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posted by Fnord666 on Tuesday February 14 2017, @06:37AM   Printer-friendly
from the that's-pretty-cool dept.

If heat is not your thing, rejoice: A thin plastic sheet may soon provide some relief from the intense summer sun. The film, made from transparent plastic embedded with tiny glass spheres, absorbs almost no visible light, yet pulls in heat from any surface it touches. Already, the new material, when combined with a mirrorlike silver film, has been shown to cool whatever it sits on by as much as 10°C. And because it can be made cheaply at high volumes, it could be used to passively cool buildings and electronics such as solar cells, which work more efficiently at lower temperatures.

During the day most materials—concrete, asphalt, metals, and even people—absorb visible and near-infrared (IR) light from the sun. That added energy excites molecules, which warm up and, over time, emit the energy back out as photons with longer wavelengths, typically in the midrange of the infrared spectrum. That helps the materials cool back down, particularly at night when they are no longer absorbing visible light but are still radiating IR photons.

[...] So they [Xiaobo Yin and his team] bought a batch of glass powder from a commercial supplier and mixed it with the starting material for a transparent plastic called polymethylpentene. They then formed their material into 300-millimeter-wide sheets and backed them with a thin mirrorlike coating of silver. When laid across objects in the midday sun, the bottom layer of silver reflected almost all the visible light that hit it: The film absorbed only about 4% of incoming photons. At the same time, the film sucked heat out of whatever surface it was sitting on and radiated that energy at a mid-IR frequency of 10 micrometers. Because few air molecules absorb IR at that frequency, the radiation drifts into empty space without warming the air or the surrounding materials, causing the objects below to cool by as much as 10°C. Just as important, Yin notes that the new film can be made in a roll-to-roll setup for a cost of only $0.25 to $0.50 per square meter.

An abstract of the paper is available online.

Yao Zhai, et al. Scalable-manufactured randomized glass-polymer hybrid metamaterial for daytime radiative cooling, Science, 09 Feb 2017, DOI: 10.1126/science.aai7899


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  • (Score: 1, Interesting) by Anonymous Coward on Tuesday February 14 2017, @08:31AM

    by Anonymous Coward on Tuesday February 14 2017, @08:31AM (#466897)

    To quote: 'When laid across objects in the midday sun, the bottom layer of silver reflected almost all the visible light that hit it: The film absorbed only about 4% of incoming photons.'

    Meaning it would be patently USELESS attached to a solar panel since it would REFLECT ALL THE PHOTONS THE SOLAR PANELS WOULD OTHERWISE USE TO GENERATE ELECTRICITY. Unless of course it is glossing over what frequencies of light the sheeting actually absorbs/reflects and in fact means it is transparent (the summary implies it is essentially a lightweight mirror, meaning *ALL* light is reflected and the silver coating is opaque)

    Now as a portable flexible reflective surface this would be quite useful, including as an ablative armor against directed energy weapons (multiple layers each reducing laser power by 96 percent before ablating could be just enough to take out a laser based anti-missile battery for instance.

    If someone has full access to the article, be sure to mirror and seed it (via I2P or similiar if possible) before it gets classified and black holed (assuming it is sufficient to manufacture a material sample with.)

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  • (Score: 1, Informative) by Anonymous Coward on Tuesday February 14 2017, @09:24AM

    by Anonymous Coward on Tuesday February 14 2017, @09:24AM (#466903)

    be sure to mirror and seed it (via I2P or similiar if possible)

    1. public info available on twitter page [twitter.com]: http://scihub22266oqcxt.onion [scihub22266oqcxt.onion]
    2. temporary enable scripts for that site
    3. type in the "DOI:10.1126/science.aai7899" and hit enter
    4. Enjoy reading the 9 pages

  • (Score: 3, Insightful) by c0lo on Tuesday February 14 2017, @10:31AM

    by c0lo (156) Subscriber Badge on Tuesday February 14 2017, @10:31AM (#466910) Journal

    multiple layers each reducing laser power by 96 percent before ablating

    Twas 96% of the Sun's irradiation at noon. No warranties for higher incoming flux.

    Look, an Al foil has a reflectivity of 88% [wikipedia.org] - only 8% lower than the TFA quoted value.
    Based on your logic, just wrap 8% more Al-foil around that missile and there you have it.

    --
    https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
    • (Score: 2) by q.kontinuum on Tuesday February 14 2017, @12:21PM

      by q.kontinuum (532) on Tuesday February 14 2017, @12:21PM (#466923) Journal

      Knowing that we are bullshitting here, just for the sake of argument:

      Look, an Al foil has a reflectivity of 88% - only 8% lower than the TFA quoted value.
      Based on your logic, just wrap 8% more Al-foil around that missile and there you have it.

      Not really. The amount of foil would probably grow exponentially or worse. Your calculation would be correct if the ablation rate was the same for both foils, but due to the higher energy-absorbtion the ablation-rate would also be increased. Additionally, it would heat up the lower layers faster, which might speed up the process even more.

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      • (Score: 2) by c0lo on Tuesday February 14 2017, @01:45PM

        by c0lo (156) Subscriber Badge on Tuesday February 14 2017, @01:45PM (#466932) Journal

        Your calculation would be correct if the ablation rate was the same for both foils, but due to the higher energy-absorbtion the ablation-rate would also be increased.

        The increase in ablation rate is compensated by the increase of the number of protected layers that need to be ablated, no BS here.

        Additionally, it would heat up the lower layers faster, which might speed up the process even more.

        One can only wish the phenomena would be that simple.
        1. higher mass means higher thermal capacity dissipation - just think of the fun of soldering/welding a thick sheet of metal with an under-powered heat source. I have a feeling that navy laser [wikipedia.org] can be easily defeated by simply "armouring" the protected surface with a layer of flowing water (if you watch the video in the linked, takes 2-3 seconds at 30kW power to destroy some unprotected ordnance. Image it being doused in water, 4 kJ to raise the temperature of 1 litre of water by one degree; low tech defence - a pump and a hose, throwing 10 l water/sec over the object to be protected);
        a2 at high and concentrated power, a significant amount of ablated material is vaporized, diffusing/scattering the energy beam. E.g. a valid counter-measure to that navy laser - just use smoke. Be smart, use a smoke flare creating titanium oxide - highly reflective (diffuse) and refractory

        --
        https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
  • (Score: 2) by JoeMerchant on Tuesday February 14 2017, @09:39PM

    by JoeMerchant (3937) on Tuesday February 14 2017, @09:39PM (#467109)

    I believe the magic foo here is the semi-one-way radiation of heat based on the combination of glass spheres and silver film - put that on the back of a solar panel and it could radiate heat more effectively than an uncoated panel because the heat energy is being radiated at a wavelength not absorbed (as much) by air as the normal heat radiation.

    Reflection of sunlight is just a very common use case, with different requirements than solar panels.

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