New concept of electromagnetic field source for magnetic refrigeration

This article reports on the latest research achievements on development of static magnetic refrigerators and heat pumps systems. In the article we present the results on the numerical investigation on the novel design of the static magnetic field source. The investigated magnetic field source represents a substantial improvement versus the solution, that concerned the use of electromagnetic field sources with the regeneration of magnetic energy and was presented by Klinar et al. [1]. The results of the study represent an important basis for the future development of static electromagnetic field sources in the domain of magnetic refrigeration and heat pumping. Electromagnets heat up during operation due to the Joule losses in the winding. By significantly reducing the Joule heat, the electromagnet can achieve energy efficiency comparable to structures of permanent magnet assemblies with motor driven rotation, which are usually applied in magnetic refrigeration or heat pumping. Fast magnetization/demagnetization process is crucial for the compactness of device, since it defines the frequency of the operation. An instant step-change of the magnetic flux density in the magnetocaloric material cannot be achieved with permanent magnets regardless the principle of the movement. By implementing the magnetic energy recovery into electromagnetic field source it is not only possible to achieve higher efficiency, but also faster field change due to accumulated electric energy in each cycle. With additional modification of previously presented electronic circuit, it is possible to ensure a constant magnetic field during magnetized state of magnetocaloric material. We have designed 14 conceptual solutions for which we have tested the feasibility of operation and implementation. The most promising concept was evaluated using the Ansoft Maxwell software tool. Based on the obtained results, we chose a geometry for more detailed analysis, for which we made numerous iterations regarding the iron core and windings, and for each geometry several iterations to obtain the most appropriate value of the magnetic flux density in the air gap. One of the most promising geometries was experimentally evaluated to confirm the numerical model. According to simulations, a form of magnetic structure can be achieved which allows the magnetic field alternately to be established efficiently in the air gap with high efficiency at the increase of operating frequency. This reflects as a lower input power, that needs to be provided to the electromagnet, which results in the lower electrical power consumption of a structure and lower heating of the windings.