Peng-Robinson-based association equation of state for mixtures of hydrofluorocarbon refrigerants

The objective of this work was to extend to mixtures of hydrofluorocarbon refrigerants a recently developed Peng-Robinson plus association equation of state for those compounds. In that equation of state, two terms constituted the residual dimensionless Helmholtz energy: the first was a substance-specific dimensionless form of the conventional Peng-Robinson equation while the second was the association term from the Statistical Associating Fluid Theory. The extension to mixtures consisted of the conventional Peng-Robinson equation to mixtures, i.e. the expressing the mixture attractive parameter as a van der Waals one-fluid mixing rule with a binary interaction parameter at the unlike-interaction term. The systems of interest were the mixtures systems (HFC-32 + HFC-125), (HFC-32 + HFC-134a), (HFC-125 + HFC-134a), (HFC-125 + HFC-143a), (HFC-134a + HFC-143a), and (HFC-134a + HFC-152a); and the ternary systems (HFC-32 + HFC-125 + HFC-134a) and (HFC-125 + HFC-134a + HFC-143a). For the important number of 98000 data, the percentage overall average absolute deviations obtained were 1.44 in pρT; 53.9 in isochoric heat capacities, 34.8 in isobaric heat capacities, 0.183 in speeds of sound, and 1.27 in bubble-point vapour pressures; and an overall average absolute difference in second virial coefficients of 41.4 cm³.mol⁻¹. Those results compared favourably with those obtained with the standard Pang-Robinson equation, with a substance-specific version of the Pang-Robinson equation, and with a cubic plus association equation.