New frontiers in magnetic refrigeration with high oscillation energy-efficient electromagnets

Abstract

This article reports on the novel resistive electromagnetic field source with the magnetic energy recovery, which enables the use of the static magnetocaloric regenerator. Most of the existing prototype magnetocaloric devices that operate near room temperature, use magnetic field sources consisting of permanent magnets. The alternating of the magnetic field that is required for the thermodynamic cycle often comes from the rotation of magnets over the refrigerant, that is, an active magnetocaloric regenerator (AMR). Such systems require moving parts and a motor drive, both of which cause additional costs and reduced energy efficiency. Further restrictions in existing devices result from the speed of the magnetisation/ demagnetisation process, which is, in addition to efficient heat transfer, crucial for the compactness of the device. Another drawback is that the instant change of the magnetic field is not feasible, regardless of the principle of movement. Permanent-magnet assemblies based on neodymium are also constrained by the use of this rare-earth-material. Therefore, a number of global research activities relate to the optimization of permanent-magnet-based magnetic field sources. However, ohmic loss, the active cooling of magnets, and considerable energy consumption are the reasons why another type of magnetic field source, that is, the electromagnet, was generally avoided by the magnetocaloric community. This article presents a novel and unique approach that enables substantially improved energy efficiency and applicable operation of rare-earth-free and static electromagnetic field sources, by implementing for the first time the magnetic energy recovery for magnetic refrigeration and heat pumping. To prove the advantages of such a system, a large number of numerical simulations, as well as an experimental proof, were conducted. A comparative analysis was made for the evaluation of the energy efficiency of the proposed novel system vs an example of the existing rotating-magnet assembly. The results of this study reveal that this new type of electromagnetic field sources provides a number of different and important advantages that can lead to new frontiers in research. However, the energy efficiency is still lower than that of the comparable rotating-magnet assembly.