Models commonly used to calculate the thermodynamic properties of refrigerants are summarized. For pure refrigerants, the virial, cubic, Martin-Hou, Benedict-Webb-Rubin, and Helmholtz equations of state and the extended corresponding states model are discussed. High-accuracy formulations for 16 refrigerants are recommended. These models may be extended to mixtures through the use of mixing rules applied either to the parameters of the equation of state or some property of the mixture components. Mixtures of a specific composition may also be modeled as a pseudo-pure fluid. Five mixture models, employing four distinct aproaches, have been compared representing mixture properties. No single model was best in all aspects, but based on its combination of excellent accuracy and great generality, we recommend the mixture Helmholtz model as the best available. Experimental data are assential to both fit the adjustable parameters in property models and to assess their accuracy. We present a surevey of the data available for mixtures of the HFC refrigerants R32, R125, R143a, R134a, and R152a and for mixtures of the natural refrigerants propane, butane, isobutane, and carbon dioxide. More than 50 data references are identified. Further data needs include caloric data for additional mixtures, comprehensive pressure-density-temperature data for additional mixture compostions, and improved accuracy for vapor-liquid equilibria data.
Citation: International Journal of Refrigeration-Revue Internationale Du Froid
Issue: No. 4
Pub Type: Journals
ammonia, azeotropes, equation of state, hydrofluorocarbons, mixtures, natural refrigerants, refrigerants, thermodynamics, zeotropes