  Polydisperse gas-solid flows, which is notoriously difficult to model due to
the complex gas-particle and particle-particle interactions, are widely
encountered in industry. In this article, a refined kinetic theory for
polydisperse flow is developed, which features single-parameter Chapman-Enskog
expansion (the Knudsen number) and exact calculation of the integrations
related to pair distribution function of particle velocity without any
mathematical approximations. The Navier-Stokes order constitutive relations for
multifluid modeling of polydisperse gas-solid flow are then obtained
analytically, including the solid stress tensor, the solid-solid drag force,
the granular heat flux and the energy dissipation rate. Finally, the model is
preliminarily validated by comparing to the discrete element simulation data of
one-dimensional granular shear flow and by showing that the hydrodynamic
characteristics of gas-solid flows in a bubbling fluidized bed containing
bidisperse particles can be successfully predicted.
