Thursday, July 30, 2009

Planck's Law Breaks at the Nanoscale

Planck's Law has long been the final word on the transfer of heat between two objects. Physicists, however, have long predicted this law breaks down when objects are very close. Now amidst the heavenly glow of Next Big Future, researchers have found heat transfers can be 1,000 times greater than Planck's Law allows:

The new findings could lead to significant new applications, including better design of the recording heads of the hard disks used for computer data storage, and new kinds of devices for harvesting energy from heat that would otherwise be wasted. By using the glass (silica) beads, they were able to get separations as small as 10 nanometers (10 billionths of a meter, or one-hundredth the distance achieved before), and are now working on getting even closer spacings.

The new findings could also help in the development of new photovoltaic energy conversion devices to harness photons emitted by a heat source, called thermophovoltaic, Chen says. "The high photon flux can potentially enable higher efficiency and energy density thermophovoltaic energy converters, and new energy
conversion devices," he says.

Next Big Future had a post on micron gap thermal photovoltaics, an obvious beneficiary of this discovery, posted earlier.

Thermal photovoltaics use solar cells to convert the light that radiates from a hot surface into electricity. The first applications will be generating electricity from waste heat, eventually the technology could be used to generate electricity from sunlight far more efficiently than solar panels do. In such a system, sunlight is concentrated on a material to heat it up, and the light it emits is then converted into electricity by a solar cell.

In a thermal photovoltaic system, light is concentrated onto a material to heat it up. The material is selected so that when it gets hot, it emits light at wavelengths that a solar cell can convert efficiently. As a result, the theoretical maximum efficiency of a thermal photovoltaic system is 85 percent.

In practice, engineering challenges will make this hard to attain, but DiMatteo says that the company's computer models suggest that efficiencies over 50 percent should be possible. The prototypes aren't this efficient: they convert about 10 to 15 percent of the heat that they absorb from the glass-factory exhaust into electricity, which DiMatteo says is enough to make the devices economical.

- Brewskie

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