Condensation of water vapor underneath an inclined hydrophobic textured surface machined by laser and electric discharge.

Condensation of water vapor on a surface plays an important role in thermal based water purification methods. Appropriate texturing of such surfaces facilitates dropwise condensation with better heat transfer coefficient and water collection. In this context, we explore texturing patterns via laser ablation to achieve lower aspect ratio (10 μm depth to 100 μm width) and via wire electric discharge machining process for higher aspect ratio (300 μm depth to 100 μm width). The transition from Cassie-Baxter to Wenzel is seen experimentally as well as through the simulations for lower aspect ratio, whereas the transition does not occur for higher aspect ratio. Simulations are also carried out for the sessile as well as pendant drop, which is more relevant to thermal based water purification. However, in the experiments the drop is always in the pendant mode. The condensing surface inclination plays a very significant role in the water collection. In order to have more water production underneath the copper plate, the optimum angle of inclination found is 35°. Unlabelled Image • Hydrophobic surface using physical texturing by laser and EDM micromachining • Simulations for transition from Cassie Baxter to Wenzel state • Water production using physically textured and plain surface in desalination system • Time required for first drop to slide off on textured and plain surface • Effect of inclination angle on drop sliding on textured and plain surface [ABSTRACT FROM AUTHOR]