Exergy-based sustainability assessment of a modified ejector-enhanced auto-cascade refrigeration cycle

Abstract This study presents a sustainability-focused assessment of previously developed auto-cascade refrigeration (ACR) models using exergy-based parameters, highlighting their performance not only in terms of energy and exergy analyses but also through sustainability indicators reported in the literature. Unlike many studies that focus solely on thermodynamic performance, the present work also evaluates the environmental and sustainability impacts of four modified cascade refrigeration (MCR) configurations, including the ejector-enhanced MCR (MECR) cycle. A binary refrigerant mixture of R170/R290 is used in the low-temperature cycle (LTC), and R1234yf in the high-temperature cycle (HTC). In the LTC, the use of low-GWP refrigerants with flammable characteristics poses a risk of elevated compressor discharge temperatures, particularly at low evaporation temperatures. To mitigate this risk, the refrigerant mixture is precooled via the cascade cycle before entering the separator, thereby reducing the compressor discharge temperature. As a result, the compressor discharge temperature is reduced by 35.1% in the MCR-1 and MCR-3 configurations and by 36.9% in the MECR configuration. Based on data reported in the literature, MCR-2 configuration exhibits improvements in exergy efficiency ranging from 9.3 to 55.5%, whereas the MECR cycle achieves increases between 11.3 and 58.2%. Furthermore, the MECR cycle reduces the ecological and environmental effect factors by up to 17.9% and 23.8%, respectively, compared to the MCR-2 configuration, while increasing the exergetic sustainability index by up to 31.2%. These findings demonstrate that the previously developed models provide significant improvements not only in thermodynamic performance but also in sustainability metrics, extending their applicability beyond energy and exergy-based analyses.