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.

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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.