Numerical simulation of CO2 two-stage compression refrigeration system with external intercooler

Abstract

The CO2 two-stage compression refrigeration system is a feasible alternative to conventional refrigeration systems for logistics cold storage cooling that provides high efficiency and environmental protection. In a previous study, we proposed a two-stage compression refrigeration cycle with an external intercooler and performed a thermodynamic analysis. Based on that, a more comprehensive simulation analysis is performed herein using the validated models. The performance, optimal discharge pressure, and intermediate pressure are investigated using a high-pressure compressor with both fixed and variable speeds. The results show that the cooling-water temperature has a significant positive linear correlation with the optimal discharge pressure, whereas the evaporator-inlet air temperature has little effect at a fixed high- pressure compressor speed. When the high-pressure speed is adjusted to achieve the optimal intermediate pressure and discharge pressure simultaneously, the coefficient of performance increases by 4.5% compared with that of the fixed-speed system, while the cooling capacity decreases by 8.4%. The correlation of optimal discharge pressure and optimal intermediate pressure is given.