Micro-PIV study on flow field characteristics of droplets in a microcavity
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摘要: 液滴已成为微流控技术的重要研究内容。为了精确调控液滴内的微环境，利用微通道矩形长凹槽生成并封裹液滴，并开展了液滴内部流场特性的显微粒子图像测速（Micro-PIV）实验，研究了雷诺数（Re）对液滴形貌、流场速度矢量场特性和剪应力分布的影响。结果表明，当Re=11.1时，液滴内部出现了一个涡胞结构；当Re=33.3时，液滴中心处的流速达到最大值，约为10 μm/s。然而，当Re=44.4时，涡胞消失，平均流速降低。同时，液滴尺寸随Re增加而减小。此外，Re对液滴内部剪应力变化无明显影响，剪应力平均值极低（< 1.5×10-4Pa）。Abstract: Droplets have become an important research content of microfluidics. In order to realize precise regulation of the droplets' microenvironment, droplets were generated and trapped in long rectangular microcavities in a microchannel, and the internal flow field characteristics were experimentally measured by using a micro-particle image velocimetry (Micro-PIV) system. The effects of the Reynolds number (Re) on the droplet morphology, internal flow velocity vector fields and the distributions of shear stress inside the trapped droplet have been investigated. The results show that at Re=11.1, a vortex structure appears inside the droplet. When Re=33.3, the flow rate at the center of the droplet reaches a maximum value of about 10 μm/s. However, when Re=44.4, the vortex structure disappears and the average flow rate decreases. Meanwhile, the droplet size decreases as the Re increases. Moreover, Re has no significant effect on the internal shear stress of the droplet, and the average value of the shear stress is extremely low (< 1.5×10-4 Pa).
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Key words:
- microfluidics /
- microcavity /
- vortex /
- droplet microenvironment /
- Micro-PIV
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图 2 不同Re下长凹槽内液滴的形貌变化
Figure 2. Morphology of droplets in the long microcavity for different Re
图 3 Micro-PIV测量的不同Re下液滴内部流线图及速度云图
Figure 3. Flow field diagram and velocity cloud diagram of droplets in the long microcavity for different Re
图 4 Micro-PIV测量的不同Re下液滴内部x和y方向的流场及速度云图
Figure 4. Diagram of flow field and velocity in x and y direction inside droplet in the long microcavity for different Re
图 5 提取的不同Re下长凹槽液滴内竖线位置的流速分布
Figure 5. The velocity distributions along the line across the droplet in the long microcavity for different Re
图 6 不同Re下的长微凹槽液滴内部流场结构及剪应力分布云图
Figure 6. Flow field structures and cloud diagram of shear stress in the droplets in the long microcavity under different Re
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