Leidenfrost effect: Accurate drop shape modeling and refined scaling laws

Sobac, Benjamin; Rednikov, Alexei; Dorbolo, Stéphane; Colinet, Pierre

doi:10.1103/physreve.90.053011

Cited by 77 publications

(138 citation statements)

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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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Dynamic Leidenfrost Effect: Relevant Time and Length Scales

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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

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“…The following section will present an overview of the dynamics of drop impact on unheated plates. 1 16 …”

Section: Drop Impact Dynamicsmentioning

confidence: 99%

“…The present model is aimed at predicting the quasi-steady state of such a drop (the slowest process being its evaporation), including both its geometry and a possible cooling of the substrate. The drop geometry is modelled by numerically matching the hydrostatic equilibrium shape of a superhydrophobic drop (for the upper part) with the lubrication equation solution for the vapour film underlying the drop (for the bottom part), quite similarly to Sobac et al [16]. However, unlike Sobac et al [16], the substrate is no longer considered isothermal, and its cooling is accounted for by solving a heat transfer problem therein.…”

Section: Formulation Of the Theoretical Modelmentioning

confidence: 99%

“…The complete (axisymetric) temperature field inside the plate can thereby be obtained. On the one hand, these experimental data, and in particular the measured temperature distribution at the plate surface, can directly be used in Leidenfrost drop modelling, which then amounts to the gas phase only, as for an isothermal substrate [16]. This enables us to calculate the distribution of heat (and evaporation) fluxes and vapour film thicknesses.…”

Section: Introduction 89mentioning

confidence: 99%

“…When theoretically deriving T L , one needs to determine the vapour 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 vapour in the gap between the substrate and the free-surface [14, 16,17,21,27,70].…”

Section: Introductionmentioning

confidence: 99%

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