Numerical Analysis of the Fluid Mixing Behaviors in a Microchannel with a Circular Cylinder and an Oscillating Stirrer

Abstract

An active micromixer equipped successively with a circular cylinder and an oscillating stirrer is designed by analyzing the mixing behaviors, i.e., the effect of the Karman vortex, the flow structure after the stirrer, etc. The mixing is calculated by using the D2Q9 model of lattice Boltzmann methods. In this study, we use the time-averaged mixing index formula DI , which was recently proposed for time-dependent flow. Four models for microchannel flows driven from combinations of the above devices are tested and the calculated mixing indices are compared. In models III and IV, one type of fluid rolls with the other type of fluid caused by the scroll effect due to the oscillation of the stirrer. Therefore, the concentration distributions becomes mushroom-shaped structures at Re = 80. These behaviors are developed up to the channel outlet. Then, the contact area and the residence time of fluid particles between the two fluids for mixing by diffusion are increased infinitely. In model IV, the mixing is enhanced and stabilized much more by the Karman vortex from the circular cylinder. We found that successive mixing by the cylinder and stirrer is a very effective method.