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Cool discovery advances magnetic refrigeration technology

An enerty-efficient and evrironmentally friendly technology, magnetic refrigeration could be commercially competitive within the next decade.

A new class of materials discovered at ISU holds the key to the future success of magnetic refrigeration, a technology that is more energy efficient and environmentally friendly than today's gas-compression coolers.

Discovered by MSE Distinguished Professor Karl Gschneidner, Jr. and Ames Lab Associate Scientist Vitalij Percharsky, the new materials are made of gadolinium-silicon-germanium. They will broaden the practical applications of magnetic refrigeration and make the technology more cost effective.

Magnetic refrigeration is based on the magnetocaloric effect - the ability of some metals to heat up when they are magnetized and cool down when removed from the magnetic field. Conventional systems use liquids that are expanded and compressed to cool the air inside while venting the warmer air outside. However, the liquids most commonly used are either chlorofluorocarbons, which have been linked to ozone depletion, or ammonia, which is a toxic material.

Because it eliminates the need to expand and compress a liquid, magnetic refrigeration consumes less electricity and can operate at 60 percent efficiency, or greater. Conventional systems have a maximum efficiency of about 40 percent, but most run at about 25 percent.

The materials discovered by Gschneidner and Percharsky are two to 10 times more effective in their cooling power than prototype alloys. In addition, their operating temperature can easily be changed over a wide range - from about 30K (-400F) to 290K (65F) - without losing the magnetocaloric effect.

The discovery helps make magnetic refrigeration more competitive with conventional technology. Gschneidner and Percharsky teamed with Astronautics Corporation of America, Madison, Wisconsin, last year to unveil the first gadolinium-based magnetic refrigeration unit. It has operated since December 1996, far surpassing the few days of operation recorded by similar units. It also has achieved cooling power 20 to 100 times greater than previous units.

Magnetic refrigeration is expected to be commercially available in five to 10 years. Potential applications include large-scale refrigeration, food processing, and heating and air conditioning; liquor distilling; grain drying; and waste separation and treatment systems. It may also expand into smaller-scale applications, such as air conditioning for homes and cars.

The wide temperature span of these new magnetic refrigeration materials also could lower the cost of producing liquid hydrogen, a clean and endless alternative fuel source.