Design And Control Of High Reflux Micromixer

Micromixer is an important part of a microfluidic system. Because the ratio of surface area to volume in the microscopic case sharply increases, the flow is laminar. Diffusion is the only mixing way, but it will take a long mixing channel to mix well, which is contrary to the mind of lab-on-a-chip, miniaturization and integration. In the macroscopic chemical reaction device, recycle flow is often used to make the reactants mix several times to improve the mixing efficiency, such as the equipments of producing polyethylene and polypropylene are designed with a special structure of reflux. However, in the microscopic field, the recycle micromixer is seldom and its reflux efficiency is very low. Therefore, it is necessary to design a high reflux micromixer.In this paper, the Coanda effect is used to design a micromixer with high reflux ratio and vortex. The factors which influence reflux rate and mixing efficiency are analyzed and model predictive control algorithm is used to control the inlet velocity of micromixer. Major work and results are as follows:1. For the issue of the microfluid difficult to mix, an approach of increasing the reflux rate is proposed. The shape of mixing chamber and feedback channel are designed by the Coanda effect, which makes the fluid attached to the channel wall and more prone to emerge reflux. The jet component is used to design mixing channel, which could enhance Coanda effect and increase reflux rate.2. In order to simulate micromixing case, ANSYS FLUENT software is used. The simulation results prove reflux existing, as well as symmetric vortex in the mixing chamber. Based on the results, reflux rates of the micromixer at the Reynolds number of28and42are17.34%and25.7%, and the mixing efficiencies are90.96%and92.76%respectively, while the other’s reflux rates are only2%and3%, and the mixing efficiencies are58.64%and74.34%in the same case. Through simulation analysis, the greater the reflux rate is, the higher mixing efficiency is, which indicates that a great deal of recycle flow contributes to mixture. 3. Continuous and efficient mixing needs a stable inlet velocity. In order to control the stability of the velocity, the model predictive control algorithm is proposed. Constraints and objective function of single-input single-output and multiple-input multiple-output system are presented. The dynamic process optimization is implemented by linear programming instead of quadratic programming, which reduces the computational complexity, shorten the computing period. The feasibility of the algorithm is verified by simulation.