  In this paper, we examine how to build coarse-grain transport models
consistently from the kinetic to fluid regimes. The internal energy of the gas
particles is described through a state-to-state approach. A kinetic equation
allows us to study transport phenomena in phase space for a non-homogeneous gas
mixture. Internal energy excitation is modeled using a binary collision
operator, whereas the gas chemical processes rely on a reactive collision
operator. We obtain an asymptotic fluid model by means of a Chapman-Enskog
perturbative solution to the Boltzmann equation in the Maxwellian reaction
regime. The macroscopic conservation equations of species mass, mixture
momentum, and energy are given, as well as expressions of the transport
properties. Reversibility relations for elementary processes are formulated in
the coarse-grain model at the kinetic level and are enforced in the collision
algorithm of the direct simulation Monte Carlo method used to solve the kinetic
equation. Furthermore, respecting these reversibility relations is key to
deriving a fluid model that is well-posed and compatible with the second law of
thermodynamics. Consistency between the kinetic and fluid simulations is
assessed for the simulation of a shock wave in a nitrogen gas using the uniform
rovibrational collisional coarse-grain model. The kinetic and fluid simulations
show consistency for the macroscopic properties and transport fluxes between
both regimes.
