Modelling the impact of low-GWP fluids as substitutes of R134a into a kW-size reciprocating piston expander

In recent decades, concern over greenhouse gases grown to include refrigerant emissions, thus motivating the development of new alternative low-global warming potential fluids. In this paper the replacement of R134a with its alternatives, as working fluids in a kW-size reciprocating piston expander, is investigated. To this purpose, a previously developed semi-empirical model of the expander has been adapted to accommodate the change of the working fluid. A semi-empirical model of a gear pump has been conceived to be integrated with the expander model with the purpose of simulating volumetric machines real operation into an ORC cycle. Models parameters related to the thermo-fluid-dynamic properties of the working fluids were updated compared to the original values calibrated and validated over R134a by means of an extensive experimental campaign. The comparison of expander performance among analyzed refrigerants identifies R1234ze(E) as the best candidate to maximize the electric power output while minimizing the environmental impact.