SAC and Gas Consumed Calculation

Linus Torvalds torvalds at
Tue Feb 11 09:48:54 UTC 2014

On Tue, Feb 11, 2014 at 9:36 AM, Linus Torvalds
<torvalds at> wrote:
> where the amount of air is *not* just "tank size times pressure in
> bar". It's a combination of: "take compressibility into account"
> (which is a fairly small issue under 220 bar - you'll see more
> differences when you do high-pressure tanks with 300bar) and "convert
> bar to atm" (which is the majority of your discrepancy).

Actually, I did the math wrong when I double-checked the numbers
(blush), and the tank compressibility is the bigger part.

 - "ideal gas, bar=atm": 1464 liters
 - "ideal gas, atm correction": 1445 liters
 - "gas compressibility and atm correction": 1367 liters

At 220 bar, the incompressibility of gas means that it actually only
has compressed as much as you'd expect an ideal gas at ~213 bar, so
that's actually much more noticeable factor than the 1.013 factor from
atmospheric pressure in bar.


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