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Thermophysical Properties of Gaseous CF4 and C2F6 From Speed-of-Sound Measurements



John J. Hurly


A cylindrical resonator was employed to measure the sound speeds in gaseous CF4 and C2F6. The CF4 measurements span the temperature range 300 K to 475 K while the C2F6 measurements range from 210 K to 475 K. For both gases, the pressure range was 0.1 Mpa or 80 % of the sample's vapor pressure. Typically, the speeds of sound have a relative uncertainty of less than 0.01 % and the ideal-gas heat capacities derived from them have a relative uncertainty of less than 0.1 %. The heat capacities agree with those determined from spectroscopic data. The sound speeds were fitted with the virial equation of state to obtain the temperature-dependent density virial coefficients. Two models for the virial coefficients were employed, one based on the square-well potentials and the second based on a Kihara spherical-core potential. The resulting virial equations reproduced the sound-speed measurements to within 0.005 %, and yield densities with relative uncertainties of 0.1 % or less. The visosity calculated from the Kihara potential is 2 % to 11 % less than the measured viscosity.
International Journal of Thermophysics
No. 2


C<sub>2</sub>F<sub>6</sub>, CF<sub>4</sub>, equation-of-state, hexafluoroethane, speed-of-sound, tetrafluoromethane, thermodynamic properties, virial coefficients


Hurly, J. (1998), Thermophysical Properties of Gaseous CF<sub>4</sub> and C<sub>2</sub>F<sub>6</sub> From Speed-of-Sound Measurements, International Journal of Thermophysics (Accessed December 2, 2023)
Created November 1, 1998, Updated June 2, 2021