Preliminary selection of r-114 replacement refrigerants using fundamental thermodynamic parameters (RP-1308)

The Peng-Robinson equation of state is used to determine the optimum thermodynamic parameters for R-114 replacements in high-temperature heat pumping applications. The critical temperature, the ideal gas specific heat at constant pressure, and the acentric factor are shown to be the three thermodynamic parameters that determine the performance (heating coefficient of performance and volumetric heating capacity, COPH and VHC, respectively) of refrigerants operating in idealized vapor-compression refrigeration cycles. It is shown that (1) the optimal range of critical temperature depends on the desired VHC; (2) to maximize COPH, the ideal gas specific heat at constant pressure (evaluated at the critical temperature) should have values ranging from approximately 48 kJ-kmol(-1)-K-1 (11.5 Btu-lbmol(-1).degrees R-1) to approximately 104 kJ.kmol(-1) .K-1 (24.9 Btu-lbmol(-1) .degrees R-1), and to increase VHC, the ideal gas specific heat at constant pressure (evaluated at the critical temperature) should have values less than approximately 138 kJ.kmol(-1) -K-' (33. 0 Btu -lbmol(-1) .degrees R-1); and (3) to increase COPH, the acentric factor should have larger values, and to increase VHC, the acentricfactor should have smaller values. Therefore, trade-offs become necessary due to the conflict between COPH and VHC. The process presented in this paper provides a framework for quickly and easily screening a large number of potential R-114 replacement refrigerants. Using this methodology, one could easily create from a much longer list a focused list of potential replacements that could then be investigated in depth using more conventional approaches such as experimentation and detailed System modeling.