Performance Analysis of an Ejector Enhanced Two-Stage Auto-Cascade Refrigeration Cycle for Low Temperature Freezer

In this paper, an ejector enhanced two-stage auto-cascade refrigeration cycle (EARC) using ternary mixture R600a/R32/R1150 is proposed for application of −80°C freezing. In EARC cycle, an ejector was employed to recover the expansion work in the throttling processes and lifted the suction pressure of the compressor. The performances of the ejector enhanced two-stage auto-cascade refrigeration cycle and conventional auto-cascade refrigeration cycle (CARC) were compared using thermodynamic analysis methods. The influences of the important operation parameters including mass fraction ratio of the mixture, fluid quality at the second separator inlet, condensation temperature, evaporation temperature, and expansion ratio of expansion valve on the performances of EARC cycle were discussed in detail. The results indicate that ternary mixture R600a/R32/R1150 has the optimal mass fraction ratio of 0.45/0.2/0.35 with respect to the maximum COP. The EARC cycle yields higher performance than the CARC cycle in terms of COP, exergy efficiency and volumetric refrigeration capacity. And 4.9%–36.5% improvement in COP and 6.9%–34.3% higher exergy efficiency could be obtained in EARC cycle comparing with CARC cycle. The finding of this study suggests that the EARC cycle has a promising application potential for low temperature freezing.