Quantifying the Durability of a Friction-Reducing Surface with Recoverable Superhydrophobicity

Abstract

The durability of super-hydrophobic surfaces in fully immersed conditions is a major obstacle to their application in engineering applications. We perform an experimental study to measure the friction factor f d as a function of time for a new super-hydrophobic surface that is capable of recovering the Cassie-Baxter wetting state. Values of f d were obtained by measuring the pressure drop and volume flux of a turbulent water flow in a 1.5 metre long duct containing one super-hydrophobic wall. The Reynolds number of the flow was approximately 4.5 × 10 4 for all experiments. Reductions in f d were 29-36 % relative to a hydraulically smooth surface. The Cassie-Baxter state could be recovered blowing air through the porous surface for 10 minutes. The durability of the drag-reduction, as quantified by the relaxation time T in which the surface loses its superhydrophobic characteristics, were measured to be between 10-60 minutes depending on the initial head. The relaxation time T was highly dependent on the pressure difference across the surface. In contrast to models based on Darcy flow through a porous medium, the study indicates that there seems to be a critical pressure difference beyond which the Cassie-Baxter state cannot be sustained for the material under consideration.

Application of a hydrophobic coating to a pressurized pipe and its effect on energy losses and fluid flow profile

“…However, the major obstacle to the successful application of the coating in engineering applications is the durability and integrity of the coating without flakes of the hydrophobic substance being peeled off by the drag of the fluid flow. Some research works have focused on the durability of superhydrophobic surfaces in fully immersed conditions 24 .…”

Application of a hydrophobic coating to the inner wall of a pressurized pipe and its effect on energy losses and fluid flow profile

“…For example, Watanabe et al (Watanabe et al, 1999) reported that a 14% drag reduction was achieved for a laminar flow of water in a pipe with highly water-repellent wall. Other research works focused on the durability of superhydrophobic surfaces in fully immersed conditions that is a major obstacle to their use in engineering applications (Auwerter Liliane C. C. et al, 2021).…”