SPP 1599: Caloric Effects in Ferroic Materials: New Concepts for Cooling

Type of Funding: DFG Programmes, Priority Programmes

Refrigeration is one of the main sinks of the German and European electricity consumption and accordingly contributes to worldwide CO2 emissions. High reduction potentials are envisaged if caloric effects in solid materials are utilized. The recent discovery of giant entropy changes associated with ferroelastic phase transformations promises higher efficiency. Ferroic transitions enhance the entropy change of magneto-, elasto-, baro- and electro-caloric effects. Furthermore, because the refrigerant is in a solid state, the technology completely eliminates the need for high global-warming potential halofluorocarbon refrigerants. The smaller footprint for operation and the scalable mechanism open up further applications such as cooling of microsystems. While the principal feasibility of magnetocaloric refrigeration is already evident, the requirement of a large magnetic field (> 2 T) hampers wide industrial and commercial applications. It is expected that this obstacle can be overcome by materials with lower hysteresis and by using other types of fields (stress, electric).

In order to accelerate research on ferroic cooling, this SPP will address the following major challenges for introducing ferroic materials in practical cooling applications: Understanding of the underlying mechanisms, energy efficiency, effect size, fatigue, and system integration.

In detail, the research programme of the priority programme will focus on four key problems related to ferroic cooling:

Which scheme is most efficient for solid state refrigeration? Giant caloric effects occur only in the vicinity of a first order transformation. For comparison experiments should focus on the direct adiabatic temperature change and cooling efficiency.

Which length and time scales are involved? Diffusionless transformations change the structure at the atomic scale. However, in real materials, the hysteretic transformation process creates complex microstructures spanning many length scales up to the macroscale. To understand hysteresis losses, collaborations should cover several length scales, consider coupling effects (thermo-mechanic-magnetic-electric) and, in particular, use suitable in-situ methods.

Which are the best materials and microstructures? Solid state cooling does not only require a maximized entropy change but also heat capacity and conductivity contribute to the cooling power. Hysteresis losses and fatigue, which are critical due to the high cycle numbers required for cooling demonstrators, should be addressed. Research should centre on environmentally friendly materials.

Which are competitive device concepts? The development of novel solid state cooling demonstrators is essential for the adaption of ferroic-caloric materials. Proposal should work out the advantage of the selected setup and consider the effort for the entire refrigeration system.

Project Website

Contact Person at UA Ruhr:
Prof. Dr.-Ing. Gunther Eggeler, Ruhr-Universität Bochum

UA Ruhr Researchers:
Prof. Dr. Ralf Drautz, Ruhr-Universität Bochum
Prof. Dr. Michael Farle, University of Duisburg-Essen
Prof. Dr.-Ing. Jan Frenzel, Ruhr-Universität Bochum
Prof. Dr. Daniel Hägele, Ruhr-Universität Bochum
Dr. Tilmann Hickel, Max-Planck-Institut für Eisenforschung
Prof. Dr.-Ing. Alfred Ludwig, Ruhr-Universität Bochum
Prof. Dr. Doru Lupascu, University of Duisburg-Essen
Dr. Vladimir Shvartsman, University of Duisburg-Essen
Prof. Dr. Heiko Wende, University of Duisburg-Essen

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