Experimental study on operational characteristics of an enhanced auto-cascade refrigeration system incorporating two-stage regeneration and flash separation

In auto-cascade refrigeration (ACR) systems, the composition separation performance of mixed refrigerant is a main factor affecting the energy efficiency. This work proposes a two-stage regeneration and flash separation enhanced ACR system. Regeneration is employed to improve the separation state and enhance the composition slip. Flashing is used to increase the vapor quality, thereby raising both flow rate and concentration of the low-boiling-point (LBP) composition entering the evaporator. The steady-state performance of the enhanced ACR system with R170/R600a is experimentally investigated under different operating conditions. The results indicate that within the tested ranges of cabinet and ambient temperature, the LBP concentration entering the evaporator in the enhanced ACR system increased by 4.33% and 5.92% compared to the conventional ACR system, while the average improvements in the COP are 13.78% and 19.13%, respectively. Lowering the flash pressure reduces the circulating flow rate but enhances the composition separation. When the opening of the flash valve is decreased from 90% to 50%, the total circulating flow rate decreased by 7.4%, while the LBP concentration entering the evaporator and the COP increased by 8.72% and 18.25%, respectively. Compared with the conventional ACR system, the enhanced system with a 50% opening of flash valve exhibits a maximum increase of 27.69% in cooling capacity and 30.31% in COP. The results indicate that the beneficial effect of the increased R170 concentration entering the evaporator outweighs the adverse effect of the reduced circulating mass flow rate.