THERMODYNAMIC PROPERTIES OF LIQUID METHANE, PROPANE, AND REFRIGERANT HFC-134A FROM SPEED-OF-SOUND MEASUREMENTS

The procedure of deriving thermodynamic properties of liquids from the speed of sound is recommended. It is based on the numerical integration of ordinary differential equations (ODEs) (rather than partial differential equations (PDEs)) connecting the speed of sound with other thermodynamic properties in the T-p domain. It enables more powerful methods of higher-order approximation to ODEs to be used (e.g. Runge-Kutta) and requires only the Dirichlet conditions. It was tested on the examples of liquid methane in the temperature range of 120-170 K and the pressure range of 5-50 MPa, liquid propane in the temperature range of 150-300 K and the pressure range of 5-50 MPa, and liquid refrigerant HFC-134a in the temperature range of 210-350 K and the pressure range of 5-50 MPa. Densities of liquid methane, propane, and HFC-134a were derived with absolute average deviation of 0.002, 0.007, and 0.003%, respectively. Isobaric molar heat capacities of liquid methane, propane, and HFC-134a were derived with absolute average deviation of 0.128, 0.136, and 0.095%, respectively. Isochoric molar heat capacities of liquid methane, propane, and HFC-134a were derived with absolute average deviation of 0.088; 0.227, and 0.057%, respectively.