Skip to comments.Refrigerator magnets: New theory predicts magnets may act as wireless cooling agents.
Posted on 07/29/2014 4:34:39 AM PDT by LibWhacker
The magnets cluttering the face of your refrigerator may one day be used as cooling agents, according to a new theory formulated by MIT researchers.
The theory describes the motion of magnons quasi-particles in magnets that are collective rotations of magnetic moments, or spins. In addition to the magnetic moments, magnons also conduct heat; from their equations, the MIT researchers found that when exposed to a magnetic field gradient, magnons may be driven to move from one end of a magnet to another, carrying heat with them and producing a cooling effect.
You can pump heat from one side to the other, so you can essentially use a magnet as a refrigerator, says Bolin Liao, a graduate student in MITs Department of Mechanical Engineering. You can envision wireless cooling where you apply a magnetic field to a magnet one or two meters away to, say, cool your laptop.
In theory, Liao says, such a magnetically driven refrigerator would require no moving parts, unlike conventional iceboxes that pump fluid through a set of pipes to keep things cool.
Liao, along with graduate student Jiawei Zhou and Department of Mechanical Engineering head Gang Chen, have published a paper detailing the magnon cooling theory in Physical Review Letters.
People now have a new theoretical playground to study how magnons move under coexisting field and temperature gradients, Liao says. These equations are pretty fundamental for magnon transport.
A cool effect
In a ferromagnet, the local magnetic moments can rotate and align in various directions. At a temperature of absolute zero, the local magnetic moments align to produce the strongest possible magnetic force in a magnet. As temperature increases, a magnet becomes weaker as more local magnetic moments spin away from the shared alignment; a magnon population is created with this elevated temperature.
In many ways, magnons are similar to electrons, which can simultaneously carry electrical charge and conduct heat. Electrons move in response to either an electric field or a temperature gradient a phenomenon known as the thermoelectric effect. In recent years, scientists have investigated this effect for applications such as thermoelectric generators, which can be used to convert heat directly into electricity, or to deliver cooling without any moving parts.
Liao and his colleagues recognized a similar coupled phenomenon in magnons, which move in response to two forces: a temperature gradient or a magnetic field. Because magnons behave much like electrons in this aspect, the researchers developed a theory of magnon transport based on a widely established equation for electron transport in thermoelectrics, called the Boltzmann transport equation.
From their derivations, Liao, Zhou, and Chen came up with two new equations to describe magnon transport. With these equations, they predicted a new magnon cooling effect, similar to the thermoelectric cooling effect, in which magnons, when exposed to a magnetic field gradient, may carry heat from one end of a magnet to the other.
Motivating new experiments
Liao used the properties of a common magnetic insulator to model how this magnon cooling effect may work in existing magnetic materials. He collected data for this material from previous literature, and plugged the numbers into the groups new model. He found that while the effect was small, the material was able to generate a cooling effect in response to a moderate magnetic field gradient. The effect was more pronounced at cryogenic temperatures.
The theoretical results suggest to Chen that a first application for magnon cooling may be for scientists working on projects that require wireless cooling at extremely low temperatures.
At this stage, potential applications are in cryogenics for example, cooling infrared detectors, Chen says. However, we need to confirm the effect experimentally and look for better materials. We hope this will motivate new experiments.
Li Shi, a professor of mechanical engineering at the University of Texas at Austin who was not involved in the research, says the magnetic cooling effect identified by the group is a highly useful theoretical framework for studying the coupling between spin and heat, and can potentially stimulate ideas of utilizing magnons as a working fluid in a solid-state refrigeration system.
Liao points out that magnons also add to the arsenal of tools for improving existing thermoelectric generators which, while potentially innovative in their ability to generate electricity from heat, are also relatively inefficient.
Theres still a long way to go for thermoelectrics to compete with traditional technologies, Liao says. Studying the magnetic degree of freedom could potentially help optimize existing systems and improve the thermoelectric efficiency.
The work was partly supported by the U.S. Department of Energy and the Air Force Office of Scientific Research.
Or a heater? Which seems to me would be an equally important discovery. 'Course, there is no way I fully understand what is going on here, but... Would they still need electricity to get the device to work, or are they saying that this could work with no other driving force behind it at all but a dumb refrigerator magnet??? Too good to be true.
Sterling silver is much better. It pumps heat from the tea cup into the atmosphere or your fingers.
The process is conduction
Honestly, I’m not sure how this is new.
For a long time in the area of cryogenics, magnetic fields have been used to remove some of the last few degrees of heat as they keep pushing for near absolute zero (which can’t be obtained according to thermodynamics, but they keep trying to see how close they can get.)
Magnets are an essential component in virtually every free energy machine, so yes, this theory may explain why they work.
Yep - same principle of heat transference via an energy source. Put a window air conditioner fully in an enclosed room and one end pumps cool while the other pumps warm - ambient temp stays the same. I guess that if it was efficient, the no moving parts facet of the device itself would be the greatest boon.
Powerful enough to cool your laptop = powerful enough to wipe the hard drive.
I can see it now! One morning I stumble into the kitchen to make coffee, and half the stuff in the kitchen is stuck to the refrigerator!
Stack a bunch of them and you can cool your processor or your beer.
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|I, for one, welcome our new Cybernetic Overlords /.|
Yes. as with all things, nothing is free. It will be interesting to see what the energy efficiency of such a cooler will be. If it's not any better than a current compressor/working fluid system, then it will go nowhere.
If it's efficiency is better, then there are posibilities.
Hard drives will become obsolete in the future. They lose e-mails like crazy for some strange reason.....................
We use peltier devices in our products..................
And for some reason, they are maliciously selective in what they lose.
would this more efficiently use solar energy than a solar cell per unit area? Or could this be stacked with a solar cell to gather more light spectrum?
Years ago, MECHANICS ILLUSTRATED magazine had an article on how to build a small refrigerator without freon using thermocouples. That was back in the 1960s.