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Which is heavier CO2 or O2?


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#1 abaca

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Posted 31 August 2006 - 06:42 AM

In an automated air exchange system; should the fresh air be pumped into the top or bottom of the chamber?

#2 Hippie3

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Posted 31 August 2006 - 07:55 AM

doesn't matter much but pump it in the bottom so it'll displace old stagnant air

#3 mason420

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Posted 31 August 2006 - 12:25 PM

For the record, CO2 is heaver.

O2 has an atomic weight of 31.9988
CO2 has an atomic weight of 44.0095 (the weight of O2 + C)

#4 Cryingblackoil

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Posted 01 September 2006 - 08:29 AM

Quite a bit heavier. You can pour it slowly into a jar and it will stay there a long time until it gradually mixes with the air.....you look like kinda a retard pouring nothing though :lol:

#5 Hippie3

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Posted 01 September 2006 - 08:49 AM

doesn't matter which molecule is heavier,
air does not layer out like that
else we would all suffocate here on the earth's surface
under a layer of CO2 several meters thick.
heat causes convection which mixes the gases of our atmosphere and in our terrariums, etc.
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#6 mason420

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Posted 01 September 2006 - 10:11 AM

doesn't matter which molecule is heavier,
air does not layer out like that
else we would all suffocate here on the earth's surface
under a layer of CO2 several meters thick.
heat causes convection which mixes the gases of our atmosphere and in our terrariums, etc.

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The question was which was heavier.

As to convection, in the atmosphere there is certainly a lot of convection (just one of many many factors that stir the air), however, depending on the design of the terrarium (the location of the heat source, the amount of thermal energy, and the differential temperature range) there may or may not be any significant convection going on at all. In a closed container, such as a rubbermaid, at a uniform temperature, the heavier molecules will, in fact, settle to the bottom.

#7 Hippie3

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Posted 01 September 2006 - 10:21 AM

there is still heat
coming in thru the walls, floor and lid
if there are cakes/casings in it
there will also be heat emanating from them
even small amounts of heat like that are plenty to drive convection,
as we see even in the coldest winter.

further
the real question he asked was

should the fresh air be pumped into the top or bottom of the chamber?

and he thought perhaps molecular weight affected that
but it does not.
the air at the bottom of the tank is not much different than higher up,
there's still O2 intermixed there,
as simply lighting a match would easily prove.

the entire content of the terrarium, not just the bottom,
needs to be flushed out
as the O2 is gradually converted into CO2 by the respiration of the fungi.

the primary problem is not settling out but instead
oxygen depletion.
the free O2 is being chemically locked up, making it unavailable.
it's not being displaced by heavier CO2.

if layering/settling was really the problem
just stirring the air would suffice,
one could even seal it up, never letting in fresh air in at all.

but that is not the case,
fresh oxygen-rich air must be brought into the chamber
and the old depleted air removed.




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