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Jon Elson[_3_]

wrote:

Just curious, I'm not transferring any gases. I was just watching the
guy fill our propane cylinder and it got me to wondering.
Here's the first situation: Let's say I have two gas cylinders of
equal size. One is filled with a gas that is liquid at room
temperature when compressed, the other is empty. The cylinders are
upright. Now the cylinders are connected with a pipe so that the gas
from the full one flows into the empty one. As the gas starts to fill
the empty cylinder it cools enough that it liquifies and rains into
the cylinder. But once the pressure equalizes the rain stops and the
end result is that both cylinders are at the same pressure but that
the originally full cylinder will have more liquid in it.
There are commerically-available cylinder heaters to empty one cylinder into
another. works with anything that is partially liquid at room temperature
and elevated pressure. You have to weigh the cylinder that is being filled
to make sure it is not OVERfilled.

Jon