Performance and energy utilization analysis of transcritical CO₂ two-phase ejector considering non-equilibrium phase changes

The use of ejectors in transcritical CO₂ refrigeration systems is of key significance for improving system performance, and the investigation of ejectors is particularly important. In this paper, a CO₂ two-phase numerical model considering non-equilibrium phase change is established to investigate the two-phase flow characteristics and entrainment performance in the ejector under different operating conditions. In particular, this study is devoted to the trade-off analysis of internal mass transfer and energy utilization efficiency. After a series of tests, the accuracy of the numerical model has been validated, and with the increase of primary inlet pressure, the entrainment performance first increases and then decreases, while the entrainment performance is greatly improved with the increase of primary temperature. There is a critical back pressure, beyond which the entrainment performance drops rapidly. If the pressure reaches 8.46 MPa and the corresponding temperature is set at 303.7 K, the efficiency of the ejector is 27%. When the temperature rises to 313 K, the efficiency increases to 31%, and the ratio of exergy destruction decreases from 48.3% to 10.2%. However, when the back pressure drops to 4.0 MPa, the working efficiency is only 1.8%, which fails to work normally. Effectively balancing the inlet conditions with energy utilization is a key strategy for optimizing ejector use.