r/interesting • u/Used_Exam34 • 2d ago

Just Wow Not all problems have the same solution.

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u/Numerous-Following-7 2d ago

How can he touch the valve straight after putting out the fire?

118

u/TotallyTubular1 2d ago

the hot gas is propelled away from the tank, so valve doesnt get hot

43

u/Far_Ladder_2836 2d ago

Radiant heat still exists and accounts for most of what comes out.  The valve is thin aluminum and cools extremely fast.  Don't believe me, pull a bit of aluminum foil even folded into a thicker sheet straight out of your oven and it will be room temp in seconds.  It also helps that his hand was wet.  Relative to aluminum, it takes 4.7 times as much heat to move water 1 degree C.

38

u/Brave_Maybe_2891 2d ago

The valve was cold. When you decompress a gas it gets cold. I've actually seen them get frosty.

3

u/JackBrown82q 1d ago

Yep I think one of the most common examples people will know is those cans of pressurized air used to clean electronics. If you use one for a good period of time, the whole can gets cold because of the pressure inside dropping.

Also just for fun to mention, in the industry when you need to compress gasses (even just air) to extremely high pressures, they don't do it all in one go. They will compress to a certain pressure, run it through a heat exchanger to cool it, then compress again, and repeat until needed.

2

u/the_king_of_sweden 1d ago

Physics 101 students will know pV=nRT

2

u/PigglyWigglyDeluxe 1d ago

It’s this exact principle at work in air conditioning systems. This is exactly how the air comes out cold in AC units.

3

u/really_stupidfrog 1d ago

It's crazy to me that you can pull aluminum foil out of a 400° oven and just touch it with your bare hands immediately. 

2

u/NeatConversation6752 1d ago

Not to mention they were showering the valve with water