h a l f b a k e r y(Serving suggestion.)
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So, a heat engine. not a specific type of engine. Just a
nominal system to extract mechanical work from a
temperature difference between two “heat reservoirs”
(not bodies of water, but an infinite source or sink of
heat
at a fixed temperature).
A heat engine’s maximum
efficiency is dictated
by the absolute temperature
difference between the hot and cold reservoir. (Hence
intercoolers on car intake, for instance)
Given limitations of engineering materials, Earth-bound
engines are usually limited by the approx 20 degree cold
reservoir.
This idea is to use conductive cooling to transport
“coldness” at -50 degrees from the stratosphere (approx
10km) to a heat engine at ground level.
Perhaps a Stirling engine. Which could use 1. Ambient
heat, 2. Geothermal, 3. Solar, 4. Waste industrial heat…
as
it’s hot-side reservoir.
10km towers, insulated (perhaps with aerogel, for
reasons), with large surface-area heat exchangers at the
top (fins, branches, fractal)
Or giant kites, with big thermally-conductive cables.
Sparkly colours of course.
Ooh, could also supply air conditioning and refrigeration
this way.
[link]
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Solar updraft towers are an engine working on this
principle. Only instead of thinking about transporting cold
down, they're transporting heat up and extracting (the
relatively small) energy from that. |
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In general, humanity doesn't give much of a stuff about
efficiency. Accessing the -50C 10km up is tricky, because
it's 10km away, in the least convenient direction. On top
of that, there's not much cold up there. That is, the air is
thin, so you're heat exchanger has to be larger, tricky,
because you have to suspend it 10km up. Thermally
conductive cables... how are these working? The closest
we've got is heat pipes. You'll have them in a laptop for
example. But you get efficiency losses with distance
which overwhelm your gains from the enhanced delta t. |
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It makes more sense to go down. The ground is reasonably
cool, and thermally speaking, there's a lot of it. |
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Some adjustments might be worth it. Mounting an AC
condenser on a roof vs the ground might get you a couple
of C, if you can shade it. But you get inefficiencies from
any extra pipe length, and it becomes tricky to service. |
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I'm all for 10km towers however. Although they might be
vulnerable to the very large legacy heat engine we like to
call "weather". |
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Just hang them from satellites in geosynchronous orbit. Ok,
35,786km is more than you need. But you'd get to add carbon
nanotubes to your materials list. |
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^String bridges to the islands in the stars. |
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Enough towers and a weather ask system is born. |
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If we were to plant on Mount Everest the thinnest spine of
titanium capable of bearing its own weight, which could simply
conduct heat out into space with no moving parts, then we
would have the added benefit of watching climbers stumbling on
to the first step of a spiral staircase with the realisation that they
weren't really at the top after all. |
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