"mike regish" wrote in message
. ..
The expansion only lasts until the tank is full to ambient pressure-a very
short time. Then it is all compression.

One mistake that some people make with the equations is not working with
temperature in degrees Kelvin... I always figured that it was a closed
system... If when you let gas out of a container the container gets cooler,
then whatever you are putting the gas into must get warmer... Work was done
with the initial compression of the gas into the tank and as such, the tank
heated up... Leave it alone long enough for the temperature to reach
equilibrium with the outside air and then let it out of the tank and you
will notice a definite drop in the temperature of the tank... For
conservation of energy to be maintained, it has to go someplace... If you
take the surrounding room out of the equation via insulation or whatever and
have one tank decanting into another tank, the only two heat sources that
you have to work with are the tanks... You can't gain energy in this system,
so if heat is being removed from one tank, it has to be added to the other
tank...