Nonequilibrium effects in model reactive systems: The role of species temperatures.

Abstract

The nonequilibrium effects for a model reactive system, A+B\ensuremath{\rightarrow} products, that arise from the perturbation of the distribution function from the Maxwellian are studied. The main objective is the calculation of the fractional decrease of the nonequilibrium rate coefficient from the equilibrium value. This effect is examined with the Chapman-Enskog method of solution of the Boltzmann equation which treats the reactive processes as a weak perturbation. The approach is referred to as weak nonequilibrium. The reactive process causes the temperatures of the two species to differ from the system temperature and this effect can play an important role in the determination of the departure of the rate coefficient from the equilibrium value. A second method is an extension of the Chapman-Enskog approach and involves the expansion of the distribution functions about Maxwellians at different temperatures and is referred to as strong nonequilibrium (SNE). A third approach is a modification of SNE and is referred to as modified strong nonequilibrium. The three methods are described and departures of the rate coefficients from their equilibrium values are computed for each case and compared, along with an explicitly time-dependent solution of the Boltzmann equation.