(140f) Mixing Enhancement by Internal Circulation Flow Using Liquid-Liquid Slug Flow in Microreactors

Flow regime in microreactors is laminar flow, enabling precise control of liquid-liquid slug flow. Since slugs in the channel move like a periodic plug flow, narrow residence time distribution can be achieved precisely. Internal circulation flow from the friction between the channel wall and fluid in the slug is expected to enhance the performance of mixing, which is mainly driven by molecular diffusion in laminar flow. If the mixing of the reactant in the slug is instant, it is sufficient to apply this liquid-liquid slug flow to reaction kinetics measurements. From this viewpoint, we estimate quantitatively the internal mixing in the slug by Computational Fluid Dynamics (CFD) simulations. The results show that the circulation flow occurs in the slug and stagnant regions exist in the front and tail parts and in the center of recirculation vortices. This circulation flow greatly reduces mixing time as compared with the mixing time when mixing is driven by only molecular diffusion. For large slugs, large stagnant regions cause long mixing time. However, the mixing time of reactants in the slug was significantly reduced with increasing velocity of slug in the channel. The way of reactant supply into the slug is also a crucial factor. The mixing time supplying two fluids for top and bottom in the channel (reactant arrangement in the axial direction) is shorter than that supplying them for left and right (reactant arrangement in the width direction). From these simulation results, the operation for designing slug sizes and shapes to reach a desired mixing performance is also shown experimentally. Combining the computational and experimental results allows us to a design method for measuring kinetics of fast reactions using liquid-liquid slugs.