Diffusion of Heat and Mass in a Chemically Reacting Mixture away from Equilibrium

Abstract

We report transport properties for the hydrogen dissociation reaction in a temperature gradient, at conditions where reactants and product concentrations are significant (ca. 50% dissociation, 10 4 K). This is the first time transport properties are obtained from nonequilibrium molecular dynamics simulations of a reaction away from chemical equilibrium, with -1 < r G/RT < 1, and in the presence of a thermal gradient larger than 10 11 K m -1. The results, which are described by nonequilibrium thermodynamic theory, show that a strongly endothermic reaction has a large impact on the transport coefficients. The thermal conductivity away from equilibrium was 4 times the value at zero mass fluxes, which was comparable to that of dense gas at high temperature (≈1 W/m K). The vibrational degrees of freedom of the molecule may help explain the large thermal conductivity away from chemical equilibrium. The observed interdiffusion coefficient was smaller than typical for gases (10 -7 m 2 /s). The coupling of heat and mass transport was found to be very large. This is in sharp contrast to the common perception of gas mixtures that this coupling, the Dufour effect, is negligible.