Design improvements of a permanent magnet active magnetic refrigerator

•A second generation permanent magnet AMR test apparatus is described in detail.•A unique triple nested Halbach configuration is explained.•Torque issues regarding the magnets are discussed.•A novel hydraulic flow control method using check valves is explained.•A no-load temperature span of 33 K is achieved using 650 g of gadolinium at 0.8 Hz.

A second-generation room-temperature permanent magnet active magnetic regenerator test apparatus using Halbach arrays is described. The magnet arrays consist of three concentric cylinders. Each cylinder is constructed using 12 permanent magnet segments. The inner magnet array is stationary while the intermediate and outer arrays are designed to rotate in opposite directions so as to create a sinusoidal magnetic field waveform with a stationary field direction. The fluid flow system utilizes a novel check valve configuration so that fluid dead volumes are minimized. The system construction is modular to allow for quick replacement of material or system components. Fringing fields near the outer and inner diameters of the arrays are found to create large forces between arrays leading to large torques. Test results using 650 g of gadolinium spheres produce a no-load temperature span of 33 K at 0.8 Hz.