Comparative analysis of a modified cascade refrigeration cycle including an auto-cascade refrigeration cycle using different zeotropic refrigerant mixtures for reducing the environmental impact

The two primary challenges in auto-cascade refrigeration (ACR) cycles are high compressor discharge temperatures and low efficiency at ultra-low temperatures. This study proposes a modified cascade refrigeration cycle (MCR) combined with an ACR cycle for cooling to -60 degrees C. The innovative aspect of this work is to improve the ACR performance with simpler designs without increasing the system complexity, contrary to the common trend. For the high-temperature cycle (HTC), a dual evaporator refrigeration cycle with R1234yf is used while an ACR cycle is used for the low-temperature cycle (LTC). Environmentally friendly refrigerant mixtures, such as R170/ R290, R170/R600a, and R170/R600, were analyzed using energy, exergy, and exergoeconomic methods. The results show that compared to R23/R134a, the R170/R600 significantly improves the performance of the MCR by increasing the COP and exergy efficiency by 24.0 %, and reducing the exergy destruction by 26 %, unit cooling cost by 11.2 %, and total investment cost by 9.7 %. Moreover, when compared with theoretical studies COP improvements range from 38.7 % to 94.1 %, demonstrating the importance and superiority of the system proposed in this study.