Volume Of O2 =what Volume Of Co2

MADDOG

I Am Thinking About The Volume Of Co2 Produced By A Given Volume Of O2 What Is The Relatinship Is The One
Like On The Tests They Do On Scrubbers Etc They Run At 1.5l Of Co2
Per Min How Much O2 Is Needed To Produce 1.5 L Of Co2 My Thinking Is Know Aproximatly How Much O2 I Use Some Waitage On Ascent
But 110l Does Me About 90 Mins
Because When I Was At School I Remember The Bell Jar Experiment
Where The Water Rise Up Inside The Jar When The O2 Is Used Up
Does That Mean All The Co2 Disoves In The Water Where Does It Go

nigelh

Well if we just add carbon to the equation we go from n mols of O2 to n mols of CO2 (since mols is virtually a head count of molecules) so the volume should be the same using the ideal gas law (PV=nRT).

The trick with the 'candle in a jar' experiments is that most of the product is H2O, which condenses out, while the most of the carbon deposits as soot.

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nigelh

Abbo

The ratio of the carbon dioxide produced to the oxygen metabolised is called the respiratory quotient. It's around 0.7 for fats, 1 for carbohydrates and as high as 4 for oxalic acid.
For glucose
C6(H2O)6 + 6O2 -> 6CO2 + 6 H2O
The ratio is 1:1 between O2 and CO2.
However, for a fat
C16 H32 O2 + 23 O2 -> 16 CO2 + 16 H2O
the ratio is 16/23, which is around 0.7.

It all depends on what you had for lunch.

Abbo

I'm not a chemist, but I would presume the answer to your bell jar question is that the candle is made of paraffin wax:
C25 H52 + 51 O2 -> 25 CO2 + 52 H2O
So the ratio is 25 CO2/ 51 O2
The water vapour condenses, so the volume of gas decreases.
It was never explained like that to me at school, though.
Interesting question.

paulraymaekers

mmmmhhhhh....

then why in the CE 14143 it is assumed to be 0.9 ?

regards
paul

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.... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...

Abbo

Because paraffin wax is relatively rare as a diver's meal?

Carbohydrate has a respiratory quotient of 1 and fat of 0.7. Perhaps the typical diver's meal averages out at 0.9? Taking into consideration the methane...

jkaterenchuk

I would suspect it also has something to do with the body getting its energy from aerobic or anaerobic activity. I suspect its very difficult for a diver to be at a high enough level of activity for a long enough time to switch over from burning carbohydrates for energy to burning fats. As a general rule in long distance running it takes roughly 30 minutes of fairly high intensity running for the body to make the switch. I am not an expert on this subject just my guess.

John

tibby

No idea about the chemistry involved but all references (including Rebreather manuals) I've read state that 1l of O2 produces ~0.9l of CO2.

I think there are even references about the CO2 absorbtion capacity of the different sorb brands out there so you can calculate scrubber duration based on O2 consumption. I assume this is why you asked this question to begin with.

I remember reading a post by Joe Radomski here on Rebreather World showing such a calculation. The only thing that puzzled me was that he used the entire weight/volume of the scrubber as part of the equation and I would think that a scrubber would reach breakthrough quite some time before using the entire sorb in the can. Of course I'm a newby and Joe is very experienced (he wrote the manual I learned from) so take my assumption with a grain of salt.

Cheers,
Tibby

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MADDOG

thanks thats what i what i was wondering just to as instead of sac we can not use this imformation to extend scrubber life but as a referance to our own co2 prduction in different conditions and to compare with official tests based
on 1.5l of co2 per min as to safty factor in % of life

nigelh

I think you'll find modern scrubbers are very good. We speak of a 'cone' of usage but the manufacturers have used insulation and such to make sure it is a very flat cone so most of the material is used.

The only caveat to that is the deeper you go the 'thicker' the reaction front
so being deep and hitting the limit is bad for your health. Run it down shallow if you have too.

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nigelh