Thermal conductivity of four polyatomic gases

Abstract

The paper presents new absolute measurements of the thermal conductivity of the four polyatomic gases hydrogen, nitrogen, carbon monoxide and methane. The measurements have been carried out at 35 °C in the pressure range 0.8–10 MPa and have an estimated uncertainty of ±0.2%.

The experimental data for methane, nitrogen and carbon monoxide have been extrapolated to zero density and used in conjunction with equally accurate viscosity data to compute ratios of the internal-energy-diffusion coefficient to the self-diffusion coefficient for each gas. For nitrogen and carbon monoxide the rotational energy diffusion coefficients are 7 and 25% below their respective mass-diffusion coefficients. These observations cannot be explained with the aid of the available theoretical analyses. For methane, vibrational internal energy is also significant, but the effective internal energy diffusion is equal to the mass diffusion coefficient within experimental error. For hydrogen the present data at zero density are consistent with the available kinetic-theory formulae although the latter are not as accurate as the experimental results.