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I'm one of the authors / people working on this. Yep, radiators like the ones on the ISS are pretty much the dominant/only ways to get heat out in space. In re
by ar813 9y ago
I'm one of the authors / people working on this. Yep, radiators like the ones on the ISS are pretty much the dominant/only ways to get heat out in space.
In response to your questions: yes, it can in fact cool below the ambient air temperature entirely passively (even during the day! -- which adds real value for cooling applications). We've shown in other recent work that you can use this effect to cool as much as 45-50°C below the ambient air temperature, if you insulate the radiator perfectly.
The reason this works here on Earth is that some upward thermal radiation isn't absorbed and re-emitted back to you. So if you start at the air temperature, looking upwards, you will be sending more heat out than the sky sends back to you. This allows an upward-looking surface to cool itself down until the heat going out and coming back to it balance out.
- leggomylibro 9y agoWow, cool. Well, thanks for doing this sort of research! Better cooling could save us a whole lot of energy :)
- bronz 9y agothis is such amazing work! how expensive are these radiators before and after scaling production? ignoring the pumps, how long should they last without repair?
- ar813 9y agoThe great thing is that we can use existing manufacturing processes (which we are already using) to do this extremely cheaply at large volumes. So the cost at scale will be competitive and make economic sense for customers. Our focus is on packaging this into a compelling product that delivers large electricity savings. Lifetimes of 20+ years are expected.
- leggomylibro 9y agoSo are those normal thin-film deposition processes? I don't know much about those, but am interested in them - are any of the materials particularly tricky to work with? Or can you just sputter the oxides one-by-one onto a silver substrate?
- killjoywashere 9y agoThanks for jumping in! How many installed square feet of real estate do I need to be equivalent to my 3 ton air conditioner (which needs 4 square feet)?
- fpoling 9y agoDoes this work when humidity is high? Water absorbs thermal infrared and emits it back.
- ar813 9y agoYou can still get cooling, but you get less heat rejection per unit area in high humidity because of the effect you point out.
- TheSoftwareGuy 9y agoAs someone who is very unknowledgeable about this subject area, what kind relationship between humidity and lost heat rejection would there be? I ask because as someone who has lived most of his life in southern Florida, this kind of device could reduce electricity bills massively around here, as long as the humidity isn't too much of a problem
- lysium 9y agoYou heat the surrounding humid air instead of sending the heat into space.
- derekp7 9y agoIf there is even a slight breeze blowing, then wouldn't that move enough of the heated humid air out of the way?
- versteegen 9y agoNo significant difference. The point is that the more opaque the air is to infrared, the more your panels are in thermal equilibrium with the surrounding air (ambient air temperature) rather than space (2.7K). They're in equilibrium with a weighted combination of those. Doesn't matter whether you heat up the surrounding air by 0.01 degrees.
- fpoling 9y ago
- remcob 9y ago> 45-50°C below the ambient air temperature That's incredible! Isn't that enough to run a heat engine on? If so, does this allow you to extract (nearly) free energy out of the ambient heat?
- jackhack 9y agoThat differential could run a Sterling engine.
- 52-6F-62 9y agoMy god, that could be a great asset to communities in water-starved regions of the planet.
- deleted 9y ago[deleted]
- GregBuchholz 9y agoYou can run a Stirling engine on much lower temperature differentials: https://en.wikipedia.org/wiki/Applications_of_the_Stirling_engine#cite_ref-39 https://en.wikipedia.org/wiki/Applications_of_the_Stirling_e... https://www.amazon.com/Three-Stirling-Engines-Without-Machine/dp/1452806578/ref=pd_bxgy_14_img_2?_encoding=UTF8&psc=1&refRID=Z2TQKMTYW3NWT3FAF5G7 https://www.amazon.com/Three-Stirling-Engines-Without-Machin...
- eternauta3k 9y agoThat differential was quoted for perfect insulation. Plugging in a heat engine is the opposite of insulation.
- TheSpiceIsLife 9y agoIt all comes down to units of thermal rejection per area per unit lifetime cost. If either one of those values is less than desirable expectations will fall short.
- clord 9y ago
- Ono-Sendai 9y agoThat's cool. But presumably any surface insulated in this way will reach equilibrium with the atmosphere/space in a similar way, correct?
- ohyes 9y agoCould you point the beams at something and heat it up? It seems like a waste just sending it into space.
- jdmichal 9y agoI can't think of any scenario where you would be better off recapturing that IR beam instead of installing photovoltaics and capturing the stronger sunlight. Also, removing heat from the Earth is probably a positive at this point in time.
- ohyes 9y agoThe problem is that the heat is in the wrong place, right? We're not going to stop needing electricity. If you've got an IR beam and you can point it at something you can heat whatever it is and run a generator. You need to cool the building anyway, so the added energy from displacing the beam to a (presumably turbine) generator would essentially be 'free.' This is more efficient than the photovoltaic because you don't have to produce install and maintain a photovoltaic (all of which costs some energy), and you were going to cool this building with this method anyway (so there's little downside to harvesting the energy aside from complexity, which is a concern). I assume you'd need line of sight from the panel to the generator, which it does seem would be tricky, but doesn't seem insurmountable. (Put the collector on a tower for example, in most areas of the country I think it wouldn't have to be higher than a few hundred feet). It just depends on how much heat you're displacing and whether you can collect enough to run the generator. If it were "I'm just trying to produce energy", I'd agree that the photovoltaic is better, but if this system happened to be dual use and doing two things we already want to do, it seems like it would be a pretty substantial win.
- diggernet 9y agoMy understanding of this is that the amount of heat transmission depends on the temperature of your target. You point it at outer space (cold), and you get a win. You point it at some sort of IR collector (necessarily at ambient temperature, or higher), and you've lost your cooling ability.
- phkahler 9y agoTwo questions: 1) Does it emit more IR at higher temperatures? In other words, would pumping hot water through/under it produce larger temperature drops? 2) Is it weather proof, or do you still need to find a coating that protects it while not blocking the IR?
- ar813 9y agoYes, it emits more radiation/ heat when hotter. A nice feature of radiation is that scales as T^4. It's pretty durable on its own. That being said, as we've moved to the product stage we've packaged it in a way to protect it further.
- todd8 9y agoI'm not sure why, but I've always thought it interesting that radiation scales as a fourth power. It's unusual to see forth power relationships in fundamental scientific processes.
- phkahler 9y agoBlack body radiation scales with T^4, but you're relying on one particular band. I suspected it scaled, but T^4 seems rather unlikely ;-)
- geomark 9y agoI would assume it scales at K*T^4 where K is a constant < 1 and gets smaller as the band narrows.
- marcosdumay 9y agoMost materials scale with T^4. You would need a very weird radiance spectrum to do anything different. That said, we are talking about something that has a weird radiance spectrum as a selling point, so, expect some deviation from the standard T^4 curve.
- xenadu02 9y agoI assume this is negatively affected by cloud cover, but I'm curious to what degree.
- mark-r 9y agoI was curious too, because the article was very specific about the wavelengths emitted. I found some sources saying that the 8-13 um wavelengths are in a band that isn't absorbed much by water vapor, e.g. https://wattsupwiththat.com/2008/06/18/a-window-on-water-vapor-and-planetary-temperature/ https://wattsupwiththat.com/2008/06/18/a-window-on-water-vap....
- samstave 9y agoCan you apply this technology - coupled with AeroGel based insulation of radiators - to shipping containers/container walls? This would allow for a really low cost refridgerated/temp-controlled containter. Then have a small requirement for a solar panel to pump some fluids. The result would be the ability to have shipping containers that can maintain temps with extremely low cost/energy requirements and you might revolutionize the ability to ship foods around places like Africa. Also - can this be applied in any way as a "paint"? Such that you paint cars, roofs or whatever with this?
- ijidak 9y agoThis is brilliant! Specifically the container idea!
- grondilu 9y ago> if you insulate the radiator perfectly. I don't quite understand what that means. If your radiator is supposed to radiate away the surrounding heat, shouldn't it on the contrary be connected as much as possible to the environment?
- throwaway76543 9y agoNo, because the heat is radiated through infrared -- not conduction and convection. Any heat transfer by conduction/convection is going to be warming the thing you want to cool and will be working counter to the purpose of the device. Conduction, convection and radiation.
- durkie 9y agomy understanding is what you're talking about only applies for traditional conduction/convection, where you're expecting moving air/water/... to act as a heat-transfer medium, so you want to maximize your surface area of your radiator and fluid flow rates to facilitate that transfer. what they're doing here is shifting the transmission characteristics of radiation to be within the infrared window (https://en.wikipedia.org/wiki/Infrared_window https://en.wikipedia.org/wiki/Infrared_window) so that it's kind of like surrounding air (and water vapor, most importantly) aren't present at all and you're radiating in to the giant cold heatsink that is space.
- durkie 9y agoany chance yall are hiring? :)
- deleted 9y ago[deleted]
- murukesh_s 9y agoWondering if the radiation tech could work in sending the heat generated from other sources like clothes dryers etc as well?
- dzhiurgis 9y agoI find hard to believe that without your special cover, the heat would travel 10-100km up to atmosphere and then reflect right back onto the radiator. What I am missing?
- yorwba 9y agoYou're missing the bits of atmosphere right under (and inside) your nose. It's also not like other wavelengths are reflected right back, but when the atmosphere can absorb them, it will also emit them. (Radiation tends to be symmetric like that.) Conversely, the emitting panel will absorb this radiation, until equilibrium is reached. That means that you need to use wavelengths where the air isn't literally glowing, if you want radiation cooling to work at all.
- nerpderp83 9y agoIs this related to how ice can form in the desert at night?