It’s no secret that the way to win fame and fortune in physics is to invent a better refrigerator. Michael Faraday and James Prescott Joule and J. J. Thomson (Lord Kelvin) were all thinkers or tinkerers in refrigeration; the Kelvinator brand alludes to the last of those pioneers. Einstein and Leo Szilard held dozens of patents on refrigerator designs. And workers in cryogenics have won at least 10 Nobel prizes, starting with Heike Kammerlingh Onnes in 1913.
Here’s the latest cool idea on how to chill out: Let the hot atoms in a fluid escape through nanopores that block the lower-energy atoms. William J. Mullin of the University of Massachusetts in Amherst and Neal Kalechofsky of Oxford Instruments America Inc. suggests three ways this might work. The abstract of their recent paper:
We consider the possibility of adding a stage to a dilution refrigerator to provide additional cooling by “filtering out” hot atoms. Three methods are considered: 1) Effusion, where holes having diameters larger than a mean-free path allow atoms to pass through easily; 2) Particle waveguide-like motion using very narrow channels that greatly restrict the quantum states of the atoms in a channel. 3) Wall-limited diffusion through channels, in which the wall scattering is disordered so that local density equilibrium is established in a channel. We assume that channel dimensions are smaller than the mean-free path for atom-atom interactions. The particle waveguide and the wall-limited diffusion methods using channels on order of the deBroglie wavelength give cooling. Recent advances in nano-filters give this method some hope of being practical.
The plan sounds a little like Maxwell’s demon without the demon. The nanopores don’t have to be opened and shut for individual atoms; they discriminate naturally between various energy states of the atoms. Or at least that’s what Mullin’s and Kalechofsky’s calculations suggest; the crucial experiment has yet to be performed.
arXiv link: Theory of cooling by flow through narrow pores.
Update 2006-05-16: Oops. Lord Kelvin = William Thompson. Lord Kelvin ≠ J. J. Thompson.