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posted by charon on Thursday February 16, @12:15AM   Printer-friendly
from the more-trouble-than-it's-worth dept.

Although scientists have been able to levitate specific types of material, a pair of UChicago undergraduate physics students helped take the science to a new level.

Third-year Frankie Fung and fourth-year Mykhaylo Usatyuk led a team of UChicago researchers who demonstrated how to levitate a variety of objects—ceramic and polyethylene spheres, glass bubbles, ice particles, lint strands and thistle seeds—between a warm plate and a cold plate in a vacuum chamber.
In the experiment, the bottom copper plate was kept at room temperature while a stainless steel cylinder filled with liquid nitrogen kept at negative 300 degrees Fahrenheit served as the top plate. The upward flow of heat from the warm to the cold plate kept the particles suspended indefinitely.

"The large temperature gradient leads to a force that balances gravity and results in stable levitation," said Fung, the study's lead author. "We managed to quantify the thermophoretic force and found reasonable agreement with what is predicted by theory. This will allow us to explore the possibilities of levitating different types of objects." (Thermophoresis refers to the movement of particles by means of a temperature gradient.)

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  • not a vacuum (how it works) (Score: 5, Informative) by butthurt (6141)

    by butthurt (6141) on Thursday February 16, @12:31AM (#467672)

    The page says the experiment was done in a vacuum chamber and that "[l]evitation of macroscopic particles in a vacuum is of particular interest" which is misleading because the Knudsen Compressor effect causing the levitation requires a gas. The pressures used were "between 1 and 10 Torr" according to the journal article, which says

    [...] air molecules coming from the hotter side transfer on average a larger momentum to the particle than those from the colder side. A net momentum transfer due to collisions with molecules overcomes gravity [...]


    • Re:not a vacuum (how it works) (Score: 5, Informative) by butthurt (6141)

      by butthurt (6141) on Thursday February 16, @12:42AM (#467677)

      more titbits that came up when I searched for information about the Knudsen Compressor effect:

      An earlier experiment of this sort was done on a rocket following a parabolic trajectory (sothat the effect of gravity was easier to overcome).

      The University of Chicago researchers have an alternate abstract on their site:

      We demonstrate levitation of micron-sized ice, ceramic, glass and polyethylene particles at low pressure (1-10 Torr) in the presence of a temperature gradient. Under thermophoresis, collisions with more energetic gas molecules from below provide a net upward momentum transfer. Particles initially levitate a few millimeters above a cold plate due to the Knudsen Compressor effect. Particles are then accelerated upwards by the thermophoretic force in the direction from hot to cold in the rarefied gas. In the appropriate pressure regime this allows for stable levitation for up to two hours. Lately we have also succeeded in levitating other materials, including thistle seeds and lint. Our future goals are to levitate water droplets, push levitated particles with a laser, and examine the dynamics behind multi-particle levitation.


  • Cute, but ... (Score: 2) by bob_super (1357)

    by bob_super (1357) on Thursday February 16, @01:04AM (#467681)

    The other night, I made some dark multi-millimeter particles levitate in an upwards flow of molecules which were rising from a hot source towards a cold one.
    Macroscopic. Normal pressure. Highly reproducible. Sub-dollar costs.
    Should I publish?

  • Sterling Engine (Score: 0) by Anonymous Coward

    by Anonymous Coward on Thursday February 16, @01:33AM (#467685)

    Isn't that how a sterling engine works?

  • Space Flight (Score: 2) by Rivenaleem (3400)

    by Rivenaleem (3400) on Thursday February 16, @08:51PM (#467954)

    This would be great to see applied to lifting space ships into orbit. They could be designed to expel vast amounts of heat downward countering the effect of gravity to produce upward motion.