The physical mechanisms of step emulsification
The physical mechanisms of step emulsification
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DOI：
10.1088/0022-3727/46/11/114003
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发表时间：
2013-03-20
影响因子：
3.4
通讯作者：
Baroud, Charles N.
中科院分区：
文献类型：
--
作者：
Dangla, Remi;Fradet, Etienne;Baroud, Charles N.
我们重新审视当两种不混溶流体之间的界面达到微通道高度的阶跃变化时发生的物理平衡。这种情况导致在称为“分步乳化”的过程中产生液滴。然而，导致液滴破裂并决定其大小的机制尚未得到简单的解释。我们提出了一种基于入口通道内螺纹曲率与台阶下游“球”曲率之间的准静态平衡的液滴破碎几何模型。我们发现这种限制限制了螺纹可以采用的最低曲率值。相反，球的曲率随着其尺寸的增加而减小，这导致了临界球半径，超过该半径两个区域就不能处于静态平衡。这会产生将球茎破碎成液滴的流动。几何分析预测的临界球半径与不同台阶和入口通道几何形状的实验测量结果非常一致。因此，分离液滴的半径从下方受该值限制，并随着分散相流速缓慢增加。
We revisit the physical balance that takes place when an interface between two immiscible fluids reaches a step change in the height of a microchannel. This situation leads to the production of droplets in a process known as 'step emulsification'. However, the mechanism that is responsible for the drop breakup and that determines its size has not been explained in simple terms. We propose a geometric model for drop breakup based on a quasi-static balance between the curvature of the thread inside the inlet channel and the curvature of the "bulb" downstream of the step. We find that the confinement limits the lowest values of curvature that can be adopted by the thread. In contrast, the bulb curvature decreases as its size increases, which leads to a critical bulb radius beyond which the two regions cannot be in static equilibrium. This leads to a flow which breaks the bulb into a droplet. The critical bulb radius predicted by the geometric analysis is in good agreement with experimental measurements for different step and inlet channel geometries. The radius of the drop that detaches is therefore bounded from below by this value and increases slowly with the dispersed phase flow rate.