Un modèle simple de réaction-diffusion-conduction thermique dans et autour d'une particule poreuse: Partie II: Diffusion externe

Abstract

The general case of chemical reactions in a porous particle subject to competition between external and internal diffusion and thermal conductivity is studied. The overall “resistance” is expressed as the sum of the external and internal resistances and the fractional external resistance is calculated. An overall efficiency η e is defined with respect to the measured values of the external temperature and concentration. η e is expressed as a function of the internal efficiency which was defined in Part I. This general relationship between η e and η i is valid for any chemical reaction and only requires that the variables C and T be separable (cf. Part I). In the special case of an isothermal first order reaction in a porous particle the multiplicity of operating points due to the heating in the boundary layer is studied. A criterion of multiplicity is proposed which is in excellent agreement with that proposed by Hlavacek and Kubicek. To illustrate the use of the method the procedure of determining the kinetics of any reaction is described even in the general case where rate measurements are affected by internal diffusion and thermal effects.