Leidenfrost Temperature—Its Correlation for Liquid Metals, Cryogens, Hydrocarbons, and Water

Baumeister, K. J.; Simon, F. F.

doi:10.1115/1.3450019

Cited by 242 publications

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“…Next to the impact velocity U, a key process that significantly affects T L is the cooling of the substrate due to its exposure to the cold liquid. T L thus strongly depends on the thermophysical properties of both the liquid and the substrate used [12,25,26]. For example, a gently deposited ethanol droplet can achieve the Leidenfrost state at T L;static ¼ 157°C on polished aluminum, whereas on pyrex glass a temperature as high as 360°C is required.…”

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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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“…Baumeister and Simon (1973) added an empirical factor to equation (3) which accounts for the effect of surface cooling caused by the impingement of a cold droplet:…”

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Heat-transfer dynamics during cryogen spray cooling of substrate at different initial temperatures

et al. 2004

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Cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during laser dermatologic therapy. However, the dominant mechanisms of heat transfer during the transient cooling process are incompletely understood. The objective of this study is to elucidate the physics of CSC by measuring the effect of initial substrate temperature (T 0 ) on cooling dynamics. Cryogen was delivered by a straight-tube nozzle onto a skin phantom. A fast-response thermocouple was used to record the phantom temperature changes before, during and after the cryogen spray. Surface heat fluxes (q ) and heat-transfer coefficients (h) were computed using an inverse heat conduction algorithm. The maximum surface heat flux (q max ) was observed to increase with T 0 . The surface temperature corresponding to q max also increased with T 0 but the latter has no significant effect on h. It is concluded that heat transfer between the cryogen spray and skin phantom remains in the nucleate boiling region even if T 0 is 80 • C.

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“…In some cases, the wall temperature can locally vary significantly [10,11]. The only unknown left in Equation 1.1 is the pressure field, through which the dynamics of the film interface is coupled with the dynamics inside the liquid phase.…”

Section: General Description 121 the Modelling Of Thin Vapour Filmsmentioning

confidence: 99%

“…Therefore we compare this boundary with T L for different pressures on a silicon substrate. Because of its high thermal conductivity k s = 148 W/(m K) at T = 300K , the silicon substrate is considered to be isothermal [10] during the evaporation of the drop. The pressure dependence of T L = T L (P ) is shown in Fig.…”

Section: Boundary Between the Contact And Transition Boiling Regimementioning

Leidenfrost Temperature—Its Correlation for Liquid Metals, Cryogens, Hydrocarbons, and Water

Cited by 242 publications

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Dynamic Leidenfrost Effect: Relevant Time and Length Scales

Dynamic Leidenfrost Effect: Relevant Time and Length Scales

Heat-transfer dynamics during cryogen spray cooling of substrate at different initial temperatures

The dynamics of Leidenfrost drops

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