Modelling the performance of a scroll expander for small organic Rankine cycles when changing the working fluid

A scroll expander modelling procedure is proposed in this work. Based on an original semi-empirical model present in literature for an open-drive scroll expander operating with HCFC-123, re-calculating some specific parameters allows to improve the simulation procedure that is now generalized to be used with fluids other than HCFC-123. low rates and shaft power outputs are calculated and compared for some working fluids, highlighting the differences in expander performance. Considering the scroll expander is not an adiabatic machine, heat transfer effects are discussed as well. The scroll expander model is later used to calculate the efficiency of a simple organic Rankine cycle, with the power output of the expander fixed at 1, 1.5 and 2 kW. Although the proper working fluid should be selected according to the specific heat source, the assessment of the expander potential with substituting fluids suggests that better cycle efficiency seems to be possible with HCFC-141b, as reported in other literature works. However, considering HCFC phase-out regulations, the results of calculations with third- and fourth-generation refrigerants are detailed as well. In particular, using HCFO-1233zd(E) as a working fluid brings about a limited efficiency penalty.