Study the Optimal Duty Cycle of a Coaxial Magnet for a Rotary Type Magnetic Refrigerator

In a design of rotary type magnetic refrigerator, a high field of coaxial magnet is desired . Typically, a high field design can be achieved with a small duty cycle which might not be optimized from the viewpoint of the thermal hydraulics of a magnetic refrigerator. Numerical simulation analysis of a coaxial magnet-designed using COMSOL program for rotary type active magnetic refrigeration (AMR) system has been performed for magnet structures based on neodymium-iron-boron permanent magnets. The AMR material considered was thin gadolinium plates. For a rotary type magnetic cooling system, from the thermal hydraulic point of view, the best duty cycle of coaxial magnet should be 50% if the magnetic field can be kept as constant during the period of duty cycles. However, the simulation calculation shows that a serious reduction of the magnetic field strength at higher duty cycles resulting in lower magnetic cooling efficiency. After considering the thermo-hydraulic part, the optimized duty cycle is around 30% if temperature drop is 10 K between hot and cold ends on a rotary type magnetic cooling system.