SELECTION OF MAGNETIC-MATERIALS FOR AN ACTIVE MAGNETIC REGENERATIVE REFRIGERATOR

High efficiencies of active magnetic regenerative refrigerators (AMRR) are strongly dependent on the correct selection of the magnetic regen erator working material. The selection process involves the thermodyna mic analysis of the AMRR cycle to determine the adiabatic temperature change profile (DELTAT versus T) over the temperature span of interest for an ideal material, and then the matching of real materials whose magnetocaloric effect (MCE) as a function of absolute temperature best fits this profile. This paper develops the calculation of the ideal m agnetic material DELTAT versus T profile for a real AMRR operating bet ween 110 and 300 K and with 1 kW of cooling power. The ideal profile w as a function of the constant entropy flux from the cold end heat load , the irreversible regenerator entropy production, and other real effe cts. To accommodate the large temperature span, several magnetic mater ials were chosen and layered in the regenerator from the cold to the h ot end by increasing the Curie temperature. The resultant DELTAT versu s T curve of the combined material provided only a rough approximation of the calculated ideal material curve. To improve this approximation , physical mixing of magnetic refrigerants was investigated. This proc edure diluted the magnetic moment, thereby reducing magnetic entropy a vailable for the cycle. Further, under adiabatic conditions, mixing pr oduced an intolerable amount of entropy during cycle execution. Simple segmentation of the regenerator with more magnetic materials that bet ter match the ideal profile is an easier way to approximate the ideal DELTAT versus T curve with real materials. Optimum segmentation will b e determined by regenerator complexity.