Drag Reduction of Anisotropic Superhydrophobic Surfaces Prepared by Laser Etching

Abstract

In this research, the anisotropic superhydrophobic surface is prepared on a stainless steel surface by laser etching, and the drag reduction property of the anisotropic surface is studied by a self-designed solid−liquid interface friction test device. Periodic arrangement structures of quadrate scales with oblique grooves are obtained on a stainless steel surface by a laser. After modification by fluoride, the surface shows superhydrophobicity and anisotropic adhesive property. Here, the inclined direction of grooves and the inverse direction are defined as RO and OR, respectively. By changing the inclination of the grooves, a surface is obtained with a contact angle of 160°and a rolling angle difference of 6°along the RO and inverse RO direction. It is verified by numerical simulation and experiment that the subjected force of water droplets on the surface is different along the RO and inverse RO direction. Furthermore, the as-prepared surface has different drag reduction effects along the two directions. With the increase of velocity, the drag reduction effect of the superhydrophobic surface decreases against the RO direction, while the drag reduction effect along the RO direction is almost unchanged. We believe the anisotropic surface will be helpful in novel microfluid devices and shipping transportation.

Superhydrophobic Civil Engineering Materials: A Review from Recent Developments

“…The WCA can be as large as 153.6 • after modification with stearic acid. Tuo et al developed an anisotropic superhydrophobic surface on a stainless steel surface by laser etching [32]. They used an ultraviolet laser to etch the steel by rotating the substrate to different angles.…”

Drag reduction methods at solid-liquid interfaces

“…After this, as turbulent boundary layer flows representing the main applications, the possibility of superhydrophobic surface drag reduction in turbulent flow turned into the next concern [98][99][100]. In 2009, Daniello et al [7] confirmed the feasibility of superhydrophobic surfaces in turbulent drag reduction, and a drag reduction approaching 50% was measured.…”

Thermohydraulic analysis of a microchannel with varying superhydrophobic roughness

“…This is because of the creation of microbubbles between substrate and water flow that leads to water slippery over the surface and thus more reduction in drag. Tuo et al [32] fabricated anisotropic SHS on stainless steel comprising inclined grooves by laser etching and fluoride treating for drag test. Comparing inclined and reversed direction of ribs, while drag-drop ratio in the first situation is about 18%, it is almost 48% in the latter under 4.48m/s flow velocity.…”