OP-II-3

OP-II-25(surface) ‘wall-reaction’ model (negligible concentration gradients inside the catalyticlayer) and reactant exhaustion at the washcoat wall due to fast reactions.The system behaviour is described by dimensionless parameters translating thecompetition between the characteristic times for transport mechanisms and/orheterogeneous reaction and depend on flow properties, geometrical relations (e.g.aspect ratio, washcoat thickness) and reaction kinetics. This multi-scale analysis willcontribute for the selection of suitable models for simulation in specific parameterranges, since operating regimes are mapped and analytical solutions available forthe relevant ones. Moreover, the ranges of validity of such regimes constitute theboundaries in the aforementioned parametric diagrams. For each regime,approximate concentration profiles are derived and simple estimates for theconversion (or equivalently, the mixing-cup concentration) provided. As aconsequence, the classical Graetz problem will be reencountered in the commonlyfound regime where convection and transverse diffusion are dominant. In this case,the main results are reviewed and systematized in the common multiparametricanalysis.Finally, the analytical approach employed results in a shortcut method for designand preliminary optimization of microreaction units. On the other hand, simplificationof the numerical procedure may be achieved by introduction of approximateanalytical solutions in the regimes of interest.References[1] P. L. Mills, D. J. Quiram and J. F. Ryley, Chem. Eng. Sci. 2007, 62, 6992-7010.[2] W. Ehrfeld, V. Hessel and V. Haverkamp in Microreactors, Vol. Wiley, 2005.[3] S. Walter, S. Malmberg, B. Schmidt and M. A. Liauw, Catal. Today 2005, 110, 15-25.[4] M. Bhattacharya, M. P. Harold and V. Balakotaiah, Chem. Eng. Sci. 2004, 59, 3737-3766.[5] W. Lewis and S. Middleman, AIChE J. 1974, 20, 1012-1014.[6] T. Gervais and K. F. Jensen, Chem. Eng. Sci. 2006, 61, 1102-1121.[7] C. M. Bender and S. A. Orszag, Advanced Mathematical Methods for Scientists and Engineers1978.[8] C. C. Lin and L. A. Segel, Mathematics Applied to Deterministic Problems in the Natural Sciences,SIAM, 1988AcknowledgementsJ. P. Lopes gratefully acknowledges financial support from FCT - Fundação para aCiência e a Tecnologia, PhD fellowship SFRH/BD/36833/2007.147