Droplet Rolling and Spinning in V-Shaped Hydrophobic Surfaces for Environmental Dust Mitigation

Abstract

<jats:p>The motion of a water droplet in a hydrophobic wedge fixture was examined to assess droplet rolling and spinning for improved dust mitigation from surfaces. A wedge fixture composed of two inclined hydrophobic plates had different wetting states on surfaces. Droplet rolling and spinning velocities were analyzed and findings were compared with the experiments. A wedge fixture was designed and realized using a 3D printing facility and a high speed recording system was adopted to evaluate droplet motion in the wedge fixture. Polycarbonate sheets were used as plates in the fixture, and solution crystallization and functionalized silica particles coating were adopted separately on plate surfaces, which provided different wetting states on each plate surface while generating different droplet pinning forces on each hydrophobic plate surface. This arrangement also gave rise to the spinning of rolling droplets in the wedge fixture. Experiments were extended to include dust mitigation from inclined hydrophobic surfaces while incorporating spinning- and rolling droplet and rolling droplet-only cases. The findings revealed the wedge fixture arrangement resulted in spinning and rolling droplets and spinning velocity became almost 25% of the droplet rolling velocity, which agrees well with both predictions and experiments. Rolling and spinning droplet gave rise to parallel edges droplet paths on dusty hydrophobic surfaces while striations in droplet paths were observed for rolling droplet-only cases. Spinning and rolling droplets mitigated a relatively larger area of dust on inclined hydrophobic surfaces as compared to their counterparts corresponding to rolling droplet-only cases.</jats:p>

Avalanche effect for chemically modified dust mitigation from surfaces

“…Different methods have been suggested and implement for dust mitigation, such as water cleaning, air-jet blowing, brushing, water droplet rolling, etc. 1 , 2 . All the suggested cleaning methods require external power to run the cleaning system.…”

On the mechanism of droplet rolling and spinning in inclined hydrophobic plates in wedge with different wetting states

“…The average roughness of the surface is about 115 nm for both surfaces. The formulation of droplet rolling is given in early work 9 . The rotational velocity of the droplet increases as the inclination angle of the wedge from the horizontal plane ( α ) increases; however, increasing the wedge angle ( ϕ, which is the angle between two plane hydrophobic surfaces in the wedge) slows the velocity of the rolling droplet in the wedge 9 .…”

“…dust mitigated area appears to have striation-like patterns, which are caused by the wobbling of the rolling droplet along its path. One of the methods of reducing the striations along the droplet path is to create a droplet spinning along its vertical axis during rolling 9 . The spinning of the rolling droplet can be achieved through creating the tangential momentum by a mechanical arrangements 9 .…”

“…One of the methods of reducing the striations along the droplet path is to create a droplet spinning along its vertical axis during rolling 9 . The spinning of the rolling droplet can be achieved through creating the tangential momentum by a mechanical arrangements 9 . The droplet fluid behavior remains important in spinning and rolling droplets for creating parallel-sided droplet paths over the dust hydrophobic surfaces.…”

“…The rolling droplet path on plain hydrophobic surface (without spinning) is also assessed and findings are compared with its counterpart obtained for rolling and spinning droplets. In addition, the rolling and spinning velocities of the droplet obtained from analytical solutions 9 are compared with the 3D predictions and the experimental data.…”