Thermodynamic performance analysis of a grade compression auto-cascade refrigeration cycle with multi-dephlegmation processes

The traditional auto-cascade refrigeration cycle with a single-stage compressor (BACR) still faces limitations such as low refrigeration efficiency and restricted refrigeration temperatures, hindering its widespread adoption. To address these issues and simultaneously reduce refrigeration temperature while improving the coefficient of performance (COP), this paper proposes a two-step dephlegmation and dual-stage compression auto-cascade refrigeration cycle (TDDCR). A theoretical comparative analysis is conducted to evaluate the effects of composition ratio, total compression ratio, condensation temperature and evaporation temperature on the thermodynamic performance of TDDCR using R1150/R600a. The results indicate that TDDCR achieves a refrigeration temperature of −80 °C and lifts the COP to 0.432, a substantial improvement over the COP of 0.226 for BACR. Within the condensation temperature range of 25 °C–35 °C, the TDDCR exhibits an increase in COP ranging from 72.39 % to 237.88 % compared to BACR. To obtain the optimal thermodynamic performance, the dephlegmation temperature in TDDCR should align with the evaporation temperature. Furthermore, the TDDCR achieves a 42.76 % reduction in total exergy destruction compared to the BACR. Environmental analysis also reveals a 47.68 % decrease in the total equivalent warming impact (TEWI) for the TDDCR compared to the BACR, demonstrating its superior environmental sustainability performance. Overall, the comparative analysis demonstrates the significant potential for performance improvement in the proposed TDDCR.