Room Temperature Magnetic Refrigeration Technology

Book Description: Refrigeration is the process of removing heat from an enclosed space, or from a substance, and moving it to a place where it is unobjectionable. The primary purpose of refrigeration is lowering the temperature of the enclosed space or substance and then maintaining that lower temperature. This book reviews research on refrigeration including an overview of up-to-date developments and technology in the field of magnetic refrigeration at room temperature (RTMR); an alternative approach based on artificial neural networks (ANNs) to determine thermodynamic properties of refrigerants; solar powered sorption refrigeration and air conditioning; the modelling of chilling and freezing processes and others.

This chapter of the book Refrigeration: Theory, Technology and Applications, presents an overview of up-to-date developments in the field of magnetic refrigeration (MR), with particular reference to magnetic refrigeration at room temperature (RTMR). RTMR technology is described both from a research and a technological oriented point of view, by means of the available literature and author's experience in the field. After a brief historical review, the chapter starts with the thermodynamic fundamentals of the magneto-thermal interactions in magnetocaloric materials, explaining the main significant thermo physical and magnetic properties involved in this phenomenon. Then a review of the refrigeration processes proposed over the last 30 years is carried out. In this section the working principle of several MR devices (systems) is explained and the main issues which still withstand to the actual engineering application of this technology at room temperature are put in evidence. The performance parameters involved in the characterization of the RTMR are outlined both for the magnet assembly and for the Magneto Caloric Effect (MCE) material characteristics. Furthermore the main overall performance parameters (temperature span, useful heat transfer rate, coefficient of performance, and so on) are defined and the criteria for their calculation are explained in actual RTMR thermodynamic cycles. There are three main technological issues involved in the realization of magnetic refrigerators competitive with traditional technologies, from both an economic and a technological point of view. The development of new materials, the design of strong magnetic sources with permanent magnets, and the definition of optimized process arrangements are essential for the improvement and the diffusion of this innovative way of cooling. The most advanced prototypes, available in open literature, are presented and their working characteristics outlined. All of the main technological problems related to RTMR, that is (i) the study for new materials with high specific MCE and the problem of measuring the MCE of each material, (ii) permanent magnets design and assembly to achieve very high magnetic fields in as far as possible large useful volumes (e.g. up to 2 Tesla in a 15mm field gap, or up to 4Tesla in a small cylindrical volume), and (iii) the design of engineering systems able to work with high efficiency in a given temperature range, are addressed and discussed. © 2011 by Nova Science Publishers, Inc. All rights reserved.