Prediction of Mixing Performance in a Microchannel Flow

Abstract

Most microfluidic chips proposed for automated and fast toxicogenomic analysis require enhanced mixing of two or more fluids because flows in a microchannel of the chip are inherently laminar. This means that the mixing process depends on slow molecular diffusion. As a result, the length of microchannel becomes unacceptably long. To improve the mixing performance, passive or active mixers are inserted into a microfluidic chip. While the passive mixer takes advantage of geometry for enhanced mixing, the active mixers uses external energy input. We predict performance of passive mixers using numerical analysis to simulate fluid mixing in microchannels. Specifically, we investigate the effects of vorticity on mixing in microchannels for four geometries: Y-channel, Y-channel with a post array along the sideline, Y-channel with a post array along the centerline, and Y-channel with a zig-zag post array. The results indicate that the strong vorticity does not always ensure high performance of mixing in a microchannel. The vorticity of centerline and zig-zag post arrays is almost same, but the zig-zag post array shows significantly better mixing than the other. Therefore, we propose a weighted vorticity method to predict the mixing performance.