Browsing by Author "Mosthaf, Klaus"

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Modeling and analysis of coupled porous-medium and free flow with application to evaporation processes
(2014) Mosthaf, Klaus; Helmig, Rainer (Prof. Dr.-Ing.)
Exchange processes between fluid-filled porous media and an adjacent free flow occur in a wide range of natural and technical systems. In the course of these processes, the flow dynamics in the porous domain and in the free flow exhibit a strong interdependency, which is often controlled by mechanisms at the common interface. Understanding and modeling these interactions is decisive for divers technical, medical and environmental applications. Prominent technical examples are the drying of products such as food, concrete or clothes. Further technical examples comprise landmine detection, industrial filtration processes, and the flow and transport processes in proton exchange membrane fuel cells (PEM-FC). A possible medical application is the exchange and transport of substances like therapeutic agents between blood vessels and tissue in the human body. Evaporation from natural soils as an environmental example is an extremely important process, since it constitutes a dominant part of the terrestrial water and energy balance and is actively involved in a variety of climatic processes. On the one hand, evaporation processes are decisively influenced by the prevailing ambient conditions, such as flow velocity, temperature and air humidity, and, on the other hand, by the porous-medium system with its fluid and solid properties and flow dynamics. A good understanding of the ongoing processes and elaborate modeling tools are crucial for climate modeling and water resources management, particularly in arid regions. The main focus of this thesis is on this environmental application: the modeling and analysis of evaporation processes from porous media like bare soils or sands which are exposed to an adjacent free flow. The objectives of this study are on one hand the development of a detailed coupled model which allows the simulation of a two-phase porous-medium system in conjunction with a single-phase free flow, and on the other hand to conduct a comprehensive analysis of the relevant processes for the mass, momentum and energy transfer of the two flow compartments. A major goal is to advance the development of an elaborate model for evaporation processes from porous media on the REV scale. This model has to take the mutual influence of the two flow compartments and the processes occurring at the common interface into account to allow for a detailed analysis of the influencing quantities. Theoretical and experimental evidence suggests that the interface between free flow and porous medium plays a crucial role for modeling evaporation processes on the REV scale.