A correlation scheme for the thermal conductivity of polyatomic gases at low density

The kinetic theory of polyatomic and multipolar gases is used to obtain a general correlation that gives the thermal conductivity at low density in terms of known quantities: other gas properties (viscosity, specific heats, and mass diffusion coefficient); structural parameters (dipole and quadrupole moments, and moments of inertia); and interaction quantities (spin-polarization correction, mean potential-energy well depth, and high-temperature limiting value of the collision number for rotational relaxation, Zrot∞). This amounts to a one-parameter correlation, because Zrot∞ is usually not known with sufficient accuracy from independent measurements of sound absorption or thermal transpiration. The crucial feature is a relation that gives the diffusion coefficient for rotational energy in terms of Zrot∞ and the reduced temperature, kTϵ. The results are compared with recent accurate thermal conductivity data for N2, CO, CO2, N2O, CH4 and CF4. Comparable data for polar gases are lacking, but some older results for HCl indicate that the correlation is also applicable to polar gases.