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So,
I've been thinking about this on and off for awhile now. It
first started with the idea of a solar trap.
Solar trap being something like having a solar collector
focusing light on a container of water, having an infra red
barrier around the container, and a black body at the
centre.
Incoming solar energy passes by the IR reflector,
absorbed by the black body and re-emitted as radiation
which is reflected by the IR reflector.
I was pleasantly surprised some form of this technique is
used in the high efficiency solar water heaters.
So what stops one doing this in reverse? having a visible
reflector, IR transmitting layer.
Could this allow solar cooling during the day? It would of
course depend on the net flux of radiation, perhaps looking
at natural sunlight spectrum there maybe a band strongly
absorbed by the atmosphere that is within the range put
out by a black body.
black body radiation
http://www.spectral...lator/blackbody.php
basic calculator for black body radiation [lostmind, Jun 12 2012]
solar radiation
http://solar.energy.free.fr/sld018.htm
solar radiation spectrum [lostmind, Jun 12 2012]
cold mirror
http://en.wikipedia.org/wiki/Cold_mirror
effectively what I was thinking of [lostmind, Jun 12 2012]
Night Sky Cooling
http://cedarmountai...p?PageID=5_TrueID=5
Half-baked version which works only at night [goldbb, Jun 14 2012]
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Annotation:
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I'm thinking something like chrome tube going into a two-piece, thick ceramic container, with a black water tank. The light is reflected down the tune into the container. |
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The inside of the ceramic container surface would be many wedges, flash-deposited with aluminium, to maximise light bounces to make sure most of it hits the water tank and is not reflected straight back out again. |
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Or is that needlessly over-complicated? |
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How dare you ask such a question within these hallowed
halls?! That kind of thinking flies in the face of Halfbakery
tradition and values going back centuries! |
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It's not going to work well during the day, as the
net radiation would not tend to be favorable. It
should work as a heat dump during the night,
allowing the cooling of a heat sink, which is then
used during the day. It wouldn't be wonderfully
efficient. |
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There is at least one short story that more or less
uses this as a premise, by rejecting the local heat
to space, they create a large(ish) low pressure
system to pull in rain. It was published in Analog
something over 8 years ago, so I can't remember
any more detail. |
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I think you could use it during the day, though it
depends what the sky's radiation in the range of 1-10
micron (approx range of a black body at 300K) is. The
solar spectrum in this region is minimal (see link)
while the black body puts out up to 250W/m^2/um |
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If you can find a low cost filter that reflects below
about 2 micron, then maybe. Below that point,
the sun wins. Good luck on the low cost though,
I've been looking for that sort of thing for
professional reasons, without much luck. |
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Also remember that you won't have a perfect
black body. You can get within a few percent if
you're willing to spend money and don't need it to
resist damage, but it's still going to be on the
wrong side, as is the less than perfect filter, and
the less than perfect reflection of every mirrored
component in the system. |
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I'm not saying it's not possible, I'm saying the ROI
is going to be poor. |
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i wonder if silicon could do the deed.
Useful Wavelength Range
(Transmission) – 1.06μm to 6.7μm
& 30μm to FIR |
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well, i found what i was thinking of. a cold mirror |
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There is nothing new under the sun. |
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//Incoming solar energy passes by the IR reflector, absorbed by the black body and re-emitted as radiation which is reflected by the IR reflector.// |
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Isn't this more-or-less a greenhouse? |
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//There is nothing new under the sun. |
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Yes, but the area under our sun must be quite small relatively speaking. Which would presumably include all the space that is far enough away to get none of our sun's light as our sun wasn't around then. |
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So, cosmically speaking there's a lot of area not under our sun, a very long way away. That doesn't really help us if that's where the really new things are being stored. |
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I must get out more often. |
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// the area under our sun must be quite small relatively
speaking. // |
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The Sun is a sphere; other than points arbitrarily
designated as poles based on the planar orientation of the
Solar System, it has no identifiable top and bottom. It is
surrounded by literally everything in the Universe, and
because it is omniradial, it likewise faces everything in the
Universe. Therefore, depending on how one chooses to
define one's own relative geometrical position, the Sun is
either over, under, or beside everything. |
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So, from an heliocentric standpoint, this means that the
area 'under' the Sun is actually a very, very large area, and
that 'everything under the Sun' is, in fact, everything. |
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//other than points arbitrarily designated as poles
based on the planar orientation of the Solar System,
it has no identifiable top and bottom.// |
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Not so - the sun rotates, and hence has definite
poles. |
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But... but... which way is up? |
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A "Reverse solar collector" is called a light bulb. |
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I am elucidated. I think? |
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So, all the new stuff is currently being stored in the centre of the sun? |
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<starts preparing for trip to centre of the sun, ponders - now a layer of sunblock 1m metre thick needs how many bottles...> |
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Okay, it has poles... If I'd been thinking, I would have
realized that it would just fly apart if it were apolar. Lack
of EM field integrity and all that. |
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But I stand by my claim that, from the heliocentric
perspective, every direction is down. Or up. There's not
really any difference on the cosmic scale. |
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Thinking there must be some neutral zone, either inside the sun, or perhaps equidistant from another sun, so both their unders cancel each other out? |
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Seeing 'under' is a definition relying on gravity, you could pick some distance where the sun's gravity is no longer detectable by our best existing equipment although this would vary as equipment and techniques got better. A less controversial method would be to define anything being outside a sphere 4.5 billion light years in radius as not "being under the sun" as that is the approximate age of Sol so gravity waves (or anything else) could not reach there yet. |
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Oddly, the sun rotates faster (about once every 25
Earth days) at its equator than it does nearer its
poles, where a rotation takes about 38 Earth days. |
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I would suggest anything within the sun's light zone
is "under the sun", if you can see it from 4.5 billion
light years. |
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Choose any table in any room in your house ('room' here
being defined as any space delineated by a floor, a ceiling,
and any number of walls). Place a book on top of the table.
The book is under the ceiling, yes? Now place the book
under the table. Is the book not still under the ceiling? |
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By extension, just because the Sun's rays do not fall upon a
particular object or area does not mean that said object or
area is exempt from being under the Sun, presuming the
observation is being made from the perspective of the Sun
(which is implied in the syntax of the saying). |
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And likewise, I don't see how gravity has anything to do
with what is 'under' or 'over' anything else. It all has to do
with relativistic spatial orientation. Under or over is
defined by the observer's point of view. If I stand on my
head, I can make a valid argument that the floor is above
the ceiling and that the book sitting on the floor is over the
table. |
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//If I stand on my head, I can make a valid argument// - ah - but can you drink a cup of tea at the same time? or paint the pincers of an earwig whilst completing a soduko with your toes? These are demanding times, and new skills are needed. |
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// but can you drink a cup of tea at the same time? // |
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// or paint the pincers of an earwig // |
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One of my hobbies is painting very small things, so yes. I
even have my own brushes. |
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// whilst completing a soduko with your toes? // |
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If it's an easy one, printed very large, and you give me all
afternoon. I really suck at soduko. I rock the NYT
crossword, though. |
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So do you see what I mean now? |
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No-one *really* sees what you mean, [Alter]. I think
you need to properly define or redefine "see" and to
use more words to describe your past experiences,
current predicaments and future intentions and
aspirations... regale us with a lot more of your
homilies and apparent humility, as it were. |
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After all, seeing is believing. |
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// If I stand on my head, I can make a valid argument that the floor is above the ceiling// I hope you can make a valid argument whilst holding your breath, as according to your definition you're under the Atlantic Ocean. |
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I think that the better definition of "under" is between one object and the centre of the local, dominant gravitational (or pseudo-gravitational) pull ie the Earth's when we're on the planet and the Sun's when we're toodling around the Solar System. Everything is relative of course, but as a practical working definition, this one works best. |
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// Oddly, the sun rotates faster (about once every 25 Earth days) at its equator than it does nearer its poles, where a rotation takes about 38 Earth days. //
So, the Sun is all twisted up, like an old phone cable? |
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I guess it must be. Can you imagine how much
farther its light and heat would reach, if someone
were to untwist it? |
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I'm still reeling from "The Sun has got poles"...I mean, where did
they stick the flag? |
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//Can you imagine how much farther its light and heat would reach, if someone were to untwist it?//
But I took a rubber band and twisted it for just a few minutes (it's a slack afternoon) and it snapped.
I know the Sun is a bit bigger, but it's been doing this for 4 billion years - when that goes, I don't want to be around. |
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Under and over are terms relative to the observer's gravitational direction. If I am under a table, turning the table upside down does not make me over the table. During the day, I am under the sun. At night, the sun is under my feet. Therefore, one can only have new ideas at night. |
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If the sun is considered to be the observer, down is the centre of the galaxy, which would mean that one could only have good ideas for 6 months of the year. (Any astronomy nerd know which 6 months?) |
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// use more words to describe your past experiences,
current predicaments and future intentions and
aspirations... regale us with a lot more of your homilies
and apparent humility, as it were. // |
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Your wish, sir, is my command. |
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ironically, I do seem to have come up with something entirely new, the mock-butt toaster, but would prefer that not to be my lasting contribution to western civilisation... |
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