Numerical simulation and performance improvement of a multi-polar concentric Halbach cylindrical magnet for magnetic refrigeration

Multi-polar concentric Halbach cylinders of magnets could generate the magnetic field varying considerably in the annular gaps, thus were applied in the rotary magnetic refrigerators. In the current investigation, a six-polar concentric Halbach cylinder is developed based on the ideal concentric one by the numerical simulation with COMSOL Multiphysics. Cylinder radii are optimized and magnet material profiles are adjusted for a better overall performance (Lambda(cool)). Moreover, the segmentation on the concentric cylinder is conducted for an easy fabrication, and the edge effect of finite-length device is studied. With the present investigation, it is found that a larger external radius of external cylinder facilitates a larger flux density in the high field region (vertical bar(B) over bar vertical bar(high)), while Lambda(cool) could be worse. Meanwhile, with the removal of magnet materials enclosed by the equipotential lines of magnetic vector potential, the magnetic flux density in low field region (vertical bar(B) over bar vertical bar(low)) drops from 0.271 to 0.0136 T, and Lambda(cool) rises from 1.36 to 1.85 T 7. Moreover, a proper segmentation would not degrade the difference between vertical bar(B) over bar vertical bar(high) and vertical bar(B) over bar vertical bar(low), on the contrary, Lambda(cool) rises by about 20.2% due to magnet materials lack for efficiency replaced by soft irons. Finally, current 3D simulation indicates the edge effect on Lambda(cool) could be trivial. (C) 2015 Elsevier B.V. All rights reserved.