3D rolling motion of droplet on inclined hydrophobic surface at different temperatures: Environmental dust removal

Water droplet rolling across contaminated hydrophobic surfaces is one of the key areas of study for improving the self-cleaning efficiency of energy-harvesting technologies. In line with self-cleaning applications, the present study investigates dust removal from hydrophobic surfaces via rolling water droplets using 3D simulations and experiments. The research focuses on the interplay between droplet dynamics, surface temperature, and removal of dust particles from inclined hydrophobic surfaces at different temperatures. The findings reveal that rolling droplets exhibit wobbling, creating oscillatory motion with a natural frequency ( f ) between 32 Hz and 40 Hz and mode of oscillation ( l ) of 2 depending on the surface inclination angle and temperature. The presence of dust on inclined hydrophobic surface alters droplet behavior while increasing the maximum droplet width with reduced maximum droplet apex height. Increasing hydrophobic surface temperature from 25 °C to 60 °C increases the droplet contact length and adhesion force by almost ∼ 4%, which slightly enhances the peak wobbling amplitude. Droplet wobbling gives rise to bulk averaged temperature and velocity oscillations in droplet fluid. The presence of dust lowers translational velocity due to small-scale fluid spreading and gives rise to increased interfacial friction and droplet mass during rolling. A mathematical relationship is established for the adhesion force ratio between dusted and undusted surfaces, which takes the form: χ_F≈CLd^m, here C is a constant L_d is normalized distance along the inclined hydrophobic surface, i.e. C varies within 0.7 to 2, and m takes the values within 0.19 to 0.23 depending on the surface inclination angle. Droplet kinetic energy dissipation due to dusted surface is about 20%.