Does the atmosphere cool with altitude due to gravity?

  • #51
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The intake is not energy absorbing but energy providing. You can harvest this energy with a piston that is pushed inside by the incoming air.



I do not talk about the expansing but about pushing the air outside away. This isobar process is not spontaneous and consumes energy. This energy is provided by the expansion and it is equal to the work of the isobar intake of air at the bottom.
Got it. I understand what you are saying now. I will have to go back and look at your math later.

EDIT: The thing that I have found confusing (and is once again confusing to me) is that the work you are describing already seems accounted for in an isothermal expansion formula. The expanding high pressure air in a cylinder expanding can generate energy. The energy it generates is during the process of moving aside a volume of low pressure air.

As I said, I am confused again, but I will look at it later.
 
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  • #52
gleem
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Unless I missed something in the previous responses wouldn't the absorption of the sun's radiant energy by the surface of the earth and the insulative effect of the air surrounding it account for a substantial ( if not most of ) gradient of temperature with altitude? Also with the re-radiation of the heat trapped in air with the subsequent returning of only some (half?) of the heat back to the earth and the loss of heat through the atmosphere above (density decreasing with altitude) also contribute to heat loss and thus temperature decrease with altitude?
 
  • #53
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Unless I missed something in the previous responses wouldn't the absorption of the sun's radiant energy by the surface of the earth and the insulative effect of the air surrounding it account for a substantial ( if not most of ) gradient of temperature with altitude? Also with the re-radiation of the heat trapped in air with the subsequent returning of only some (half?) of the heat back to the earth and the loss of heat through the atmosphere above (density decreasing with altitude) also contribute to heat loss and thus temperature decrease with altitude?
That is the explanation I have always seen. Certainly that has to be a factor.

In googling around I found a comment that the molecules of a gas are moving randomly, but that they still have mass. Moving up, they get slowed by gravity, moving down, they get accelerated by gravity. So it might be possible to conclude that air molecules that have moved to the bottom are more accelerated than ones that are moved to the top.

That seems intuitively sound, but I like to see actual proof ... so I had not quoted that idea to this thread ... I've no idea of the source now. It might be nonsense ...

And besides the thread turned into analysis of a rather weird thought experiment.
 
  • #54
jbriggs444
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That is the explanation I have always seen. Certainly that has to be a factor.
If the temperature gradient resulting from surface heating from below combined with purely conductive heat transfer is greater than the relevant adiabatic lapse rate then you will have convection. Warm air from the surface will rise through the layers above, even though it cools as it rises. The result of convection is then to reduce the temperature gradient. *voila*. The resulting temperature profile matches the adiabatic lapse rate.
 
  • #55
Votingmachine,

Excuse the late response; I was had a conference last week and have been flat out catching up with things.

At the top, the nbottom is expanded and preforms work, but not without clearing room for the gas in the atmosphere, which requires work.

At the bottom, ntop has to be compressed and that requires work. The energy harnessed comes from expanding the atmosphere into the void created in the vessel when ntop has been compressed.

The compressing and expanding of the atmosphere cancel out, leaving the sum of the two expansion to be f(nbottom) - f(ntop) which equals f(ndelta).

This is exactly half of what was calculated in the medium post and result in the device producing zero energy.
 
  • #58
Ugh, so much maths... it eats my brain.

After several months, It still doesn't make any sense why gravity wouldn't just cool gas particles as they move against it.

Look at the Atmospheric Escape wiki page which says "The more massive the molecule of a gas is, the lower the average velocity of molecules of that gas at a given temperature, and the less likely it is that any of them reach escape velocity". https://en.wikipedia.org/wiki/Atmospheric_escape

If the gas particles just maintained their velocity/temperature as moved upwards, they would just fly off into space!!!
 
  • #59
Drakkith
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After several months, It still doesn't make any sense why gravity wouldn't just cool gas particles as they move against it.

If the situation was solely about how the kinetic energy of a gas particle behaves as it moves away from a source of gravity, then you would probably be right. But there are many other effects to take into account, such as convection, radiation, etc.
 
  • #60
Let me try to distil this new device down to something simple for Kyle.

The barometric formula for an isothermal body of gas is Ptop=Pbasee-Mgh/RT

Because temperature is found in the denominator of the negative exponent, the higher the temperature, the less pressure falls for a given increase in altitude. Hence the hotter column must be taller for the columns to have a "proportional pressure" between the tops and bottoms (e.g. the tops are half the pressure of the bottoms). This height difference is then exploited by an elevator mechanism which lowers gas from the top of the hot column, to the top of the cool column.

Once you get your head around its principles, it seems quite elegant. Yet elegance can be deceptive...:nb)
 
  • #61
If the situation was solely about how the kinetic energy of a gas particle behaves as it moves away from a source of gravity, then you would probably be right. But there are many other effects to take into account, such as convection, radiation, etc.

Convection some posters have stated the whole reason that we have lapse rate in our atmosphere is due to adiabatic cooling and heating of convected parcels of air. Their logic is that no convection = no lapse. Are those people wrong?

Radiation makes a lot of sense, but would could completely overwhelm the effects of gravity or just reduce the lapse?
 
  • #62
Drakkith
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Convection some posters have stated the whole reason that we have lapse rate in our atmosphere is due to adiabatic cooling and heating of convected parcels of air. Their logic is that no convection = no lapse. Are those people wrong?

No idea. My point was simply that trying to think of this in terms of the kinetic energy of a single gas particle moving against gravity isn't likely to get you anywhere because the situation is far more complicated than that.

Radiation makes a lot of sense, but would could completely overwhelm the effects of gravity or just reduce the lapse?

I would think that depends on the altitude, density of the gas, type and intensity of the incoming/outgoing radiation, etc. The thermosphere is a good example. It's warmer than the underlying air layer because it absorbs X-ray and UV radiation from the Sun.
 
  • #63
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Convection some posters have stated the whole reason that we have lapse rate in our atmosphere is due to adiabatic cooling and heating of convected parcels of air.

That's the reason for the adiabatic lapse rate. There would also be a lapse without convection but it would be dominated by radiative heat transfer.
 
  • #64
some posters have stated the whole reason that we have lapse rate in our atmosphere is due to adiabatic cooling and heating of convected parcels of air. Their logic is that no convection = no lapse. Are those people wrong?

I'm pretty sure I said that :cool:

And I get where your coming from with the whole "one molecule in a box", but Drakkith is right. A gas isn't just one molecule, it's many and that makes it way more complicated.

Despite earlier successes, this VO is once again insisting that hydrostatic equilibrium must exist because his "Drop Down Cycle" would create energy. Last time a wrong formula was used, so what is it going to be this time?
 

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