Theoretical investigation on the performance of R600/R170/R14/R50 four stage regenerator-enhanced auto cascade refrigeration system.

In multi-stage auto cascade refrigeration (ACR) systems, the component selection and ratio optimization of zeotropic mixed refrigerants is important. A four-stage regenerator-enhanced ACR (RACR) system using R600/R170/R14/R50 was proposed. Influences of refrigerant mixture ratio, high-boiling-point components, gas-phase fraction before throttling (x4) and gas-liquid separation temperature (TS1∼TS3) on the system performance were explored. Exergy loss ratios of components were compared and analyzed. The results demonstrated that increasing the mass fraction of R170 and reducing that of R50 significantly improve the energy efficiency, and reduce discharge temperature. To obtain -140 °C, a minimum x4 (x4 min) could optimize the coefficient of performance (COP). R600/R170/R14/R50 (mass fraction of 0.38/0.20/0.17/0.25 and x4 min of 0.12) had the best COP of 0.192 and exergy efficiency of 0.330 under variable x4 conditions. To improve the energy efficiency, appropriately reducing TS1 and TS3, or increasing TS2 could be adopted. The top three components in the RACR system accounted for the largest exergy loss proportion were compressor, throttle at the evaporator inlet and condenser, accounting for 26.0 %, 18.3 % and 15.7 %, respectively.