Visualization Study of Dropwise Condensation on a Super-Hydrophobic Surface

Compared with conventional filmwise condensation, dropwise condensation has the advantage of high heat transfer coefficient when properly enhanced. To better understand the inherent mechanism of this outstanding performance and optimize the structure of the condensation surface, this paper focuses on the visualization experiments of dropwise condensation on a superhydrophobic surface to study the dynamic behaviors of droplet nucleation and growth. The surface is fabricated by chemically growing an n-octadecanethiol self-assembled monolayer coating with microscopic roughness on a copper surface. Some characteristics of interest such as the droplet nucleation, the droplet diameter, the number and the path of the droplets are obtained using image processing software. The experimental results indicate that the nucleation sites of the droplets are fixed, which in turn verifies the droplet nucleation theory. In addition, the nucleation of the small droplets together with the coalescence of the existing droplets contributes significantly to the variation of the number of the droplets.