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A First: Directing Heat in Solids

A device that controls the direction of heat flow could one day have valuable uses in microelectronics and energy-efficient buildings.

By Prachi Patel

Wednesday, November 22, 2006

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Scientists have been precisely controlling electric current for decades, building diodes and transistors that shuttle electrons around and make computers and cell phones work. But similarly controlling the flow of heat in solids stayed in the realm of theoretical physics--until now.

Alex Zettl and his colleagues at the University of California, Berkeley (UC Berkeley), have shown that it is possible to make a thermal rectifier, a device that directs the flow of heat, with nanotubes. If made practical, the rectifier, which the researchers described in last week's Science, could be used to manage the overheating of microelectronic devices and to help create energy-efficient buildings, and it could even lead to new ways of computing with heat.

Heat can be thought of as made of tiny packets of vibrations called phonons. A thermal rectifier allows phonons to move only in one direction. But rectifying heat is much harder than rectifying electric current, because most heat transport in materials is by diffusion, which is random, says Arunava Majumdar, a mechanical engineer at UC Berkeley and a coauthor of the Science paper. "The vibrations are not charged, so you can't bias them."

The nanotube thermal rectifier is the first experimental proof that such a device works. "From that point of view, I think it's really interesting," says Michel Peyrard, theoretical physicist at the Ecole Normale Superieure, in Lyon, France. Four years ago, Peyrard and a team of fellow European physicists first proposed a plan for making a thermal rectifier. The basis of the European physicists' scheme was that dissimilar materials conduct heat in various ways at different temperatures. They proposed making a thermal rectifier by combining such materials. But they never ventured into experimental physics to demonstrate their idea.

Other theorists have suggested that if a one-dimensional system has more mass at one end, heat would flow from that end to the low-mass end. Zettl's graduate student Chih-Wei Chang decided to test this theory by making rectifiers with nanotubes, because their extremely narrow width makes them nearly one-dimensional. Plus, they're known to be efficient heat conductors.

Comments

  • Heat Diode
    Nanotubes in heat pipes?
    Rate this comment: 12345

    abcarterjr
    11/23/2006
    Posts:45
    Avg Rating:
    4/5
    • Re: Heat Diode
      I'm no nano engineer but it sounds to me like they are making nano tubes in random plates of metal and putting a controlled surge of energy through it to find out where the heat goes. once they figure out where the heat goes they can figure out why and how it works that way so we can possibly make devices that utilize this technology which would in turn make electronic devices more efficient.
      Rate this comment: 12345

      pickleman
      11/28/2006
      Posts:1
      • Re: Heat Diode
        geometry and type of material will certainly matter to constact a HEAT DIODE OR RECTIFIERs.
        Rate this comment: 12345

        sanjeevkumar
        02/12/2007
        Posts:1
  • More Infomation
    Im curently doing a thesis on understanding more about the thermal rectifier.. can anyone lead me in the right way? any reference are greatly appreciated..
    Rate this comment: 12345

    salvo
    08/28/2007
    Posts:1

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