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THE EFFECT OF PLATE GEOMETRY ON FLOW AND HEAT TRANSFER

ACROSS A PARALLEL PLATE HEAT EXCHANGER

CHO WEI YANG

B041110217

Email: [email protected]

Projek Sarjana Muda

Supervisor: DR. FATIMAH AL-ZAHRAH BT. MOHD SA’AT

Faculty of Mechanical Engineering

Universiti Teknikal Malaysia Melaka

JUNE 2015

SUPERVISOR DECLARATION

“I hereby declare that I have read this thesis and in my opinion this thesis is

sufficient in terms of scope and quality for the award of the degree of

Bachelor of Mechanical Engineering (Automotive)”

Signature: ……………………………..

Supervisor: DR. FATIMAH AL-ZARAH BT. MOHD SA’AT

Date: …………………………….

THE EFFECT OF PLATE GEOMETRY ON FLOW AND HEAT TRANSFER ACROSS A PARALLEL PLATE HEAT EXCHANGER

CHO WEI YANG

This thesis is submitted as partial fulfilment of requirements for the award of Bachelor of Mechanical Engineering (Automotive) (Hons.)

Faculty of Mechanical Engineering Universiti Teknikal Malaysia Melaka

JUNE 2015

ii

DECLARATION

“I hereby declare that the work in this thesis is my own except for summaries and

quotations which have been duly acknowledged.”

Signature: ………………….

Author: CHO WEI YANG

Date: ………………….

iii

To my beloved father and mother

iv

ACKNOWLEDGEMENT

First and foremost, I would like to express my sincere gratitude to my supervisor,

Dr. Fatimah Al-Zahrah Mohd Sa’at, for guiding me throughout the entire PSM process.

Without the advices and help from her, carrying out this study would be almost

impossible. Therefore, I consider it as an honor to be able to work as a student under her.

I would also like to express my deepest gratitude to my university, Universiti

Teknikal Malaysia Melaka (UTeM), and my faculty, Faculty of Mechanical Engineering,

for granting me such great platform to learn and grow for the last four years.

Furthermore, I would like to thank all my friends who gave me support and

encouragement throughout my process of learning here in UTeM. Without them, I may

not be able to progress as smooth in my studies.

In addition, I would also like to take this opportunity to thank my parents and my

siblings in showering me with care and words of encouragement. Without them, I would

not be able to reach this stage. I am indebted to my family members for keep picking me

up when I fell down telling me not to give up.

v

ABSTRACT

When a flow is flowing past a blunt body or solid boundaries, there will be

formation of flow patterns and interactions between flow and the solid bodies. Other

than that, heat transfer can also take place if there is a temperature difference between

the flow and solid bodies. In this study, a pile of parallel-plates was considered as the

solid bodies. A simplified model of parallel-plate heat exchanger was chosen as the

computational domain in order to study of effect of plate geometry and channel

dimensions on the flow and heat transfer across a parallel-plate heat exchanger. There

will be an oscillatory flow where the flow moves back and forth across the solid

boundaries. The study was carried out using ANSYS software. Drawing of the

computational domain, meshing of the domain, solver settings and validation of the

model were carried out before the study can be recognized. After having done validation,

the results and data from the original model were compared with other three cases. One

of the three cases has round-shaped edges for its parallel-plates heat exchanger. The

remaining two cases have triangle-shaped edges with one having two times longer edge

length of the other one. All the cases were compared in terms of vorticity contours, total

and average surface heat flux and last but not least, velocity profile inside the channel.

The study shows that the shape of the edge affects the flow and the heat transfer of the

system. Vortices discontinuities were eliminated through the changing of edge shapes.

Heat energy transfer across the surface also changes when the shape of the edge changes.

vi

ABSTRAK

Apabila sesuatu aliran mengalir melepasi satu badan pepejal, akan berlakunya

pembentukan corak aliran dan interaksi antara aliran dan badan pepejal. Tambahan pula,

pemindahan haba juga boleh berlaku sekiranya terdapat perbezaan suhu antara aliran

dengan badan pepejal tersebut. Badan pepejal dalam kajian ini adalah timbunan plat

yang diaturkan secara selari. Satu model penukar haba plat-selari yang mudah dijadikan

sebagai domain untuk mengkaji tentang kesan penukaran geometri plat dan jarak antara

plat terhadap aliran dan juga pemindahan haba melalui penukar haba plat-selari. Aliran

berayun yang mana aliran tersebut akan beralir pergi dan balik akan dipilih sebagi jenis

aliran dalam kajian ini. Kajian ini dijalankan melalui penggunaan perisian ANSYS.

Lukisan domain, ‘meshing’ untuk domain, penetapan penyelesaian dan juga pengesahan

domain perlu dijalankan supaya kajian ini boleh diiktiraf. Setelah mengesah kesesuaian

model original, data model tersebut dibandingkan dengan tiga model yang lain. Salah

satu model mempunyai sisi yang bulat. Dua model mempunyai sisi segi tiga dan salah

satu mempunyai sisi yang dua kali lebih panjang daripada model yang satu lagi. Semua

model yang tersebut dibandingkan melalui kontur kepusaran, pemindahan tenaga haba

dan profil halaju dalam saluran. Kajian ini menunjukkan perubahan dari segi aliran dan

permindahan haba dalam sistem apabila bentuk sisi diubah.

vii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF FIGURES x

LIST OF TABLES xii

LIST OF ABBREVIATION AND SYMBOL xiii

LIST OF APPENDIXES xv

CHAPTER 1 INTRODUCTION

1.1 Background 1

1.2 Problem Statement 3

1.3 Motivation of Study 4

1.4 Objectives 4

1.5 Scope 4

CHAPTER 2 LITERATURE REVIEW

2.1 Flow 6

2.2 Heat Transfer 10

2.3 Heat Exchanger 12

2.4 Thermoacoustics 14

2.5 Working Principle of Thermoacoustic Device 15

viii

2.6 Effect of Geometry of Parallel-Plates on Flow

and Heat Transfer 17

CHAPTER 3 METHODOLOGY

3.1 Pre-Processing 22

3.2 Solver Settings 26

3.3 Pre-Processing for Different Geometries 30

CHAPTER 4 RESULTS AND ANALYSIS

4.1 Validation 32

4.2 Vorticity Contours 34

4.2.1 Original Model 35

4.2.2 Case 1 36

4.2.3 Case 2 37

4.2.4 Case 3 38

4.3 Total Surface Heat Flux 39

4.3.1 Original Model 40

4.3.2 Case 1 42

4.3.3 Case 2 43

4.3.4 Case 3 45

CHAPTER 5 DISCUSSION

5.1 Comparison of Local Surface Heat Flux

Between All the Cases at Point A 47


Between All the Cases at Point B 48


Between All the Cases at Point C 49

5.4 Comparison of Average Total Surface Heat

Flux Over Time at Hot Heat Exchangers

Between All Cases 50

ix

5.4 Vorticity Contours Comparison at the Edges

of All the Cases 51

5.5 Velocity Profile Comparison between All

the Cases 52

CHAPTER 6 CONCLUSION AND RECOMMENDATION 54

REFERENCES 55

APPENDIX A 58

x

LIST OF FIGURES

NO. TITLE PAGE

1.1 Illustration on position of heat exchangers and stack. 2

2.1 Illustration of laminar and turbulent flow. 7

2.2 Von Karman vortex (Cesareo de La Rosa Siqueira, 2005). 9

2.3 All three types of heat transfer process. 10

2.4 Illustration of double-pipe heat exchanger in parallel flow. 13

2.5 Illustration of double-pipe heat exchanger in cross flow. 13

2.6 PLIF image of heat transfer at the parallel-plates heat exchangers

from Jaworski and Piccolo (2012). 16

2.7 Illustration on the flow pattern at the end of sharp-edged plate. 20

2.8 Results from ANSYS Fluent 13 simulation on vortex generation

by Mohd Sa’at and Jaworski (2013). 21

3.1 Flow chart of this study. 22

3.2 Illustration of the computational domain and its dimensions. 23

3.3 Drawing of domain using ICEM. 24

3.4 Drawing of domain using ANSYS Workbench after creating surface. 25

3.5 Meshing of the domain after adjusting the sizing of the meshes. 25

3.6 FLUENT window. 26

3.7 Illustration of some important positions for calculation and validation

works. 28

3.8 Surface monitor setting changes for 1 cycle simulation. 29

3.9 Position of last point of curve after 1 cycle simulation. 29

3.10 Position of last point of curve for phase 0. 30

3.11 All simulation models with different geometries. 31

xi

4.1 Changes of x-velocity of point M at different phases. 32

4.2 Grid sensitivity test. 34

4.3 Vorticity contours of original model simulation at different phases. 35

4.4 Illustration of flow over original model from phase 0 to 10. 35

4.5 Illustration of flow over original model from phase 11 to 20. 36

4.6 Vorticity contours of case 1 model simulation at different phases. 36

4.7 Illustration of flow over case 1 model from phase 0 to 10. 37





4.12 Location of point A, B and C. 39

4.13 Local surface heat flux at point A, B and C for original model. 40

4.14 Average total surface heat flux at point A, B and C for original model. 41

4.15 Local surface heat flux at point A, B and C for case 1. 42

4.16 Average total surface heat flux at point A, B and C for case 1. 42





5.1 Local surface heat flux at point A for all the cases. 47

5.2 Local surface heat flux at point B for all the cases. 48

5.3 Local surface heat flux at point C for all the cases. 49

5.4 Average total surface heat flux at hot heat exchangers for all cases 50

5.5 Vorticity contours at the edges of all the models at phase 10. 51

5.6 Velocity profile for all the cases at phase 5. 52

5.7 Velocity profile for all the cases at phase 15. 53

xii

LIST OF TABLES

NO. TITLE PAGE

3.1 Properties of several types of gas at temperature

of 300 K (Swift, 2001). 27

3.2 Values needed in calculating boundary conditions 28

xiii

LIST OF ABBREVIATIONS AND SYMBOLS

Re = Reynolds number

ρ = Density

Vavg = Average velocity

D = Geometry characteristic length

μ = Dynamic viscosity

ν = Kinematic viscosity

CFD = Computational Fluid Dynamics

�̇� = Rate of heat transfer

k = Thermal conductivity

A = Surface area

𝑑𝑇

𝑑𝑥 = Temperature gradient

h = Convection heat transfer coefficient

Ts = Surface temperature

𝑇∞ = Surrounding temperature

σ = Stefan-Boltzmann constant

ɛ = Emissivity of the surface

𝛿𝑘 = Thermal penetration depth

ω = Angular frequency

Cp = Constant pressure heat capacity per unit mass

𝛿𝑣 = Viscous penetration depth.

BR = Blockage ratio

xiv

LIST OF ABBREVIATIONS AND SYMBOLS

yo = Half distance between parallel plates

l = Length of heat exchanger

PLIF = Planar Laser Induced Fluorescence

PIV = Particle Image Velocimetry

SIMPLE = Semi-Implicit Method for Pressure-Linked Equations

xv

LIST OF APPENDIXES

NO. TITLE PAGE

A Gantt Chart 58

1

CHAPTER 1

INTRODUCTION

1.1 BACKGROUND

When a flow is flowing past a blunt body or solid boundaries, there will be

interactions between the flow and the solid bodies. In this study, the solid boundaries will

be a pile of parallel-plates acting as heat exchangers. There will be formation of various

flow patterns when a flow flows past the parallel-plates. Other than flow patterns, there is

also interaction in terms of heat transfer since the parallel-plates will be acting as heat

exchangers. The temperature difference around the plates region will cause the occurrence

of heat transfer between the flow and the plates due to the temperature gradient. The focus

of this research is to study how the changes in the plate geometry (shape or dimensions of

parallel-plate) may disturb or affect the flow and heat transfer across a parallel-plate heat

exchanger. In discussing the flow and heat transfer across a parallel-plate heat exchanger,

the working medium used is very important too. Oscillatory flow which the flow will

propagate forth and back will be used in this research.

An example of application of oscillatory flow is as used in a reactor. Besides

thermoacoustics, this knowledge has been adapted into other technology such as

oscillatory flow reactor. Through different configurations of the reactor, it can serve

different purposes. The most common configuration is to operate as a mixer. Having an

oscillating flow can enhance the mixing as the mass and heat transfer rates are increased

2

significantly due to the back and forth movement. Oscillatory flow mixing technology can

also be found widely in chemical and process engineering. Another application of

oscillatory flow, which is also the focus of our research, is a thermoacoustic heat

exchanger. This heat exchanger extracts and supplies heat obtained from the

thermoacoustic system.

The main working medium behind thermoacoustics is a type of flow called

oscillatory flow. This flow is formed from sound waves with amplitudes high enough to

transfer heat from one place to another. On the other hand, sufficiently high temperature

gradient can also be used to create sound waves of high amplitudes. This flow plays an

important role because the oscillatory flow will move back and forth expanding and

contracting in order to do work.

Figure 1.1: Illustration on position of heat exchangers and stack.

A simple explanation about devices using thermoacoustics principle may be

explained with the aid of Figure 1.1. Generally the thermoacoustic effects occur within an

area inside the device where structures shown in Figure 1.1 are placed. The structures, in

general, contain a pile of solid metal known as ‘stack’. This ‘stack’ is sandwiched between

a pair of heat exchangers with temperature gradient. Thermoacoustic effects occur when

the oscillatory flow inside the device interacts with the ‘stack’. Depending on the source

3

of energy, the interaction between the flowing fluid and the solid surface of the stack may

produce either cooling effect or power.

The heat exchangers at the ends of ‘stack’ are responsible to effectively remove

heat from the system and provide cooling capacity to the refrigerated space that is attached

to the system. On the other hand, if the heat exchangers provide a high enough temperature

gradient to the fluid, such that allows the fluid particle to excite, power will be produced.

The energy produced may then be harnessed for other useful application.

1.2 PROBLEM STATEMENT

The challenge in commercializing the thermoacoustic technologies lies, among

others, on understanding the behavior of the flow and heat transfer phenomena inside the

system. Current analytical solution used in designing the thermoacoustic system is based

on a one-dimensional linear model. However, in practical system, the flow may consist of

irregularities such as natural convection, streaming and vorticity. It is pertinent that these

effects are investigated so that a proper understanding may be gained. This involves the

fundamental knowledge of oscillatory flow. The study on heat transfer phenomenon in a

heat exchanger across oscillatory flow is important. There are many types of heat

exchanger and the parallel-plate heat exchanger is one of them. As the geometry of the

parallel-plates structure is changed, the flow properties near the plates will also change.

This may somehow affect the interactions between the oscillatory flow and the solid

surfaces. The changing of geometry may also create disturbances or other effects on the

flow. The usual shape of the plates is rectangle with sharp edges. It will be interesting to

study what changes may be observed if the shape of the plates is changed for example, to

round edges or to other shapes.

4

1.3 MOTIVATION OF STUDY

Often the other parameters are taken into consideration when studies are carried

out regarding the oscillatory flow or heat transfer near solid structures. Geometry and gap

dimensions however get less attention as compared to other parameters. Considering the

fact that changing geometry will affect the contact surface of the plate and also the

possibility of creating disturbances to the flow, researches should be carried out more

about this factor. The purpose of this study is to gain more information on the effect of

geometry of the parallel-plates on the heat transfer and flow so that this concept appears

attractive to the industry sooner.

1.4 OBJECTIVES

There are several objectives in completing the study. The objectives are to:

i) Study the thermoacoustic heat exchanger and to understand the working

principle and knowledge related to it.

ii) Formulate simplified models for the purpose of comparison of flow and heat

transfer between different geometries.

iii) Validate the model with available published work; experimental or theoretical

data.

iv) Analyze the results and study the effect of parallel-plates geometry on the flow

and heat transfer around the heat exchanger.

1.5 SCOPE

There are several parameters that can be manipulated in order to study the factors

affecting the flow and heat transfer such as the mean pressure, velocity amplitude,

frequency and also phase difference. However in this study, the focus will only be on the

effect of geometry of the parallel plates on the flow behavior of the system. This involves

5

several different shape of the edge of the heat exchanger plates. The parallel plates in this

research will be used to represent the heat exchangers used in real thermoacoustic devices.

This research will cover only the oscillatory flow encountered in a thermoacoustic system.

A simplified model of parallel plates will be formulated for the research.

6

CHAPTER 2

LITERATURE REVIEW

2.1 FLOW

Over the years, numerous researches had been carried out in the field of

thermoacoustics. In thermoacoustic applications, fluid may be considered as the working

medium. One important aspect that needs to be understood is the flow of the fluid. Flow

is the propagation of fluid from one place to another along a stream. There are three phases

of fluid flow; laminar, transition and turbulent flow. As shown in figure 2.1, laminar flow

is the early stage of a flow where it is often represented by smooth and highly-ordered

motion. When the flow velocity increases, the flow will change gradually from small

fluctuations in the motion to large fluctuation. In this situation, the fluid is said to be in

the transition stage. Transition stage happens gradually instead of sudden changing of

phase in between laminar and transition. Transition is a phase in between laminar and

turbulent. If the velocity of fluid keeps on increasing, the flow will finally reach turbulent

phase where the motion of flow is random and highly-disordered. Fluctuation in velocity

can also be seen in turbulent phase. Cengel and Ghajar (2010) mentioned that the rapid

fluctuations during turbulent flow resulting in intense mixing of the fluid enhances heat

and momentum transfer between fluid particles. These in turn increase the friction force

on the surface and the convection heat transfer rate. When the flow becomes fully

turbulent, heat transfer coefficient will become maximum value. The heat transfer rate

will be of greater amount compared to in laminar stage. The friction coefficient too will

7

become maximum when the flow is fully turbulent. This will requires more input to

overcome the large friction forces.

Figure 2.1: Illustration of laminar and turbulent flow.

The classification of the three phases mentioned earlier is made possible with the

help of a dimensionless number, the Reynolds number. Reynolds numbers, Re, was

discovered by Osborne Reynolds in 1880s. He found out that the flow regime or the order

of the flow is highly dependent on the ratio of inertial forces to viscous forces in the fluid.

Inertial force can be considered as the amount of force a fluid put up to resist any change

in its motion. Viscous force can be explained as the shear force experienced by the flow

when it flows past a solid body. In easier analogue, viscous force can be considered as

frictional force. Reynolds number can be expressed as;

Re = inertial forces

viscous forces = 𝜌𝑉𝑎𝑣𝑔𝐷

𝜇 (2.1)

where ρ is the density of medium, Vavg is the average velocity of the flow, D is the

geometry characteristic length and μ is the dynamic viscosity of the medium. Reynolds

number can also be expressed in terms of kinematic viscosity;

Re = 𝑉𝑎𝑣𝑔𝐷

𝜈 (2.2)

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