Thermodynamic analysis of a modified auto-cascade refrigeration cycle using mixture R290/R170

Conventional auto-cascade refrigeration cycle (ARC) with single-stage compression faces significant challenges in larger pressure ratio and lower efficiency for low-temperature refrigeration applications. To solve this problem, a modified auto-cascade refrigeration cycle (MARC) using a vapor-injection compressor is proposed in this paper. In the modified cycle, the vapor-injection compressor could decrease the pressure ratios for each stage compression process, resulting in higher compressor efficiency. Furthermore, two vapor–liquid separators associated with two cascade heat exchangers are used to achieve much more effective phase separation for the low-boiling component, leading to performance enhancement. A thermodynamic evaluation of the MARC with zeotropic mixture R290/R170 was carried out under various operating conditions and compared with the conventional ARC. The analysis results show that under typical operating conditions, the conventional ARC demonstrates the coefficient of performance (COP_c) of 0.415, while the MARC exhibits the COP_c of 0.624, which achieves a 50.36% improvement. Additionally, the volumetric cooling capacity increases by 89.37%, and exergy efficiency improves by 50.47%. The compressor discharge temperature is reduced by 55.76%, contributing to enhanced compressor efficiency and a reduction in exergy destruction by 27.57%. By investigating the effect of different parameter variations on the two cycles’ performance, it was found that in the modified cycle, the vapor quality at the second separator inlet and the condenser outlet temperature have a considerable effect on the coefficient of performance and exergy efficiency. The findings demonstrate that the MARC offers a promising solution for low-temperature refrigeration, significantly outperforming conventional ARC systems in terms of both energy and exergy efficiency.