An equivalent temperature based approach for selection of the most appropriate working fluids for refrigeration cycles

This article presents a novel comprehensive approach for the selection of the most appropriate working fluids and the conceptual design of vapor-compression refrigeration cycles, subject to minimal overall conductance for fixed cooling capacity with fixed temperatures of the external fluids entering the condenser and the evaporator. The approach consists of three sequential steps: the first step is the refrigerant independent calculation of the minimum thermal conductance of the system via constrained optimization. The second law analysis constrains the optimization problem where some thermodynamic considerations of h-s diagram and equivalent temperature concept provide the ability to calculate the entropy generation in each component of the system. The optimization results establish thermodynamic criteria for the pre-selection of potential refrigerants. Since the optimum conditions obtained are expressed in terms of equivalent temperatures, in the second step, a reconstruction procedure is introduced to correlate the equivalent temperatures with the essential thermodynamic characteristics of the system such as working pressures, temperatures, and mass flow rate for each pre-selected refrigerant. The last step of the approach is the final selection of the optimal refrigerant among the candidates using a capital-operating cost performance criterion. A case study was presented to illustrate the application of the novel selection approach.