Single- and double-stage absorption cycles based on fluorocarbon refrigerants and organic absorbents

Abstract

A comparison between different fluorocarbon refrigerants and organic absorbents as working fluids in single- and double-stage absorption heat pumps was undertaken. The refrigerants included R22 (monochlorodifluoromethane), R134a (1,1,1,2-tetrafluoroethane), R124 (2-chloro-1,1,1,2,-tetrafluoroethane) and R32 (difluoromethane), and various organic compounds such as DMAC ( N, N′-dimethylacetamide), DMEU (dimethylethyleneurea), DMETEG (dimethylether tetraethyleneglycol), NMP ( N-methyl-2-pyrrolidone), and MCL ( N-methyl ε-caprolactam) constituted the absorbents. The single- and double-stage cycles were calculated for the following working conditions: cooling capacity of 100 kW, generator temperature of 100°C, evaporator temperature of −10°C, water-cooled components outlet temperature of 35°C, and the air-cooled components outlet temperature of 50°C. The performance characteristics of the working fluids in both cycles in terms of the coefficient of performance (COP) and the circulation ratio ( f), the heat transfer in the main components, the refrigerant and solution mass flow-rates, and the water flow-rates were calculated and compared. Under these working conditions, the performance of the working fluids based on R22 are superior to those based on R124 in both cycles. The working fluids based on R134a cannot be used in a single-stage absorption cycle while in a double-stage cycle the performances were the worst; solutions based on R32 cannot be used in either cycles.