Experimental investigation of wetting behavior of falling films inside inclined tubes

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The aim of this research project is to investigate the stability of falling films in slightly inclined evaporation tubes in dependence of internal structuring, inclination angle, fluid properties and mass flow rate. Furthermore, surfaces for a better wetting will be investigated and evaluated. Therewith forecasts concerning wetting rate, film stability and capillary transport should be possible in future. Within this research project, a test plant for falling film evaporation with the possibility of exchanging the evaporation tubes and visual access was built and an existing autoclave for contact angle measurements was enhanced.The already obtained results lead to a better understanding of the stability of a falling film in inclined internally structured tubes. The experiments with water/ air and propane conducted so far allow to draw conclusions about the wetting behavior in combination with the knowledge of contact angle, surface energy and structure. Adjustments to models for the calculation of the transport capacity within the grooves (mainly responsible for the film spreading) were realized, too. More investigations with the selected fluids deionized water and ethanol are necessary to conclude general statements about the film stability. Additionally, the measurement of the contact angle will be improved to measure drops with a smaller capillary length. The calculation of the advancing contact angle will be validated with tilting plate experiments for propane, ethanol and water, too.