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Accueil du site → Doctorat → Arabie Saoudite → WATER DROPLET BEHAVIOR ON INCLINED DUSTY HYDROPHOBIC SURFACE : DUST CHARACTERISTICS AND DROPLET DYNAMICS

King Fahd University of Petroleum and Minerals. (KFUPM) 2020

WATER DROPLET BEHAVIOR ON INCLINED DUSTY HYDROPHOBIC SURFACE : DUST CHARACTERISTICS AND DROPLET DYNAMICS

GHASSAN ABDELMAGID

Titre : WATER DROPLET BEHAVIOR ON INCLINED DUSTY HYDROPHOBIC SURFACE : DUST CHARACTERISTICS AND DROPLET DYNAMICS

Auteur : GHASSAN ABDELMAGID

Université de soutenance : King Fahd University of Petroleum and Minerals. (KFUPM)

Grade : Doctor of Philosophy (PhD) 2020

Résumé
Climate change gives rise to frequent dust storms and the settlement of environmental dust particles on the surfaces of energy harvesting devices, such as solar photovoltaic and concentrated troughs. Several methods are tailored removing dust from surfaces and some of these methods include gas assisted removal, water jet spraying, electrostatic repelling, ultrasonic and acoustic excitation, mechanical scrubbing, and water droplet self-cleaning. Most of the cleaning processes adopted require external power sources and the sustainable operation of these processes remains costly because of the required pumping/compression, electric power, and high repelling forces to remove such particles. To reduce the power requirements, introducing micro/nano size air gaps between the dust particles and the selective surface becomes critical. In addition, lowering surface energy of selective surface is also favorable to reduce the dust adhesion on surfaces. The present study aims to investigate the mechanisms of dust particles removal from hydrophobic surfaces by means of rolling water droplets. To achieve surface texture giving rise to Cassie & Baxter wetting state, the solution crystallization of polycarbonate surfaces is realized. The surface texture created composes of hierarchically distributed micro-size spheroids and fibrils, which demonstrates hydrophobic characteristics with high contact angle hysteresis. The surface texture arrangement results in increased water droplet pinning and suppresses the dynamic motion of droplet on the hydrophobic surfaces. To reduce the contact angle hysteresis, the functionalized nanosize silica particles are deposited on the prepared and crystalized surfaces via using the dip coating technique. The resulting surface displays a high droplet contact angle (158° ±2°) and low contact angle hysteresis (3° ±1°). One of the main mechanisms for the dust particles removal from a hydrophobic surface, by rolling liquid droplet, is associated with the droplet fluid cloaking of the dust particles during its transition on the surface. Hence, the study is extended to include the influence of droplet hydrostatic pressure on the fluid infusion (cloaking) into dust layer, which enables to further explore the dust removal mechanisms. The effective length of infusion height in the dust layer is estimated incorporating the experimental data. High speed and thermal cameras are used to monitor the infusion front velocity in the dust layer. The findings reveal that droplet fluid (water) spreads onto the dusty hydrophobic surface and cloaks the dust particles. In addition, sperading of a droplet liquid on a dusty hydrophobic surface is also considered and the fluid infusion into the dust layer is investigated in relation to dust removal from the hydrophobic surfaces via rolling/sliding droplets. It is shown that the Cloaking velocity decays sharply with time and the weight gain of the dust particles is about 17% of the original dust weight after cloaking. The droplet acceleration, due to increased surface inclination angle, has an effect on the rate of dust particles removed from the surface, which is more apparent for the large droplet volumes. Increasing droplet acceleration improves the coverage area of the clean surface. The droplet puddling causes striations like structures along the droplet path and close examination of the few residues of the dust particles reveals that the droplet picks up considerably large amount of dust from the surfaces. As the rolling droplet picks up dust, some dust compounds (alkaline metal compounds) dissolve in the droplet fluid while enhancing the surface tension by almost 4%. This increases the droplet pinning (adhesion) on the dusty surface.

Présentation

Page publiée le 16 mars 2022