Soret coefficient

(physics) A tabulated value used in binary thermal diffusion calculations in gaseous systems; expressed as D′/D = α X₁X₂, where D′ is the coefficient of thermal diffusion, D is the coefficient of ordinary diffusion, α is the thermal diffusion constant, X₁ is the mole fraction of the lower-molecular-weight component, and X₂ is the mole fraction of the higher-molecular-weight component.