Engineers at Penn State have developed a new method of running a refrigerator that doesn’t require a compressor. Rather, it changes the level of organization in a solid to change the temperature. This change in entropy results in heat-transfer.
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.
The researchers report a change in temperature for the material of about 22.6 degrees Fahrenheit, in today’s (Aug. 8) issue of Science. Repeated randomizing and ordering of the material combined with an appropriate heat exchanger could provide a wide range of heating and cooling temperatures.
“These polymers are flexible and can be used for heating and cooling, so there may be many different possible applications,” said Zhang, also a faculty member of Penn State’s Materials Research Institute.
Aside from the issue of environmental contamination from some coolants, this technology looks like it would be really helpful in making smaller cooling elements. While the actual temperature where these experiments were performed was around 160 degrees F (70 degrees C) — a little high to use in a refrigerator, the researchers indicate that there are many different types of these polymers. Some may be functional at lower temperatures.
Interesting stuff. The actual paper is here.