Performance characteristics of ejector expander transcritical CO2 refrigeration cycle

Abstract

The effects on the performance of the basic CO2 refrigeration cycle when using an ejector as the expander to recover expansion work were investigated. A two-phase constant area ejector flow model was used in the ejector analysis. The coefficient of cooling performance and gas cooler pressure that yielded the maximum exergy efficiency, suction nozzle pressure drop, and optimum values for the ejector area ratio were determined for various evaporator and gas cooler outlet temperatures. Parametric studies were performed using engineering equation solver. The suction nozzle pressure drop had a significant effect on the ejector area ratio, coefficient of cooling performance, and exergy efficiency. It is necessary to design an ejector with the optimum area ratio to achieve the optimum pressure drop and maximum performance. Cycle that use the ejector as an expander always has higher coefficient of performance and exergy efficiency than conventional cycle under any operating condition. The irreversibility decreases compared to the classic refrigeration cycle when the ejector or turbine are used as an expander. The analysis results showed that – under a gas cooler pressure of 9.5 MPa, gas cooler outlet temperature of 40 °C, evaporator temperature of 5 °C, and cooling capacity of 3.5 kW – the total irreversibility of the ejector system was lower than those of the basic and turbine expander systems by 39.1% and 5.46%, respectively.