Thermodynamic Properties of Carbon Dioxide Derived from the Speed of Sound

Thermodynamic properties of CO2 are derived from speed of sound in the temperature range 300 to 360 K (from 0 to 6 MPa),and 300 to 220 K (from 0 to 90% of the saturation pressure). The density, the specific heat capacity at constant pressure, and the specific heat capacity at constant volume are obtained by numerical integration of differential equations connecting the speed of sound with other thermodynamic properties. The set of differential equations is solved as the initial value problem, with the initial values specified along the isotherm at 300 K in terms of several accurate values of the density and the specific heat capacity at constant pressure. The density, the specific heat capacity at constant pressure and the specific heat capacity at constant volume are derived with the absolute average deviations of 0.018%, 0.19%, and 0.18%, respectively. The results of numerical integration are extrapolated to the saturation line for ρ, cp, and cv with the absolute average deviations of 0.056%, 2.31%, and 1.32%, respectively.