Relation between Thermal Conductivity and Viscosity for Some Nonpolar Gases

Abstract

The dimensionless ratio f = λM/ηC_v relating the thermal conductivity, molecular weight, viscosity, and constant‐volume molar heat capacity has been determined experimentally for helium, argon, nitrogen, oxygen, and hydrogen in the range 90°–290°K. The experimental method provides a direct determination of f by measurement of the subsonic temperature recovery factor. For helium, f = 2.503, and for argon, f = 2.506, in complete accord with the rigorous Chapman‐Enskog kinetic theory for monatomic gases. Data on nitrogen, oxygen, hydrogen, and also carbon dioxide confirm, at least qualitatively, a recent approximate theory which relates deviations from the modified Eucken approximation to the relaxation times of internal energy states. Collision numbers for rotational relaxation derived from the experimental data are: nitrogen, 6.8; oxygen, 6.0; and carbon dioxide, 2.4. These collision numbers are very nearly independent of temperature. The results confirm the fact that the interchange of translational and rotational energy is unusually difficult for hydrogen.