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Thread: Volume Of O2 =what Volume Of Co2

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    RBW Member MADDOG is an unknown quantity at this point MADDOG's Avatar
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    Volume Of O2 =what Volume Of Co2

    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

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    Re: Volume Of O2 =what Volume Of Co2

    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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    Megalodon

    Re: Volume Of O2 =what Volume Of Co2

    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.

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    Re: Volume Of O2 =what Volume Of Co2

    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.

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    Re: Volume Of O2 =what Volume Of Co2

    Quote Originally Posted by Abbo  View Original Post
    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.
    mmmmhhhhh....

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

    regards
    paul
    www.rEvo-rebreathers.com
    ...."Yes you have to pre-breathe to activate the scrubber sorb, anyone who says different doesn't know what they are talking about!"...
    .... to get more accurate CO2 injection in the breathing machine we put 2 mass flow controllers in series ...
    .... The noise is a few tens of nano-volts, so DL were able to reduce the output voltage ...
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    Re: Volume Of O2 =what Volume Of Co2

    Quote Originally Posted by paulraymaekers  View Original Post
    mmmmhhhhh....

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

    regards
    paul
    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...

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    Re: Volume Of O2 =what Volume Of Co2

    Quote Originally Posted by Abbo  View Original Post
    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...
    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

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    Re: Volume Of O2 =what Volume Of Co2

    No idea about the chemistry involved but all references (including rb 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 RBW 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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    Re: Volume Of O2 =what Volume Of Co2

    Quote Originally Posted by tibby  View Original Post
    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
    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

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    Re: Volume Of O2 =what Volume Of Co2

    Quote Originally Posted by tibby  View Original Post
    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.
    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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