Thermodynamic performance evaluation of transcritical carbon dioxide refrigeration cycle integrated with thermoelectric subcooler and expander

New configurations of transcritical CO2 refrigeration cycle combined with a thermoelectric (TE) subcooler and an expander (TES+EXPHM and TES+EXPML) are proposed. The expander can operate between the high-pressure to the vessel pressure, or from vessel pressure to evaporation pressure. A power system is utilized to balance and supply power to thermoelectric subcooler and compressor. Thermodynamic performance optimizations and analyses are presented. Comparisons are carried out with the BASE, EXPHM, EXPML, and TES cycles. The results show that the coefficient of performance (COP) improvement is more notable when the expander is installed between the liquid receiver and the evaporator. Maximum COP is obtained for the new cycles with a simultaneous optimization of discharge pressure and subcooling temperature. The new proposed TES+EXPML cycle shows an excellent and steady performance than other cycles. It operates not only with the highest COP, but also the lowest discharge pressure. Under the working conditions of high gas cooler outlet temperature or low evaporation temperature, the merits of COP improvement and discharge pressure reduction are more prominent. The new cycle is more suitable for the hot regions where the CO2 can not be sufficiently subcooled or the refrigerated space operates at low evaporation temperature.