微通道入口角度对微液滴生成过程的影响

Effect of Inlet Angle on Droplet Generation in Microchannel

为研究不同流体物性参数条件下微通道入口角度对微液滴生成过程的影响,采用流体体积(volume of fluid,VOF)法对错流微通道内液滴生成过程进行了三维数值模拟,对液滴生成过程中两相压差及液滴生成周期和尺寸进行了研究.结果表明:拉伸挤压流型下,微液滴尺寸随着通道入口角度增大呈现先减小后增大趋势.表面张力较大或连续相黏度较小时,入口角度为90°的微通道有利于生成较短液滴;表面张力较小或连续相黏度较大时,入口角度为120°的微通道有利于生成较短液滴.对于固定的入口角度,微液滴尺寸随着表面张力系数增大而增大,随连续相黏度增大而减小.当流体物性参数不同时,生成最短液滴的通道结构不同.综合考虑通道入口角度、表面张力系数和连续相黏度,提出了预测拉伸挤压流型下量纲一液滴长度的经验关联式,为微液滴系统的设计和应用提供了指导.

To study the effect of microchannel inlet angle on the droplet generation process under the condition of varying fluid physical parameters,a three dimensional numerical simulation in the cross-flow microchannel was proposed by the volume of fluid( VOF) method. The two-phase pressure difference in the droplet generation process,the time period and size of the microdroplet were studied. The results show that the microdroplet size decreases firstly and then increases gradually with the increase of the inlet angle in the squeezing regime. A 90° inlet angle is helpful to generating shortest droplet for high surface tension or low viscosity of continuous phase; A 120° inlet angle is conducive to generating shortest droplet for low surface tension or high viscosity of continuous phase. For constant inlet angle,the microdroplet size rises with the increase of the surface tension coefficient and reduces with the increase of the viscosity of continuous phase. The shortest droplet is generated in different microchannel for varying fluid physical parameters. Considering the inlet angle,surface tension coefficient and viscosity of continuous phase,the new correlation of the dimensionless droplet length for the squeezing regime is proposed which can provide guidance for the design and application of the microdroplet system.