Engelhardt, Andreas (2010) Investigation of several critical issues in screen mesh heat pipe ...

380 Pages·2017·13.99 MB·English

by  Christine Middleton

Investigation Of Several Critical
Issues In Screen Mesh Heat Pipe
Manufacturing And Operation

Andreas Engelhardt, MEng (Hons),
Dipl. Ing. (FH)

Thesis submitted to

for the Degree of Doctor of Philosophy

February 2010
Abstract PhD Thesis Andreas Engelhardt

The PhD thesis with the title “Investigation of several critical issues in screen
mesh heat pipe manufacturing and operation” presented hereafter describes
work carried out in four main areas. Initially the relevant literature is reviewed
and presented, followed by the presentation of theoretical work regarding
screen mesh heat pipe fill calculations, heat pipe processing and an
investigation into the capillary or lifting height for screen mesh heat pipes.
Further, the possibility of tailoring screen mesh heat pipes towards certain
applications was investigated and it was found that further work is required in
this area to allow a conclusive judgement whether a coarser or finer wick at
the wall provides a distinguish advantage over two wraps of a medium coarse
type. Within this approach a calculation method for the determination of the
optimum working fluid fill of a screen mesh heat pipe based on geometrical
parameters of the wick was developed and successfully implemented for the
production of the later tested samples.
The investigation into the effects of bending on the heat pipe performance,
both using single phase flow CFD as well as experimentation, was performed
using five different geometrical cases, each with five samples. These were
tested in order to minimise the effects of sample variation. The test cases
investigated contained the deformation angles of 0° (straight), 45°, 90°, 135°
and 180°. During all test cases the orientation of the samples was kept
constant at 0° to minimise additional influences like the effects of gravity on
the reduction of available power handling capability. The test results show in
deviation from CFD results that screen mesh heat pipe performance is
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significantly affected when bends are introduced and the reduction in power
handling capability can be up to nearly 50% of a straight heat pipe value.
Finally this thesis advances into the field of water heat pipe freeze thaw and
the possibility of screen mesh heat pipes with changed shapes to withstand
multiple freeze thaw cycles. It was found that correctly engineered screen
mesh copper water heat pipes can be used in applications where they are
subjected to multiple freeze thaw cycles. The fluid charge for water heat pipes
subjected to these conditions needs to be adjusted in such a way, that
accumulation of working fluid in certain areas, regardless of orientation or
process variation during filling, is avoided.

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ACKNOWLEDGEMENTS

The author would like to take the opportunity to thank Xudong Zhao of the
School of Built Environment at the University of Nottingham and David
Mullen of Thermacore Europe for their continuous support and offering of
advice when required over the entire duration of this PhD.

Further thanks have to go to Saffa Riffat of the School of Built Environment at
the University of Nottingham and Kevin Lynn of Thermacore Europe for their
understanding and their support during the period of the work conducted.

Since most of the experimental work was carried out at the sponsoring
company, Thermacore Europe, an additional large thank you has to go to all
the co-workers there for their support and help. But a special thank you has to
go to Ian Davies for the production of the test samples and advice when
required. Without his knowledge and skills the production of test samples with
certain characteristics would have been more time consuming and less
successful then it was.

Last but not least the author would like to thank the EPSRC (Engineering and
Physical Sciences Research Council), which made this PhD thesis possible
through their financial support under the Grant number EP/P501733/1.
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COPYWRITER DECLARATION

I declare that this thesis is the result of my own work and has not, whether in
the same or a different form, been presented to this or any other university in
support of an application for any degree other than that of which I am now a
candidate.
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TABLE OF CONTENTS

Abstract i
Acknowledgements iii
Copyright Declaration iv
Nomenclature xi
List of Figures xv
List of Tables xxiii

CHAPTER 1 – INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 DESCRIPTION OF THE RESEARCH . . . . . . . . . . . . . . . . . . . . . 4
1.3 WORK INVOLVED IN THE RESEARCH. . . . . . . . . . . . . . . . . . . 7

CHAPTER 2 - LITERATURE REVIEW HEAT PIPE
TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.1 HEAT PIPE CONSTRUCTION . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.1.1 Container Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.1.2 Working Fluids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.1.3 Performance Limits Of Heat Pipes . . . . . . . . . . . . . . . . . . 24
2.1.4 Types Of Heat Pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.2 HEAT PIPE APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2.2.1 Typical Heat Pipe Applications . . . . . . . . . . . . . . . . . . . . . 36
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2.2.2 Detail Focused Investigation Of Heat Pipe Behaviour (Start-
Up; Freeze- Thaw) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
2.3 MATHEMATICAL MODELLING OF HEAT PIPES . . . . . . . . 44
2.3.1 General Approaches To Heat Pipe Performance Modelling
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
2.3.2 Heat Pipe Modelling Using Commercial CFD Codes . . . 52
2.3.3 Modelling Of Multiphase Flow Using Commercial CFD
Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
2.3.4 Numerical Investigation Of The Effects Of Bends And
Shape-Changes In Related Areas . . . . . . . . . . . . . . . . . . . . 57
2.4 EXPERIMENTAL TECHNIQUES WITH FOCUS ON HEAT
PIPES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
2.4.1 Test Rig Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
2.4.2 Temperature Measurement Techniques . . . . . . . . . . . . . . 66
2.4.3 Previous Experimental Work On The Subject Of Bending .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
2.5 LATEST TECHNOLOGY DEVELOPMENTS IN THE HEAT
PIPE AREA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
2.6 SCOPE OF THE WORK OF THIS THESIS AND ITS NOVEL
ASPECTS TO THE SCIENTIFIC COMMUNITY . . . . . . . . . . . .70
2.7 AREAS OF FURTHER RESEARCH REQUIRED . . . . . . . . . . . 73

CHAPTER 3 – INVESTIGATIONS OF HEAT PIPE FILLING
AND VENTING TECHNIQUES . . . . . . . . . . . . . . . . . . . . . . . 75
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3.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
3.2 MESH HEAT PIPE FILL CALCULATIONS . . . . . . . . . . . . . . . 77
3.2.1 Weight Of Water Required For Generating Saturated
Steam Within The Vapour Space . . . . . . . . . . . . . . . . . . . . 80
3.2.2 Mathematical Foundations Of The Porosity Calculation For
Screen Meshes Used As Heat Pipe Wicks . . . . . . . . . . . . . 83
3.2.3 Development And Implementation Of VB Based Screen
Mesh Wick Heat Pipe Fill Calculation Software . . . . . . . . 88
3.3 ANALYTICAL INVESTIGATION OF THE CAPILLARY OR
LIFTING HEIGHT FOR DIFFERENT WICK STRUCTURES . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
3.4 VENTING OR PROCESSING OF HEAT PIPES. . . . . . . . . . . . 100
3.4.1 Venting Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100
3.4.2 Venting Technique Applied To The Heat Pipes Used For
This Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
3.4.3 Most Common Venting Failure Modes . . . . . . . . . . . . . . 107
3.5 SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . .113

CHAPTER 4 – INVESTIGATION OF THE USE OF
DISSIMILAR SCREEN MESHES AS HEAT PIPE WICKS . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 115
4.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
4.2 DISSIMILAR SCREEN MESH WICK HEAT PIPE
INVESTIGATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
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4.2.1 Design And Manufacturing Considerations For Dissimilar
Mesh Wick Heat Pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
4.2.2 Experimental Results And Analysis Of Dissimilar Mesh
Wick Heat Pipe Investigations. . . . . . . . . . . . . . . . . . . . . . 121
4.3 CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

CHAPTER 5 – BENDING OF SCREEN WICK HEAT PIPES .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
5.1 FLOW SIMULATION THROUGH PIPE BENDS USING CFD
SOFTWARE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131
5.1.1 Introduction Into Separate Phase Modelling Theory . . . 132
5.1.2 Separate Phase Modelling . . . . . . . . . . . . . . . . . . . . . . . . . .134
5.1.3 Calculation Of Flow Parameters . . . . . . . . . . . . . . . . . . . .135
5.1.3.1 Liquid Film Height Calculation . . . . . . . . . . . . . . . . . . . . 135
5.1.3.2 Reynolds Number Calculation . . . . . . . . . . . . . . . . . . . . . .137
5.1.4 Theory Used For Obtaining The CFD Settings . . . . . . . . 141
5.1.4.1 Flow Models and Boundary Conditions used . . . . . . . . . . 145

5.1.4.2 Settings as per Heat Pipe Theory disregarding Validity of
Mathematical Models for certain Flow Conditions . . . . . .145
5.1.5 CFD Results And Result Plots . . . . . . . . . . . . . . . . . . . . . . 150
5.1.5.1 Results And Plots From Runs Of Annular Flow Per Heat
Pipe Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
5.1.5.2 Results And Plots From Runs Of Full Pipe Flow At Flow
Velocity From Heat Pipe Theory. . . . . . . . . . . . . . . . . . . . . 152
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5.1.6 Creating The Link Between The Pressure Results From The
CFD Model And The Experimental Results . . . . . . . . . . 155
5.2 TEST RIG DESIGN FOR BENT HEAT PIPES . . . . . . . . . . . . . 161
5.2.1 Purpose Of The Test Rig And Introduction To The Principle
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
5.2.2 Instrumentation Used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
5.2.3 Water Side And Cold Plates . . . . . . . . . . . . . . . . . . . . . . . 164
5.2.4 Test Side And Heater Blocks . . . . . . . . . . . . . . . . . . . . . . .166
5.2.5 Adaptability For Different Heat Pipe Diameters And
Shapes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
5.3 EXPERIMENTAL TRIALS WITH BENT HEAT PIPES . . . . . 169
5.3.1 Experimental Methodology . . . . . . . . . . . . . . . . . . . . . . . 170
5.3.2 Figures Of Experimental Procedure For One Single Heat
Pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
172
5.3.3 Failure Mode Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
5.3.4 Analysis Of The Thermal Load Transmitted By The Heat
Pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
5.3.5 Comparison Of The CFD Simulation Results To
Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
5.4 DEVELOPMENT OF A MATHEMATICAL APPROXIMATION
FOR PERFORMANCE LOSSES DUE TO THE BEND ANGLE . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
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