Bilayer staggered herringbone micro-mixers with symmetric and asymmetric geometries

Abstract

Micro-mixing is an important research area for various applications in sensing and diagnostics. In this paper, we present a performance comparison of several different passive micromixer designs based on the idea of staggered herringbone mixers (SHM). The working principle in such designs includes the formation of centers of flow rotation thus leading to multiple laminations with decreasing sizes of the lamellae as the flow passes over staggered structures. We have realized different layout designs of staggered herringbones inside micro-channels and compared their mixing performance. An overall reduction in mixing time and length has been observed as the degree of asymmetry within these structures is increased. The layouts of these staggered structures are based on herringbone bilayers wherein these layers are positioned on the top and bottom walls of a micro-channel. Fluorescence microscopy and computational fluid dynamics (CFD) based modeling have been used to observe the extent of mixing and understand the reasons behind the enhanced mixing effects. We have further varied the degree of asymmetry of the herringbone bilayers and investigated mixing as a function of the asymmetry. We have developed a novel microfabrication strategy to realize these micro-devices using an inexpensive non-photolithographic technique which we call micro-replication by double inversion (MRDI). The paper basically attempts to develop an overall understanding of the mixing process by letting two fluids flow pass over a variety of asymmetric structures.