Lumped dynamic analysis and design of a high-performance reciprocating-piston expander

A spatially - lumped dynamic model of a reciprocating - piston expander is presented in this paper. The model accounts for the three main loss mechanisms in realistic piston machines, namely: pressure losses through the intake and exhaust valves, heat transfer between the gas and the surrounding cylinder walls, and the mass leakage between the compression/expansion chamber and the crankcase throu gh the piston rings. The model also accounts for real - gas effects with the fluid properties calculated from t he NIST database using REFPROP. The numerical calculations are first compared with experimental pressure - volume - temperature data obtained on a cust om reciprocating - piston gas spring over a r ange of oscillation frequencies. The comparison between numerical and experimental results shows good agreement. It also allows the most accurate heat transfer correlation to be selected for calculating the gas - to - wall in - cylinder heat transfer. The semi - heuristic modelling tool is then used to design an expander for specific pressure ratio s and mass flowrate, and to predict the thermodynamic performance of the piston device over a range of part - load conditions