Influence of thermophysical properties of working fluids on the performance of a double-stage organic flash cycle with an evaporator and an ejector

This paper presents a comparative study on the net power output between the double-stage organic flash cycle (DOFC) and DOFC with an evaporator and an ejector (EE-DOFC). It further investigates the influence of the critical parameters and the ratio of the latent heat of vaporization to the specific heat (γ/cp) of the working fluid on the EE-DOFC performance. The results demonstrate that substituting the high- and low-stage throttle valves in the DOFC with an evaporator and an ejector can significantly reduce irreversible losses during throttling, while concurrently lowering pump irreversibility and heat source exergy destruction. The EE-DOFC exhibits substantial variation in power output enhancement depending on the working fluid, with improvements ranging from 12.7 % to 84.6 %. The thermophysical properties of the working fluid significantly influence EE-DOFC performance enhancement. Specifically, a reduced critical pressure lowers the evaporation pressure, while a decreased γ/cp improves ejector entrainment ratio, both contributing to system performance improvement. Working fluids with higher critical temperature or lower critical pressure generally exhibit better thermal performance. This performance advantage is further enhanced when the working fluid exhibits a lower γ/cp, leading to a synergistic enhancement in EE-DOFC performance.