Magnetic refrigeration

Caloric Cooling and Heating

Caloric cooling and heating is based on the use of so-called ‘caloric’ materials – solid materials which change their thermal state in response to an externally applied field (magnetic, electric, stress/strain, pressure). Such materials can be used as the active components in a refrigeration cycle together with water or alcohol as the medium for heat transport. The technology has great potential for low energy consumption and environmentally friendly cooling at a competitive price.

Traditional refrigeration technology, as found in, e.g., household refrigerators, relies on compressors to achieve a cooling cycle consisting of the liquefaction and evaporation of a gaseous refrigerant. This is a mature and reliable technology but it has a number of drawbacks – in particular, that the most widely used refrigerants are greenhouse gases and that small-scale compressors are inherently inefficient.

Our research in this field began 15 years ago with the realization that one of the cathode materials used for solid oxide fuel cells also exhibits a sizable magnetocaloric effect near room temperature: The temperature of the material changes when a magnetic field is applied to it under adiabatic conditions. This is a fundamental thermodynamic property of magnetic materials close to the temperature at which they lose their magnetism. Similar effects occur in other materials when subjected to, e.g., mechanical stress (elastocaloric materials) or electrical fields (electrocaloric materials).

 A refrigeration cycle based on one of the caloric effects utilizes an active regenerator made of a caloric material in combination with a water-based heat transfer fluid. Such a cycle can be more efficient than the traditional vapour compression cycle because it avoids the throttling, superheat and compressor losses inherent to the latter technology. Caloric refrigeration also avoids the use of gases with high global warming potential such as hydrocarbons or ammonia.

Magnetocaloric refrigerator built at DTU Energy

The department has managed a number of major research projects which have led to the building of two magnetocaloric demonstration devices with a third, to be used as a domestic heat pump, under construction. Our effort covers all the different aspects of caloric cooling, from materials research, regenerator design, heat transfer and flow modelling, permanent magnet optimization and systems design and construction. Notable achievements have been the highest performance magnetic refrigeration device and the first demonstration of an elastocaloric regenerator.

Research topics include:

  • Properties of magnetic materials (scaling close to phase transitions, hysteresis, characterization of magnetic and magnetocaloric properties)
  • Magnetostatic modelling, including design of permanent magnet structures
  • Heat and mass flow modelling
  • Regenerator and system design and optimization of magnetocaloric and elastocaloric devices.

Contact

Christian Bahl
Senior Scientist
DTU Energy
+45 46 77 54 91