Concentration-dependent viscous mixing in microfluidics: modelings and experiments

Abstract

In microfluidic mixing, great attention has been devoted to the structural design to enhance mixing efficiency. However, the influence of the variant viscosity in the mixing process is rarely discussed due to the practical challenges originated from the strong and complex couplings between species concentration and other fluid properties such as density, viscosity and diffusion coefficient. In this work, a group of coupling relationships among concentration, density, viscosity, as well as diffusion coefficient are introduced to accurately simulate the mixing process with a viscous flow involved. Compared with the traditional linear approximation, the new approach is more suitable to simulate the concentration-dependent viscous mixing in microfluidics. Furthermore, a planar passive micromixer is designed to validate the coupling approach from both modeling and experiment perspectives. By comparing experimental and numerical results, it turns out that the coupling approach achieves higher accuracy than the traditional linear approximation. In addition, four derived models are experimentally tested and numerically simulated by adopting the new method. The results of each model reach a good agreement between modeling and experiment.