A Water Droplet Pinning and Heat Transfer Characteristics on an Inclined Hydrophobic Surface

Al‐Sharafi, Abdullah; Yilbaş, Bekir Sami; Ali, Haider; Al-Aqeeli, N.

doi:10.1038/s41598-018-21511-w

Cited by 46 publications

(24 citation statements)

References 37 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In case B the stripe between 2 mm and 3 mm has a control value which is slightly lower than the equilibrium value obtained again in the stripe [1,2]mm. This results in a more rapid receding of the droplet on that stripe in case B.…”

Section: Cases a And Bcontrasting

confidence: 54%

Optimal Control of Droplets on a Solid Surface Using Distributed Contact Angles

2020

View full text Add to dashboard Cite

Controlling the shape and position of moving and pinned droplets on a solid surface is an important feature often found in microfluidic applications. However, automating them, e.g., for high-throughput applications, does rarely involve model-based optimal control strategies. In this work, we demonstrate the optimal control of both the shape and position of a droplet sliding on an inclined surface. This basic test case is a fundamental building block in plenty of microfluidic designs. The static contact angle between the solid surface, the surrounding gas, and the liquid droplet serves as the control variable. By using several control patches, e.g., like done in electrowetting, the contact angles are allowed to vary in space and time. In computer experiments, we are able to calculate mathematically optimal contact angle distributions using gradientbased optimization. The dynamics of the droplet are described by the Cahn-Hilliard-Navier-Stokes equations. We anticipate our demonstration to be the starting point for more sophisticated optimal design and control concepts.

show abstract

Section: Cases a And Bcontrasting

confidence: 54%

Optimal Control of Droplets on a Solid Surface Using Distributed Contact Angles

2020

View full text Add to dashboard Cite

show abstract

“…If the gravitational force exceeds the maximum retention force, the droplet will slide. However, in the present study, a partial depinning [28][29][30] of the droplet occurs in majority of the cases, where the rear edge of the TL is sliding and the front edge remains pinned throughout the evaporation process.…”

Section: A Evaporation Kinetics At Different Substrate Declinationsmentioning

confidence: 53%

Surface declination governed asymmetric sessile droplet evaporation

2020

View full text Add to dashboard Cite

The article reports droplet evaporation kinetics on inclined substrates. Comprehensive experimental and theoretical analyses of the droplet evaporation behaviour for different substrate declination, wettability and temperatures have been presented. Sessile droplets with substrate declination exhibit distorted shape and evaporate at different rates compared to droplets on the same horizontal substrate and is characterized by more often changes in regimes of evaporation. The slip-stick and jump-stick modes are prominent during evaporation. For droplets on inclined substrates, the evaporative flux is also asymmetric and governed by the initial contact angle dissimilarity. Due to smaller contact angle at the rear contact line, it is the zone of a higher evaporative flux. Particle image velocimetry shows the increased internal circulation velocity within the inclined droplets. Asymmetry in the evaporative flux leads to higher temperature gradients, which ultimately enhances the thermal Marangoni circulation near the rear of the droplet where the evaporative flux is highest. A model is adopted to predict the thermal Marangoni advection velocity, and good match is obtained. The declination angle and imposed thermal conditions interplay and lead to morphed evaporation kinetics than droplets on horizontal heated surfaces. Even weak movements of the TL alter the evaporation dynamics significantly, by changing the shape of the droplet from ideally elliptical to almost spherical cap, which ultimately reduces the evaporative flux. The life time of the droplet is modelled by modifying available models for non-heated substrate, to account for the shape asymmetry. The present findings may find strong implications towards microscale thermo-hydrodynamics.

show abstract

“…The droplet bulges during sliding while the wetting diameter alters along the surface . The volume of droplet is important for droplet bulging and the droplet size comparable with the capillary length remains almost spherical on the surface.…”

Section: Resultsmentioning

confidence: 99%

Solar energy harvesting and a water droplet cleaning of micropost arrays surfaces

2019

View full text Add to dashboard Cite

Summary Solar energy harvesting in dusty environments initiates many challenges for sustainable operation of photovoltaic panels. Environmental dust reduces photovoltaic device performance and requires regular cleaning of active surfaces. Self‐cleaning of surfaces by water droplets offers advantages in terms of reduced cost and sustainable operation. The present study investigates dust removal from hydrophobic and optically transparent micropost arrays surfaces in relation to solar energy applications. The micropost arrays are replicated using polydimethylsiloxane (PDMS) casting on textured silicon wafers. The replicated micropost arrays result in hydrophobic surface with contact angle of about 147.6° ± 5° and the hysteresis of 16° ± 2°. In relation to self‐cleaning, water droplet behavior on the inclined replicated micropost arrays is simulated and droplet movement is examined experimentally. The optical transmittance of micropost arrays is tested in outdoor dusty environments. It is found that droplet slides on the inclined micropost surface and expanding droplet size enhances the sliding velocity. Alkaline dust compounds dissolve in droplet while increasing pH from 4.35 to 7.94 and surface tension from 0.072 to 0.120 N/m. This alters droplet pinning and lowers the sliding velocity from 0.2 to 0.15 m/s. Optical transmittance of the samples was tested in outdoor dusty environments improve considerably by sliding water droplet cleaning on daily bases (transmittance reduces only 3% or less as reference to surface being kept indoor environments). Hence, introducing micropost arrays on photovoltaic panel protective cover surface can provide self‐cleaning effect, via droplet rolling, while slightly reducing optical transmittance of cover glass (approximately 2.5%‐3%) in outdoor environments.

show abstract

A Water Droplet Pinning and Heat Transfer Characteristics on an Inclined Hydrophobic Surface

Cited by 46 publications

References 37 publications

Optimal Control of Droplets on a Solid Surface Using Distributed Contact Angles

Optimal Control of Droplets on a Solid Surface Using Distributed Contact Angles

Surface declination governed asymmetric sessile droplet evaporation

Solar energy harvesting and a water droplet cleaning of micropost arrays surfaces

Contact Info

Product

Resources

About