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Rapid decompression cooling? Answered

Is a possible way to super cool a gas (nitrogen or oxygen) to liquid temperatures by using a sub-zero tank of 5000 psi compressed air to blast that gas over a radiator and therefore cool the gas in the radiator to a liquid, then quickly pump it to a chilled high pressure insulated tank.



Best Answer 7 years ago

Like an AC, the cooling occurs at the expansion valve, wherever you put it.
After that expansion, the expanded gas mixes and sucks ambient air through
the radiator.
Releasing a 5000 psi or 3000 psi dive tank cools the valve enough to
capture and freeze moisture in the air as frost.

Liquid air is made by compressing air through cooling coils to 3000 psi
then letting it escape and cool in expansion also used to cool further
compression. Eventually the air cannot expand further it has become a liquid.

Because Oxygen boils at 90K and Nitrogen boils at 77K it can be boiled
out of liquid air, leaving a concentrated liquid oxygen as the result.


It won't get anywhere near cold enough.
You could blast it with carbon dioxide, but you'd still be way too hot.
Also, if your formally-compressed air was that cold it would be liquid anyway.


No it wouldn't, it takes a little below freezng to condence oxygen I am pretty sure.

Oxygen boils at 183oC below freezing (or 3000 F below) - where did you get "a little below"?


It was a sarcastic remark, you said that the air in the tank would be a liquid anyway, and it wouldn't just because it is stored at high pressure and cooled as much as you can in your average freezer doesn't mean it would be a liquid.

I said "if your formally-compressed air was that cold it would be liquid anyway."
-Meaning the gas you imagine blasting over a radiator to cool the gas in the radiator to a liquid.


Yes, I know thats what you meant, but it actually isn't a liquid

That is the point: not cold enough.


Liquid air and othe gasses removed from the air by liquidation are indeed produced by compressing the gas and rapidly releasing it to cool the gas stream.

Not a new process BUT very hard to do at home.



Reportedly, it isn't all _that_ hard to build a system of that sort which will condense liquid nitrogen out of the air. Though since LN2 was less expensive per quart than milk last time I checked, it may not be worth the effort.

Depends on your skill lever and what you define as "difficult" :-)

I guess anyone who hasn't done some basic research is going to lack the necessary skill and equipment.

... and it probably requires either having a lathe or having money or both.


7 years ago

You can use a stack of peltier coolers for a lot less trouble.

Peltier cells chill out around -50C, for any remotely practical levels of pumping