T型微流控芯片中微液滴破裂的数值模拟

Numerical simulation of micro-droplet breakup in T-shaped micro-fluidic chip

利用VOF模型对T型结构微流控芯片中微液滴的三维破裂过程进行了数值模拟,获得了液滴发生破裂和不会破裂两种流型。一定轴向长度的微液滴对应着一个临界毛细数,当主流流体的毛细数大于此临界毛细数时,微液滴发生破裂并分别流向T型结构两侧;否则不会发生破裂,微液滴流向任意一侧。通过多个工况的计算,拟合了临界毛细数与微液滴相对轴向长度的关系,探讨了黏度比对微液滴破裂的影响。发现黏度比越小,微液滴越易发生破裂。

Three dimensional numerical simulation of micro-droplet breakup in a T-shaped microfluidic chip was carried out using the VOF method, and the regimes of breakup and non-breakup were observed, respectively. For a droplet with a specific axial length, there existed a critical capillary number, which could be used to describe the transition between these two regimes. The results showed that micro-droplet would break up when the capillary number was high enough and turned into two daughter droplets. Otherwise nonbreakup of droplet would occur while the capillary number was small and micro- droplet would flow into either side of the micro-channel randomly. The correlations between the critical capillary number and the non-dimensional length of micro-droplet were obtained based on numerical simulation. The critical capillary number decreased with increasing droplet size, when the droplet was large enough to obstruct the channel and the pressure accumulated to split the droplet and the critical capillary number was relatively small. When the droplet was too small to obstruct the channel and the pressure was released fast without helping to split the droplet, the critical capillary number was relatively high. Finally, the effect of viscosity ratio on the breakup was discussed and it was found that the higher the viscosity of continuous phase, the higher the capillary number which was needed to break up the droplets, and the critical capillary number decreased with increasing viscosity ratio.