Hydrodynamics of Leidenfrost droplets in one-component fluids

Xu, Xinpeng; Qian, Tiezheng

doi:10.1103/physreve.87.043013

Cited by 24 publications

(21 citation statements)

References 56 publications

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“…When theoretically deriving T L , one needs to determine the vapor thickness profile. In the case of a gently deposited droplet, this can be accomplished since the shape of the droplet is fixed except for the bottom surface, which reduces the problem to a lubrication flow of vapor in the gap between the substrate and the free surface [15][16][17][18][19][20]. For impacting droplets on an unheated surface at high Weber number We ≡ ρU 2 D 0 =σ (here, D 0 is the equivalent diameter of the droplet and ρ and σ are the density and the surface tension of the liquid, respectively), it is known that the neck around the dimple beneath the impacting droplet rams the surface.…”

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confidence: 99%

Dynamic Leidenfrost Effect: Relevant Time and Length Scales

et al. 2016

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When a liquid droplet impacts a hot solid surface, enough vapor may be generated under it to prevent its contact with the solid. The minimum solid temperature for this so-called Leidenfrost effect to occur is termed the Leidenfrost temperature, or the dynamic Leidenfrost temperature when the droplet velocity is non-negligible. We observe the wetting or drying and the levitation dynamics of the droplet impacting on an (isothermal) smooth sapphire surface using high-speed total internal reflection imaging, which enables us to observe the droplet base up to about 100 nm above the substrate surface. By this method we are able to reveal the processes responsible for the transitional regime between the fully wetting and the fully levitated droplet as the solid temperature increases, thus shedding light on the characteristic time and length scales setting the dynamic Leidenfrost temperature for droplet impact on an isothermal substrate. DOI: 10.1103/PhysRevLett.116.064501 Boiling and spreading of droplets impacting on hot substrates have been extensively studied since both phenomena strongly affect the heat transfer between the liquid and the solid. Applications include spray cooling [1], spray combustion [2], and others [3].At room temperature, an impacting droplet spreads on a solid surface and entraps a bubble under it [4][5][6]. At temperatures higher than the boiling temperature T b , vapor bubbles appear which disturb and finally rupture the free surface, resulting in the violent spattering of tiny droplets [7,8]. On even hotter surfaces, however, beyond the socalled Leidenfrost temperature T L , the droplet interface becomes smooth again without any bubbles inside it. In this regime the droplet lives much longer, as now it levitates on its own vapor layer: the well-known Leidenfrost effect [9,10].In order to determine the Leidenfrost temperature T L and its dependence on the impact velocity U, phase diagrams have been experimentally produced for various impacting droplets with many combinations of substrates and liquids: water on smooth silicon [8], water on microstructured silicon [11], FC-72 on carbon nanofiber [12], water on aluminium [13], and ethanol on sapphire [14]. All of these phase diagrams show a weakly increasing behavior of T L with U. When theoretically deriving T L , one needs to determine the vapor thickness profile. In the case of a gently deposited droplet, this can be accomplished since the shape of the droplet is fixed except for the bottom surface, which reduces the problem to a lubrication flow of vapor in the gap between the substrate and the free surface [15][16][17][18][19][20]. For impacting droplets on an unheated surface at high Weber number We ≡ ρU 2 D 0 =σ (here, D 0 is the equivalent diameter of the droplet and ρ and σ are the density and the surface tension of the liquid, respectively), it is known that the neck around the dimple beneath the impacting droplet rams the surface. In this cold impact case, the neck propagates outwards like a wave [21]. For impact on a superheated s...

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Dynamic Leidenfrost Effect: Relevant Time and Length Scales

et al. 2016

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“…However, the initial size of the Leidenfrost droplet is limited. Indeed, for large drops, a Rayleigh-Taylor instability arises at the bottom of the drop 18,25 . For water, the instability occurs when the droplet radius exceeds R c ' 9.6 mm 18 .…”

Section: Liquid Droplet Wrapped In a Monolayer Of Grainsmentioning

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Organization of microbeads in Leidenfrost drops

2014

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We investigated the organization of micrometric hydrophilic beads (glass or basalt) immersed in Leidenfrost drops. Starting from a large volume of water compared to the volume of the beads, while the liquid evaporates, we observed that the grains are eventually trapped at the interface of the droplet and accumulate. At a moment, the grains entirely cover the droplet. We measured the surface area at this moment as a function of the total mass of particles inserted in the droplet. We concluded that the grains form a monolayer around the droplet assuming (i) that the packing of the beads at the surface is a random close packing and (ii) that the initial surface of the drop is larger than the maximum surface that the beads can cover. Regarding the evaporation dynamics, the beads are found to reduce the evaporation rate of the drop. The slowdown of the evaporation is interpreted as being the consequence of the dewetting of the particles located at the droplet interface which make of the effective surface of evaporation smaller. As a matter of fact, contact angles of the beads with the water deduced from the evaporation rates are consistent with contact angles of beads directly measured at the air -water interface in a container.

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“…The dielectric discontinuity across the interface leads to induced charges which repel ions from the interface [14,[38][39][40][41]. This is different from a conductor which leads to an ionelectrode attraction [42].…”

Section: Theorymentioning

confidence: 99%

Adsorption of cationic polyions onto a hydrophobic surface in the presence of Hofmeister salts

Santos

Levin

2013

Soft Matter

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We study, using extensive Monte Carlos simulations, the behavior of cationic polyelectrolytes near hydrophobic surfaces in solutions containing Hofmeister salts. The Hofmeister anions are divided into kosmotropes and chaotropes. Near a hydrophobic surface, the chaotropes lose their solvation sheath and become partially adsorbed to the interface, while the kosmotropes remain strongly hydrated and are repelled from the interface. If the polyelectrolyte solution contains chaotropic anions, a significant adsorption of polyions to the surface is also observed. On the other hand, the kosmotropic anions have only a small influence on the polyion adsorption. These findings can have important implications for exploring the antibacterial properties of cationic polyelectrolytes.

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Hydrodynamics of Leidenfrost droplets in one-component fluids

Cited by 24 publications

References 56 publications

Dynamic Leidenfrost Effect: Relevant Time and Length Scales

Dynamic Leidenfrost Effect: Relevant Time and Length Scales

Organization of microbeads in Leidenfrost drops

Adsorption of cationic polyions onto a hydrophobic surface in the presence of Hofmeister salts

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