Speed of Sound and Ideal-Gas Heat Capacity at Constant Pressure of Gaseous Difluoromethane

Abstract

The speed of sound of gaseous difluoromethane (HFC-32) was measured for temperatures from 273.15 K to 333.15 K and pressures from 48 kPa to 390 kPa with a cylindrical, variable-path acoustic interferometer operating at 156.252 kHz. The uncertainty of the speed of sound was less than ±0.1%. The ideal-gas heat capacity at constant pressure and the second acoustic virial coefficients were determined over the temperature range from the speed of sound measurements. The ideal-gas heat capacity at constant pressure results and second virial coefficients calculated from these speed of sound measurements were compared with results from the literature determined from PVT measurements and from speed of sound measurements. The uncertainty of the ideal-gas heat capacity at constant pressure was estimated to be less than ±1%.