Research And Design Of Chaotic Micromixer Based On Liquid-Liquid Heterogeneous System

With the popularization and application of micro-electromechanical technology in the fields of chemistry, biology, medicine and environmental engineering, the corresponding equipment and instruments are also developing towards the direction of miniaturization and integration. As an important part of microfluidic chip, micromixer has the advantages of high efficiency, easy to process and control, low cost and good integrated performance. Therefore, the structure design of micro-mixer has become one of the hot spots in domestic and international research. Due to the micro-scale fluid flow is laminar, mixing of fluid mainly depends on diffusion effect. In order to achieve the purpose of rapid and efficient mixing, chaotic mixing mechanism was introduced into micro-mixing technology and chaotic micro-mixer with various structures was designed, such as herringbone structures, folding three-dimensional structures and zigzag structures.This paper was based on the droplet forming and fusion technology, the mixed reagent was wrapped in the droplet to form an independent mixing region. The chaotic mixing effect was induced by the internal circulation function of the droplet and the shear action of the micro channel, so it can achieve the effect of fast and efficient mixing. The main contents of this paper are as follows:(1) Numerical simulation method based on computational fluid dynamics was conducted to study the formation and fusion process of droplets in the cross shaped micro channel, which lays the foundation for the study of the mixing process inside the droplet. A cross shaped micro-channel model was established to simulate the two-phase flow of water and oil, studying the effects of parameter conditions on the formation of stable droplet flow and the control of different flow patterns. The effects of two phase flow rate, viscosity and surface tension on the size of droplet were studied, and the droplet size can be controlled by adjusting the fluid parameters.(2) Three kinds of micro-mixer models with different structures were established, which were the straight channel, V-shaped and U-shaped micro-mixer, and the mixing process in the micro-mixer was simulated using the fluid volume function (VOF) and the scalar equation method (UDS). The mixing effect of these three kinds of micro-mixer was compared using scalar tracer concentration analysis, and the energy consumption was compared by analyzing the internal pressure drop value. In addition, the mixing situation and mechanism of the droplet type micro-mixer was also studied.(3) The mixing mechanism and structure optimization of V-shaped micro-mixer was further studied. Through orthogonal experiment, the influence of different structure parameters of the micro-mixer on the mixing degree and the pressure drop value was studied, and the structure of the micro-mixer was optimized to satisfy the high efficient mixing and the energy saving. Because the mixing effect inside the droplet is greatly influenced by the physical properties of fluid, the effects of water fraction, Reynolds number and capillary force number on the mixing efficiency of V-shaped micro-mixer were studied in this research.(4) The high-speed camera, micro-injection pump and cross micro-channel chip was used to build an experimental platform. The formation and fusion process of water droplet was observed, and the effect of fluid parameters (velocity ratio of the two-phase fluid and viscosity of the continuous phase) on the size of droplet was studied. The experimental results and simulation results were compared, and these two method has good agreement. The results of experiment and simulation show the same variation trend of the droplet size with the fluid parameters.The results of this paper provide a theoretical basis for the reagent mixing using the droplet micro-mixer, and also provide reference for the design and optimization of the micro-mixer structure.