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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-421-2

International Heat Transfer Conference 15
August, 10-15, 2014, Kyoto, Japan

Study on Heat Transfer Characteristics of Active Magnetic Regenerator in Magnetic Refrigeration System

Get access (open in a dialog) DOI: 10.1615/IHTC15.acr.008563
pages 939-948

Résumé

Magnetic refrigeration is one of the emerging technologies to replace conventional vapor compression technology. Basic principles rely on magnetocaloric effect (MCE) of solid refrigerants and thermodynamic regeneration cycle. Magnetocaloric material (MCM) heats up when it enters magnetic field and cools down when it comes out of the field. Adiabatic temperature change of typical MCM, Gadolinium (Gd) compound, Gd5Si2Ge2, is about 4 K at 1 T of magnetic field density. Utilizing this small temperature change on a material level, thermodynamic regenerative cycle enables large temperature span of several tens of Kelvin. Regeneration process is largely dependent on heat transfer efficiency between solid refrigerant and heat transfer medium. Active magnetic regenerator (AMR), where the regeneration process occurs, is the heart of the magnetic refrigeration system. For last two decades, many studies have been carried out on AMR by several groups. However, satisfactory design rule still cannot be found. In this paper, we have studied performance of AMR from a view of heat transfer efficiency. Multi-layer AMR has been studied experimentally and analytically. Multi-layer AMR is made of several MCMs in series with different Curie temperatures, and it has been adopted in many magnetic refrigeration systems for its potential capability. For experimental investigation, magnetic refrigeration test-beds were constructed; two linear and two rotary ones. Two kinds of MCMs were used. One is Gd as a reference material and the other is non-rare earth MnFe(Manganese-Iron)-compound. Several multi-layer AMRs were tested to measure temperature span between cold and hot ends. A simplified analytical expression for temperature span was obtained by newly introducing effectiveness of MCE. Temperature span is expressed as a function of effectiveness, number of layers and operating temperature nature of MCM (i.e., full-width-at-half-maximum, FWHM). Analysis of experimental results indicated that the effectiveness is closely related to both AMR heat transfer efficiency and number of layers. In multi-layer AMR, we found that heat transfer characteristic is strongly affected by layer composition and operation type of refrigeration system. From this finding, design direction could be proposed for temperature span of more than 60 degrees Celsius, which is comparable to that from vapor compression technology. The present study emphasizes importance of careful heat transfer design of AMR in magnetic refrigeration systems. This study will give a building block to facilitate the advent of new era of solid-state refrigeration technology.