US engineers pave way for 'flat panel fridge'

The bulky compressors and pipes that refrigerators rely on could one day be replaced by flat sheets of polymers, according to American researchers who are investigating materials that change temperature in an electric field.

In a project backed by the US Department of Energy, engineers at Penn State University have been looking at how they could harness the properties of ferroelectric polymers that exhibit temperature changes at room temperature under an electrical field.

Most conventional cooling systems rely on the change in density of gases as they are pumped through a network of pipes. Other groups have explored magnetic field refrigeration, but the Penn State team believe electricity will prove to be a more convenient alternative.

Their approach exploits the way in which the molecular structure of some polarpolymers, such as poly(vinylidene fluoride-trifluoroethylene) and poly(vinylidene fluoride-trifluoroethylene)-chlorofluoroethylene, changes from its natural disorganised state to an organised one in the presence of an electric field. This means the material gives off heat and becomes colder, absorbing heat and reverting to its disordered state when the electricity is turned off.

Writing in the 8 August 2008 issue of Science, the researchers claim to have achieved a change in temperature of about 22.6 degrees Fahrenheit and predict that repeated randomizing and ordering of the material combined with an appropriate heat exchanger could provide a wide range of heating and cooling temperatures.

"This is the first step in the development of an electric field refrigeration unit," said Professor Qiming Zhang, who led the research. "For the future, we can envision a flat panel refrigerator. No more coils, no more compressors, just solid polymer with appropriate heat exchangers."

Because the polymers are flexible and can be used for both heating and cooling, they have many potential applications, Zhang added. In clothing, for example, he suggests they could be used to make protective gear for fire fighters, mittens and socks, or even for  making the heavy costumes worn by sports mascots and theme park characters more comfortable.



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