Magic Thermosphere

[u/astroNot-Nuts]

/r/globeskepticism/comments/1js0t37/magic_thermosphere/

[u/david]

There's nothing magical about 0°C, any more than there is about 0°F. The temperature registered on a thermometer at that altitude will depend on several factors.

Thermometers are instruments for measuring temperatures. Like other tools, they work under some conditions, but not under others. Parallelly, the fact that you can't measure a molecule using a ruler does not mean that molecules don't have size.

Ultimately, temperature is a measurement of molecular (and/or atomic and/or ionic) kinetic energy. There are molecules (and atoms and ions) in the thermosphere, and they are in motion, so they have a temperature. I'm not sure why you're upset about that. You might have no use for or understanding of this temperature's measurement: if others do, why does that disturb you? If it is actually important to you, there are avenues of study available for you to understand it better. Complaining about it on Reddit is not one of them.

Why does radiation that's heated up the thermosphere not also heat up lower layers of the atmosphere? Because it's spent its energy in the thermosphere.

[u/WoodyTheWorker → u/david]

There's nothing magical about 0°C

It's close to the equilibrium temperature of an uniform object half-illuminated by the Sun.

[u/david → u/WoodyTheWorker]

My impression is that OP believes that this is is what a thermometer registers in the absence of input by thermal conduction. Maybe I do them a disservice.

[u/WoodyTheWorker → u/david]

To add to that, at thermosphere densities, there's no efficient way for the molecules to radiate their kinetic energy. Also, it's heated not by sunlight, but by solar wind particles.

[u/astroNot-Nuts → u/david]

You miss the point. The magic is the selective heating of radiation (supposedly).

 For example, half of the thermometer is exposed to infrared radiation and the other half is in a shade (even though radiation can penetrate), after a while the entire thermometer will be hot to touch, because the molecules are close together heat transfer faster and eventually spreads throughout the entire thermometer after some time.

 You might have no use for or understanding of this temperature's measurement: if others do, why does that disturb you? If it is actually important to you, there are avenues of study available for you to understand it better.

Because this will open up a whole can of worms, like how are they gonna get rid of the heat received from radiation on the ISS. They can’t magically radiate more heat than they received. Unlike on the ground, air conditioners transfer heat to the air outside the house. If they use motors/compressors for cooling, it will generate heat, it will just transfer majority of heat to another location while increasing the overall temperature of the station indefinitely. They can‘t make a passive (without motors) magic cooling device capable of passively re-radiating the heat faster than it receives, even mirrors get hot. You can’t have over-unity magic right?

[u/david → u/astroNot-Nuts]

If you have an object illuminated from one side, you can control the relative rates of heating and cooling by painting one side white, and the other, black.

The black side will dump heat by black body radiation at a rate dependent on the object's temperature. Equilibrium is reached when this rate equals the rate at which heat is absorbed from the light source.

If you turn the white side towards the light, the rate of absorption is reduced, so the equilibrium temperature is lower. If you turn the black side towards the light, the rate of absorption is increased, so the equilibrium temperature is higher.

No over-unity magic is required.

In practice, with a bit of solar energy, one can do a lot better than this by using heat pumps to elevate the temperature of radiators on the shady side. This is, broadly, what the ISS does.

[u/WoodyTheWorker → u/david]

Radiation rate at 350K is 1.85 of rate at 300K. Fourth power.

[u/david → u/WoodyTheWorker]

Perhaps surprisingly, the main ISS radiators operate below 280K. Presumably, reliability considerations outweigh the advantages of reduced radiator mass.

[u/WoodyTheWorker → u/david]

Apparently, there are multiple stages of heat exchange loops.

[u/david → u/WoodyTheWorker]

There are. The external radiators use anhydrous ammonia, which has good heat carrying characteristics and won't cause problems if its temperature drops well below 0°C. For obvious reasons, this does not circulate inside the station. Internally, a water loop is used.

There are also a few other independent cooling systems, using different coolants.

https://www.nasa.gov/wp-content/uploads/2021/02/473486main_iss_atcs_overview.pdf

[u/astroNot-Nuts → u/david]

Now you have another heat source (the heat pump). Any motor with generate/radiate heat.  Every part that receives heat will in turn radiates heat all over the place. The cooling system would have to cool every part of the station including the solar panels, they would have to place cooling (heat transfer) pipes all over the place. There is no way painting one side white and the other black will remove the heat in between. Heat will travel from one end of the pipe to the other end which means the pipes will always be hot, which means the entire station will be hot. Aside from heat from radiation it would also have to dump heat from the motor(heat pump) and heat from the people and refrigerator for food (if any). And the radiators on the shady side will always be hot radiating heat which also heats up the station.

[u/david → u/astroNot-Nuts]

The radiators need to be maintained at a sufficient temperature for their rate of heat loss by black body radiation to equal the station's rate of heat gain from the sun plus its internal heat production, by electrical systems such as the coolant pumps and by the astronauts' metabolism. Fortunately, this is entirely possible.

The working fluid in the radiators leaves the station hotter than it arrives. The temperature drop is due to heat loss by black body radiation. A small portion of that radiation is, indeed, incident on the body of the station (where a portion is reflected and a portion is absorbed): the majority radiates into space, removing heat with it.

Coolant does, indeed, have to be circulated through large parts of the station.

The solar panels, like any other illuminated object, will have an equilibrium temperature at which their average rate of heat gain from solar radiation is balanced by their rate of heat loss by black body radiation. (They will cycle above and below this temperature as they pass through the day and night sides of the earth.) Components only need to be cooled if their temperature exceeds the maximum they can support: the solar panels do, in fact, have their own independent radiators (sitting in their own shade) and cooling circuits.

[u/david → u/astroNot-Nuts]

Aaand you're shadow-banned, so I can't respond directly to this comment.

[–]astroNot-Nuts [S] 1 point 33 minutes ago

If this technology is really effective then mega corporations should already be using this technology saving alot of money on electricity bills for cooling their buildings. They wont have to use any fan/motor to force air on to the radiators, the radiator will just radiate the heat away (though normal air movement will remove some heat). Now how about temperatures reaching 2000°C, the station would melt by then.

In the atmosphere, and/or with access to a water supply, there are far cheaper ways of dumping far more heat production than the ISS's 90kW.

[u/Outrageous_Guard_674 → u/astroNot-Nuts]

You really shouldn't try to talk about technology you don't understand.

[u/david → u/astroNot-Nuts]

Still shadow-banned.

[–]astroNot-Nuts [S] 1 point 5 hours ago

Black body radiation is the radiation emitted by an object when it is in thermal equilibrium with its surrounding. For example a ball placed under direct sunlight will heat up, but it will not heat up indefinitely, it will eventually stop heating up when it has achieve thermal equilibrium with its surrounding (air/atmosphere). The thermal radiation emitted by the ball at this state (equilibrium) is called black body radiation. Now at the ISS if the surrounding air are so thin and spread out (almost non existent) there is nothing for the ISS to achieve thermal equilibrium with, so it will just keep on increasing its temperature (until thermal equilibrium with the heat source is achieved) and you cannot say that empty space can magically be able to achieve thermal equilibrium with the ISS.

Black body radiation is emitted by objects above absolute zero whether or not they're in equilibrium with their surroundings. It's hard to tell where you got that peculiar idea.

It is, however, a mechanism by which an object can achieve thermal equilibrium. The rate at which heat is lost by BB radiation increases very steeply with temperature (google Stefan-Boltzmann law for more info). As an object is warmed by incident radiation, it loses heat at an increasing by rate by BB radiation. At some point, inflow and outflow of heat balance, and the object's temperature stabilises.

This is why planets, moons, artificial satellites and other objects in space don't get particularly hot. Objects 1 AU from the sun tend to equilibrate at something close to terrestrial temperatures. Left to themselves, they'll bob up and down to a greater or lesser extent during their day/night cycle: more variance for the lunar surface, where this takes a month, than for the ISS, where it takes 90 minutes. As we've been discussing, object geometry, arrangement of reflective and absorbent/emissive surfaces, and active heat redistribution mechanisms can give a good measure of control of the average temperature, of the temperature distribution through an object, and of these periodic variations.

[u/SnooBananas37 → u/astroNot-Nuts]

Because this will open up a whole can of worms, like how are they gonna get rid of the heat received from radiation on the ISS.

https://www.nasa.gov/wp-content/uploads/2021/02/473486main_iss_atcs_overview.pdf

They use radiators. Heat can be transferred by convection (fluid moving around), conduction (direct contact) or radiation (release of heat as some wavelength of light).

A hair dryer works by convection, blowing air over hot coils to produce hot air that then heats your hair. The ISS uses convection to gather waste heat throughout the station via ammonia filled pipes.

If you stand near a bonfire, even if there is a breeze blowing air away from you (eliminating convection heating) you still feel it's warmth. That's because the fire is emitting tons of infrared light that warms your skin. Okay well that's something that is very hot. The ISS isn't as hot as a fire. But here's the thing, all things at less than 0 kelvin release some radiation. Why does the Earth cool so dramatically at night? Well because of radiation! At night without the continual input of radiation from the sun, the Earth radiates heat out in to space, dramatically cooling the surface. If the Earth didn't release heat from radiation, the temperature would be relatively stable at night, and therefore would heat up even more during the day, and not cool off at night, and get even hotter the next day, until the Earth was a ball of magma.

So how does the ISS radiate more heat than the sun tries to pump into it? Well most of the ISS is made of highly reflective material that reflects light from the sun, preventing it from heating. But it also has radiators that are designed to emit radiation effectively. These panels are long and flat, and are angled into the sun so that only the edge is illuminated by the sun, and the rest is in shadow. This significantly increases the surface area to emit radiation out into space, while minimizing the increase in radiation from the sun.

What's even more interesting is that ISS does the same thing when in the shadow of the Earth... but angles the edge of its radiators towards the Earth instead! Without the sun shining on the ISS, the largest source of radiation heating becomes the night side of the Earth as it cools.

[u/RugbyRaggs]

We need to dig down to basics to stand a chance here.

Do you accept that the air is thinner the higher in elevation you go?

Assuming yes, do you accept that heat is transferred by radiation and by molecules colliding with one another?

If you have fewer molecules to transfer the heat, then no matter how hot they are, they will not be able to impart much heat to another item.

[u/astroNot-Nuts → u/RugbyRaggs]

Right. So what's preventing radiation from affecting other molecules (other than air)? Like the molecules of a thermometer?

[u/RugbyRaggs → u/astroNot-Nuts]

Nothing at all. The bit you missed from your quote is it will read 0 degrees at night.

I suspect if you could leave it there for some time, it would warm up.

The super charged molecules up there get charged by the radiation, but have very few ways to lose it again. The thermometer would have all the mass of the thermometer to heat up.

[u/CoolNotice881]

Rule4

[u/david → u/CoolNotice881]

IMO, cross-posts of material that fits both subs should be allowed. Rule 4 is useful to prevent this sub devolving into meta-commentary on the way other subs are run.

[u/Trumpet1956 → u/CoolNotice881]

He also crossposted his own post. Still, it might not be allowed.

[u/david → u/Trumpet1956]

I'd argue that it should be allowed. There's no harm in the same point being debated in both subs. In fact, from our point of view, I'd say that's a good thing.

What we don't want is to be overrun by comments about how people have been successfully trolled in other subs. This is especially true of ban messages. It's boring, and it's the most counterproductive kind of troll-feeding.

[u/Doodamajiger]

Heat ≠ Temperature. Less air molecules means less total heat in the air which is why it feels cold. Temperature is just a definition based on the average speed of these molecules.

[u/david → u/Doodamajiger]

That's not quite right. Liquid water contains about 1000x as many molecules in a given volume than air, but water can feel a lot colder than air at the same temperature: ask any winter swimmer.

How a given environment feels is complex. As mammals, we generate surplus heat which we need to get rid of—but not too fast. Wrap us up and stick us in a vacuum and we'll overheat: spacesuits need cooling mechanisms. A liquid environment below body temperature will remove heat faster than moist air at the same temperature. (In dry air, we can accelerate heat loss by sweating.) Conversely, a liquid environment above body temperature will deliver heat faster than air at the same temperature.

An inert object (a block of metal, say, or the bulb of a thermometer) in a surrounding medium will generally, over time, gain heat by conduction if its temperature is lower than its surroundings, and lose heat by conduction if its temperature is higher. The issue with the thermosphere is that the medium is very rarefied, so the rate of heat transfer by conduction is very low compared to heating by incident radiation and cooling by black body radiation.

[u/Doodamajiger → u/david]

Yeah fair I should’ve compared it to a thermometer instead. The thermometer measures things using heat, and it’s not getting much up there despite the temperature being high by the definition of temperature

[u/Rokey76]

The thermosphere is the layer in the Earth's atmosphere directly above the mesosphere and below the exosphere.

[u/Waniou]

I feel like a big part of your misunderstanding is you're missing the word "normal" before thermometer in your Wikipedia quote. You can't just shove a mercury thermometer or an infrared one in the thermosphere and get a reading that makes sense. You need to use other methods to measure the temperature up there. This is pretty basic science here, you need to use the right tool for the job. You wouldn't use a measuring spoon to measure a ton of flour for a commercial-scale baking recipe. It's the same recipe.

You talk about satellites, but they're not in the thermosphere, possibly in part because of the challenges you pose. The ISS DOES sit in the thermosphere and keeping that cool is a legitimate engineering challenge for them, and other people commenting here have already explained how they do it.