Magnetic Nanoparticles Could Improve Cooling Everything From Computers To Nuclear Reactors
Cooling unwanted heat is a challenging but unavoidable task in every electricity or heat based manufacturing and production enterprise. The systems constructed to cool are generally designed on circulating water through coils.
The current researches on cooling technology makes the water based medieval cooling technology look rather primitive. Researchers in Australia and at MIT have designed the magnetic field based cooling system that will not only cool 300 percent better than plain water but also prevent hot spots that can cause system failures. The method of magnetic field to cool can actually cool almost everything from electronic devices to fusion reactors, according to researchers in Australia and MIT. The cooling system makes use of slurry of tiny magnetite particles, a form of iron oxide as described in the International Journal of Heat and Mass Transfer. MIT researchers Jacopo Buongiorno and Lin-Wen Hu have co-authored the paper along with four others.
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Several years of research on nanofluids (that is, nanoparticles dissolved in water) have led to the new results, according to Hu, associate director of MIT's Nuclear Reactor Laboratory. Experiments involving the flow of nanofluid through tubes and manipulation by magnets placed outside the tubes were conducted.
The magnets attract the particles that are closer to the heated surface of the tube resulting in highly enhanced transfer of heat from the fluid into the outside air through the walls of the tube, Hu says. The fluids behave just like water, without the magnets in place. However, the heat transfer co-efficient is higher, according to Hu, with the magnets, and up to 300 percent better than with plain water in the best case. "We were very surprised," Hu says, commenting about the magnitude of improvement. Conventional methods with features like grooves and fins to increase surface area, and thus heat transfer, work to an extent, Hu says, but not nearly as well as magnetic particles. Also, fabrication of these features can be expensive.
The magnetic field tends to cause particles to clump together, according to Hu, possibly forming a chainlike structure on the side of the tube closest to the magnet. This disrupts their flow leading to an increase in the local temperature gradient, says Hu. The theory has been there for a long time, but never proved in action before, according to Hu. "This is the first work we know of that demonstrates this experimentally," she says. This system will be impractical when applied to an entire cooling system, but is useful in any system where hotspots appear on the surface of cooling pipes, according to Hu.
"It's a neat way to enhance heat transfer," says Buongiorno, an associate professor of nuclear science and engineering at MIT. "You can imagine magnets put at strategic locations," and if those are electromagnets that can be switched on and off, "when you want to turn the cooling up, you turn up the magnets, and get a very localized cooling there."
Buongiorno claims that this approach can be useful for advanced fusion reactors as well because of the presence of localized hotspots where "the heat flux is much higher than the average." However, Buongiorno admits, these applications remain well in the future, "This is a basic study at the point."
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