Drag reduction in internal turbulent flow by fabricating superhydrophobic Al2O3/waterborne polyurethane coatings

Abstract Nowadays, increasing the CO2 emissions are one of the inevitable challenges in the world. In addition, in many industries, fossil fuels are the main source of energy demands which worsen the problem. Since in most applications, the performance and energy loss are highly affected by the drag force, many investigations have been proposed to improve the surface properties to moving surface against the water, and consequently, increasing drag reduction. To this end, one effective way is utilizing superhydrophobic coatings. In this study, we prepare two different superhydrophobic coatings using Al2O3 nanoparticles (NPs) modified by HMDS (1,1,1,3,3,3-Hexamethyldisilazane) and PDMS (Hydroxy-terminated polydimethylsiloxane), which are named HS and PS, respectively, in a waterborne polyurethane (WBPU) resin. The coated substrates show a significant water repellency and the measured contact angles are 158.6° and 153.2° for HS and PS coatings, respectively. Furthermore, the results indicate that the drag reduction is improved up to 18.771% and 16.141% for PS and HS coatings, respectively. Besides, it is observed that the friction coefficient in the superhydrophobic pipes decreases significantly. Also, to show the durability of the resultant surfaces, immersion tests in pure water, sea-water, alkaline, and acidic solutions are used.