Air Flow And Temperature Distribution Analysis In An Air Conditioned Car.
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AIR FLOW AND TEMPERATURE DISTRIBUTION ANALYSIS IN AN AIR CONDITIONED CAR
KHOR MEI YIN B041110056
BMCT
Email: meiyin7770@gmail.com
Draft Final Report Projek Sarjana Muda II
Supervisor: DR. TEE BOON TUAN
Faculty of Mechanical Engineering Universiti Teknikal Malaysia Melaka
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SUPERVISOR DECLARATION
“I hereby declare that I have read this thesis and in my opinion this report is sufficient in terms of scope and quality for the award of the degree of
Bachelor of Mechanical Engineering (Thermal-Fluids)”
Signature : ……… Supervisor : ………
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AIR FLOW AND TEMPERATURE DISTRIBUTION ANALYSIS IN AN AIR CONDITIONED CAR
KHOR MEI YIN
This Technical Report is submitted to
Fakulti Kejuruteraan Mekanikal, Universiti Teknikal Malaysia Melaka In partial fulfilment for
Bachelor of Mechanical Engineering (Thermal-Fluids) with honours
Fakulti Kejuruteraan Mekanikal Universiti Teknikal Malaysia Melaka
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DECLARATION
“I hereby declare that the work in this report is my own except for summaries and quotations which have been duly acknowledged.”
Signature : ………. Author : KHOR MEI YIN Date : ……….
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ACKNOWLEDGEMENT
First of all, I would like to express my gratitude to my supervisor, Dr. Tee Boon Tuan, who has helped me so much by constantly imparting his knowledge and ideas so that I could complete this project successfully. Sincere thanks to Dr. Yusmady Mohamed Arifin for evaluating my final year project. The ideas and suggestions given were valuable for me to complete this project.
Besides that, I would also like to thank Faculty of Mechanical Engineering (FKM), Universiti Teknikal Malaysia Melaka (UTeM) for giving me this opportunity to complete this project and allowing me to utilize all the necessary equipment and tools needed for this study.
Finally, I would like to acknowledge with much appreciations to my family and friends for their continuous support and encouragement throughout the project period.
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ABSTRACT
Temperature and velocity are the environmental factors that affect the human comfort level. The purpose of this study is to determine the temperature and velocity distribution inside the passenger compartment of an air-conditioned vehicle. Computational Fluid Dynamics (CFD) simulation is carried out by using ANSYS FLUENT software. The measurements of air velocity and temperature are taken at different location of the passenger seat. The difference in distribution of air flow and temperature with and without human load inside the passenger compartment are being investigated. The results obtained from physical measurement and CFD simulation is analyzed and compared. The actual average temperature increases with number of occupants while the simulation temperature remains constant, where the largest percentage of error is 19.1 %. The simulation velocity shows highest reading at head level and decreases as flows to chest level and knee level of passengers seats. The trend of actual velocity is similar to simulation velocity, except at driver seat where the highest value is at chest level. Based on the result, recommendations and suggestions are made to improve the thermal comfort level inside the passenger compartment.
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ABSTRAK
Kadar keselesaan manusia boleh berubah disebabkan oleh faktor-faktor alam sekitar seperti suhu dan aliran udara. Kajian ini dijalankan untuk menentukan taburan suhu dan halaju dalam kenderaan berhawa dingin melalui kaedah eksperimen dan simulasi. Simulasi Pengkomputeran Dinamik Bendalir (CFD) akan dijalankan dengan menggunakan perisian ANSYS FLUENT. Pengukuran halaju dan suhu udara akan diambil pada lokasi tertentu tempat duduk kereta. Perbezaan dalam taburan suhu dan aliran udara di dalam kereta terhadap perubahan bilangan penumpang turut dikaji. Keputusan yang diperolehi daripada pengukuran fizikal dan simulasi CFD dianalisis dan dibandingkan. Purata suhu eksperimen meningkat dengan penambahan penumpang di dalam kenderaan manakala suhu simulasi adalah malar, di mana peratusan kesilapan terbesar adalah 19.1 %. Halaju simulasi menunjukkan bacaan tertinggi di paras kepala dan semakin turun apabila mengalir ke paras dada dan paras lutut penumpang. Trend halaju eksperimen adalah sama dengan halaju simulasi, kecuali di tempat duduk pemandu di mana nilai tertinggi adalah pada tahap dada. Berdasarkan keputusan yang diperolehi, penambahbaikan dicadangkan untuk meningkatkan tahap keselesaan penumpang dalam kenderaan berhawa dingin.
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TABLE OF CONTENTS
CHAPTER TITLE PAGE
SUPERVISOR DECLARATION ii
DECLARATION iv
ACKNOWLEDGEMENT vi
ABSTRACT vii
ABSTRAK viii
TABLE OF CONTENTS ix
LIST OF TABLES xiii
LIST OF FIGURES xv
LIST OF SYMBOLS xviii
LIST OF APPENDICES xix
LIST OF ABBREVIATIONS xx
CHAPTER 1 INTRODUCTION
1.1 OVERVIEW 1
1.2 PROBLEM STATEMENT 1
1.3 OBJECTIVES 2
1.4 SCOPES 2
1.5 EXPECTED OUTCOMES 2
CHAPTER 2 THEORY
2.1 OVERVIEW 3
2.2 ENVIRONMENTAL PARAMETERS OF
VEHICLE 3
2.3 THERMAL COMFORT 4
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CHAPTER TITLE PAGE
2.3.2 Personal Factors 5 2.3.3 Predicted Mean Vote (PMV) 6 2.3.4 Predicted Percentage Dissatisfied (PPD) 6 2.4 HEATING, VENTILATION AND AIR
CONDITIONING (HVAC) SYSTEM IN
VEHICLES 7
2.4.1 Air Flow Operation 7 2.4.2 Air Conditioning Operation 8 2.5 COMPUTATIONAL FUID DYNAMICS (CFD) 9
2.5.1 Geometry Modelling 10 2.5.2 Mesh Generation 10
2.5.3 Solver Method 11
2.5.4 Display Of Results 12 2.6 TURBULENCE MODELLING 13 CHAPTER 3 LITERATURE REVIEW
3.1 OVERVIEW 15
3.2 CFD ANALYSIS OF AIR FLOW AND
TEMPERATURE DISTRIBUTION IN AN AIR CONDITIONED CAR BY
RAMESHKUMAR et al. (2013) 15
3.2.1 Methodology 16
3.2.2 Results And Discussion 17
3.2.3 Conclusion 19
3.3 NUMERICAL ANALYSIS OF AIR FLOW AND TEMPERATURE FIELD IN A PASSENGER CAR COMPARTMENT BY
HASLINDA et al. (2011) 20
3.3.1 Methodology 20
3.3.2 Results And Discussion 21
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CHAPTER TITLE PAGE
3.4 STUDIES OF THE THERMAL COMFORT
INSIDE OF THE PASSENGER COMPARTMENT USING THE NUMERICAL SIMULATION BY
IVANESCU et al. (2010) 23
3.4.1 Methodology 23
3.4.2 Results And Discussion 25
3.4.3 Conclusion 27
3.5 NUMERICAL SIMULATION OF AIR CONDITIONING VEHICLE USING
COMPUTATIONAL FLUID DYNAMICS BY
WANG AND XIANG (2009) 28
3.5.1 Methodology 28
3.5.2 Results And Discussion 29
3.5.3 Conclusion 31
3.6 COMPUTATIONAL ANALYSIS OF THERMAL DISTRIBUTION WITHIN PASSENGER CAR
CABIN BY ZEYA AND JOMON (2013) 32
3.6.1 Methodology 32
3.6.2 Results And Discussion 33
3.6.3 Conclusion 34
3.7 COMPARISON OF PREVIOUS STUDIES 34 CHAPTER 4 METHODOLOGY
4.1 OVERVIEW 35
4.2 EXPERIMENTAL METHOD 35
4.2.1 Experimental Procedures 38
4.3 NUMERICAL METHOD 39
4.3.1 Geometry Process 40 4.3.2 Meshing Process 41 4.3.3 Setup Process 42 4.3.4 Solution Process 44 4.3.5 Post Processing 45
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CHAPTER TITLE PAGE
4.4 THERMAL COMFORT ANALYSIS METHOD 45 4.4.1 Thermal Comfort Analysis Procedures 46 CHAPTER 5 RESULTS AND DISCUSSION
5.1 OVERVIEW 47
5.2 EXPERIMENTAL RESULTS 47 5.3 SIMULATION RESULTS 51 5.4 COMPARISON OF EXPERIMENTAL
RESULTS AND SIMULATION RESULTS 50 5.4.1 Comparison of Temperature Distribution
Inside Passenger Compartment With
Various Human Loads 50 5.4.2 Percentage Of Error 52 5.5 GRAPHIC SIMULATIONS 53 5.5.1 Simulations of Temperature Distribution 54 5.5.2 Simulations of Air Velocity Distribution 56 5.6 THERMAL COMFORT ANALYSIS 58
CHAPTER 6 CONCLUSION AND RECOMMENDATIONS
6.1 CONCLUSION 61
6.2 RECOMMENDATIONS 62
REFERENCES 63
APPENDIX A: Flow Chart 67
APPENDIX B: Gantt Chart 68
APPENDIX C: Actual Flow of Temperature 69
APPENDIX D: Actual Flow of Air Velocity 69
APPENDIX E: Simulation Flow of Temperature 70
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CHAPTER TITLE PAGE
APPENDIX G: Percentage of Error for Temperature
Distribution 71
APPENDIX H: Percentage of Error for Air Velocity
Distribution 71
APPENDIX I: Thermal Comfort Analysis Evaluation
Report at Driver Seat 72
APPENDIX J: Thermal Comfort Analysis Evaluation
Report atPassenger Seat at Front Region 73
APPENDIX K: Thermal Comfort Analysis Evaluation
Report atRight Side of Rear Passenger
Seat 74
APPENDIX L: Thermal Comfort Analysis Evaluation
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LIST OF TABLES
NO. TITLE PAGE
2.1 Predicted Mean Vote Scale (ISO 7730) 5 2.2 Difference between Experimental Methods and CFD simulation
(Dmitri, 2007) 9
3.1 Computed Values of Air Velocity for Various Human Loads
(Rameshkumar et.al, 2013) 17
3.2 Computed Values of Temperature for Various Human Loads
(Rameshkumar et.al, 2013) 17
3.3 General Boundary Conditions (Ivanescu et.al, 2010) 25 3.4 External Boundary Conditions (Ivanescu et.al, 2010) 25 3.5 Air Conditioning Unit Characteristics (Ivanescu et.al, 2010) 25 3.6 Experimental Results and Simulation Results for Air Velocity
(Ivanescu et.al, 2010) 25
3.7 Experimental Results and Simulation Results for Temperature
(Ivanescu et.al, 2010) 26
3.8 Thermal Comfort Indices with Knob of Air Flow Range Inlet on Position 2 (Ivanescu et.al, 2010) 27 3.9 Comparison of Previous Studies 34 4.1 Location of Measuring Point 38
4.2 Turbulence Model Setup 42
4.3 Material Properties 43
4.4 Boundary Conditions Setup 43
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LIST OF FIGURES
NO. TITLE PAGE
2.1 Air Flow Sensation Curve (Musat and Helerea, 2009) 3 2.2 Graph of PPD against PMV (ISO 7730) 6 2.3 Mechanical electronic switches (Zhou, 2013) 7 2.4 Automatic Control of Automobile Air Conditioning
(Janotkova and Pavelek, n.d.) 8 2.5 Overview of ANSYS Workbench (Delfel, 2013) 10
2.6 Mesh Generation Process 11
3.1 Location of Measuring Points inside the Cabin
(Rameshkumar et.al, 2013) 16
3.2 Air Velocity Distribution for Human Load of 4
(Rameshkumar et.al, 2013) 18
3.3 Temperature Distribution for Human Load of 4
(Rameshkumar et.al, 2013) 18
3.4 Comparison of Velocity Distribution for Various Human Loads
(Rameshkumar et.al, 2013) 19
3.5 Comparison of Temperature Distribution for Various Human
Loads (Rameshkumar et.al, 2013) 19 3.6 Temperature Distribution for No Glazing Windscreen
(Mohamed Kamar et al., 2011) 21
3.7 Temperature Distribution for CIL Glazing Windscreen
(Mohamed Kamar et al., 2011) 21
3.8 Temperature Distribution for GIL Glazing Windscreen
(Mohamed Kamar et al., 2011) 21
3.9 Air Velocity Distribution (Mohamed Kamar et al., 2011) 22 3.10 The Measuring Points for Velocity (Ivanescu et.al, 2010) 24
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NO. TITLE PAGE
3.11 The Measuring Points for Temperature (Ivanescu et.al, 2010) 24 3.12 Temperature and Velocity Distribution for Knob of Air Flow Range
Setting in Position 2 (Ivanescu et.al, 2010) 26 3.13 Graph of Thermal Comfort Indices against Time with Knob on
Air Flow Inlet in Position 2 (Ivanescu et.al, 2010) 27 3.14 Velocity Distribution at Section x=6.86 m
(Wang and Xiang, 2009) 29
3.15 Velocity Distribution at Section x=9.14 m
(Wang and Xiang, 2009) 29
3.16 Temperature Distribution at Section x=6.86 m
(Wang and Xiang, 2009) 30
3.17 Temperature Distribution at Section x=9.14 m
(Wang and Xiang, 2009) 30
3.18 Comparison of Experimental and Simulation Temperature on
section x=6.86 m (Wang and Xiang, 2009) 31 3.19 Temperature Distribution (Ahmad Quadri and Jose, 2013) 33 3.20 Temperature Distribution with Air Inlets and Outlets
(Ahmad Quadri and Jose, 2013) 33
4.1 Toyota Corolla E110 36
4.2 Interior Arrangement 36
4.3 Dashboard 36
4.4 HVAC System Switches 37
4.5 Anemometer 37
4.6 Location of Measuring Points 37 4.7 Physical Measurement at Head Level of Passenger Seat 39
4.8 CFD Simulation Outline 40
4.9 Dimensions of Toyota Corolla E110 41
4.10 3D Car Cabin Model 41
4.11 Tetrahedrons Method Assembly Meshing 41 4.12 Thermal Microclimate HD32.1 46 4.13 Physical measurement at driver seat 47 5.1 Graph of Average Temperature against various Human Loads 51
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NO. TITLE PAGE
5.2 Graph of Average Air Velocity against various Human Loads 51 5.3 Graph of Percentage of Error for Temperature Distribution 52 5.4 Graph of Percentage of Error for Air Velocity Distribution 53 5.5 Temperature Contour with no Human Load inside Passenger
Compartment 54
5.6 Temperature Contour with 1 Human Load inside Passenger
Compartment 55
5.7 Temperature Contour with 2 Human Loads inside Passenger
Compartment 55
5.8 Temperature Contour with 3 Human Loads inside Passenger
Compartment 55
5.9 Temperature Contour with 4 Human Loads inside Passenger
Compartment 56
5.10 Velocity Vector with No Human Load inside Passenger
Compartment 56
5.11 Velocity Vector with 1 Human Load inside Passenger
Compartment 57
5.12 Velocity Vector with 2 Human Loads inside Passenger
Compartment 57
5.13 Velocity Vector with 3 Human Loads inside Passenger
Compartment 57
5.14 Velocity Vector with 4 Human Loads inside Passenger
Compartment 58
5.15 Graph of PPD against PMV for Driver Seat 59 5.16 Graph of PPD against PMV for Passenger Seat at Front Region 59 5.17 Graph of PPD against PMV for Passenger Seat at Right Side of
Rear Region 59
5.18 Graph of PPD against PMV for Passenger Seat at Left Side of
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LIST OF SYMBOLS
° = degree
°C = degree Celcius % = percentage atm = atmosphere
clo = clothing insulation
σε = turbulent Prandtl numbers for ε σ turbulent Prandtl numbers for k � = turbulent dissipation
G = turbulence kinetic energy due to buoyancy
G = turbulence kinetic energy due to the mean velocity gradients k = turbulent kinetic energy
K = Kelvin kg = kilogram m = meter Pa = Pascal s = second
T = temperature, °C V = air velocity, m/s W = watt
YM = fluctuating dilatation in compressible turbulence to the overall dissipation rate
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LIST OF APPENDICES
NO. TITLE PAGE
A Flow Chart 67
B Gantt Chart 68
C Actual Flow of Temperature 69
D Actual Flow of Air Velocity 69 E Simulation Flow of Temperature 70 F Simulation Flow of Air Velocity 70 G Percentage of Error for Temperature Distribution 71 H Percentage of Error for Air Velocity Distribution 71 I Thermal Comfort Analysis Evaluation Report at Driver
Seat 72
J Thermal Comfort Analysis Evaluation Report atPassenger
Seat at Front Region 73
K Thermal Comfort Analysis Evaluation Report atRight Side
of Rear Passenger Seat 74
L Thermal Comfort Analysis Evaluation Report atLeft Side
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LIST OF ABBREVIATIONS
3D = three dimensional
ASHRAE = American Society of Heating, Refrigeration and Air- Conditioning Engineers
ASM = algebraic stress model CAD = Computer Aided Design
CFD = Computational Fluid Dynamics CIL = clear insulated laminate tint DTS = Dynamic Thermal Sensation eqn = equation
GIL = green insulated laminate tint
HVAC = Heating, Ventilation and Air Conditioning IAQ = Indoor Air Quality
PMV = Predicted Mean Vote
PPD = Predicted Percentage of Dissatisfied RANS = Reynolds Averaged Navier-Stokes RNG = Re-Normalisation Group
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CHAPTER 1
INTRODUCTION
1.1 OVERVIEW
Thermal comfort of vehicle passengers has been emphasized due to the increasing in time of people spends inside the vehicles. The passenger compartment is the place which shows significant effect on thermal comfort. It is exposed to internal disturbances such as the speed of vehicle, the number of passengers inside the car cabin and the temperature of engine, and also external disturbances such as air temperature, velocity of wind and solar radiation. (Mezrhab & Bouzidi, 2006) A great temperature control inside the vehicles will provide driver a good physical state of driving and a great visibility by avoiding fogging inside the vehicles. (Alahmer et al., 2010) In order to improve the thermal comfort inside a vehicle, an acceptable range of distribution of air velocity and temperature are to be considered. This project will focus on analyzing the distribution of temperature and velocity inside the vehicle compartment.
1.2 PROBLEM STATEMENT
Air flow and temperature distribution in an air conditioned car will change according to the various human loads. Based on the proposed simulation, this project is aimed to investigate the velocity and temperature distribution inside an air conditioned car which relate to human comfort level. Measuring points of air velocity and temperature can be taken at different location of the passenger seat by physical measurements and Computational Fluid Dynamics (CFD) simulation. CFD
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2 simulation can predict the airflow numerically without creating a prototype, thus save cost, time and manpower. Hence, an optimum environment should be able to simulate by using CFD software in analyzing the temperature and air flow inside passenger compartment, in order to improve the thermal comfort level. Thermal comfort of passengers inside vehicle can be evaluated by Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD).
1.3 OBJECTIVES
i. To investigate the temperature and air flow distribution with and without human loads inside the passenger compartment.
ii. To perform thermal comfort analysis inside vehicle.
1.4 SCOPES
i. Evaluate the air flow and temperature distribution by experimental method (measurement) and CFD simulation.
ii. Only indoor environmental condition of the car is taken into consideration. iii. Boundary parameters are determined for valid CFD modelling to be applied
in the car.
1.5 EXPECTED OUTCOMES
i. Physical measurement of distribution of temperature and air velocity in an air conditioned vehicle.
ii. CFD simulation of distribution of temperature and air velocity in an air conditioned vehicle.
iii. Compare results between physical measurement and numerical simulation. iv. Thermal comfort analysis inside the air conditioned vehicle.
v. Recommendations to improve the thermal comfort level inside the passenger compartments.
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CHAPTER 2
THEORY
2.1 OVERVIEW
All the principles and definitions related to the case study should be included in this chapter. The theories such as thermal comfort, Heating, Ventilation and Air Conditioning (HVAC) system in vehicles, CFD and turbulence modelling are studied and compiled in this chapter for better understanding.
2.2 ENVIRONMENTAL PARAMETERS OF VEHICLE
A vehicle is exposed to both internal disturbances such as car speed, engine temperature and passengers inside car cabin, and also external disturbances such as temperature, sun and wind. This project will focus on environmental parameters that are temperature and air velocity distribution inside the air conditioning car. Figure 2.1 shows the relationship between air velocity and temperature. The air velocity will increase with temperature.
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4 When the air conditioning system is switched on, the temperature will drop slightly as the cooled air is suddenly directed into the passenger compartment and will rise steadily as time passed. Due to the small space inside passenger compartment, the temperature will be affected by the heat exchange in the space (Zhou, 2013). When there are occupants inside the vehicle cabin, the temperature will increase due to the sensible heat transferred from human body. (Mohamed Kamar et. al., 2013)
The air flow inside the vehicle is directed to a small section due to the limited space of car. The air flows from air conditioning vents will increase the air velocity. It will be blocked by the front seats and rear seats and formed recirculating flow patterns. This flow pattern is well mixed with the cold air from air conditioning inlets and the surrounding heated air inside vehicle cabin, and then directed back to the air conditioning outlets (Jalal and Haider, 2007). Hence, the air velocity will decrease as human loads will occupy certain spaces inside the passenger compartment.
2.3 THERMAL COMFORT
American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) Standard 55 defines thermal comfort as “that condition of mind which expresses satisfaction with the thermal environment”. However, different people have different sensations towards the thermal environment. Hence, six factors are used as an indicator of thermal comfort:
i. Air temperature ii. Air velocity
iii. Radiant temperature iv. Humidity level
v. Clothing insulation vi. Activity level
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LIST OF APPENDICES
NO. TITLE PAGE
A Flow Chart 67
B Gantt Chart 68
C Actual Flow of Temperature 69 D Actual Flow of Air Velocity 69 E Simulation Flow of Temperature 70 F Simulation Flow of Air Velocity 70 G Percentage of Error for Temperature Distribution 71 H Percentage of Error for Air Velocity Distribution 71 I Thermal Comfort Analysis Evaluation Report at Driver
Seat 72
J Thermal Comfort Analysis Evaluation Report atPassenger Seat at Front Region 73 K Thermal Comfort Analysis Evaluation Report atRight Side
of Rear Passenger Seat 74 L Thermal Comfort Analysis Evaluation Report atLeft Side
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3D = three dimensional
ASHRAE = American Society of Heating, Refrigeration and Air- Conditioning Engineers
ASM = algebraic stress model CAD = Computer Aided Design
CFD = Computational Fluid Dynamics CIL = clear insulated laminate tint DTS = Dynamic Thermal Sensation eqn = equation
GIL = green insulated laminate tint
HVAC = Heating, Ventilation and Air Conditioning IAQ = Indoor Air Quality
PMV = Predicted Mean Vote
PPD = Predicted Percentage of Dissatisfied RANS = Reynolds Averaged Navier-Stokes RNG = Re-Normalisation Group
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CHAPTER 1
INTRODUCTION
1.1 OVERVIEW
Thermal comfort of vehicle passengers has been emphasized due to the increasing in time of people spends inside the vehicles. The passenger compartment is the place which shows significant effect on thermal comfort. It is exposed to internal disturbances such as the speed of vehicle, the number of passengers inside the car cabin and the temperature of engine, and also external disturbances such as air temperature, velocity of wind and solar radiation. (Mezrhab & Bouzidi, 2006) A great temperature control inside the vehicles will provide driver a good physical state of driving and a great visibility by avoiding fogging inside the vehicles. (Alahmer et al., 2010) In order to improve the thermal comfort inside a vehicle, an acceptable range of distribution of air velocity and temperature are to be considered. This project will focus on analyzing the distribution of temperature and velocity inside the vehicle compartment.
1.2 PROBLEM STATEMENT
Air flow and temperature distribution in an air conditioned car will change according to the various human loads. Based on the proposed simulation, this project is aimed to investigate the velocity and temperature distribution inside an air conditioned car which relate to human comfort level. Measuring points of air velocity and temperature can be taken at different location of the passenger seat by physical measurements and Computational Fluid Dynamics (CFD) simulation. CFD
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1.3 OBJECTIVES
i. To investigate the temperature and air flow distribution with and without human loads inside the passenger compartment.
ii. To perform thermal comfort analysis inside vehicle.
1.4 SCOPES
i. Evaluate the air flow and temperature distribution by experimental method (measurement) and CFD simulation.
ii. Only indoor environmental condition of the car is taken into consideration. iii. Boundary parameters are determined for valid CFD modelling to be applied
in the car.
1.5 EXPECTED OUTCOMES
i. Physical measurement of distribution of temperature and air velocity in an air conditioned vehicle.
ii. CFD simulation of distribution of temperature and air velocity in an air conditioned vehicle.
iii. Compare results between physical measurement and numerical simulation. iv. Thermal comfort analysis inside the air conditioned vehicle.
v. Recommendations to improve the thermal comfort level inside the passenger compartments.
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CHAPTER 2
THEORY
2.1 OVERVIEW
All the principles and definitions related to the case study should be included in this chapter. The theories such as thermal comfort, Heating, Ventilation and Air Conditioning (HVAC) system in vehicles, CFD and turbulence modelling are studied and compiled in this chapter for better understanding.
2.2 ENVIRONMENTAL PARAMETERS OF VEHICLE
A vehicle is exposed to both internal disturbances such as car speed, engine temperature and passengers inside car cabin, and also external disturbances such as temperature, sun and wind. This project will focus on environmental parameters that are temperature and air velocity distribution inside the air conditioning car. Figure 2.1 shows the relationship between air velocity and temperature. The air velocity will increase with temperature.
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Kamar et. al., 2013)
The air flow inside the vehicle is directed to a small section due to the limited space of car. The air flows from air conditioning vents will increase the air velocity. It will be blocked by the front seats and rear seats and formed recirculating flow patterns. This flow pattern is well mixed with the cold air from air conditioning inlets and the surrounding heated air inside vehicle cabin, and then directed back to the air conditioning outlets (Jalal and Haider, 2007). Hence, the air velocity will decrease as human loads will occupy certain spaces inside the passenger compartment.
2.3 THERMAL COMFORT
American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) Standard 55 defines thermal comfort as “that condition of mind which expresses satisfaction with the thermal environment”. However, different people have different sensations towards the thermal environment. Hence, six factors are used as an indicator of thermal comfort:
i. Air temperature ii. Air velocity
iii. Radiant temperature iv. Humidity level
v. Clothing insulation vi. Activity level