1. High-Efficiency Reciprocating Compressors and Expanders
Luona Yu1, Aly I. Taleb1, Paul Sapin1, Caroline Willich2, Drazen Fabris1
Alexander J. White2, and Christos N. Markides1
1 Clean Energy Processes (CEP) Laboratory, Department of Chemical Engineering, Imperial College London, London SW7 2AZ, U.K.
2 Cambridge University Engineering Department, Trumpington Street, Cambridge CB2 1PZ, U.K.

2. Outline Introduction and Motivation PTES, CAES, etc.
Organic Rankine Cycles/Thermohydraulic Generators
Thermofluidic Oscillators (NIFTE)
Simplified analytical models
Fundamental understanding and design
Gas Springs
Why gas springs?
Experiment
Simulation
Reciprocating-Piston Compressors / Expanders
Loss mechanisms
State of the art
Conclusion

3. Pumped-Thermal Energy Storage (PTES)
from White, Parks & Markides (2013),
Thermodynamic analysis of pumped thermal electricity storage. 
Applied Thermal Engineering, 53(2),
Isentropic Ltd. Valve,
Pat. No

4. Other systems with reciprocating machines/processes
Condenser
Evaporator
Expander
Generator
Pump

5. Reciprocating-piston compressors/expanders
Loss Mechanisms:
Pressure losses across valves at intake and exhaust
Heat losses
Mass leakage
(Mechanical, not considered here)
(Mechanical losses, etc.)

6. Why Gas Springs?
Focus on thermodynamic losses due to thermal-energy exchange processes in reciprocating components

7. Fluid: Lumped, dynamic analytical model
Kornhauser & Smith (1994). Journal of Heat Transfer, 116(3),

8. (And what not to do…)

9. Solid: Conjugation and thermal impedance
(There are also nonlinear conjugate processes that give rise to frequency spreading in the heat exchange)

10. Still, missing information on the HTC/Nusselt number…
Results
“Effect of the solid”:
materials, geometry
Still, missing information on the HTC/Nusselt number…

11. CFD simulation: Velocity field

12. CFD simulation: Temperature field

13. Experimental apparatus
Measurement of 3 bulk parameters:
Pressure P - pressure transducer
Pressure V - rotary sensor
Temperature T - ultrasonic sensor

14. Experimental results: P, V, T

15. Experimental results: P-V diagram
Only unknown

16. Comparison CFD – Model – Experiment

17. Reciprocating-piston expanders: Steady-state models

18. Lumped, dynamic analytical model
Imposed motion:
Perfect gas:
Mass conservation:
Energy conservation:

19. Model results: P-V indicator diagrams

20. Model results: Heat transfer
Newton’s law:
Complex Nusselt:
Still working on this and need insight from CFD/experiments…

21. Model results: Bringing it all together
Pressure
Thermal

22. Conclusions Interest in reciprocating compression/expansion machines
Significant losses in system performance from these processes
Dynamic/unsteady heat transfer process
Conjugate (and nonlinear) heat transfer effects
Valve losses and coupling to heat transfer
Theory, CFD and experimental tools aimed at:
Understanding underlying loss mechanisms/performance
Designing components and systems