Thermodynamic performance and the exergy destruction of the transcritical CO2 two-stage compression and ejector expansion direct cooling ice making system

Abstract

The transcritical CO2 direct cooling technology was used for the first time in the indoor venues of the 2022 Beijing Winter Olympic Games. The technology has a series of advantages, such as compact structure, uniform ice temperature, energy saving and environmental protection. In order to further reduce the power consumption and improve the performance, two-stage compression and low-pressure ejector direct cooling ice making system (TCLES) and two-stage compression and intermediate-pressure ejector direct cooling ice making system (TCIES) are studied. The performance of the systems is simulated by constructing a one-dimensional thermodynamic model. The impacts of the gas cooler pressure, gas cooler outlet temperature, evaporation temperature and intermediate pressure on these systems are considered. It is showed that TCLES and TCIES have their own advantages when the system is without and with heat recovery, and found that two-stage compression improves the system performance more than the ejector when only the cooling performance is considered. On this basis, conventional exergy and advanced exergy analysis of both systems are carried out. Advanced exergy analysis shows that exergy destruction can be avoided mainly in low-pressure and high-pressure compressors of both systems. Besides, the influence of gas cooler pressure on exergy destruction characteristics is discussed. When controlling the gas cooler pressure at 9.0 MPa, the avoidable endogenous exergy destruction of compressors and ejector is reduced by a maximum of 4.14% and 13.92% for TCLES and reduced by a maximum of 16.15% and 28.04% for TCIES.