Study finds ultimate fate of Leidenfrost droplets depends on their size

A new study shows the ultimate fate of Leidenfrost droplets, liquid drops that levitate above very hot surfaces. Larger drops explode violently with an audible crack. Smaller ones simple shrink and fly away.

Enlarge / A new study shows
the ultimate fate of Leidenfrost droplets, liquid drops that
levitate above very hot surfaces. Larger drops explode violently
with an audible crack. Smaller ones simple shrink and fly away.
(credit: Lyu/Mathai)

In 1756, a German scientist named Johann
Gottlob Leidenfrost
reported his observation of an unusual
phenomenon. Normally, water splashed onto a very hot pan sizzles
and evaporates very quickly. But if the pan’s temperature is well
above water’s boiling point, “gleaming drops resembling
quicksilver” will form and will skitter across the surface. It’s
known as the “Leidenfrost
effect
” in his honor.

In the ensuing 250 years, physicists came up with a viable
explanation for why this occurs. If the surface is at least 40
degrees Fahrenheit (well above the boiling point of water),
cushions of water vapor, or steam, form underneath them, keeping
them levitated. The Leidenfrost effect also works with other
liquids, including oils and alcohol, but the temperature at which
it manifests will be different. In a
2009 Mythbusters episode
, for instance, the hosts demonstrated
how someone could wet their hand and dip it ever so briefly
into molten
lead
without injury, thanks to this effect.

But nobody had been able to identify the source of the
accompanying cracking sound Leidenfrost reported. Now, an
international team of scientists has filled in that last remaining
gap in our knowledge with a recent paper in
Science Advances.

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Source: FS – All – Science – News
Study finds ultimate fate of Leidenfrost droplets depends on their size