Heat Capacities at Constant Volume of Pure Water in the Temperature Range 412−693 K at Densities from 250 to 925 kg·m-3

Abstract

The heat capacity at constant volume CV of pure water has been measured in the temperature range from 412 K to 693 K at 13 isochores between 250 kg·m-3 and 925 kg·m-3. Measurements cover the critical region and coexistence curve. Measurements have been made in both the one- and two-phase regions near the phase transition points. The measurements were made in a high-temperature, high-pressure adiabatic nearly constant-volume calorimeter. The uncertainty of the heat capacity measurements is estimated to be within ±2.5%. Liquid and vapor one- ( ) and two-phase ( ) heat capacities, temperatures (TS), and densities (ρS) at saturation were obtained by the method of quasi-static thermograms. The parameters (c, T*,V*) of the simplified-perturbed-hard-chain-theory (SPHCT) equation of state have been optimized to allow calculations of heat capacities for water in the vapor and liquid phases. The relative average deviations for H2O were within about ±4.5%, except in the critical region where differences reached 15−2...