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

Abstract

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.