Suspension droplet wall impingement and particle deposition

该项目旨在通过实验和数值模拟分析悬浮液滴对壁面的影响。这是一个复杂且很少被研究的课题，但对许多技术过程具有重要的基础意义。这些是：喷漆、喷雾干燥、复合表面涂层、药品涂层和单液滴工艺，如喷墨打印、生物材料和电子电路的打印。实验将得到液滴的沉积、回弹和飞溅等冲击状态，并通过相关的无量纲参数进行总结。此外，还将研究液滴的扩散、壁面沉积物的形成以及反弹碎片的性质。实验计划为毫米大小的液滴，不同的冲击角度，速度和壁材料。将考虑各种液体和不同体积分数的固体颗粒，以全面了解复杂的液滴壁面撞击。此外，将考虑不同尺寸和材料密度的封闭颗粒，以分析颗粒惯性对冲击的影响。为了实现液滴撞击的可视化，将采用直接阴影成像技术，结合LED照明和高速摄像机记录。这些技术不仅可以研究可能的液滴撞击结果，还可以监测扩散液滴内部的粒子运动以及最终的粒子分布。将进行互补的数值模拟，以预测液滴在撞击过程中的行为以及液滴内部的粒子运动，最终预测壁面沉积的结构。为了处理如此复杂的三相流问题，必须对现有的基于欧拉/拉格朗日原理的数值代码进行许多扩展。数值模拟的基础将是OpenFOAM库，该库已经在研究所扩展，具有当前任务所需的许多功能。液滴本身在壁面撞击时的行为将通过VoF方法求解，并使用等矢量对液体界面进行几何重建。在考虑所有相关力的情况下，用点粒子拉格朗日方法处理分散在液滴内部的固体颗粒。还将考虑双向耦合和粒子间碰撞。此外，颗粒与液滴界面和固体壁面的相互作用需要考虑额外的力。最后，将考虑颗粒壁的粘附性，以预测颗粒沉积在壁上的形成。所需的模型参数将由详细的实验研究提供，例如液体中的粒子壁碰撞。扩展的数字代码将通过彻底的实验进行验证。总的来说，这个项目将带来详细的知识，并为应用悬浮液滴壁碰撞的过程提供设计规则。

The project aims to analyse suspension droplet wall impacts experimentally and by numerical simulations. This is a complex and rarely studied topic, but is of fundamental importance for numerous technical processes. These are: spray painting, spray drying, composite surface coating, coating of pharmaceuticals, and single droplet processes, such as ink-jet printing, printing of biomaterials and electronic circuits. Experiments will be conducted for obtaining the regimes of droplet impact, such as deposition, rebound and splashing, summarised by relevant non-dimensional parameters. Moreover, droplet spreading, formation of deposits on the walls and the properties of rebound fragments will be studied.Experiments are planned for millimetres droplet sizes, different impact angles, velocities, and wall materials. Various liquids and different volume fractions of solid particles will be considered to obtain a comprehensive understanding of the complex droplet wall impact. Also, different sizes and material densities of the enclosed particles will be considered to analyse the effect of particle inertia on the impact. For visualising the droplet impingement direct shadowgraph imaging techniques will be applied in combination with LED illumination and high-speed camera recording. These techniques will allow not only to study possible drop impact outcomes but also to monitor particle motion inside spreading drops along with final particle distribution.Complementary numerical simulations will be conducted for predicting droplet behaviour during impact as well as the particle motion inside the droplet and eventually the structure of wall deposition. For dealing with such a complex three-phase flow problem a number of extensions of the available numerical code based on the Euler/Lagrange principle have to be done. The basis of the numerical simulations will be the OpenFOAM library, which was already extended at the institute with a number of features needed for the present task. The behaviour of the droplets itself during wall impact will be solved by a VoF method with geometrical reconstruction of the liquid interface using the isoAdvector. The solid particles dispersed inside the droplet will be treated by a point-particle Lagrangian method, considering all relevant forces. Two-way coupling and inter-particle collisions will be also considered. Moreover, the interaction of the particles with the droplet interface and the solid wall requires additional forces to be considered. Finally, particle wall adhesion will be considered in order to predict the formation of the particle deposits on the wall. Model parameters needed, will be provided by the detailed experimental studies, e.g. for the particle-wall collisions in a liquid. The extended numerical code will be verified with the thorough experiments. Overall, this project will lead to a detailed knowledge and provide design rules for processes applying suspension droplet wall collisions.