Enhancing active electro-kinetic micro-mixer efficiency by introducing vertical electrodes and modifying chamber aspect ratio

Micro-mixers are considered as vital components of Micro Total Analysis systems (IJTAS). Major objective in the design of micro-mixers is achieving high mixing quality in short mixing times. In this paper, numerical simulation of some micro-mixer designs has been carried out to understand the detailed flow pattern and thereby to propose modifications for improving mixing efficiency. It is well known that inducing convection will provide turbulent like behavior with corresponding mixing enhancement. In micro systems to drive the flow, electroosmotic force is usually used by introducing electrodes. In this work, mixing electrodes have been implemented to induce convection and eddies. This numerical study addresses the problem by solving the system of inter coupled Poisson-Nernst-Planck-Navier-Stokes equations using Rayan (in-house code). These equations compared to their simplified forms, provide much more realistic physical description by including diffusion, electro-migration and convection mechanisms. In cases of active AC electrodes, all of these mechanisms play important roles. The traditional Poisson-Boltzmann model loses its accuracy in cases of complex geometry or AC electrodes especially with high frequencies. As a result of modifications proposed herein by strategic placement of vertical and horizontal electrodes and extending mixing chamber length a mixing quality of 96.2% was achieved just in 1.8 s.