Magnetocalorics - cooling technology for the future

Heating & cooling systems without harmful refrigerants

Cooling technology is one of the fastest growth areas for additional energy demand. Over 72,000 GWh of electrical power per annum is consumed for technical cooling in Germany which is a relatively cool country. Technical cooling today almost exclusively uses compressor-based systems, whereby the heat is dissipated via the changed physical state of a refrigerant. The problem: all conventional refrigerants have a global warming potential to a greater or lesser extent. And: they require a great deal of space, generate noise, are subject to wear and need to be serviced at great expense. Reasons enough for Fraunhofer IPM scientists to work in the promising field of magnetocaloric cooling.

Based on the magnetocaloric effect, energy efficient cooling systems can be developed, operating entirely without refrigerants. They are based on what are called magnetocaloric (MC) materials. MC materials are magnetizable materials which heat up when exposed to a magnetic field and accordingly cool down again when the field is removed. This is how it is possible to implement a cooling cycle.

System design makes a crucial contribution to cooling performance

Magnetocaloric materials have become far more efficient and better value for money in recent years. However, it must be possible for them to be manufactured on a large scale, and it will be necessary to develop a system for material shaping and system development for structuring cooling systems in order for them to be suitable for use on an industrial scale. System design makes a crucial contribution to cooling performance. When designing thermal systems and thermal coupling of components, Fraunhofer IPM takes recourse to its experience in the fields of thermoelectrics.

Scientists at the Institute research into the optimization of heat transfer from magnetocaloric material to the medium to be cooled or heated. The techniques used achieve up to 1,000 times higher heat transfer rates than would be possible, for instance, by pure thermal conductivity of copper.

The principle of magnetocaloric cooling

© Daniel Hellweg/Fraunhofer IPM

The heat is »driven forward« in only one direction according to the principle of a thermal diode: The heat generated by the magnetic field causes the fluid in the MC material to evaporate (1), increasing the pressure in the segment. The pressure relief valve opens, allowing the vapor to flow into the adjoining element (2). Once the magnet has been switched off, the MC material cools down below the starting temperature (3) and the vapor pressure drops. A vacuum develops in relation to the previous segment. Gaseous fluid flows in and heat from the previous segment is absorbed (4).