Thermodynamic modeling and performance optimization of transcritical CO2 dual-evaporator refrigeration system enhanced with ejectors

Abstract

The utilization of ejectors in transcritical CO2 refrigeration systems is known to enhance system performance significantly. However, the operational conditions play a crucial role in determining the system’s overall efficiency. This study introduces a thermodynamic model for transcritical CO2 ejector refrigeration systems and investigates the influence of operating conditions on system performance for four different refrigeration systems, and the optimization of the Nakagawa sound velocity model coefficient in the ejector modeling is carried out to enhance the accuracy of the model. Meanwhile, these research contents are also the innovation of the research. Key conclusions include: (1) Increasing the Nakagawa coefficient to 1.1 improves model accuracy. (2) Ejector inclusion enhances system COP, with one configuration showing a 43.36 % increase and another a 53.23 % increase, recommending different system setups for large spaces like supermarkets and smaller areas like refrigerated vehicles. (3) Higher evaporating pressures result in better COP for ejector systems, with a suggested maximum air cooler pressure of 9 MPa. COP also benefits from increased ejector outlet pressures. (4) AR (area ratio) of the ejector affects mass flow rates and cooling capacity significantly, while its impact on COP is minimal. Adjusting the primary throat area can control cooling capacity for varied needs. The study provides actionable insights for improving the design and efficiency of transcritical CO2 ejector refrigeration systems.