We show that the entropy method, that has been used successfully in order to prove exponential convergence towards equilibrium with explicit constants in many contexts, among which reaction-diffusion systems coming out of reversible chemistry, can also be used when one considers a reaction-diffusion system corresponding to an irreversible mechanism of dissociation/recombination, for which no natural entropy is available.
Starting from the Grad 13-moment equations for a bimolecular chemical reaction, Navier-Stokes-type equations are derived by asymptotic procedure in the limit of small mean paths. Two physical situations of slow and fast reactions, with their different hydrodynamic variables and conservation equations, are considered separately, yielding different limiting results.
We show that the entropy method, that has been used successfully in order
to prove exponential convergence towards equilibrium with explicit constants in many contexts,
among which reaction-diffusion systems coming out of reversible chemistry, can also be used
when one considers a reaction-diffusion system corresponding to an irreversible mechanism of
dissociation/recombination, for which no natural entropy is available.
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