Investigation of chemical etching on flow in channel

Abstract

Seven different grades of sandpaper were selected to study the effect of creating a rough surface pre-etching would attain a higher contact angle after incorporating with chemical etching approach. A two-step chemical etching approach was adopted in this study for fabricating the superhydrophobic surfaces. Aluminum Alloy 6061 material were selected as test specimen as it is most commonly used in fluid flow applications. A total of 4 different preliminary experiments were conducted to obtain the optimum combination of concentration, etching duration, grades of sandpaper and motion of sanding for fabricating surfaces with the highest degree of hydrophobicity. The hydrophobicity of the surface is characterized by its contact angle, surface morphology and roughness. Based on the results, selected parameters would utilize to fabricate large samples for pressure drop test experiment to corelate hydrophobicity with pressure drop. Incorporating sanding of surfaces before two-step etching method produces an elevated water contact angle of 162.36° compared to the non-polished specimen of 156.38°. The comparison of above data was obtained from Preliminary Experiment D 2M concentration. The best result of 162.36° was obtained by polishing the specimen with grit 80 sandpaper in circular manner for 20 times and undergo a two- step chemical etching method whereby the primary etchant concentration and duration were 2M 2.5mins and the secondary etchant concentration and duration were 0.5M 6mins. From the experimental results, superhydrophobic surfaces were able to significantly reduces the amount of skin drag friction, however, it deteriorated by 10% due to accelerating fluid flow and submersion in water for 24hours. The percentage further increases to thrice the amount after being submerged for 48hours and undergoing various accelerating flow in the process. The water contact angle after the pressure drop and submersion experiments were also found to drop significantly by approximately 16% by the end of the experiments. All these indicates a transition of wetting behavior from Cassie-Baxter model to Wenzel model.