Kinetic Rate Law and Diffusional Flux

When the chemical kinetics are nth-order and irreversible in terms of the molar 

The characteristic molar density of reactant A is calculated in the vicinity of the external surface of the catalyst, and k is an nth-order kinetic rate constant on a volumetric basis when molar densities are used in the rate expression. The units of k are (volume/mole) Vtime. One-dimensional diffusion is written in three 

The dimensionless spatial coordinate rj is measured in the thinnest dimension of rectangular catalysts. For cylindrical and spherical catalysts, r) is measured in the radial direction. The characteristic length L required to make the spatial coordinate dimensionless [i.e., r] = spatial coordinate /L] is 

One-half the thickness of catalysts with rectangular symmetry, measured in the thinnest dimension, 

18-2 MASS TRANSFER EQUATION IN THREE COORDINATE SYSTEMS 

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