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

Published

November 1, 1998

Author(s)

John J. Hurly

Abstract

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.

Citation

International Journal of Thermophysics

Volume

20

Issue

No. 2

Pub Type

Journals

Keywords

C₂F₆, CF₄, equation-of-state, hexafluoroethane, speed-of-sound, tetrafluoromethane, thermodynamic properties, virial coefficients

Citation

Hurly, J. (1998), Thermophysical Properties of Gaseous CF₄ and C₂F₆ From Speed-of-Sound Measurements, International Journal of Thermophysics (Accessed November 6, 2025)