Magnetic refrigerator gets down and homey

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.

Rotating ring (center), roughly the diameter of a compact disk, cycles powdered magnetic material in and out of a gap in the powerful magnet at rear. Astronautics

As gadolinium enters a magnetic field and becomes magnetized, the material’s atoms align, causing it to get hot. A fluid (red) carries that heat away. As the gadolinium exits the field, the atoms absorb heat from the recirculated fluid (blue) that chills a space. V. Pecharsky/Ames Lab.

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: 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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