Direct spatiotemporally resolved fluorescence investigations of gas absorption and desorption in liquid film flows

• We combine Planar Laser Induced Fluorescence with fluorescence quenching.
• We investigate liquid film flow over microstructured surfaces.
• We examine dissolved oxygen concentration around the perimeter of a microstructure.
• We show the positive influence of a microstructure on gas transfer into film flow.

An optical measuring technique, combining Planar Laser Induced Fluorescence (PLIF) with the effect of fluorescence quenching, is used for the local concentration analysis of a gas absorbed and desorbed in a thin liquid film flow. The absorption and desorption process is visualized by using oxygen in a mixture of water, ethanol and glycerol. Fluorescence is strongly reduced by the presence of molecular oxygen as a result of dynamic quenching. The resulting decrease in intensity is detected and interpreted through image processing. The image analysis provides a spatiotemporal value of fluorescence intensity and therefore enables the direct characterization of local transport phenomena in the liquid film flow. In this way, the impact of a single pyramidal microstructure on mass transfer into the film flow is examined. The results are compared to liquid film flow over a smooth surface. The measuring methodology is validated through diffusion experiments.

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