Octagonal Halbach Magnet Array Design for a Magnetic Refrigerator

An effective magnet array design for magnetic refrigeration systems is crucial given the space limitations and need for maintaining the required cooling capacity. Here, Halbach permanent magnet arrays (HPMA) in an octagonal orientation are studied using NdFeB permanent magnets. Gadolinium is selected as the magnetocaloric material (MCM) for the aperture inside the octagonal HPMA. The optimum outer-to-inner radii ratio for the octagonal HPMA and MCM system is found to be 2, at which the cooling energy per volume of magnet has a peak. For this ratio, the effect of using soft magnetic material, which in this study is FeVCo, inside and outside the HPMA is evaluated over a range of material thicknesses. The optimum soft magnetic material thickness outside the HPMA is obtained to be 3% of the external radius. At this thickness, soft magnetic material is also placed inside the array as a concentrator. It is found that although using soft magnetic material inside the magnet array increases the average flux, cooling energy is decreased due to using less MCM inside the aperture because of the space occupied by the soft magnetic material.