scholarly journals The crackling sound of Leidenfrost stars

2018 ◽  
Vol 850 ◽  
pp. 1-4 ◽  
Author(s):  
P. Brunet
Keyword(s):  
Free Surface ◽  
Standing Wave ◽  
Pressure Fluctuations ◽  
Hot Plate ◽  
Liquid Drops ◽  
Boiling Crisis ◽  
Drop Dynamics ◽  
Leidenfrost Effect ◽  
Vapour Flux

Liquid drops deposited on a hot plate can experience a boiling crisis, when the vapour flux is strong enough to ensure the levitation of the drop and the relative insulation of the liquid from the solid. It is often denoted Leidenfrost effect, after the German Johann Gottlob Leidenfrost, who first reported it in 1756. While many studies have encompassed various applied issues associated with this phenomenon, aiming to control and prevent its appearance, Ma & Burton (J. Fluid Mech., vol. 846, 2018, pp. 263–291) focused on the spontaneous appearance of a standing wave at the free surface, together with temporal oscillations, making the drop adopt the shape of a star. Their far-reaching study presents exhaustive results using six different liquids with a range of different volumes and temperatures, in which they systematically extracted the drop dynamics together with the pressure fluctuations in the vapour cushion below.

Impact of Drops on Various Non-Wetting Surfaces

2009 ◽  
Author(s):  
Philippe Brunet ◽  
Alain Merlen
Keyword(s):  
Experimental Study ◽  
Contact Angle ◽  
Thin Layer ◽  
Initial Velocity ◽  
Liquid Drop ◽  
Spray Cooling ◽  
Lateral Extension ◽  
Hot Plate ◽  
Boiling Crisis ◽  
Leidenfrost Effect

We have carried out an experimental study of liquid drop impact on various superhydrophobic substrates. Our surfaces are of two kinds (1) a carpet of chemically coated nanowires and (2) a smooth warm substrate. In the latter case, the Leidenfrost effect (also called ‘boiling crisis’) ensures the existence of a thin layer of air coming from the evaporation of the drop, thus preventing the drop to touch the warm surface. Technically, in this latter situation the contact angle can then be considered as equal to 180 degrees, with no hysteresis. Due to its initial inertia, the drop experiences a flattening phase after it hits the surface, taking the shape of a pancake. Once it reaches its maximal lateral extension, the drop begins to retract and bounces back. We have extracted the lateral extension of the drop, and we propose a model that explains the trend. We find a limit initial velocity beyond which the drop (1) protrudes into the nanowire carpet (2) touches the hot plate, provoking a local violent boiling. We discuss the relevance of practical issues in terms of self-cleaning surfaces or spray-cooling.

Experimental Study on the Frequency of a Free Surface Fluctuation in a Vessel With or Without an Internal Structure

2009 ◽  
Author(s):  
Ho-Yun Nam ◽  
Byoung-Hae Choi ◽  
Jong-Man Kim ◽  
Byung-Ho Kim
Keyword(s):  
Experimental Study ◽  
Free Surface ◽  
Internal Structure ◽  
Standing Wave ◽  
Side Wall ◽  
Vessel Diameter ◽  
Dominant Frequency ◽  
Wave Region ◽  
Surface Fluctuation ◽  
Structure Water

An experimental study has been performed to investigate the frequency of a free surface fluctuation in a vessel with and without an internal structure. Water flows in from the bottom nozzle and flows out at the side wall nozzles. There are two dominant frequency regions which are generated by a standing wave and a jet. In the standing wave region, the frequency is well described by f(4πdV/g)1/2 = 1.07 in a circular vessel. The frequency generated by a jet can be described by a dimensionless period and Froude number according to its fluctuation stability. In the case of a vessel with an internal structure, it needs a geometry factor which is described by a vessel diameter to a hydraulic diameter ratio in a standing wave region.

scholarly journals The set-down and set-up of directionally spread and crossing surface gravity wave groups

2017 ◽  
Vol 835 ◽  
pp. 131-169 ◽  
Author(s):  
M. L. McAllister ◽  
T. A. A. Adcock ◽  
P. H. Taylor ◽  
T. S. van den Bremer
Keyword(s):  
Free Surface ◽  
Gravity Wave ◽  
Standing Wave ◽  
Wave Pattern ◽  
Surface Gravity ◽  
Linear Wave ◽  
Surface Gravity Wave ◽  
Wave Groups ◽  
Single Wave ◽  
Set Up

For sufficiently directionally spread surface gravity wave groups, the set-down of the wave-averaged free surface, first described by Longuet-Higgins and Stewart (J. Fluid Mech. vol. 13, 1962, pp. 481–504), can turn into a set-up. Using a multiple-scale expansion for two crossing wave groups, we examine the structure and magnitude of this wave-averaged set-up, which is part of a crossing wave pattern that behaves as a modulated partial standing wave: in space, it consists of a rapidly varying standing-wave pattern slowly modulated by the product of the envelopes of the two groups; in time, it grows and decays on the slow time scale associated with the translation of the groups. Whether this crossing wave pattern actually enhances the surface elevation at the point of focus depends on the phases of the linear wave groups, unlike the set-down, which is always negative and inherits the spatial structure of the underlying envelope(s). We present detailed laboratory measurements of the wave-averaged free surface, examining both single wave groups, varying the degree of spreading from small to very large, and the interaction between two wave groups, varying both the degree of spreading and the crossing angle between the groups. In both cases, we find good agreement between the experiments, our simple expressions for the set-down and set-up, and existing second-order theory based on the component-by-component interaction of individual waves with different frequencies and directions. We predict and observe a set-up for wave groups with a Gaussian angular amplitude distribution with standard deviations of above $30{-}40^{\circ }$ ($21{-}28^{\circ }$ for energy spectra), which is relatively large for realistic sea states, and for crossing sea states with angles of separation of $50{-}70^{\circ }$ and above, which are known to occur in the ocean.

Liquid Metal Free Surface Motion Submerged in an AC Magnetic Field

2007 ◽  
Vol 561-565 ◽  
pp. 1071-1074
Author(s):  
Kazuhiko Iwai ◽  
Shigeo Asai
Keyword(s):  
Magnetic Field ◽  
Free Surface ◽  
Liquid Metal ◽  
Standing Wave ◽  
Skin Layer ◽  
Alternating Magnetic Field ◽  
Liquid Gallium ◽  
Field Frequency ◽  
Surface Motion ◽  
The Magnetic Field

Free surface motion of a liquid metal submerged in an alternating magnetic field has been examined. A copper vessel filled with a liquid gallium is set in a coil for the imposition of the alternating magnetic field. The alternating magnetic field penetrates into a liquid gallium only from an upper free surface because thickness of the copper vessel is larger than the electromagnetic skin layer of copper. Time variation of displacement of the standing wave loop excited on the free surface is detected by a laser level sensor. The standing wave was suppressed not only by intensification of the magnetic field magnitude but also increase of the magnetic field frequency.

scholarly journals Generalizing the Multimodal Method for the Levitating Drop Dynamics

2012 ◽  
Vol 2012 ◽  
pp. 1-19 ◽  
Author(s):  
M. O. Chernova ◽  
I. A. Lukovsky ◽  
A. N. Timokha
Keyword(s):  
Free Surface ◽  
Almost Periodic ◽  
Modal System ◽  
Periodic Oscillations ◽  
Weakly Nonlinear ◽  
Modal Theory ◽  
Drop Dynamics ◽  
Finite Dimensional ◽  
Multimodal Method ◽  
Good Agreement

The present paper extends the multimodal method, which is well known for liquid sloshing problems, to the free-surface problem modeling the levitating drop dynamics. The generalized Lukovsky-Miles modal equations are derived. Based on these equations an approximate modal theory is constructed to describe weakly-nonlinear axisymmetric drop motions. Whereas the drop performs almost-periodic oscillations with the frequency close to the lowest natural frequency, the theory takes a finite-dimensional form. Periodic solutions of the corresponding finite-dimensional modal system are compared with experimental and numerical results obtained by other authors. A good agreement is shown.

On the form of the highest progressive and standing waves in deep water

1973 ◽  
Vol 331 (1587) ◽  
pp. 445-456 ◽  
Keyword(s):  
Free Surface ◽  
Numerical Integration ◽  
Gravity Wave ◽  
Standing Wave ◽  
Deep Water ◽  
Standing Waves ◽  
Infinite Depth ◽  
Single Term

The form of a progressive gravity wave on deep water, which generally must be found by numerical integration (Michell 1893) is shown to be approximated with remarkable accuracy by a single term. Six consecutive waves are transformed conformally so as to surround the point corresponding to infinite depth. The free surface then corresponds closely to the boundary of a hexagon. In a similar way the profile of a standing wave is closely approximated to by transforming four consecutive waves conformally and taking the profile as the boundary of a square. The profile agrees closely with that calculated by Penney & Price (1952) and with the experiments of Taylor (1953).

scholarly journals Triple Leidenfrost Effect: Preventing Coalescence of Drops on a Hot Plate

2021 ◽  
Vol 127 (20) ◽  
Author(s):  
F. Pacheco-Vázquez ◽  
R. Ledesma-Alonso ◽  
J. L. Palacio-Rangel ◽  
F. Moreau
Keyword(s):  
Hot Plate ◽  
Leidenfrost Effect

Leidenfrost drop dynamics: a forgotten past and modern day rediscoveries

2021 ◽  
Author(s):  
Seán Stewart
Keyword(s):  
Thin Layer ◽  
Boiling Point ◽  
Dynamic Behaviour ◽  
Dynamical Behaviour ◽  
Drop Dynamics ◽  
Leidenfrost Effect ◽  
History Of ◽  
Hot Surface

Abstract When drops of liquid are placed onto highly heated substrates at temperatures well above their boiling point, the drops float on a thin layer of vapour formed between the liquid and the hot surface. In a 290 year old phenomenon referred to as the Leidenfrost effect, drops freed from contact with the surface below can undergo a range of surprising and unexpected dynamical behaviour. In this paper we trace various early developments associated with the dynamics of Leidenfrost drops. By showing how many of the more recent discoveries found in the dynamic behaviour of Leidenfrost drops were either anticipated or antedated, we hope to draw attention to the long, rich, and largely overlooked history of the Leidenfrost effect and show there is much one can learn from its forgotten past.

Cavity formation by the impact of Leidenfrost spheres

2012 ◽  
Vol 699 ◽  
pp. 465-488 ◽  
Author(s):  
J. O. Marston ◽  
I. U. Vakarelski ◽  
S. T. Thoroddsen
Keyword(s):  
Free Surface ◽  
Contact Line ◽  
Liquid Pool ◽  
Physical Contact ◽  
Cavity Formation ◽  
Cavity Structure ◽  
Leidenfrost Effect ◽  
Contact Line Pinning ◽  
The Impact ◽  
Initial Entry

AbstractWe report observations of cavity formation and subsequent collapse when a heated sphere impacts onto a liquid pool. When the sphere temperature is much greater than the boiling point of the liquid, we observe an inverted Leidenfrost effect where the sphere is encompassed by a vapour layer that prevents physical contact with the liquid. This creates the ultimate non-wetting scenario during sphere penetration through a free surface, producing very smooth cavity walls. In some cases during initial entry, however, the liquid contacts the sphere at the equator, leading to the formation of a dual cavity structure. For cold sphere impacts, where a contact line is observed, we reveal details of the contact line pinning, which initially forms a sawtooth pattern. We also observe surface waves on the cavity interface for cold spheres. We compare our experimental results to previous studies of cavity dynamics and, in particular, the influence of hydrophobicity on the entry of the sphere.

An experimental investigation of screech noise generation

1999 ◽  
Vol 378 ◽  
pp. 71-96 ◽  
Author(s):  
J. PANDA
Keyword(s):  
Shear Layer ◽  
Standing Wave ◽  
Pressure Fluctuations ◽  
Length Scale ◽  
Generation Process ◽  
Noise Generation ◽  
Sound Waves ◽  
Sonic Nozzle ◽  
Hydrodynamic Fluctuations ◽  
Partial Interference

The screech noise generation process from supersonic underexpanded jets, issuing from a sonic nozzle at pressure ratios of 2.4 and 3.3 (fully expanded Mach number, Mj=1.19 and 1.42), was investigated experimentally. The extremely detailed data provide a fresh, new look at the screech generation mechanism. Spark schlieren visualization at different phases of the screech cycle clearly shows the convection of the organized turbulent structures over a train of shock waves. The potential pressure field (hydrodynamic fluctuations) associated with the organized structures is fairly intense and extends outside the shear layer. The time evolution of the near-field pressure fluctuations was obtained from phase-averaged microphone measurements. Phase-matched combined views of schlieren photographs and pressure fluctuations show the sound generation process. The individual compression and rarefaction parts of the sound waves are found to be generated from similar hydrodynamic fluctuations. A partial interference between the upstream-propagating sound waves and the downstream-propagating hydrodynamic waves is found to be present along the jet boundary. The partial interference manifests itself as a standing wave in the root-mean-square pressure fluctuation data. The standing wavelength is found to be close to, but somewhat different from, the shock spacing. An outcome of the interference is a curious ‘pause and go’ motion of the sound waves along the jet periphery. Interestingly, a length scale identical to the standing wavelength is found to be present inside the jet shear layer. The coherent fluctuations and the convective velocity of the organized vortices are found to be modulated periodically, and the periodicity is found to match with the standing wavelength distance rather than the shock spacing. The reason for the appearance of this additional length scale, different from the shock spacing, could not be explained. Nevertheless, it is demonstrated that an exact screech frequency formula can be derived from the simple standing wave relationship. The exact relationship shows that the correct spacing between the sources, for a point source model similar to that of Powell (1953), should be a standing wavelength (not the shock spacing).

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