A Theory of Thermal Diffusion in Liquids

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Abstract
A theory of thermal diffusion in liquids has been developed based on Denbigh's interpretation of the ``net heat of transport'' which arises in the thermodynamics of irreversible processes. The thermal diffusion ratio α is expressed in terms of the energies of vaporization of the pure components, the excess energy, entropy and volume of mixing, and the concentration dependence of ΔUc. The efficiency with which the two species pack together is also introduced. The Hildebrand-Scatchard solution theory is applied to these results and α is expressed in terms of solubility parameters, molal volumes and packing efficiencies. The equations are compared with previously published experimental results, and reasonably explainable packing efficiencies are obtained. In the appendices the effects of nonrandomness of mixing are considered and the theory is extended to ternary mixtures.