Using materials developed at the US Department of Energy’s Ames Laboratory, researchers have successfully demonstrated the world’s first room temperature, permanent magnet, magnetic refrigerator. Milwaukee-based Astronautics Corporation of America developed the refrigerator as part of a co-operative research and development agreement with Ames Laboratory.
Instead of ozone-depleting refrigerants and energy-consuming compressors found in conventional vapour-cycle refrigerators, this new style of refrigerator is said to use gadolinium metal that heats up when exposed to a magnetic field, then cools down when the magnetic field is removed.
‘We’re witnessing history in the making,’ said Ames Laboratory senior metallurgist Karl Gschneidner Jr. ‘Previous successful demonstration refrigerators used large superconducting magnets, but this is the first to use a permanent magnet and operate at room temperature.’
Initially tested in September, 2001 at the Astronautics Corporation of America’s Technology Centre, the new refrigerator is undergoing further testing. The goal is to achieve larger temperature swings that will allow the technology to provide the cooling power required for specific markets, such as home refrigerators, air conditioning, electronics cooling, and fluid chilling.
According to Gschneidner the magnetic refrigerator employs a rotary design. It consists of a wheel that contains segments of gadolinium powder – supplied by Ames Laboratory – and a high-powered, rare earth permanent magnet.
The wheel is arranged to pass through a gap in the magnet where the magnetic field is concentrated. As it passes through this field, the gadolinium in the wheel exhibits a large magnetocaloric effect and heats up.
After the gadolinium enters the field, water is circulated to draw the heat out of the metal. As the material leaves the magnetic field, the material cools further as a result of the magnetocaloric effect. A second stream of water is then cooled by the gadolinium. This water is then circulated through the refrigerator’s cooling coils.
The overall result is a compact unit that runs virtually silent and nearly vibration free, without the use of ozone-depleting gases, a dramatic change from the vapour-compression-style refrigeration technology in use today.
‘The permanent magnets and the gadolinium don’t require any energy inputs to make them work,’ Gschneidner said, ‘so the only energy it takes is the electricity for the motors to spin the wheel and drive the water pumps.’
Though the test further proves the technology works, two recent developments at Ames Laboratory could lead to even greater advances on the magnetic refrigeration frontier.
Gschneidner and fellow Ames Laboratory researchers Sasha Pecharsky and Vitalij Pecharsky have developed a process for producing kilogram quantities of Gd5 (Si2Ge2) alloy using commercial-grade gadolinium. Gd5 (Si2Ge2) exhibits a giant magnetocaloric effect, which offers the promise to outperform the gadolinium powders used in the current rotary refrigerator.