Shape change of rough particles

Abstract

In the analysis of solid combustion and other fluid-solid noncatalytic reactions, it is customary to treat reacting particles as spherical to simplify the solution of the relevant reaction-transport equations. The analysis of the spherically symmetric problem is generally assumed to set the correct trends on the effect of various parameters, even when the reacting particles are nonspherical. In this work, the authors analyze reaction and external diffusion for nonspherical, but axially symmetric, particles to determine the change in the shape of a particle due to consumption of the solid material. The shape change can be pronounced over extended conversion even when the initial particle shape is only slightly nonspherical. The most important noncatalytic gas-solid reaction is coal or char combustion. However, under conditions of high Thiele modulus, that is, shrinking core combustion, external heat transfer, as well as mass transfer, needs to be considered. In this note, the authors assume isothermal conditions and consider the external mass-transfer problem only. However, the methodology presented is applicable, with suitable extensions, to simultaneous heat and mass transfer. The latter problem was discussed earlier by Choi and Gavalas (1993) with the focus on coal combustion. Two technique are used to treat the problem ofmore » reacting nonspherical particles. The first is domain perturbation (DP) (Brenner, 1964; Acrivos and Taylor, 1964), the second is the boundary integral technique (BI) (Brebbia and Walker, 1980; Liggett and Liu, 1972).« less