In this paper, thermo-economic optimization and comparative analysis of a cascade refrigeration system configured with flash gas removal in its high-temperature cycle (HTC) and flash intercooling with indirect subcooling in lower temperature cycle (LTC) using different natural refrigerant pairs is performed. Thermo-economic optimization is carried out to maximize the exergetic efficiency and minimize the overall cost rate. The optimization model involves six design variables which include subcooling and de-superheating parameters, LTC evaporation and condensation temperatures, HTC condenser temperature and cascade temperature difference. The comparative analysis of twenty-two natural refrigerant pairs based on the results of thermodynamic and economic optimizations reveals that R717-R290 is most efficient pair and R290-R1150 is least efficient refrigerant pair thermodynamically whereas R717-R1270 is the best and R600a-R290 is the worst pair economically. Seven potential refrigerant pairs are chosen via the thermodynamic and economic optimization results and they are further compared based on their performances obtained through multi-objective optimization (maximization of exergetic efficiency and minimization of total cost rate). Multi-objective genetic algorithm is used for optimization which results in seventy non-dominated Pareto optimal solutions where the TOPSIS method is used to select a unique solution for each refrigerant pair. A comparison of refrigerant pairs using these unique solutions shows that R717-R1270 is the best refrigerant pair for the cascade system under consideration. It is also found that R717-R1270 results in 7.77% rise in COP and 5.32% reduction in overall cost when compared with NH₃–CO₂ refrigerant pair working under identical operating conditions.

本文对采用不同天然制冷剂对的高温循环 (HTC) 闪蒸脱气和低温循环 (LTC) 间接过冷闪蒸中间冷却的复叠制冷系统进行了热经济优化和比较分析。 . 进行热经济优化以最大化火用效率并最小化总成本率。优化模型涉及六个设计变量，包括过冷和减温参数、LTC 蒸发和冷凝温度、HTC 冷凝器温度和串级温差。基于热力学和经济优化结果对 22 对天然制冷剂的比较分析表明，R717-R290 是最有效的一对，R290-R1150 是热力学效率最低的制冷剂对，而 R717-R1270 是最好的，R600a-R290 是经济上最差的一对。通过热力学和经济优化结果选择了七个潜在的制冷剂对，并根据通过多目标优化获得的性能（热效率最大化和总成本率最小化）进一步比较它们。多目标遗传算法用于优化，产生七十个非支配帕累托最优解，其中使用 TOPSIS 方法为每个制冷剂对选择唯一的解。使用这些独特解决方案的制冷剂对的比较表明，R717-R1270 是所考虑的复叠系统的最佳制冷剂对。还发现与 NH 相比，R717-R1270 的 COP 提高了 7.77%，总成本降低了 5.32%₃ –CO ₂制冷剂对在相同的操作条件下工作。