Effects of critical temperature, critical pressure and dryness of working fluids on the performance of the transcritical organic rankine cycle

Thermodynamic properties of working fluids have significant effects on the system performance of the transcritical organic Rankine cycle, and the optimal working fluid is related to the heat source temperature. In this paper, both separate and combined effects of the critical temperature (Tcri), critical pressure (Pcri) and dryness (ξ) of working fluids on the performance of TORCs were investigated under different heat source temperatures. The trends in variation of maximum net power output (Wmax) based on the increase of the critical temperatures of working fluids were also investigated. The results indicated that a lower Tcri of working fluids would lead to an increase in the expander’s outlet temperature and a worse thermal match in the condenser. However, a higher Tcri would result an increase in the heat source outlet temperature and a worse thermal match in the vapor generator. In addition, a higher Pcri would lead to an uneven temperature curve for the working fluid and a worse thermal match in the vapor generator. A larger ξ would result in high superheat at the condensation pressure and a worse thermal match in the condenser. Working fluids with suitable Tcri, lower Pcri and lower ξ could achieve better net power output performance. •The lower and higher critical temperature lead to worse thermal match in the vapor generator.•The higher critical pressure results in the uneven temperature curve in the vapor generator.•The larger dryness of working fluid leads to the higher superheat degree in the condenser.