The use of the first and of the second order phase magnetic transition alloys for an AMR refrigerator at room temperature: A numerical analysis of the energy performances

The magnetic refrigeration is a new highly efficient and environmentally protective technology, which could be an actual solution for the typical problems of the vapour compression systems. The core of a magnetic refrigerator system is the Active Magnetic Regenerator (AMR). It is a special kind of thermal regenerator made of magnetic material which works both as a refrigerating medium and as a heat regenerating medium. The performance of an AMR system strongly depends on the magnetocaloric effect of the magnetic material used to build the regenerator.In the present paper, a model to simulate the thermal behaviour of an AMR has been introduced for predicting the performance of an AMR refrigerator system. Different magnetic materials have been considered as refrigerant: pure gadolinium, second order phase magnetic transition binary rare earth alloys (SOMT) and first order phase magnetic transition alloys (FOMT). The SOMT are GdxDy1−x and GdxTb1−x whereas the FOMT are Gd5(SixGe1−x)4 and MnAs1−xSbx. The magnetocaloric behaviour of gadolinium can be correctly predicted by the Weiss molecular field theory. This approach can be generalized for binary alloys with a second order phase transition. The behaviour of the MnAs1−xSbx alloys is described by means of a model based on the phenomenological approach of Bean Rodbell. Interpolation of empirical data is utilized for the evaluation of the magnetocaloric effect of Gd5(SixGe1−x)4 alloys.With this model, the refrigeration capacity, the power consumption and consequently the Coefficient of Performance of the cycle can be predicted. The results of the simulation clearly show that Gd5(SixGe1−x)4 is the best magnetic material with a COP that is always greater then that of a traditional vapour compression plant in the same operating conditions (from a minimum of +40% to a maximum of +62%).

► A comparison between vapour compression plant and magnetic refrigeration.
► Model of an active magnetic regenerative refrigeration cycle.
► Comparison between different magnetic materials.
► Gd5(SixGe1−x)4 is the best magnetic material.