Numerical simulations are performed to investigate the breakup of air bubble in flow focusing configuration; the CLSVOF (coupled level set with volume of fluid) method is employed to track the interface, which allows a better identification of the liquid–gas interface via a function called level set. The CFD simulations showed that the velocity ratio, the interfacial tension, the outer channel diameter, the continuous phase viscosity, the orifice width and length play an important role in the determination of the air bubble’s size and shape. However, at low capillary number, increasing the flow velocity ratio gives a smaller bubble size in shorter time, while the increase in interfacial tension leads to a bigger bubble. Moreover, the carrier fluid is found to slightly affect the bubbling mechanism, while the smallest bubbles were obtained with the smallest orifice size. In addition, three breakup regimes are observed in this device: disc-bubble (DB), elongated bubble (EB) and the slug bubble (SB) regime flows. This work also demonstrates that the CLSVOF is an effective method to simulate the bubbles breakup in flow focusing geometry. In addition, a comparison of our computational simulations with available experimental results reveals reasonably good agreement.

Graphic abstract

中文翻译：

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使用CLSVOF方法的DNS的单个微气泡破裂和流聚焦动力学

进行了数值模拟，以研究流动聚焦结构中气泡的破裂。CLSVOF（液位与液位耦合）方法用于跟踪界面，从而通过称为液位集的功能更好地识别液-气界面。CFD仿真表明，速度比，界面张力，外通道直径，连续相粘度，孔口宽度和长度在确定气泡尺寸和形状方面起着重要作用。然而，在较低的毛细管数下，提高流速比可以在更短的时间内产生较小的气泡，而界面张力的增加则会导致较大的气泡。此外，发现载液会稍微影响起泡机制，同时获得最小的气泡和最小的孔口尺寸。另外，在该装置中观察到三种破裂状态：盘状气泡（DB），细长气泡（EB）和团状气泡（SB）流动。这项工作还表明，CLSVOF是一种模拟流动聚焦几何形状中气泡破裂的有效方法。此外，将我们的计算模拟与可用的实验结果进行比较，可以得出相当好的一致性。

图形摘要