Early induction of secondary vortices for micromixing enhancement

In the present work a new type of micromixer has been proposed and its mixing characteristic has been analyzed. The micromixer can be viewed as a U-tube with a side inlet. Here micromixing is enhanced by the secondary vortex generation induced by the curvature of the tube. The flow in the mixer geometry is investigated theoretically to understand micro-mixing using computational fluid dynamics (CFD). For this we use the Navier-Stokes equations coupled with species transport. Mixing is quantified using mixing quality which is a measure of the uniformity of the concentration in a given geometry. Special attention is paid to the occurrence of the secondary vortices close to the mid point of the outer wall and its role in mixing. Simulations are also done to study the flow in U shaped channels. The simulation results show that the new design leads to an early introduction of secondary vortices than a simple U tube. Thus in the new design the secondary vortices are induced at a Re = 120 as opposed to the classical value of Re = 400 (when there is no side inlet) reported in the literature. Mixing is studied for different diffusivities and combination of inlet velocities. We also compare the performance of our design with the classical T and Y mixers. The early induction implies that we can have good mixing at low Re. Consequently, when used as a micro-reactor we can combine good mixing with high residence times to obtain good conversions in our system.