Experimental investigation of wetting behavior of falling films inside inclined tubes

本研究的目的是研究微倾斜蒸发管内降膜的稳定性与内部结构、倾角、流体性质和质量流量的关系。此外，将对更好的润湿表面进行调查和评估。因此，对润湿率、膜稳定性和毛细传递的预测在未来应该是可能的。在本研究项目中，建立了降膜蒸发实验装置，可更换蒸发管和目视通道，并改进了现有的用于测量接触角的高压釜。到目前为止，在水/空气和丙烷中进行的实验结合接触角、表面能和结构的知识，可以得出关于润湿行为的结论。还实现了对槽内输送能力(主要负责膜扩散)的计算模型的调整。需要对所选择的流体去离子水和乙醇进行更多的研究，以得出关于膜稳定性的一般性声明。此外，接触角的测量将得到改进，以测量毛细较小的液滴。丙烷、乙醇和水的倾斜板实验也验证了推进接触角的计算。

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.