Analysis of the Onsager Relations by Analytic Methods in Kinetic Gas Theory

The well-known Onsager relations L ₁₂=L ₂₁ are verified within the framework of kinetic gas theory with allowance for the mass and heat fluxes localized in the Knudsen layer. On the basis of an analytic solution of the BGK (Bhatnagar-Gross-Krook) equation, it is shown that the Onsager relations are fulfilled correct to at least exponential corrections (–1/Kn) in the Knudsen number Kn.