Breakup dynamics of droplets in an asymmetric bifurcation by mu PIV and theoretical investigations
Breakup dynamics of droplets in an asymmetric bifurcation by mu PIV and theoretical investigations
复制标题
mu PIV 不对称分叉中液滴的破碎动力学及理论研究
DOI：
10.1016/j.ces.2018.12.030
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发表时间：
2019
影响因子：
4.7
通讯作者：
Yan Pang
中科院分区：
文献类型：
--
作者：
Xiang Wang;Zhaomiao Liu;Yan Pang
利用高速显微镜系统和微粒子图像测速系统（μPIV）对非对称分叉中液滴的三种破碎模式进行了实验研究。分析了液滴长度和毛细管数对颈部厚度演化的影响。对于阻塞微通道的液滴，从理论上计算了液滴破碎过程中的压降，并讨论了其与颈部收缩的关系。基于质量守恒定律，建立了液滴几何形状的理论预测模型，液滴后帽半径和颈部厚度与实验结果吻合较好。证明了该理论模型同样适用于非对称分岔，且该模型适用于任意角度的分岔。当液滴与通道侧壁之间存在间隙时，颈部的减薄过程和液滴流场的变化与液滴受阻破碎时有明显的不同。对于无破碎区，液滴尖端的回流伴随着涡流，并首次揭示了液滴内部两种不同的涡流分布，这两种分布由液滴长度分隔。揭示了决定液滴流过分叉后是否破碎的临界颈部厚度，并与其他工作进行了比较。
Dynamics of the three breakup regimes of droplets in an asymmetric bifurcation is experimentally studied by a high-speed microscope system and a micro-particle image velocimetry (μPIV) system. Effects of the droplet length and the capillary number on the evolution of the neck thickness are analyzed. For droplets that obstruct the microchannel, the pressure drop across the droplet during the breakup process is theoretically calculated and its relationship with the neck shrinkage is discussed. Based on mass conservation law, the theoretical prediction on the geometric shape of droplets can be constructed and both the radius of droplet rear cap and the neck thickness agree well with experimental results. It is proven that the theoretical model could also be successfully constructed for asymmetric bifurcations and the model in this paper could be applied to bifurcations with arbitrary angles. If gaps are present between the droplet and channel sidewalls, it is found that the thinning process of the neck and variations of the flow field of droplets are distinctly different from the obstructed breakup. For no breakup regime, the vortex flow accompanies the backflow of the droplet tip and two different vortex distributions within the droplet are disclosed for the first time, which are separated by the droplet length. The critical neck thickness that determines whether droplets break after flowing through the bifurcation is revealed and compared with other works.