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.

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

Pumped-Thermal Energy Storage (PTES) from White, Parks & Markides (2013), Thermodynamic analysis of pumped thermal electricity storage.  Applied Thermal Engineering, 53(2), 291-298. Isentropic Ltd. Valve, Pat. No. 20100308250

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

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.)

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

Fluid: Lumped, dynamic analytical model Kornhauser & Smith (1994). Journal of Heat Transfer, 116(3), 536-542.

(And what not to do…)

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

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

CFD simulation: Velocity field

CFD simulation: Temperature field

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

Experimental results: P, V, T  

Experimental results: P-V diagram Only unknown

Comparison CFD – Model – Experiment

Reciprocating-piston expanders: Steady-state models

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

Model results: P-V indicator diagrams

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

Model results: Bringing it all together Pressure Thermal

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