I’ve got some CO₂ cartridges intended for inflating bicycle tyres; to attach them to the bicycle valve I use a right-angled adapter with a built-in spring valve; when it’s all attached, the sprung part is depressed, releasing the gas and inflating the tyre. The setup, without the wheel, looks a little like this:

When I use it to inflate a tyre, the CO₂ cylinder gets very cold – water condenses and then freezes on it. This is expected, and is due to adiabatic cooling:as the gas expands, it extracts heat from around it. The metal adapter also freezes, though. While there is some expansion in the adapter, I’d have expected the friction of the gas to heat it more than it’s being cooled, but it seems to get colder than the cylinder (subjectively – I haven’t measured it.)

Why does the adapter cool so much?

bump.

what is the cylinder made from?
what is the adaptor made from?
maybe the thermal properties are different if they are different metals.
can’t see friction from the gas making much heat.

My guess: The major expansion occurs at and after the bicycle valve, so the expansion drags heat from the air through the metal of the adapter. (The valve-stem being rubber and a good insulator.)

I suspect it is in the subjective bit. The adapter has a much larger surface area, and will therefore feel colder to touch.

sibeen said:

I suspect it is in the subjective bit. The adapter has a much larger surface area, and will therefore feel colder to touch.

Pretty sure MV has a point with the greater point of expansion. The widest point in the nozzle is where the expansion pressure has to equilibrate.

Boris said:

bump.

what is the cylinder made from?
what is the adaptor made from?
maybe the thermal properties are different if they are different metals.
can’t see friction from the gas making much heat.

The adapter is made of aluminium, but I don’t know what the cylinder’s made of. It sounds like a steel. I’ve just had a close look at one, but there’s no indication of what it’s made of.

sibeen said:

I suspect it is in the subjective bit. The adapter has a much larger surface area, and will therefore feel colder to touch.

No, the adapter has a much smaller surface area. It may well be in the subjective bit, though.

btm said:

sibeen said:

I suspect it is in the subjective bit. The adapter has a much larger surface area, and will therefore feel colder to touch.

No, the adapter has a much smaller surface area. It may well be in the subjective bit, though.

Ahh, sorry, I thought the adapter was only the bit that pointed south west. I’d still claim subjective :)

the right angle deflection is another bit.

btm said:

Boris said:

bump.

what is the cylinder made from?
what is the adaptor made from?
maybe the thermal properties are different if they are different metals.
can’t see friction from the gas making much heat.

The adapter is made of aluminium, but I don’t know what the cylinder’s made of. It sounds like a steel. I’ve just had a close look at one, but there’s no indication of what it’s made of.

Brief update: the cylinder is ferromagnetic.