Investigation of flow over textured surfaces

• Main Author: Hock, Ker Yuen
• Other Authors: Chan Weng Kong
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Mechanical engineering
• Online Access: https://hdl.handle.net/10356/141080
• Institution: Nanyang Technological University

Frictional loss in fluid flows occurs in many aspects of industrial engineering application. This phenomenon is undesirable as it induces energy losses. More energy is therefore required in the transportation of the fluid which drives up the operation cost. Several research studies have shown that superhydrophobic surfaces possess favourable microstructures which aid in reducing frictional loss in fluid flows. There are various fabrication methods available in the market, however, chemical etching is one of the less costly and simpler method compared to other techniques. The immersion of samples in the chemical agents before lowering the surface energy with a suitable agent is required to obtain superhydrophobic surfaces. A two-step chemical etching approach was adopted in this study for fabricating the hydrophobic surfaces. The Aluminium Alloy 6061 material samples were selected for the etching process as it is widely used in fluid flow applications. A total of 6 different preliminary experiments were conducted to obtain the optimum combination of concentration and etching duration for fabricating surfaces with the highest degree of hydrophobicity. The hydrophobicity of the surface is characterized by its contact angle, surface morphology and roughness. Selected parameters were used to fabricate large samples for the pressure drop experiment to relate hydrophobic levels and pressure drop. From the experimental results, a single-step etching process of 2M NaOH for 2.5min at elevated temperature produces a contact angle approximately 146°. Alternatively, in a two-step etching process of 2M NaOH for 2.5min followed by 0.5M NaOH for 6min at elevated temperature, higher superhydrophobic surface with a contact angle of approximately 166° was produced. The interstices between the peaks and valleys of a dual scale roughness surfaces were able to trap more air bubbles, thereby reducing the wettability of the surface. The two-step etching method produces surfaces with superhydrophobic properties despite its cost and simplicity amongst other fabrication methods. The success of the two-step etching method could be potentially applicable to industrial engineering applications.