Liquid nitrogen hovers over the surface of a hot pan

The Leidenfrost Effect is a lovely sounding name for some very strange and nifty physics.

When you heat up a liquid, it will, eventually, boil away into a gas. Different liquids have different boiling points. But here's the weird catch: When you suddenly put a liquid in contact with something much, much hotter than its boiling point, the liquid doesn't instantly evaporate. Instead, it forms a little cushion of vapor between itself and the heat source. You can imagine it like a hovercraft moving over the surface of a lake. The cushion doesn't prevent evaporation—and it doesn't last long—but it does slow down evaporation enough that you can see the liquid moving around on the hot surface for little bit like everything is just fine and dandy.

This video was made as a promotional piece for Modernist Cuisine. The Leidenfrost Effect matters for cooking because it allows you to tell when you have successfully heated up a pan. If the temperature of the pan is above the Leidenfrost point, then you can sprinkle it with water and watch the droplets bandy about on the hot metal. In this case, though, they used liquid nitrogen.

Via Geeksaresexy and cafonso

Maggie Koerth-Baker is the science editor at BoingBoing.net. She writes a monthly column for The New York Times Magazine and is the author of Before the Lights Go Out, a book about electricity, infrastructure, and the future of energy. You can find Maggie on Twitter and Facebook.

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MORE: Cooking • liquid nitrogen • modernist cuisine • physics • Science • videos • Weird

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This is in contrast to the Lederhosen effect which is characterized by heavy beer drinking and speaking of German.
- http://maggiekb.com/ Maggie Koerth-Baker
  
  Lederhosen Effect states that the drunker you get, the better you become at dancing the polka.
slippy0

A while back in a class on strobe photography, we were given access to high speed cameras, so we recorded some instances of the Leidenfrost effect. I think this was my favorite:
http://www.youtube.com/watch?v=CyRxKVL22XA&feature=plcp

A constant stream of water from an eyedropper that “bounces” off the plate, spending 90% of the time without actually making contact.

We also messed up once, and got a nice video of explosive evaporation instead of the Leidenfrost effect:
http://www.youtube.com/watch?v=3ByqLCLsbcA#t=27s .
bzishi

This is also important for nuclear reactors (for PWRs). With inadequate cooling or a reduction in the boiling temp due to a pressure drop of the coolant, an insulating layer of steam can form around the fuel elements while the inner part of the channel is still liquid. With heat still being generated by the fuel, its temperature will then suddenly skyrocket until the fuel element fails. There is a nice graph in Wikipedia that describes this condition (note that everything to the right of the initial peak is an unstable transition state if your hot surface is also generating heat).
- digi_owl
  
  I take it that at such point it will be worthless to attempt to put more coolant on the fuel.
  - bzishi
    
    It isn’t worthless. But as TMI-2 demonstrated, it will likely shatter the fuel as the zirconium cladding will be mostly oxidized by that point.
RKTR ♫soundcloud.com/rktr

Was this shot on a phantom camera?
JeffF

I’ve watched liquid nitrogen do this on floors and lab benches. So I think the pan only needs to be hot to do it with water.

The droplets also seem to tend to pick up dust and lint so at the end once it all boils off you are often left with a little spheroid of dust.

It’s also why you are reportedly able to plunge your hand briefly into liquid nitrogen to grab something out. The boiling creates a gas layer which conducts heat slowly enough that you are ok… if you do it quick and the thing you are grabbing and the container the liquid nitrogen are in are poor conductors of heat (eg plastic and styrofoam). Definately don’t try to grab a penny out of one of those metal or glass vacuum insulated containers. Haven’t tried it myself (my liquid nitrogen was in the vacuum container, and there was only a cup or two of it). The guy who said he did, back in the day, had all his fingers though.
Mighty Blowhole

Looks like Rover from The Prisoner!
http://www.facebook.com/profile.php?id=41203083 Joe Alfano

Jearl Walker demonstrates how the Leidenfrost effect allows you to dip your (wetted) finger into molten lead. http://www.youtube.com/watch?v=k-ZSXkyFyOE
http://www.facebook.com/samson.glass Sam Glass

I’m sure I’ve seen this effect with water drops hitting standing water of a similar temperature. Anyone else? Is this due to vapour too?
http://pocketprogressive.org Uncle Geo

…and walk across hot coals.
relawson

I’ve seen this myself with plain water on a VERY VERY hot pan. Dinner was about 10 mins late that night as I tried to see how many drops I could get to bounce around before they eventually evaporated completely.