Quantifying the Durability of a Friction-Reducing Surface with Recoverable Superhydrophobicity
Liliane C. C. Auwerter, Christopher Cheeseman, Michael R. Templeton, Maarten van Reeuwijk
Journal of Hydraulic Engineering · 2021
Abstract
The durability of superhydrophobic surfaces in fully immersed conditions is a major obstacle to their application in engineering applications. We perform an experimental study to measure the friction factorfd as a function of time for a new superhydrophobic surface that is capable of recovering the Cassie-Baxter wetting state. V alues offd were obtained by measuring the pressure drop and volume flux of a turbulent water flow in a 1.5 m long duct containing one superhydrophobic wall. The Reynolds number of the flow was approximately 4.5 × 104 for all experiments. Reductions in fd were 29% –36% relative to a hydraulically smooth surface. The Cassie-Baxter state could be recovered by blowing air through the porous surface for 10 min. 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 and 60 min 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. DOI: 10.1061/(ASCE)HY.1943-7900.0001857. © 2021 American Society of Civil Engineers. Introduction The transportation of dense fluids is an energy-intensive activity. To deliver water in pipelines from the treatment plant via a pressurised distribution system to the end-user, the water industry consumes globally 180 TW·ho fe n e r g y(IEA 2016). Major energy losses (Δ H) occur in the water distribution as a result of friction with pipe walls. The power P w needed to maintain a volume flux Q (m3=s) of fluid with density ρ (kg=m3) for a pipe with Darcy-Weissbach friction factor fd is given by Nakayama ( 2018) Pw ¼ αfdU3 ð1Þ where α ¼ AL=2D encapsulates the pipe geometry;U = fluid veloc- ity; A = cross-sectional
Funding
- EP/L016826/1