Synergistic Optimization of Cycle Enhancement and Refrigerant Substitution in Ultra-Low Temperature Cascade Refrigeration Systems

Abstract

This study proposes seven new cascade refrigeration cycle schemes that integrate efficiency-enhancement components to improve system efficiency. Comparative analysis shows that the coefficients of performance (COP) of the newly established systems are significantly improved compared to the conventional cascade refrigeration system (CRS). Additionally, the new system is optimized with 12 pairs of low global warming potential (GWP<150) refrigerants and is comprehensively evaluated in four key dimensions: energy, exergy, economic, and environmental. Results show that the enhanced cascade refrigeration system (EFCRS), with a flash tank in the high-temperature cycle and an ejector in the low-temperature cycle, has the best COP, which is increased by 38.19% compared to the CRS. For EFCRS with R170/R600a, the COP is improved by 7.13%, the exergy destruction is reduced by 14.09%, and the exergy efficiency is improved by 6.31% compared to the R1150/R717. The Life Cycle Climate Performance (LCCP) assessment finds that R170/R600a reduces emissions by approximately 26.89% compared to conventional refrigerants and by 7.6% compared to the environmentally friendly refrigerant. Additionally, the total cost rate of R170/R600a is reduced by 5899.98 CNY per year compared with R1150/R717. In summary, the EFCRS using R170/R600a shows excellent comprehensive performance.

Keywords: Ultra-low temperature, Cascade refrigeration systems, Cycle optimization, Low GWP (<150), 4E analysis