Performance analysis of a new transcritical R744 refrigeration cycle with expander-mechanical overheating

In this paper, a transcritical R744 refrigeration cycle with expander mechanical overheating coupling is proposed. When the reasonable superheat and the pressure difference front and rear of expander are selected, the coefficient of performance of R744 refrigeration cycle can be significantly improved and the discharge pressure can be reduced. Compared with the base R744 refrigeration cycle and the R744 refrigeration cycle with expander, the coefficient of performance of the expander mechanical overheating coupling transcritical R744 refrigeration cycle can increase by 20.17% and 10.59%. In addition, in the expander mechanical overheating coupled transcritical R744 refrigeration cycle system, with the increase of superheat, the minimum optimal pressure can be reduced by 8.63% and the maximum coefficient of performance can be increased by 131.17%. With the increase of pressure difference front and rear of expander, the minimum optimal pressure can be reduced by 6.14% and the maximum coefficient of performance can be increased by 72.19%. Therefore, from the perspective of improving the comprehensive performance of the system, the superheat should be properly increased, supplemented by the pressure difference front and rear of expander, which can not only reasonably improve the comprehensive performance of the system, but also reduce the design difficulty of the expander.