A new conceptual mixing strategy for micro mixers

Micro-devices such as microfluidic channels have been extensively studied over the last decade because of the increasing interest in the lab-on-a-chip concept where chemical or bio-chemical reactions are carried out with micro volumes of reagents.

The main obstacle associated to these devices relates to mixing. Indeed, in small dimension channels, the flow appears to be laminar, with typical Reynolds number below 100. Since turbulence does not occur in such micro-channels, the mixing phenomenon only occurs through molecular diffusion. But the kinetics of this mechanism appear to be much too slow when compared to these of the chemical reactions to be carried out. Therefore, the absence of turbulence considerably limits the mixing of the reactants and the yield of the reaction.

A recent active mixing strategy based on a bypass transition mechanism has been proposed by the partners of this project. This process involves the interaction between two pairs of counter-rotating vortices near the wall of the channel, acting as turbulence actuators, and generating a new streamwise vorticity zone (light brown structures on the image on the right). This process is suspected to be independent from the Reynolds number of the flow, and could therefore be exploited to enhance mixing in microfluidic channels or micro devices through the generation of “synthetic” turbulence in a laminar flow.

The process was tested through numerical simulation, where the pair of counter­‐rotating vortices was introduced in the flow in the form of stream functions represented by analytical expressions. While this approach was quite legitimate from a fundamental perspective, one can now question the technical feasibility of the generation of the pairs of counter-rotating vortices. The aim of this proposal is therefore to test the proof of concept and validate the feasibility of using two synthetic wall jets interacting in the span wise direction to produce the pairs of counter rotating vortices in the flow.