Magnetic Refrigeration may be closer than we think

The interest in magnetic refrigeration as a new solid state, competitive cooling technology has grown considerably over the past 10 years. This effectively coincides with growing concerns about global warming and ever-increasing energy consumption.

At the Second International Conference on Magnetic Refrigeration at Room Temperature in 2007 (Thermag II), it was pointed out that some 15% of the total worldwide energy consumption is related to the use of refrigeration  -- be it air conditioning, refrigeration, freezing, or chilling. It was the thought that magnetic refrigeration had the potential to lower energy consumption by 20–30% over conventional vapor compression technology.

As reported by Karl Gschneidner, a renowned metallurgist at Iowa State University and the U.S. Department of Energy's Ames Laboratory noted in his September 2008 paper in the International Journal of Refrigeration(Vol. 31 Issue 6 pg 945 – 961), “the potential of magnetic cooling has not gone unnoticed by fundamental sciences as well. The number of published papers per annum on the magnetocaloric effect has grown at an exponential rate in the past 10 years. We have estimated, based on the number of papers published in the first three quarters of 2007, that on the average a paper on the magnetocaloric effect appears in print every working day (5 days per week).

Richard Stone, in his paper in September 2009 edition of Science(Vol. 325. no. 5946, pp. 1336 – 1337), reported: ”the noisy apparatus perched on a wooden desk here at the Baotou Research Institute of Rare Earths (BRIRE) is a prototype magnetic refrigerator. Inside the setup is a white cylinder set of neodymium magnets—that slides along a tube filled with an alloy of another rare earth element, gadolinium. As the magnet traverses the tube, it reorients atoms in the alloy, releasing heat. After the magnet passes, the atoms disorient and soak up heat from their surroundings.  With each cycle, a glass flask inside the box grows chillier. Within several minutes, the flask has cooled by about 20°C. Refrigeration with magnets is the wave of the future as long as there is a steady supply of rare earths.”

Gschneidner, is a personal exchange of e-mails recently noted that “Basically what Richard Stone reports is correct.  Although I have not seen the magnetic refrigerator, I believe what the Chinese told Stone is reasonable.  Work on magnetic cooling is picking up and I am optimistic that we may see commercialization in a few years.”  The 4th International Conference on Magnetic Refrigeration is to he held In Baotou, China next August.

Some magnetic materials heat up when they are placed in a magnetic field and cool down when they are removed from a magnetic field… otherwise known as the magnetocaloric effect. German physicist Emil Warburg discovered this effect in 1881 in pure iron, where the magnitude of the effect had been around 0.5 to 2°C per Tesla change in magnetic field (One Tesla is about 20,000 times the earth's magnetic field). Although the magnetocaloric effect of certain metals has been known for decades, it wasn’t until 1997 when Karl Gschneidner and his colleagues at the Ames Labs demonstrated a robust effect using a rare earth alloy, gadolinium silicon germanium Gd5(Si2Ge2). It is also understood that praseodymium alloyed with nickel (PrNi5) has such a strong magnetocaloric effect that it has allowed scientists to approach within one thousandth of a degree of absolute zero.

Currently, alloys of gadolinium producing 3 to 4 K per tesla (K/T) of change in a magnetic field can be used for magnetic refrigeration or power generation purposes. Experimental refrigerators based on the magnetocaloric effect have been tested in laboratories using magnetic fields of around 5T produced by superconducting magnets.

"Room-temperature magnetic refrigeration cannot be put into practical application without rare earths," says Huang Jiaohong, a senior scientist at BRIRE whose lab discovered in 2005 that a lanthanum-based composite, doped with boron, also has shown a powerful magnetocaloric effect.

Apparently labs in at least 10 countries have developed prototype refrigerators, While Huang predicts the first models should come on the market in several years, other experts say that could take a decade or longer.