THERMAL CONDUCTIVITY OF REAL GASES, PART III.

In a real gas, in the presence of a temperature gradient, the relative concentrations of the molecular clusters vary from point to point this leads to a diffusion of the larger clusters towards the warm regions and of the smaller clusters and monomolecules towards the cold parts of the apparatus, where they respectively dissociate or recombine with the absorption or liberation of the heat of formation. The increase in the thermal conductivity of the gas resulting from this circulation of the heat of formation of the clusters can be evaluated with reasonable accuracy at low pressures when only simple and double molecules need to be taken into account. This effect is negligible at high temperatures above the Boyle point, where the variation of thermal conductivity with pressure can be represented to a high degree of accuracy by Enskoygs theory it increases with decreasing temperature, and becomes approximately equal to Enskogs effect in the neighborhood of the critical temperature it is evaluated that in the case of argon the increase is of the order of 6 per atm. at the boiling point.