SOLUTION OF UNSTEADY-STATE SHRINKING-CORE MODELS BY MEANS OF SPECTRALFIXED-POINT METHODS - NONUNIFORM REACTANT DISTRIBUTION AND NONLINEAR KINETICS/

We present a method for solving moving-boundary problems in the presen ce of nonuniformities and nonlinearities. The method is based on the s pectral decomposition of the concentration field of reacting/diffusing species in a suitable system of eigenfunctions and on the solution of the corresponding system of ordinary differential equations for the F ourier coefficients by means of fixed-point methods. The method propos ed by Selim and Seagrave is improved upon and extended to solve moving -boundary problems in the presence of position-dependent diffusion coe fficients and nonlinearities in kinetic rates. We apply this method to solve isothermal and nonisothermal shrinking-core models for fluid-so lid noncatalytic reactions by focusing on the influence of spatial non uniformities in the solid reactant distribution.