| Original Message |
upriver
Posted Aug 30, 2012 9:21 AM
in a compressed air system P1V1 = P2V2 I don't know what your ^.71 is for.
PV can is energy, when you cancel the units you end up with in-lbs which can be converted into joules, BTUs or whatever
PV (or stored energy) for the Scuba tank and HPA tank =
(pressure scuba tank * volume of scuba tank) + (Pressure HPA + Volume HPA)
you keep the PV for the scuba and the PV for the HPA separate because they are not joined together yet to form one air system. This accounts for the pressure (energy) left in the HPA tank before the refill.
when you hook the two tanks together and open the value you get:
PV = unknown pressure * (volume of scuba tank + volume of HPA tank)
knowing that PV = PV (and ignoring heat issues)
so the new pressure = ((Pscuba * Vscuba) + (Phpa * Vhpa)) /(Vscuba + Vhpa)
when this was discussed back in 2004 or so I put together this spreadsheet.
this assumes a 68 cuin HPA tank and that a scuba tank is 650 cuin
and the HPA tank is refilled once it reachs 1000 psi.
and ignores the loss from heat and the volume of air lost when disconnecting
Scuba HPA Final
psi psi psi
3000 0 2716
2716 1000 2553
2553 1000 2406
2406 1000 2273
2273 1000 2153
2153 1000 2043
2043 1000 1945
1945 1000 1855
1855 1000 1774
1774 1000 1701
1701 1000 1634
1634 1000 1574
1574 1000 1520
1520 1000 1471
If I am wrong with this please let me know as I'll need to recalibrate my brain.
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