An entropy criterion for the validity of Navier-Stokes order continuum theory for gas-solid flow: Kinetic theory analysis

•Kinetic theory was used to analyze the entropy of gas-solid systems.•The local thermodynamic equilibrium postulate and N-S continuum models are self-consistent.•Entropy criterion for the validity of N-S order continuum model was proposed.•The criterion is a function of the gradient of hydrodynamic variables and particle inelasticity.