Characteristics of Droplet Growth Behavior on Hydrophobic Micro textured Surfaces

Abstract

For occurring dropwise condensation, the droplet growth behavior such as single droplet growth, coalescence, and falloff of large droplets play a major role in regard to condensation heat transfer and water harvesting. The present study visualized the droplet growth behavior of dropwise condensation which might be controlled by the surface tension. We used three copper plate with different hole area fraction (i.e., د•=0, 0.148 and 0.439). Surface texturing was conducted by using a خ¼computer numerical control (خ¼CNC) machine and composed of microholes (diameter: 300 خ¼m, depth: 200 خ¼m) with 691 خ¼m, 401 خ¼m pitch. To make the hydrophobic surfaces, the copper surfaces were coated selfassembled monolayer (SAM). From the results, it was found that for only SAM coated surface, random coalescence occurred and affected the droplet growth significantly, whereas for textured SAM coated surfaces, the droplet started to be grown up at the textured holes and coalesced near the holes, indicating that capillary effects might affect the droplet growth mechanism. In particular, the falloff time at which a coalesced droplet is removed away from the surface increased when the textured surfaces was used, because of surface tension effect increased by the textured holes.