Composite materials for Ericsson-like magnetic refrigeration cycle

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Abstract
The ideal magnetic Ericsson refrigeration cycle should have a constant induced magnetic entropy change as a function of temperature over the whole refrigeration range. To realize this condition using composite materials, a numerical method has been developed to determine the optimum proportions of the component materials in such refrigerants. This paper investigates the effects of increasing the number (n) of the components on the constancy of the magnetic entropy change of the composite (ΔScom), and suggests some new composite refrigerants. For this purpose, the Gd1−x–Dyx (with x=0, 0.12, 0.28, 0.49, and 0.70) alloys, have been used. The values of ΔS have been calculated both from mean-field theory as well as from experimental magnetization curves of these alloys, in the 0.1–7 T magnetic field range and the 200–300 K temperature range. Two sets of composite materials have then been proposed as refrigerants, operating, respectively, over the temperature range 240–290 K and 210–290 K. The ΔS data of the individual Gd–Dy alloys were then used to calculate the optimum mass ratio of the composites. The resultant ΔScom is practically constant in the required temperature range and amounts to 8.0 and 7.3 J/kg K for the two respective sets. The results show that a subsequent increase of n can improve the constancy of the value of ΔScom, and, hence, the corresponding refrigerant should operate more efficiently. Thus, it is found that the appropriate values of n are 3 and 4, respectively, for the first and the second set.