Theoretical study on a modified single‐stage autocascade refrigeration cycle with auxiliary phase separator

In order to improve the cycle performance of a conventional single-stage autocascade refrigeration cycle (ARC), an auxiliary separator is considered to be introduced. In the modified autocascade refrigeration cycle (MARC), the auxiliary separator located after an expansion device is used to further collect the vapor enriched with low-boiling components. In this case, the MARC enables to improve the cycle performances by utilizing more zeotropic mixture enriched with the low-boiling components to realize a higher evaporation pressure at the given evaporation temperature in the evaporator of the cycle. The performances of the MARC and ARC are compared utilizing energy, exergy and exergo-economic analysis methods, and several important parameters are also discussed in detail. The results indicate that the MARC using zeotropic mixture R290/R170 is feasible and there are obvious improvements in terms of the COP, volumetric refrigeration capacity and exergy efficiency. It is found that compared to the ARC, the COP improvement of MARC can reach up to 16.1%. The exergy efficiency of MARC is increased by 10.23% and the overall cost rate of MARC is decreased by 2.51% under a typical operating condition. In addition, the COP of MARC has a maximum value at given conditions when the mass fraction of R290 at the compressor inlet is around 0.3. In general, the performance characteristics of the proposed cycle demonstrate its potential applications in low-temperature freezers.