Energy Transport by Thermocapillary Convection during Sessile-Water-Droplet Evaporation

Ghasemi, Hadi; Ward, C. A.

doi:10.1103/physrevlett.105.136102

Cited by 88 publications

(112 citation statements)

References 20 publications

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“…Our work supports the prediction of Deegan et al (10) that the flow within the droplet arises from mass conservation, since Marangoni convection from the contact line to the apex would lead to higher velocities along the base of the drop than those required to satisfy mass conservation due to evaporation. At first sight it contradicts that of Ghasemi and Ward (4) .…”

Section: Water Dropletsmentioning

confidence: 70%

“…Deegan et al (9,10) have studied ring formation from suspension and particle containing water drops, from which they infer that internal flow in the drop is driven by mass conservation to replenish fluid evaporating preferentially at the outer edge of the drop. In contrast, Ghasemi and Ward (4) report that in a reduced pressure environment, flow in evaporating water drops is driven by thermocapillary convection, such as was observed by Buffone et al (11) for a meniscus within a capillary.…”

Section: Introductionmentioning

confidence: 91%

“…The evaporation and wetting of pure droplets has been extensively studied in the recent years (1)(2)(3)(4) . This interest is driven by many technological and biological applications, e.g.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The Flow Characteristics of an Evaporating Ethanol Water Mixture Droplet on a Glass Substrate

Hamamoto

Christy

Sefiane

2012

JTST

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Droplet evaporation has attracted much interest recently, being relevant to a wide range of biological and technological applications. The underlying mechanisms for this phenomenon are still poorly understood. We report on experimental results, from micro-Particle Image Velocimetry (µPIV), of the spatial and temporal velocity field within pure water and ethanol-water mixture droplets evaporating on a glass substrate. The drop profile, evaporation rate and surface temperature were also measured. For pure water droplets, the redial velocity is found to exhibit a maximum spatially towards the three-phase contact line and to increase dramatically towards the end of the drop lifetime. For ethanol-water droplets, three flow phases of (I) vortical flow, (II) transient flow and (III) radial flow were observed. Phase I has vortices, driven, we believe, by concentration differences arising during the preferential evaporation of ethanol. Phase II sees an exponential decay in vorticity with remaining vortices migrating towards the contact line, accompanied by the formation of one large toroidal vortex, possibly due to ethanol depletion at the apex of the drop leading to a surface tension instability. Phase III is characterized by radial flow towards the contact line, matching the evaporative flux and identical to the flow measured for pure water.

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Section: Water Dropletsmentioning

confidence: 70%

Section: Introductionmentioning

confidence: 91%

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The Flow Characteristics of an Evaporating Ethanol Water Mixture Droplet on a Glass Substrate

Hamamoto

Christy

Sefiane

2012

JTST

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“…The other important characteristic of the DLS is its hydrophilicity, which promotes fluid flow to the surface. The capillary force in the exfoliated graphite layer enhances the evaporation rate of the fluid through several mechanisms: formation of thin films on the surface of graphite sheets 21 , enhanced surface area for evaporation 22 and formation of three-phase contact lines at the edges of the capillaries 23,24 . The graphite structure has hydrophobic surfaces as evidenced by the contact angle ( Supplementary Fig.…”

Section: Resultsmentioning

confidence: 99%

Solar steam generation by heat localization

et al. 2014

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Currently, steam generation using solar energy is based on heating bulk liquid to high temperatures. This approach requires either costly high optical concentrations leading to heat loss by the hot bulk liquid and heated surfaces or vacuum. New solar receiver concepts such as porous volumetric receivers or nanofluids have been proposed to decrease these losses. Here we report development of an approach and corresponding material structure for solar steam generation while maintaining low optical concentration and keeping the bulk liquid at low temperature with no vacuum. We achieve solar thermal efficiency up to 85% at only 10 kW m À 2 . This high performance results from four structure characteristics: absorbing in the solar spectrum, thermally insulating, hydrophilic and interconnected pores. The structure concentrates thermal energy and fluid flow where needed for phase change and minimizes dissipated energy. This new structure provides a novel approach to harvesting solar energy for a broad range of phase-change applications.

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“…The orientation and intensity of this flow in the case of single component drops can depend on the relative thermal properties of the substrate and liquid, Ristenpart et al (2007). Furthermore, these flows can be the result of temperature and/or concentration gradients and may play a major role in energy transport, Ghasemi & Ward (2010). Generally, surface tension driven flows in single component volatile drops are essentially thermocapillary in nature, i.e.…”

Section: Introductionmentioning

confidence: 99%

Vortices, dissipation and flow transition in volatile binary drops

Bennacer

Sefiane

2014

J. Fluid Mech.

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(Received ?; revised ?; accepted ?. -To be entered by editorial office)Despite its fundamental and practical relevance, flow structure and evolution within volatile mixture drops remains largely unexplored. We study experimentally, using particle image velocimetry (PIV), the evolution of internal flow during the evaporation of ethanol-water mixture drops for different initial concentrations. The investigation revealed the existence of three stages in the evolving flow behaviour within these binary volatile drops. We propose an analysis of the nature of the flow and focus on understanding successive flow stages as well as transition from multiple vortices to a monotonous outward flow. We show that the existence of multiple vortices during the first stage is driven by local concentration gradients along the interface. When the more volatile component (in this case ethanol) is depleted, the intensity of this M arangoni flow abruptly declines. Towards the end of the first stage, ethanol is driven from the bulk of the drop to the interface to sustain weakening concentration gradients. Once these gradients are too weak, the solutal M arangoni number becomes sub-critical and the driving force for the flow switches off. The evolution of flow structure and transition between stages is found to be well correlated with the ratio of Marangoni and Reynolds numbers. Furthermore, we argue that whilst the observed vortices are driven by surface tension shear stress originating at the liquid/vapour interface, the transition in flow and its dynamics is entirely determined by viscous dissipation. The comparison between the analytical expression for vorticity decay based on viscous dissipation and the experimental data show a very good agreement. The analysis also shows that regardless of the initial concentration, for same size drops, the transition in flow follows exactly the same trend. This further supports the hypothesis of a viscous dissipation transition of the flow. The last stage is satisfactorily explained based on non-uniform evaporation and continuity driven flow.

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Energy Transport by Thermocapillary Convection during Sessile-Water-Droplet Evaporation

Cited by 88 publications

References 20 publications

The Flow Characteristics of an Evaporating Ethanol Water Mixture Droplet on a Glass Substrate

The Flow Characteristics of an Evaporating Ethanol Water Mixture Droplet on a Glass Substrate

Solar steam generation by heat localization

Vortices, dissipation and flow transition in volatile binary drops

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