Drop impact process on a hydrophobic grooved surface

Kannan, R.; Sivakumar, D.

doi:10.1016/j.colsurfa.2007.12.005

Cited by 103 publications

(62 citation statements)

References 40 publications

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“…Recent experiments revealed the splash formed when a low-viscosity liquid, such as water or ethanol, first collides with a dry smooth wall at several m/s owes its existence entirely to the presence of air [13,14,15,16]. These results are motivating new studies on the large-scale deformations created by impact when air effects are absent as well as how a splash forms [17,18,19,20,21,22,23].Here we focus on the impact of a viscous liquid drop when air effects are absent. Recent experiments show that reducing the ambient gas pressure also suppresses the splash of a silicone oil drop.…”

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confidence: 99%

Impact of a Viscous Liquid Drop

et al. 2010

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We simulate the impact of a viscous liquid drop onto a smooth dry solid surface. As in experiments, when ambient air effects are negligible, impact flattens the falling drop without producing a splash. The no-slip boundary condition at the wall produces a boundary layer inside the liquid. Later, the flattening surface of the drop traces out the boundary layer. As a result, the eventual shape of the drop is a "pancake" of uniform thickness except at the rim, where surface tension effects are significant. The thickness of the pancake is simply the height where the drop surface first collides with the boundary layer.The impact of a liquid drop onto a dry solid surface lies at the heart of many important technological processes [1,2], from the application of a thermal spray [3,4,5,6,7,8,9] to atomization of fuel in a combustion chamber [8,10,11,12]. Recent experiments revealed the splash formed when a low-viscosity liquid, such as water or ethanol, first collides with a dry smooth wall at several m/s owes its existence entirely to the presence of air [13,14,15,16]. These results are motivating new studies on the large-scale deformations created by impact when air effects are absent as well as how a splash forms [17,18,19,20,21,22,23].Here we focus on the impact of a viscous liquid drop when air effects are absent. Recent experiments show that reducing the ambient gas pressure also suppresses the splash of a silicone oil drop. However, the form of the splash is very different. While the splash from a lowviscosity liquid develops within a few 10 µs of impact, the splash from a silicone oil develops slowly, becoming evident only after most of the liquid drop has fallen and flattened into a thin pancake [24,25]. We use an axisymmetric Volume-of-Fluid (VOF) code to simulate the impact at reduced ambient pressure [26,27,28]. Our results show that a boundary layer, corresponding to a thin region where the radial flow created by impact adjusts to the no-slip condition at the wall, is created by the impact. The boundary layer has uniform thickness. As impact nears its end, the drop surface flattens onto the boundary layer, evolving into a pancake of uniform thickness.The Volume-of-Fluid simulation solves the NavierStokes equations, together with constraint of incompressibility, for both the liquid interior and the gas exterior at reduced pressure. Physically appropriate boundary conditions, in particular the Laplace pressure jump across the surface due to surface tension, are enforced [26]. In a typical run, an initially spherical liquid drop with radius a collides with a dry, smooth solid surface at an impact speed U 0 of several m/s. The ambient air density ρ g is kept so small that 2-fold changes in in the value of ρ g have little effect on the liquid dynamics. The bottom surface of the liquid drop is not broken upon impact, which corresponds to maintaining an apparent contact angle of 180 • where the liquid rim meets the wall (Fig. 2a) [29]. We require that the velocity field inside the drop satisfies both the no-flux an...

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confidence: 99%

Impact of a Viscous Liquid Drop

et al. 2010

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“…The outcome after a droplet impacts on a surface is a fascinating problem and has received considerable attention in the literature dating back to over a century ago [3]. Various impacting substrates have been employed, ranging from dry [4] and pre-wetted surfaces [5], surfaces with physical [6] and chemical heterogeneities [7,8], thin [9] and deep liquid layers [10,11], porous media [12], heated [13,14], sublimating [15], and electrically-conducting [16], elastic membranes [17], and granular materials [18]. Non-Newtonian [19,20], surfactant-laden [21], and liquid-metallic droplets [22,23] have also been studied.…”

Section: Introductionmentioning

confidence: 99%

Impact of droplets on inclined flowing liquid films

2015

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The impact of droplets on an inclined falling liquid film is studied experimentally using highspeed imaging. The falling film is created on a flat substrate with controllable thicknesses and flow rates. Droplets with different sizes and speeds are used to study the impact process under various Ohnesorge and Weber numbers, and film Reynolds numbers. A number of phenomena associated with droplet impact are identified and analysed, such as bouncing, partial coalescence, total coalescence, and splashing. The effects of droplet size, speed, as well the film flow rate are studied culminating in the generation of an impact regime map. The analysis of the lubrication force acted on the droplet via the gas layer shows that a higher flow rate in the liquid film produces a larger lubrication force, slows down the drainage process, and increases the probability of droplet bouncing. Our results demonstrate that the flowing film has a profound effect on the droplet impact process and associated phenomena, which are markedly more complex than those accompanying impact on initially quiescent films.

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“…In their experiments, the maximum spreading diameter parallel to the grooves is larger than the one perpendicular to the grooves. Kannan et al [28] reported that the droplet would spread slower in the perpendicular direction on the grooved surface.…”

Section: Introductionmentioning

confidence: 99%

Contact angle and impinging process of droplets on partially grooved hydrophobic surfaces

Song

et al. 2015

Applied Thermal Engineering

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Drop impact process on a hydrophobic grooved surface

Cited by 103 publications

References 40 publications

Impact of a Viscous Liquid Drop

Impact of a Viscous Liquid Drop

Impact of droplets on inclined flowing liquid films

Contact angle and impinging process of droplets on partially grooved hydrophobic surfaces

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