Speed-of-sound measurements using spherical resonator and acoustic viral coefficients for gaseous 1,1,1-trifluoroethane (R143a)

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, we applied a spherical resonator to measure the speed of sound in gaseous 1,1,1-trifluoroethane, R143a. Seventy speed-of-sound values were obtained along five isotherms from 303 K to 343 K and up to 500 kPa in pressure. In addition, c_p° values and acoustic second viral coefficients were determined at each temperature of isotherm. Sample purity was 99.95% of the gas chromatograph area fraction analyzed by the manufacturer. The expanded uncertainties with k = 2 are estimated to be 8 mK in temperature, 0.2 kPa in pressure, and 72 ppm in speed of sound. We compared the c_p° values determined from the measurements with those from theoretical calculation and confirmed the agreement between them within ±0.1%.