Ideal-Gas Heat Capacities and Virial Coefficients of HFC Refrigerants

Thermodynamic properties of HFC (hydrofluorocarbon) compounds have been extensively studied with worldwide iInterest as alternative refrigerants. Both quality and quantity in the experimental data far exceed those for the CFC and HCFC refrigerants. These data now provide a great opportunity to examine the validity of theoretical models, and vice versa. Among them, the ideal-gas heat capacity (C0 p) and virial coefficients derived from the experimental data are of particular iInterest, since they are directly related to the intramolecular and iIntermolecular potentials through the statistical mechanical procedure. There have been some discrepancies reported in the observed and theoretical C0 p for HFC compounds. We have performed new calculations of C0 p for several HFCs. The present results are consistent with the selected experimental values. The second (B) and third (C) virial coefficients have been reported for these HFC refrigerants from speed of sound data and Burnett PVT data. Often, a square well-type iIntermolecular potential is employed to correlate the data. However, the model potential cannot account consistently for both B and C coefficients with the same potential parameters. We have analyzed the data with the Stockmayer potential and obtained self-consistent results for various HFC (R-23, R-32, R-125, R-134a, R-143a, and R-152a) compounds with physically reasonable potential parameters.