Transfer and Reaction Coupling in the Fluid Film

2 Mass Transfer and Reaction Coupling in the Fluid Film 

The component fluxes Nf entering into Eqs. (10.3) and (10.4) are determined based on the mass transport in the film region. As the key assumptions of the film model result in the one-dimensional mass transport normal to the interface, the differential component balance equations including simultaneous mass transfer and reaction in the film are as follows  

Equations (10.16) that are generally valid for any liquid film phase represent simply a differential mass balance for the film region with the account of the source term due to the reaction. To link this balance to the process variables, like component concentrations, some additional relationships, often called constitutive relations (see [42]) are necessary. For the component fluxes Nj, these constitutive relations result from the multicomponent diffusion description (Eqs. (10.1) and (10.2)) whereas for the source terms, they follow from the reaction kinetics description. 

The latter strongly depends on the specific reaction mechanism, stoichiometry, and presence or absence of parallel reactions schemes [64]. The rate expressions for Rj usually represent nonlinear dependences on the mixture composition and temperature. Equations (10.16) should be completed by the boundary conditions relevant to the film model. These conditions specify the values of the mixture composition at both liquid film boundaries  

Combining Eqs. (10.16) with the boundary conditions (10.17) written in a vector form and using the constitutive relations, like Eqs. (10.1) and (10.2), we obtain a vector-type boundary-value problem that permits the component concentration profiles to be obtained as functions of the film coordinate. These concentration profiles, in turn, allow the component fluxes to be determined. Thus the boundary-value problem describing the film phenomena has to be solved in conjunction with all other model equations. 

---