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DTSTAMP:20260424T143256Z
UID:64fac8743e6da254677652@ist.ac.at
DTSTART:20231116T110000
DTEND:20231116T120000
DESCRIPTION:Speaker: Ambre Bouillant\nhosted by Scott Waitukaitis\nAbstract
 : A water droplet placed on a hot solid levitates on a cushion of its own 
 vapor. This is known as the so-called Leidenfrost effect\, discovered in 1
 756. This gas layer\, continually renewed\, mechanically and thermally iso
 lates the liquid\, which\, by limiting its evaporation and suppressing boi
 ling\, enables the drops to survive quietly for minutes. This levitation s
 tate also prevents the liquid from wetting its substrate\, giving the drop
 let a pearl-like shape\, and creating a friction-free situation. This make
 s Leidenfrost droplets very sensitive to any external perturbations\, such
  as gravity or air flow\, and therefore\, as has been widely accepted\, ex
 plains their extreme mobility.However\, we have observed that droplets dep
 osited without initial velocity on strictly horizontal substrates self-pro
 pel in random directions. In this seminar\, I will first discuss the origi
 n of Leidenfrost droplets mobility and show that their motion is generated
  by confinement. PIV measurements reveal that\, as the drop aspect ratio o
 f the drop becomes of order unity\, the (intense) internal motions of liqu
 id switch from symmetric to asymmetric rolling. Such a flow reshapes the v
 apor cushion and tilts it\, as evidenced by interferometric measurement. H
 ence\, this leads to propulsion. Droplets are thus found to generate their
  own dynamics and self-propel even in the absence of external field\, whic
 h contributes to their legendary mobility.In the second part of the talk\,
  I will discuss another spontaneous dynamic occurring during Leidenfrost d
 rops life. Above a certain size\, Leidenfrost puddles often suddenly and u
 nexpectedly start to oscillate with star shapes\, a phenomenon first repor
 ted about 140 years ago\, but not yet understood. It is known that similar
  deformations can be triggered when a liquid is subjected to an external p
 eriodic forcing. However\, a periodic forcing could not be identified in t
 he context of the Leidenfrost phenomenon. I will show that Leidenfrost bod
 ies are subjected to an internal periodic forcing\, which unravels the ori
 gin of Leidenfrost stars. I will then discuss the frequency of the vibrati
 ons and show that they can excite Faraday-like surface standing waves. Dro
 ps being close cavities\, deformations only get amplified when their polar
  perimeter can accommodate an integer number of wavelengths. This resonanc
 e condition explains the discrete and sporadic response of the liquid and\
 , more generally\, how the drop natural modes can be locked on throughout 
 the drops life.These two dynamics\, orchestrated by evaporation-driven con
 finement\, highlight the richness of this system that involves capillarity
 \, phase changes\, thermal effects\, aerodynamics\, and hydrodynamics.
LOCATION:Moonstone Bldg / Ground floor / Seminar Room F (I24.EG.030f)\, IST
 A
ORGANIZER:cpetz@ist.ac.at
SUMMARY:Ambre Bouillant: Self-propulsion and self-oscillations of Leidenfro
 st droplets
URL:https://talks-calendar.ista.ac.at/events/4586
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