Greetings fellow nerds.
Back in July of 2009 I stuck my hand into liquid nitrogen to demonstrate the Leidenfrost effect.
Now that I have a better camera I thought I’d do it again.
I have here a standard laboratory heater plate
and I'm going to put some water on it and turn on the heat.
As expected, it's going to boil.
Now when it gets really hot, an interesting effect takes over.
Water now just beads up and rolls off the plate.
What's happening is that on contact the water vaporizes so fast
that it creates a cushion of steam that lifts up the remaining water drop.
So the water is now riding around on a cushion of it's own steam.
This makes the water last longer and slows down the heat conduction
needed to completely vaporize it
This is called the Leidenfrost effect.
This effect can be seen at home with a frying pan if you heat it high enough.
Let me adjust the camera here, you can clearly see the water is beading up.
Now I’m holding a drop with my pipette and as you can see
it can't wet the surface even though I’m dragging it around.
The extreme heat of the hotplate continuously vaporizes enough water
to create a gas barrier between the two.
The Leidenfrost effect also occurs with liquid nitrogen.
As you can see here the liquid nitrogen skirts away as I pour it on the floor,
without actually soaking into the floor.
Liquid nitrogen boils at -196 Celsius.
And this laboratory floor is room temperature.
So from the liquid nitrogen's perspective the floor is super hot.
Here are some drops of liquid nitrogen rolling around on the floor
just like the water on the hot plate.
The Leidenfrost effect protects the liquid nitrogen from being instantly vaporized,
and consequently the floor from being instantly frozen.
Now the Leidenfrost effect does not last forever.
With enough liquid nitrogen the floor is eventually cooled enough
that the temperature difference no longer supports the effect
and the liquid nitrogen soaks in.
So if I do put it on my hand I can only do so for a moment.
Nonetheless, the Leidenfrost effect will protect my hand from being instantly frozen.
Now this works great for a single drop, but what about a whole hand?
Well there is only one way to find out.
I got here a steel Dewar flask and here is the liquid nitrogen.
It's boiling since the Dewar was at room temperature
and thus extremely hot to the liquid nitrogen.
It'll settle once it cools.
Ok here we are, time for me to prove my scientific reasoning.
Even though I’ve done this before I still get nervous.
Ok...Ready...3...2...1...
Oh yeah, that's cold... that's REALLY cold... but I still got all my fingers and my hand is perfectly fine.
Feels like ice though.
Nonetheless I’m going to try the experiment again, but this time in slow motion.
We can see the liquid nitrogen boiling around the hand
and creating the gas barrier that's slowing down the thermal transfer.
The liquid nitrogen isn't wetting my hand.
As you can see my hand appears to be super hot
as the liquid nitrogen instantly boils off of it.
For a better view we're going to use this clear Dewar.
Now my hand is slightly too large for this Dewar,
while I could probably get it in if I scrunched my fingers
I don't want to risk getting stuck in there.
So I'm going to get Argentia to do this.
Here she goes, 3..2..1...
You can clearly see the liquid nitrogen boiling off her hand
and forming the gas barrier that's protecting her from being frostbitten.
From this angle it looks like a force field
is preventing the liquid nitrogen from touching her.
Once again, do not try this yourself.
And there you go, that was liquid nitrogen and the Leidenfrost effect.
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Here are few extra takes we filmed while trying to make this video.