Helmholtz energy and extended corresponding states model for the prediction of thermodynamic properties of mixtures of refrigerants

•A Helmholtz energy model was presented for mixtures of refrigerants.•The Helmholtz energy was obtained from an extended corresponding states model plus temperature- and density-dependent corrections.•For eight systems the percentage AAD in pρT data was 0.347 percent.•Percentage AADs were 0.467 for vapour pressures, 1.108 for isobaric heat capacities and 0.073 for speeds of sound.•Results compared favourably with another Helmholtz energy model for mixtures of refrigerants.

This work was concerned with developing an accurate model for the prediction of thermodynamic properties of mixtures of refrigerants. That model was the extension to mixtures of a recent work by the author about a Helmholtz and extended corresponding states model for refrigerants.In the proposed model the residual Helmholtz energy of the mixture was expressed as the contribution of three terms: one from an extended corresponding states model and the other two were corrections in terms of one-fluid mixing rules of functions of reduced temperature and density. The extended corresponding states model was based on the temperature- and density-dependent shape factors that the author has presented previously in the literature and the reference fluid was R-32 with properties calculated with the Tillner-Roth and Yokozeki reference equation of state.The fluids of interest were six binary systems and two ternary systems: (R-32 + R-125), (R-32 + R-134a), (R-125 + R-134a), (R-125 + R-143a), (R-134a + R-143a), (R-134a + R-152a), (R-32 + R-125 + R-134a) and (R-125 + R-134a + R-143a). The following were the obtained percentage overall average absolute deviations: 0.347 in pρT data, 1.836 in isochoric heat capacities, 1.108 in isobaric heat capacities, 0.073 in speeds of sound, 0.467 in bubble-point saturation pressures and an overall average absolute difference of 3.367 cm3 mol−1 was obtained in second virial coefficients. These results compared satisfactorily with those from other models for mixtures of refrigerants.