Proposal and performance study on a component-based double-stage compression auto-cascade refrigeration cycle

It is difficult for the conventional single-stage compression auto-cascade refrigeration cycle to achieve higher refrigeration efficiency and lower refrigeration temperature, because the stream rich in high boiling point component from the phase separator bottom undergoes a single-stage compression process of high pressure lift ratio. Based on the concept of the evaporating temperature of the high/low boiling point component matching the grade compression of two streams from the phase separator, a component-based double-stage compression auto-cascade refrigeration (CDACR) cycle using R170/R600a is proposed in this paper. In the novel cycle, one dedicated compressor with two suction ports is used as the substitute for a conventional compressor with the sole suction port to realize grade compression process of the component of the refrigerant mixtures, and the stream enriched with high boiling point component from the separator bottom is sucked into the high-pressure suction port and undergoes the low-pressure-lift-ratio compression process, while the stream rich in low boiling point component from the separator top is sucked into the low-pressure suction port and executes the high-pressure-lift-ratio compression process, so as to cut down the compressor power consumption and obtain a lower refrigeration temperature. The mathematical model of the proposed cycle is developed to evaluate the thermodynamic performance of the system and comparisons with the conventional single-stage compression auto-cascade refrigeration (SCACR) cycle are also discussed. The results indicate that application of the component-based grade compression to the conventional auto-cascade refrigeration cycle dramatically improves the performance of the CDACR cycle, and there is optimum composition ratio of refrigerant mixtures for the CDACR cycle to obtain the highest coefficient of performance (COP). It is also shown that the performance of the CDACR cycle is significantly better than that of the SCACR cycle. As compared with those of the SCACR cycle, the compressor power consumption of the CDACR cycle decreases by 44.83%-53.17%, and its COP increases by 0.34–0.43, as the evaporating temperature at the evaporator outlet ranges from −60 °C to −40 °C. In addition, at the condenser outlet temperature in the range of 26 °C- 40 °C, the compressor power consumption for the proposed cycle is 37.74%-47.03% lower than that for the SCACR cycle, while COP of the CDACR cycle is 0.29–0.42 higher than that of the SCACR cycle.