Combustion of a spherical carbon particle in slow viscous flow

Abstract

A theory for the quasisteady behavior of a carbon particle in the slow viscous flow of an oxidizing ambient gas is developed. Oxidation and gasification of carbon through the heterogeneous surface reactions C + 1 2 O 2 → CO and C + CO 2 → 2CO are combined with the concept of a flame sheet in the gas to represent the chemical kinetics. The heterogeneous reactions produce radial convection from the particle, which couples with ambient convection and diffusion to affect the rate of particle mass loss and the nature of the flame sheet. Both the radial convection and the ambient convection are of the same order and are characterized by a mass loss parameter and a Reynolds number defining the slow viscous flow. The theory predicts that the particle mass loss rate is increased relative to that for spherically symmetric combustion, and that the drag is decreased relative to that prevailing in the absence of chemical reaction.