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

The objective of this work was to develop an association equation of state for hydrofluorocarbons. The functional form of the proposed equation was the dimensionless Helmholtz energy given by the sum of two terms: one from a modified Peng-Robinson equation and the other from the Statistical Associating Fluid Theory equation. The equation included seven adjustable coefficients fitted, for each component, to pρT, vapour pressures, isochoric heat capacities and speeds of sound. The fluids studied were difluoromethane (HFC-32), pentafluroethane (HFC-125), 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,1-trifluoroethane (HFC-143a), and 1,1-difluoroethane (HFC-152a). The calculated percentage overall average absolute deviations were 2.084 in pρT, 5.278 in vapour pressures, 2.282 in saturated-liquid densities, 3.459 in isochoric heat capacities, 3.613 in isobaric heat capacities, and 4.637 in speeds of sound. Those results were significantly better than the accuracy of the standard Peng-Robinson equation for the fluids of interest. This work included an ancillary equation in the same formalism of the proposed equation of state but having only to the cubic term, thus constituting a refitted modified Peng-Robinson-like equation. Finally, this work also included a preliminary application to the system (HFC-32 + HFC-125) with AADs in pρT and in vapour pressures of 2.703 and 3.661%, respectively.