la6b00574_si_001.avi (21.79 MB)
Inverse Leidenfrost Effect: Levitating Drops on Liquid Nitrogen
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posted on 2016-04-07, 00:00 authored by M. Adda-Bedia, S. Kumar, F. Lechenault, S. Moulinet, M. Schillaci, D. VellaWe
explore the interaction between a liquid drop (initially at
room temperature) and a bath of liquid nitrogen. In this scenario,
heat transfer occurs through film-boiling: a nitrogen vapor layer
develops that may cause the drop to levitate at the bath surface.
We report the phenomenology of this inverse Leidenfrost effect, investigating
the effect of the drop size and density by using an aqueous solution
of a tungsten salt to vary the drop density. We find that (depending
on its size and density) a drop either levitates or instantaneously
sinks into the bulk nitrogen. We begin by measuring the duration of
the levitation as a function of the radius R and
density ρd of the liquid drop. We find that the levitation
time increases roughly linearly with drop radius but depends weakly
on the drop density. However, for sufficiently large drops, R ≥ Rc(ρd), the drop sinks instantaneously; levitation does not occur. This
sinking of a (relatively) hot droplet induces film-boiling, releasing
a stream of vapor bubbles for a well-defined length of time. We study
the duration of this immersed-drop bubbling finding similar scalings
(but with different prefactors) to the levitating drop case. With
these observations, we study the physical factors limiting the levitation
and immersed-film-boiling times, proposing a simple model that explains
the scalings observed for the duration of these phenomena, as well
as the boundary of (R,ρd) parameter
space that separates them.