Simultaneous experimental analysis of concentration and velocity fields in liquid film flows when flowing over microstructured surfaces

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The application of microstructured surfaces in process equipment such as packing columns, evaporators or condensers not only ensures improved wetting, but also significantly increases mass transfer in the liquid film that forms. However, it has not yet been fully elucidated in which way microstructures influence the momentum distribution and subsequently the mass transport within liquid film flows. In this research project, the influence of single and multiple microstructures on the mass transfer from a gas flow into gravity-driven liquid film flows on inclined plate elements with different microstructures is therefore investigated. In order to be able to experimentally analyse the coupling of the momentum distribution with the gas transfer, the concentration field of the absorbed gas component is to be measured simultaneously with the velocity field within the liquid film in the immediate vicinity of the microstructure. For this purpose, a measurement setup combining a planar laser induced fluorescence method for concentration field measurement with stereoscopic particle image velocimetry for velocity field measurement through the backside of transparent microstructure mouldings will be realised first. Subsequently, the influence of the shape of individual microstructures and the influence of the distance between several microstructures will be systematically investigated for different gas and liquid loads. The planned measurement campaigns include the overflow of unidirectional microstructures (cuboid, prism and half-cylinder stages) and the flow around and over bidirectional microstructures (pyramid, hemisphere and cube).This research project will thus make a fundamental contribution to the identification and basic understanding of the phenomenological microstructure influence and provide a database for the validation of numerical flow simulations for microstructure optimisation, thus making a further contribution to the fundamental understanding of mass transfer processes and to the design and development of novel and optimal structures.