Isochoric heat capacity measurements for light and heavy water near the critical point

The isochoric heat capacity was measured for D2O at a fixed density of 356. 075 kg.m(-3) and for H2O at 309.905 kg.m(-3). The measurements cover the ra nge of temperatures from 623 to 661 K. The measurements were made with a hi gh-temperature. high-pressure, adiabatic calorimeter with a nearly; constan t inner volume. The uncertainty of the temperature is 10 mK, while the unce rtainty of the heat capacity is estimated to be 2 to 3%. Measurements were made in both the two-phase and the one-phase regions. The calorimeter instr umentation also enables measurements of PVT and the temperature derivative (partial derivativeP/partial derivativeT)(V) along Each measured isochore. A detailed discussion is presented on the experimental temperature behavior of C-V in the one and two-phase regions including the coexistence curve ne ar the critical point. A quasi-static thermogram method was applied to dete rmine values of temperature at saturation T-S(rho) on measured isochores. T he uncertainty of the phase-transition temperature measurements is about +/ -0.02 K. The measured C-V data for D2O and H2O are compared with values pre dicted from a recent developed parametric crossover equation of state and I APWS-95 formulation.