New magnetic fridge technology raises efficiency
A US company has been working on a prototype of a new energy-efficient fridge that works by using magnets to provide a cooling effect.
Magnetic refrigerators would also dispense with the need to use chlorofluorocarbons (CFCs), which destroy the ozone layer and which have meant that under a new EC directive fridges now have to be disposed of at certified sites, creating a huge fridge mountain in the UK (see related story).
According to the New York Times, the Astronautics Corporation of America, based in Milwaukee, already has a working prototype cooling unit.
The technology is based on a discovery by German physicist Emil Warburg, in 1881, that metal placed near a strong magnet warms up.
Magnetic refrigerators work by switching a magnetic field on and off. In comparison, refrigerators on the market today work by compressing and expanding a gas, which, as it expands, cools and is used to chill the fridge’s contents.
The new technology works on the theory that a magnetic field affects the atoms in some metals, aligning them so that they are parallel with the field. This is a lower energy state than the atoms’ normal random distribution, so the surplus energy makes the metal heat up. It was realised decades ago that this effect could be used to draw heat away from an object, and magnetic refrigeration is already used in laboratories to cool items to within a degree of absolute zero.
The refrigerator works by placing a magnet and a circulating water system so that they straddle a segment of a spinning metal disk. As the disk spins into the magnetic field, the atoms in the part beneath the magnet line up, and produce heat, which is removed from the disk by the circulating water.
As the section of disk moves away from the magnet, the atoms return to their normal distribution and the disk cools to below room temperature. A second stream of water, passed over the disk, is cooled in turn and is used to chill the refrigerator.
Researchers have been looking for the optimum metal to maximise the heating/cooling effect. The latest device uses a CD-sized disk of gadolinium, which is used in video recorders’ recording heads.
Prototypes for the device used superconducting magnets, which have to be cooled to extremely low temperatures in order to work. The new device uses a normal permanent magnet, which is said to produce a field nearly as strong at room temperature.
Researchers at the University of Amsterdam reported in last month’s Nature that they had created an iron-based compound that also exhibits a large warming effect, and scientists working on the project believe this would be a more feasible option for production because it is cheaper and works at warmer temperatures.
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