Magnetic cooling enables efficient, 'green' refrigeration

June 10, 2014
Magnetic cooling enables efficient, 'green' refrigeration
The rotation of the HoMn2O5 crystal in a constant magnetic field around 10K changes its temperature, which can be used for the liquefaction of helium and hydrogen. Credit: Applied Physics Letters/ M. Balli, et. al

Magnetic cooling is a promising new refrigeration technology boasting several advantages – ranging from lower energy consumption to eliminating the use of hazardous fluids – that combine to make it a much more environmentally friendly option than today's standard fluid-compression form of refrigeration.

One novel magnetic cooling approach, developed by a team of Canadian-Bulgarian researchers, relies on solid magnetic substances called magnetocaloric to act as the refrigerant in miniaturized magnetic refrigerators. As the team describes in the journal Applied Physics Letters,from AIP Publishing, these materials are the key to the development of a "green" cooling technology whose efficiency is able to scale directly with the generated magnetocaloric effect.

The magnetocaloric effect is "the thermal response of a magnetic material to the change of an external , which manifests as a change in its temperature," explained Mohamed Balli, a researcher in the physics department at the Université de Sherbrooke in Quebec, Canada.

Ferromagnetic materials, for example, are known to heat up when magnetized and to cool down when the magnetic field is removed.

"The presence of a magnetic field makes ferromagnetic materials become more ordered. This is accompanied by disorder within the atomic lattice, which causes an increase in the material's temperature," Balli said. "Inversely, the absence of a magnetic field means that the atomic lattice is more ordered and results in a temperature decrease. Magnetic refrigeration essentially works by recapturing produced cooling energy via a heat transfer fluid, such as water."

The researchers originally set out to measure the standard magnetocaloric effect in the multiferroic compound HoMn2O5, because this material possesses an insulating behavior that prevents energy losses associated with electric currents passing through it when altering its magnetic field.

But, much to their surprise, they discovered that a giant magnetocaloric effect can be obtained by simply rotating a crystal of HoMn2O5 within a constant magnetic field – without requiring moving it in and out of the magnetic field zone (which is the case for materials exhibiting standard magnetocaloric effects).

This discovery is an important step toward the development of magnetic cooling technology, and will likely lead to efficient, "green" cooling systems for both domestic and industrial applications. "Using the rotating magnetocaloric effect means that the energy absorbed by the machine can be largely reduced," Balli noted. "It also opens the door to building simplified, efficient, and compact systems in the future."

Next, the team plans to explore the possibility of improving the rotating magnetocaloric effect in HoMn2O5 crystals and related materials.

Explore further: GE to take next leap in magnetocaloric refrigeration (w/ video)

More information: "Anisotropy-enhanced giant reversible rotating magnetocaloric effect in HoMn2O5 single crystals," by M. Balli, S. Jandl, P. Fournier, M. M. Gospodinov. Applied Physics Letters June 10, 2014 (DOI: 10.1063/1.4880818). :

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3.8 / 5 (4) Jun 10, 2014
So I wonder how cold you can get things with this. Say if I built a motor armature out of this stuff. (Ideal location with the inherent magnetic field.) If the motor winding's were made from superconducting wire would it get cold enough to keep them cold enough to super-conduct?. That would be awesome because the main thing keeping us from making superconducting electric motors in electric vehicles is the fact that you have to cool them. Superconducting motors are more efficient through all torque ranges and able to deliver higher torque per volume. So smaller motors, less weight, higher rpm = more mileage.
Jun 10, 2014
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5 / 5 (1) Jun 10, 2014
What coefficient of power over what temperature differential?

That would be awesome because the main thing keeping us from making superconducting electric motors in electric vehicles is the fact that you have to cool them.

The issue isn't really cooling them, but insulating them from outside heat. You can make things very cold very easily, but keeping it from getting hot again is the difficult part, and you won't have much joy out of your superconducting motor because you have to spend a significant amout of power to pump the heat out.

5 / 5 (1) Jun 10, 2014
jalmy, cool idea but I doubt it would be able to cool down fast enough if it were solely within the motor itself.

Our best bet for super-conducting motors are the 'high temperature' ones that 'only' require liquid nitrogen. A magnetic cooling system would be able to chill down to that level easily.

However, we do not yet have a suitable high-temp superconducting material. I do expect it to happen eventually though, as we're currently starting to understand superconductivity down at the atomic level.
not rated yet Jun 10, 2014
I don't know which they type they are (high or low temp) are but the Navy is using superconducting motors in a ship
3 / 5 (2) Jun 10, 2014
This can apparently create very cold temperatures if it can liquify hydrogen (< 33 Kelvin). I wonder if this can be scaled up to your kitchen refrigerator and if we'll have them sometime in the future, or perhaps for auto air conditioners. That would change the industry and reduce freon use.

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