Numerical investigation into the mixing performance of micro T-mixers with different patterns of obstacles

Abstract

Microsystems are made up of components < 100 μm in size. At this size range, the flow of substances typically experiences a laminar behavior with the Stokes flow condition (Re < 1). To the mixing operation, diffusion dominates the mixing, which further leads to the problem of the increased length of microchannel (mixing length for short) and increased length of time. Development of a new principle of mixing, which may increase the mixing efficiency, will be useful to alleviate this problem. There are two directions of measures for new principles: passive and active. In short, the passive principle is related to designing the structure of the mixer, while the active principle is to additional sources of energy for mixing. The mixing efficiency plays a significant role in designing micromixers as the most essential parts of lab-on-chip (LoC), because increasing this index can result in reducing mixing length so that not only it is cost-efficient but also it helps to miniaturize the LoC devices, but achieving adequate mixing performance in simple geometries is a serious challenge. This paper presents a study of the optimal design of a passive micro T-mixer, which consists of the prescribed patterns of barriers and furrows with different geometries. Simulation with COMSOL was taken to conduct this study. The study concluded that the mixing efficiency can be improved by at least 25%; as well the mixing length can be improved. Additionally, the role of the diffusion coefficient was examined, leading to the finding that a greater diffusion coefficient could result in a shorter length of microchannel for the same mixing efficiency. This finding is in agreement with the general theory of diffusion in laminar fluids.