The Leidenfrost Effect

Aaron Keller, Chemistry Teacher, talks about and demonstrates the Leidenfrost effect using both liquid nitrogen and water. The Leidenfrost effect occurs when a liquid comes in contact with a surface much hotter than its boiling point. A layer of evaporated (gaseous) vapor forms between the liquid and the hot surface, preventing further rapid boiling. The gas transports heat less efficiently than the liquid and if the liquid is in the form of drops, then the drops last much longer than intuition would lead you to believe.

Category:

Education

Tags:

• liquid
• gas
• leidenfrost
• effect
• boiling
• boil
• vapor
• evaporate
• nitrogen
• water

[blinknbcr]

Love your videos, but I have two questions for you. #1, what would happen if you left your hand in liquid nitrogen for a long period of time? Would it become brittle and really be able to be shattered? 2nd, what would happen if you poured liquid nitrogen on that heater that you poured water onto? Would the properties change vastly?

[aaronakeller]

I read on The Straight Dope (a great site) that you probably couldn't shatter frozen tissue. You could definitely get a bad case of gangrene after freezing a hand in liquid nitrogen, though.

[aaronakeller]

If you pour liquid nitrogen on a hot surface like the heater it might just vaporize without exhibiting the Leidenfrost effect. That's just a guess based on some reading I have done about how water behaves. When the surface is too hot, no Leidenfrost.

[cwr9394]

i had know a teacher that would gargle liquid nitrogen, i guess this is how. but one time he accidently swallowed some and had to have surgery because he burnt himself

[aaronakeller]

Gargling liquid nitrogen is foolhardy and asking for trouble. I read about someone who did it frequently as part of a demonstration...at least until he cracked a number of his teeth because of the low temperature and ended up with a huge dental bill. I also heard about someone blowing a hole in their stomach because of the explosive power of rapidly boiling liquid nitrogen. Scary stuff.

[ktulu6]

i used to spray water on my mom's iron just for fun when i was a kid :P

[MrJeansy95]

@blinknbcr if your poured liquid nitrogen on a hot plate it would vaporize without the leidenfrost effect but if you pour it on the floor it will exibit a bit of the leiden frost effect for a small amount of time because the floor is boiling to the nitrogen

[InDepth24]

@aleo897 that wasn't a skin, it was heart. Just a muscle, without any skin on it

[aleo897]

@blinkbcr i think you actually CAN shatter skin. at least according to NurdRanges demonstration on youtube you can. watch his video.

[Dullahan2132]

i thought i wus teh only one that did that