INFLUENCE OF THE INTERFACIAL REACTION RATE ON MACROSCOPIC SYSTEMS.
Advancing the chemical engineering fundamentals
Transport Phenomena in Porous/Granular Media - II (T2-7b)
Keywords: jump condition; interfacial reaction; Porous media; CTSR; Fixed bed reactor
The development of models for macroscopic transport processes in multiphase systems has been the subject of intense research activity in the last decades. Most of the efforts have been devoted to the statement of effective medium conservation equations which are usually valid in the homogeneous regions of the system. This gives rise to the problem of describing transport phenomena in the transition zone (the inter-region) between two (or more) homogeneous regions. This difficulty can be overcome by posing the corresponding jump boundary conditions that match the transport equations of the homogeneous regions (Ochoa-Tapia and Whitaker, 1995). Moreover, the use of new materials in the reaction-transport processes enhances the idea that the conditions under which the imposition of the condition of mass flux continuity may fail. Recently, Valdés-Parada et al. (2006), using the method of volume averaging (Whitaker, 1999), proposed a jump boundary condition for the mass flux which involves a reaction term.
Therefore, in this work we carry out an analysis to determine the effect of including the reaction term proposed by Valdés-Parada et al. (2006) in the modeling of the steady-state diffusive mass transport with first-order kinetics taking place in a porous catalytic pellet inside a CSTR and a fixed-bed reactor. The results show a strong dependence with the Thiele modulus (Φ), the Biot number (Bi), the residence time in the system and the ratio between the internal and external areas of the catalytic pellet. More explicitly, for Φ>5 and BiЄ[1,10] the results from the model that takes in account the surface reaction term exhibit the highest deviations from those assuming continuity in the mass flux. Of all the output variables computed, the interfacial mass flux exhibited the biggest deviations. As above mentioned, these conditions are more likely to be exhibited, for example, by materials with highly fractured porous surface (Coppens, 1999). The results from this analysis can also be extended to more complicated systems and transport mechanisms.
References
Coppens M.O. (1999). The effect of fractal surface roughness on diffusion and reaction in porous catalysts – from fundamentals to practical applications. Catalysis Today, Vol. 53, 225-243.
Ochoa-Tapia J.A., Whitaker S. (1995). Momentum transfer at the boundary between a porous medium and a homogeneous fluid-I. Theoretical development. International Journal of Heat and Mass Transfer. Vol. 38, No. 14, 2635-2646.
Valdés-Parada F.J., Goyeau B., Ochoa-Tapia J.A. (2006). Diffusive mass transfer between a microporous medium and an homogeneous fluid: Jump boundary conditions. Chemical Engineering Science, Vol. 61, 1692-1704.
Whitaker S. (1999). The method of volume averaging, Kluwer academic publishers.
Presented Tuesday 18, 16:40 to 17:00, in session Transport Phenomena in Porous/Granular Media - II (T2-7b).
