Experimental investigation of ejector performance and transcritical CO2 dual-evaporator ejector expansion refrigeration cycle performance

Abstract

To enhance the efficiency of CO₂ transcritical refrigeration systems, numerous novel CO₂ dual-evaporator ejector expansion refrigeration cycles (DEECs) have been proposed in recent years. However, there are few experimental studies on the performance of the novel CO₂ dual-evaporator cycles in the literature, especially under household air conditioning conditions. This work sequentially built a CO₂ two-phase ejector performance test bench and a modified transcritical CO₂ dual-evaporator ejector expansion refrigeration cycle (MDEEC) test bench. The performance of the CO₂ two-phase ejector under specific conditions, as well as the impact of variations in compressor frequency and electronic Expansion Valve (EXV) pulse number on the thermodynamic behavior of the MDEEC were analyzed. In ejector performance test, as the pressure of the primary flow increases from 8.45 to 9.43 MPa, the entrainment ratio rises accordingly, from 0.183 to 0.334, which is in line with the expected performance. In MDEEC test, an increase in compressor frequency from 40 to 60 Hz results in a rise in power consumption from 0.74 to 1.526 kW. Even though the cooling capacity increases, the coefficient of performance (COP) decreases from 4.02 to 2.915, which remains significantly higher than that of traditional transcritical CO₂ systems, and is somewhat close to the performance of traditional refrigerants under the same working conditions. As the number of EXV pulses increases, the low-temperature evaporation temperature increases correspondingly. However, under multiple factors, the impact of EXV pulse number on both cooling capacity and COP is negligible. Furthermore, the entrainment ratio of the ejector in MDEEC test is closely comparable to the results from CO₂ two-phase ejector performance test, demonstrating its robust and stable performance. This work can provide reference for the utilization of CO₂ two-phase ejectors and application of MDEEC in the field of household air conditioning.