Thermodynamic analysis of a modified transcritical CO2 two-stage compression dual-temperature refrigeration cycle with an ejector

Abstract

In this paper, a modified transcritical CO₂ two-stage compression dual-temperature refrigeration cycle with an ejector is proposed. The thermodynamic analysis based on energy and exergy is conducted, discussing the effects of discharge pressure, gas cooler outlet temperature, evaporation temperature, and refrigeration capacity ratio. The particle swarm optimization algorithm is employed to determine the optimal discharge pressure. The results indicate that the modified cycle outperforms the basic cycle, achieving a maximum COP and exergy efficiency improvement of 24.76 % at the optimal discharge pressure. The maximum reduction in the high-pressure compressor discharge temperature is 24.95 °C, and the total compressor displacement decreases by up to 20.00 %. The performance enhancement of the ejector-enhanced cycle tends to be greater in the transcritical model compared to the subcritical model. Exergetic analysis reveals that the exergy destruction of the expansion device in the modified cycle is 22.9 kW, which is 37.38 % lower than that in the basic cycle, demonstrating the considerable expansion work recovery effect of the ejector. Finally, the correlation formula of the optimal high-pressure discharge pressure is fitted at the operating parameters.