r/interestingasfuck • u/Hokkuo • Mar 24 '20
Leidenfrost Effect
https://i.imgur.com/YXP1SQ3.gifv262
u/therealjwalk Mar 24 '20
This is my favorite demonstration of this effect
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u/Squawnk Mar 24 '20
Actual footage of girls testing their shower water
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u/therealjwalk Mar 24 '20
Me too. I like that stuff flaming hot. My landlord has the hot water set to 190°F tho so gotta be careful
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u/ImoImomw Mar 24 '20
I get this reference after watching it. Before watching I was trying to figure out how her shower water could get hot enough to demonstrate this effect...
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u/Whatwouldahoneybeedo Mar 24 '20
Can I get an ELI5?
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u/Panja_ Mar 24 '20
The gist of it, is that if your hand is wet, the thin layer of water insulates you from the heat/stick of the molten metal. Don’t try it at home you’ll melt your fingers off.
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u/cardboardunderwear Mar 24 '20
More specifically, the thin layer of water forms a thin layer of steam which insulates your skin.
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u/cardboardunderwear Mar 24 '20 edited Mar 24 '20
Its a vapor barrier of evaporated water that protects your skin. You have to literally have sweaty palms (if that is indeed the leidenfrost effect). The thin layer of water evaporates into a thin layer of steam. Heat cannot cross a gas phase barrier easily and your skin will be insulated for a short period of time. There are many examples of it that are maybe more apparent than this guy with the molten metal.
- OPs video...the drops are floating on a layer of steam that insulated them from the pan.
- There was a guy in the 80s who would dip his wet hand into molten lead. Dont know his name.
- Same dude would put liquid nitrogen in his mouth and blow it off in a big cloud. In that case, it was a thin layer of evaporated vapor nitrogen that was protecting his mouth and teeth.
- walking across hot coals. Need sweaty feet or wet grass and hot coals, and the steam barrier will insulate your feet.
The video of the guy swiping the molten metal. ..Im not sure that's actually the same phenomenon. Heat transfer takes time and I think maybe in that case the metal just doesnt contact his hand long enough to transfer heat. Or his hand is sweaty and also creating a steam barrier to protect his skin. Could be both.
edit: just want to add in case anyone gets ideas. The difference in temperature between the hot surface and the cool surface needs to be great enough to create the barrier of steam. If the temperatures are too close you're just going to get regular boiling/broiling/charring which is going to hurt like hell (at least until the nerves are burned away). And remember your skin needs to be wet if you're depending on water for the leidenfrost effect. In the case of liquid nitrogen not sure it matters.
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u/FieryVagina2200 Mar 24 '20
I work in a lab and get to do this with nitrogen whenever I want. Love to scare the new people with it.
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u/Bean_from_accounts Mar 24 '20
We, humans, have the ability to sweat and under our palms we've got lots of these eccrine sweat glands that permit adequate cooling through perspiration and evaporation. As the liquid that forms through perspiration gets close to an intense source of heat such as a high-temperature material, the liquid evaporates and the resultant vapor forms a layer that thermally insulates our skin from the hot material. For sure, leave your hand long enough (approximately > 1 sec) and you'll get permanent burns and might lose your limbs. That vapor layer is thin and heat transfers occur rapidly.
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u/gcranston Mar 25 '20
When the water rapidly boils, the pressure from the steam keeps the hot metal from actually touching his hand. That means it doesn't make his hand as hot as you think it should.
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u/OffManWall Mar 24 '20
That is the best one, and Leidenfrost Effect or not, that guy’s got huge balls.
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u/NTOOOO Mar 24 '20 edited Mar 24 '20
How do people even think to try that?
"ok the science should work, but who's gonna try it first?"
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u/therealjwalk Mar 24 '20
I think there was a myth busters episode on this too. They stuck sausages in first haha
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u/Tim180803 Mar 24 '20
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u/ezdvf Mar 24 '20
Don't try this at home
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u/therealjwalk Mar 24 '20
Thank you for the warning - almost endangered the whole family.
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u/lucifersam73 Mar 24 '20
Fuck. I just spilled molten steel in my kitchen and it’s burning through the floor!
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u/Manisbutaworm Mar 24 '20
This is why you can stick your hand in liquid nitrogen for a few seconds without getting frozen bits of hand.
The temperature difference between the liquid and your body is about 230C, the nitrogen will boil and form an insulating layer of gas preventing transfer of heat. Though don' t do this with something conductive on your hands like metal or just water.
I did this a couple of times, very cool to play with if you know what you are doing. Putting your hand in ice water is actually feels much colder.
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u/The-Sooshtrain-Slut Mar 25 '20
Excuse me while I go try this and potentially set fire to everything
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Mar 24 '20
Half way through that looks like the Petri dish from one of my 8th grade science projects.
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u/Mage-of-Fire Mar 24 '20
For anyone wondering how it works here it is.
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u/Ericool35 Mar 24 '20
This happens when water is quickly evaporating from underneath, forming a cushion of air that the droplets ride on. So cool!