Thermodynamic Performance Analysis and Refrigerant Evaluation of Enhanced Cascade Vapor-Injection Refrigeration Systems

To enhance the compression efficiency and refrigerant flow capacity for low-temperature refrigeration applications, the vapor-injection strategy is innovatively synthesized with two-stage cascade refrigeration systems. Two cascade vapor-injection configurations with subcoolers and flash tanks (CSVIRS and CFVIRS) are compared with the conventional cascade refrigeration system (CCRS) through integrated thermodynamic simulations. The impacts of crucial temperature and injection parameters are comprehensively analyzed through energy and exergy methods, while the performance comparisons of various refrigerant combinations are also conducted. The coefficient of performance (COP) of the CFVIRS exceeds that of the CCRS and CSVIRS by 33.84% and 2.10% under the default condition. The cascade vapor-injection configurations exhibit a performance advantage at higher condensation temperature and lower evaporation temperature of the low-temperature cycle (LTC). The evaporation temperature of the high-temperature cycle (HTC) and injection pressures are examined with optimum solutions. Decreasing the entrainment ratio of the HTC and increasing the entrainment ratio of the LTC within appropriate ranges are beneficial for the refrigeration performance. R1270-R170 demonstrates superior energy and exergy performance, whereas R143a-R23 shows the highest improvement ratio among the compared refrigerants. The implementation of cascade vapor injection substantially reduces exergy destruction in the compression and expansion devices, while the exergy characteristics of various refrigerant pairs are extensively investigated.