Milestone in magnetic cooling

Monday 10 September 2007

The first milestone in magnetic cooling has been achieved. Between 5 and 10 degrees of cooling – this was the success criteria for the first milestone in a project involving magnetic cooling at Risø National Laboratory – Technical University of Denmark (DTU). And the figure is currently at 8.7°C – this means that a refrigerator at room temperature (20°C) can be cooled to almost 11°C. Of course, this is not quite enough to keep the milk cold, but the project’s test setup also has only the one objective of conducting research in different materials, varying operating conditions and the strength of the magnetic field.

How is a magnetic field used for cooling?
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 – and this becomes heat. Conversely, when the magnetic field is again 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.

Why magnetic cooling?
It is natural to wonder: Why magnetic cooling? After all, there are decent and also relatively energy-efficient refrigerators on the market. But 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 we use on our refrigerator doors, only stronger. These do not get worn out, and thus do not need replacing, which is very good for the environment.

This leads to the second major benefit, namely the fluid, which could turn out to be just plain water. Consequently, there would not be the same environmental impact as with today’s compressor-based refrigerators. The third great potential difference is the noise level. Bahl expects their demonstration model, which should be ready in 2010, to be practically silent. The opportunities are obvious.

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