Molecular Diffusion Studies in Gases at High Temperature. II. Interpretation of Results on the He–N2 and CO2–N2 Systems

Abstract

Experimental data on the binary diffusion coefficients of He–N₂ and CO₂–N₂ obtained by the ``point source'' technique over the temperature range 300–1150°K are discussed in terms of intermolecular potential energies. For He–N₂, the data can be satisfactorily represented by a purely repulsive potential. The data include the extremes of the concentration dependence for DHe–N₂, i.e., with either He or N₂ present only as a trace component, and this effect is taken into account in the theoretical interpretation. It is shown that, at their upper temperature limit, the data come within 150° of overlapping the range of validity for the diffusion coefficient predicted from the repulsive potential obtained by Amdur et al. from molecular scattering experiments. A slight interpolation indicates quite remarkable agreement between the two types of experiments. This is good evidence of the validity of predicting high‐temperature transport properties from scattering potentials in certain cases—a possibility first pointed out by Amdur. A modified Buckingham (Exp‐Six) potential is also obtained which covers both the diffusion and scattering potentials. For CO₂–N₂, the data are fitted with a Lennard‐Jones (6–12) potential. It is shown that (for both He–N₂ and CO₂–N₂) the predictions derived from viscosity parameters for the pure components and simple combining rules are quite unreliable at high temperatures.