Liquid Cooling

Magnetic Nanoparticles Prevent Hotspots in Cooling Systems

An international team comprised of researchers at MIT and in Australia has discovered a way to enhance heat transfer using magnetic fields, a method they say could prevent hotspots that can lead to system failures.

The new system, which relies on tiny particles of magnetite, a form of iron oxide, is the result of several years of research on nanofluids—nanoparticles dissolved in water—and could be used to cool everything from small electronic devices to advance fusion reactors. The recent work involved experiments where magnets were placed on the outside of tubes containing magnetite nanofluid. Under normal circumstances, the fluid exhibits similar cooling properties to that of water.

However, says Lin-Wen Hu, associate director of MIT’s Nuclear Reactor Laboratory, placing the magnets near the tubes containing the magnetite nanofluid increases the heat transfer coefficient of the nanofluid up to 300 percent that of plain water. This is because application of the magnets “attracts the particles closer to the heated surface” of the tube, where they clump together, possibly forming “a chainlike structure on the side of the tube closest to the magnet, disrupting the flow there and increasing the local temperature gradient.”

Though the idea has been suggested before, “this is the first work we know of that demonstrates this experimentally,” Hu said.

The system is impractical for application to an entire cooling system, she added, but could be used in any system where hotspots appear on the surface of cooling pipes. Electronic systems with specific areas subjected to strong heat, such as “lab on a chip” microsystems, could also benefit from the selective cooling provided by the technology. The approach could even be useful for fusion reactors, says Jacopo Buongiorno, an associate professor of nuclear science and engineering at MIT, where there can be “localized hotspots where the heat flux is much higher than the average.”

“It’s a neat way to enhance heat transfer,” Buongiorno said. “You can imagine magnets put at strategic locations” and if those are electromagnetic that can be switched on and off, “when you want to turn the cooling up, you turn up those magnets, and get a very localized cooling there.”

However, any potential applications for the technology remain well in the future, the researchers say.

“This is a basic study at the point,” Buongiorno said. “It just shows this effect happens.”

The research, co-authored by Buongiorno, Hu, and four others, is published in the International Journal of Heat and Mass Transfer.

By Aliza Becker