Page last updated at 02:22 GMT, Tuesday, 19 August 2008 03:22 UK

Flat-panel fridge method unveiled

fridge of plenty
Cooling this is costly and noisy

A new approach to refrigeration and cooling could make for high-efficiency, portable, and quiet refrigerators in the future.

The method works by repeatedly applying an electric field to long molecules called polar polymers.

Advocates of the method say it will achieve a significant increase of efficiency over conventional cooling.

The technology could also be applied to flexible applications such as self-cooling clothing.

Such a scheme could take a bite out of the 15% of total energy consumption in the UK that is dedicated to refrigeration.

Cooling with rubber

Conventional refrigeration and air conditioning work by compressing a refrigerant, which grows cold as it is allowed to rapidly expand. The refrigerant is then circulated around to remove heat from fridges or air that is then used for cooling.

While environmentally unfriendly chemicals have been removed from air conditioners and refrigerators, the process is still noisy and relatively inefficient.

The new method instead takes its cooling power from the ordering and disordering of the polymers, which are distributed in a thin film just a millionth of a metre thick.

In an electric field, the molecules spontaneously line up, creating heat. Removing the field causes the polymers to cool down again as a result of the electrocaloric effect.

This energy-from-order is evidenced when stretching and releasing a rubber band; stretching it lines up the mess of its constituent long molecules, warming it up.

If the temperature at which these transitions occur is near the temperature of the desired cooling, the effect can be exploited.

Though the temperature range of the new work is still too high to result in ice-cold beer, it has achieved a cooling of 12C, showing that polar polymers might just do the trick.

Cooling with magnets

A similar idea called magnetic refrigeration has existed for years, employing certain materials with "magnetic dipoles" that act like tiny compass needles. Cycling the materials through a magnetic field performs a similar order/disorder dance that can remove heat.

laptop thermal image
The approach could do away with laptop fans

That approach is projected to be 40% more efficient than conventional cooling. But it presents a number of engineering difficulties, and for the moment relies on gadolinium, a rare metal, to achieve significant results.

The electrocaloric approach will be much more efficient than magnetic cooling, according to Qiming Zhang, the Pennsylvania State University professor who published the new results in the journal Science.

"Compared with magnetic cooling, electric field-regulated cooling devices are much easier to operate, with much lower cost," says Prof Zhang.

The approach could make for simpler, lighter portable coolers, and could be applied to cooling everything from microelectronics to firefighters' protective clothing.

Karl Sandeman, a materials scientist from the University of Cambridge who works on magnetic cooling says that the electrocaloric approach might prove to have certain advantages particularly for miniature applications like electronics.

However, Dr Sandeman says, magnetic cooling solutions are closer to market and many of the engineering challenges that have faced magnetic cooling will crop up in the case of electrocalorics.

In both cases, the market will be hard to break into. "The refrigeration industry has had a solution that works for the last 100 years, so innovation teams are usually quite small," he says.




SEE ALSO
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