Current concerns with climate change have resulted in greatly increased interest in power recovery from low grade heat sources. This includes both hot fluid streams which can be expanded directly to produce mechanical power and those which act as a source of heat to closed cycle power generation systems. Power recovery from low grate heat by means of screw expanders with a generalised overview of how best to recover power from such sources, based on thermodynamic considerations, which differs to the approach used in classical thermodynamics textbooks and which includes an introductory description of the types of working fluid that are used in systems used to recover power from such sources and the criteria that must be taken into account in their selection. This is followed by a description of the mathematical modelling of twin screw machine geometry. The modelling of the thermodynamics and fluid flow through such machines is then given, together with how this is used to predict their performance. Finally a detailed description is given of systems currently used or projected both for direct expansion of the source fluid and by recovery of heat from it, which includes those which are particularly suited to the use of screw expanders in place of turbines.
- A novel generalised approach to the thermodynamics of power recovery from low grade heat systems
- Gives criteria for working fluid selection
- Provides details of, and how to model, screw expander geometry
- Details how to estimate screw expander performance
- Surveys types of system used for power recovery from low grade heat and where this can be improved by the use of screw expanders.
Current concerns with climate change have resulted in greatly increased interest in power recovery from low grade heat sources. This includes both hot fluid streams which can be expanded directly to produce mechanical power and those which act as a source of heat to closed cycle power generation systems. Power recovery from low grate heat by means of screw expanders with a generalised overview of how best to recover power from such sources, based on thermodynamic considerations, which differs to the approach used in classical thermodynamics textbooks and which includes an introductory description of the types of working fluid that are used in systems used to recover power from such sources and the criteria that must be taken into account in their selection. This is followed by a description of the mathematical modelling of twin screw machine geometry. The modelling of the thermodynamics and fluid flow through such machines is then given, together with how this is used to predict their performance. Finally a detailed description is given of systems currently used or projected both for direct expansion of the source fluid and by recovery of heat from it, which includes those which are particularly suited to the use of screw expanders in place of turbines. A novel generalised approach to the thermodynamics of power recovery from low grade heat systems Gives criteria for working fluid selection Provides details of, and how to model, screw expander geometry Details how to estimate screw expander performance Surveys types of system used for power recovery from low grade heat and where this can be improved by the use of screw expanders.
List of figures
1.1 Types of positive displacement machines 3
1.2 Assembled view of a screw expander 4
1.3 Exploded view of a screw expander 4
1.4 Principle of operation of a screw expander 5
1.5 Illustration of a blow-hole 7
1.6 Oil-flooded and oil-free compressors 9
1.7 Oil-free compressor/expander lubrication system 11
1.8 Oil-injected expander lubrication system 12
2.1 Internal combustion engine 14
2.2 Power plant receiving heat from process steam 17
2.3 Power plant receiving heat from a hot fluid 18
2.4 Infinitesimal heat engine 20
2.5 Temperature–entropy diagram for ideal recovery of power from a hot fluid stream 20
2.6 Ideal cycles between a finite heat source and an infinite heat sink 21
2.7 Power plant receiving heat from and rejecting to external fluid streams 22
2.8 Ideal cycles between a finite heat source and a finite heat sink 23
2.9 Comparison of Carnot cycle with ideal trilateral cycle 24
2.10 The effect of the fluid exit temperature on ideal efficiency and power output 26
2.11 Pressure–volume diagrams for power plant cycles based on flow and non-flow processes 27
2.12 The effect of work ratio on practical cycle efficiency 30
2.13 The ideal trilateral cycle using a perfect gas 31
2.14 Comparison of ideal and achievable trilateral cycle efficiency using a perfect gas 32
2.15 The ideal quadlateral cycle using a perfect gas 33
2.16 Comparison of ideal and achievable quadlateral cycle efficiencies using a perfect gas 33
2.17 Ideal trilateral and quadlateral cycles matched to the heat source and sink 35
2.18 Ideal Stirling cycle on p–V and T–s coordinates 36
2.19 Heat transfer as a function of temperature for a single-phase heating medium 37
2.20 Temperature–entropy diagram of ideal Stirling cycle with heat source and sink 38
2.21 Comparison of performance of ideal quadlateral and Stirling cycles using a perfect gas 39
2.22 Comparison of performance of practical quadlateral and Stirling cycles 40
2.23 Simple Rankine cycle system using steam as the working fluid 42
2.24 Comparison of ideal steam Rankine and ideal gas cycles 43
2.25 Comparison of practical steam Rankine and practical gas cycles 43
2.26 Trilateral flash cycle (TFC) system and components 44
2.27 Comparison of performance of trilateral flash cycles (TFC) and ideal trilateral cycle 45
2.28 TFC temperature matching to a limited minimum temperature heat source 47
2.29 Improving the Rankine cycle matching to its heat source 47
2.30 Temperature–entropy diagram for various working fluids 49
2.31 Matching the cycle to the heat source with saturated, superheated and supercritical cycles 50
2.32 Improving the cycle efficiency with a recuperative heat exchanger 52
2.33 The relationship between saturated vapour pressure and temperature for pure fluids 55
2.34 Common working fluids with a saturated liquid line slope approximately equal to that of water 56
3.2 Most popular screw compressor rotors 65
3.3 Coordinate system of helical gears with non-parallel and non-intersecting axes 67
3.4 Example of a gate rotor enveloped by its main counterpart using direct digital simulation 72
3.5 Screw expander rotors with parallel shafts and their coordinate systems 72
3.6 Demonstrator profile with its details 77
3.7 City University ‘N’ profile details 79
3.8 ‘N’ rotors compared with Sigma, SRM ‘D’ and Cyclon rotors 80
3.10 Rotor manufacturing tools: hobbing tool and milling/grinding tool 86
3.11 Rotor and tool coordinate systems 88
4.1 An example of volumetric change with rotation in a screw expander 94
4.2 A typical estimated p–V diagram of a two-phase expansion process 114
4.5 Pressure forces acting on screw machine rotors 117
5.1 General layout of process fluid bearing lubrication for closed-cycle organic fluid power system 130
5.2 General layout of expander-generator within a larger system 131
5.3 A 100 kWe industrial process steam screw expander 134
5.4 Single flash steam system for geothermal power generation 135
5.5 Double flash steam system for geothermal power generation 135
5.6 Single flash steam system with screw expander 136
5.7 Double flash steam system with single screw expander 137
5.8 Basic vapour compression refrigeration system 139
5.9 Vapour compression refrigeration system with economiser 140
5.10 An expressor in a vapour compression system 141
5.11 The effect of the wrap angle on the trapped volume 142
5.12 Expansion and recompression in one pair of rotors 143
5.13 The expressor as a single rotor pair unit 144
5.15 Prototype expressor units 145
5.16 Expressor rotor pair for separating the working chamber into two sections 146
5.17 Expressor rotor profile 146
5.18 Cross-section of an expressor with separate expansion and compression working chambers 147
5.19 Expressor casing with separate expansion and compression working chambers 147
5.20 Screw compressor-expander 148
5.21 Carbon dioxide refrigeration system 150
5.23 Estimated performance improvement in a subcritical CO2 system using a compressor expander 151
5.24 Prototype fuel cell compressor-expander components 152
5.25 Fuel cell compressor-expander revised casing design 152
5.26 Saturated Rankine cycle system with organic working fluid 155
5.27 Wet organic Rankine cycle (WORC) 156
5.28 A 50 kWe screw expander-driven industrial WORC system 157
5.29 Trilateral flash cycle (TFC) 157
5.30 Higher temperature two-phase expansion cycle system 159
5.31 Recuperated higher temperature two-phase expansion system 160
| Erscheint lt. Verlag | 15.8.2014 |
|---|---|
| Sprache | englisch |
| Themenwelt | Naturwissenschaften ► Physik / Astronomie |
| Technik ► Maschinenbau | |
| ISBN-10 | 1-78242-190-4 / 1782421904 |
| ISBN-13 | 978-1-78242-190-0 / 9781782421900 |
| Haben Sie eine Frage zum Produkt? |
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