Performance analyses of transcritical organic Rankine cycles with large variations of the thermophysical properties in the pseudocritical region

This study analyzed the influence of the thermophysical properties variations in the pseudocritical region on the transcritical organic Rankine cycles (ORCs) performance. An optimization method is proposed using the net power output, the thermal efficiency and the total vapor generator area as indicators. The effect of the turbine inlet temperature and the vapor generation pressure is investigated for transcritical ORCs. The variations of the vapor generator area are discussed based on the thermophysical property changes. The results show that the total vapor generator area varies with the turbine inlet temperature along an N-shaped curve. For any heat source temperature, the suitable working fluid should have a pronounced N-shaped curve of the total vapor generator area to guarantee the existence of the optimal parameter region in which selected indicators are optimized. This provides a working fluid selection criterion for heat sources of different temperatures. The analysis simplifies the selections of the operating parameters and the working fluids.