十字型微通道内气泡形成的实验观察

Formation of Dispersed Small Bubbles in Flow-Focusing Microchannels

采用高速摄像仪对聚焦十字型微装置内分散小气泡的生成进行了研究。方形截面微通道的尺寸分别为400μm×400μm和600μm×600μm。氮气为气相,加入表面活性剂十二烷基硫酸钠(sodium dodecyl sulfate,SDS)(0～0.5%(wt))的水—甘油(25%(wt),50%(wt),62%(wt))溶液为液相。考察了不同的操作条件如液体流速、黏度和表面张力对气泡生成尺寸的影响。泡状区内生成的气泡尺寸随连续相流体流量和黏度的增大而减小,随表面张力的增大而增大。讨论了气泡的生成机理,提出了一个新的指数模型来描述气泡生成尺寸与局部毛细管数的关系。

The formation of dispersed small bubbles in microfluidic flow-focusing devices was investigated experimentally by means of using a high speed camera.The dimensions of the experimental square microchannels are 400 m×400 m and 600 m×600 m,respectively.N2 was used as the gas phase,and water-glycerol mixtures（25%（wt）,50%（wt） and 62%（wt）） with different concentrations（0～0.5%（wt）） of surfactant SDS（sodium dodecyl sulfate） were used as liquid phase.The parameters,such as liquid flow rate,the viscosity and the surface tension of the liquid phase,which influence the size of formed small bubbles,were studied.It was found that the bubble size in bubbly regime decreases with the increase of the flow rate and the viscosity of the liquid phase,while it increases with the increase of the surface tension of the liquid phase.The bubble formation mechanism was discussed,and it was conclude that the small bubbles are formed due to the viscosity force and interfacial forces.A new power law model was proposed to describe the relationship between the size of formed bubbles and the local capillary number.