Convective transport processes

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Wilko Rohlfs

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+49 241 80 97463

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Convective transfer mechanisms strongly influence our daily lives and are present in nigh on every technical application, ranging from mass transfer inside (human) kidneys with flow channels whose diameters are in the order of micrometres, over apparatus used in chemical and process engineering plants, to movements of air in the atmosphere. Convection plays a significant role in heat or mass transfer within liquid or gaseous media, i.e. the transfer of thermal energy or mass through moving flows.

Current research at the WSA focusses on three distinctive types of flows covering falling liquid films, jet impingement, and membrane channel flows. Thereby, numerical and experimental methods are both used complementary. Each of the three types of flows can be found in various apparatus utilised in energy, chemical, and process engineering applications. E.g. falling liquid films are used to evaporate temperature-sensitive fluids as well as in ad- and desorption processes. Jet impingement finds its application in drying processes in addition to refrigeration and cooling as this type of flow is characterised by its favourable high heat and mass transition coefficients. Membrane channels allow an efficient separation of different phases; they find use in sea water desalination plants among other applications.

A common similarity of all three types of flows is the presence of instabilities which cause for instance ripples in falling films or the formation of vortices in such flows. Thus they impact the process’s course in a significant manner. One of the questions we address with our research is in which conditions such instabilities are formed and how exactly these impact the flow and convective transfer processes.

To reach a broad and detailed knowledge of flow characteristics we utilise a multitude of means to measure and quantify results experimentally. Among others there are three dimensional light field particle image velocimetry (PIV) and high speed visualisation. Furthermore several methods of temperature measurement are used, such as infrared thermography or liquid crystal thermography. On the numerical side high resolution simulations are being conducted while the models they are based upon are constantly put to the test and are improved based on experimental data.

 

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