In Reply to: Overall volume & heat posted by Ken Kurtis on February 23, 2007 at 14:24:40:

There are two aspects to consider here.

The air that is already in his tank, say at 1000 psi, will be pressurized up, and heat up accordingly.

However, the air that is coming into his tank is coming in from a higher pressure. That air will be 'expanding' from its previous pressure and will reduce temperature accordingly. Also, if 2000 psi is added to the tank, there will be twice as much air 'getting cooler' as there is air 'getting warmer'.

However, the air getting warmer is going from 1000 psi to 3000 psi, while the air getting colder may be going from 4000 psi to 3000 psi, so there is twice as much 'heating' as 'cooling'.

We assume that both the air already in the tank and the air in the 'bank' are starting at room temperature.

In the balance, whether the tank that is getting filled gets warmer or cooler in the end really depends on the specific pressures and amount of air involved. Assuming adiabatic filling it is easy to calculate, I just don't have the numbers available.

So it is easily possible to the tank to heat up, cool down, or remain unchanged. It's all in the numbers.