Zhu Pingan, Kong Tiantian, Lei Leyan, Tian Xiaowei, Kang Zhanxiao, Wang Liqiu
Department of Mechanical Engineering, the University of Hong Kong, Hong Kong.
HKU-Zhejiang Institute of Research and Innovation (HKU-ZIRI), 311300, Hangzhou, Zhejiang, China.
Sci Rep. 2016 Feb 22;6:21527. doi: 10.1038/srep21527.
We investigate the influences of expansion-contraction microchannels on droplet breakup in capillary microfluidic devices. With variations in channel dimension, local shear stresses at the injection nozzle and focusing orifice vary, significantly impacting flow behavior including droplet breakup locations and breakup modes. We observe transition of droplet breakup location from focusing orifice to injection nozzle, and three distinct types of recently-reported tip-multi-breaking modes. By balancing local shear stresses and interfacial tension effects, we determine the critical condition for breakup location transition, and characterize the tip-multi-breaking mode quantitatively. In addition, we identify the mechanism responsible for the periodic oscillation of inner fluid tip in tip-multi-breaking mode. Our results offer fundamental understanding of two-phase flow behaviors in expansion-contraction microstructures, and would benefit droplet generation, manipulation and design of microfluidic devices.
我们研究了扩张-收缩微通道对毛细管微流控装置中液滴破碎的影响。随着通道尺寸的变化，注射喷嘴和聚焦孔处的局部剪切应力会发生变化，这对包括液滴破碎位置和破碎模式在内的流动行为有显著影响。我们观察到液滴破碎位置从聚焦孔向注射喷嘴的转变，以及最近报道的三种不同类型的尖端多次破碎模式。通过平衡局部剪切应力和界面张力效应，我们确定了破碎位置转变的临界条件，并对尖端多次破碎模式进行了定量表征。此外，我们还确定了尖端多次破碎模式下内部流体尖端周期性振荡的机制。我们的结果为扩张-收缩微结构中的两相流行为提供了基本认识，并将有助于微流控装置的液滴生成、操控和设计。
