Towards powerful magnetocaloric devices with static electro-permanent magnets

INTRODUCTION: Magnetocaloric energy conversion represents an alternative to existing refrigeration, heat pump and energy harvesting technologies. A crucial part of a magnetocaloric device concerns the magnetic field source. It uses mainly rare-earth materials and consists of moving parts and a drive system while displaying a limited energy efficiency and unavailability of fast and variable control of the magnetic field. Recent advances in efficient heat transfer for high-frequency magnetic cooling call for new developments of magnetic field sources that can operate with high efficiency at high frequencies. OBJECTIVES: We report the concept of an electro-permanent magnetic (EPM) field source that efficiently recovers magnetic energy. In contrast to existing magnets, it allows very well-controlled operation without any moving parts. The main objective of this paper is to present a numerical and experimental study in which such an EPM was designed, built and tested. METHODS: An extensive numerical investigation of the proposed design was carried out in terms of various geometrical and operating parameters. One of the design variations was built and experimentally evaluated for its energy efficiency and temperature increase at various operating frequencies. RESULTS: We demonstrate an energy efficiency of these magnets of over 80% and operation with frequencies up to 50 Hz, which is crucial for future high-power-density and high-frequency magnetocaloric devices. CONCLUSIONS: Considering high energy efficiency at high operating frequencies, such EPMs would allow for miniaturization, making them a viable option for future compact magnetocaloric devices.