Magnetic Curie valve

Senior Scientist Christian Bahl and Development Engineer Dan Eriksen from Risø DTU have invented a three-way valve that controls the flow through a magnetic material which is attracted by an external magnet when the liquid reaches a certain temperature. The design is promising and the group is now looking for a partner in the industry who would like to join them in this work.

To be, or not to be - magnetic

Christian Bahl is a Senior Scientist in the Fuel Cells and Solid State Chemistry Division and works mainly with magnetic refrigeration. Magnetic refrigeration is an energy-efficient cooling technique that could help save substantially on electricity consumption in the long term. Through this, Christian Bahl has knowledge of the Curie temperature of different substances.

At the Curie temperature the material switches between being magnetic and non-magnetic. And precisely this property inspired the group to create a shunt valve controlled by magnets.

“If you imagine in your house at home that you had one of our valves connected to the hot water circulation, running through your radiators, then the valve would be able to lead the water through the radiators again, provided the water is hot enough. The rest would go to reheating,” explains Dan Eriksen, who was employed on this project as a Development Engineer in July 2008.

A simple principle

The idea behind this new type of valve is that the liquid flows past a material with a certain Curie temperature. When the liquid temperature falls below this temperature, the material is attracted by a magnet outside the valve. If the temperature rises again, the material is less attracted to the magnet and is pushed back to its starting position by a spring. This movement is used to activate the valve.

In short, there is one inlet for the liquid, and two possible outlets in the valve. Inside the valve is a mechanism which closes either one or the other outlet. This mechanism is controlled by the temperature of the liquid flowing into the valve.

By having several materials with different Curie temperatures in one valve, it is possible to make the valve operate at different temperatures. This principle is used in the group’s shunt valve prototype so that the thermostat becomes temperature-adjustable. The technique is thus totally independent of power and cannot be compared with any 'magnetic valves' on the market which are controlled by an electromagnet.

Right now, the valve prototype operates at temperatures between 10 and 40 °C, but there is plenty of potential to produce valves active at temperatures of up to several hundred degrees and down to the cold temperatures of, for example, liquid nitrogen, as magnetic materials with Curie temperatures exist throughout the whole interval.

Valve with fear of contact

There are obviously many types of valves on the market already, but the conventional valves generally have a penetration of the system if they are to be regulated from the outside. This means that the flow is controlled by a small pivot, as seen on ordinary radiators. These openings may be blocked by lime, or the liquid may leak out. In Risø’s model it is possible to change the activation temperature from the outside by moving a magnet, thus no penetration will be necessary.

You can do this because you are able to produce materials with exactly the Curie temperatures you want. Ceramic magnetic materials are especially promising in this respect.

“The project has drawn heavily on existing knowledge in the division, both in terms of magnetism, but also in terms of the use of ceramic materials, which are similar to the materials used in fuel cells. In time, the manufacturing and processing knowledge in the Fuel Cells and Solid State Chemistry Division could prove to be a huge advantage,” explains Christian Bahl.

Also, ceramic materials are not exposed to corrosion when in contact with oxidising or corrosive chemicals.

Prototype made of nylon

The prototype is partly made of nylon parts ordered from a company that makes 3D materials using rapid prototyping technology.

“One of the major benefits of creating prototypes of this material is that it is cheap to order … when you have to make even the smallest adjustments. This way you can easily find the design that works best,” explains Dan Eriksen, adding that the final choice of material must, of course, be adapted to the purpose of the valve.

“And the applications are potentially many, although this is a niche product,” says Christian Bahl, who hopes to find a partner in the industry with the desire to go ahead with the project.

For further information, please contact: Hanne Krogh, hanne.krogh@risoe.dk