Comparative energy, exergy and economic analysis of a cascade refrigeration system incorporated with flash tank (HTC) and a flash intercooler with indirect subcooler (LTC) using natural refrigerant couples

In this paper, comparative energy, exergy and economic analysis of natural refrigerant couples working in a cascade refrigeration system incorporated with a flash tank in its higher temperature cycle and a flash intercooler with indirect sub-cooler in its lower temperature cycle have been done. An analysis is conducted using seventeen refrigerant couples from eight natural refrigerants, namely R717, R290, R600a, R744, R744a, R170, R1150 and R1270. Comparison based on COP, exergy efficiency, system cost rates, and exergy destruction rate, to identify the best alternative refrigerant couple, is performed. Thermodynamic optimization has also been carried out with evaporator temperature, condenser temperature, LTC condenser temperature, cascade temperature difference, de-superheating and subcooling parameter of LTC intercooler, as six design variables. To evaluate the economic accountability of refrigerant couples a simple payback analysis has been done at the thermodynamic optimal conditions of the system. Results of analysis and optimization show that R717-R290 is the best refrigerant couple for this system from thermodynamic as well as economic points of view. The maximum COP and exergy efficiency obtained is 1.917 and 39.14% respectively and the corresponding total annualized system cost is 836,395 $/yr for R717-R290 refrigerant couple.