Reaction performance in T-, X- and arrow-shaped microdevices

Microreactors are widely used for continuous flow operations. The assessment of their performance has a crucial role in determining the optimal geometries and working conditions. Among the most common geometries, we compare T-, X- and arrow-shaped devices to highlight how flow features, mixing degree and residence time affect the reaction yield and productivity. We focus on the steady flow regimes occurring in the three devices fed with reactive streams for varying Reynolds numbers. The Reynolds number, Rei, is herein based on the bulk velocity and the inlet-channel hydraulic diameter. The flow regimes presenting a central vortex in the mixing channel, found in X- and arrow-microreactors, lead to the best mixing and reaction yield. For Rei≤ 120 the maximum productivity is obtained with the X-microreactor, whereas above Rei = 120, with the arrow-reactor. Conversely, lower reaction yields and productivities are found in the T-microreactor, which exhibits an engulfment regime with two co-rotating vortices in the mixing channel. It is thus evident that the spiral pattern induced by a single central vortex extends the contact area between the reactants and leads to better performance. In terms of reaction cost, for the lower productivity values, the associated pressure drops are similar for all three geometries. For higher productivities, the best performance, i.e., the lowest pressure drops, is reached in the arrow-microreactor, followed by the T- and, then, by the X-device.