# Compressed air hot or cold?

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I believe compressed air should be colder. Like when you have an air duster can. Or even a car’s turbocharger which compressed air and cools it right? But also, when there is pressure on air parcels doesnt that pressure increase its heat? At the bottom of a valley, the atmospheric pressure is higher so the air that falls to the bottom of the valley is more compressed and hot. It seems to me like compressed air is both hot and cold then? Could someone explain please? 😅

In: Physics

Are will heat when it’s compressed. What’s happening with an air duster is the opposite. When they put it in the can, it would have been warmer. Now, when you use it, you’re lowering pressure and therefore cooling the contents.

The act of compression inherently will heat the gas involved However, objects tend towards thermal equilibrium with each other, so the warm compressed air will gradually cool to the ambient pressure without losing much pressure.

Similarly, the act of expansion will inherently cool the gas.

>Or even a car’s turbocharger which compressed air and cools it right?

The turbocharger compresses and heats the air; you typically install an intercooler immediately after the turbocharger to remove heat from the compressed air before it goes into the engine.

Part of your understanding issue is a problem of scale.

A can of compressed air has 47 psi (on average)

Air at sea level is 14.7 psi.
Air at one mile above sea level is 12 psi.
Air pressure doesn’t really change enough to impact temperature moving from a valley to a hill. That’s mostly wind and sun exposure that does that.

Canned air gets cold because of the energy of its heat. Inside the can it’s not any colder then the room it’s in. But as it’s sprayed that air expands quickly and fills up a big space. The heat energy that makes the can room temperature is now spread out over a huge area. Temperature is a measure of energy / area. Increase the area and temperature goes down.