Thermodynamic performance analysis of the fractionation and flash separation auto-cascade refrigeration cycle using low GWP refrigerant

Abstract

The auto-cascade refrigeration is a critical technical approach to achieve below −40 °C. The separation efficiency of mixed refrigerant is a main factor affecting the performance. Fractionation purifies low-boiling composition but reduces refrigerant flow rate within the evaporator, which may decline the performance. This paper proposes two novel cycles combining fractionation and flash separation. The novel configurations purify the composition and increase the mass flow rate of refrigerant within the evaporator. The thermodynamic analysis results indicate that the presented cycles outperform the fractionation cycle and the basic cycle in terms of energy and exergy efficiency. Under the design condition, the mass fraction of low-boiling composition in the fractionation-enhanced cycle and the fractionation-modified cycle increased by 4.21 % and 2.97 % compared to the basic cycle. The mass flow rate within the evaporator of novel cycles increased by 25.87 % and 34.78 %. The COP and exergy efficiency of the fractionation-enhanced cycle and the fractionation-modified cycle is 42.57 % and 45.44 %, 46.61 % and 55.15 % higher than those of the basic cycle. Generally, the combination of fractionation and flash separation addresses the issues of low composition separation efficiency in the basic cycle and low flow rate of the fractionation cycle, enhancing the performance of the auto-cascade cycle.