Speed-of-sound measurements using spherical resonator and acoustic virial coefficients for gaseous pentafluoroethane (R125)

Speed-of-sound measurement with a spherical resonator is recognized as one of the most precise and reliable approaches to determine ideal-gas heat capacities and to reveal thermodynamic properties of rarefied gases. In this study, a spherical resonator was used to measure the speed of sound in gaseous pentafluoroethane, R125. Eighty speed-of-sound values were obtained along five isotherms from 277 K to 343 K and up to 600 kPa in pressure. In addition, c _p^o values and second acoustic virial coefficients were determined at each temperature. Sample purity was 99.9% of the gas-chromatograh area fraction analyzed by the manufacturer. The expanded uncertainties with k = 2 are estimated at 11 mK in temperature, 0.31 kPa in pressure, and 72 ppm in speed of sound. The c_p^o values reported here were compared with those from spectroscopic data. The agreement between them was within ±0.2%.