Inside Iowa State
Feb. 6, 1998
The big chill
Magnetic refrigeration makes a cool debut
by Steve Karsjen, Ames Laboratory
Refrigerators and air conditioners of the future may owe their "cool" in part to the efforts of Ames Laboratory scientists Karl Gschneidner and Vitalij Pecharsky. The scientists and their team of rare earth materials specialists, and engineers at Astronautics Corp. of America have combined their expertise to develop a new magnetic refrigerator, a technology that may revolutionize the refrigeration industry.
Unlike conventional refrigerators, which cool by compressing and decompressing gas, magnetic refrigerators use magnetic substances as the refrigerant material. The substance in this case is gadolinium, a rare earth metal. Gadolinium has a large magnetocaloric effect -- the ability to heat up when magnetized and cool back down when demagnetized. This process is much more energy-efficient than current gas compression/decompression systems.
Although the magnetocaloric effect was discovered in 1881 and first explained in 1918, its practical application has eluded scientists until recently. Gschneidner likens the breakthrough of using gadolinium to produce efficient magnetic refrigeration to the scientific breakthrough in atomic power achieved in 1942.
"I believe we are witnessing history in the making," he said. "When we've told engineers and scientists about our work on magnetic refrigeration, they've almost always said they're interested, but finish by saying, 'Show me.' Well, we're showing the world it works."
The new magnetic refrigerator, which is located at the Astronautics Technology Center in Madison, Wis., has been operating for approximately 1,200 hours over the past 12 months, which far exceeds the few hours or days of operation recorded by other units. During this time, the refrigerator has achieved record cooling power.
"We have achieved cooling power that exceeds that of previously built magnetic refrigeration units by 20 to 100 times," Gschneidner said.
Also pleasing to the Ames Lab/Astronautics team is the fact that magnetic refrigerators operate without harmful environmental effects. Conventional refrigerators use as heat transfer fluids chlorofluorocarbons, hydrochloro- fluorocarbons or ammonia, which release vapors that are toxic or damaging to the ozone layer.
"Our heat transfer mechanism, on the other hand, causes zero environmental damage," said Carl Zimm, senior scientist at the Astronautics Technology Center, "because the transfer medium we use is water, which is also cheap, non-flammable and has very good thermal conductivity."
Antifreeze is added to the water when cooling below the freezing point.
In addition to eliminating environmental hazards, magnetic refrigeration is produced with much less energy loss. Conventional vapor cycle refrigerators can achieve about 25 percent efficiency.
"We're expecting that our unit should be able to achieve 50 to 60 percent efficiency," said Zimm. He added that generating this efficiency for large-scale industrial users remains one of the greatest challenges of magnetic refrigeration. "We need to figure out how to increase the size of magnetic refrigerators to accommodate industry's needs."
Magnetic refrigeration is most appropriate for use in energy- intensive industrial and commercial refrigeration systems, such as large-scale air conditioners and heat pumps, and supermarket refrigeration units.
"The first place we're going to look is to the user where the energy bill for refrigeration is huge, such as large supermarket chains, big shopping malls and food storage warehouses. Those will be the first people who will be interested in us," Zimm said.
Despite Zimm's enthusiasm, he admits that it will take five to 10 years to move magnetic refrigeration from the laboratory to the marketplace. Use in home refrigerators and air conditioners is still many years down the road. The average citizen, however, could see some benefits from industry's use of the units, he said.
"Everything people buy should cost less as stores and processors see greater savings through magnetic refrigeration," Zimm said.
Beyond these applications, Zimm says magnetic refrigeration also has a potential for use in producing cheap liquid hydrogen, an alternative automobile fuel that is environmentally safe and in unlimited supply.
Not content to rest on their accomplishments, the scientists already are experimenting with new materials to improve the performance of magnetic refrigeration. An intermetallic compound of gadolinium-silicon-germanium already is proving to be 25 to 200 percent more powerful as a magnetic refrigeration material than gadolinium and other prototype materials.
Gschneidner compares today to the period in the mid-1760s when James Watt introduced the first steam engine. But he added that he expects magnetic refrigeration to come to fruition much more quickly than Watt's steam engine because of today's inventive and technologically advanced climate.
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