Rebreather World - View Single Post - Rate of PO2 drop changes with depth true/false

Sutty · 25th December 2006, 08:46

Could a moderator please split this off to a new thread eg from post 126 - entitled something like "rate of PO2 drop changes with depth true/false".

It all goes back to the definition of PO2 - "the pressure that would be applied by the gas under consideration were it to occupy the volume alone", this means that to produce the same PO2 in the same volume requires the same number of molecules of the gas irrespective of absolute pressure. The "extra" pressure in our case is made up by more diluent molecules.

Quote:

So we now have 5 times the moles of gas in the loop, although the volume is the same. That is, we have 10 liters of O2 (at STP) in the loop and 40 liters (at STP) of diluent. Since the gas is at 5 ATA it occupies 10 liters, not the 50 it would occupy on the surface.

I think where Genesis is going wrong here is that this assumes that the FO2 has not dropped as we descend - yes we do have 5 times the moles of gas, but a higher proportion is diluent if we maintain the same PO2.

Neil

25th December 2006, 08:46	#10 (permalink)
Sutty Classic Kiss diver Current Rebreather/s: Classic Kiss Other Rebreather/s: Join Date: Jun 2005 Location: Glossop, Derbyshire, UK Posts: 801	Re: why do we do it? Could a moderator please split this off to a new thread eg from post 126 - entitled something like "rate of PO2 drop changes with depth true/false". It all goes back to the definition of PO2 - "the pressure that would be applied by the gas under consideration were it to occupy the volume alone", this means that to produce the same PO2 in the same volume requires the same number of molecules of the gas irrespective of absolute pressure. The "extra" pressure in our case is made up by more diluent molecules. Quote: So we now have 5 times the moles of gas in the loop, although the volume is the same. That is, we have 10 liters of O2 (at STP) in the loop and 40 liters (at STP) of diluent. Since the gas is at 5 ATA it occupies 10 liters, not the 50 it would occupy on the surface. I think where Genesis is going wrong here is that this assumes that the FO2 has not dropped as we descend - yes we do have 5 times the moles of gas, but a higher proportion is diluent if we maintain the same PO2. Neil __________________ Never forget that life is a finite resource.
(Offline)