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Science Technology

Carbon Nanotube Device Channels Heat Into Light (phys.org) 102

An anonymous reader quotes a report from Phys.Org: Rice University scientists are designing arrays of aligned single-wall carbon nanotubes to channel mid-infrared radiation (aka heat) and greatly raise the efficiency of solar energy systems. Their invention is a hyperbolic thermal emitter that can absorb intense heat that would otherwise be spewed into the atmosphere, squeeze it into a narrow bandwidth and emit it as light that can be turned into electricity. The aligned nanotube films are conduits that absorb waste heat and turn it into narrow-bandwidth photons. Because electrons in nanotubes can only travel in one direction, the aligned films are metallic in that direction while insulating in the perpendicular direction, an effect called hyperbolic dispersion. Thermal photons can strike the film from any direction, but can only leave via one. Adding the emitters to standard solar cells could boost their efficiency from the current peak of about 22%. "By squeezing all the wasted thermal energy into a small spectral region, we can turn it into electricity very efficiently," he said. "The theoretical prediction is that we can get 80% efficiency." The study has been published in the journal ACS Photonics.
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Carbon Nanotube Device Channels Heat Into Light

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  • How does a material become one way only for electrons?

    • by ceoyoyo ( 59147 )

      When they say one way I think they mean in one dimension only. The electrons can move longitudinally along the tubes (either direction) but they can't move in either perpendicular direction (through the walls).

    • Re:Maxwell's Demon (Score:5, Informative)

      by ShanghaiBill ( 739463 ) on Friday July 12, 2019 @11:20PM (#58917838)

      How does a material become one way only for electrons?

      Diodes do it all the time.

    • DIODES, one way for electrons is what they do. semiconductor ones have been around since 1874.

      nothing maxwell demonish about diodes.

      Nanotubes can do the diode thing too.

      • by bobby ( 109046 )

        DIODES, one way for electrons is what they do. semiconductor ones have been around since 1874.

        Hmmmm?????

        • by tricorn ( 199664 )

          Lead sulfide, "galena cat whisker", I built an AM radio as a kid from a kit using one.

          • I'm always amused at people who think everything electrical and electronic was done in the 20th century. Motors and batteries existed in the 1700s, The first fax was sent in the 1860s.

        • "In 1874, German scientist Karl Ferdinand Braun discovered the "unilateral conduction" across a contact between a metal and a mineral. " -- wikipedia

          it would be 26 years later that effect would be used in some radio receivers. Note the other type of diode at the time was thermionic, "vacuum tube", and it was invented within a year of that solid state device.

          • by bobby ( 109046 )

            Thank you for both posts. I'm an EE but have only a smattering of electronic history knowledge. Too busy studying other things. I wasn't aware that motors existed in the 1700s, but I know batteries (Voltaic Pile) and electromagnetism were discovered then. I think of 1800s as lots of electromagnets, (motors, generators, ballasts, magnets, Morse, telephone earpiece, Marconi set coils, Tesla coils, etc.) and some interesting microphones, etc. And then the thermionic emission device (vacuum tube / valve) -

    • I couldn't give you the physics details of it, but restricting movement to one direction and not the other isn't anything new. Your electronics devices have diodes, which are components that prevent the electrons from going one way, but not the other. The thing in the article is doing something similar, though I suspect it's a bit more complicated than the average diode. :)
    • If you happen to work for Monster cable, you just draw a directional arrow on the cable.

  • Holy fuck!

    • Even if they can only deliver on half of what they claim, that's still at least a "holy fuck" without the exclamation mark.

      The challenge is going to be in making this affordable, and mass-producible. Without that, these super-panels are going to be limited to space applications where weight is key and delivery cost dominates component cost.

      • by HiThere ( 15173 )

        I suspect it will be like most semi-conductor gizmos. The first 1,000 or 100,000 cost an arm and a leg. Then they figure out how to make them "easily", build the factory, and they're a lot cheaper than (well, than the competition anyway).

        The question here is how precisely does the fabrication need to be controlled, and just off hand, it sounds like "nano-scale should be good enough".

    • I'm trying to figure out from the article whether that 80% is referring to a) the efficiency of the heat conversion to narrow-band photons, b) the overall efficiency of converting the "waste" heat fraction to electricity (heat to photons + conversion to electricity), or c) the potential final efficiency of the solar cell to convert sunlight to electricity. TFA makes it sounds like c), but knowing scientific journalism sometimes, it could very well be a) or b).

      • Re: 80% efficiency (Score:4, Interesting)

        by vtcodger ( 957785 ) on Saturday July 13, 2019 @06:54AM (#58918718)

        I RTFA yesterday and I'm as confused as you are. I don't think the article author understood what the scientists told him or her. My best **GUESS** is that "they" take "waste heat" which is basically non-coherent, broadband IR radiation and pass it through the nanotubes which act as a bandpass filter that emits only a narrow band of IR frequencies on the far side? That filtered signal can then (conceptually) be converted to electricity with 80% efficiency by a suitably designed cell? What happens to the rest of the IR which is rejected(?) by the filter? I have no clue. Reflected? Absorbed and re-emitted? Transported through a wormhole to a galaxy far, far away? I would think that almost all the energy in the IR would be in the portion that has been disappeared, not the portion that is passed through and converted to electricity. i.e -- the overall conversion efficiency -- total_IR_in to electricity_out would likely be **VERY** low?

        Anyway, this sounds like it might have practical uses -- perhaps in sensors or communications. But it's far from clear to me that converting "waste heat" to electric power is one of the potential practical uses.

        • by Anonymous Coward

          It's fake news. Sure they did this in the lab, but people have tried to make carbon naotubes at industrial scale for decades. Everyone has failed; it's just too hard.

          This is a nice science experiment, but it basically says: hey we did this! Now for the easy part, making this in an industrial, high throughput way! (which is actually the hard part, what they did is easy).

        • I dug into it yesterday, and I got essentially what you got out of it.

          Prior to this, there wasn't a good way to transfer the energy in broadband IR into electricity. (Heating water -> steam turbines is the current technology.) This solves half that problem by taking potentially 80% of that broadband IR and focusing it into a narrow band IR. That makes designing a way to harness it much easier.

          Think of this as a lens for IR. Broadband IR hits the top, comes out the bottom focused.

          Where does the rest go? I

          • Not a lens? I think that if you want to focus IR, you can do that with a parabolic mirror? Maybe more like a "mechanical filter" in radio work that "stacks" a bunch of narrowband resonators to end up with a bandpass filter with a tailored bandwidth? You construct a bunch of filters with different center frequencies? And you follow each filter with a photovoltaic cell tuned to its center frequency?

            Yeah. Maybe that would work ... maybe ... I'd anticipate a few annoying problems actually getting the piec

          • by HiThere ( 15173 )

            From the summary it sounded like they were doing a frequency up-conversion.

    • I agree. 80% is pretty much a holy grail efficiency level for photovoltaics.
  • by aberglas ( 991072 ) on Saturday July 13, 2019 @12:30AM (#58917962)

    This sounds like a good way to make a perpetual motion machine.

    • Also, how does it handle minor, temporary temperature increases, like farts?

    • Low energy photons into high energy ones, Entropy?

      This sounds like a good way to make a perpetual motion machine.

      Huh? We do this all the time, it's only a perpetual motion machine if you have an impossibly high efficiency.

      A solar panel driving a UV LED converts low energy photons to higher energy ones.

    • Not even close to perpetual motion. After all, it didn't say how much energy in infrared it needs to convert it into the same amount of energy in that different frequency. Changing frequency is done all the time, both up and down, but nobody ever said the total energy changed, just the form.
  • by blindseer ( 891256 ) <blindseerNO@SPAMearthlink.net> on Saturday July 13, 2019 @04:55AM (#58918488)

    I'll believe this when I see it on the market. I expect this to cost too much to bother.

    This might make one of those pocket sized solar cell phone chargers 4 times more powerful but if it also makes it 10 times more expensive then I have my doubts on it selling to anyone but NASA and it's contractors.

    I did some work on solar power stuff in university and it became clear that the goal was not raising efficiency but lowering costs. A 10% or 20% PV panel is fine for many cases because making something bigger is typically very cheap. A solar collection power plant out in the desert is already using real cheap land. At a maximum of about 1000 watts per square meter, under a midday sun, isn't that much to work with from the start. Add in weather and day/night cycles, and it's more like 100 watts on the average. Make it cheap and we can spread it out to where this shifting sunlight isn't as detrimental on the whole. Putting that money into something expensive and efficient just means putting your time, money, and materials, into a spot that might not have been a good choice because of some random local event.

  • we're bringing back coal! Your fancy cancer-causing solar cell gimmick that no one wants will never be as cheap as good ol' W. Virginia bituminous coal. #MAGA!

    • Re: (Score:2, Interesting)

      by blindseer ( 891256 )

      we're bringing back coal! Your fancy cancer-causing solar cell gimmick that no one wants will never be as cheap as good ol' W. Virginia bituminous coal. #MAGA!

      Maybe if we didn't have the stupid laws on the mining of rare earth elements we could put those coal miners to work mining for monazite. In that monazite is all kinds of goodies for making windmill magnets and these high efficiency solar PV cells. What makes it too expensive to mine here is that the thorium and uranium byproducts are worthless. Worse than worthless. Unless there is a market for the thorium and uranium then it is considered a controlled nuclear waste material and would have to be hauled

  • Refrigeration (Score:4, Interesting)

    by ghoul ( 157158 ) on Saturday July 13, 2019 @06:52AM (#58918712)

    I know its cool to be talking renewable energy and global warming to get research funds nowadays but this (if it works) may have more application for refrigeration. Imagine ice boxes which dont need electricity to run. They just keep absorbing heat and emitting light. I can see brightly glowing refrigerator trucks driving down the highway.

  • This invention is notable not because it harvests mid-infrared light, but that it does so across a wide bandwidth. Still, it is expensive for the application indicated in the article, which is supplement PV solar panels and improve their efficiency. It will be more useful to provide a drastic improvement in RTG (Radioisotope Thermoelectric Generator) performance. The Seebeck Effect generators currently used are not very efficient, yet is used because it is solid-state and long-lasting, which is a requiremen

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