Performance analysis of a modified dual-ejector and dual-evaporator transcritical CO2 refrigeration cycle for supermarket application

Abstract

This paper proposes a modified dual-ejector and dual-evaporator transcritical CO2 refrigeration cycle for supermarket application. Based on the conventional dual-evaporator transcritical CO2 refrigeration cycle, the modified cycle introduces two ejectors and a flash tank. The first liquid-vapor ejector sucks partial throttling flash vapor flowing to the low-temperature evaporator into the high-temperature evaporator; the second vapor-vapor ejector takes the vapor from the high-temperature evaporator as the primary flow to entrain the vapor from the low-temperature evaporator, and then the compressor suction pressure is lifted. Furthermore, the introduction of the first ejector increases the primary flow of the second ejector, and then improves the ability of the second ejector to lift the suction pressure of the compressor. The performance comparison between the two cycles is conducted by adopting energy and exergy analysis methods, and the efficiencies of the two ejectors are also analyzed. The comparison results demonstrate that the use of dual-ejector reduces the compressor pressure ratio by up to 19.1% under a typical working condition, and the improvements of the COP and exergy efficiency could reach up to 15.9–27.1% and 15.5–27.5% under all given working conditions. In addition, the modified cycle has an optimal gas cooler pressure of around 8.15 MPa, which is lower than the 8.3 MPa of the conventional cycle. The performance comparison results state clearly the energy-saving potential of the modified cycle and its application prospect in supermarket refrigeration.