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Lazz45 t1_j3ljpxo wrote

For all things not including (Hydrogen, Neon, and helium) they usually will not cool down when compressed. That's not how pressure and temperature are related for most substances.

A perfect example is the ideal gas law PV=nRT

Where:

P= pressure of the observed system

T= temperature of observed system

As you can see, Pressure becomes divided by Temperature or vice versa (depending on what you're solving for), which means they are directly proportional (instead of inversely proportional, where if pressure went up, the temperature would drop)

Now, I can go more into detail as to WHY this physically happens (hint, temperature is a measure of energy in a system, as you compress a system things, they bump more, create more friction, etc.) but I did not want to just unload a ton of info if you didn't need it to answer what you are actually asking

Edit: accounted for the Joule Thompson effect as described below in comments

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SamQuan236 t1_j3mwlrk wrote

Anything with a negative jt coefficient will get colder when compressed, eg nitrogen and hydrogen over their relevant temperature ranges.

http://en.wikipedia.org/wiki/Joule-Thomson_coefficient

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Lazz45 t1_j3n5wos wrote

This genuinely never came up in school even once, and I'm a chemical engineer! Very interesting concept, thank you! I'll edit my reply

It appears it would be useful for refrigeration or leak finding when combined with thermal imaging. Microleaks are extremely hard to detect even with leak detectors

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