Researchers at the Massachusetts Institute of Technology (MIT) and the University of Newcastle in Australia have found a new method of enhancing heat transfer by using magnetic fields to prevent hotspots that lead to system failures. The method could be applied to cooling everything from electronic devices to advanced fusion reactors.
In a system, the method relies on a slurry of tiny particles of magnetite, a form of iron oxide, where the magnetite nanofluid flows through tubes and is manipulated by magnets placed on the outside of the tubes.
The results of the experimental system are the culmination of several years of research on nanofluids, which are nanoparticles dissolved in water, according to Lin-Wen Hu, associate director of MIT's Nuclear Reactor Laboratory.
Hu explained that the magnets "attract the particles closer to the heated surface" of the tube, greatly enhancing the transfer of heat from the fluid, through the walls of the tube and into the outside air. Without the magnets in place, the fluid behaves just like water, with no change in its cooling properties.
With the magnets, the heat transfer coefficient is higher—in the best case, about 300 percent better than with plain water. "We were very surprised" by the magnitude of the improvement, said Hu.
Conventional methods to increase heat transfer in cooling systems rely on features such as fins and grooves on the surfaces of the pipes, increasing their surface area. While these features improve heat transfer, they do not approach the results of using magnetic particles, according to Hu. Also, she pointed out these conventional features are expensive to fabricate.
In the improved new system, the magnetic field tends to cause the particles to clump together, thus 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, according to Hu.
"This is the first work we know of that demonstrates this experimentally," Hu said.
"It's a neat way to enhance heat transfer," said Jacopo Buongiorno, a co-author of the paper and an associate professor of nuclear science and engineering at MIT. "You can imagine magnets placed at strategic locations. When you want to turn the cooling up, you turn up the magnets and get a very localized cooling there."
Buongiorno suggested numerous applications where systems 'require not necessarily system-wide cooling, but localized cooling,' such as microchips and other electronic systems in which local areas are subject to strong heating.
The research was performed by the teams at MIT and in Australia and was supported by the University of Newcastle, Granite Power Ltd., the Australian Research Council and King Saud University in Saudi Arabia.
The method is described in the International Journal of Heat and Mass Transfer.
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