Demagnetizing effects in active magnetic regenerators

Magnetic refrigeration (MR) relies on the ability of a magnetic substance to undergo a significant change in magnetic entropy due to the application or removal of an applied magnetic field. In active magnetic regenerators (AMR) the working material tends to operate near the magnetic ordering temperature, and, because the AMR creates a temperature gradient through the bed, the local magnetic permeability can vary widely. Due to geometry and non-uniform properties, an AMR bed is subject to non-negligible demagnetizing effects which can reduce the entropy change due to an applied field as compared to that of a long-thin specimen. A numerical model is used to examine the effects of demagnetizing fields in an AMR. Model results for a single material AMR and a layered bed composed of two materials show the impacts of temperature, shape and materials on effective magnetization, and suggest that demagnetization effects influence the magnetic work performed at each location in the AMR.