Numerical investigation of liquid flow topology in structured packings

在气-液单元中分离流体混合物，例如在蒸馏、吸收或解吸中，对于过程工业是非常重要的。分离效率在很大程度上取决于相流的类型和形式以及接触相之间的界面的可用面积。通过应用规整填料作为塔内件，可以增加界面面积。填料的倾斜角、宏观和微观结构等几何参数影响流型。其它影响因素是物理系统性质，例如粘度、润湿性和密度差，以及操作条件，例如特定的液体和气体负载、液体供应和流动行为。对局部流动现象的详细了解对于分离设备的优化设计是必不可少的。相比之下，目前可用的模型的界面面积和持液量的描述假设简化，经验评估的部分润湿的几何填料表面，具有恒定的液膜厚度。然而，在斜板和填充柱上进行的研究表明，在现实中，膜，溪流，并最终液滴流以及停滞区可以满足。这些不同的流动形式具有非常不同的特定相界面，在流体动力学模型中应考虑这些相界面。在本项目中，应创建用于以膜流为主的分离单元，特别是填充柱的实际设计的基本方法。为了达到这一目标，结构表面上的流动的拓扑结构应研究不同的物理性质，几何形状和操作条件。这将通过数值模拟来完成，从而产生对规整填料中复杂流体动力学的基本见解。研究结果将提供局部流动现象和停留时间分布的知识。基于这些知识，将推导出允许改进设备设计的相关性。

Separation of fluid mixtures in gas-liquid units, e.g. in distillation, absorption or desorption, is of major importance for the process industries. Separation efficiency strongly depends on the type and form of the phase flow as well as on the available area of the interface between the contacting phases. The interfacial area can be increased through the application of structured packings as column internals. Geometrical packing parameters like inclination angle, macro and micro structure affect the flow pattern. Further influencing factors are physical system properties, e.g. viscosity, wettability and density difference, as well as operational conditions, e.g. specific liquid and gas loads, liquid supply and flow behavior. Detailed knowledge on local flow phenomena is essential for the optimal design of separation equipment. In contrast, currently available models for the description of the interfacial area and holdup assume simplified, empirically evaluated partial wetting of the geometrical packing surface, with a constant liquid film thickness. However, investigations carried out on inclined plates and in packed columns demonstrate that in reality, film, rivulet and eventually droplet flows as well as stagnant zones can be met. These different flow forms have very different specific phase interfaces which should be considered in the fluid dynamic models.In this project, the basic methods for a realistic design of separation units with predominant film flow, especially packed columns, should be created. To reach this goal, the topology of the flow on structured surfaces should be studied for varied physical properties, geometry and operating conditions. This will be done via numerical simulations, thus yielding fundamental insights into the complex fluid dynamics in structured packings. The investigation results will provide the knowledge on the local flow phenomena and residence time distribution. Based on this knowledge, correlations allowing an improved equipment design will be derived.