Simulation Study on the Performance Characteristics of a $CO_2$ Cooling System with an Expander

A cycle shows large throttling loss during the expansion process. The application of an expander into the cycle can reduce the throttling loss and then improve system performance. In this study, the performance of a transcritical cycle with an expander was analytically investigated in order to improve the cooling performance of the system. The expander was applied to the single-stage and two-stage compression cycles. The performance was analyzed with the variations of compressor frequency, outdoor temperature, and expander efficiency. The single-stage and two-stage compression cycles with the expander showed COP improvement of 25% and 32%, respectively, over the single-stage cycle with an EEV.