The Air Engine: Stirling Cycle Power for a Sustainable Future

305 Pages·2007·4.32 MB·English

by  Allan J. Organ

The air engine
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The air engine
Stirling cycle power for a
sustainable future
Allan J. Organ
CRC Press
Boca Raton Boston New York Washington, DC
W
OODHEAD PUBLISHING LIMITED
Cambridge England
iv
Published by Woodhead Publishing Limited, Abington Hall, Abington,
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First published 2007, Woodhead Publishing Limited and CRC Press LLC
© 2007, Woodhead Publishing Limited
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Contents
Notation xi
Preface xvii
Introduction: an invention ahead of its time xxi
Part I A long-overdue reappraisal
1 The famous engine that never was 3
1.1 Status quo 3
1.2 The legend 5
1.3 History reconstructed 6
1.4 Exploratory firing tests 7
1.5 Reassessment 9
1.6 Postscript 10
2 What Carnot efficiency? 13
2.1 Ideal cycle – or perfect alibi 13
2.2 What Carnot efficiency? 14
2.3 Old heat exchanger, new air pre-heater 15
2.4 Resources for first-principles gas path design 16
2.5 A further take on friction factor C – and not the last 22
f
2.6 Beyond the sound barrier 24
2.7 Geometric descriptors for the wire matrix 25
2.8 Inconsistencies uncovered 26
2.9 Résumé 27
3 Counter-flow spiral heat exchanger – Spirex 29
3.1 Heat provision as an integral part of the engine 29
3.2 Thermal analysis 30
3.3 Heat transfer and flow friction correlations 34
3.4 Special case of high NTU* 35
3.5 Numerical integration 35
3.6 Specimen solutions 36
3.7 Discussion 37
vi Contents
4 A high-recovery-ratio combustion chamber 39
4.1 The design problem 39
4.2 Principle 40
4.3 Operation 43
4.4 Materials 43
4.5 Preliminary operating experience 44
4.6 Second design iteration 45
Part II Living with incompressible flow data
5 The regenerator problem brought down to size 55
5.1 Background 55
5.2 Assumptions 55
5.3 Defining equations 57
5.4 Boundary conditions 58
5.5 Flush ratio 59
5.6 Integration algorithm 60
5.7 Specimen temperature profiles 61
5.8 Design criterion for N 61
TCR
5.9 Alternative formulation in corroboration 64
5.10 Conclusions 66
6 The regenerative annulus and shuttle heat transfer 67
6.1 Introduction 67
6.2 Background 68
6.3 Reformulation 69
6.4 Assumptions 69
6.5 Analysis 70
6.6 Cyclic shuttle loss 74
7 The rotating-displacer air engine 77
7.1 Résumé 77
7.2 An alternative 80
7.3 Taylor parameter 84
7.4 A rotating-displacer air engine 85
7.5 Academic design exercise 89
8 The strange case of the self-regulating air engine 94
8.1 Background 94
8.2 Some realities 95
8.3 Constructional details 96
8.4 Exploratory power and torque measurement 99
Contents vii
8.5 ‘Self-regulation’ 101
8.6 Tentative explanation 102
8.7 Conclusions 105
9 Some light on the inner workings of the
‘thermal lag’ engine 107
9.1 The concept 107
9.2 ‘Thermal lag’ engine 108
9.3 Ideal gas process sequence 109
9.4 A detailed model of the thermal processes 110
9.5 Limited heat transfer 120
9.6 Flow losses 123
9.7 A practical ‘thermal lag’ engine 128
9.8 Preliminary operating experience 129
9.9 Afterthought 131
Part III Working with the reality of compressible flow
10 New correlations for old 135
10.1 Right data – wrong application 135
10.2 The misleading C – Re correlation 135
f
10.3 Flow data acknowledging Ma 136
10.4 Dynamic Similarity to the rescue 140
10.5 Farewell to friction factor 142
10.6 The new format 143
10.7 What the new format reveals about ‘incompressible’
flow data 144
10.8 Epitaph 144
11 Regenerator thermal analysis – unfinished business 147
11.1 Regenerator design in context 147
11.2 Assumptions 148
11.3 Modified diffusion law 149
11.4 Numerical solution 151
11.5 Parameters of operation 151
11.6 Pressure and velocity fields 152
11.7 Inevitable asymmetry of flow cycle 153
11.8 Anisotropic matrix 157
11.9 Discussion 159
12 Flow passage geometry 161
12.1 Scope 161
12.2 Symmetrical gauze – flow perpendicular to plane
of weave 162
viii Contents
12.3 Flow parallel to plane of weave 171
12.4 Commercial availability 174
12.5 Specimen isotropic material – metal foam 175
12.6 Résumé 177
13 Beyond the performance envelope 179
13.1 Introduction 179
13.2 Method of Characteristics 180
13.3 ‘Unit process’ of the integration sequence 183
13.4 High-speed operation – the wave engine 184
13.5 Discussion 189
Appendix 190
14 For the sceptic 192
14.1 What does it all add up to? 192
14.2 Flow in the isolated gauze aperture 192
14.3 Defining equations 194
14.4 Radial component of kinetic energy 197
14.5 The not-so-square-weave wire gauze 198
14.6 Kinetic energy of rotation 200
14.7 ‘Real’ (van der Waals) gas 201
14.8 Downstream pressure recovery 201
14.9 Simulated correlation ∆p/p = ∆p/p{Sg, Ma, γ, d m } 202
w w
14.10 Implications for first-principles design 205
14.11 Résumé 206
Part IV Some design considerations
15 Scaling – and the neglected art of back-of-the-
envelope calculation 211
15.1 The overriding objective 211
15.2 Gas path scaling – update 211
15.3 Back-of-the-envelope Ma and Re in the regenerator 214
15.4 Limiting Ma 217
15.5 Compressibility vulnerability chart 217
15.6 Heat transfer 220
15.7 Implications for back-of-envelope design 221
15.8 A ‘screening’ test 224
15.9 The wider rôle of scaling 225
16 ‘How to make a business out of Stirling engines
today’ 226
16.1 Tribal wisdom 226
Contents ix
16.2 From alchemy to appropriate technology 226
16.3 What else has changed? 229
16.4 The VDF-750(aS) 231
16.5 Drive mechanism/kinematics 235
16.6 General mechanical construction 236
16.7 Pressure-balanced seal 249
16.8 Beyond 2006 250
Appendix I Draft patent specification 252
What I claim is … 255
Abstract 256
Appendix II Crank mechanism kinematics 257
Appendix III Equilibrium or ‘temperature-determined’
picture of thermal lag engine 260
Appendix IV Tribal wisdom 261
References and bibliography 262
Index 268