Thursday, August 7, 2008
University Park, Pa. -- Refrigerators and other cooling devices may one day
lose their compressors and coils of piping and become solid state, according to
Penn State researchers who are investigating electrically induced heat effects
of some ferroelectric polymers.
"This is the first step in the development of an electric field refrigeration
unit," says Qiming Zhang, distinguished professor of electrical engineering.
"For the future, we can envision a flat panel refrigerator. No more coils, no
more compressors, just solid polymer with appropriate heat exchangers."
Other researchers have explored magnetic field refrigeration, but electricity
is more convenient.
Zhang, working with Bret Neese, graduate student, materials science and
engineering; postdoctoral fellows Baojin Chu and Sheng-Guo Lu; Yong Wang,
graduate student, and Eugene Furman, research associate, looked at ferroelectric
polymers that exhibit temperature changes at room temperature under an
electrical field. These polarpolymers include poly(vinylidene
fluoride-trifluoroethylene) and poly(vinylidene
fluoride-trifluoroethylene)-chlorofluoroethylene, however there are other
polarpolymers that exhibit the same effect.
Conventional cooling systems, -- refrigerators or air conditioners -- rely on
the properties of gases to cool and most systems use the change in density of
gases at changing pressures to cool. The coolants commonly used are either
harmful to people or the environment. Freon, one of the fluorochlorocarbons
banned because of the damage it did to the ozone layer, was the most commonly
used refrigerant. Now, a variety of coolants is available. Nevertheless, all
have problems and require energy-eating compressors and lots of heating
coils.
Zhang's approach uses the change form disorganized to organized that occurs
in some polarpolymers when placed in an electric field. The natural state of
these materials is disorganized with the various molecules randomly positioned.
When electricity is applied, the molecules become highly ordered and the
material gives off heat and becomes colder. When the electricity is turned off,
the material reverts to its disordered state and absorbs heat.
Full story.