A proposed subcooling method for vapor compression refrigeration cycle based on expansion power recovery

• Expansion power recovery based subcooling method for liquid refrigerant is proposed.
• Maximum COPs increase by 67.76%, 19.27% and 17.73% for compared systems respectively.
• Optimal refrigerant combinations are R717 and R744 for the hybrid system.
• Impacts of operating conditions on the proposed system are evaluated.
• Effects of key parameters on the COP difference of three systems are disclosed.

This study proposes a new subcooling method for vapor compression refrigeration cycle based on expansion power recovery. In a main refrigeration cycle, expander output power is employed to drive a compressor of the auxiliary subcooling cycle, and refrigerant at the outlet of condenser is subcooled by the evaporative cooler, which makes the hybrid system get much higher COP. Various refrigerants, including R12, R134a, R22, R32, R404A, R41, R507A, R717, and R744, are considered. Thermodynamic analysis is made to discuss the effects of operation parameters (expander efficiency and inlet temperature of cooling water) on the system performance. Results show that the proposed hybrid vapor compression refrigeration system achieves much higher COP than the conventional vapor compression refrigeration system, conventional mechanical subcooling system and conventional expansion power recovery system, with maximum COP increments 67.76%, 19.27% and 17.73%, respectively when R744 works as the refrigerant in the main refrigeration cycle. It is most beneficial for R12 and R717 in the auxiliary subcooling cycle and R744, R404A and R507A in the main refrigeration cycle.