Search

Self-cleaning of surfaces becomes challenging for energy harvesting devices because of the requirements of high optical transmittance of device surfaces. Surface texturing towards hydrophobizing can improve the self-cleaning ability of surfaces, yet lowers the optical transmittance. Introducing optical matching fluid, such as silicon oil, over the hydrophobized surface improves the optical transmittance. However, self-cleaning ability, such as dust mitigation, of the oil-impregnated hydrophobic surfaces needs to be investigated. Hence, solution crystallization of the polycarbonate surface towards creating hydrophobic texture is considered and silicon oil impregnation of the crystallized surface is explored for improved optical transmittance and self-cleaning ability. The condition for silicon oil spreading over the solution treated surface is assessed and silicon oil and water infusions on the dust particles are evaluated. The movement of the water droplet over the silicon oil-impregnated sample is examined utilizing the high-speed facility and the tracker program. The effect of oil film thickness and the tilting angle of the surface on the sliding droplet velocity is estimated for two droplet volumes. The mechanism for the dust particle mitigation from the oil film surface by the sliding water droplet is analyzed. The findings reveal that silicon oil impregnation of the crystallized sample surface improves the optical transmittance significantly. The sliding velocity of the water droplet over the thick film (~700 µm) remains higher than that of the small thickness oil film (~50 µm), which is attributed to the large interfacial resistance created between the moving droplet and the oil on the crystallized surface. The environmental dust particles can be mitigated from the oil film surface by the sliding water droplet. The droplet fluid infusion over the dust particle enables to reorient the particle inside the droplet fluid. As the dust particle settles at the trailing edge of the droplet, the sliding velocity decays on the oil-impregnated sample.

Summary: The self‐cleaning of surfaces via impacting water droplets is examined pertinent to solar energy applications. The mechanism of spreading and retraction of the impacting droplet onto the dust and cleaned hydrophobic surfaces is considered in the analysis. The spreading factor of the impacting droplet is formulated incorporating the energy balance on the hydrophobic surface. High‐speed photography is used to monitor the impacting droplet behavior. The functionalized silica particles coating is introduced towards generating hydrophobic wetting state on the glass surfaces. Environmental dust particles are characterized prior to self‐cleaning impacting tests. It is found that spreading rate predicted for the impacting droplet agrees well with that obtained from the experiments. The droplet Weber number incorporated in the experiments does not result in droplet breaking on the surface upon impacting. The dusts are dissimilar in shapes and consist of several elements. Impacting droplet gives rise to cloaking of the dust on the surface during spreading and retraction. Almost all the dusts are removed from the surface through the impacting droplets; however, few dust residues are left on the impacting surface, which cover only 0.03% of the total surface area. Hence, we have demonstrated that self‐cleaning of a surface can be achieved by an impacting droplet for renewable energy applications. [ABSTRACT FROM AUTHOR]

Water droplet cleaning of a dusty hydrophobic surface is examined. Environmental dust are used in the experiments and cloaking velocity of a dust layer by a droplet fluid is measured and hemi-wicking conditions for the dust layer are analyzed adopting the pores media wick structure approach. A droplet motion on dusty and inclined hydrophobic surface is analyzed using a high speed digital imaging system. Influences of dust layer thickness, droplet volume, and surface inclination angle on the mechanisms of dust removal by a rolling droplet are evaluated. The findings revealed that dust cloaking velocity decreases exponentially with time. The droplet fluid can cloak the dust layer during its transition on the dusty surface. The transition period of droplet wetted length on the dusty surface remains longer than the cloaking time of the dust layer by the droplet fluid. Translational velocity of rolling droplet is affected by the dust layer thickness, which becomes apparent for small volume droplets. Small volume droplet (20 µL) terminates on the thick dust layer (150 µm) at low surface inclination angle (1°). The quantity of dust picked up by the rolling droplet increases as the surface inclination angle increases. The amount of dust residues remaining on the rolling droplet path is relatively larger for the thick dust layer (150 µm) as compared to its counterpart of thin dust layer (50 µm). [ABSTRACT FROM AUTHOR]