Investigation of flow over textured surfaces

Abstract

It is established that a superhydrophobic surface is critical in reducing the frictional drag of flow over surfaces. In many engineering industries, such as the pipeline industry, drag reduction is essential, as lesser energy is wasted due to frictional force. In this study, experiments will be conducted to investigate the material surface roughness and surface energy as these are the two essential principles for hydrophobicity. Past studies have shown that treating the surface of magnesium alloy with 1-step chemical etching or 2-steps chemical etching was able to create a superhydrophobic surface. Some studies also showed that superhydrophobic surfaces could also be achieved using sandpaper to polish the material surface. However, the combined effect of both methods has yet to be researched. This project found that the AZ91D magnesium alloy that was polished in parallel with 120 grit sandpaper, then etched with 0.1M of sulfuric acid for 4 minutes, followed by etched with 0.2M copper (II) sulphate for 30 seconds, and finally passivated in 0.05M ethanolic stearic acid for 30 minutes achieved the most optimal surface with an average contact angle of 164.72°. In addition, chemical etching that was done after polishing with 120 grit increased the contact angle by 4.51% as compared to unpolished. Finally, pressure-drop experiments showed that the fabricated surface with a higher contact angle could effectively reduce frictional drag between the fluid and the surface. The submersion results showed that a higher contact angle has better corrosion resistance.