The large area-to-volume ratio of micro-reactors gives prospect of better yield and selectivity than for conventional designs, since diffusive fluxes of mass and heat in micro-devices scale with the area, while the rate of changes corresponding to sources and sinks are proportional to the volume. Indeed, theoretical considerations of the scaling behavior support the fact that micro-reactors allow for faster chemical reactions and provide better thermal control; cf., e.g., [1]. For applications in Chemical Reaction Engineering, the mixing of chemical species is of special interest, since it is an essential condition for chemical reactions to occur. Avoiding large pressure drops, laminar flow fields with secondary flows are chosen to increase the contact area between the inflowing educts. In this laminar but complex flow, the mixing state is determined by the interplay of convective and diffusive transport phenomena and, hence, a thorough CFD-simulation of yield and selectivity of such a reacting flow requires the resolution of the finest length scales of both the velocity and the concentration field. In order to reduce the numerical complexity we employ a simplified mathematical model of the relevant convection-diffusion-reaction equations similar to the parabolized Navier-Stokes system.

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