............ 59

B-2 Contours of CO2 for CC in X-Y plane (100 ACPH)..............................................60

B-3 Contours of CO2 for CC in Z-X plane (100 ACPH) ............................................. 60

B-4 Contours of NH3 for CC in X-Y-Z plane (100 ACPH)................. .................61

B-5 Contours of NH3 for CC in X-Y plane (100 ACPH)..............................................61

B-6 Contours of NH3 for CC in Z-X plane (100 ACPH) ..............................................62

B-7 Contours of CO2 for LM in X-Y plane (60 ACPH) ............. ............... 62

B-8 Contours of CO2 for LM in X-Y-Z plane (60 ACPH) .............. ............... 63

B-9 Contours of CO2 for LM in Z-X plane (60 ACPH).......................................63

B-10 Contours of NH3 for LM in X-Y plane (60 ACPH).... ............................64

B-11 Contours of NH3 for LM in X-Y-Z plane (60 ACPH) .............. ................ 64

B-12 Contours of NH3 for LM in Z-X plane (60 ACPH) .............. ............... 65

B-13 Contours of CO2 for OW in X-Y-Z plane (60 ACPH)............................65

B-14 Contours of CO2 for OW in X-Y plane (60 ACPH) ............ ............... 66

B-15 Contours of CO2 for OW in Z-X plane (60 ACPH).... ............................66

B-16 Contours of NH3 for OW in X-Y plane (60 ACPH) ............................. 67

B-17 Contours of NH3 for OW in Z-X plane (60 ACPH)...... ........................67

B-18 Contours of NH3 for OW in X-Y-Z plane (60 ACPH) .............. .............. 68

B-19 Contours of CO2 for CC in X-Y plane (20 ACPH)............................. ...............68

B-20 Contours of CO2 for CC in X-Y-Z plane (20 ACPH)............................................69

B-21 Contours of CO2 for CC in Z-X plane (20 ACPH) ..............................................69









B-22 Contours of NH3 for CC in X-Y plane (20 ACPH)......................................... 70

B-23 Contours of NH3 for CC in X-Y-Z plane (20 ACPH)............... .... .............. 70

B-24 Contours of NH3 for CC in Z-X plane (20 ACPH) ...............................................71

B-25 Contours of CO2 for OW in X-Y-Z plane (40 ACPH)............................71

B-26 Contours of CO2 for OW in Z-X plane (40 ACPH)...... ........................72

B-27 Contours of CO2 for OW in X-Y plane (40 ACPH) ............ ............... 72

B-28 Contours of NH3 for OW in X-Y-Z plane (40 ACPH) .............. .............. 73

B-29 Contours of NH3 for OW in Z-X plane (40 ACPH)...........................73

B-30 Contours of NH3 for OW in X-Y plane (40 ACPH) .............. ............... 74

B-31 Contours of CO2 for CC in X-Y plane (60 ACPH)............................. ...............74

B-32 Contours of CO2 for CC in Z-X plane (60 ACPH) ...............................................75

B-33 Contours of NH3 for CC in X-Y plane (60 ACPH).......................................75

B-34 Contours of NH3 for CC in X-Y-Z plane (60 ACPH).................. .............. 76

B-35 Contours of NH3 for CC in Z-X plane (60 ACPH) ................................................76

B-36 Contours of CO2 for CC in X-Y plane (40 ACPH)................ ....................77

B-37 Contours of CO2 for CC in X-Y-Z plane (40 ACPH).................. ................77

B-38 Contours of CO2 for CC in Z-X plane (40 ACPH) ..............................................78

B-39 Contours of NH3 for CC in X-Y plane (40 ACPH)............................................78

B-40 Contours of NH3 for CC in X-Y-Z plane (40 ACPH)............... .... .............. 79

B-41 Contours of NH3 for CC in Z-X plane (40 ACPH) ............................................... 79

E -1 Single m house in Y direction ........................................................................ .. .... 84

E-2 Two mice in the center of cage in X- direction.......................................................84

E-3 Four mice in the center of cage in Y- direction..................................................... 85

E-4 Four mice in the center of cage in X- direction..................................................... 85














NOMENCLATURE

CFD Computational Fluid Dynamics

ACPH Air Changes per hour

CO2 Carbon dioxide

NH3 Ammonia

W Weight of each mouse

V Volume of each mouse

d Diameter of each mouse

L Length of each mouse

OW Outside wall case

LM Four mice case

CC Center cage case

Qi Flow rate in feet3 per minute for 100 ACPH

Q2 Flow rate in feet3 per minute for 60 ACPH

Q3 Flow rate in feet3 per minute for 40 ACPH

Q4 Flow rate in feet3 per minute for 20 ACPH

P1 Power at 100 ACPH for 140 cages

P2 Power at 60 ACPH for 140 cages

P3 Power at 40 ACPH for 140 cages

P4 Power at 20 ACPH for 140 cages

P5 Power at 30 ACPH for 140 cages









Si Savings per year at 60 ACPH

S2 Savings per year at 40 ACPH

S3 Savings per year at 20 ACPH

S4 Savings per year at 30 ACPH

K Turbulent kinetic energy

v Velocity

M Number of elements in the system

N Number of species

div Divergence

Greek

E Dissipation rate

I Viscosity

p Density of each mouse

7r, Shear Stress

g, Body force in the ith coordinates

,j Krockner delta

a, Empirical constants

cI, Empirical constants

c,2 Empirical constants

Jj Mass molecular flux of species i in jth direction

D Diffusion Coefficient

Z, Mass fraction of ith element









Y, Mass fraction of species

/U, Turbulent exchange coefficient

A/, Number of kilograms of element i in a kilogram of species j

w Mass rate of creation of species i















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

COMPUTATIONAL FLUID DYNAMICS ANALYSIS OF THE EFFECTS OF
RODENT ACTIVITIES IN VENTILATED CAGES

By

Jatin Lamba

December 2005

Chair: Herbert Ingley III
Major Department: Mechanical and Aerospace Engineering

The purpose of this study was to perform a computational fluid dynamics analysis

to study the effects of rodent activities on selected air quality indicators (e.g., carbon

dioxide, ammonia and humidity) in a ventilated rodent cage. The individually ventilated

cage system is the most widely used method for rodent housing. Various studies have

been performed to develop the optimum ventilation performance in the ventilated rodent

cage. These studies have included variables such as ventilation rates, the structure of the

cage and various other parameters as they affect the microenvironment variables of

temperature, relative humidity, ammonia and carbon dioxide. The Guide for Care and

Use ofLaboratory Animals, The Institute of Laboratory Animal Resources and the

American Society of Heating Refrigerating and Air Conditioning Engineers Applications

and Fundamentals Handbook provide guidelines for these microenvironment variables.

Computational fluid dynamics (CFD) was used for analyzing the rodent cage

environment. A conventional Allentown rodent cage PC7115RT was used for the CFD









modeling. Various locations in the cage were analyzed in the GAMBIT software. The

rodents were modeled as half cylinders generally representing the size of rodents for the

analyses. The cylinders were then treated as sources of carbon dioxide. FLUENT

software was used to determine the effects of these sources on the microenvironment of

the cage.

The results for 100 and 60 ACPH agreed with the previously published

experimental and CFD results. The prevailing concentrations of CO2 and NH3 for the case

with two mice positioned near the inlet nozzle of the cage were 970 ppm and 6 ppm

respectively at 100 ACPH and 4300 ppm and 27 ppm respectively at 20 ACPH. The

average concentrations of CO2 and NH3 for the case with four mice positioned along the

y-axis were 1350 ppm and 9 ppm respectively at 60 ACPH. The most prevalent

concentrations of CO2 and NH3 for the case with two mice bodies positioned at the outer

walls opposite to each other away from the nozzle were 1000 ppm and 11 ppm

respectively at 60 ACPH.

The CO2 and NH3 concentrations increased with a decrease in air change rates.

From the plots it could be seen that 30 ACPH is an optimum air change rate in terms of

acceptable cage environment conditions and savings as compared to 100 ACPH. With

further CFD studies it may be possible to produce a design that could effectively ventilate

rodent cages.














CHAPTER 1
INTRODUCTION

At present the use of rodents as research subjects is playing an extremely

significant role in medical research. Laboratory mice have been a major component of

medical research since the 1880's.The microenvironment as defined by the levels of

carbon dioxide, ammonia, temperature, and humidity must be maintained properly for

research and the well being of the animals. In order to provide proper care for the

animals, criteria for the needs of the animals are required (Institute of Laboratory Animal

Resources, 1996). As there is no specified acceptable CO2 concentration for mice so

assuming acceptable CO2 concentrations for humans that is 5000 ppm as a standard. The

acceptable NH3 concentration specified by the guide for ventilated cages is 25 ppm.

Guidelines for experiments with rodents are provided by the Guide for Care and

Use ofLaboratory Animals, the Institute of Laboratory Animal Resources and the

American Society of Heating Refrigerating and Air Conditioning Engineers Applications

and Fundamentals Handbooks. The guide recognizes computational fluid dynamics as a

technique for studying the optimum performance of ventilated cages.

The two major types of rodent caging systems in use today are static and ventilated

cages. The static cages with filter tops have been known to provide a protective barrier

for rodents and thereby reduce the transcage coupling of microenvironment

contaminants. Studies have shown these cages effectively reduce cross-contamination by

particulate materials. However studies have also shown that the use of filter top cages can









cause large accumulations of carbon dioxide, ammonia and relative humidity which have

adverse effects on the health of rodents and thereby, their performance in medical studies.

Ventilated cages help in reducing the high levels of carbon dioxide, ammonia and

humidity in the cages. This technology has led to a significant increase in the use of

ventilated cages as a method of housing research mice.

Various designs are being utilized to provide ventilation to rodent cages. The basic

difference between them is in the way the air is introduced into the cages. Air can be

supplied directly by a portable blower and filter through a coupling attached to the cage.

The top of the cage and the base of the cage can be used to provide air to the cage.

Automatic watering may be combined with the system if air is provided at the base of the

cage. Automatic watering saves labor (White, 2001).

An indirect method of supplying air is by using individually mounted rack blowers.

The blower supplies air at high velocity over the filter on the cage, which pushes the air

through the filter into the cage. This method reduces the chance of contamination that

may be caused due to inadequate disinfection of cage couplings used in ventilation.

Filters should be changed regularly as the length of use affects the resistance provided by

the cage, which can affect the ventilation efficiency (A Guide to Research Rodent

Housing).

Captured exhaust is another method of providing air to ventilated system. Air can

be pulled directly into the cage through a filtered cage connection. A vacuum port above

the filter top can also be used to pull in exhaust air. The port is not directly connected to

the exhaust of the cage and it does not capture all the exhaust air from the cage. This









method provides reduction in heat load, and moisture (A Guide to Research Rodent

Housing).

Pandey (2005) conducted a computational fluid dynamics analysis of ventilated

cages. A conventional Allentown cage PC 7115RT was used for the study. The cage was

analyzed for two different air change rates for carbon dioxide, ammonia, relative

humidity, and temperature. The covers of the cages were selected as latrine areas and

were also considered as sources of carbon dioxide due to mice respiration. For the second

case the whole bottom of the cage was selected as a source of carbon dioxide, ammonia,

and relative humidity. However, mice bodies were not included in the geometry and the

bottom of the cage was taken as a source of carbon dioxide, ammonia, heat, and humidity

for one case.

The geometry of a conventional Allentown rodent cage PC 7115RT was also used

in the current study. Computational fluid dynamics was used to construct the cage and

determine the flow of air in the cage. FLUENT 6.2.16 and Gambit 2.2.30 provided the

computational software for these analyses. Gambit was used to construct the geometry of

cage and also to specify the rodent position. The geometry was then analyzed in

FLUENT for the concentration distribution of microenvironment variables like carbon

dioxide, and ammonia. In the current study cylinders generally representing the size of

the rodents simulated mice bodies. The cylinders were treated as source of carbon

dioxide. Different positions of mice and latrines were then analyzed. A study of the

effects of rodent activity on microenvironment variables in the ventilated cages could

help in improving the performance of these cages.









Three different locations were analyzed for the study. For the first case two mice

were located in the center of the cage near the inlet nozzle. This case was analyzed for

20, 40, 60, and 100 ACPH. The mice bodies were positioned next to each other to reduce

the complexity of the model. This case was analyzed for 40 and 60 ACPH. Two mice

were positioned opposite to each other along the outer wall of the cage for the second

case. For the third case two half cylinders were positioned a small distance away from the

center of the cage. The two half cylinders were double the length of the other mice bodies

analyzed in the study. The two half cylinders represented four mice present in the cage.

This case was analyzed for 60 ACPH.














CHAPTER 2
LITERATURE REVIEW

This chapter reviews literature relevant to the microenvironment parameters such as

carbon dioxide, ammonia, temperature, and relative humidity for ventilated rodent cages.

Krohn et al. (2003B) studied the effect of the presence of CO2 in rodent cages. The

presence of CO2 on heart rate and blood pressure of the mice was studied by considering

concentrations of 1%, 3% and 5% of CO2 in the air in the cages. Figure: 2.1 (Krohn et al.,

2003B) shows the effects of CO2 on mice. The figure shows the distribution of dwelling

time of mice at day and night in ventilated cages and in cages with 1% and 3%

concentrations of CO2. It can be seen that for the case of 1% C02, there is very little

difference between the dwelling times of mice in ventilated and ones with fixed

concentration of CO2. However, for the case of 3% C02, the mice prefer ventilated cages.

The study showed that rodents were not affected at levels up to 3% CO2 but were

affected significantly at concentrations of CO2 above 3% in the air.

In another study, Krohn et al. (2003A) analyzed the effect of air speed in ventilated

cages. The study was conducted for air speeds less than 0.2 m/s and greater than 0.5 m/s

and how these air speeds affect the performance of rats. Figure 2-2 (Krohn et al., 2003A)

shows the distribution of dwelling time of mice in ventilated cages in comparison to low

air speeds and high air speeds. It can be seen that the mice prefer to stay in cages with

high air velocity than lower air velocity.








Ventilated cage


Cage with C02


I I


I I


Period Set-up


)ay



N ght




)ay




Na ht


I I I I
0 10 20 30 40 50 60 70 80 90 100

Percent of total time (%)
Figure 2-1. Effect of 1% and 3% CO2 on mice preference (Krohn et al., 2003B)
The effect of 50, 80 and 120 air changes on rats was also analyzed by Krohn et al
(2003A). It can be seen from Figure 2-3 (Krohn et al., 2003A) that mice prefer to dwell in
cages with an 80 ACPH over cages with ACPH 50 and 120 respectively. The dwelling
time of mice in cages with 120 ACPH is greater than that of cages with ACPH of 50.
Thus preferred ACPH in cages lays around 80 ACPH.










Cage with lowairspeed Period Sex


0 10 20 30 40 50 60 7~ 80 SO 100


0 10 20 30 40 50 60 70 80 90 100
Percent of total time (%)

Figure 2-2. Effect of airspeeds on mice preference (Krohn et al., 2003A)


E
Night IL



Day


Night


0 10 20 30 40 50 60 70 80 90 100
Percent of total time (%)


Normal cage Cage Wth high airspeed Period Sex


E
0
Night


Day

E
Night


Normal cage











Unventilated cage


Cage wth 50 airchanges Period Sex


0 10 20 30 40 50 60 70 80 90 100
Percent of total time (%)


Unventilated cage


r I I
[ T T

J, L ,k J


Cage with 80 air changes Period Sex





Night


k ,NI


0 10 20 30 40 50 60 70 80 90 100
Percent of total time (%)


Unventilated cage


Cage with 120 air changes Period Sex

Day


Night


Day


Night


0 10 20 30 40 50 60 70 80 90 100
Percent of otal time (%)

Figure 2-3. Effect of air change rates on preference of mice (Krohn et al., 2003A)










Reeb et al. (2001) studied the health of mice and the microenvironment of cages for

bed changing frequencies of 7, 14 and 21 days, for ventilation rates of 30, 60 and 100 air

changes per hour. The concentrations of ammonia, CO2 and relative humidity and

temperature changes were analyzed over a period of 4 months. Three mice each were

housed in all the cages. Maxi-Miser PIV cages were used for the study. Table: 2.1 (Reeb

et al., 2001) show the effect of ventilation rates and the frequency of cage changes on the

microenvironment of the cage. It can be seen that the concentration of ammonia

decreases with the decrease in the frequency of cage changes. However, the concentration

of ammonia was lower at higher ventilation rates. The relative humidity of the air in the

cages did not vary significantly with either the change in ventilation rates or the

frequency of cage changes. The concentration of CO2 increased with the decrease in the

frequency of cage changes. Figure 2.4 (Reeb et al., 2001) shows the effect of air change

rates on ammonia and relative humidity based on the results from Table 2-1.

Table 2-1. Effect of cage ventilation and frequency of cage changes on microenvironment
Frequency of cage change, days [mean SEM (n)*]

7 14 21
Ammonia (ppm)
30 air changes h 26.3 5.7ta (12) 62.8 17.6a (5) 73.0 15.4a (4)
60 air changes/h 1.50.2tb (14) 14.6 6.7b (10) 26.9 19.1b (9)
100 air changes/h 1.1 0.2 b (13) 3.7 &1.5b (8) 15.4 7.4b (6)
Relative humidity (%)
30 air changes/h 57 1a 52 2 57+4
60 air changes/h 48 2b 53 4 52 3
100 air changes/h 48 2b 51 3 462
Carbon dioxide (ppm)
30 air changes h 21904185a 147590 2050215a
60 air changes/h 1310 145b 1775 300 1415 240ab
100 air changes/h 1110 110b 1575 270 945 200b
Temperature (OC)
30 air changes/h 24.4+0.2 24.4 0.3 24.8+0.6
60 air changes h 24.1 0.4 24.1 0.6 23.410.5
100 air changes/h 23.2 0.3 23.2 0.2 24.1 0.5
*(n) is the number of measurements and applies to all parameters; tValue is significantly different from 14 and 21 day
conditions in same row (P<0.05) 5 Value is significantly different from 21 day condition in same row (P<0.05); aWithin a
column, values with different superscript letters differ significantly (P< 0.05)
(Reeb et al., 2001)











100 M7 day
*14 day
[21 day
75
E

E 50-
0


25




Static 30 ACH 60 ACH 100 ACH
(a) Cage Ventilation

f------- i
70 17 day
*14 day
60 [21 day

S50

i 40

S30

20

10


Static 30 ACH 60 ACH 100 ACH
(b) Cage Ventilation
Figure 2-4. Cage microenvironment (Reeb et al., 2001)

Krohn and Hansen (2002) conducted a study to estimate the time required for CO2

concentrations to reach 3% of the cage volume. CO2 levels were measured over time in

different types of individually ventilated cages when no ventilation was provided to the

cages. Seven different types of commercially available cages were used for the study. A

standard mouse per air volume ratio of 20 gram/liter was reached by providing a number

of 8-10 month old rats. Table: 2.2 (Krohn and Hansen 2002) shows the response time











required for CO2 concentrations to exceed the 3% concentration in different cages.

Figure: 2.5 (Krohn and Hansen. 2002) graphically represent the change in CO2

concentration in different types of cages over a period of time. It can be seen that for

standard static filter top, US filter top, and ventirack type of cages, the concentration of


CO2 never exceeded 3% of the total cage volume.

Table 2.2. Response time needed for CO2 concentrations to reach above 3%
Bio.A.S Bio.A.S
Standard with with Quantum-Air
static filter SealSafe internal external Maxi-Seal
top US filter top VentiRack filter top WB WB System
(Tecniplast) (Tecniplast) (Biozone) (Tecniplast) (Ehret) (Ehret) (Arrowmight)
Cage volume (I) 11 9 6 9 12 9 6.5
Response Unlimited Unlimited Unlimited 457 277 239 2716
time (min)
WB= water bottle

(Krohn and Hansen, 2002)

9.0
-+-SealSafe Filtertop (Tecnplast)
8.0 -.- Bio.A.S. wilh intemal W.B. (Ehret)
-A-Bio.A.S. iilh extemal W.B. (Ehret)
7.0 --G-QuaniurmAir-Maxi-Seal System(Arrownighit)
-i- Static filtertop (Tecniplast)
--*-US-fllltrtop rrecnlplaqvt
4.0
6.0 -+-Venlirack (izonze)

5.0




3.0
0
2.0 1

1.0

0.0
0 20 40 Tlm6 in) 80 100 120

Figure 2-5. CO2 concentrations in different types of sealed filter top cages (Krohn and
Hansen, 2002)

Smith et al. (2004) compared different types of bedding and the effect of these

types of bedding on selected micro environmental parameters such as ammonia, carbon









dioxide, relative humidity, and temperature. Results were compared for Nestpaks and

loose bedding. C57BL/6J mice and NOD/Ltd mice were used for the study. The results

showed that the effect on temperature and relative humidity by bedding type were

minimal. The type of bedding significantly affected ammonia concentrations. The cages

with hardwood bedding had lower concentrations of ammonia. The study also showed

that ventilated cages have significantly lower ammonia concentrations.

Hoglund and Renstrom. (2001) conducted a study to measure the concentrations of

ammonia in two different types of individually ventilated cages. BioZone VentiRack,

IVC1, and Techniplast SealSafe, IVC2S were the two types of ventilated systems used

for the study. The systems were analyzed for negative and positive pressure in the cages

for a period of 10 days. Table: 2.3 (Hoglund and Renstrom. 2001) shows the ammonia

concentration for negative pressure in both type cages. Table: 2.4 (Hoglund and

Renstrom. 2001) shows the ammonia concentration for positive pressure in both types of

cages. At the end of 10 days the results showed the ammonia concentration to be lower

than 10 ppm in both types of cages. The ammonia concentration was found to be higher

in cases where urine had accumulated in the cages.

Memarzedah et al. (2004) conducted a study to compare the environment in static

and ventilated cages for different velocities and ventilation designs. The different types of

cages used were ventilated cages with exhaust air forced through filters, ventilated cages

with forced air inlets and a static cage. The results showed that ventilated cages had

higher air velocities, lower relative humidity and lower carbon dioxide and ammonia

concentrations.







Table 2-3. Ammonia concentrations in IVC2S & IVC1 for negative pressure

Cage
position 1 2 3 4 5 6 7


IVC2S NH3 (ppm)
1 1* (3)
2 3.5 (3)
3 0(3)
4 2(3)
5 8* (3)
6 2,5 (3)


1,5 (3) 7.5
3 (3)
3,5 (3)
2.5 (3)
20- (3)
6" (3)


NH3 (ppm)
85 (1) 9(2)
5 (3) 40 (3)
4(3) 10(3)
7 (1)


7 (3)

5 (3)


5,5 (3)


6(3)

6(3)


12
6,5(3)


6 (3)

7 (3)


5 (3) 20* (3)
5 (3)
5 (3)
20(3)
4,5 (3)
6(3)
8(2)


Figures within parentheses are number of animals in each
cage, Cages where wet corners were noted, Cages in position
4:1 were reference cages that contained no animals,
IVC= individually ventilated cage
(Hoglund and Renstrom. 2001)


11" (3)


5,5" (3)


7 (3)


4.5 (1)
2 (3) 1 (3) 6,5 (3)
3 (3)


8,5" (3)


IVC25
1
2
3
4
5






Table 2-4. Ammonia concentrations in IVC2S & IVC1 for positive pressure
Cage
position 1 2 3 4 5 6 7


NH3 (ppm)
0(3)
6,5 (3)
2,5 (3)
1,5 (3)
6 (3)
1,5 (3)


IVC2S NH, (ppm)
1 2 (1)
2 0
3 0,5 (3)
4 4.!
5 15 (3)


(3)


1.5 (3) 4
1,0 (3)
1.5 (3)
3,5 (3)
7.5 (3)
5 (3)


1.5 (3) 4,5
1 (3)
2, 0 (3)


5 (1)


1 (3)


0(3)


1 (3)

2(3)


4,0 (3)

0,5 (3)


5,.5 (3)

1,0 (3)

3,5 (3)


1,0 (3)

1,5 (3)


1.5 (3)

2,0 (3)

3,5 (3)


0.5 (3)


1 (3)


1 (3)


1.5 (3)


5,5* (3)

6* (3)


2 (2)


Figures within parentheses are number of animals in each
cage. Cages where wet corners were noted. Cages in
position 1:4 were reference cages that contained no animals,
IVC = individually ventilated caqe
(Hoglund and Renstrom. 2001)


IVC1
1
2
3
4
5
6







Hasegawa et al. (1997) analyzed the relationship between carbon dioxide
concentrations, oxygen and air change rate in forced-air-ventilated micro-isolation
systems (FVMIS). Three 8-week-old Wistar strain male rats were used for the study.
Figure: 2.6 (Hasegawa et al., 1997) shows the apparatus used for the study.

Room air


SAir supply fan





Intake Filter Outlet


FVMIS cage







.B* Gas detector

Figure 2-6. Schematic diagram of Hasegawa apparatus (Hasegawa et al., 1997)
Air change rates were varied from 10 ACPH to 120 ACPH and temperature,
relative humidity, CO2 and 02 were analyzed in the cages. It was noted that with an
increase in air change rates, CO2 concentrations decreased significantly. As no standard









CO2 concentration in microenvironment of laboratory animals was specified, 5000 ppm

was considered as a standard for the study. The air change rate required to maintain the

level of CO2 similar to conventional housing that is less than 5000 ppm (parts per

million) was 60 ACPH. Figure: 2.7 (Hasegawa et al., 1997) shows the CO2 concentration

in FVMIS cages at different air changes per hour

SO. N I





E 4(U)U
I 3000 .. .. .....
U 2000
o --------- I-


10 30 45 50 60 80 120 control room
Air Changae per Hour
Figure 2-7. CO2 concentrations in FVMIS cages (Hasegawa et al., 1997)

Pandey (2005) conducted computational fluid dynamics analyses of ventilated

cages. Air velocity profiles and concentration distributions for carbon dioxide, ammonia,

and water vapor were obtained from the study. A conventional Allentown cage PC

7115RT was analyzed by Pandey. The cage was assumed to house 5 ICR mice. However,

the actual mouse geometry was not simulated. The bottom of cage was assumed as a

source of carbon dioxide, ammonia, and water vapor in one case, and in the other case

small areas at the corners of the cage were considered sources of carbon dioxide,

ammonia, and water vapor for second case. The height of cage was reduced by 1" to









compensate for the bedding. The cage geometry was constructed using GAMBIT

software. Figure: 2.8 (Pandey, 2005) shows the geometry of the Allentown cage.


Figure 2-8. Geometry of Allentown cage (Pandey, 2005)

The analyses show that the higher concentrations of CO2 and NH3 were towards the

opposite corners of the inlet nozzle for both the cases. Figure 2-9: (Pandey, 2005) shows

the contours of CO2 for the corer bottom case. Figure 2-10: (Pandey, 2005) shows the

contours of CO2 for the whole bottom case.































Figure 2-9. Contours of CO2 for corner bottom at 100 ACPH (Pandey, 2005)


Figure 2-10. Contours of CO2 for whole bottom at 100 ACPH (Pandey, 2005)









The analyses were carried out for 60 and 100 air changes per hour. The results were

validated with the study conducted by Heurkamp et al. (1994). Table: 2.5 (Pandey, 2005)

shows validated results. Table: 2.6 (Pandey, 2005) shows the concentrations of ammonia,

and carbon dioxide, for 60 ACPH and 100 ACPH for both whole bottom and corner

bottom cases.

Table 2-5. Comparisons of C02, and NH3, concentrations
Species WB CB Huerkamp, M.J.,
Lehner, N.D.M,
(100 ACPH) (100 ACPH) Lehner, N
(1994) at 112
ACPH


NH3 8.5 ppm 6.5 ppm 68 ppm
CO2 1190 ppm 1020 ppm 1050200 ppm


(Pandey, 200:
Table 2-6. Results of C02, and NH3, concentrations
WB WB CB CB
Species
(100 ACPH) (60 ACPH) (100 ACPH) (60 ACPH)

NH3 8.5 ppm 14.3 ppm 6.5 ppm 13 ppm
CO2 1190 ppm 2160 ppm 1020 ppm 1920 ppm
WB= Whole Bottom Case, CB= Corer Bottom
(Pandey, 200:
The study conducted by Pandey (2005) is most pertinent to the current study. The

current study is an extension of Pandey's work.


5)








5)














CHAPTER 3
APPROACH

The mice in a rodent cage are sources of sensible and latent heat, water vapor and

carbon dioxide. The fecal matter produced by mice, acts as a source of ammonia and

moisture. The concentrations of ammonia, and carbon dioxide were analyzed in the

ventilated cage to study the effects of rodent activities on the cage microenvironment. To

study the cage environment for mice, parameters like the geometry of the cage, bedding,

number of mice, and position of the mice must be modeled. Modeling of the physical

properties such as flow profiles and concentration distribution inside the cage

microenvironment was carried out using FLUENT software.

A conventional Allentown PC 7115RT was used as a model for the study. The cage

geometry was modeled using GAMBIT software. For this study, it was assumed that ICR

mice, weighing 30 grams, were present in the cage. The mouse body was modeled as a

cylinder. The size of this cylinder was calculated based on the following assumptions

Density of mouse (p) = 1 gm/cm3

Weight of mouse (W) =30 gm

The volume of each mouse is equal to

V= W/p = 30 cm3 3-1

The diameter (d) of each mouse was assumed to be 2.54 cm (1 inch). The length of

each mouse (L) is thus equal to

Hd2
L -d= 2.5 inches 3-2
4V









The type of cage bedding in the current analysis was assumed to be a typical

corncob bedding of one inch depth. Corncob bedding is porous in nature and is known to

reduce the concentration of ammonia. However the bedding offers resistance to the

momentum of the fluid. To model the bedding in the cage, the height of the cage was

reduced by one inch.

To reduce the complexity of the analysis, the mice bodies were assumed to be

stationary. To further reduce the complexity of the model, mice were modeled as half

cylinders. The mouse body was considered to be a source of CO2 with CO2 coming out

uniformly from the half cylinder. In one case the mice were positioned parallel to the

length of the cage. For the second case, they were positioned perpendicular to the length

of the cage. Figure 3-1 shows the two cylinders positioned along the x-axis at the outer

walls of the cage and away from the inlet air nozzle. Figure 3-2 shows the two cylinders

positioned along the y-axis. The cylinders in this case are twice the length of one mouse.

This is the geometry that was used to model four mice in the cage. Figure 3-3 shows the

two cylinders along the x-axis near the center if the cage and also near the inlet nozzle.

It is noted that mice select specific corners for their latrines. Latrines, being a major

source of ammonia, carbon dioxide and moisture, had to be considered in the model. The

four corners of the cage were assumed to be the areas of the latrines. The ammonia and

CO2 concentration from the latrines were assumed to be independent of the number of

mice present in the cage. Assuming 16 ppm of ammonia to be present in the condition of

steady state the mass flow rate of ammonia was back calculated. The mass flow rate used

for ammonia is 4e-06 kilogram per second and mass flow rate of CO2 1.7e-05 kilogram

per second.









Air at 75F and 50% RH was supplied to the cage through the inlet nozzles at 20,

40, 60, and 100 ACPH.


Figure 3-1. Mice positioned at the outer walls of the cage


Figure 3-2. Mice positioned along the y-axis









































figure 3-3. Mice positioned at the center ot the cage

The geometry was then meshed in the GAMBIT software. The top part of the cage

was meshed with a structured mesh of size 0.15 inches. The lower part of the cage was

also meshed with a structured mesh of size 0.1 inches. The lower geometry that included

the mice bodies was meshed with an unstructured mesh of size 0.1 inches. This was

because the geometry was too complex to be meshed by a structured mesh. The portion

of the cage with the nozzle was meshed with a size .05-inch mesh as the size of nozzle is

0.15 inch and the smaller mesh gave better results. The figures showing mesh schemes

used in other cages are provided in appendix A.





































0.1 Inch Sturctured
Mesh 0.05 inch
Unstructured Mesh
Y"

Figure 3-4. Meshing scheme used in the LM case

The geometry was then analyzed in FLUENT. First order upwind is used for this

case as flow is aligned with the grid. The relaxation factors are used to control the

iterations of the model. By setting a lower value the model remains more stable. The

following settings were used in FLUENT.

Table 3-1. Model definitions
Model Type Settings
Space 3D
Time Steady
Viscous Standard k-epsilon turbulence model
Wall treatment Standard Wall Functions
Heat Transfer Enabled
Solidification and Melting Disabled
Radiation None
Species Transport Non reacting


l











Table 3-2. Discretization scheme
Variable
Pressure
Pressure-Velocity Coupling
Momentum
Turbulence Kinetic Energy
Turbulence Dissipation Rate
CO2
NH3
Air
Energy
H20

Table 3-3. Variable definitions
Variable
Pressure
Density
Body Forces
Momentum
Turbulence Kinetic Energy
Turbulence Dissipation Rate
Turbulent Viscosity
CO2
NH3
Air
Energy
H20


Scheme
Standard
Simple
First Order Upwind
First Order Upwind
First Order Upwind
First Order Upwind
First Order Upwind
First Order Upwind
First Order Upwind
First Order Upwind


Relaxation Factor
0.2
0.5
0.5
0.40000001
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5














CHAPTER 4
RESULTS AND DISCUSSION

The purpose of this study was to study the effects of rodent activities on cage

microenvironments. Computational fluid dynamic methods were used to find and plot the

concentrations within the cage and also the flow profiles in the cage. The simulated mice

bodies were positioned in various parts of the cage using GAMBIT software and the

effect of mice positions on the microenvironment was then analyzed using the FLUENT

software. Each mouse body was considered to be a source of CO2. Three different mouse

positions were analyzed in the study. In the first case two mouse bodies were positioned

at the outer wall of the cage. The outer wall case was referred to with an abbreviation

"OW". Figure 4-1 shows the OW case.

In the second case, two mouse bodies were positioned along the center of the cage

near the inlet nozzle of the cage, referred to with an abbreviation "CC". Figure 4-2 shows

the CC case. For the third case, two longer cylinders were positioned along the y-axis,

referred to with an abbreviation "LM". Four mice bodies were simulated in the cage by

doubling the length of the cylinders in the cage. Figure 4-3 shows the LM case.

As there is no specified acceptable CO2 concentration for mice so assuming

acceptable CO2 concentrations for humans that is 5000 ppm as a standard. The acceptable

NH3 concentration specified by the guide for ventilated cages is 25 ppm.




































Figure 4-1. Outside wall case


figure 4-2. Center ot cage case








































figure 4-J. Pour mice case

The CC case was analyzed for an air change rate of 100 ACPH. For 100 ACPH the

velocity of inlet air was 8.57 m/s. The NH3 mass flow rate was 4e-06 kg/s, and the CO2

mass flow rate was 1.7e-05 kg/s. Figure 4-4 shows the air velocity profiles for this case.

As expected, the profiles show that more circulation of air takes place near the nozzle of

the cage. A slight bump could be seen in the velocity profile due to the presence of a

mouse body at the center of the cage. The air velocity in the vicinity of the mouse was

1.02 meters per second. Assuming a comfortable air velocity of a mouse to be equal to

that for a human (0.15 m/s-0.25 m/s), it can be seen that the air velocity is much higher

than the acceptable level and can be concluded that the mouse would not stay at that









position for very long and move away towards the corner of the cage where the air

velocity would be less. Figure 4-5 shows the contours for the CO2 concentration in the

cage at 100 ACPH. It can be seen from the figure that the CO2 concentration near the

mice bodies is less than in other areas of the cage. This is because in this case the mice

are positioned near the inlet nozzle and the high air velocity forces the CO2 to the back

side of the mouse and also the air exchange rate causes the concentration to be less near

the mouse body. The concentration that was most prevalent in the cage was assumed to

be the average concentration of CO2 and NH3 in the cage.






























Figure 4-4. Velocity profiles for center of cage at 100 ACPH









































Figure 4-5. Contours of mole fraction of CO2 for center of cage (100 ACPH)

The concentration of CO2 in the cage was found to be 970 ppm. Figure 4-6 shows

the contours for mole fractions of NH3. The NH3 present within the cage is 6 ppm. It can

also be seen that the concentration of NH3 near the mouse body is very low, again

because the mouse body is a source of CO2 and not ammonia, and also because the air is

flowing directly on the mouse body. Figure 4-7 shows the contours of mole fraction of

NH3 viewed from the top of the mouse cage. The four corer areas defined as latrines are

visible in this figure. The latrines show an NH3 concentration of 25 ppm, which decreases

as we move away from the corners and the NH3 mixes with the air coming in the cage.
































Figure 4-6. Contours of mole fraction of NH3 for center of cage (100 ACPH)


Figure 4-7. Top view of contours of mole fraction of NH3 for center of cage (100 ACPH)









The LM case was run for 60 ACPH. For 60 ACPH the velocity of inlet air was

5.143 m/s. The NH3 mass flow rate was 4e-06 kg/s, and the CO2 mass flow rate was 1.7e-

05 kg/s. Figure 4-8 shows the velocity profiles for the LM case at 60 ACPH. It can be

seen that airflow is concentrated near the inlet nozzle of the cage. The air velocity in the

vicinity of the mouse was 0.60 meters per second, which is higher than acceptable

comfortable level of 0.15 m/s-0.25 m/s. Again it can be concluded that the mice would

not stay at that position for very long and would move away towards the corner of the

cage where the air velocity would be less. Figure 4-9 shows the contours of mole fraction

of CO2 concentrations in the cage. It can be seen from the figure that CO2 concentrations

are highest in the vicinity of the mouse body since mice are the major sources of CO2 in

the cage. The concentration is much lower near the nozzle of the cage as the fresh air is

flowing into the cage. The CO2 concentration in the cage is about 1350ppm. Figure 4-10

shows the contours of mole fraction of NH3 in the cage. The concentration of NH3 is less

near the mouse body as the mouse is not a source of ammonia in the cage and also near

the inlet as the air is flowing in to the cage. The NH3 concentration in the cage is 9 ppm.


Figure 4-8. Velocity profiles for four mice at 60 ACPH






























Figure 4-9. Contours of mole fraction of CO2 for four mice (60 ACPH)


Figure 4-10. Contours of mole fraction of NH3 for four mice (60 ACPH)































Figure 4-11. Top view of contours of mole fraction of NH3 for four mice (60 ACPH)

Figure 4-11 shows the top view of the mole fraction of NH3 for the LM case. It can

be seen that in the vicinity of the latrines ammonia concentrations are about 25 ppm,

which decreases with the increase in the distance from the corners.

The OW case was run for 60 ACPH. For 60 ACPH the velocity of inlet air was

5.143 m/s. The NH3 mass flow rate was 4e-06 kg/s, and the CO2 mass flow rate was 1.7e-

05 kg/s. Figure 4-12 shows the velocity profiles in the cage. The airflow is concentrated

near the inlet to the cage. A slight bump can be seen near the outer walls of the cage away

from the nozzle, which shows the presence of a mice body at that location in the cage.

The air velocity in the vicinity of the mouse was 0.275 meters per second, which is

slightly higher than acceptable comfortable level of 0.15 m/s-0.25 m/s. It can be

concluded that the mice would not stay at that position for very long and move away

towards the corer of the cage where the air velocity is less. Figure 4-13 shows the









contours of CO2 concentration in the cage at 60 ACPH. The concentration of CO2 is

highest near the mouse body. It can also be seen that the higher CO2 concentration is

more towards the back end of the mouse body. This is because the air coming from the

nozzle impinges on the front side of the mice and forces the CO2 in that direction. The air

hits the mouse body and passes above the body, not causing much effect on the CO2

coming out from the back end of the body. The C02 concentration in the cage is 1000

ppm. Figure 4-14 shows the mole fraction of concentration of NH3 in the cage. The NH3

concentration within the cage is about 11 ppm. The NH3 concentration is lowest near the

mouse as it is not a source of ammonia. Figure 4-15 shows the top view of the contours

of mole fraction of NH3 concentration in the cage. The ammonia concentration is high at

the corners of the cage.


Figure 4-12. Velocity profiles for outside wall at 60 ACPH
































Figure 4-13. Contours of mole fraction of CO2 for outside wall (60 ACPH)


Figure 4-14. Contours ot mole traction ot NH3 tor outside wall (6U ACPH)







































Figure 4-15. lop view ot contours ot mole traction ot NH3 tor outside wall (60 ACPH)

The CC case was also run at 20 ACPH. For 20 ACPH the velocity of inlet air was

1.71 m/s. The NH3 mass flow rate was 4e-06 kg/s, and the CO2 mass flow rate was 1.7e-

05 kg/s. Figure 4-16 shows the velocity profile for this case. The velocity profile is

similar to all the other cages with more airflow near the nozzle and less away from the

nozzle. A slight bump can also be seen near the nozzle showing the presence of a mice

body at that location in the cage. The air velocity in the vicinity of the mouse was 0.182

meters per second, which is within the acceptable comfortable level of 0.15 m/s-0.25 m/s.

It can be concluded that the mouse could stay at almost any position in the cage, as the air

velocity is not very high.









































Figure 4-16. Velocity profiles for center of cage case at 20 ACPH

Figure 4-17 shows the contours of mole fraction of CO2 concentration in the cage

at 20 ACPH. It can be seen that the concentration is low at the front end of the mouse

body because it is positioned very near to the inlet nozzle and the fresh air coming in

from the inlet reduces the concentration of CO2 in that area. A small area can be seen just

to the back of the mouse body where a large concentration of CO2 exists. This is because

the air is not in direct contact with the mouse body in that area. The CO2 concentration in

the cage is 4300 ppm. It can be seen that CO2 concentration is very high; this is because

of a lower air change rate of 20 air changes per hour.










































Figure 4-17. Contours of mole fraction CO2 for center of cage (20 ACPH)

Figure 4-18 shows the contours of mole fraction of NH3 in the CC case at 20

ACPH. The concentration of NH3 near the mouse body is less, as the mouse body is not a

source of ammonia. Figure 4-19 shows the top view of the contours of NH3 concentration

in the CC case at 20 ACPH. It can be seen that the latrines show the highest concentration

of ammonia. The center of the cage experiences low concentrations of ammonia, as the

airflow is high within that region. The concentration of ammonia decreases away from

the corners of the cage. The NH3 concentration in the cage is about 27 ppm. This high

concentration is due to lower air change rate of 20 air changes per hour.
































Figure 4-18. Contours of mole fraction of NH3 for center of cage (20 ACPH)


Figure 4-19. Top view of contours of mole fraction of NH3 for center of cage (20 ACPH)









The OW case was also run for 40 ACPH. For 40 ACPH the velocity of inlet air was

3.42 m/s. The NH3 mass flow rate was 4e-06 kg/s, and the CO2 mass flow rate was 1.7e-

05 kg/s. Figure 4-20 shows the velocity profile for OW at 40 ACPH. It can be seen that

the velocity is concentrated more towards the inlet nozzle. A bump can be seen showing

the presence of a mouse body in the cage. The air velocity in the vicinity of the mouse

was 0.158 meters per second, which is within the acceptable comfortable level of 0.15

m/s-0.25 m/s. It can be concluded that the mouse could stay at that position and be

comfortable. Figure 4-21 shows the contours of mole fraction of CO2 concentration for

OW at 40 ACPH. The concentration of CO2 is higher near the latrines. The CO2

concentration in the cage is 2200 ppm.


Figure 4-20. Velocity profiles for outside wall at 40 ACPH































Figure 4-21. Contours of mole fraction of CO2 for outside wall (40 ACPH)


Figure 4-22. Contours of mole fraction of NH3 for outside wall (40 ACPH)




































Figure 4-23. Top view of contours of mole fraction of NH3 for outside wall (40 ACPH)

Figure 4-22 shows the contours of mole fraction of NH3 concentration for the OW

case at 40 ACPH. Figure 4-23 shows the top view of the contours of the NH3

concentration for OW case at 40 ACPH. The ammonia concentration is higher at the

corners and less near the mouse body. The NH3 concentration in the cage is 22 ppm.

Figure 4-24 shows the velocity profile for the CC case at 60 ACPH. For 60 ACPH

the velocity of inlet air was 5.143 m/s. The NH3 mass flow rate was 4e-06 kg/s, and the

CO2 mass flow rate was 1.7e-05 kg/s. As expected the velocity is concentrated near the

inlet nozzle. The air velocity in the vicinity of the mouse was 0.678 meters per second,

which is higher than acceptable comfortable level of 0.15 m/s-0.25 m/s. It can be

concluded that the mouse would not stay at that position for very long and move away









towards the corer of the cage where the air velocity would be lesser. Figure 4-25 shows

the contours of mole fraction of CO2 concentrations for this case. The highest

concentration is in the vicinity of the mouse body. The concentration of CO2 in the cage

is 1100 ppm. Figure 4-26 shows the mole fraction of NH3 concentrations for this case.

Figure 4-27 shows the top view of mole fraction of ammonia for this case. The highest

concentration of ammonia is in the vicinity of the latrines. The concentration of ammonia

in the cage is approximately 10 ppm.


Figure 4-24. Velocity profiles for center of cage at 60 ACPH































Figure 4-25. Contours of mole fraction of CO2 for center of cage (60 ACPH)


Figure 4-26. Contours of mole fraction of NH3 for center of cage (60 ACPH)































Figure 4-27. Top view of contours of mole fraction of NH3 for center of cage (60 ACPH)

Figure 4-28 shows the velocity profiles for the CC case at 40 ACPH. For 40 ACPH

the velocity of inlet air was 3.42 m/s. The NH3 mass flow rate was 4e-06 kg/s, and the

CO2 mass flow rate was 1.7e-05 kg/s. As expected the velocity is concentrated near the

inlet nozzle. The air velocity in the vicinity of the mouse was 0.376 meters per second,

which is higher than acceptable comfortable level of 0.15 m/s-0.25 m/s. It can be

concluded that the mouse would not stay at that position for very long and move away

towards the corer of the cage where the air velocity would be lesser. Figure 4-29 shows

the contours of mole fraction of CO2 concentration at 40 ACPH. The concentration of

CO2 in the cage is 2000 ppm. Figure 4-30 shows the contours of mole fraction of NH3

concentrations for this case. Figure 4-31 shows the top view of the contours of NH3

concentrations for this case. The highest ammonia concentration is in the vicinity of the

latrines. The concentration of ammonia in the cage is approximately 18 ppm.
















3.1 190



2.4 +0













I








Figure 4-28. Velocity profiles for center of cage case at 40 ACPH


Figure 4-29. Contours of mole fraction of CO2 for center of cage case (40 ACPH)

































Figure 4-30. Contours of mole fraction of NH3 for center of cage case (40 ACPH)


Figure 4-31. Top view of contours of mole fraction of NH3 for center of cage case (40
ACPH)









Table 4-1 shows the CO2 and NH3 concentrations for all the results obtained from

the CFD simulations. The concentration represented by the most prevalent color present

in the cage is taken as the average concentration of the cage.

Table 4-1. Results from CFD simulations
CC LM OW CC OW CC CC
100 60 60 60 40 40 20
Species ACPH ACPH ACPH ACPH ACPH ACPH ACPH
No. of
Mice 2 4 2 2 2 2 2
970 1350 1000 1100 2100 2000 4300
CO2 ppm ppm ppm ppm ppm ppm ppm
11 10 20 18 27
NH3 6 ppm 9 ppm ppm ppm ppm ppm ppm

As the CC case was analyzed for several levels of ACPH a comparison of ACPH

effects can be made for this case. Table 4-2 shows this comparison for the CC case.

Table 4-2. CO2 and NH3 concentrations Vs. ACPH for center of cage case
ACPH
Species 100 ACPH 60 ACPH 40 ACPH 20 ACPH
Number of
Mice 2 2 2 2
CO2 970 ppm 1100 ppm 2000 ppm 4300 ppm
NH3 6 ppm 10 ppm 18 ppm 27 ppm


Figure 4-32 shows the variation of CO2 concentrations with increase in ACPH. It

can be seen from the figure that CO2 concentration increases with decrease in ACPH. The

highest concentration of CO2 is 4300 ppm at 20 ACPH. At 3000 ppm the ACPH comes

about 30 ACPH. Figure 4-33 shows the variation of NH3 with increase in ACPH. The

highest concentration of NH3 is 27 ppm at 20 ACPH, which is higher than the 25 ppm

prescribed by the guide. An ACPH rate of 25 results in amid concentration of 28 ppm.

25-30 ACPH seems to be a logical choice to maintain acceptable levels of CO2 and NH3

in the cage.







50



C02 Concentrations Vs ACPH for CC case


5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0


20 40 60 100


ACPH


Figure 4-32. CO2 concentrations Vs. ACPH


NH3 Concentrations Vs ACPH for CC case


20 40 60 100


ACPH


Figure 4-33. NH3 concentrations Vs. ACPH









Three cases were run for 60 ACPH, CC, LM and OW. As four mice are considered

for the LM case, the CO2 concentrations cannot be compared. Since it was assumed that

ammonia concentrations are independent of the number of mice bodies, the ammonia

concentration for all the three cases at 60 ACPH can be compared. Table 4-3 shows the

comparison of NH3 concentrations for three cases at 60 ACPH. It can be seen from the

table that concentrations are very similar.

Table 4-3. Comparison of NH3 concentrations for different cases at 60 ACPH
60 ACPH
Species CC OW LM

NH3 10 ppm 11 ppm 9 ppm

The CO2 concentrations for CC and OW can be compared for 60 ACPH. The CO2

concentration for CC at 60 ACPH is 1000 ppm and 1100 ppm for OW at 60 ACPH. The

CO2 concentrations are almost equal.

Pandey (2005) carried out similar analysis on Allentown cages for five mice but

without considering mice bodies in the geometry. As the ammonia in the cage is

independent of the number of mice in the cage, the results for ammonia for the current

study can be compared with the results of the analysis carried out by Pandey. Table 4-4

shows the comparison of results at 100 ACPH. Table 4-5 shows the comparison of results

at 60 ACPH. The results show a good agreement with results reported by Pandey

Table 4-4. Comparisons of NH3 concentrations against results reported by Pandey (2005)
at 100 ACPH
Center of Cage Pandey (2005) Corner
Species (100 ACPH) Bottom (100 ACPH)

NH3 6 ppm 6.5 ppm









Table 4-5. Comparisons of NH3 concentrations against results reported by Pandey (2005)
at 60 ACPH
Pandey
(2005) Corner
Center of Cage Four Mice (60 Outside Wall Bottom (60
Species (60 ACPH) ACPH) (60 ACPH) ACPH)


NH3 10 ppm 9 ppm 11 ppm 13 ppm


As the flow rate of air decreases from 100 to 60 to 40 to 20 ACPH the ventilation

from power consumed is less and savings are more. The savings by using lower air

change rates as compared to 100 ACPH are shown below. The calculations are for

savings and power consumed are provided in Appendix C. Pi is the power of fan at 100

ACPH.

Savings for 60 ACPH is 79% which comes out to Si= $549.4Pi per year

Savings for 40 ACPH is 93.7% which comes out to S2= $656.6P1 per year

Savings for 30 ACPH is 97.3% which comes out to S4= $681.9Pi per year

Savings for 20 ACPH is 99.3% which comes out to S3= $695.9Pi per year

At 30 ACPH the savings are 97.3% of money used at 100 ACPH.

The mass flow rate for CO2 used in the study can also be verified by the

calculations shown in Appendix D. It can be seen that at 20 and 40 ACPH the percent

error is very less 3% and 6% respectively. The error for 100 ACPH is 18%, this is due to

the fact that most prevalent concentration was assumed as the CO2 leaving the cage is

lower, and there are areas in the cage where the concentration of CO2 is much higher than

the prevalent concentration. At 60 ACPH the error is highest 38%, this is again due the

prevalent CO2 is very less and there are areas near the mice and latrines where CO2

concentration is much higher than prevalent concentration.














CHAPTER 5
SUMMARY AND CONCLUSIONS

The purpose of this study was to perform a computational fluid dynamic analysis to

study the effect of rodent activity on ventilated cages. The air velocity profiles and

concentrations of ammonia, carbon dioxide were developed for each cage configuration.

The concentrations were calculated at 20, 40, 60, and 100 ACPH. Stationary mice bodies

were simulated in the cage. Different positions were analyzed for the mice bodies. An

Allentown rodent cage PC 7115RT was used for the study.

Three different mice positions were considered for the study. The concentration

that was most prevalent in the cage was assumed to be the average concentration of CO2

and NH3 in the cage. Two mice were positioned at the outer wall of the cage, away from

the inlet nozzle, referred to with an abbreviation "OW". This case was analyzed for 40,

and 60 ACPH. The results CO2 concentration was 1000 ppm for 60 ACPH and 2100 ppm

for 40 ACPH. The NH3 concentration was 11 ppm for 60 ACPH and 20 ppm for 40

ACPH.

For the second case two mice bodies were positioned near the center of the cage

and close to the inlet nozzle, referred to with an abbreviation "CC". This case was run for

20, 40, 60, and 100 ACPH. The resulting CO2 and NH3 concentrations were 970 ppm and

6 ppm respectively for 100 ACPH, 4300 ppm and 27 ppm respectively for 20 ACPH,

1100 ppm and 10 ppm respectively for 60 ACPH, and 200 ppm and 18 ppm respectively

for 40 ACPH.









Two mice bodies were positioned near the center of the cage along y-axis of the

cage, referred to with an abbreviation "LM". The lengths of the cylinders were doubled to

simulate four mice. This case was analyzed for 60 ACPH. The average CO2 and NH3

concentrations were 1350 ppm and 9 ppm respectively at 60 ACPH.

The following conclusions are based on the results obtained from the simulations

1. The ammonia concentrations for all the models at 100 and 60 ACPH agreed with the

results reported by Pandey (2005) for ammonia.

2. As the ventilation rate was decreased from 100 ACPH to 20 ACPH, the average

concentration of carbon dioxide increased from 970 ppm to 4300 ppm, and the

average ammonia concentrations increased from 6 ppm to 27 ppm in the cage.

3. The concentration of carbon dioxide also increased with an increase in the number of

mice as expected.

4. The size of the cylinder would also have an effect on the CO2 concentrations in the

cage. The bigger the mouse more CO2 it produces.

5. The concentrations of ammonia and carbon dioxide were much less in the vicinity of

the inlet nozzle due to the fresh air introduced by the nozzle.

6. The area of the mouse body that comes in direct contact with the air indicates a lower

concentration of CO2 than the area, which is not in contact with the direct airflow.

7. In the CC case for 100 ACPH, the mice body is placed near the inlet nozzle and

shows a lower concentration of CO2 near the mice body. The air hits the mouse body

with a volumetric flow rate of 1.27e-07 m3/s, and the CO2 concentration in that area is

695 ppm, which increases to 850 ppm moving away from that area. In the LM case

for 60 ACPH, in the area where the flow hits directly, the CO2 concentration is 700









ppm and increases to 1450 ppm moving away from the nozzle. In the OW case, for 60

ACPH the CO2 concentration at the area of direct contact with the air is 838 ppm,

which is higher than the other two cases as the mouse body is further away from the

nozzle. The CO2 concentration on the rest of the mouse body is 1390 ppm and

decreases with the increase in distance from the body.

8. It can be seen that by introducing mice bodies in the cage and by positioning mice at

different locations, affects the overall performance of the cage ventilation system. It

can be seen that the mouse position has an effect on the concentration of CO2 in that

area. An increase was also seen in the concentration of CO2 for the same air change

rates when the numbers of mice were increased in the cage.

9. At 100, and 60 ACPH the air velocity was much higher in the cage than the assumed

acceptable levels. At 40 ACPH the air velocity was higher near the inlet nozzle but

was within the acceptable level away from the nozzle. At 20 ACPH the air velocity

level was within the comfortable level throughout the cage.

10. As the flow rate of air decreases from 100 ACPH the power consumed by the fan also

decreases, and the savings increase. The savings compared to 100 ACPH are

a. 79% for 60 ACPH

b. 93.7% for 40 ACPH

c. 97.3% for 30 ACPH

d. 99.3% for 20 ACPH.

With further CFD studies it may be possible to produce a design that could effectively

ventilate rodent cages in the 20-30 ACPH range, which could result in significant energy

savings over current practices.















CHAPTER 6
RECOMMENDATIONS

1. A model to analyze the urea and water reactions in the cage should be investigated.

This model can simulate ammonia as it is produced due to composition of urea in real

cages.

2. Improve the model for the mouse geometry. The mouse body can be simulated as a

full cylinder for better airflow analysis in the cage. Other locations for mouse and

latrines can also be analyzed.

3. The mouse body can also be simulated to be a source of heat and water vapor in the

cage. This should be added to the model.

4. As it was seen that NH3 concentrations exceeded the acceptable level of 25ppm for 20

ACPH, simulations should be run for other ACPH to optimize around the acceptable

NH3 concentrations.

5. Redesign the inlet nozzle and model the effects with CFD. Ammonia and carbon

dioxide concentrations should be analyzed for two inlet nozzles opposite to each other

and air being injected at a lower ACPH. By using a lower air change rate the savings

also increase. The savings are within the range of 90-99% of power being consumed

at 100 ACPH.

6. Conduct experiments to validate the CFD model. Both live and simulated mice

should be used for the study.















APPENDIX A
MESH CAGE PROFILES

This appendix includes the plot showing the type of mesh used in the cage. Figure

A-i shows the type of mesh used in the CC cage. The top and sides of the cage are

meshed with 0.15 inch structured mesh. The inside volumes are meshed with 0.1 inch

structured mesh. The nozzle area is meshed with an unstructured mesh of 0.05 inch, this

is because the nozzle size is very small.


figure A-I. iviesn usea Ior L. case




































figure A-z. iviesn usea Ior uw case

Figure A-2 shows the mesh used for OW cage. The top and sides are meshed with a

structured mesh on size 0.15 inches. The inside volumes is divided into two parts as it

was not possible to mesh the whole volume with a structured mess. The upper part of the

volume is meshed with 0.1 inch structured mesh. The lower part is meshed with 0.1 inch

unstructured mesh. The part with nozzle is meshed with 0.05 inch unstructured mesh as

the size of nozzle is very small.














APPENDIX B
CONTOURS OF DIFFERENT SPECIES

This appendix includes the plots of contours of carbon dioxide and ammonia for

CC case at 100 ACPH, and LM and OW cases for 60 ACPH
























Figure B-l. Contours of CO2 for CC in X-Y-Z plane (100 ACPH)































-z. contours or CLU2 tor LL in A-Y plane (1uu AL


Figure B-3. Contours of CO2 for CC in Z-X plane (100 ACPH)































Figure B-4. Contours of NH3 for CC in X-Y-Z plane (100 ACPH)


Figure B-5. Contours of NH3 for CC in X-Y plane (100 ACPH)































Figure B-6. Contours of NH3 for CC in Z-X plane (100 ACPH)


Figure B-7. Contours of CO2 for LM in X-Y plane (60 ACPH)































Figure B-8. Contours of CO2 for LM in X-Y-Z plane (60 ACPH)


Figure B-9. Contours of CO2 for LM in Z-X plane (60 ACPH)








4.61-1 1





Fig3& -105 otuso U o Mi ln 6 CH


for LM in X-Y-Z plane (60 AC


































Figure B-12. Contours of NH3 for LM in Z-X plane (60 ACPH)


figure B-13. Contours ot CU2 tor UW in X-Y-Z plane (OU ACLH)





























Figure B-14. Contours of CO2 for OW in X-Y plane (60 ACPH)


Figure B-15. Contours of CO2 for OW in Z-X plane (60 ACPH)






























Figure B-16. Contours of NH3 for OW in X-Y plane (60 ACPH)


Figure B-17. Contours of NH3 for OW in Z-X plane (60 ACPH)






































figure i5-1i. Contours oI 0N113 Ior .


Figure B-19. Contours of CO2 for CC in X-Y plane (20 ACPH)


in A- Y -z. pane kou At-































Figure B-20. Contours of CO2 for CC in X-Y-Z plane (20 ACPH)


Figure B-21. Contours of CO2 for CC in Z-X plane (20 ACPH)
































Figure B-22. Contours of NH3 for CC in X-Y plane (20 ACPH)


Figure B-23. Contours of NH3 for CC in X-Y-Z plane (20 ACPH)

































Figure B-24. Contours of NH3 for CC in Z-X plane (20 ACPH)


Figure B-25. Contours of CO2 for OW in X-Y-Z plane (40 ACPH)

































Figure B-26. Contours of CO2 for OW in Z-X plane (40 ACPH)


Figure B-27. Contours of CO2 for OW in X-Y plane (40 ACPH)

































Figure B-28. Contours of NH3 for OW in X-Y-Z plane (40 ACPH)


Figure B-29. Contours of NH3 for OW in Z-X plane (40 ACPH)

































Figure B-30. Contours of NH3 for OW in X-Y plane (40 ACPH)


Figure B-31. Contours of CO2 for CC in X-Y plane (60 ACPH)
































Figure B-32. Contours of CO2 for CC in Z-X plane (60 ACPH)


Figure B-33. Contours of NH3 for CC in X-Y plane (60 ACPH)
































Figure B-34. Contours of NH3 for CC in X-Y-Z plane (60 ACPH)


Figure B-35. Contours of NH3 for CC in Z-X plane (60 ACPH)































Figure B-36. Contours of CO2 for CC in X-Y plane (40 ACPH)


Figure B-37. Contours of CO2 for CC in X-Y-Z plane (40 ACPH)
































Figure B-38. Contours of CO2 for CC in Z-X plane (40 ACPH)


Figure B-39. Contours of NH3 for CC in X-Y plane (40 ACPH)
































Figure B-40. Contours of NH3 for CC in X-Y-Z plane (40 ACPH)


Figure B-41. Contours of NH3 for CC in Z-X plane (40 ACPH)














APPENDIX C
CALCULATIONS FOR POWER CONSUMPTION AND SAVINGS

As the flow rate of air decreases from 100 to 60 to 40 to 20 ACPH the power

consumed by the ventilation fan also decreases. As typical ventilated rack contains 140

cages, so the change in power consumed for 140 cages can be estimated:

The mass flow rate in cubic feet per minute for 100 ACPH Q = 0.460079 ft3/min

Qi for 140 cages= 64.411 ft3/min

The power at 100 ACPH is P1

The volume flow rate in cubic feet per minute for 60 ACPH Q2 = 0.276047 ft3/min

Q2 for 140 cages= 38.647 ft3/min

The power at 60 ACPH is P2

Savings at 60 ACPH is S,

The volume flow rate in cubic feet per minute for 40 ACPH Q3 = 0.184032 ft3/min

Q3 for 140 cages= 25.764 ft3/min

The power at 40 ACPH is P3

Savings at 40 ACPH is S2

The volume flow rate in cubic feet per minute for 20 ACPH Q4= 0.092016 ft3/min

Q4 for 140 cages= 12.882 ft3/min

The power at 20 ACPH is P4

Savings at 20 ACPH is S3

The volume flow rate in cubic feet per minute for 30 ACPH Q4= 0.138024 ft3/min

Q5 for 140 cages= 19.323 ft3/min









The power at 30 ACPH is P5

Savings at 30 ACPH is S4

As air change rate is reduced from 100 to 60 ACPH based on the fan law the

change in power consumed can be calculated:

P1/P2= (Q1/Q2)3

We get P2= .216P1

Similarly

P3= 0.063P1

P4= 0.007Pi

P5= 0.027P1

The savings that can be obtained per year by reducing the airflow rate from 100

ACPH to 20 ACPH can be calculated:

S3= (Pi-0.007P1)

S3= 0.993Pi

Assuming $0.08 per kilowatt-hour, savings per year can be calculated:

S3= 24*365*.993Pi*0.08

S3= $695.9Pi per year

Similarly

S1= $549.4P1

S2= $656.6P1

S4= $681.9P1














APPENDIX D
CALCULATIONS FOR VERIFICATION OF MASS FLOW RATE

For 100 ACPH for Center of Cage case
The most prevalent CO2 concentration in the cage is in the range of 850-970 ppm.
Assuming the CO2 coming out of the cage to be Co= 970 ppm
The volumetric flow rate is F= 0.000217 cubic meters per second
Concentration of CO2 entering the cage Ci= 350 ppm
Co-Ci= 970-350= 620 ppm
For 620 ppm the mass flow rate = 620*.000217*44*/(1000000*22.4) = 2.632e-07 kg/s.
Actual mass flow rate= 3.58e-07 kg/s.
Using this mass flow rate and back calculating CO2 in the cage:
Co-Ci = 3.58e-07*22.4*1000000/(.000217*44)= 840 ppm
Co= 840+350= 1190 ppm
% Error in amount of CO2 leaving the cage= (1190-970)*100/1190= 18.5%
It can be seen that the amount of CO2 assumed to be leaving the cage is less than amount
of CO2 that should actually leave the cage. This error is due to the fact that the most
prevalent concentration is used for the calculation. There are some areas in the cage near
the latrines where CO2 concentration is more than the assumed concentration.

For 60 ACPH for Center of Cage case
The most prevalent CO2 concentration in the cage is in the range of 980-1130 ppm.
Assuming the most prevalent CO2 concentration in the cage Co= 1130 ppm
The volumetric flow rate is F= 0.00013 cubic meters per second
Concentration of CO2 entering the cage Ci = 350 ppm
Co-Ci= 1130-350= 780 ppm
For 780 ppm the mass flow rate= 780*.00013*44*/(1000000*22.4)= 2.00e-07 kg/s.
Actual mass flow rate= 3.58e-07 kg/s.
Using this mass flow rate and back calculating CO2 in the cage:
Co-Ci= 3.58e-07*22.4*1000000/(.00013*44)= 1400 ppm
Co= 1400+350= 1750 ppm
% Error in amount of CO2 leaving the cage= (1750-1130)*100/1750= 35.5%
It can be seen that the amount of CO2 assumed to be leaving the cage is less than amount
of CO2 that should actually leave the cage. This error is due to the fact that the most
prevalent concentration is used for the calculation. There are some areas in the cage near
the latrines where CO2 concentration is more than the assumed concentration.

For 40 ACPH for Center of Cage case
The most prevalent CO2 concentration in the cage is in the range of 1920-2300 ppm.
Assuming the most prevalent CO2 concentration in the cage Co= 2300 ppm
The volumetric flow rate is F= 0.0000869 cubic meters per second
Concentration of CO2 entering the cage Ci= 350 ppm









Co-Ci= 2300-350= 1950 ppm
For 1950 ppm the mass flow rate= 1950*.0000869*44*/(1000000*22.4)= 3.32e-07 kg/s.
Actual mass flow rate used for the analysis was 3.58e-07 kg/s.
Using this mass flow rate and back calculating CO2 in the cage:
Co-Ci= 3.58e-07*22.4*1000000/(.0000869*44)= 2098 ppm
Co= 2098+350= 2448 ppm
% Error in amount of CO2 leaving the cage= (2448-2300)* 100/2448= 6.0%
The error in this case is 6%, which is very small as compared to errors at 100 and 60
ACPH. The CO2 concentrations agree with the concentration calculated using the mass
flow rate of CO2 used for the simulation.

For 20 ACPH for Center of Cage case
The most prevalent CO2 concentration in the cage is in the range of 3500-4400 ppm.
Assuming the most prevalent CO2 concentration in the cage Co= 4400 ppm
The volumetric flow rate is F= 0.0000434 cubic meters per second
Concentration of CO2 entering the cage Ci= 350 ppm
Co- Ci= 4400-350= 4050 ppm
For 4050 ppm the mass flow rate= 4050*.0000434*44*/(1000000*22.4)= 3.427e-07 kg/s.
Actual mass flow rate= 3.58e-07 kg/s.
Using this mass flow rate and back calculating CO2 in the cage:
Co-Ci= 3.58e-07*22.4*1000000/(.0000434*44)= 4200 ppm
Co= 4200+350= 4550 ppm
% Error in amount of CO2 leaving the cage= (4550-4400)* 100/4550= 3.0%
The error in this case is 3%, which is very small as compared to errors at 100 and 60
ACPH. The CO2 concentrations agree with the concentration calculated using the mass
flow rate of CO2 used for the simulation.
















APPENDIX E
CASES THAT DID NOT WORK


r figure r-1i. single mouse in Y direction


z. iwo mice in tne center or cage in A- direction