A numerical analysis of an active magnetic regenerative cascade system

Magnetic refrigeration is an emerging green technology based on the magnetocaloric effect (MCE) in solid-state refrigerants with environmentally desirable characteristics. The active magnetic regenerator is a special kind of regenerator for the active magnetic regenerative cycle (AMR), in which the magnetic material matrix works both as a refrigerating medium and as a heat regenerating medium, while the fluid flowing in the porous matrix works as a heat transfer medium. The MCE is maximal at the Curie temperature, and is large only in the temperature interval around this temperature. It is therefore advantageous that the operating point of the refrigeration plant and this temperature interval of optimal MCE coincide. Therefore a good solution is to work with a cascade system, where each unit has its own optimally adapted working temperature. In the present paper, a practical model for predicting the performance and efficiency of an AMRC (Active Magnetic Regenerative Cascade cycle) system has been developed. The model simulates both the ferromagnetic material and the entire cycle of an AMRC operating in conformity with a Brayton regenerative cycle. In addition, the model simulates a two-stage cascade systems with each stage operating at its optimal point. The program simulates a cascade system working with the Gd-x Tb1-x alloys as constituent materials for the regenerator of the first and of the second stage, varying the composition of the alloy. The heat transfer medium is a water-glycol mixture (50% by weight). With this model, the refrigeration capacity, the power consumption and consequently the coefficient of performance can be predicted. The aim of this paper is to provide some useful indications for the design of an AMR prototype. In this simulation attention is paid on both the temperature span enlargement and the compactness of the AMR system. Copyright (C) 2010 John Wiley & Sons, Ltd.