Magnetic refrigerator gets down and homey

Peter Weiss

Household fridges and magnets have long had a surface relationship. Now, they may be warming up—actually, cooling off—to a more intimate involvement. Researchers have unveiled a new cooling system that chills by means of magnets, operates at room temperature, and can fit inside home appliances.

Magnetic refrigerators and air conditioners promise to be more efficient than conventional ones, says Karl A. Gschneidner Jr. of the Department of Energy's Ames (Iowa) Laboratory. Also, magnetic appliances would circulate water or relatively benign antifreeze fluids instead of ozone-depleting refrigerants, he adds.

Not a new technology, magnetic cooling has been used for more than 50 years by cryogenics specialists to chill already ultracold substances to even lower temperatures. A few years ago, a team led by Gschneidner and Carl B. Zimm of the Astronautics Technology Center in Madison, Wis., demonstrated a magnetic refrigeration unit that operated at room temperature (SN: 3/28/98, p. 197: http://www.sciencenews.org/pages/ sn_arc98/3_28_98/fob3.htm). However, the device required a cryogenically cooled, electrically powered superconducting magnet, making it impractical for homes.

Now, the team has replaced the superconducting magnet with a custom-designed permanent magnet, dramatically shrinking the unit's size. The feat required overcoming tough engineering obstacles, such as synchronizing movements of heat-conducting fluids through portions of a rotating ring, Zimm says. The researchers announced their achievement last month.

Like its superconducting predecessor, the new unit takes advantage of the so-called magnetocaloric effect. Conventional refrigerators compress a volatile gas and then permit it to rapidly expand, pulling heat from the surroundings. In contrast, the magnetic device exploits magnetically induced heating and cooling of a powder of the element gadolinium. The powder is stuffed in pockets inside the ring that carries it through the field of the permanent magnet.

If the device does what the scientists claim, "it is a significant achievement," says Robert D. Shull of the National Institute of Standards and Technology in Gaithersburg, Md. However, he notes, the design's efficiency "ultimately will determine whether this advance will be useful or not."

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References:

2001. Magnetic refrigerator successfully tested. Ames Laboratory news release. Dec. 7. Available at http://www.external.ameslab.gov/news/release/01magneticrefrig.htm.

Further Readings:

2001. Astronautics Corporation of America demonstrated the world's first successful room temperature, permanent magnet, magnetic refrigerator at its Technology Center in Madison, Wisconsin. Astronautics Corporation of America press release. Oct. 23. Available at http://www.astronautics.com/PressRelease/Files/MagFrig.PDF.

Wu, Corinna. 1998. Magnetic materials keep fridges cool. Science News 153(March 28):197. Available at http://www.sciencenews.org/pages/sn_arc98/3_28_98/fob3.htm.

______. 1994. Better magnetic refrigeration. Science News 145(April 23):271.

For online information about magnetic refrigeration and, in particular, about research at the University of Victoria, British Columbia, see: http://www.cfs.me.uvic.ca/. Click on magnetic refrigeration link.

Sources:

Karl A. Gschneidner Jr.
Ames Laboratory
Department of Materials Science and Engineering
Iowa State University
Ames, IA 50011-3020

Robert D. Shull
Magnetic Materials Group
National Institute of Standards and Technology
100 Bureau Drive
Gaithersburg, MD 20899-8552

Carl B. Zimm
Astronautics Corporation of America
Astronautics Technology Center
5802 Cottage Grove Road
Madison, WI 53728-1387

From Science News, Volume 161, No. 1, January 5, 2002, p. 4.