基于流动聚焦结构的微液滴形成机理

Formation Mechanism of the Micro Droplet Based on the Flow-Focusing Structure

基于COMSOL Multiphysics 4.3的两相流模型,通过数值模拟研究了基于流动聚焦结构微通道内液滴形成机理及影响因素。通过水平集方法考虑表面张力的影响,实现对油-水界面的追踪,获得了W/O液滴的形成状态,并对影响微液滴体积大小的关键因素进行了研究。结果表明,微液滴的形成分为液滴头部伸长和液滴颈部断裂两阶段,整个过程中连续相对分散相产生夹流聚焦效应;两相流速及连续相黏度是影响液滴体积大小的关键因素,分散相流速一定的情况下,连续相流速增大,液滴的体积减小;连续相流速一定的情况下,分散相流速增大,液滴的体积增大。连续相和分散相的流速比越大,所生成的液滴体积越小;随着连续相黏度的逐渐增加,所形成液滴体积明显减小。通过对比分析,得出数值仿真分析结果与已有实验结果基本一致,验证了仿真理论分析的正确性。

Based on the two-phase flow model in the COMSOL Multiphysics 4.3,the formation mechanism and influence factors of the droplet in the microchannel based on the flow-focusing structure were researched by the numerical simulation.The level set method was adopted to take into account the effect of the surface tension and to track the oil-water interface.The formation state of the W/O droplet was obtained,and the critical factors effecting the droplet size were researched.The research results show that the formation of the micro droplet can be divided into two stages,i.e.head elongation and neck breaking of micro droplet.The continuous phase has flow-focusing effect on the dispersion phase in the whole process.The critical factors effecting the droplet size are the two-phase flow velocity and continuous phase viscosity.At a constant dispersion phase velocity,the droplet volume decreases when the continuous phase velocity increases.At a constant continuous phase velocity,the droplet volume increases when the dispersion phase velocity increases.The greater the flow rate ratio of the continuous phase and dispersion phase,the smaller the generated droplet volume.The droplet volume decreases significantly with the gradual increase of the continuous phase viscosity.By the comparison and analysis,the numerical simulation result and experiment result are in substantial agreement to verify the correctness of the simulation theoretical analysis.