The Ames Laboratory at Iowa State University hosted a magnetic refrigeration conference that drew an international audience in Des Moines Iowa on May 12, 2009. The focus of the four-day event was on an energy efficient form of refrigeration that replaces gas compressors and ozone-depleting refrigerants with a system that uses special alloys and a magnetic field to provide the cooling and environmentally benign coolants to circulate that cooling power through the refrigeration loop.
A magnetic refrigeration system works by applying a magnetic field to a magnetic material – some of the most promising being metallic alloys – causing it to heat up. This excess heat is removed from the system by water, cooling the material back down to its original temperature. When the magnetic field is removed the material cools down even further. This is the cooling property that researchers hope to harness for a wide variety of cooling applications.
Conference organizer Karl Gschneidner, a senior metallurgist at the U.S. Department of Energy’s Ames Laboratory and the Anson Marston Distinguished Professor at Iowa State University, is a pioneer in magnetic refrigeration and a world-renowned expert in the rare-earth metals used in the technology. Gschneidner says, “ Magnetic cooling and refrigeration is 20 to 30 percent more energy efficient than conventional vapor-compression refrigeration. The magnetic refrigerants are solids, so the hazardous, ozone-depleting and greenhouse chemicals are completely eliminated, making magnetic refrigeration one of the few, positively clean technologies.”
The first operational laboratory prototype magnetic refrigerator will be on display. It was built by Astronautics Corporation of America, Milwaukee, Wis., with assistance from Ames Laboratory scientists who worked on the magnetic refrigerant materials.
Refrigeration and air conditioning units pose a major load to the planet’s energy consumption – in the U.S. in the summer months they account for approximately 50 percent of the country’s energy use.
Then on May 15th Dr James Moore and Professor Lesley Cohen, from Imperial Collage London, Department of Physics, paper was published in Advanced Materials. The new study shows that the pattern of crystals inside different alloys – otherwise known as their microstructure – has a direct effect on how well they could perform at the heart of a magnetic refrigerator system. The Imperial College London says this could, in the future, help them to custom-design the best material for the job.
Professor Cohen explains that by using unique probes designed at Imperial, her team was able to analyze what happens to different materials on a microscopic level when they are magnetized and demagnetized. This enabled the team to pinpoint what makes some materials better candidates for magnetic refrigeration than others. She says, “We found that the structure of crystals in different metals directly affects how dramatically they heat up and cool down when a magnetic field is applied and removed. This is an exciting discovery because it means we may one day be able to tailor-make a material from the ‘bottom up’, starting with the microstructure, so it ticks all the boxes required to run a magnetic fridge. This is vitally important because finding a low-energy alternative to the fridges and air conditioning systems in our homes and work places is vital for cutting our carbon emissions and tackling climate change.”
This new research follows another study published by the same Imperial group in Physical Review B last month, in which they used similar probing techniques to precisely measure the temperature changes that occur when different materials are removed from a magnetic field, and to analyze the different ways they occur. The lead scientist Kelly Morrison found that at the molecular level two different temperature change processes, known as first- and second- order changes, happen simultaneously in each material. The team thinks that the extent to which each of these two processes behave in a material also affects its cooling capabilities.
Professor Cohen says this means that the majority of research to perfect magnetic refrigeration worldwide has tended to involve analyzing and testing large samples of materials, the key to finding a suitable material for everyday applications may lie in the smaller detail, “Our research illustrates the importance of understanding the microstructure of these materials and how they respond to magnetic fields on a microscopic level.”
The research was carried out in collaboration with the Ames Laboratory at Iowa State University.
Improving refrigeration by about 25% would be a significant improvement. With threats to living comfortably, storing foods and other important task threatened by cap and trade costs, 25% might get consumers back closer to something affordable. Most of America is air-conditioned some or a lot of the year. Refrigeration is a continuous job. These two energy driven jobs deserve intense attention and this work might be just what is needed.