Two dimensional Leidenfrost droplets in a Hele-Shaw cell

Celestini, Franck; Frisch, Thomas; Cohen, Alexandre; Raufaste, Christophe; Duchemin, Laurent; Pomeau, Yves

doi:10.1063/1.4867163

Cited by 26 publications

(21 citation statements)

References 17 publications

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“…1a). Since the 1950's, a number of studies have investigated these oscillations, often with different conclusions as to their physical origin based on the complicated interplay between thermal and hydrodynamic effects in both the liquid and gas phases [13][14][15][16][17][18][19]. A simple underlying mechanism for the onset of star oscillations remains unknown.…”

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confidence: 99%

Star-shaped oscillations of Leidenfrost drops

Liétor-Santos

Burton

2017

Phys. Rev. Fluids

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We experimentally investigate the self-sustained, star-shaped oscillations of Leidenfrost drops. The drops levitate on a cushion of evaporated vapor over a heated, curved surface. We observe modes with n = 2 − 13 lobes around the drop periphery. We find that the wavelength of the oscillations depends only on the capillary length of the liquid, and is independent of the drop radius and substrate temperature. However, the number of observed modes depends sensitively on the liquid viscosity. The dominant frequency of pressure variations in the vapor layer is approximately twice the drop oscillation frequency, consistent with a parametric forcing mechanism. Our results show that the star-shaped oscillations are driven by capillary waves of a characteristic wavelength beneath the drop, and that the waves are generated by a large shear stress at the liquid-vapor interface.PACS numbers: 47.35.Pq, 47.15.gm, 47.85.mf The Leidenfrost effect can be easily observed by placing a millimeter-scale water drop onto a sufficiently hot pan. The drop will levitate on a thermally-insulating vapor layer and survive for minutes [1][2][3][4]. For small drops, the geometry and dynamics of the vapor layer have been recently characterized [5,6]. The complex interactions between the liquid, vapor, and solid interfaces have led to a broad range of applications such as turbulent dragreduction [7], self-propulsion of drops on ratcheted surfaces [8,9], green nanofabrication [10], fuel combustion [11], and thermal control of nuclear reactors [12].Large Leidenfrost drops are well-known to form selfsustained, star-shaped oscillations (Fig. 1a). Since the 1950's, a number of studies have investigated these oscillations, often with different conclusions as to their physical origin based on the complicated interplay between thermal and hydrodynamic effects in both the liquid and gas phases [13][14][15][16][17][18][19]. A simple underlying mechanism for the onset of star oscillations remains unknown. Drops subjected to external, periodic excitations can form star oscillations with a frequency half that of the external excitation due to a parametric coupling mechanism [20,21]. However, if a parametric mechanism causes Leidenfrost stars, then the source of the periodic excitation is unclear. Recently, Bouwhuis et al. investigated the star oscillations of drops levitated by an air flow over a porous surface [22]. They showed that the onset of star oscillations occurs when the flow rate of air beneath the drop reaches a threshold, suggesting that a hydrodynamic coupling between the gas flow and liquid interface initiates the oscillations.Here we report measurements of star-shaped oscillations of six different liquids on a hot, curved surface. We observe stars with n = 2 − 13 lobes around the drop periphery. Although the number of observed modes depends on the liquid viscosity and substrate temperature, we find that the wavelength and frequency of the modes only depend on the capillary length, l c = γ/ρ l g, where γ and ρ l are the surface tension and ...

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confidence: 99%

Star-shaped oscillations of Leidenfrost drops

Liétor-Santos

Burton

2017

Phys. Rev. Fluids

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“…8 Several studies are actually also devoted to the possible control of these droplets under the action of different kinds of external forces. 9,10 We have recently shown 11 that Leidenfrost droplets in a confined Hele-Shaw geometry exhibit two new phenomena: an intriguing morphogenic instability and a spontaneous hole nucleation and growth above a critical size. This latter point is the subject of this study.…”

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“…The experimental setup has been previously described in Celestini et al 11 A liquid droplet is confined between two horizontal plates separated by a spacing d. The plates' temperature is controlled and set to values largely higher than the Leidenfrost temperature. As a consequence, the presence of insulating vapor layers on both faces avoids any direct contacts between the droplet and the surfaces.…”

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Hole growth dynamics in a two dimensional Leidenfrost droplet

et al. 2015

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We studied the behaviors of Leidenfrost droplets confined in a Hele-Shaw cell. These droplets are unstable above a critical size and a hole grows at their center. We experimentally investigate two different systems for which the hole growth dynamics exhibits peculiar features that are driven by capillarity and inertia. We report a first regime characterized by the liquid reorganization from a liquid sheet to a liquid torus with similarities to the burst of micron-thick soap films. In the second regime, the liquid torus expands and thins before fragmentation. Finally, we propose models to account for the experimental results.

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“…The thickness of the vapor film is about 1-2 µm, which is typically one order of magnitude lower than the vapor film thickness reported in the literature for sessile droplets (ie. at thermal equilibrium and for W e = 0) [15]. For the high W e, the thickness of the vapor film still decreases with W e, but very moderately.…”

Section: Influence Of the Impact Velocitymentioning

confidence: 82%

Instantaneous heat transfers at the impact of a droplet onto a hot surface in the film boiling regime

Chaze¹,

Castanet²,

Caballina³

et al. 2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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Heat and mass transfers at the impact of a droplet onto a hot solid surface are investigated experimentally. Millimetersized water droplets impinges onto a perfectly flat sapphire surface heated at 600°C. The temperature of the liquid inside the droplet is measured using the two-color laser-induced fluorescence (2cLIF) technique. Water is seeded with a temperature-sensitive fluorescent dye, while a nanosecond pulsed laser is used for the excitation of the fluorescence. The ratio of fluorescence signal detected in two appropriate spectral bands allows to determine the liquid temperature. One advantage of this non-intrusive optical technique is that it eliminates adverse effects associated with signal variations caused by droplet shape during its impact. In parallel, the temperature of the solid surface is characterized using infrared thermography. The latter measurements are made possible by the deposition of a nanosize coating of titanium aluminium nitride (TiAlN) on the upper surface of the sapphire window. Thanks to the high frame rate of the IR camera, the time evolution of the heat flux distribution at the solid surface can be reconstructed. A comparison of IR and 2cLIF techniques enable to correlate the heating of the liquid with the cooling of the wall. This reveals that most of the heat removed from the solid surface is devoted to the heating of the liquid, the energy used for liquid vaporization being significantly lower. IntroductionMany industrial applications require a rapid cooling of surfaces from high temperatures. Among the cooling technologies, spray cooling is certainly one of the most attractive for the thermal management of high heat flux systems. Compared to jet impingement, it has the capability of cooling a relatively wider surface area with a single nozzle. It also has an unrivalled cooling efficiency, meaning that significant quantities of coolant liquid can be saved to remove the same amount of heat. These features explain why it is widely employed in many industrial applications, especially in metal production and processing industry. However, while it is applied for decades, its integration remains a complex and cumbersome process because of still incomplete knowledge of the fluid flow and heat transfer characteristics. In particular, scientific investigations focused on individual droplets are still required to understand the underlying physics behind the interactions between droplets and a hot solid surface. When a drop impacts a hot wall, different behaviours are observed. The drop can spread over the solid surface and remain attached to it due to wettability forces. It can splash and creates several smaller secondary droplets or simply rebounds. Extensive experimental investigations were carried out in the past to characterize the parameters influencing the drop behavior at the impact. Among them, some can be related to the dynamic of the impacting droplets (velocity, diameter, etc.), the physical properties of the liquid (viscosity, surface tension, etc.), and the solid su...

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Two dimensional Leidenfrost droplets in a Hele-Shaw cell

Cited by 26 publications

References 17 publications

Star-shaped oscillations of Leidenfrost drops

Star-shaped oscillations of Leidenfrost drops

Hole growth dynamics in a two dimensional Leidenfrost droplet

Instantaneous heat transfers at the impact of a droplet onto a hot surface in the film boiling regime

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