Numerical Investigation of Mass Transfer with Two-Phase Slug Flow in a Capillary

The multiphase flow of two immiscible liquids in a circular capillary micromixer was investigated numerically. The mass transfer characteristics of this flow pattern are of primary interest in this study. A simple neutralization titration reaction was chosen as the basis. The liquid-liquid two phase slug flow was formed during the mixing. The mixing was quantified for different volume flow rates of the reactants. To simplify the computational procedure, instead of applying different volume flow rate, the wall was moved with different average slug flow velocity. It was shown that the residence time required for reaction completeness was dominated by the average flow velocity for this type of micromixer. Furthermore, a parametric two-dimensional model was implemented with COMSOL Multiphysics to investigate mixing phenomenon within the slugs. The COMSOL model allows for rapid analysis of different microchannel geometries and flow rates. The results show a dramatic intensification of the reaction as the aspect ratio, which is the ratio of slug length to capillary radius, decreases with a constant average flow velocity.