Why do highly pressurized cans/gas cylinders ( like eg. lighter gas, propane cylinders etc) go cold when the pressure is released?
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It’s a [basic (physics) law of gases](https://en.wikipedia.org/wiki/Ideal_gas_law) that pressure, volume, and temperature are related. P * V / T = constant.
It’s because [when you look at atoms and molecules of a gas](https://www.youtube.com/watch?v=WhP6zJbSxec), you can think of them as a bunch of tennis balls bouncing around wildly. The pressure is the force they apply as they bounce off the walls of the can, the volume is the space they bounce in, and the temperature is the energy with which they bounce.
In any case, a pressurized cylinder has a fixed volume, the gas can’t inflate it like a balloon. So the relationship above, P * V / T = constant, becomes P * constant / T = constant, or P / T = constant. You decrease the pressure (by letting gas out), and the temperature decreases so that the ratio P / T stays constant.
The medium is under pressure and in liquid state while inside the vessel, but would normally be in a gaseous state at room temperature and atmospheric pressure.
Releasing the gas allows for a change in state from liquid to gas. The state change process absorbs heat from the surrounding area, thus creating a cooling effect.
This principal is exploited in the refrigeration process and is essentially how air reconditioning and refrigerators work.
Because they’re stored in a liquefied state under pressure in the can. When they get released, they’re rapidly turning back into a gas and they pull the energy to do so from the environment.
Just like how you need to apply heat (i.e. energy) to water to make it boil, the liquid to gas transition needs heat, and the surrounding environment is the source for it
When you release gas from the cannister, the residual gas expand to fill the volume, doing so the molucules of gas slow down a little bit. And since the speed (/kinetic energy) of the molecules is perceived as heat, the gas is getting colder.
All good answers so far, but let’s see if I can ELI5:
Things are hot because the tiny parts of them called atoms are moving fast. Some atoms are moving fast, some slow. Inside a pressure can atoms are crammed in there very tightly and want to spread out, but they can’t.
When you open a pressure can, the atoms are pushed out by thier neighbors. The faster ones are able to leave faster and more often, leaving the slow ones behind. This means the slow ones are the cold ones…
This is why opening a pressure container colds or down.
The other explains (energy pet volume drop etc) are also correct, but are either another way to say it more analytically, or use a bit of abstraction (like energy).
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