Modeling of Thermo-Magnetic Phenomena in Active Magnetic Regenerators

The active magnetic regenerator (AMR) is at the heart of the thermo-magnetic Brayton cooling cycle. It consists of a porous matrix heat exchanger whose solid phase is a magnetocaloric material (solid refrigerant) that undergoes a reversible magnetic phase transition when subjected to a changing magnetic field. The cooling capacity of the cycle is proportional to the mass of solid refrigerant, operating frequency, volumetric displacement of the working fluid (generally an aqueous solution) and regenerator effectiveness. AMRs can be modeled via a porous media approach and a model has been developed to simulate the time-dependent fluid flow and heat transfer processes. Gadolinium (Gd) is usually adopted as a reference material for magnetic cooling at near room temperature and, in this study, its magnetic temperature change and physical properties were accounted for using a combination of experimental data and the Weiss-Debye-Sommerfeld theory. In this paper, the influence of the applied magnetic field waveform and of demagnetizing effects on the AMR performance is investigated numerically. An evaluation of the model is also carried out in the light of a comparison against experimental data for a regenerator containing spherical Gd particles.