Molar heat capacity at constant volume of 1,1-difluoroethane (R152a) and 1,1,1-trifluoroethane (R143a) from the triple-point temperature to 345 K at pressures to 35 MPa

Molar heat capacities at constant volume (C-v) of 1,1-difluoroethane (R152a ) and 1,1,1-trifluoroethane (R143a) have been measured with an adiabatic ca lorimeter. Temperatures ranged from their triple points to 345 K, and press ures up to 35 MPa. Measurements were conducted on the liquid in equilibrium with its vapor and on compressed liquid samples. The samples were of high purity, verified by chemical analysis of each fluid. For the samples, calor imetric results were obtained for two-phase (C-v((2))), saturated-liquid (C -sigma or C-x'), and single-phase (C-v) molar heat capacities. The C-sigma data were used to estimate vapor pressures for values less than 105 kPa by applying a thermodynamic relationship between the saturated liquid heat cap acity and the temperature derivatives of the vapor pressure. The triple-poi nt temperature and the enthalpy of fusion were also measured for each subst ance. The principal sources of uncertainty are the temperature rise measure ment and the change-of-volume work adjustment. The expanded relative uncert ainty (with a coverage factor k = 2 and thus a two-standard deviation estim ate) for C-v is estimated to be 0.7%, for C-v((2)) it is 0.5%, and for C-si gma it is 0.7%.