Marangoni convection during droplet birth and coalescence

Marangoni效应显著改善了传质，并直接影响局部流体动力学，特别是在液滴诞生和聚结期间。然而，由于缺乏对局部现象的详细定量理解，因此在工业设计中被忽视了。萃取柱中液滴的寿命包括形成、上升或下降和聚结。这些阶段是强耦合的，并且取决于流体动力学条件和质量传递。当液滴形成时，开始进行传质。在随后的上升阶段，液滴可能与其他液滴碰撞，并与它们合并或反弹。聚结概率和上升时间以及因此液滴在装置中的停留时间都取决于上升速度。此外，聚结行为影响液滴尺寸分布，这反过来又决定了可用于传质的界面面积。物质的传输可以引起界面张力梯度，这导致在界面处的额外的剪切应力。因此，引起界面的运动，产生强烈和不规则的流动模式。这种现象称为Marangoni效应，它导致了动量和质量传递的极强耦合，对这些复杂现象的研究通常通过研究单个液滴的流体动力学和质量传递特性来进行。修正系数，然后用来考虑这种非理想的马兰戈尼对流。在设备模拟的最新技术中，这种局部现象通常被完全忽略。在该研究项目中，开发了新的测量系统和方法，用于现场高分辨率实验研究Marangoni对流对时空质量输运的影响。然而，液滴形成的第一秒只能用数值方法捕捉。计划的延长期将用于建立一个数据库，并验证新开发的建模方法，以便为技术单元模拟创建新的核心。目前，Marangoni对流在装置设计中未被考虑。

Marangoni effects significantly improve mass transfer and directly influence local hydrodynamics, especially during droplet birth and coalescence. However, a detailed quantitative understanding of local phenomena is missing and therefore neglected in industrial design.The lifetime of a droplet in an extraction column comprises formation, rise or fall and coalescence. These stages are strongly coupled and depend on the fluid dynamic conditions and mass transfer. Mass transfer set in while the droplet is being formed. During the following rise stage, the droplet may collide with other droplets and either coalesce with them or bounce. Both the coalescence probability and the rise time - and, consequently, the droplet residence time in the apparatus - depend on the rise velocity. Moreover, the coalescence behaviour influences the droplet size distribution, which, in turn, governs the interfacial area available for mass transfer. Species transport can evoke interfacial tension gradients, which lead to additional shear stresses at the interface. Thereby, a movement of the interface is induced, creating strong and irregular flow patterns. This phenomenon, called Marangoni effect, leads to extremely strong coupling of momentum and mass transfer.Investigation of these complex phenomena is often performed via studying of fluid dynamics and mass transfer characteristics of single droplets. Correction factors are then used to account for such non-idealities as is Marangoni convection. In the state-of-the-art of apparatus simulation such local phenomena are usually completely ignored.In the research project, new measuring systems and methods have been developed for an in situ, high resolution experimental investigation of the influence of Marangoni convection on mass transport in space and time. However, the first seconds of droplet formation can only be captured with numerical methods. The planned extension period will be used to generate a data pool and to validate newly developed modelling methods enabling creation of new kernels for technical unit simulation. Currently, Marangoni convection is out of consideration in the apparatus design.