Enhancement of Mixing in a Microchannel by Using AC-Electroosmotic Effect

Abstract

This study has focused on optimizing the AC-electroosmotic micro-mixer, which is composed of a microchannel with an array of rectangular electrodes attached on the bottom wall. The electrode array is spatial-periodically arranged in pairs symmetric with respect to the longitudinal central line. An AC electrode field is applied to the electrodes, which drives the secondary transverse flow in a circulating cell mode near the electrodes. The main flow along the channel longitudinal direction plus this secondary transverse flow contribute to the stretching and folding of the fluid flow, that is the chaotic behavior, and thus to the enhancement of the fluid mixing. To design the better micro-mixer, numerical simulations have been performed by using a commercial code (CFX 10). In the simulations, the concept of mixing index is employed to evaluate the mixing performance as well as to optimize the size and spacing of each electrode in one pair. It is found that the optimum design of one electrode pair, which leads to the best mixing performance, is not simply harmonic one. When the length ratio of the two electrodes in a pair closes to 2:1, the best mixing effect can be attained. The flow pattern was visualized. Furthermore, the velocity field will be measured with a PTV technique to validate the numerical simulations.