Performance of NH3/CO2 cascade refrigeration system with ejector.

Abstract

Use of ejector-expansion is a method to improve the performance of the cascade refrigeration system. Ejectorexpansion is recognized as a potential method of improving the performance of cascade vapor-compression refrigeration cycle by the recovery of the expansion work normally lost in the expansion valve or capillary tube. Over the past years, many researchers have applied the ejector-expansion method to enhance the performances of vapour compression cycle (VCC) systems in the various applications including refrigeration, heat pump and air conditioning systems. Thermodynamic analysis of cascade refrigeration systems with ejector operating on NH3 and CO2 refrigerants has been carried out in this work based on first and second law for low temperature refrigeration. The systems taken for study are cascade with ejector in both circuits, ejector in low temperature circuit only, ejector in high temperature circuit only and conventional cascade system. The parameters studied are COP, second law efficiency and exergy destruction rate(EDR). The study shows that the maximum COP and maximum second law efficiency of the cascade with ejector in both cascade circuits increased by 8.1 and 8% respectively as compared to the conventional cascade system. The COP of cascade system with ejectors in both circuits is definitely better than either of the systems but for low temperature refrigeration the COP of the system with ejector in both circuits is marginally higher than that of cascade with ejector in high temperature circuit.