Molar heat capacity at constant volume of trifluoromethane (R23) from the triple-point temperature to 342 K at pressures to 33 MPa

Molar heat capacities at constant volume (C, of trifluoromethane (R23) have been measured with an adiabatic calorimeter, Temperatures ranged From the triple point to 342 K, and pressures up to 33.5 MPa. Measurements were cond ucted on the liquid in equilibrium with its vapor and on compressed liquid and gaseous samples. The samples were of high purity, as verified by chemic al analysis. Calorimetric quantities are reported for the two-phase (C-v((2 ))), saturated-liquid (C-sigma or C-x'), and single-phase (C-v) molar heat capacities. The C-v((2)) data were used to estimate vapor pressures for val ues less than 100 kPa by applying a thermodynamic relationship between the two-phase internal energy U-(2) and the temperature derivatives of the vapo r pressure. The triple-point temperature and the enthalpy of fusion were al so measured. The principal sources of uncertainty are the temperature rise measurement and the change-of-volume work adjustment. The expanded relative uncertainty (with a coverage factor k = 2 and thus a two-standard deviatio n estimate) is estimated to be 0.7% for C-v, 0.5% for C-v((2)) and 0.7% for C-sigma.