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Thermodynamics (out of main)
- Thread starter KarenRei
- Start date
This joke-solution is not as dumb as it sounds first. If they built a space-elevator (powered by clean renewable energy) to lift big containers of water from the ocean high enough to freeze than bring it back down using heat-shield on re-entry, it could almost work...
Something something first/second law of thermodynamics something...
Yes but those are human laws so we can just ignore them...
As I read it, this does not violate any thermo laws.
It is displaced radiant cooling. Would be simpler to pump a liquid to space into black radiators to cool and then back down. Technically, the colder water is more dense so with a large pipe, you would get free therm buoyant pumping. Similar to the Alaskan pipeline and its ammonia based permafrost refrigeration system. That gets you the efficiency of the phase change.
(original idea would not need heat shield since the down weight would cancel the upweight)
This is so OT, it's all gonna get moved to "Stupid ways to cool the outdoors".
Meanwhile, assuming there is wind, just fly about 2,000 kites at various levels and force the upper atmosphere down into the stadium. The same device also gathers drinking water through "cloud harvesting." Kites paid for by marketing Hi-Fliers.
For radiant cooling, you need something on the outside to radiate the thermal energy to. On the surface, you get that for free using surface pressure air. In space, you have little to no atmosphere, so your only radiation would be light-based(far IR mostly at these temps). You could use the water, itself, to radiate the heat, but then you’re losing your free pumping, and that pumping, itself, is going to generate a lot of heat on the surface.
Earth isn’t quite a closed system, but it’s awfully close. We only lose energy to space in the form of reflected and radiated light.
Probably .
I think you are talking convection at the beginning. Cooling via radiation is the only type that occurs in space. You don't radiate the energy to something, it just travels away. if it hits something and bounces back, you loose cooling efficiency. That is why dry deserts are so cold at night, no cloud cover to reflect the heat back. The Merlin vacuum engine bell is radiantly cooled (temperature^4).
Yeah, Earth (in space) loses heat via radiation, that is what green house gasses prevent by reflecting IR back to the surface.
Thus saying you need to pump to space, outside of the atmosphere.
Yes, basically a giant (and very inefficient) heat-pump from surface to space.
If the motors operating the elevator/pump are outside the atmosphere, then even their waste-heat is released to space.
What makes it impossible is not thermodynamics, but the required tensile-strength of the material to build the elevator / pipe to withstand the gravitational force acting on it.
For fun:
Since you do not care about achieving orbital velocity, a sufficiently tall tower would work (Ad Astra style). Lower sections could be supported by hydrogen bags.
Taken further, one could imagine heating water at Earth's surface, letting that migrate to the upper atmosphere where it would partly radiate its energy to space, then return to surface to repeat the cycle. Side benefit could be reflecting sunlight while in the upper atmosphere.
Replying to this post (since it has its own thread now), since it brings us back to the joke comment's feasibility. Your points about heat radiating are fine, but the thermo dynamics is violated with the poster's suggestion of a heat shield - heat is lost through conduction into the atmosphere.
Besides, to get high enough where most of the heat is lost through radiation versus conduction would also evaporate the water wouldn't it?
Yeah, the kinetic energy converted to heat is a net heat detractor. I was picturing a sealed vessel of water (with some expansion space), so no evaporation.
Ah. Hmmm ... In that case, haul up tropical water in water bag, freeze in space, unwrap (why bother heat-shielding ICE?!) and drop an ice bomb on any unsuspecting pirate ships? Sorry, my mind has juvenile tendencies, and dropping heavy things from high up fits right in.
Doggydogworld
Active Member
Unless you insulate the bag well or lift it quickly the water will freeze before it gets to space. Temp above 36k feet is -70F.
Ambient temperature vs air density for convection vs radiation vs mass of the water vs starting temperature of the water vs ....
Wouldn't insulating the bag kind of defeat the purpose of freezing the water through radiation?
Doggydogworld
Active Member
You'd have to 'uninsulate' it when you got to space. Otherwise you're just moving heat from the surface to the stratosphere. IPCC theory is a little CO2-based high altitude warming kicks off a feedback cycle that increases water vapor (the real greenhouse gas). Based on that theory transferring heat to the stratosphere would be the last thing you'd want to do.
