Advances in thermal design of heat exchangers : a numerical approach : direct-sizing, step-wise rating, and transients

530 Pages·21.414 MB·English

by  Eric M Smith

Advances in Thermal Design of
Heat Exchangers
A Numerical Approach:
Direct-sizing, step-wise rating, and transients
Eric M Smith
Professional
John Wiley & Sons, Ltd
AdvancesinThermalDesignofHeatExchangers:ANumericalApproach:Direct-sizing,step-wise
rating,andtransients.EricM.Smith
Copyright2005JohnWiley&Sons,Ltd.ISBN:0-470-01616-7
Advances in Thermal Design of Heat Exchangers
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Advances in Thermal Design of
Heat Exchangers
A Numerical Approach:
Direct-sizing, step-wise rating, and transients
Eric M Smith
Professional
John Wiley & Sons, Ltd
Copyright © 2005 Eric M. Smith
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A catalogue record for this book is available from the British Library
ISBN 1-86058-461-6
Typeset by Techset Composition Limited, Salisbury, Wiltshire
Printed and bound in Great Britain by Antony Rowe, Ltd, Chippenham, Wiltshire
This book is printed on acid-free paper responsibly manufactured from sustainable forestry
in which at least two trees are planted for each one used for paper production.
This volume is dedicated to Dorothy my wife
for her unfailing kindness and understanding,
and to my three sons for their consistent support.
'If you can build hotter or colder than anyone else,
If you can build higher or faster than anyone else,
If you can build deeper or stronger than anyone else,
If...
Then, in principle, you can solve all the other problems in between.'
(Attributed to Sir Monty Finniston, FRS)
Contents
Preface xxiii
Chapter 1 Classification 1
1.1 Class definition 1
1.2 Exclusions and extensions 1
1.3 Helical-tube, multi-start coil 3
1.4 Plate-fin exchangers 5
1.5 RODbaffle 6
1.6 Helically twisted flattened tube 7
1.7 Spirally wire-wrapped 7
1.8 Bayonet tube 8
1.9 Wire-woven heat exchangers 9
1.10 Porous matrix heat exchangers 9
1.11 Some possible applications 10
Chapter 2 Fundamentals 19
2.1 Simple temperature distributions 19
2.2 Log mean temperature difference 21
2.3 LMTD-Ntu rating problem 23
2.4 LMTD-Ntu sizing problem 25
2.5 Link between Ntu values and LMTD 26
2.6 The 'theta' methods 26
2.7 Effectiveness and number of transfer units 27
2.8 e-Ntu rating problem 31
2.9 e-Ntu sizing problem 32
2.10 Comparison of LMTD-Ntu
and e-Ntu approaches 33
2.11 Sizing when Q is not specified 34
2.12 Optimum temperature profiles in
contraflow 35
2.13 Optimum pressure losses in contraflow 40
2.14 Compactness and performance 42
2.15 Required values of Ntu in cryogenics 42
2.16 To dig deeper 45
2.17 Dimensionless groups 47
Chapter 3 Steady-State Temperature Profiles 59
3.1 Linear temperature profiles in contraflow 59
3.2 General cases of contraflow and parallel flow 61
viii Contents
3.3 Condensation and evaporation 66
3.4 Longitudinal conduction in contraflow 67
3.5 Mean temperature difference in unmixed crossflow 74
3.6 Extension to two-pass unmixed crossflow 79
3.7 Involute-curved plate-fin exchangers 82
3.8 Longitudinal conduction in one-pass unmixed crossflow 83
3.9 Determined and undetermined crossflow 90
3.10 Possible optimization criteria 92
3.11 Cautionary remark about core pressure loss 92
3.12 Mean temperature difference in complex arrangements 93
3.13 Exergy destruction 94
Chapter 4 Direct-Sizing of Plate-Fin Exchangers 99
4.1 Exchanger lay-up 99
4.2 Plate-fin surface geometries 101
4.3 Flow-friction and heat-transfer correlations 103
4.4 Rating and direct-sizing design software 103
4.5 Direct-sizing of an unmixed crossflow exchanger 106
4.6 Concept of direct-sizing in contraflow 110
4.7 Direct-sizing of a contraflow exchanger 113
4.8 Best of rectangular and triangular ducts 120
4.9 Best small, plain rectangular duct 125
4.10 Fine-tuning of ROSF surfaces 127
4.11 Overview of surface performance 127
4.12 Headers and flow distribution 130
4.13 Multi-stream design (cryogenics) 130
4.14 Buffer zone or leakage plate 'sandwich' 130
4.15 Consistency in design methods 132
4.16 Geometry of rectangular offset strip fins 133
4.17 Compact fin surfaces generally 138
4.18 Conclusions 138
Chapter 5 Direct-Sizing of Helical-Tube Exchangers 143
5.1 Design framework 143
5.2 Consistent geometry 145
5.3 Simplified geometry 151
5.4 Thermal design 153
5.5 Completion of the design 159
5.6 Thermal design results for t/d = 1.346 162
5.7 Fine tuning 163
5.8 Design for curved tubes 168
5.9 Discussion 172
5.10 Part-load operation with by-pass control 174
5.11 Conclusions 174
Contents ix
Chapter 6 Direct-Sizing of Bayonet-Tube Exchangers 177
6.1 Isothermal shell-side conditions 177
6.2 Evaporation 178
6.3 Condensation 189
6.4 Design illustration 190
6.5 Non-isothermal shell-side conditions 191
6.6 Special explicit case 194
6.7 Explicit solution 196
6.8 General numerical solutions 199
6.9 Pressure loss 201
6.10 Conclusions 204
Chapter 7 Direct-Sizing of RODbaffle Exchangers 207
7.1 Design framework 207
7.2 Configuration of the RODbaffle exchanger 208
7.3 Approach to direct-sizing 208
7.4 Flow areas 209
7.5 Characteristic dimensions 209
7.6 Design correlations 210
7.7 Reynolds numbers 211
7.8 Heat transfer 211
7.9 Pressure loss tube-side 213
7.10 Pressure loss shell-side 214
7.11 Direct-sizing 215
7.12 Tube-bundle diameter 217
7.13 Practical design 217
7.14 Generalized correlations 220
7.15 Recommendations 222
7.16 Other shell-and-tube designs 222
7.17 Conclusions 224
Chapter 8 Exergy Loss and Pressure Loss 229
Exergy loss 229
8.1 Objective 229
8.2 Historical development 230
8.3 Exergy change for any flow process 231
8.4 Exergy loss for any heat exchangers 233
8.5 Contraflow exchangers 234
8.6 Dependence of exergy loss number on absolute
temperature level 236
8.7 Performance of cryogenic plant 238
8.8 Allowing for leakage 240
8.9 Commercial considerations 242
8.10 Conclusions 242