On Sun, 25 Aug 2002, Russell McMahon wrote:

>> Ok, I found a formula for the power in compressed air.
>> Pair [W] = Qv [m^3/sec] * Press [kgf/m^2]
>> 300bar is ~3x10^6 kgf/m^2
>
>Your calculations are probably approximately correct BUT they rely on a
>statement by the manufacturer that was accidentally misleading AND there is
>a need to alter your formula to account for the practical situation.
>
>Firstly, the stated tank volume of 90 m^3 was (probably) intended as the
>volume of gas at ambient after expansion (or before compression). The real
>tank volume is less than a cubic metre. (Note the size of the car itself is
>probably in the order of 5 cubic metres. They correct this error somewhere
>on their site (in the FAQ?). For the E=QP formula to apply the pressure used
>must be maintained throughout the "work stroke" represented here by the
>Volume. (You use m^3/sec which is the instantaneous power but if you take
>total volume and remove the time term you get total available energy).

I know, I deliberately tried to calculate for the max. available energy,
with some shortcuts.

I missed the car volume (5m^3) vs tank volume (90m^3). The messages about
gas bags on top of cars suddenly make sense ;-)

Peter

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