Researchers in the Risø National Laboratory at the Technical University of Denmark (DTU) have achieved their first milestone in magnetic cooling – between 5 and 10° of cooling. Currently the team has achieved 8.7°C, which means that a refrigerator at room temperature (20°C) can be cooled to almost 11°C. While this would be inadequate for a domestic refrigerator, the project's test setup is highly appropriate for conducting research into different materials, varying operating conditions and the strength of the magnetic field.
Christian Bahl, a postdoctoral student attached to the project for one year, states: “The setup is not the largest of its type, but the most important thing is that it is easy to exchange parts in the machine. With the knowledge that we gain along the way, we will ultimately be able to build the very best magnetic cooling system.”
More than E2.8million (DKK21million) in new funding has made it possible to appoint three PhD students to work on the Magcool project, and two more PhD students are to be appointed in the autumn.
Magnetic cooling technology exploits the fact that when a magnetic material, in this case the element gadolinium, is magnetised, heat is produced as a by-product of entropy. The principle of entropy is that there will always be a constant amount of order/disorder in a substance. When the magnet puts the substance in ‘order’, it has to get rid of the excess disorder – which it outputs as heat. Conversely, when the magnetic field is removed, the substance becomes cold. The heat is transferred to a fluid that is pumped back and forth past the substance inside a cylinder. The end that becomes cold will be located inside the refrigerator and the warm end will be outside.
Although relatively energy-efficient refrigerators are already available on the market, there are three good reasons why this type of cooling has a future.
First, the technology is potentially more energy-efficient than the alternatives. It only really uses energy to move the magnetic field to and from the magnetic material. The model currently under development produces the magnetic field through a system of powerful blocks of magnets similar to those found on refrigerator doors, only stronger. These do not wear, and therefore do not need replacing – which is good for the environment.
This leads to the second major benefit, namely the fluid, which could potentially be plain water. Consequently there would not be the same environmental impact as with today's compressor-based refrigerators.
The third potential benefit is the noise level. Bahl expects the demonstration model, which should be ready in 2010, will be practically silent. The opportunities are obvious.
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