KINETIC-MODELS FOR DIFFUSION IN SHEAR-FLOW

The kinetic models proposed by Garzo et al. [Phys. Fluids A 1, 380 (1989)] and Gross and Krook [Phys. Rev. 102, 593 (1956)] are used to study diffusion in uniform shear flow. The kinetic equations are solved by means of a generalized Chapman-Enskog expansion for Maxwell molecules. The main peculiarity of the method is that the successive approximations to the velocity distribution functions retain all orders in the shear rate. Two cases are considered, namely the self-diffusion and the tracer diffusion in a system under shear flow. The relevant transport properties and the distribution functions are explicitly obtained. A comparison with previous results derived from the Boltzmann equation and between both models is carried out.