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FLUID AND HEAT FLOW PERFORMANCE
IN HEAT EXCHANGER
NURLIYANA BINTI MOHD NADZRI
THIS DISSERTATION IS SUBMITTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENT FOR THE AWARD OF THE DEGREE OF
BACHELOR OF MECHANICAL ENGINEERING
(THERMAL-FLUIDS)
Faculty of Mechanical Engineering
Universiti Teknikal Malaysia Melaka
APRIL 2010
‘Saya/Kami* akui bahawa telah membaca
karya ini dan pada pandangan saya/kami* karya ini
adalah memadai dari segi skop dan kualiti untuk tujuan penganugerahan
Ijazah Sarjana Muda Kejuruteraan Mekanikal (Termal Bendalir)’
Tandatangan : …………………………
Nama Penyelia 1 : ........................................
Tarikh : .........................................
Tandatangan : .........................................
Nama Penyelia 2 : .........................................
Tarikh : .........................................
*Potong mana yang tidak berkenaan
“I declare that this report is done by my own exclude citation with the mentioned
references for each.”
Signature : ……………………
Author : …………………….
Date : ……………………
i
ACKNOWLEDGEMENT
I would like to express my special thanks to my supervisor, Dr. Mohd Yusoff
Bin Sulaiman for his advices, continual guidance and commitment in helping me
doing the research. He always gives me the idea and knowledge in helping me to
carry out the research in a better way. His knowledge is very useful for me to do the
research appropriately.
Finally yet importantly, my research would not be carried out smoothly
without the continuing supports and encouragements given by my parents, course-
mates, and friends. I would like to express my sincere gratitude to them especially
for their helping during the time in need.
ii
ABSTRACT
Heat exchanger is a device used to transfer from one fluid to another without
direct contact of the fluid. They are widely used in space heating, refrigeration, air
conditioning, power plants, chemical plants, petrochemical, chemical plants,
petroleum refineries and natural gas processing. The methodology of this project
consists of several approaches and procedures. The procedures that had been taken
are referred from literature review through many journals and articles about the
automotive heat exchangers. The experiment to obtain the flow and heat transfer
performance of a heat exchanger is done by using the wind tunnel to determine the
heat loss and also using CFD technique in order to define the flow inside the
automobile radiator. Using this method, the fluid flow in the radiator can be
measured only by using a complete sketch. The sketch is inserted into the program
and then the fluid flow can be measured according to the fixed color code after
simulation using FLUENT software. The simulation had been successfully created in
two type which is 2d and 3D. According to the calculation of heat exchanger
performance, APM radiator could dissipate heat more than Wira radiator.
Meanwhile, for the compactness heat exchanger, APM radiator has an addition of
9.492% of compactness performance than Wira radiator.
iii
ABSTRAK
Alat pemindahan haba digunakan untuk memindahkan haba daripada bendalir
kepada bendalir yang lain tanpa persentuhan terus dengan bendalir tersebut. Ia
diunakan secara meluas dalam ruang pemanasan, penyejukan, penghawa dingin,
industri petroleum dan pemprosesan gas asli. Metodologi bagi projek ini
mengandungi beberapa kaedah dan prosedur. Di antara prosedur yang telah
dilakukan adalah dengan membuat kajian ilmiah melalui pelbagai jenis jurnal dan
artikel tentang alat automotif pemindah haba. Selain itu, eksperimen untuk mengkaji
aliran air dan udara serta kecekapan alat pemindah haba telah dilakukan dengan
menggunakan “Wind Tunnel”. Ia bertujuan untuk menguji kehilangan haba pada alat
pemindah haba. Selain itu juga, CFD turut digunakan untuk mengkaji aliran air di
dalam automotif radiator. Melalui kaedah ini, halaju aliran air di dalam radiator dapat
dilihat dan diperolehi. Draft rekaan yang telah dilakar akan dipindah masuk ke dalam
CFD dan proses simulasi akan dilakukan menggunakan perisian FLUENT. Proses
simulasi telah Berjaya dilakukan dalam dua jenis bentuk iaitu 2D dan 3D.
Berdasarkan pengiraan kecekepan pengubah haba, didapati bahawa radiator APM
dapat mengurangkan haba lebih baik daripada radiator Wira. Sementara itu pula, bagi
kepadatan pengubah haba menunjukkan bahawa radiator APM mempunyai kelebihan
kepadatan sebanyak 9.492% berbanding radiator Wira.
iv
TABLE OF CONTENTS
CHAPTER TITLE PAGE NUMBER
ACKNOWLEDGEMENT i
ABSTRACT ii
ABSTRAK iii
CONTENT iv
LIST OF TABLES vii
LIST OF FIGURES viii
LIST OF SYMBOLS xi
LIST OF APPENDICES xiii
CHAPTER I INTRODUCTION 1
1.1 Background of the study 1
1.2 problem Statement 2
1.3 Research Objective 3
1.4 Scope of the Study 3
CHAPTER II LITERATURE REVIEW 4
2.1 Introduction 4
2.2 Heat Exchanger 11
2.3 Mathematical Formulation 17
and Numerical Model
2.3.1 Governing Equations 17
2.3.2 Turbulence Model and 18
Wall Function
v
2.3.3 Relations for Surface and 19
Core Geometry
2.3.4 Air Flow 23
2.3.5 Fins 24
2.3.6 Tubes 26
2.4 Wind Tunnel 27
CHAPTER III METHODOLOGY 30
3.1 Introduction 30
3.2 Automotive heat exchanger experiments 30
3.2.1 Wind Tunnel Experiment 31
3.3 Fluid flow and heat transfer simulation 34
Using CFD
3.4 Calculation of the automotive heat 35
exchanger performance.
3.4.1 Calculation of heat transfer 35
3.4.2 Calculation of compact heat exchanger 35
3.4.3 Calculation for mass flow rate 36
3.4.2.1 Experimental method 36
3.4.2.2 Theoretical Method 36
3.5 Flow Chart 37
CHAPTER IV RESULT 39
4.1 Wind Tunnel Test
4.2 Calculation for existing radiator and new 42
design of radiator
4.3 Computational Fluid Dynamic (CFD) 43
4.3.1 2D Flow - Conventional Radiator 43
4.3.2 2D Flow - Circular Radiator 47
vi
4.3.3 3D Flow - Circular Radiator 49
CHAPTER VI CONCLUSION & RECOMMENDATION 52
REFERENCE AND 53
BIBLIOGRAPHY
APPENDIX A 55
APPENDIX B 57
APPENDIX C 58
APPENDIX D 59
APPENDIX E 60
APPENDIX F 62
vii
LIST OF TABLES
NO. TITLE PAGE NUMBER
3.1 Specification of APM radiator 59
3.2 Specification of Wira radiator 59
4.1 Data for Proton Wira radiator at 60°C 60
4.2 Data for Proton Wira radiator at 65°C 60
4.3 Data for APM radiator at 60°C 60
4.4 Data for APM radiator at 65°C 61
viii
LIST OF FIGURES
NO. TITLE PAGE NUMBER
2.1 Radiator 5
2.2 Radiator Fan 6
2.3 Pressure Cap 8
2.4 Water Pump 9
2.5 Thermostat 10
2.6 Radiator 11
2.7 Effect of inlet coolant temperature and volume 12
flow rate on heat dissipation
2.8 Effect of inlet coolant temperature and air velocities 13
on heat dissipation
2.9 Under hood air flow profiles in a typical passenger car 15
2.10 Discretisation strategy for flat tube/corrugated fin 23
automotive radiators; macro volume concept.
2.11 Experimental apparatus configuration efficiency 24
measurement.
ix
2.12 Schematic diagram of one-tube plate fin heat exchangers 25
with the fin spacing.
2.13 Physical geometry of a two-dimensional annular circular 25
fin with measurement locations and sub-fin regions.
2.14 Nodes at the interface of two-neighboring sub-fin areas. 26
2.15 Schematic diagram of Wind Tunnel 28
2.16 The arrangements of electrodes 29
3.1 Schematic diagram of Wind Tunnel 32
3.2 Mounted radiator 32
3.3 Wind tunnel 33
3.4 Detail drawing of existing radiator 34
3.5 Detail drawing of circular radiator 35
4.1 Graph point of speed vs. velocity at temperature 39
60°C and 65°C for Wira radiator
4.2 Graph point of speed vs. volume flow rate at 40
temperature 60°C and 65°C for Wira radiator
4.3 Graph point of speed vs. velocity at temperature 41
60°C and 65°C for APM radiator
4.4 Graph point of speed vs. volume flow rate at 41
temperature 60°C and 65°C for APM radiator
x
4.5 Existing radiator 43
4.6 Meshing cells 44
4.7 The square angle of meshing cells 44
4.8 Contours of velocity magnitude (m/s) 45
4.9 Velocity vectors by static temperature 46
4.10 Iterations chart 46
4.11 Circular radiator 47
4.12 Contours of velocity magnitude (m/s) 48
4.13 Contours of static temperature 48
4.14 Contours of velocity magnitude (m/s) 49
4.15 Side view of the 3D circular 50
4.16 Iteration chart 50
xi
LIST OF SYMBOLS
αa = Ratio of total heat transfer area of one side of the
exchanger to its volume, m2/m
3
A = Total heat transfer area, m2
A0 = Free flow area of one side of exchanger, m2
Afr = Frontal area of one side of the exchanger, m2
B = Air flow length in the exchanger, m
Ca = Stream heat capacity rate for air
pc = Specific heat loss of coolant
Cw = Stream heat capacity rate for water
C = Heat capacity rate ratio
C = Specific heat at constant dynamic viscosity
,p aC = Specific heat of air
= Heat exchanger effectiveness
f = Friction factor
g = Gravity
aG = Core mass velocity
aj = Multiplied factor of heat exchanger
L = Length of each tube
pL = Louver pitch
cm = Coolant mass flow rate
,u wN = Nusselt’s number
Q = Heat Loss
tR = Ratio of the convection heat transfer characteristic to the convection mass
transfer characteristic for the simultaneous convection heat and mass
transfer for tube.
xii
Re = Reynold’s number
hr = Fin radius
Ti-T0 = Temperature Drop
Ua = Air side area
V = Total volume of the exchanger, m3
aW = Specific thermal resistance of air
= Water density
= Viscosity
t = Viscosity in tube
xiii
LIST OF APPENDICES
NO. TITLE PAGE NUMBER
A Gantt Chart 55-56
B Conventional Radiator 57
C Circular Radiator 58
D Table of Radiator Specifications 59
E Table of Results 60-61
F Calculation of Heat Exchanger Performance 62-65
1
CHAPTER I
INTRODUCTION
1.1 Background of the Study
A heat exchanger is a device built for efficient heat transfer from one medium to
another, whether the media are separated by a solid wall so that they never mix, or
the media are in direct contact. They are widely used in space heating, refrigeration,
air conditioning, power plants, chemical plants, petrochemical plants, petroleum
refineries, and natural gas processing. One common example of a heat exchanger is
the radiator in a car, in which the heat source, being a hot engine-cooling fluid,
water, transfers heat to air flowing through the radiator.
Heat exchanger maybe classified according to their flow arrangement. In parallel-
flow heat exchanger, the two fluids enter the exchanger at the same end, and travel in
parallel to one another to the other side. In counter-flow heat exchangers, the fluids
enter the exchanger from opposite ends. The counter current design is most efficient,
so that it can transfer the most heat. In a cross-flow heat exchanger, the fluids travel
roughly perpendicular to one another through the exchanger.
A cooling system is used to remove this excess heat. Most automotive cooling
systems consist of the following components: radiator, water pump, electric cooling
fan, radiator pressure cap, and thermostat. Of these components, the radiator is the
most prominent part of the system because it transfers heat. As coolant travels
through the engine's cylinder block, it accumulates heat. Once the coolant
2
temperature increases above a certain threshold value, the vehicle's thermostat
triggers a valve which forces the coolant to flow through the radiator. As the coolant
flows through the tubes of the radiator, heat is transferred through the fins and tube
walls to the air by conduction and convection.
Depending upon the size of the engine and the cooling requirements, one, two,
three or four cores can be used. There is also an inlet and outlet tank. These tanks
hold the coolant before it goes into the radiator or into the block. The inlet tank also
has a hose connection to allow coolant to flow from the engine into the radiator. The
outlet tank has a hose connection to allow coolant pass back to the engine. In
addition, there is a filler neck attached to one of the tanks. The radiator cap is placed
here.
1.2 Problem Statement
In an automobile, fuel and air produce power within the engine through
combustion. Only a portion of the total generated power actually supplies the
automobile with power, the rest is wasted in the form of exhaust and heat. If this
excess heat is not removed, the engine temperature becomes too high which results
in overheating and viscosity breakdown of the lubricating oil, metal weakening of the
overheated engine parts, and stress between engine parts resulting in quicker wear,
among other things.
From the laws of thermodynamics, we know that heat transfer increases as we
increase the surface area of the radiator assembly. That said, the demand for more
powerful engines in smaller hood spaces has created a problem of insufficient rates
of heat dissipation in automotive radiators. As a result, many radiators must be
redesigned to be more compact while still having sufficient cooling power
capabilities. It is the objective of the project to untaken redesigning for compactness
configuration and at the same time increasing the rate of heat dissipation.
3
1.3 Research Objectives
The objectives of this research are:
i. To compare the performance of the existing heat exchanger with the new
design of heat exchanger.
ii. To simulate 2D CFD flow of the design.
1.4 Scope of the Study
The scopes of the studies are:
i. Heat exchanger system that will be used to conduct the experiment will be the
automotive radiator.
ii. Experiments will be conducted to compare the fluid and heat flow of the
existing exchanger system with a new circular heat exchanger design.
iii. Simulation of the fluid flow is using the Computational Fluid Dynamic
(CFD) software.
4
CHAPTER II
LITERATURE REVIEW
2.1 Radiator
The radiator core is usually made of flattened aluminum tubes with aluminum
strips that zigzag between the tubes. These fins transfer the heat in the tubes into the
air stream to be carried away from the vehicle. On each end of the radiator core is a
tank, usually made of plastic that covers the ends of the radiator,
On most modern radiators, the tubes run horizontally with the plastic tank on
either side. On other cars, the tubes run vertically with the tank on the top and
bottom. On older vehicles, the core was made of copper and the tanks were
brass. The new aluminum-plastic system is much more efficient, not to mention
cheaper to produce. On radiators with plastic end caps, there are gaskets between the
aluminum core and the plastic tanks to seal the system and keep the fluid from
leaking out. On older copper and brass radiators, the tanks were brazed (a form of
welding) in order to seal the radiator.
5
Figure 2.1: Radiator
The tanks, whether plastic or brass, each have a large hose connection, one
mounted towards the top of the radiator to let the coolant in, the other mounted at
the bottom of the radiator on the other tank to let the coolant back out. On the top of
the radiator is an additional opening that is capped off by the radiator cap. More on
this later.
Another component in the radiator for vehicles with an automatic
transmission is a separate tank mounted inside one of the tanks. Fittings connect this
inner tank through steel tubes to the automatic transmission. Transmission fluid is
piped through this tank inside a tank to be cooled by the coolant flowing past it
before returning the transmission.
2.1.1 Radiator Fans
Mounted on the back of the radiator on the side closest to the engine is one or
two electric fans inside a housing that is designed to protect fingers and to direct the
air flow. These fans are there to keep the air flow going through the radiator while
the vehicle is going slow or is stopped with the engine running. If these fans stopped
working, every time you came to a stop, the engine temperature would begin
6
rising. On older systems, the fan was connected to the front of the water pump and
would spin whenever the engine was running because it was driven by a fan belt
instead of an electric motor. In these cases, if a driver would notice the engine begin
to run hot in stop and go driving, the driver might put the car in neutral and rev the
engine to turn the fan faster which helped cool the engine. Racing the engine on a
car with a malfunctioning electric fan would only make things worse because you are
producing more heat in the radiator with no fan to cool it off.
The electric fans are controlled by the vehicle's computer. A temperature
sensor monitors engine temperature and sends this information to the computer. The
computer determines if the fan should be turned on and actuates the fan relay if
additional air flow through the radiator is necessary.
If the car has air conditioning, there is an additional radiator mounted in front
of the normal radiator. This "radiator" is called the air conditioner condenser, which
also needs to be cooled by the air flow entering the engine compartment. You can
find out more about the air conditioning condenser by going to our article on
Automotive Air Conditioning. As long as the air conditioning is turned on, the
system will keep the fan running, even if the engine is not running hot. This is
because if there is no air flow through the air conditioning condenser, the air
conditioner will not be able to cool the air entering the interior.
Figure 2.2 : Radiator Fan
7
2.1.2 Pressure cap and reserve tank
As coolant gets hot, it expands. Since the cooling system is sealed, this
expansion causes an increase in pressure in the cooling system, which is normal and
part of the design. When coolant is under pressure, the temperature where the liquid
begins to boil is considerably higher. This pressure, coupled with the higher boiling
point of ethylene glycol, allows the coolant to safely reach temperatures in excess of
250 degrees.
The radiator pressure cap is a simple device that will maintain pressure in the
cooling system up to a certain point. If the pressure builds up higher than the set
pressure point, there is a spring loaded valve, calibrated to the correct Pounds per
Square Inch (psi), to release the pressure.
When the cooling system pressure reaches the point where the cap needs to
release this excess pressure, a small amount of coolant is bled off. It could happen
during stop and go traffic on an extremely hot day, or if the cooling system is
malfunctioning. If it does release pressure under these conditions, there is a system
in place to capture the released coolant and store it in a plastic tank that is usually not
pressurized. Since there is now less coolant in the system, as the engine cools down
a partial vacuum is formed. The radiator cap on these closed systems has a
secondary valve to allow the vacuum in the cooling system to draw the coolant back
into the radiator from the reserve tank (like pulling the plunger back on a hypodermic
needle) There are usually markings on the side of the plastic tank marked Full-Cold,
and Full Hot. When the engine is at normal operating temperature, the coolant in the
translucent reserve tank should be up to the Full-Hot line. After the engine has been
sitting for several hours and is cold to the touch, the coolant should be at the Full-
Cold line.
8
Figure 2.3 : Pressure Cap
2.1.3 Water Pump
A water pump is a simple device that will keep the coolant moving as long as the
engine is running. It is usually mounted on the front of the engine and turns
whenever the engine is running. The water pump is driven by the engine through
one of the following:
A fan belt that will also be responsible for driving an additional component
like an alternator or power steering pump
A serpentine belt, which also drives the alternator, power steering pump and
AC compressor among other things.
The timing belt that is also responsible for driving one or more camshafts.
The water pump is made up of a housing, usually made of cast iron or cast
aluminum and an impeller mounted on a spinning shaft with a pulley attached to the
shaft on the outside of the pump body. A seal keeps fluid from leaking out of the
pump housing past the spinning shaft. The impeller uses centrifugal force to draw
the coolant in from the lower radiator hose and send it under pressure into the engine
block. There is a gasket to seal the water pump to the engine block and prevent the
flowing coolant from leaking out where the pump is attached to the block.