Numerical investigation of liquid flow topology in structured packings

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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.