Film theory effective diffusivity method

Numerical simulations of Sardesai s experiments are discussed by Webb and Sardesai (1981) and Webb (1982) (who used the Krishna-Standart (1976), Toor-Stewart-Prober (1964) and effective diffusivity methods to calculate the condensation rates), McNaught (1983a, b) (who used the equilibrium model of Silver, 1947), and Furno et al. (1986) (who used the turbulent diffusion models of Chapter 10 in addition to methods based on film theory). It is the results of the last named that are presented here. 

Ks do not match with each other. This is partly the result of the effects of the specific surface which was different in the two methods. However, the mechanisms of the dissolution kinetics seem to be identical. The reaction rate of the acid with carbonate mineral would be controlled by diffusion of the reactant into and the products out of the pores. Therefore, the availability of only the contact surface is not adequate. The type of surface in terms of relevant diffusion model and the closest theory to that model, such as film, penetration, or any other, should also be specified. 

This method requires three fundamental assumptions the first might be termed the "effective medium theory assumption." Because polypyrrole is microporous (15), it is a biphasic system (i.e., it is composed of solvent-swollen polymer and solvent-filled pores). We assume, however, that as an ion diffuses through the pol3rmer film, it makes so many transitions between these two microphases that its motion can be described by an apparent diffusion coefficient, D pp. This Dapp diffusion... 

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