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Post by hairball on May 30, 2010 18:03:02 GMT
In the absence of gravity the aptly named space would be a very tenuous and cold place. Collisions between atoms would be infinitesimally rare at this stage in the universe's development. Luckily for the existence of everything but Hydrogen, Helium and a minuscule amounts of slightly heavier elements, gravity heats gases by compressing them.
The End.
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Post by socold on May 30, 2010 19:56:01 GMT
I think heat is only generated if the volume the gas is in is contracting
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Post by hairball on May 30, 2010 20:26:27 GMT
Well, think of it this way; If you have a sealed syringe of air and you push down on the plunger the air inside will warm. This is because the molecules are in motion and repel each other. You would have to keep applying force to the plunger to stop it from being pushed back out by the motion of the molecules. If there were a vacuum outside, the heat would soon be lost, the air inside would cool and there would no longer be any need to push on the plunger. But if you did the same inside a sealed room and kept pushing on the plunger for a very long time, eventually the force you applied to the plunger would have been converted to enough heat to warm the entire room. Now, if you were to just place a heavy weight on top of the plunger gravity would do all the work and over a very long period of time gravity would heat the sealed room. This is a very small effect. I understand. But Venus' atmosphere has 90x the pressure here on Earth and for such pressures to exist at such high temperatures the weight of the atmosphere must be many, many times the weight of our atmosphere. Gravity is acting on each of those molecules, squashing them together and heating them up. While hot, they radiate photons, cooling them and they are then warmed again by gravity compression. Can Venus' atmosphere absorb the IR emitted by molecules at 400C? Maybe. If not then it emits a fair bit more energy than it absorbs and is in a constant state of contraction. Tuoko has inspired me to design a gravity power plant along these principles, which I intend to send to the Bill and Melissa Gates foundation for their perusal. Here is the design just before it goes into commission. Any comments welcome:  |
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Post by poitsplace on May 30, 2010 20:52:38 GMT
What you guys are talking about is the distribution of velocities of the molecules in the atmosphere. I forget the name of the law (or whatever it is) but basically...due to gravity there is a natural temperature gradient that develops. It determines the stable lapse rate for the atmosphere.
Adding water vapor changes things of course...the stable rate for a dry oxygen/nitrogen atmosphere is actually unstable for a moist atmosphere.
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Post by socold on May 30, 2010 21:13:18 GMT
A nice diagram, especially the wind turbine in a field of dead birds
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Post by hairball on May 30, 2010 21:21:53 GMT
Why thank you. I guess the issue is whether Venus emits significantly more energy that it absorbs. If it does then I contend that a measurable amount of its temperature is due to pressure rather than just GHG. I'm sure this has been studied but perhaps not from orbit there. Unfortunately search engines get mired in the AGW debate when I try to find the relevant information. Can the Venusian atmosphere absorb IR from a 400C source? Anyone?
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Post by icefisher on May 30, 2010 21:30:49 GMT
I think heat is only generated if the volume the gas is in is contracting Indeed and adding CO2 to the atmosphere will contract the volume of gas by its weight. Increase the volume of gas and the lapse rate does not change as it is proportional to the weight of the gases on top of it. The public has had a glimpse inside the AGW science consortium where total loyalty is rigidly enforced and assumptions and extensions of oddities to the absolute limit of believability is the culture that rules. Having done big modeling I understand that from experience as having no limitation on the error margin in a modeling exercise of this magnitude while every point can be contended and argued endlessly as being within a range of real possibility but the results are not. The liklihood of all the variables lining up so well even if each is a real possibility is so remote as to be ridiculously unlikely. What the sage advice is that before tackling big projects try practicing on small ones and produce some bacon first. The world is full of people who have no experience who believe no experience is needed. |
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Post by curiousgeorge on May 30, 2010 22:33:48 GMT
In the absence of gravity the aptly named space would be a very tenuous and cold place. Collisions between atoms would be infinitesimally rare at this stage in the universe's development. Luckily for the existence of everything but Hydrogen, Helium and a minuscule amounts of slightly heavier elements, gravity heats gases by compressing them. The End. What's your point? |
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Post by hairball on May 30, 2010 22:40:15 GMT
In the absence of gravity the aptly named space would be a very tenuous and cold place. Collisions between atoms would be infinitesimally rare at this stage in the universe's development. Luckily for the existence of everything but Hydrogen, Helium and a minuscule amounts of slightly heavier elements, gravity heats gases by compressing them. The End. What's your point? The subject was hogging the Arctic ice thread. Actually surface temperatures on Venus are just hot enough to emit visible red light. CO2 still doesn't absorb this, although H2O (20ppm) and molecular Oxygen can. The Venus Express spacecraft is up there now, but it's not clear to me how you could avoid overestimating the planet's albedo by mistaking emission for reflection. |
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Post by stranger on May 31, 2010 0:59:21 GMT
One need to have done nothing more complex than pumping a bicycle tire, or tyre for the Brits, to realize compressing gas makes a great deal of heat. So much heat that a reasonably vigorous person with a hand pump may very well burn their hand when they stow the pump.
Spray a gas out of a spray can, and the reduced pressure will drop temperatures very quickly. While the freon "chill sprays" for professional electronic work are an exemplary example, the principle works for hair spray, for spray lubricants, and for or the canned CO2 used to clean computer keyboards.
On a planetary scale, Sigurdur can tell you all about the "Chinook," a result of westerlies coming over the Rockies and heating as the air falls down the east slopes - and across the more gradual slope from the Rockies eastward.
All of this should be common knowledge - but it seems it is not.
Stranger
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Post by hairball on May 31, 2010 1:20:23 GMT
Yeah, the point Socold is making is that the heating/cooling is one-time (and reversible in the case of filling a spray can or letting the air out of a tyre). This is perfectly correct but, as is the case with Jupiter, if the gas cools by radiation then gravity can compress it again thus constantly generating energy by gravity alone. It occurs to me that all planets with atmospheres must (usually immeasurably) do this but that Venus' thick atmosphere generates much more than, say, Jim Hansen might think.
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Post by stranger on May 31, 2010 1:36:53 GMT
Well, let me rephrase my previous post. Starting with the axiom that "Perpetual motion machines are not possible."
The postulate of radiation cooling, gravity heating, is as much a sort of perpetual motion machine as the concoction of magnets and copper slugs that passed for one a century ago.
Like the magnetic perpetual machines, the output of such a "semi-eternal perpetual motion machine" declines with time, at a rate that is rapid at first, but transitions into a rate of decline that is parallel to the asymptote.
That is, the output will drop relatively quickly at a rate determined by the depth of the gravity well and the amount of energy lost to radiation. After the initial period of rapid cooling has been completed, the temperature will decline more slowly until after an infinite period of time it will reach a rest state.
Since recompression alone cannot raise the temperature to the previous cycle's high temperature, and infalling radiation must be either constant or declining, the eventual temperature reached after a long but less than infinite period of time must be close to the rest state of the atmosphere in question. Which will be either the freezing point of the atmosphere in question or absolute zero, whichever comes first.
Slainte!
Stranger
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Post by hairball on May 31, 2010 1:55:23 GMT
 How depressing. Spacecraft sent to Venus measured it's albedo as 0.8 to within 1% accuracy. But Venus' albedo is officially 0.75. Because if it was 0.8 the thermal budget wouldn't balance. Bah, CO2 is a supercritical fluid for the bottom couple of km. Venus makes my brain hurt. |
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Post by julianb on May 31, 2010 9:20:54 GMT
I think you are right hairball, Venus cannot be allowed to be cooling because that would support Velikovski’s prediction that Venus is cooling, and that supports his theory that Venus was formed much more recently than most other planets.
As far as lapse rates go, as long as there are temperature differences to support atmospheric vertical circulation, there is a constant re-pressuring of the gas column resulting in heat, not a perpetuum mobile but fueled by the Sun. Circulation seems to work with low temperatures (by our standards) as Neptune has 1000kmh winds, but as far as I know , the lapse rate has not been measured there.
Interestingly, it has come out that NASA has been sitting on data for 40+yrs that shows that the Moon has a greenhouse effect of 40% above calculated surface temperatures, caused by absorption and slow release of heat from surface material, and other planets have the same discrepancy. So that would make all greenhouse gases responsible for ~40% less effect than has been attributed to them ? ;0
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Post by hairball on May 31, 2010 9:23:47 GMT
Nothing would surprise me  |
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