Experimental investigation and CFD simulation of cavity flow effects on liquids mixing in vortex-based microfluidic chips: Quantitative visualization and optimization by response surface method (RSM)

摘要

In the present study, a joint experimental and numerical study on mass transfer inside vortex-based micro-capillary channels by virtue of chaotic mixing theory is presented. Three different microfluidic chips with different embedded barrier shapes, including cubic, angled cubic, and cylindrical barriers with the same blockage ratio posed behind a couple of symmetric semi-cylinder barriers as mixing promoters inside the channel were designed. To find the optimum geometrical parameters, Optimal Design (OD) method was employed. The results showed that different patterns of vortices can be achieved when the shape of embedded barriers change. The mass transfer or disturbance posed by vortices which were made by streamlines on the local position based on cavity was not only dependent on its vorticity, but also correlates with the fluid stretching based on the Lyapunov exponent theory. Consequently, the application and recognition of suitable vortex patterns play important parts in mixing enhancement. Additionally, three different micromixers with three different embedded barrier shapes produced different vortices sizes at different Re numbers ranging from 0.05 to 93, leading to different mixing performances. The micromixer with middle cubic barriers showed a better mixing trends due to the higher vortex size and lateral fluid velocity. Both experimental findings and numerical results showed that more asymmetric shapes lead to better fluid mixing. It was observed that when the semi-cylinder obstacle radius is greater than 180 mu m, large vortices are formed after the obstacles act as hydrodynamic barriers, which in turn promote the cavity-based trapped vortex and fluid stretching.