Convegni ATI - Accesso riservato soci CTI

Autore: C. Aprea, A. Greco, A. Maiorino, V. Sergi

Collana: CA - 66 - Rende 2011

Note:
Modern refrigeration is almost entirely based on vapour compression cycle. Magnetic refrigeration is an emerging technology based on the magneto-caloric effect in solid-state refrigerants. Compared to conventional vapour compression systems, magnetic
refrigeration can be an efficient and environmentally friendly technology. The Active Magnetic Regenerative refrigeration (AMR) cycle is a special kind of regenerator for the magnetic refrigerator, in which the magnetic material matrix works both as a refrigerating medium and as a heat regenerating medium. The performance of an AMR cycle depends strongly on the magnetocaloric effect of the magnetic material that is used to built the regenerator. A larger MCE in refrigerant material results in a greater change of internal energy and provides more cooling that needs to be transferred out of the bed by the exchange fluid. In the present paper, a practical model for predicting the performance and efficiency of an AMR cycle has been developed.The model simulates both the magnetic material and the entire cycle of an AMR operating in conformity with a Brayton
regenerative cycle in a temperature range of 280 – 295 K, in conformity with the room temperature range. The model simulates a regenerator made of:pure gadolinium, binary rare earth alloys which present a second order phase transition, alloys which present a
first order phase transition. The second order phase transition alloys are: GdxDy1-x and GdxTb1-x. The first order phase transition alloys 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. A model based on the phenomenological approach of Bean Rodbell is utilized to describe the behaviour of the MnAs1-x Sbx alloys. 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.