An experimental investigation of frictionless flow in channels
Soh, Zhen Wei
Date of Issue2017
School of Mechanical and Aerospace Engineering
Fluid flow is a fundamental aspect in many modern engineering applications. However, frictional loss has always been a cause of concern. Researchers have found that due to their favourable surface microstructures, surfaces with superhydrophobic property generate less friction when fluid flow pass. Among various methods of fabricating superhydrophobic surfaces, chemical immersion is one of the cheapest and most efficient method. The method constitutes 2 main steps: the etching of a surface followed by the lowering of its surface energy level. From past studies, it was found that both concentration of etchant and duration of etching affect the hydrophobicity of a surface. Thus, an optimal combination of the two parameters is required to produce an ideal superhydrophobic surface. As 6061 Aluminium Alloy is widely used in many fluid flow applications, it was naturally chosen as the material for the fabrication of superhydrophobic surfaces in this study. This study aims to improve the results of current research by exploring different techniques, different etchants, as well as different combinations of etchant concentration and etching duration on 6061 Aluminium Alloy, and to investigate the drag reducing ability of the fabricated surfaces in this study. 3 different preliminary experiments were initially conducted, and the one that produced a surface with the highest contact angle was selected as the fabrication method on large 6061 Aluminium Alloy plates (200mm X 50mm X 5mm) in the actual experiment. The selected method utilises boiling Sodium Hydroxide (NaOH) solution as the etchant and Ethanolic Stearic Acid (SA) as the chemical reagent for the lowering of the samples' surface energy. To determine the drag reducing ability of the fabricated samples, a pressure drop experiment was designed to measure the pressure drop as water flow across the fabricated samples. Generally, samples etched in boiling 2M NaOH solution exhibited better drag reducing abilities than those etched in 0.25M, 0.5M, and 1M boiling NaOH solutions. In fact, the greatest pressure drop reduction was achieved by the sample etched in boiling 2M NaOH solution for 2.5 minutes. Results have also shown that different NaOH concentrations require different optimal etching durations for better pressure drop reduction. Samples that possessed better drag reducing abilities were also found to have more complex surface microstructures as a result of the etching process. These surface profiles were found to be characterisable by fractal dimension.
Final Year Project (FYP)
Nanyang Technological University