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Numerical and Experimental Study of the Squeezing-to-Dripping Transition in a T-Junction
Microgravity Science and Technology ( IF 1.8 ) Pub Date : 2020-05-26 , DOI: 10.1007/s12217-020-09794-z
S. Arias , A. Montlaur

In this work, we study the transition from squeezing to dripping during the formation of bubbles in a capillary T-junction in conditions relevant to microgravity. The junction is formed by two perpendicular cylinders of equal section (1mm of internal diameter). The capillary number Ca (based on the continuous phase) is used as the key parameter of the study. For the range of Ca covered in this paper, the same two common bubble formation mechanisms as the ones described in the related literature have been observed: squeezing regime at low Ca and dripping regime for higher Ca. This paper provides a new value of the critical Ca for the transition from squeezing to dripping. This value has been obtained with two independent approaches, experimentally and numerically. Experimental photographs have been used to determine the value of Ca at which a gap appears between the forming bubble and the capillary’s wall, as an evidence of the activation of the shearing mechanism related to the dripping regime. Additionally, the dependence of the bubble volume on the capillary number and the gas/liquid flow rate ratio has been analysed. In this work, we also propose a new numerical approach, complementary to the experimental one, carried out with the Computational Fluid Dynamics solver ANSYS Fluent v15.0.7. Numerical simulations have been performed to study the geometry and the behaviour of the gas-liquid interface during the cycle of bubble formation. Upstream the T-junction, as the fluctuation in pressure decreases, the vertical movement of the rear meniscus (gas-liquid interface in contact with the solid vertical capillary) also decreases, and the shear stresses begins to play an active role until overcoming the squeezing mechanism. Numerical simulations presented in this paper support the experimental observations, confirming that Computational Fluid Dynamics studies can be a useful tool to improve the experimental knowledge.

中文翻译:

T形结挤压-滴落过渡的数值和实验研究

在这项工作中,我们研究了在与微重力有关的条件下,在毛细管T型接头中气泡形成过程中从挤压到滴落的过渡过程。接合处由两个等截面(内径1mm)的垂直圆柱形成。毛细管数C a(基于连续相)用作研究的关键参数。对于本文涵盖的C a范围,已观察到与相关文献中描述的相同的两种常见气泡形成机理:低C a的挤压状态和较高C a的滴落状态。本文提供了关键的新值Ç一个从挤压到滴水的过渡。该值已通过两种独立的方法通过实验和数值获得。实验照片已用于确定C a的值形成气泡和毛细管壁之间出现缝隙,作为与滴落状态有关的剪切机制激活的证据。另外,已经分析了气泡体积对毛细管数和气/液流速比的依赖性。在这项工作中,我们还提出了一种新的数值方法,作为对实验方法的补充,它是使用计算流体动力学求解器ANSYS Fluent v15.0.7进行的。已经进行了数值模拟以研究气泡形成循环期间气液界面的几何形状和行为。在T型接头的上游,随着压力波动的减小,后弯液面的垂直运动(与固体垂直毛细管接触的气液界面)也减小,剪应力开始发挥积极作用,直到克服挤压机制。本文提供的数值模拟支持了实验观察,证实了计算流体动力学研究可以作为提高实验知识的有用工具。
更新日期:2020-05-26
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