Research On Mixing Mechanism Of Bubble Induced Micromixers And Periodic Electro-osmotic Flow Micromixers

The micro-and nano-industrial equipments have been widely used in the field of aviation, life sciences, health care, automotive industry, human-like robots and domestic appliance. The micromixer is an important part of it. Characterized by shorter mixing time, shorter mixing length, wide selectivity and suitable for extremely low Reynolds number, the active micromixer has aroused enthusiasm in the world. Up to now, however, the problems of poor mixing performance for simple geometries and lacking theoretical models have not been solved. Using the software FLUENT and COMSOL Multiphysics, the thesis makes intensive studies of bubble induced and periodic electro-osmotic flow (EOF) active micromixer, respectively. By comparing the results between numerical simulations and experiments, this paper further optimizes the mixing performance, reveals the law for the effect of different parameters on mixing efficiency and lays the theoretic foundation for the optimization and design of active micromixer.In virtue of COMSOL Multiphysics, the effect of three new parameters (namely direct current electric field EDC, phase difference φ and the length of constriction L) on the mixing efficiency for periodic EOF active micromixer have been investigated. The results indicate that the influence of phase difference φ on the mixing performance is not significant for a mixer with a shorter length L but significant for a longer one and the lower value of EDC and the longer length L improve mixing performance significantly with an optimized phase differenceφ.A mathematical model, based on the structural features of the Lagrange function rather than its application, is proposed to establish a relationship between the mixing performance and these three parameters for the periodic EOF active micromixer. The feasibility analysis has been carried out and the results are verified to produce useable forecasts or optimum parameters by the data from simulation and experiment. The study referring to the design and optimization of micromixer is very important for many microfluidic devices and microanalysis system.By means of FLUENT, the active micromixer induced by isolate bubbles has been studied. Based on the theory of isolate bubble formation and combining the idea of velocity pulsing and obstructions in the microchannel, this paper presents a method of mixing enhancement in microfluidic straight channel by introducing the isolate bubbles as obstructions. The results of simulation show that the new method can improve the mixing efficiency and guide the experiment for active micromixers to some extent.