Evaluation Performance Of Louvered-Fin Compact Heat Exchanger.
EVALUATION PERFORMANCE OF LOUVERED-FIN COMPACT HEAT
EXCHANGER
HASZIL ADHA BIN HASLAN
Laporan ini dikemukakan sebagai
memenuhi sebahagian daripada syarat penganugerahan
Ijazah Sarjana Muda Kejuruteraan Mekanikal (Termal-Bendalir)
Fakulti Kejuruteraan Mekanikal
Universiti Teknikal Malaysia Melaka
Mac 2007
‘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 I:………………………………..
Tarikh :………………………………………….
Tandatangan:……………………………………
Nama Penyelia II:………………………………
Tarikh:………………………………………….
ii
“Saya akui laporan ini adalah hasil kerja saya sendiri kecuali ringkasan dan
petikan yang tiap-tiap satunya saya telah jelaskan sumbernya”
Tandatangan :……………………………..
Nama Penulis :……………………………
Tarikh :……………………………………
iii
ACKNOWLEDGEMENT
Alhamdulillah with His Mercy and Blessings, my greatest gratitude to Allah
the Almighty for the chances given to me to complete this project. My first
acknowledgement goes to Mr Shamsul Bahari Bin Azraai, my project supervisor.
Thanks for his tremendous help, advice, inspiration and unending guidance to me
until completing this research. Without him, this project will not exist. The
fundamental idea behind this project is his and he never stop from giving me support
and encouragement in completing this project. Without his valuable guidance, I
would not have been able to achieve the objectivity of this project.
Not forgotten, to my beloved parents, Mr Haslan Bin Hassan and Mrs Nur
Aziah Binti Abdul Latif. Your love and caring really touched me. My sister and
brother, Haszianaliza Binti Haslan and Hasziq Hafify Bin Haslan. Thanks so much
for giving me lifelong encouragement, inspiration and support. May Allah bless all
of you.
Lastly, my acknowledgement go to the technician, Mr. Razmi who have lend
to me some help. My friends who really understand and willing to cooperate with me
in the process of completing this project. Without your supports, I will never go this
far.
iv
ABSTRACT
The research of performance of louvered-fin Compact Heat Exchanger is
done by simulating the problem using Ansys CFX Software. This report will
represent the result from the simulation done by CFX Software along with the
discussion and conclusion. The fluid used in the simulation is air at 25°C and the
speed of the air enter through the inlet is 15m/s. At the end of this study the optimum
geometry that is suitable for mass use will be discussed. This study have found that
the optimum geometry to enhance the heat transfer performance for louvered fin
compact heat exchanger is 29° louver angle and 1.30mm louver pitch. The results of
the optimum geometry of the louvered fin have been validated by study done by
previous academician. The performance of this louvered fin type compact heat
exchanger has been evaluated by monitoring the temperature drop at the fin by the
observing of the temperature contour. The conclusion of this study is that the
louvered fin will enhance the heat transfer performance because of the increasing in
the heat transfer surface area. And when the air is flowing through the louvered fin
array, the flow is louver directed pattern and will cause great temperature drop at the
fin plat. Louver directed flow and axial directed flow will be the main reason in
enhancing the heat transfer performance of the louvered fin compact heat exchanger.
v
ABSTRAK
Kajian tentang kecekapan penukar haba padat bersirip tetingkap dilakukan
dengan mensimulasikan masalah tersebut dengan menggunakan perisian Ansys CFX.
Laporan ini akan memaparkan keputusan daripada simulasi yang dilakukan bersamasama dengan perbincangan tentang keputusan yang diperolehi dan juga kesimpulan
yang dapat dibuat. Bendalir yang digunakan dalam simulasi ini adalah udara pada
25°C dan kelajuan udara tersebut melalui masukan adalah 15m/s. Diakhir kajian ini,
rekabentuk optimum yang sesuai untuk penggunaan secara besar-besaran akan
dibincangkan. Kajian ini telah menemui bahawa geometri optimum untuk
meningkatkan kecekapan penukaran haba untuk penukar haba padat bersirip
tetingkap adalah 29° sudut tetingkap dan 1.30mm jarak tetingkap. Keputusan yang
diperolehi tentang rekabentuk geometri optimum telah di sahkan dengan merujuk
kepada kajian yang telah dilakukan oleh pengkaji sebelum ini. Kecekapan penukar
haba padat bersirip tetingkap telah dinilai dengan melihat kepada pengurangan suhu
yang berlaku pada sirip tersebut dengan melihat kepada kontor suhu. Kesimpulan
yang dapat dibuat daripada kajian ini adalah sirip jenis tetingkap akan dapat
menambahkan kecekapan penukaran haba kerana pertambahan luas permukaan
penukaran haba. Dan apabila udara melalui susunan sirip tetingkap tersebut, aliran
udara tersebut akan menjadi aliran berarahkan tetingkap dan ini akan menyebabkan
kejatuhan suhu yang banyak pada plat sirip tersebut. Aliran berarahkan tetingkap dan
aliran berarahkan paksi menjadi penyebab utama dalam menambahbaikkan
kecekapan penukaran haba pada penukar haba padat bersirip tetingkap.
vi
TABLE OF CONTENT
CHAPTER
TITLE
PENGAKUAN
ACKNOWLDGEMENT
ABSTRACT
ABSTRAK
TABLE OF CONTENT
LIST OF TABLES
LIST OF FIGURES
LIST OF SYMBOLS
LIST OF ABBREVIATIONS
LIST OF APPENDICES
PAGE NO
ii
iii
iv
v
vi
viii
ix
xi
xiii
xiiii
CHAPTER I
INTRODUCTION
1.1 Introduction
1.2 Objectives
1.3 Scopes
1.4 Problem Statement
1
1
2
2
3
CHAPTER II
LITERATURE REVIEW
2.1 Introduction
2.2 Compact Heat Exchanger
2.3 Louvered Fin Compact Heat Exchanger
2.4 Evaluation Performance of Compact Heat
Exchanger
2.4.1 Computational Fluid Dynamics
2.4.2 Log Mean Temperature Different
2.4.3 Calculation of Performance
Parameters
2.5 Flow and Heat Transfer
2.5.1 Reynolds Number
2.5.2 Geometrical Parameters
5
5
6
7
9
CHAPTER III
METHODOLOGY
3.1 Introduction
3.2 Ansys CFX
3.3 Ansys Workbench
3.3.1 Geometry Designing
3.3.2 Meshing
3.4 CFX-Pre
3.4.1 Boundary Conditions
3.4.2 Domain Interface
3.4.3 Solver Control
9
9
10
11
11
13
15
15
15
16
16
17
18
20
20
20
vii
CHAPTER
TITLE
3.5
3.6
CFX-Solver
CFX-Post
3.6.1 Plane Creating
3.6.2 Contour Creating
3.6.3 Streamline Creating
3.6.4 Velocity Vector
PAGE NO
21
21
21
22
22
22
CHAPTER IV
RESULTS & DISCUSSION
4.1 Introduction
4.2 Drawing with Dimension
4.3 Initial State
4.4 Flow Phenomena
4.5 Fin Temperature Distribution
4.6 Louver Effect Angle
4.7 Pressure Distribution
23
23
23
24
25
29
34
37
CHAPTER V
CONCLUSION
5.1 Conclusion
39
39
CHAPTER VI
RECOMMENDATIONS
6.1 Recommendations
40
40
REFERENCES
APPENDIX A: RESULT FOR θ = 22°, L P
= 0.81MM
APPENDIX B: RESULT FOR θ = 29°, L P
= 0.81MM
APPENDIX C: RESULT FOR θ = 32°, L P
= 0.81MM
APPENDIX D: RESULT FOR θ = 22°, L P
= 1.30MM
APPENDIX E: RESULT FOR θ = 29°, L P
= 1.30MM
APPENDIX F: RESULT FOR θ = 32°, L P
= 1.30MM
APPENDIX G: GEOMETRY DRAWING
WITH DIMENSION
41
42
43
44
45
46
47
48
viii
LIST OF TABLES
TABLES
TITLE
PAGE NO
2.1
Geometrical Parameters of CHE’s
14
4.1
Initial Condition Value
24
ix
LIST OF FIGURES
FIGURES TITLE
PAGE NO
1.1
Louvered fin type CHE
2
1.2
An Array of louvered fin with geometrical parameters
3
1.3
Schematic of louvered fin design to be considered
4
2.1
Schematic of Heat Exchanger
5
2.2
Compact Heat Exchanger cores (a) Fin-tube (flat tubes,
6
continuous plate fins). (b) Fin-tube (circular tubes,
continuous plate fins). (c) Plate-fin (single pass). (d)
Plate-fin (multipass)
2.3
Car radiator that use louvered fin CHE
7
2.4
Example of louvered fin CHE
8
2.5
Louver directed flow and axial directed flow
8
2.6
Louvered fin with 22˚ louvered angle, 0.81 louvered pitch
14
2.7
Louvered fin with 29˚ louvered angle, 0.81 louvered pitch
14
2.8
Louvered fin with 32˚ louvered angle, 0.81 louvered pitch
14
3.1
Ansys CFX Flow Chart
16
3.2
Definitions of Boundary Condition
20
4.1
An array of louvered fin for the 22° louver angle and
24
1.30mm louver pitch
4.2
Computed Velocity for (a) Lp = 0.81mm (b) Lp =
26
1.30mm
4.3
Computed Temperature (K) for 29° louvered angle and
27
0.81mm louvered pitch
4.4
Computed Temperature (K) for 29° louvered angle and
1.33mm louvered pitch
28
x
4.5
Static Temperature Contours on fin for (a) θ = 22°, Lp =
30
1.30mm (b) θ = 29°, Lp = 1.3mm
4.6
Fin Temperature against Fin Position
31
4.7
Velocity Vector at the first six arrays for (a) Lp = 0.81mm
32
(b) Lp = 1.30mm
4.8
Velocity Vector after the 7th fin for (a) Lp = 0.81mm (b)
33
Lp = 1.30mm
4.9
Computed Temperature for (a) θ = 22° (b) θ = 32°
35
4.10
Variation of Fin Temperature
36
4.11
Velocity Streamline Used For Flow Simulation
37
4.12
Computed Air Pressure Distribution Around Louvered Fin
38
xi
LIST OF SYMBOLS
q
=
Total Heat Transfer, W
U
=
Overall Heat Transfer Coefficient, W/m².K
Tm
=
Mean Temperature Different, K
f
p
=
Friction Factor
=
Pressure Different, N/m²
=
Density, kg/m³
A
Ac
St
hc
cp
Q
LMTD
To
Ti
Ta
Tf
Re
=
Total Heat Transfer Area, m²
=
Minimum Flow Area, m²
=
Stanton Number
=
Heat Transfer Coefficient, W/m².K
=
Specific Heat at Constant Pressure, kJ/kG.˚C
=
Heat Transfer Rate, W
=
Log Mean Temperature Different
=
Outlet Temperature, K
=
Inlet Temperature, K
=
Air Temperature, K
=
Fin Temperature
=
Reynolds Number
s
=
Mean Fluid Velocity, m/s
L
=
Characteristic Length, m
=
Dynamic Fluid Viscosity, kg/m.s
=
Kinematic Fluid Viscosity, m²/s
=
Louver Pitch, m
=
Hydraulic Diameter, m
=
Fin Length, m
=
Reynolds Number Based On Hydraulic Diameter
=
Louvered Angle
Fp
=
Fin Pitch, m
v
Lp
dh
Ls
Red
xii
Tp
=
Transverse Pitch, m
xiii
LIST OF ABBREVIATIONS
CHE
=
Compact Heat Exchanger
CFD
=
Computational Fluid Dynamics
etc
=
Etcetera
LMTD
=
Log Mean Temperature Different
xiiii
LIST OF APPENDIXES
BIL
TITLE
PAGE NO
A
RESULT FOR θ = 22°, L P = 0.81MM
41
B
RESULT FOR θ = 29°, L P = 0.81MM
42
C
RESULT FOR θ = 32°, L P = 0.81MM
43
D
RESULT FOR θ = 22°, L P = 1.30MM
44
E
RESULT FOR θ = 29°, L P = 1.30MM
45
F
RESULT FOR θ = 32°, L P = 1.30MM
46
G
GEOMETRY DRAWING WITH DIMENSION
47
1
CHAPTER I
INTRODUCTION
This chapter is to introduce the definition of CHE. The purpose, scope and
problem statement for this research is also stated here.
1.1
Introduction
Compact Heat Exchanger is commonly used to enhance the heat transfer rate
in application that involves with high temperature. Generally there are two types of
CHE which are plate-fin type and tube-fin type. CHE is only used for gas-gas or gasliquid application [1]. Plate Fin Compact Heat Exchanger is widely used in gas-gas
application [1]. In this study we will consider plate-fin type with louvered fin.
Nowadays CHE is widely used in various type of industries such as
automotive, aeronautics and astronautics, electric and electronic equipment,
refrigeration and else. CHE is preferred for application that needs heat exchanger
because of its compactness, high-effectiveness, low cost needed, small volume and
low in weight [1].
Because of it is widely used in industries, so the optimization of CHE design
is important. This optimization can be done by using various type of design and
selection of good material to reduce cost but give high effectiveness. There are
several parameters to consider CHE performance such as the outlet temperature, heat
duty involves and pressure drop in the CHE.
2
There are some parameters that could be change in order to evaluate the
performance of CHE. The geometry parameters such as louver pitch, louver angle,
fin pitch and tube pitch. Figure 1.1 shows the louvered fin type of CHE.
Figure 1.1: Louvered fin type CHE [2]
1.2
Objectives
The objectives of this study are stated as below:
To study the effect of louver directed flow and axial directed flow around the
louvered fin array in the heat transfer enhancement
To visualize the pressure, velocity and temperatures profiles around louvered
fin array
To determine the optimum geometry design of louvered fin array for better
heat transfer
1.3
Scopes
The scopes of this study are detailed as below:
3
Study the various geometry design in louvered fin array by varying the value
of louver angle and louver pitch
1.4
Design CFD Louvered fin geometry using CFX software (Design Modeler)
Simulate air flow through louvered fin array
Study the effect of flowing air through the louvered fin array
Problem Statement
The problem that we have to consider here is by comparing the performance
of this type of CHE by varying geometrical parameter such as louvered angle and
louver pitch.
Figure 1.2 shows an array of louvered fin with geometrical parameters in
CHE. This study will only focus the effects of varying the value of louver angle and
louver pitch.
The flow phenomena of the air will be either axial directed flow or louver
directed flow or both. The effects of the flow phenomena will be discussed to
determine the heat transfer efficiency between the flowing air and the louvered fin
array. The value of fin pitch will remain constant at 2.11mm.
Figure 1.2: An Array of louvered fin with geometrical parameters [3]
4
Figure 1.3 shows the schematic of louvered-fin design. The studied air will be
flowing into the louvered fin array from the inlet and will be drawn out through the
outlet. The symmetry part will be transform later in CFX Post to view the real
simulation of the fin array.
Figure 1.3: Schematic of louvered-fin design to be considered [2]
Air flows through a louvered array at air velocity which ranging from 10m/s
to 30m/s. The temperature of the fin is maintained constant at specific temperature.
Ansys CFX Software is used to simulate air flow through a fin array. Finally, the
heat transfer rate by means of temperature drop of the louvered fin will be
determined from observation of velocity, temperature and pressure profile.
5
CHAPTER II
LITERATURE REVIEW
This chapter will discuss about all the equations, theory, past studies and
parameters used in this research.
2.1
Introduction
Heat exchanger is a device that efficiently transfers or exchange heats from a
fluid to another fluid without any contact between those two [4]. Figure 2.1 shows
the simplest heat exchanger.
Figure 2.1: Schematic of Heat Exchanger
Fluid A will cool down Fluid B as both of the fluid moves. The cooling
process is by convection as both of the fluid does not contact with each other because
of the barrier in the middle. All heat exchanger concepts are base on this. What
differs is only the design of each heat exchanger.
6
2.2
Compact Heat Exchanger
The definition of CHE is based on heat exchanger definition but in CHE,
compact is added. And so, based on heat exchanger definition the definition of CHE
will be; a heat exchanger that is compact which means it has small volume, small
size and also low in weight. CHE are typically used when a large heat transfer
surface area per unit volume is desired or at least one of the fluids is a gas [5]. A
CHE can reach an area density higher than 500m2/m3 with respect to 100 m2/m3 200 m2/m3 of the shell and tube heat exchanger [6]. There are generally two types of
CHE which are plate-fin type or tube-fin type [1]. Figure 2.2 shows the example of
plate-fin type CHE.
Figure 2.2: Compact Heat Exchanger cores. (a) Fin-tube(flat tubes, continuous
plate fins). (b) Fin-tube (circular tubes, continuous plate fins). (c)
Plate fin (single pass). (d) Plate fin (multipass) [5]
7
CHE appliances that are commonly used are car radiator or automotive
radiator. In this case of CHE, the heat exchanger is used to cool the engine as the
engine is heated because of the combustion process. Because of the combustion
process of the engine, the engine’s temperature will later increased and to avoid
overheating of the engine, CHE is used where in this case, fluid in the CHE is
commonly called as coolant and this coolant will move around the engine and cooled
it down. The coolant is cooled because of the air flowing through the geometry of the
CHE act as a cooling fluid to the fin array. Figure 2.3 shows the car radiator that use
louvered fin CHE.
Figure 2.3: Car radiator that use louvered fin CHE [7]
Coolant will enter the tube from the coolant inlet tank and as the coolant
moves through the tube, heat transfer happened between the coolant and air. As a
result of this heat transfer process, the coolant will later being cooled down and exit
to the coolant outlet tank.
2.3
Louvered Fin Compact Heat Exchanger
Louvered is defined as an open window liked geometry. So in this type of
CHE, louvered fin CHE means a CHE that have fin geometry like an open window.
To make this matter clearer, Figure 2.4 shows the schematic of louvered fin CHE.
8
Figure 2.4: Example of louvered fin CHE [3]
When this louvered fin was firstly introduced, it was believed that increased
heat transfer was due to added turbulence initiated by flow through the louvered
array [3]. But this theory was later proved wrong by the visualization studies on
scaled up louver design [3]. It was observed that as air passes through the louver, the
flow resulted in two distinct flow directions to be classified: axial (or duct) directed
flow and louver flow. Axial flow occurs when the flow maintains the directions of
the inlet flow. Louver directed flow occurs when the flow was aligned parallel to the
louver [3]. Figure 2.5 shows clearly the two directions indicated in the louvered fin
cross section.
Figure 2.5: Louver directed flow and axial directed flow [3].
The explanation for increased heat transfer came from the realization that
along with the new boundary layer that formed on each of these louver arrays, came
a corresponding high heat transfer coefficient.
9
2.4
Evaluation Performance of Compact Heat Exchanger
There are generally two ways in evaluating the performance of CHE which
are by numerical predictions using Computational Fluid Dynamic or by experimental
measurement where direct experiment was done in order to obtain data needed for
the performance calculation. For this research, CFD method is used in evaluating the
performance of CHE. Software used for this simulation is Ansys CFX.
2.4.1
Computational Fluid Dynamic
CFD is a branch of fluid dynamics where it is use widely to solve and analyze
problem that involve with fluid flow and heat transfer using numerical method and
algorithm [8]. Supercomputer or computer that works together in parallel is used to
solve millions of equation required to simulate interaction of fluid and gasses.
However, whatever value we get from CFD is only approximate solutions until the
results have been validated by experimental results. The basic of solving any CFD
equations is by using the Navier-Stokes equations, which defines any single-phase
fluid flow. These equations will be simplified later by removing terms describing
viscosity to yield the Euler equation. Later, by removing terms describing vorticity it
will yields full potential equations. Finally these equations can be linearized to yield
the linearized potential equation [8].
2.4.2
Log Mean Temperature Different
To design or to predict the performance of a heat exchanger, it is essential to
relate the total heat transfer rate to quantities such as the inlet and outlet fluid
temperatures, the overall heat transfer coefficient, and the total surface area for heat
transfer [5]. Two such relations may readily be obtained by applying overall energy
EXCHANGER
HASZIL ADHA BIN HASLAN
Laporan ini dikemukakan sebagai
memenuhi sebahagian daripada syarat penganugerahan
Ijazah Sarjana Muda Kejuruteraan Mekanikal (Termal-Bendalir)
Fakulti Kejuruteraan Mekanikal
Universiti Teknikal Malaysia Melaka
Mac 2007
‘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 I:………………………………..
Tarikh :………………………………………….
Tandatangan:……………………………………
Nama Penyelia II:………………………………
Tarikh:………………………………………….
ii
“Saya akui laporan ini adalah hasil kerja saya sendiri kecuali ringkasan dan
petikan yang tiap-tiap satunya saya telah jelaskan sumbernya”
Tandatangan :……………………………..
Nama Penulis :……………………………
Tarikh :……………………………………
iii
ACKNOWLEDGEMENT
Alhamdulillah with His Mercy and Blessings, my greatest gratitude to Allah
the Almighty for the chances given to me to complete this project. My first
acknowledgement goes to Mr Shamsul Bahari Bin Azraai, my project supervisor.
Thanks for his tremendous help, advice, inspiration and unending guidance to me
until completing this research. Without him, this project will not exist. The
fundamental idea behind this project is his and he never stop from giving me support
and encouragement in completing this project. Without his valuable guidance, I
would not have been able to achieve the objectivity of this project.
Not forgotten, to my beloved parents, Mr Haslan Bin Hassan and Mrs Nur
Aziah Binti Abdul Latif. Your love and caring really touched me. My sister and
brother, Haszianaliza Binti Haslan and Hasziq Hafify Bin Haslan. Thanks so much
for giving me lifelong encouragement, inspiration and support. May Allah bless all
of you.
Lastly, my acknowledgement go to the technician, Mr. Razmi who have lend
to me some help. My friends who really understand and willing to cooperate with me
in the process of completing this project. Without your supports, I will never go this
far.
iv
ABSTRACT
The research of performance of louvered-fin Compact Heat Exchanger is
done by simulating the problem using Ansys CFX Software. This report will
represent the result from the simulation done by CFX Software along with the
discussion and conclusion. The fluid used in the simulation is air at 25°C and the
speed of the air enter through the inlet is 15m/s. At the end of this study the optimum
geometry that is suitable for mass use will be discussed. This study have found that
the optimum geometry to enhance the heat transfer performance for louvered fin
compact heat exchanger is 29° louver angle and 1.30mm louver pitch. The results of
the optimum geometry of the louvered fin have been validated by study done by
previous academician. The performance of this louvered fin type compact heat
exchanger has been evaluated by monitoring the temperature drop at the fin by the
observing of the temperature contour. The conclusion of this study is that the
louvered fin will enhance the heat transfer performance because of the increasing in
the heat transfer surface area. And when the air is flowing through the louvered fin
array, the flow is louver directed pattern and will cause great temperature drop at the
fin plat. Louver directed flow and axial directed flow will be the main reason in
enhancing the heat transfer performance of the louvered fin compact heat exchanger.
v
ABSTRAK
Kajian tentang kecekapan penukar haba padat bersirip tetingkap dilakukan
dengan mensimulasikan masalah tersebut dengan menggunakan perisian Ansys CFX.
Laporan ini akan memaparkan keputusan daripada simulasi yang dilakukan bersamasama dengan perbincangan tentang keputusan yang diperolehi dan juga kesimpulan
yang dapat dibuat. Bendalir yang digunakan dalam simulasi ini adalah udara pada
25°C dan kelajuan udara tersebut melalui masukan adalah 15m/s. Diakhir kajian ini,
rekabentuk optimum yang sesuai untuk penggunaan secara besar-besaran akan
dibincangkan. Kajian ini telah menemui bahawa geometri optimum untuk
meningkatkan kecekapan penukaran haba untuk penukar haba padat bersirip
tetingkap adalah 29° sudut tetingkap dan 1.30mm jarak tetingkap. Keputusan yang
diperolehi tentang rekabentuk geometri optimum telah di sahkan dengan merujuk
kepada kajian yang telah dilakukan oleh pengkaji sebelum ini. Kecekapan penukar
haba padat bersirip tetingkap telah dinilai dengan melihat kepada pengurangan suhu
yang berlaku pada sirip tersebut dengan melihat kepada kontor suhu. Kesimpulan
yang dapat dibuat daripada kajian ini adalah sirip jenis tetingkap akan dapat
menambahkan kecekapan penukaran haba kerana pertambahan luas permukaan
penukaran haba. Dan apabila udara melalui susunan sirip tetingkap tersebut, aliran
udara tersebut akan menjadi aliran berarahkan tetingkap dan ini akan menyebabkan
kejatuhan suhu yang banyak pada plat sirip tersebut. Aliran berarahkan tetingkap dan
aliran berarahkan paksi menjadi penyebab utama dalam menambahbaikkan
kecekapan penukaran haba pada penukar haba padat bersirip tetingkap.
vi
TABLE OF CONTENT
CHAPTER
TITLE
PENGAKUAN
ACKNOWLDGEMENT
ABSTRACT
ABSTRAK
TABLE OF CONTENT
LIST OF TABLES
LIST OF FIGURES
LIST OF SYMBOLS
LIST OF ABBREVIATIONS
LIST OF APPENDICES
PAGE NO
ii
iii
iv
v
vi
viii
ix
xi
xiii
xiiii
CHAPTER I
INTRODUCTION
1.1 Introduction
1.2 Objectives
1.3 Scopes
1.4 Problem Statement
1
1
2
2
3
CHAPTER II
LITERATURE REVIEW
2.1 Introduction
2.2 Compact Heat Exchanger
2.3 Louvered Fin Compact Heat Exchanger
2.4 Evaluation Performance of Compact Heat
Exchanger
2.4.1 Computational Fluid Dynamics
2.4.2 Log Mean Temperature Different
2.4.3 Calculation of Performance
Parameters
2.5 Flow and Heat Transfer
2.5.1 Reynolds Number
2.5.2 Geometrical Parameters
5
5
6
7
9
CHAPTER III
METHODOLOGY
3.1 Introduction
3.2 Ansys CFX
3.3 Ansys Workbench
3.3.1 Geometry Designing
3.3.2 Meshing
3.4 CFX-Pre
3.4.1 Boundary Conditions
3.4.2 Domain Interface
3.4.3 Solver Control
9
9
10
11
11
13
15
15
15
16
16
17
18
20
20
20
vii
CHAPTER
TITLE
3.5
3.6
CFX-Solver
CFX-Post
3.6.1 Plane Creating
3.6.2 Contour Creating
3.6.3 Streamline Creating
3.6.4 Velocity Vector
PAGE NO
21
21
21
22
22
22
CHAPTER IV
RESULTS & DISCUSSION
4.1 Introduction
4.2 Drawing with Dimension
4.3 Initial State
4.4 Flow Phenomena
4.5 Fin Temperature Distribution
4.6 Louver Effect Angle
4.7 Pressure Distribution
23
23
23
24
25
29
34
37
CHAPTER V
CONCLUSION
5.1 Conclusion
39
39
CHAPTER VI
RECOMMENDATIONS
6.1 Recommendations
40
40
REFERENCES
APPENDIX A: RESULT FOR θ = 22°, L P
= 0.81MM
APPENDIX B: RESULT FOR θ = 29°, L P
= 0.81MM
APPENDIX C: RESULT FOR θ = 32°, L P
= 0.81MM
APPENDIX D: RESULT FOR θ = 22°, L P
= 1.30MM
APPENDIX E: RESULT FOR θ = 29°, L P
= 1.30MM
APPENDIX F: RESULT FOR θ = 32°, L P
= 1.30MM
APPENDIX G: GEOMETRY DRAWING
WITH DIMENSION
41
42
43
44
45
46
47
48
viii
LIST OF TABLES
TABLES
TITLE
PAGE NO
2.1
Geometrical Parameters of CHE’s
14
4.1
Initial Condition Value
24
ix
LIST OF FIGURES
FIGURES TITLE
PAGE NO
1.1
Louvered fin type CHE
2
1.2
An Array of louvered fin with geometrical parameters
3
1.3
Schematic of louvered fin design to be considered
4
2.1
Schematic of Heat Exchanger
5
2.2
Compact Heat Exchanger cores (a) Fin-tube (flat tubes,
6
continuous plate fins). (b) Fin-tube (circular tubes,
continuous plate fins). (c) Plate-fin (single pass). (d)
Plate-fin (multipass)
2.3
Car radiator that use louvered fin CHE
7
2.4
Example of louvered fin CHE
8
2.5
Louver directed flow and axial directed flow
8
2.6
Louvered fin with 22˚ louvered angle, 0.81 louvered pitch
14
2.7
Louvered fin with 29˚ louvered angle, 0.81 louvered pitch
14
2.8
Louvered fin with 32˚ louvered angle, 0.81 louvered pitch
14
3.1
Ansys CFX Flow Chart
16
3.2
Definitions of Boundary Condition
20
4.1
An array of louvered fin for the 22° louver angle and
24
1.30mm louver pitch
4.2
Computed Velocity for (a) Lp = 0.81mm (b) Lp =
26
1.30mm
4.3
Computed Temperature (K) for 29° louvered angle and
27
0.81mm louvered pitch
4.4
Computed Temperature (K) for 29° louvered angle and
1.33mm louvered pitch
28
x
4.5
Static Temperature Contours on fin for (a) θ = 22°, Lp =
30
1.30mm (b) θ = 29°, Lp = 1.3mm
4.6
Fin Temperature against Fin Position
31
4.7
Velocity Vector at the first six arrays for (a) Lp = 0.81mm
32
(b) Lp = 1.30mm
4.8
Velocity Vector after the 7th fin for (a) Lp = 0.81mm (b)
33
Lp = 1.30mm
4.9
Computed Temperature for (a) θ = 22° (b) θ = 32°
35
4.10
Variation of Fin Temperature
36
4.11
Velocity Streamline Used For Flow Simulation
37
4.12
Computed Air Pressure Distribution Around Louvered Fin
38
xi
LIST OF SYMBOLS
q
=
Total Heat Transfer, W
U
=
Overall Heat Transfer Coefficient, W/m².K
Tm
=
Mean Temperature Different, K
f
p
=
Friction Factor
=
Pressure Different, N/m²
=
Density, kg/m³
A
Ac
St
hc
cp
Q
LMTD
To
Ti
Ta
Tf
Re
=
Total Heat Transfer Area, m²
=
Minimum Flow Area, m²
=
Stanton Number
=
Heat Transfer Coefficient, W/m².K
=
Specific Heat at Constant Pressure, kJ/kG.˚C
=
Heat Transfer Rate, W
=
Log Mean Temperature Different
=
Outlet Temperature, K
=
Inlet Temperature, K
=
Air Temperature, K
=
Fin Temperature
=
Reynolds Number
s
=
Mean Fluid Velocity, m/s
L
=
Characteristic Length, m
=
Dynamic Fluid Viscosity, kg/m.s
=
Kinematic Fluid Viscosity, m²/s
=
Louver Pitch, m
=
Hydraulic Diameter, m
=
Fin Length, m
=
Reynolds Number Based On Hydraulic Diameter
=
Louvered Angle
Fp
=
Fin Pitch, m
v
Lp
dh
Ls
Red
xii
Tp
=
Transverse Pitch, m
xiii
LIST OF ABBREVIATIONS
CHE
=
Compact Heat Exchanger
CFD
=
Computational Fluid Dynamics
etc
=
Etcetera
LMTD
=
Log Mean Temperature Different
xiiii
LIST OF APPENDIXES
BIL
TITLE
PAGE NO
A
RESULT FOR θ = 22°, L P = 0.81MM
41
B
RESULT FOR θ = 29°, L P = 0.81MM
42
C
RESULT FOR θ = 32°, L P = 0.81MM
43
D
RESULT FOR θ = 22°, L P = 1.30MM
44
E
RESULT FOR θ = 29°, L P = 1.30MM
45
F
RESULT FOR θ = 32°, L P = 1.30MM
46
G
GEOMETRY DRAWING WITH DIMENSION
47
1
CHAPTER I
INTRODUCTION
This chapter is to introduce the definition of CHE. The purpose, scope and
problem statement for this research is also stated here.
1.1
Introduction
Compact Heat Exchanger is commonly used to enhance the heat transfer rate
in application that involves with high temperature. Generally there are two types of
CHE which are plate-fin type and tube-fin type. CHE is only used for gas-gas or gasliquid application [1]. Plate Fin Compact Heat Exchanger is widely used in gas-gas
application [1]. In this study we will consider plate-fin type with louvered fin.
Nowadays CHE is widely used in various type of industries such as
automotive, aeronautics and astronautics, electric and electronic equipment,
refrigeration and else. CHE is preferred for application that needs heat exchanger
because of its compactness, high-effectiveness, low cost needed, small volume and
low in weight [1].
Because of it is widely used in industries, so the optimization of CHE design
is important. This optimization can be done by using various type of design and
selection of good material to reduce cost but give high effectiveness. There are
several parameters to consider CHE performance such as the outlet temperature, heat
duty involves and pressure drop in the CHE.
2
There are some parameters that could be change in order to evaluate the
performance of CHE. The geometry parameters such as louver pitch, louver angle,
fin pitch and tube pitch. Figure 1.1 shows the louvered fin type of CHE.
Figure 1.1: Louvered fin type CHE [2]
1.2
Objectives
The objectives of this study are stated as below:
To study the effect of louver directed flow and axial directed flow around the
louvered fin array in the heat transfer enhancement
To visualize the pressure, velocity and temperatures profiles around louvered
fin array
To determine the optimum geometry design of louvered fin array for better
heat transfer
1.3
Scopes
The scopes of this study are detailed as below:
3
Study the various geometry design in louvered fin array by varying the value
of louver angle and louver pitch
1.4
Design CFD Louvered fin geometry using CFX software (Design Modeler)
Simulate air flow through louvered fin array
Study the effect of flowing air through the louvered fin array
Problem Statement
The problem that we have to consider here is by comparing the performance
of this type of CHE by varying geometrical parameter such as louvered angle and
louver pitch.
Figure 1.2 shows an array of louvered fin with geometrical parameters in
CHE. This study will only focus the effects of varying the value of louver angle and
louver pitch.
The flow phenomena of the air will be either axial directed flow or louver
directed flow or both. The effects of the flow phenomena will be discussed to
determine the heat transfer efficiency between the flowing air and the louvered fin
array. The value of fin pitch will remain constant at 2.11mm.
Figure 1.2: An Array of louvered fin with geometrical parameters [3]
4
Figure 1.3 shows the schematic of louvered-fin design. The studied air will be
flowing into the louvered fin array from the inlet and will be drawn out through the
outlet. The symmetry part will be transform later in CFX Post to view the real
simulation of the fin array.
Figure 1.3: Schematic of louvered-fin design to be considered [2]
Air flows through a louvered array at air velocity which ranging from 10m/s
to 30m/s. The temperature of the fin is maintained constant at specific temperature.
Ansys CFX Software is used to simulate air flow through a fin array. Finally, the
heat transfer rate by means of temperature drop of the louvered fin will be
determined from observation of velocity, temperature and pressure profile.
5
CHAPTER II
LITERATURE REVIEW
This chapter will discuss about all the equations, theory, past studies and
parameters used in this research.
2.1
Introduction
Heat exchanger is a device that efficiently transfers or exchange heats from a
fluid to another fluid without any contact between those two [4]. Figure 2.1 shows
the simplest heat exchanger.
Figure 2.1: Schematic of Heat Exchanger
Fluid A will cool down Fluid B as both of the fluid moves. The cooling
process is by convection as both of the fluid does not contact with each other because
of the barrier in the middle. All heat exchanger concepts are base on this. What
differs is only the design of each heat exchanger.
6
2.2
Compact Heat Exchanger
The definition of CHE is based on heat exchanger definition but in CHE,
compact is added. And so, based on heat exchanger definition the definition of CHE
will be; a heat exchanger that is compact which means it has small volume, small
size and also low in weight. CHE are typically used when a large heat transfer
surface area per unit volume is desired or at least one of the fluids is a gas [5]. A
CHE can reach an area density higher than 500m2/m3 with respect to 100 m2/m3 200 m2/m3 of the shell and tube heat exchanger [6]. There are generally two types of
CHE which are plate-fin type or tube-fin type [1]. Figure 2.2 shows the example of
plate-fin type CHE.
Figure 2.2: Compact Heat Exchanger cores. (a) Fin-tube(flat tubes, continuous
plate fins). (b) Fin-tube (circular tubes, continuous plate fins). (c)
Plate fin (single pass). (d) Plate fin (multipass) [5]
7
CHE appliances that are commonly used are car radiator or automotive
radiator. In this case of CHE, the heat exchanger is used to cool the engine as the
engine is heated because of the combustion process. Because of the combustion
process of the engine, the engine’s temperature will later increased and to avoid
overheating of the engine, CHE is used where in this case, fluid in the CHE is
commonly called as coolant and this coolant will move around the engine and cooled
it down. The coolant is cooled because of the air flowing through the geometry of the
CHE act as a cooling fluid to the fin array. Figure 2.3 shows the car radiator that use
louvered fin CHE.
Figure 2.3: Car radiator that use louvered fin CHE [7]
Coolant will enter the tube from the coolant inlet tank and as the coolant
moves through the tube, heat transfer happened between the coolant and air. As a
result of this heat transfer process, the coolant will later being cooled down and exit
to the coolant outlet tank.
2.3
Louvered Fin Compact Heat Exchanger
Louvered is defined as an open window liked geometry. So in this type of
CHE, louvered fin CHE means a CHE that have fin geometry like an open window.
To make this matter clearer, Figure 2.4 shows the schematic of louvered fin CHE.
8
Figure 2.4: Example of louvered fin CHE [3]
When this louvered fin was firstly introduced, it was believed that increased
heat transfer was due to added turbulence initiated by flow through the louvered
array [3]. But this theory was later proved wrong by the visualization studies on
scaled up louver design [3]. It was observed that as air passes through the louver, the
flow resulted in two distinct flow directions to be classified: axial (or duct) directed
flow and louver flow. Axial flow occurs when the flow maintains the directions of
the inlet flow. Louver directed flow occurs when the flow was aligned parallel to the
louver [3]. Figure 2.5 shows clearly the two directions indicated in the louvered fin
cross section.
Figure 2.5: Louver directed flow and axial directed flow [3].
The explanation for increased heat transfer came from the realization that
along with the new boundary layer that formed on each of these louver arrays, came
a corresponding high heat transfer coefficient.
9
2.4
Evaluation Performance of Compact Heat Exchanger
There are generally two ways in evaluating the performance of CHE which
are by numerical predictions using Computational Fluid Dynamic or by experimental
measurement where direct experiment was done in order to obtain data needed for
the performance calculation. For this research, CFD method is used in evaluating the
performance of CHE. Software used for this simulation is Ansys CFX.
2.4.1
Computational Fluid Dynamic
CFD is a branch of fluid dynamics where it is use widely to solve and analyze
problem that involve with fluid flow and heat transfer using numerical method and
algorithm [8]. Supercomputer or computer that works together in parallel is used to
solve millions of equation required to simulate interaction of fluid and gasses.
However, whatever value we get from CFD is only approximate solutions until the
results have been validated by experimental results. The basic of solving any CFD
equations is by using the Navier-Stokes equations, which defines any single-phase
fluid flow. These equations will be simplified later by removing terms describing
viscosity to yield the Euler equation. Later, by removing terms describing vorticity it
will yields full potential equations. Finally these equations can be linearized to yield
the linearized potential equation [8].
2.4.2
Log Mean Temperature Different
To design or to predict the performance of a heat exchanger, it is essential to
relate the total heat transfer rate to quantities such as the inlet and outlet fluid
temperatures, the overall heat transfer coefficient, and the total surface area for heat
transfer [5]. Two such relations may readily be obtained by applying overall energy