To my understanding when a gas is rapidly expanding it cools and when it is rapidly compressed it heats up. So how come when you fill up a canister with helium/nitrogen/propane, etc. the canister is cold even though you’re compressing the gas into it?
In: Physics
If you are using a compressor to fill the tank then the compressor will heat up and the tank become cool according to the differential in pressure between the compressors input pressure and the pressure inside the tank. If you are filling the tank from a larger tank, the same will occur with the nozel on the larger tank seeing the heating. Once equilibrium is reached, or you shut off the flow at the max pressure rating of the tank, the heating and cooling will cease also. If you think about it, a compressor is taking a large volume of air, and pressurising it down a pipe into a chamber where it expands. This has a max throughput of the max pressure inside the pipe from the compressor (otherwise the flow would be reversed from the tank back into the compressor). Once you realise where the compression and expansion might be, you can figure out what components will get hot, and which will cool.
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