Prediction of the reaction yield in a X-micromixer given the mixing degree and the kinetic constant

An adequate comprehension of the flow regimes and mixing process inside microreactors is a crucial factor to obtain high reaction yields. In the present paper, we carry out jointly simulations and experiments to characterize the flow regimes and reaction occurring in a X-microreactor up to Reynolds number, Re, based on the inlet bulk velocity and mixing channel hydraulic diameter, equal to 600. For Re > 375, an unsteady periodic regime is found, characterized by the presence of a central vortical flow structure that periodically collapses leading to symmetric vorticity shedding in both outlet channels. In the meanwhile, two counterrotating vortices form in the confluence region of the inlet streams, come closer, and merge creating again the central vortex. Compared to the steady engulfment regime, previously described in the literature and characterized by a single steady central vortex, a higher mixing degree is found in the unsteady regime. However, despite the increased mixing, the reaction yield remains similar, as the enhanced mixing is counterbalanced by the reduced residence time of the reactants. Based on the obtained results we developed a model to predict the reaction yield, given the mixing degree and the nominal kinetic constant as input data. The proposed law successfully predicts the reaction yield in all the flow regimes, including the unsteady engulfment one regime, and for the Damkohler numbers in the range 10(-1) < Da < 10(3) (chemistry slower and faster than flow convection).