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Scientists Develop "Paint" To Help Cool the Planet
AaronW writes Engineers at Stanford University have developed an ultrathin, multilayered, nanophotonic material that not only reflects heat away from buildings but also directs internal heat away using a system called "photonic radiative cooling." The coating is capable of reflecting away 97% of incoming sunlight and when combined with the photonic radiative cooling system it becomes cooler than the surrounding air by around 9F (5C). The material is designed to radiate heat into space at a precise frequency that allows it to pass through the atmosphere without warming it.
Cars being greenhouse ovens is a terrible issue. Not just because it's uncomfortable getting into the car on a hot day, but because people accidentally kill pets and children by leaving them in a hot car every year (and others not so accidentally). Surely there's better tech than what we use today to prevent our automobiles from becoming lethal ovens.
The Global Warming Scare is now over! Thanks paint!
Certainly there is. You can just cook your kids and pets at home, no need to waste the gas going out at all. Home ovens have been large enough to do this for decades now. People are so wasteful!
--Hannibal
What about the cost? If it's anything higher than $50, you can suck a D.
Scientists Develop "Paint" To Help Cool the Planet
They're calling it "White".
Seriously, though, it's a mirrored silver paint with some nanoparticles mixed in to make it even cooler (pun intended). But if people aren't painting their roofs white and silver today, do they really think their paint will change that?
On the other hand, a radiator that reflects sunlight sounds promising for other applications, like heatsinks for space probes.
How can I believe you when you tell me what I don't want to hear?
According to Wikipedia's entry on hafnium, "Hafnium reserves are projected to last under 10 years if the world population increases and demand grows."
According to the report The State of the Global Coatings Industry, the world produced 34 billion liters of paints and coatings in 2012. ...
If we assume paint production has, in recent decades, followed the economy and grown at about 3% per year, that means the total amount of paint produced equals the current yearly production times 34.[6]\((1+\tfrac{1}{0.03})\) That comes out to a little over a trillion liters of paint. At 30 square meters per gallon, "Square meters per gallon" is a pretty obnoxious unit, but I think it's not quite as bad as acre-foot (a foot by a chain by a furlong), which is an actual unit used in technical papers I was trying to read this week. that's enough to cover 9 trillion square meters—about the area of the United States.
So the answer is no; there's not enough paint to cover the Earth's land, and—at this rate—probably won't be enough until the year 2100.
It must have been something you assimilated. . . .
Vegetarian Stew
Serves 20
Peel, core, and slice one vegetarian.
Place in trunk of black car for two days.
Season to taste.
Passively cooling an object below ambient temperature seems... counterintuitive. I think I understand what's going on here, but I'd like to see some more thorough discussion. Particularly, I'd like to know how you can find any passband in which an object at ambient temperature radiates more heat than it takes in from direct solar exposure, except the bands blocked by the atmosphere.
This painting reflects infrared instead of radiating it, but does it change anything to global warming? If there is too much CO2 in the atmosphere, the heat is trapped, does reflecting instead of radiating changes the game?
Or is it just about making sure visible light is not turned into infrared by radiation?
Someone beat you to that already: http://www.bbc.co.uk/news/magazine-23944679
Sorry, not possible, as per the first law of thermodynamics.
Nope, quite possible per the first law of thermodynamics, as well as the second and zeroth laws. If the atmosphere is transparent and the object is exposed to the sky, heat can radiate from the object to space (which, even accounting for solar exposure, has a mean effective temperature well below that of air temperature in many places ~ 230K). If the air is still and the object can reflect most of the incident radiation, there is no reason why the object can't cool below air temperature. It is a completely separate mechanism of heat transfer to a different heat sink.
Left MS Windows for Linux Mint and never looked back!
Vote for Bernie in 2016!
Thank you for being a friend
Traveled down the road and back again
Your heart is true, you're a pal and a cosmonaut
And if you threw a party
Invited everyone you knew
You would see the biggest gift would be from me
And the card attached would say, thank you for being a friend.
If the air is in contact with the painted surface (at constant pressure etc.), will the warmer air not transfer its heat, so as to produce an equilibrium of equal temperatures?
It sucked. Why did they have to be on a train? That didn't make any sense at all.
For those fortunate enough to have institutional access, the research paper is here.
Quickly picking some highlights:
The atmospheric transmission window is between 8 and 13 microns. They achieved 4.9C below ambient in direct sunlight at 850 watts per square metre. Cooling power was 40.1 watts per square metre. Emissivity (equivalently absorptivity) averages about 70% in the 8-13 micron window (estimated from a plot.)
Here's a quick back-of-the-envelope calculation
90% reflective white paint: absorbs 85W/m^2
97% reflective foil: absorbs 25.5W/m^2, an improvement over white paint of ~60W/m^2
This film: emits 40W/m^2, an improvement over simple foil of ~60W/m^2.
So in this scenario, the special film gives twice the benefit compared to just going for something simple and reflective. (The 90% for white paint is guess-work. The 97% for 'foil' is just matching the special film. Perhaps someone can update the calculations with better founded values.)
The summary title is highly misleading.
It is not paint, it is a manufactured film. It cools buildings, not planets. Yes, with enough you could cool the planet, but if you wanted to take that route, it would be much more cost effective to just use aluminium foil and use a marginally larger area of it (or, indeed, white paint.) Back in the real world, the way this invention cools the planet is by reducing electricity demand for air conditioning. (I saw another article about this in which one of the authors makes exactly this point.)
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
Yes, but the equilibrium temperature of the object will be between the air temperature and the sky temperature. The object will be cooler than the air, and so heat transfer due to convection will go from the air to the object. However, the object will still be warmer than the sky, so heat transfer due to radiation will go from the object to space.
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Vote for Bernie in 2016!
Direct solar exposure is reflected, then the reflected light and internal heat radiation is modulated to a frequency that passes easily through the atmosphere. I'd have to question the efficiency of modulation, which seems to be where their breakthrough occurred.
"Ambient" is important to define here. The temperature of the air is not actually playing much of a role in the black body equation. If the sky was made of more buildings at ambient temperature, then the story would be different, but other than the sun it's mostly an open pit into which anything radiated never returns. Also keep in mind that that figure may be referencing the temperature of the air near the whole building including the lower floors; it is cooler up high on tall buildings.
The idea is that the heat provided from within the building and the heat from the 3% of sunlight that gets through the mirror all pools and the mirror material then converts it to a specific passband. So you have more heat pooling than what comes in on that passband.
How effective this system remains when contaminated with a coat of dust is a question. Also comparative advantage to absorbing the heat/light and using it to power AC.
Someone had to do it.
OK. So the original question remains how the temperature of the object can be multiple degrees cooler, in the steady state, than the ambient air. Why would those two heat flows not apprx. balance?
Been there, done that.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
You're right, the heat flows do balance; the heat entering the object from the air must exactly balance the heat leaving to space due to radiation. But heat flows from high temperature to low, so that means that Tair > Tobject > Tspace i.e. the object can (and must) be cooler than the air.
Left MS Windows for Linux Mint and never looked back!
Vote for Bernie in 2016!
They can use the old Sherwin Williams slogan: "Cover the World!"
XML is like violence. If it doesn't solve your problem, you're not using enough of it. --AC
It is possible, because the environment is not in thermal equilibrium. In particular, the film 'sees' colder temperatures at some wavelengths than at others.
Did you not think before you posted that just maybe a bunch of scientists publishing in this area and the reviewers for one of the worlds top scientific journals might possibly have a better understanding of thermodynamics than you do?
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
Is it so cheap that using this tech to get rid of excess solar energy is better than using that energy to produce electricity, to cook, to provide hot water or for some other use? I am much inclined to doubt that.
Your understanding of the process could use some polishing too.
Left MS Windows for Linux Mint and never looked back!
Vote for Bernie in 2016!
In some ways Venus is a much more attractive target for off-Earth human expansion than any of the other possibilities. Notably, it is closer to the Sun so anything solar-powered would work about twice as well. In other ways it is very unattractive indeed. One of those is surface temperature, several hundred degrees too high for most Earth life forms.
Could this stuff, or something related, help us reduce temperatures on Venus? http://en.wikipedia.org/wiki/Terraforming_of_Venus/
There was recently a building who's glass front formed a mirror reflecting sunlight enough to melt cars in London. Now they want to intentionally mass produce it?
Also, this was known and exploited long before we understood thermodynamics:
http://en.wikipedia.org/wiki/R...
How can I believe you when you tell me what I don't want to hear?
Thanks scientists.
What the material is doing (or is claimed to do, anyway) is to re-radiate incident radiation at a wavelength that can pass through through the atmosphere back out to space without being absorbed (i.e. it won't heat up the atmosphere). Since the surface can absorb heat due to convection from the air, it can re-radiate that heat as well into space. This material is not merely reflective, its radiation properties are such that essentially acts as a refrigerator; it can pull heat from the air and radiate it to space.
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Vote for Bernie in 2016!
This "modulation" happens all the time, few things in this universe are true blackbodies, most prefer to radiate in specific bands. They're apparently using a material that tends to radiate only on one narrow band at regular earth temperatures.
Not sure how much benefit this provides to the building owner, to the point that they'd be willing to cover their building in hafnium-and-silver coated panels, rather than just white paint...
You look beautiful! Incidentally, my favorite artist is Picasso.
Now we just need to develop a kick ass portal gun...
It's already Friday where I am, you insensitive clod!
It's not the ambient temperature of air that's key here, it's the ambient temperature of space, which is about 2,7K.
All objects are constantly radiating energy and receiving energy back from other things that are radiating. When two objects in radiative exchange are roughly the same temperature, this balances out. But when one is hotter than the other, the hotter one loses more energy than it takes in, and vice versa. And it's not just a little difference - radiative heat loss is proportional to the absolute temperature to the fourth power, that's a pretty big exponent. So when you're exchanging energy with space, which is so cold that it takes very sensitive instruments to be able to measure *anything*, well, that heat is simply lost.
You can see this effect for yourself by noting how cloudy nights are usually warmer than clear nights. Clouds are cold, but they're not as cold as space!
The effect of the combination of radiation, absorption, and reflection, with different band peaks for each phenomenon, manifests itself in atmospheres as a greenhouse effect (positive or negative) versus the radiative equilibrium temperature.
You look beautiful! Incidentally, my favorite artist is Picasso.
Would you care to be more specific? My explanation is pop-science simplified, but I don't see an error in it.
More detailed explanation:
In the 8-13 micron (wavelength) window, atmospheric transmittance averages about 80% (estimated from a plot in the paper.) So the energy received is about 20% of what you'd get from a black body at atmospheric temperature (plus 80% of what you'd get from space, which is negligible in comparison.) So the brightness temperature at 8-13 microns is lower than ground level atmospheric temperature. How much lower depends on the average temperature of the atmosphere along the line of sight, and where 8-13 microns falls on the black body curve at that temperature (even this is oversimplifying) and I can't be bothered figuring that out. However, if we can reflect/insulate all energy except 8-13 micron radiation, then our thermal equilibrium temperature will be the brightness temperature at 8-13 microns to which we are exposed. This is, as noted, less than atmospheric temperature at ground level.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
Is this anything more than a punchline these days? Or do some people really still take it seriously? Besides the UN and 0bama, of course. Two objects which are punchlines in their own right.
What the material is doing (or is claimed to do, anyway) is to re-radiate incident radiation at a wavelength that can pass through through the atmosphere back out to space without being absorbed (i.e. it won't heat up the atmosphere).
More importantly: If the wavelength were one that was absorbed by the atmosphere, it is also one where the atmosphere radiates heat back toward the paint.
If your frequency slot is one with "absorption", you "see" the temperature of the atmosphere - a bit cooler than the surface of the (greenhouse-effect boosted) planet, but not by enough to be exciting.
If your slot is one that is essentially fully transparent, you "see" the cosmic background (except for the tiny part of the sky that shows the sun's or moon's disk). That's about 2.7 degrees K, call it -457 Fahrenheit. Liquid helium is substantially warmer at -452.2.
The slow radiation of heat at the sky is almost completely overwhelmed by conductive and other transfers of heat into the paint, of course. Of the 530ish degrees F difference from room temperature, only nine are left.
But that's nothing to sneeze at. The inside of my well-insulated desert house gets up to about 85 in the day without air conditioning. If I could drop that by nine degrees it would be a relatively comfortable 76. (It would likely actually drop more, because the lower temperature of the surface would slow the heating and tend to even the daily cycle of temperature out further.) 85 or more is debilitating. 76, with drastically low humidity (dew point typically about 35), is actually comfy.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
the roofing materials that are used around here have been used for a long time because they do the job and also are known to me safe for capturing drinking water. What is the toxicity of this stuff? we just had our first real summer temps the other day at 42c/107.6f. I would love a cooler house but not if it is going to poison my family.
The microlayer is also highly reflective in the near infrared range as a not insignificant portion of the sun's radiation is in the near IR. It is the far IR that the material highly absorptive/emissive.
A Shadeless room is a brighter room.
"it becomes cooler than the surrounding air by around 9F (5C)"
Sorry, not possible, as per the first law of thermodynamics.
How in the hell do you think dew gets deposited on grass, cars, etc? Dew forms when the surface temperature drops below the dew point of the air, which cannot be any higher than the ambient air temperature.
FWIW, a problem from my engineering heat transfer course indicated that frost can form when the air temp is 9F/5C above freezing.
A Shadeless room is a brighter room.
Just plant s&%t loads of trees... ...10 per human per year should do it... ...surely? Thoughts?
I foresee an ice age in our future!
I'm trying to teach myself to set people on fire with my mind... Is it hot in here?
In the same way that a glass of water with an ice cube in it will be at a lower temperature than the air around it. If the ice cube was essentially infinite (ie like space) then the water will always be at a lower temperature than the air. Energy will flow from the air to the water and from the water to ice cube.
Given that heat transfer is not instant there will always be a temperature differential at each stage.
...drop everything you’re doing RIGHT NOW and come here to Siberia. 32C today, 27 this weekend.
Great innovation. I hope i can see it very soon in market for customer like us.
Sophie Evans
There is a cheaper alternative. Coat the surface with small crystals of oxidane. Its very good at reflecting heat. In large quantities it is very good at absorbing heat..
I have a driveway full that you can have for free, just bring your own shovel.
Unfortunately, it will also kill your dog and blind your children [the wavelength is just right for killing eyeball cells as they develop].
And it tastes bad. Paste is WAY better.
Sleep your way to a whiter smile...date a dentist!
White paint only reflects light, and inhibits radiative cooling since radiation follows the same curve as absorption. This surface might actually be *less* effective than a good roof-white* paint at reflecting incoming sunlight. But if you've ever been in the desert and noticed how rapidly it cools at night you've gotten a little taste of what a dramatic effect radiating into the near absolute zero blackness of space can have. There they accomplish it by having extremely low water levels in the local atmosphere, making it more transparent to normal thermal IR frequencies.
This material though promises to let us have things both ways. Even perfect blackbodies have a "preferred" frequency - the peak power band of an ideal black body object shifts with temperature, the higher the temperature the higher the frequency of peak radiation. A blackbody at Earth-normal temperatures radiates mostly in the far infrared, whereas at 5000K the sun has a fairly narrow peak centered on the visual spectrum. So a material that's reflective in (and near) the visible spectrum can reflect the majority of incoming solar energy. Meanwhile it's tuned to have good narrow-band absorption/radiation somewhere in the far infrared where the atmosphere is highly transparent, so radiated energy will be almost entirely transmitted into space and,so as long as it's pointed up at the sky, it won't be receiving much in terms of incoming energy.
* side not: roof-white is a very different color than "normal" white, since it's "whiteness" extends well outside the visible spectrum to reflect most of the sun's high-energy spectrum, whereas typical paints don't care at all what "color" they are outside the the narrow spectrum visible to our eyes.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
Look at this in another way: there is some planet with different objects placed on its surface, and these are well--isolated from each other. It would not be surprising, that each of these objects has a different temperature, would it? Because of e.g. its colour or its radiation surface. Now, let one of these objects be the air, and the other be some well--isolated, well--radiating building. Would not it be cool to put a thermodynamic engine in that building, in order to produce energy by reversing the greenhouse effect?
Selective surface coatings have been around. Regular white paint may have emissivity of 90% or more. That is what Stanford researchers are doing. The paint reflects in the visible and short IR while having high emissions in the long IR. It's actually paint that is low emissivity/low absorption in visible to long IR that's hard to find. There is silly aluminum bits in paint that's available and supposedly titanium oxide pigment would work that way but if only a little Magnesium oxide or other pigment is present then the emissivity in long IR shoots up fast.
It looks like the Stanford researchers have optimized for a transmission peak or something. There certainly isn't only one "precise frequency" that allows IR to space. Ancient people in the Middle East made ice where the air temp never dropped below freezing by using radiative cooling.
That's all I've got.
too much white there.
Since it is 1 degree (f) here this morning, I would like the paint / cover to warm my house. Although the snow on my roof does provide some insulation and would interfere with the collection of solar heat.
Passionately Indifferent
The actual article is a bit shallow on detail, but here's my interpolation...
Infra-red is quite a broad bit of the spectrum. It starts at about 800nm as light we can't quite see, and security cameras use this band with an infra-red illuminant. If we go down to about 2000nm, we are into the mid-band where some IR cameras operate. These can see hot objects but cannot people by their radiated body heat. There is a gap at about 3500nm where water vapour absorbs and emits, and cameras do not work well. Then there is another band at about 7000nm where the thermal cameras that can pick up body heat work. The cooler you are, the greater fraction of long wavelength you emit. (NB: if the exact wavelengths are important, please check as I am typing this off the top of my head).
Most black paints absorb all infra-red wavelengths equally. Some white paints will absorb the far-infra-red. What you want, and what I think they have done is to make somethng that reflects down to 2000nm, and then absorbs beyond about 400nm. This will reflect a lot of the heat from the sun, but will still radiate the heat from the building.
Does it work? Will it still work when it is dirty? I don't know, but at least it does not violate any thermodynamic principles.
Underrated film but I seem to recall that painting the atmosphere (or something similar) caused a global catastrophe. Obviously not saying this will result in the same unfortunate scenario but just found it interesting.
Bark less. Wag more.
The dust causes a problem only when it becomes so dense as to completely obscure the paint. The dust will heat up from sunlight and also heat up from the radiation from the paint. As the dust heats it will radiate infra-red back towards the paint. As long as the paint supports some level of heat conduction 'horizontally' through the paint, those tiny areas of paint that are not obscured by dust will start to radiate more and more until heat equilibrium is again established.
A light covering of dust that covered 50% of the paint would have an insignificant effect.
To improve the paint, they should add a layer of water-repellant material. The material would have to allow the transmission of the paint's radiation, but that should not be a problem. That water-repellant layer would greatly enhance the breakup of deposition of dust, dirt, and 'stuff' on the paint into small and tiny clusters. As long as the human eye can see the correct color of the paint through the grime, the paint can likely function effectively.
So what's better for the planet? Painting my roof with this stuff or covering it with solar panels?
The surface area to paint is insufficient to have a meaningful intended effect. 1) It won't stay clean for long reducing effectiveness. I know, as the former white roof of my business is now a spotted light gray. 2) Coating adhesion is not eternal. It's expensive to repaint often. 3) The greenhouse effect would just bounce much of the reflected infrared right back to heat up some other part of the earth. Paint to cool the planet is a nice idea, but terribly useless. Just go plant a tree somewhere and call it a day .
There's actually some truth to this, albeit in harsh words. Slaves were bought, not stolen, from tribal elders who didn't care except for the riches they received in exchange for their own people. And U.S. didn't start the trade, it was started way before america was discovered, about 10,000 years ago. It still exists today, but not in the U.S. Racial inequality? Does not exist, you are creating this yourself. Act like a human being and you will be treated as one. People should do their homework before jumping to conclusions. It's already over, has been for a long time, get over it and make your own life better without blaming everyone else. You are in control of your life, do something about it, or continue as you are and be miserable.
Yes, one of those will be better, but which one depends on what you do, and you haven't given any details to work that out, so you'll have to make do with just a "Yes".
Think of a ground frost. At night thermal radiation from the ground goes through the atmosphere resulting in cooling but air can only radiate weakly (it is transparent) so cools far less. The result is that the ground ends up colder than the air.
I'm tired of all these green-eyed fanatics wanting to terraform earth back to their own favorite version of 1970. How about instead of permenantly altering the biosphere, you do this: make a giant glass window the size of a truck tire. Launch it into space and put it far enough away that all of the light that the earth receives is through that window. Now you can electrically "tint" that windown and restrict all the sunlight you want...and if you screw anything up, we can reverse it and btch slap all of you and take your remote control away. We all win. Thank you, earth.
Free energy. If it's constantly cooler than ambient, paint the bottom of a peltier, expose the top to sunlight.
I wonder if one could paint this on a wood stove to increase the heart output.