Thermodynamic analysis of double-compression flash intercooling transcritical CO2 refrigeration cycle

Abstract

The performance of double-compression flash intercooling (DCFI) transcritical CO2 refrigeration cycle is evaluated by thermodynamic analysis in comparison with the double-compression external intercooling (DCEI) cycles. The effect of expander isentropic efficiency and position on the performance of DCFI cycle is investigated. Six double-compression refrigeration cycles are studied in the paper. The results show that the DCFI cycle performs better than DCEI cycle when the throttle valve is used as the expansion device. The replacement of the throttle valve with the expander yields less coefficient of performance (COP) improvement for DCFI cycle compared with DCEI cycle, especially at low evaporating temperatures or high gas cooler outlet temperatures. The COP of the two cycles is nearly equivalent when the isentropic efficiency of the expansion processes reaches 1.0. The DCFI cycle with only one throttle valve replaced with an expander shows lower COP compared with the corresponding DCEI expander cycle. The replacement of the main throttle valve with an expander results in higher COP compared with the auxiliary throttle valve replacement in the DCFI cycle. The substitution throttle valve for expander in the DCFI cycle is not economical compared with DCEI cycle. Furthermore, the optimum gas cooler pressure, the optimum intermediate pressure and the mass flow rate ratio are also discussed in the paper.