CO and CO2, heavier or lighter than air? Focusing

Warming and Climate Change: causes, consequences, analysis ... Debate on CO2 and other greenhouse gas.
Christophe
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by Christophe » 21/11/11, 19:07

LeJuste, Gaston posted above a video which illustrates in image the image of Did67 of CO2 which "overflows" (he edited his message that you can not be seen therefore?):



In the absence of convection wind movements, the brownian is not enough to mix the gases ... otherwise there would not be the problem of the cellars ...

So ditto for the vial: the CO2 will necessarily focus in the lower part after a while ... I'm not saying that 100% will be there (as a water-oil mixture) but a large proportion ...

So I rest (ter) my question c): does anyone have the variation of the composition of the atmosphere as a function of altitude?
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by highfly-addict » 21/11/11, 22:04

Christophe wrote:...

So I rest (ter) my question c): does anyone have the variation of the composition of the atmosphere as a function of altitude?


Rhoo! Christophe! You've said it yourself ... excellently explained also by Remundo and others: The turbulence is the dominant phenomenon in the lower layers untilthe tropopause.

Your question can only have a meaning very locally in space and time.

And his answer is eminently variable as said above by Remundo: 80 / 20 + riddles.
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by Christophe » 21/11/11, 22:26

Well, it would be nice to have an example no? My initial question was about the evolution of the mass and volume composition ...

And simply knowing the concentration in CO2 according to the altitude would answer indisputably to the problematic of this subject ...
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by highfly-addict » 21/11/11, 22:45

Christophe wrote:Well, it would be nice to have an example no? My initial question was about the evolution of the mass and volume composition ...

Take one then: the thermal.
How could the composition be varied from the bottom up? I think it does not vary. Turbulence.

And simply knowing the concentration in CO2 according to the altitude would answer indisputably to the problematic of this subject ...


As already said, it can be considered homogeneous in low layers except local accident (fire for example).
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by chatelot16 » 21/11/11, 23:29

even without turbulence the gas of different density mixes

the history of CO2 down in a tank or fermente, it is because there is regular production of CO2, production superior to the speed of mixing with the air

when the fermentation is finished in a tank the CO2 ended up disappearing

once the CO2 is mixed it never separates from the air, it may have a tendency to go down, but the various turbulences mix it

it's not the same for light gases. Helium, for example, has a tendency to rise, the turbulence has the nice mix, it climbs anyway and leaves the atmosphere ... permanently lost
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by Did67 » 22/11/11, 09:56

Christophe wrote:
So ditto for the vial: the CO2 will necessarily focus in the lower part after a while ... I'm not saying that 100% will be there (as a water-oil mixture) but a large proportion ...



I am not sure. Not sure of the opposite either, I admit.

I would just tend to say that it mixes evenly! Unlike the liquids you mention, which are not miscible ! So there, no photo, the denser is found at the bottom.

If you put sugar in the water [or alcohol!], And wait "infinitely", it seems to me that for the same reason for Brownian agitation, it will end up being "moderately sweet" all over. ..
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by Did67 » 22/11/11, 09:59

chatelot16 wrote:
it's not the same for light gases. Helium, for example, has a tendency to rise, the turbulence has the nice mix, it climbs anyway and leaves the atmosphere ... permanently lost


There either, I do not think!

Helium in a balloon will eventually rise ...

The helium in the air will not finish diluting, dilute ... But there is! As far as I know, it is a rare gas, contained in the air, that is produced by distalliation of the liquid air ... Finally, perhaps, separations in the gas phase today ...
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by Did67 » 22/11/11, 10:05

Found that. Not famous, but for lack of better:

http://eduscol.education.fr/obter/appli ... tmos22.htm

Where :

http://astrosurf.com/luxorion/meteo-atmosphere.htm

who says:

The air in the troposphere has a remarkably homogeneous composition as a result of the continuous mixing of air in this part of the atmosphere. The lack of stratification (staging) is explained by the thermal agitation (turbulence). At rest the kinetic energy of the molecules is proportional to the ambient temperature (3 / 2kT, with k the Boltzmann constant and T the temperature expressed in Kelvin). This effect greatly exceeds the difference in potential gravitational energy (rgh, where r is the density, g is the acceleration of gravity, and h is the height relative to the reference level). This is why the thermal agitation is sufficient to maintain the homogeneous mixture over a great height.

Knowing that the composition of a gaseous medium follows the statistical Maxwell-Boltzmann law characterizing the distribution of particles according to their energy, the stratification at rest obeys the following relation:

C = Co [-rgh / (3 / 2kT)]

C being the concentration of the gas considered (N2, O2, etc.).

We will see that stratification occurs nevertheless at very high altitude, which is why the Earth loses its hydrogen.


Which seems to me reasonable and ... well founded and ... consistent with the observations.
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by Did67 » 22/11/11, 10:15

And so if I understand correctly, contrary to what I wrote, without turbulence, there would be stratification!

But I am not sure anyway, because it is also question of the kinetic energy of the molecules, at rest, higher than the difference of potential energy ...
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by Christophe » 22/11/11, 11:31

Yes did67: without turbulence, it stratifies inevitably (more or less) ...

Did67 wrote:If you put sugar in the water [or alcohol!], And wait "infinitely", it seems to me that for the same reason for Brownian agitation, it will end up being "moderately sweet" all over. ..


Good example but not agree: it is certainly moderately sweet everywhere but the bottom of the cup is very often sweeter, yet there is more "solid" sugar at the bottom ...

With the mixture of gas not agitated, it is the same: moderately mixed but more important concentration at the bottom!
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