Speeds of Sound and Derived Thermodynamic Properties of Liquid and Supercritical Difluoromethane (R32)

Difluoromethane (R32) is a widely adopted low-global-warming-potential refrigerant and a common constituent of other important refrigerant blends. Nonetheless, low-uncertainty thermodynamic properties are scarce for this compound. This work reports experimental sound speeds of liquid and supercritical difluoromethane at temperatures from (306 to 373) K and at pressures up to 40 MPa, measured using a double-path pulse-echo apparatus with standard uncertainties between (0.02 and 0.15) %. Using the method of thermodynamic integration, these data were combined with low-uncertainty density data from the literature to derive a comprehensive set of thermodynamic properties in the liquid phase. This extends the range of data available for this crucial compound, particularly in the supercritical region. The low-uncertainty experimental sound-speed data and derived thermodynamic properties are expected to aid the development of an improved equation of state for difluoromethane.