(a) Variation of as a functionof the mole fraction x₁ of the first compound. The quantity is chosen, because it represents the sensitivity of the system to a gradient of temperature. In this panel, all quantities are related to the ideal gas state (marked by the “0” superscript). (b) Similar plot using the thermal diffusion coefficient provided by Haase’s theory (see Eq. (B.19)). In both panels, the solid line is associated with the C₂ H₆-CH₄ system, while the dashed line is related to N₂-CH₄. All computations represented in this figure assume a pressure of 1.5 bar and a temperature of 90 K.