Statistical Mechanics of Transport in Fluids

Transport processes in fluids are discussed in the framework of ensemble theory. A nonequilibrium ensemble is constructed by explicit consideration of the external forces which bring about the deviation from equilibrium. The resulting ensemble has the form of a product of factors, one characteristic of local equilibrium and the other containing a description of the irreversible processes. For states near equilibrium (to which the discussion is restricted) the ensemble depends linearly on the thermodynamic parameters which specify the deviation from equilibrium. Transport relations are obtained which are, in general, nonlocal in space and time; that is, the transport coefficients are frequency and wavelength dependent. An approximation procedure is used which amounts to an expansion in powers of the wave number, and in the lowest approximation one obtains the familiar local transport relations.