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

High-efficiency vapor compression refrigeration systems are critical for energy conservation and environmental protection across various essential industries. 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 COP of CFVIRS exceeds CSVIRS and CCRS by 2.13% and 33.92% under the default condition. The cascade vapor-injection structures exhibit competence 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 optimal solutions. Decreasing the entrainment ratio of HTC and increasing the entrainment ratio of LTC within appropriate ranges, while strengthening the heat transfer effectiveness of subcoolers, are also constructive on the refrigeration efficiency. R1270-R170 exhibits superior energy and exergy performance, whereas R143a-R23 shows the highest improvement ratio among the compared refrigerants. The implementation of cascade vapor-injection demonstrates substantial reductions in the exergy losses of compression and expansion devices, and the exergy consumption, destruction and output of different refrigerant pairs are extensively investigated. The research conclusively ‌reveals‌ the advantages of the cascade vapor-injection strategy, ‌thus providing‌ a theoretical foundation for further research ‌on‌ novel refrigeration systems.