Half a croissant, on a plate, with a sign in front of it saying '50c'
h a l f b a k e r y
Flaky rehab

idea: add, search, annotate, link, view, overview, recent, by name, random

meta: news, help, about, links, report a problem

account: browse anonymously, or get an account and write.



Please log in.
Before you can vote, you need to register. Please log in or create an account.

Inverted solar tower

Sweet sweet coolth.
  [vote for,

Solar towers - thinking of flying them, reading of cities with them.

But consider that sweaty, sweltering city. No doubt at ground level it is hottest, because the earth captures radiant heat and then heats the adjacent air. I here assert that a spectacular thermocline exists in such circumstances.

The inverted solar tower is reflective chrome, like a toaster. This will prevent the sun from heating the structure and the air within. The top is open to the sweet coolness prevalent at 100+ meters. Maybe there is a swiveling scoop on the top to orient according to prevailing winds up there, encouraging the wind to enter. Maybe an evaporative element is included, like a swamp cooler to cool the air further.

Given an path unobstructed by rising hot air, this cool air from high above ground will fall in an accelerating wind to surface level - or better, subsurface level. It can generate power. Better, it can be used to air condition indoor dwelling spaces.

The towers will be awesome looking too.

bungston, Mar 11 2014

In reverse. http://en.wikipedia...Solar_updraft_tower
[2 fries shy of a happy meal, Mar 11 2014]

Downdraft tower http://en.wikipedia...y_tower_(downdraft)
[bs0u0155, Mar 11 2014]


       As one who lives almost exactly on top of a 100m contour, I regret to have to tell you that the coolth here is not all it's cracked up to be. In fact it's hot and muggy down here in this valley.   

       I've ventured up to the 200m contour (aka going to the shops) and a little beyond, and can almost imagine that I feel a little less like the Sunday roast up there, but not refreshed enough to imagine piping that hot air down to displace this hot air.   

       In fact, I've even been up to the 600m contour (aka visiting my cousin a few clicks away). And now we're talking palpable cooling. It's not so hot there, anyway.   

       Bearing in mind that this is not Central Australia (or indeed the Victoria\ NSW border, even), it looks like in milder climates a 500m tower is about the bare minimum.   

       So now your towers look even cooler!   

       How about 1km? There's definitely a lot of cooler air up there. (And to use the 21st century technical jargon, your towers would go from cool to aWeSome.)
skoomphemph, Mar 11 2014

       (+) An un-chromed tower surrounded by acres of shade cloth has the same effect. [link]
You could get a lot more bang-for-your-buck combining these two concepts by raising the mirrors off the ground to act as the shade cloth.

       Makes its own micro climate beneath as well.   

       Maybe blimps at 1km dangling plastic pipes down into your curio shop? Good advertising too.
bungston, Mar 11 2014

       Baked. <link>
bs0u0155, Mar 11 2014

       A sweat-free curio shop would be a wonder all would come from miles round to behold.   

       How about coupling the two basic baked variants together, and taking up station in the airflow resulting?   

       So on this side, here, we have a pipe up to the world-view blimp (whose rope ladder the entrepid may climb for a mere mention in the will). This blimp flies as high as possible, at an altitude Marketing has decided will be called "a mile", regardless of the facts. It will breathe in cold air due to a pressure gradient set up by the updraught chimney.   

       I suppose the updraft chimney on that side might be painted black, and have wind-driven extractor fan up top.   

       There may be a hole or two in this scheme, just looking at what's already been tried.
skoomphemph, Mar 11 2014

       Not baked. The downdraft tower shown on the wiki isn't tall enough to use natural coolth, so they have to manufacture artificial coolth using water spray. As noted in the link, this limits the locations to hot dry climates with lots of water available. Also, the resulting cool air might not be as useful for air conditioning since it would have much higher humidity.
scad mientist, Mar 11 2014

       Problem with the coolth at altitude is that it's a result of pressure reduction. So to bring it down, we have to compress it, resulting in similar temperatures to ambient. ...   

       We need to grab the coolth, not the air; and there are probably cheaper alternatives.
skoomphemph, Mar 11 2014

       Is the coolth at altitude from pressure reduction? When you reduce pressure on things they get cooler, but just because something is at lower pressure that does not mean it is cooler.   

       I thought the difference was distance from the earth's surface where most of the sun's energy is deposited. This also accounts for visits to various spots on the contour, all of which are on the earths surface.   

       That linked concept uses water and pumps and fuss. I would accept relatively air pouring out of a pipe in the wall with no energy inputs.   

       I like the rope ladder very much.
bungston, Mar 11 2014

       Hmm .. OK gravity means all air molecules dream of being crushed flat somewhere in the centre of the Earth. They all fight for the right to be crushed like this, but only the most energetic get to attack the surface of the unyielding Earth, which they bounce off.   

       The surface of the Earth vibrates according to how much sunlight smacks into it. Lots of light means lots of vibration, which means air molecules coming closest to achieving their gravitational ambitions get hit for 6 (or for a home run in most places outside India) by the throbbing Earth.   

       These surface-struck molecules are hit opposite to gravitation. Instead of being merged with the magma core, they fly out, smashing into Earthward-tending fellow air molecules, altering their destinies unfavorably, and dumping energy as they so collide.   

       The net short term result for any individual air molecule that reaches the ground is that it ends up travelling at a reduced speed, some distance above the ground.   

       For bodies of air, columns of hotter air tunnel up from hotter spots, lifting air up into less gravitationally desireable spots, which are also poorer in collision energy than the heated surface of the Earth. Molecules falling tend to get knocked back up by the air below. And sb on ..   

       Anyway, (before I now completely lose the plot) because air doesn't like being a kilometre above the ground, there tends to be less of it up there. Because there's less, there are less collisions, and temperature is collisions -- are collisions ... is just a byproduct of the collisions.   

       So as I could've said without getting tripped up in my own shoelaces about a week ago, less molecules per cc means less collission opportunities. That's the direct reason for the higher altitude temperature drop. (Down near the ground it gets complicated).   

       The whole lot is driven by gravity vs radiation, but the effect comes from density reduction with altitude.   

       Oh... Yes, maybe the blimp and rope ladder could be wangled into a kind of sky hook, using a variation of the pumped water abomination. This is imperfect honesty in marketing (but then so is Hansel and Gretel): Keep a kettle boiling up there, so as to generate a cloud that hides the blimp, and then give people to believe that the tether just dangles from some anomaly in the sky.   

       Those who climb high enough to uncover your secret would slip on the mist-drenched steps at some point and fall to their deaths - which is sad but convenient, as I'd like to imagine Edward Lear would've put it.
skoomphemph, Mar 11 2014

       I thought that lack of collision opportunities also meant less opportunity to hand off heat to nearby molecules. I am pretty sure I read somewhere (probably the IKECE idea) that this led to very high temperatures in those molecules present in the rarified high atmosphere. Probably this is well above 1 km though.
bungston, Mar 11 2014

       I'nt it just less heat per volume ? If you have a candle in a cubic metre it's warm, have 1,000 candles it's somewhat warmer.
FlyingToaster, Mar 11 2014

       // Problem with the coolth at altitude is that it's a result of pressure reduction. So to bring it down, we have to compress it, resulting in similar temperatures to ambient. //   

       I didn't believe that, so I did some calculations and proved myself wrong.   

       According to my calculations, if you bring 0 deg C nitrogen down from 2000ft (.61km) to sea level, the compression will increase the temperature by 5.5 deg C. (please check my calcs below)   

       In the troposphere, the temperature gradient is approximated by 60 deg C / 11km = 5.4 C/km. So the temperature gradient for 610m = 3.2 deg C. So [skoo...] is correct.   

       I'm sure the temperature gradient in the atmosphere is fairly dynamic, so we might find a larger gradient during the midafternoon when the air near the ground has been heated more than the air at higher altitudes, and I could imagine that being more than 5.5 C, but I doubt that will be enough to make this useful.   

       I suppose someone might be able to call "bad science" on this idea, but I'm leaving my bun here since I learned something new.   

       (check my calculations here)   

       altitude 2000ft (610m) -> 94.2kPa   

       altitude 0 -> 101kPa   

       assume air temp at altitude = 0C ~= 273k   

       P*V^y = constant   

       for nitrogen, y=7/5   

       94.2kPa * 1L^(7/5) = 94.2kPaL^(7/5)   

       101kPa * V^(7/5) = 94.2kPaL^(7/5)   

       V^(7/5) = 0.9327 * L^(7/5)   

       V = (V^(7/5))^(5/7) = (0.9327 * L^(7/5))^(5/7) = 0.9514L   


       PV/T = constant = 94.2kPa * 1L/273k   

       T = PV/(94.2kPa * 1L/273k) = 101kPa * 0.9514L * 273K / (94.2kPa * 1L) = 278.5K
scad mientist, Mar 11 2014

       Though I won't say I'm inspired by convinced with the explanation [skoo...] gives.   

       // and temperature is collisions // I'm not so sure about that. Isn't the ideal gas law derived based on no collisions?   

       It seems like a simpler explanation would be: Some component of the temperature gradient is indeed caused by the pressure difference because if any air currents move a mass of air from lower altitude to higher, the pressure drop will cause the temperature to drop in that mass of air.   

       Furthermore, if this idea could work, this would happen naturally. You'd get regions of warm air rising (thermals) and regions of cool air falling. Oh, wait, it does happen: gnerally not at night or in the early morning, but turbulence increases duringthe day after the sun has been out for a while. I guess as long as you're happy with this only being effective during part of the day when it's hot out, it seems like this could work.   

       In a large city, you might need a taller tower because there might be a rising column of warm air above the whole city. If the wind blows that column enough to the side so your tower gets fresh cool air, it will work. If you tower is inside the column of warm air from the city, it won't.
scad mientist, Mar 11 2014

       I just thought to myself, "Why is PV = nRT ?", and then really just speculated some. I'd forgotten the model got rid of complications like collisions.   

       "Temperature is collisions" is terrible science, but I'll attempt to clarify the bad science I was fumbling for through the dim memories. It's just this: temperature measurement as a mechanism would be based on the particles of the measured substance communicating with those of the measured substance - the simplest such, being direct impacts. So with one's skin as measuring instrument (and pretending not to know of strange things like radiation tickling one's electrons etc) the temperature you perceive will at least be partially attributable to air molecules colliding with you, and dumping some energy as they're reflected...   

       And as I write this, I find I'm reflecting (the other way), and it more and more seems that impacts would have a fairly small causative effect, and that there's a lot more of this strange radiation stuff than I'd bargained for.   

       So Why is PV = nRT ? (The equation says T goes down, as you go up, in quite a direct way, but maintains innocence as to the mucky details of why).   

       And yes, upon reflection, all you really need for a lower temperature is less of the stuff that causes it - however the causes may operate.
skoomphemph, Mar 11 2014


back: main index

business  computer  culture  fashion  food  halfbakery  home  other  product  public  science  sport  vehicle