Magnetic refrigeration with GdN by Active Magnetic Refrigerator cycle
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Magnetic refrigeration with GdN by Active Magnetic Refrigerator cycle Yusuke Hirayama1, Hiroyuki Okada1, Takashi Nakagawa1, Takao. A. Yamamoto1, Takafumi Kusunose2, Numazawa Takenori3, Koichi Mastumoto4, Toshio Irie5, and Eiji Nakamura5 1
Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan 3 Exploratory Materials Research Laboratories for Energy and Environment, National Institute for Materials Science, Tsukuba, Ibaraki 305-0003, Japan 4 Department of Physics, Kanazawa University, Kanazawa 920-1192, Japan 5 SANTOKU corporation, Kobe, Hyogo 674-0093, Japan 2
ABSTRACT A magnetic refrigeration test was performed using a test device filled with spherical GdN material synthesized by the hot isostatic pressing (HIP) method. Refrigeration with an active magnetic regenerator cycle was tested in the temperature range between 48 and 66 K, with the field changing from 1.2 to 3.7 T and 2.0 to 4.0 T at upper and lower sides of the regenerator bed filled with the GdN spheres, respectively. Temperature spans about of 2 K were obtained at both sides, and the total temperature span in each cycle attained about 5 K. The specific heat of the material was measured to calculate the magnetic entropy change ΔS and the adiabatic temperature change ΔT induced by the magnetic field change ΔH. It was suggested that for a given ΔH, larger ΔS and ΔT can be exploited when demagnetized to lower H, especially, to zero field. INTRODUCTION Magnetic refrigeration has been studied by many research groups in temperature ranges, under or around 20 K [1-3] and room temperature [4-8]. This technology is based on the magnetocaloric effect (MCE) occurring on a magnetic refrigerant, in which a magnetic field change, ΔH, induces a temperature change, ΔT. The cooling heat is extracted from the refrigerant through the relation, Q = TΔS, where ΔS is magnetic entropy change induced by the ΔH. A large ΔS, leading to a large ΔT, may be extracted from a ferromagnet by changing external field around its Curie temperature TC. In 1982, a new concept of magnetic refrigeration cycle was introduced by Barclay [9], which is now known as Active Magnetic Regenerator (AMR) cycle. In this cycle working substance serves not only as refrigerant but also regenerator. By swinging magnetic field applied to a bed filled with the substance, a temperature gradient is built up across the bed giving a temperature span larger than that given by simple cycle. A fluid is blown through the AMR bed to transfer the heat across it. Each section along the regenerator bed may be understood as undergoing each sub-cycle described by each local temperature and local changing magnetic field. The total cycle is constructed by all the sub-cycles, and a large temperature span may be obtained as that corresponds to the temperature gap between one end and the other of the series.
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