Development of selection criteria of zeotropic mixtures as working fluids for the trans-critical organic Rankine cycle

The trans-critical organic Rankine cycle (TCORC) can achieve a better thermal match in the heating process of the working fluid compared to the subcritical cycle. By using zeotropic mixtures as working fluids, the thermal match in the cooling process can be further optimized, reducing the system's irreversibility. As the selection criteria are not systematically formulated, screening zeotropic mixtures for the TCORC is challenging. In this work, the thermodynamic and thermo-economic analysis was carried out to investigate how the thermal match in the heating/cooling processes affects the system performance, which is represented by the overall exergy efficiency and the levelized energy cost. Results show that the mixture's critical temperature is a key factor influencing the system performance. Then, the mixtures having a proper condensation temperature glide can further improve the system performance. The thermo-economic analysis shows that the mixtures selected according to these criteria can also provide better thermo-economic performance, although the heat exchanger area has been enlarged during the improvement of the thermal match in heat exchangers.