PERFORMANCE ANALYSIS OF CASCADE REFRIGERATION SYSTEM

Abstract

Ammonia/CO2 mixture is presently considered to be the best for cascade refrigeration up to 216.58ºK. However to approach temperatures lower than 216.58ºK the mixture of CO2 with other refrigerants are required. The aim of present work was to study the possibility of using carbon dioxide mixtures in those applications where temperatures below CO2 triple point (216.58 K) are needed. The blends considered for analysis purpose are R744/R125, R744/R41, R744/R32, and R744/R23. The analysis of cascade refrigeration cycle has been carried out with the help of a computer program developed using Engineering Equation Solver (EES). The composition of CO2 is varied from a mole fraction of 0.1 to 0.8 along with R23, R32, R41 and R125. The mixtures properties of the investigated blends (R744/R125, R744/R41, R744/R32, and R744/R23) were calculated by Ref Prop 7.0 and used in EES program. Ammonia is used as refrigerant in hightemperature- circuit. Blend of CO2 with R125 having a mole fraction ratio of 0.3/0.7 is the best among all the blends considered as it offers highest COP values. Up to mole fraction ratio 0.5/0.5, CO2/R125 blend is better than other blends for same mole fraction ratio. At mole fraction ratio of 0.8/0.2, the blends R744/R125, R744/R41and R744/R32 have almost same values of COP and that of R744/ R32 blend is lowest. Hence R744 blends are an attractive option for the low-temperature circuit of cascade systems operating at temperatures approaching 200 K.