Cooling systems generally rely on water pumped through pipes to remove unwanted heat. Now, researchers at MIT and in Australia have found a way of enhancing heat transfer in such systems by using magnetic fields, a method that could prevent hotspots that can lead to system failures. The system could also be applied to cooling everything from electronic devices to advanced fusion reactors, they say.
The system, which relies on a slurry of tiny particles of magnetite, a form of iron oxide, is described in the International Journal of Heat and Mass Transfer, in a paper co-authored by MIT researchers Jacopo Buongiorno and Lin-Wen Hu, and four others.
Hu, associate director of MIT’s Nuclear Reactor Laboratory, says the new results are the culmination of several years of research on nanofluids — nanoparticles dissolved in water. The new work involved experiments where the magnetite nanofluid flowed through tubes and was manipulated by magnets placed on the outside of the tubes.
The magnets, Hu says, “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. But with the magnets, the heat transfer coefficient is higher, she says — in the best case, about 300 percent better than with plain water. “We were very surprised” by the magnitude of the improvement, Hu says.
Conventional methods to increase heat transfer in cooling systems employ features such as fins and grooves on the surfaces of the pipes, increasing their surface area. That provides some improvement in heat transfer, Hu says, but not nearly as much as the magnetic particles. Also, fabrication of these features can be expensive.
The explanation for the improvement in the new system, Hu says, is that the magnetic field tends to cause the particles to 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.
While the idea has been suggested before, it had never been proved in action, Hu says. “This is the first work we know of that demonstrates this experimentally,” she says.
Such a system would be impractical for application to an entire cooling system, she says, but could be useful in any system where hotspots appear on the surface of cooling pipes. One way to deal with that would be to put in a magnetic fluid, and magnets outside the pipe next to the hotspot, to enhance heat transfer at that spot.
“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.”
While heat transfer can be enhanced in other ways, such as by simply pumping the cooling fluid through the system faster, such methods use more energy and increase the pressure drop in the system, which may not be desirable in some situations.
There could be numerous applications for such a system, Buongiorno says: “You can think of other systems that require not necessarily systemwide cooling, but localized cooling.” For example, microchips and other electronic systems may have areas that are subject to strong heating. New devices such as “lab on a chip” microsystems could also benefit from such selective cooling, he says.
Going forward, Buongiorno says, this approach might even be useful for fusion reactors, where there can be “localized hotspots where the heat flux is much higher than the average.”
But these applications remain well in the future, the researchers say. “This is a basic study at the point,” Buongiorno says. “It just shows this effect happens.”
The team also included Thomas McKrell, a research scientist in MIT’s Department of Nuclear Science and Engineering, and Elham Doroodchi, Behdad Moghtaderi, and Reza Azizian of the University of Newcastle in Australia. The work was supported by the University of Newcastle, Granite Power Ltd., the Australian Research Council, and King Saud University in Saudi Arabia.
Written by: David L. Chandler, MIT News Office
Sarah McDonnell | EurekAlert!
Jelly with memory – predicting the leveling of com-mercial paints
15.12.2017 | Fraunhofer-Institut für Produktionstechnik und Automatisierung IPA
Fraunhofer researchers develop measuring system for ZF factory in Saarbrücken
21.11.2017 | Fraunhofer-Institut für Zerstörungsfreie Prüfverfahren IZFP
A study carried out by an international team of researchers and published in the journal Physical Review X shows that ion-trap technologies available today are suitable for building large-scale quantum computers. The scientists introduce trapped-ion quantum error correction protocols that detect and correct processing errors.
In order to reach their full potential, today’s quantum computer prototypes have to meet specific criteria: First, they have to be made bigger, which means...
Since 2016, German and Spanish researchers, among them scientists from the University of Göttingen, have been hunting for exoplanets with the “Carmenes”...
DNA molecules that follow specific instructions could offer more precise molecular control of synthetic chemical systems, a discovery that opens the door for engineers to create molecular machines with new and complex behaviors.
Researchers have created chemical amplifiers and a chemical oscillator using a systematic method that has the potential to embed sophisticated circuit...
MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.
Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...
Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...
11.12.2017 | Event News
08.12.2017 | Event News
07.12.2017 | Event News
18.12.2017 | Physics and Astronomy
18.12.2017 | Studies and Analyses
18.12.2017 | Medical Engineering