Thermodynamic performance of the fractionated auto-cascade refrigeration cycle coupled with two-phase ejector using R1150/R600a at −80 °C temperature level

Abstract

The auto-cascade refrigeration cycle (ACRC) is suitable for low temperature refrigeration fields. From the perspective of fractionation purification matching expansion work recovery, a fractionated auto-cascade refrigeration cycle coupled with the two-phase ejector (FACRC-TPE) using environmentally-friendly R1150/R600a is proposed in this paper. In the novel cycle, the two-phase ejector is substituted for the throttle valve at the liquid stream passage from the separator bottom to recover expansion work and cut down the energy consumption, while the fractionation heat exchanger is applied for purification of low boiling point component in the vapor stream from the separator top to boost the cycle exergy efficiency and achieve a refrigeration temperature below −80 °C. The energetic and exergetic analysis methods are used to evaluate and compare the performances of the three cycles, and comparisons of superiority and irreversibility of FACRC-TPE are also made with the unfractionated auto-cascade refrigeration cycle with the two-phase ejector (UACRC-TPE) and the fractionated auto-cascade refrigeration cycle (FACRC). The results show that the cooperative application of the fractionation heat exchanger coupled with the two-phase ejector not only significantly boosts COP of FACRC-TPE and obtains lower refrigeration temperature, but also cuts down the total exergy loss of FACRC-TPE. With R1150 mass fraction varying in the range of 0.29–0.48, the average COP of FACRC-TPE is 10.57% higher than that of UACRC-TPE, and is 15.18% higher than that of FACRC, whereas FACRC-TPE has a lower evaporator inlet temperature of −100.48 °C to −87.96 °C, as compared with UACRC-TPE. In addition, FACRC-TPE obtains the highest exergy efficiency of 32.23%, while the UACRC-TPE exergy efficiency of 26.99% is slightly higher than the FACRC exergy efficiency of 25.19%.