For Refrigeration Problems, a Magnetically Attractive Solution

January 28, 2009
Conventional and magnetic refrigeration cycles use different physical effects to cool things off. [Top] When a gas is compressed (2), it heats up, but if it is cooled and then allowed to expand (3), its temperature drops much lower than it was originally (4); this principle keeps food in your home refrigerator cool. But a magnetocaloric material [bottom] heats up when magnetized (b); if cooled and then demagnetized (c), its temperature drops dramatically (d). NIST scientists may have found a way to use magnetocalorics in your fridge. Credit: Talbott, NIST

(PhysOrg.com) -- Your refrigerator’s humming, electricity-guzzling cooling system could soon be a lot smaller, quieter and more economical thanks to an exotic metal alloy discovered by an international collaboration working at the National Institute of Standards and Technology (NIST)’s Center for Neutron Research (NCNR).*

The alloy may prove to be a long-sought material that will permit magnetic cooling instead of the gas-compression systems used for home refrigeration and air conditioning. The magnetic cooling technique, though used for decades in science and industry, has yet to find application in the home because of technical and environmental hurdles—but the NIST collaboration may have overcome them.

Conventional and magnetic refrigeration cycles use different physical effects to cool things off. [Top] When a gas is compressed (2), it heats up, but if it is cooled and then allowed to expand (3), its temperature drops much lower than it was originally (4); this principle keeps food in your home refrigerator cool. But a magnetocaloric material [bottom] heats up when magnetized (b); if cooled and then demagnetized (c), its temperature drops dramatically (d). NIST scientists may have found a way to use magnetocalorics in your fridge. Credit: Talbott, NIST

Magnetic cooling relies on materials called magnetocalorics, which heat up when exposed to a powerful magnetic field. After they cool off by radiating this heat away, the magnetic field is removed, and their temperature drops again, this time dramatically. The effect can be used in a classic refrigeration cycle, and scientists have attained temperatures of nearly absolute zero this way. Two factors have kept magnetic cooling out of the consumer market: most magnetocalorics that function at close to room temperature require both the prohibitively expensive rare metal gadolinium and arsenic, a deadly toxin.

But conventional gas-compression refrigerators have their own drawbacks. They commonly use hydrofluorocarbons (HFCs), greenhouse gases that can contribute to climate change if they escape into the atmosphere. In addition, it is becoming increasingly difficult to improve traditional refrigeration. “The efficiency of the gas cycle has pretty much maxed out,” said Jeff Lynn of NCNR. “The idea is to replace that cycle with something else.”

The alloy the team has found—a mixture of manganese, iron, phosphorus and germanium—is not merely the first near-room-temperature magnetocaloric to contain neither gadolinium nor arsenic—rendering it both safer and cheaper—but also it has such strong magnetocaloric properties that a system based on it could rival gas compression in efficiency.

Working alongside (and inspired by) visiting scientists from the Beijing University of Technology, the team used NIST’s neutron diffraction equipment to analyze the novel alloy. They found that when exposed to a magnetic field, the newfound material’s crystal structure completely changes, which explains its exceptional performance.

“Understanding how to fine-tune this change in crystal structure may allow us to get our alloy’s efficiency even higher,” says NIST crystallographer Qing Huang. “We are still playing with the composition, and if we can get it to magnetize uniformly, we may be able to further improve the efficiency.”

Members of the collaboration include scientists from NIST, Beijing University of Technology, Princeton University and McGill University. Funding for the project was provided by NIST.

* D. Liu, M. Yue, J. Zhang, T.M. McQueen, J.W. Lynn, X. Wang, Y. Chen, J. Li, R.J. Cava, X. Liu, Z. Altounian and Q. Huang. Origin and tuning of the magnetocaloric effect for the magnetic refrigerant MnFe(P1-xGex). Physical Review B. Vol. 79, 014435 (2009).

Provided by NIST

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7 comments

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E_L_Earnhardt
3 / 5 (1) Jan 29, 2009
Amen! long overdue! Let's do it! The electric bill would be cut in half!
Ashibayai
1 / 5 (1) Jan 29, 2009
So is it strictly one or the other, or is it possible to use both in one system?

Although I kinda doubt it would be required...
DGBEACH
not rated yet Jan 29, 2009
One thing I don't understand is how they evacuate the heat from the interior of the fridge.
A gas-filled system transports it from the interior to the exterior of the fridge, using a condenser, a fan and an evaporator. Likewise, a Peltier-cooled fridge pulls the heat (induction) from the interior (one side of the element) of the fridge to the exterior (other side of the element) of the fridge.
So where is the "heat transport" portion of THIS system? Or have I missed something?
VOR
not rated yet Jan 29, 2009
cool
VOR
not rated yet Jan 29, 2009
I have long had the irrational fantasy that cooling could be and exothermic process. The childlike thinking goes--you are removing heat, which is a higher energy state, so you get energy right? lol.
3432682
3 / 5 (2) Jan 29, 2009
Cost savings? Where? 3rd to last paragraph "a system based on it could rival gas compression in efficiency." Apparently there is no efficiency advantage over current technology.

The benefit would be to replace the poisonous gases in industrial processses.
deatopmg
1 / 5 (2) Feb 01, 2009
what is the overall environmental cost to build 1) the magnetic and 2)the gas based systems?? I suspect when HFC's are included in the calcs. the pendulum shifts to the mag. system. If ammonia (by far the most efficient gas to use) is used instead then to pendulum would likely swing towards the gas system.

One does NOT have to use HFC's though as the motive gas (that is legislated in the US. A political payoff like corn ethanol in gasoline???) In the EU, propane/isobutane mixtures are used (at a small fraction of the quantity of HFC's) in automotive et al AC systems. I've refilled my old empty (R-12) auto AC system with a ca. 60 g. of a propane/isobutane mix vs. ca. 1 kilo of R-134a. Works like new.

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