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8.9.3 Thermal Diffusion Coefficients

The thermal diffusion coefficients can be defined as constants, polynomial functions, user-defined functions, or using the following empirically-based composition-dependent expression derived from [ 188]:

 D_{T,i} = -2.59 \times 10^{-7} T^{0.659} \left[ \frac{M_{w,i... ...}} {\displaystyle{\sum_{i=1}^N M_{w,i}^{0.489} X_{i}}} \right] (8.9-13)

This form of the Soret diffusion coefficient will cause heavy molecules to diffuse less rapidly, and light molecules to diffuse more rapidly, towards heated surfaces.

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