X-Message-Number: 18667 From: Date: Wed, 27 Feb 2002 15:47:41 EST Subject: New magnetic refrigerators. --part1_132.9c8c0fb.29ae9fed_boundary Content-Type: text/plain; charset="UTF-8" Content-Language: en Short Article from New York Times... February 19, 2002 Building a Better Refrigerator, With Magnets By KENNETH CHANG The Astronautics Corporation of America in Milwaukee has been working on prototypes of magnetically operated refrigerators. In 1881, Emil Warburg, a German physicist, placed a piece of metal near a strong magnet. The metal warmed up. Present-day scientists and engineers hope to take advantage of that phenomenon not for heating, but the opposite: for building a new type of refrigerator that is quiet and efficient. They say large commercial refrigerators or air-conditioning systems based on the technology may be no more than a year or two away from the market. A company in Wisconsin has a prototype cooling unit plugged in and working. The cooling power of today's refrigerators comes from the repeated compression and expansion of a gas. As the gas expands, it cools and is cycled around an insulated compartment, chilling the contents. By contrast, magnetic refrigerators cool by repeatedly switching a magnetic field on and off. In certain metals, atoms act like tiny bar magnets pointing in random directions. When placed in a magnetic field, the bar magnets quickly pivot, so they are parallel with the field. That is a lower energy state, and the surplus energy makes the atoms vibrate, producing heat. In other words, the metal warms up. Engineers realized decades ago that they could turn around this process to draw heat away from an object and, thus, cool it. Magnetic refrigeration has been used in laboratories to cool within a degree above absolute zero. Now the same principles can be applied at everyday temperatures. Here is how a spinning metal disk, a magnet and some water could one day chill your food: The magnet straddles one part of the disk. As a part of the disk spins into a magnetic field, the tiny bar magnets in the disk line up, and the temperature rises. Water circulates over that part of the disk, cooling it. When that part of the disk leaves the magnetic field, the bar magnets are no longer forced into lining up. Part of the heat energy is dissipated into jostling the bar magnets back into random directions, cooling the disk below room temperature. A second stream of water runs over the disk, and that cool water is used to chill the refrigerator. Although the concept is straightforward, researchers have been refining the details, first looking for metals that maximize the magnetocaloric effect. The current prototype uses a disk, about the size of a CD, made of gadolinium, a metal used in the recording heads of video recorders. Earlier prototypes also used superconducting magnets which themselves have to be chilled to very low temperatures to generate the magnetic field. In the latest prototype, the scientists fashioned a permanent magnet that generates a field nearly as strong. "This is getting closer to a real machine that you put in a real device," said Dr. Karl A. Gschneidner Jr., a senior metallurgist at the Ames Laboratory in Iowa, who has been working on the prototypes with colleagues at Ames and a company, the Astronautics Corporation of America in Milwaukee. The use of a permanent magnet is "definitely a nice advance," said Dr. Robert D. Shull, leader of the magnetic materials group at the National Institute of Standards and Technology in Gaithersburg, Md. But Dr. Shull said he wanted to know more details. "I don't know what the efficiency of it is," he said. "That's one of the critical numbers one needs to know whether it can be commercialized." There is still room for improvement. In an article published in the journal Nature last month, scientists at the University of Amsterdam reported that they had created an iron- based compound that also exhibits a large warming effect in a magnetic field. Iron and the other ingredients in the compound are considerably less expensive than gadolinium. Dr. Ekkes Br ck, a physics professor and an author of the paper, called the compound "probably more feasible" for production, "because it is a lot cheaper." Dr. Shull said another advantage of the iron compound was that it worked at warmer temperatures, operating in 100-degree heat, when gadolinium might falter. "That is what is particularly nice about it," Dr. Shull said. "It has these very large effects at slightly larger temperatures." But Dr. Gschneidner worried that an ingredient in the iron compound was the poison arsenic, while gadolinium is harmless to animals and plants. "I just wouldn't want that much arsenic floating around in the world," he said. Dr. Shull said he doubted that the arsenic would pose a health risk. It would be bound to the other atoms. Dr. Br ck noted that cellphones had gallium arsenic. Because gadolinium and the magnet are not cheap, a magnetic refrigerator would cost more than a conventional one. But it would also be more energy efficient, costing less to operate. And the magnetic type would not use chlorofluorocarbons, which eat away ozone in the upper atmosphere that protects Earth from harmful ultraviolet radiation. "It's environmentally much more friendly," Dr. Gschneidner said. Something else is missing, said Robert P. Herman, a senior engineer at Astronautics, the hum and whir of present-day compressors. "The only thing you may hear is a very low noise from the motor," Mr. Herman said. "That's about it. Once in an enclosure, you don't even hear that." --part1_132.9c8c0fb.29ae9fed_boundary Content-Type: text/html; charset="UTF-8" [ AUTOMATICALLY SKIPPING HTML ENCODING! ] Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=18667