Thermal conductivity of gaseous methane and sulfur hexafluoride under pressure.

Abstract

The thermal conductivity of gaseous methane and sulfur hexafluoride was measured at temperatures from 25.00°C (298.15 K) to 100.00°C (373.15 K) under pressures up to 90 bar (9 MPa). The measurements were carried out in a vertical coaxial cylinder apparatus on a relative basis. The apparatus was calibrated using Ar, N2, Ne and CO2 as the standard gases. The uncertainty of the thermal conductivity obtained is estimated to be within 2% except in the critical region. The thermal conductivity of methane increases steadily with pressure and (∂λ/dT)p is positive throughout the range of experimental conditions. On the other hand, the thermal conductivity isotherms of sulfur hexafluoride intersect each other between 25 and 35 bar. (∂λ/dT)p is positive at low pressures and becomes negative at high pressures. The thermal conductivity of SF6 is found to increase steeply with pressure near the critical point, which may be due to the critical anomaly. The experimental results are analyzed and the thermal conductivities are expressed as functions of temperature and pressure and of density.