Investigation of flow over superhydrophobic surfaces

Abstract

In this study, the effects of three important parameters were investigated by subjecting superhydrophobic AZ91D alloy through a pressure-driven fluid flow within the laminar flow regime and submerging the alloy underwater for 2 days in a test chamber. These parameters are the wetting behaviour, the drag-reducing property and the wetting transition of the superhydrophobic surfaces. Superhydrophobic AZ91D surfaces can be fabricated using a 2-step chemical etching technique with the exact optimum condition found. It was found that superhydrophobic surfaces were able to significantly reduce the drag experienced by 60% at low Re (<831) and 44% at higher Re (>1000). The drag-reducing property was found to deteriorate by 10% in the presence of accelerating fluid flow and submerging underwater for a day. This percentage would increase 3 to 4 times after the second day. The contact angle of the superhydrophobic surface was found to drop by 5% at the end of the second day. All these indicate an exchange between the trapped air and liquid on the textured surfaces which show a transition of wetting behaviour from the Cassie-Baxter model to the Wenzel model.