Ideal-Gas Heat Capacity Values and Equations for Hydrofluorocarbon (HFC) Refrigerants Based on Speed-of-Sound Measurements

Final values of ideal-gas heat capacity c ⁰ _p derived from speed-of-sound measurements using an acoustic spherical resonator and equations of c ⁰ _p as a simple function of temperature are provided from an overall assessment of speed-of-sound measurements for five hydrofluorocarbon (HFC) refrigerants, difluoromethane (R32), pentafluoroethane (R125), 1,1,1,2-tetrafluoroethane (R134a), 1,1,1-trifluoroethane (R143a), and 1,1-difluoroethane (R152a). Some of the experimental results had systematic errors in comparison with theoretical calculations based on spectroscopic data, which seem to result from the impurity of the sample fluids. The agreement of the experimentally determined and theoretically calculated c ⁰ _p values was confirmed for HFC refrigerants. The uncertainty of c ⁰ _p values calculated from the proposed equations is estimated to be 0.1 or 0.2% corresponding to an ISO uncertainty with a coverage factor of k=1. An erratum for Table I in a previous report by Yokozeki et al. in 1999 is provided as an appendix.