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Source: Fraunhofer-GesellschaftWorldwide, many groups are working on refrigerators, industrial cooling systems and air conditioning systems that pump heat using magnetocaloric materials (see box). The cycle of heating and cooling generated by magnetization can be used for cooling. At the Fraunhofer Institute for Physical Measurement Techniques IPM in Freiburg, the physicist dr. Kilian Bartholomé and his team rely on this technology to develop a highly efficient concept for heat transfer that works without harmful refrigerants. There is a great need for innovative cooling technology. Today’s fluorinated hydrocarbons (HFCs) have a high global warming potential. The EU has therefore significantly restricted its use. As an alternative to HFC there are natural refrigerants, such as butane or propane. These gases are used in household refrigerators. They are flammable, however. The amount contained in household refrigerators is considered safe. However, they are not an option for large refrigeration systems such as in supermarkets. The industry is working on alternative refrigerants. But until now, there are no convincing solutions. Environmentally friendly lanthanum-iron-silicon alloy as a magnetocaloric materialA magnetocaloric cooling system works without harmful refrigerants. As magnetocaloric material, the researchers use an environmentally friendly lanthanum-iron-silicon alloy, which heats up when a magnetic field is applied and cools down again when switched off. Kilian Bartholomé and his team have developed and patented a special process for dissipating the heat generated. He relies on the use of latent heat in the construction of his chiller – this is the energy required for a liquid to evaporate. “Because water absorbs a great deal of energy when it changes from a liquid to a gaseous state, we use the evaporation process to transfer the heat,” explains the Ph.D. physicist. “That way, the thermal energy can be transferred very efficiently.” Kilian Bartholomé and his colleague Jan König came up with the idea of using the evaporation process for heat transport through heat pipes, which are used as tube collectors in solar systems or for computer cooling. The heatpipes consist of a vacuum tube, in which some liquid is trapped. If one side of the tube is heated, the fluid evaporates on this side and condenses on the cold side. High heat transfer rates are achieved. However, the magnetocaloric heatpipe developed at the Fraunhofer IPM is much more complex. It consists of many small chambers in which the magnetocaloric material is located. So that the alloy can be optimally penetrated by water vapor, it has a fine-porous structure. The recipe for the production of the porous alloy comes from Dr. med. Sandra Wieland and dr. Martin Dressler from the Fraunhofer Institute for Manufacturing Technology and Applied Materials Research IFAM.New World Record for Magnetocaloric Cooling Systems To further increase efficiency, Bartholomé circles the segments of the heatpipe and rotates a magnet in the middle. When the demonstrator is ready by the end of the year, it should have a capacity of 300 watts. For comparison, the compressor of a household refrigerator has a capacity of 50 to 100 watts. Even now, the system can be run at a very high frequency. Therefore, the Freiburg research group has decided to break the world record for magnetocaloric cooling systems with the demonstrator – in terms of system frequency. The long-term goal is to achieve 50 percent of the theoretical maximum efficiency. Today, comparable systems achieve around 30 percent. The industry is already showing great interest, for example Philipp Kirsch GmbH, which manufactures special refrigerators for medical laboratories, pharmacies and hospitals. The traditional German company cooperates with the Fraunhofer IPM in a project funded by the Federal Ministry of Economics. “We want to launch a minus 86 degree device based on magnetocalorics,” says Managing Director Jochen Kopitzke. »Magnetocaloric has a great deal of disruptive potential and could replace compressor cooling in the medium term. We see a clear market there that we can open up to. “


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