Magnetocaloric Properties Desired for Magnetic Refrigeration System near Room Temperature
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Magnetocaloric Properties Desired for Magnetic Refrigeration System near Room Temperature H. Wada Department of Physics, Kyushu University, Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581, Japan
ABSTRACT In order to realize the magnetic refrigeration system, it is necessary to develop a 100 W class refrigerator with COP > 7.5. This requires us to find new magnetic refrigerant materials, of which cooling capacity is 2.5 times higher than that of Gd. In this paper, first we discuss the cooling capacity of magnetic refrigerant materials to achieve COP = 7.5. Then, we compare the experimental results of MnAsSb, MnFe(PGe) and La(FeCoSi)13 compounds with the calculated cooling capacity. It is suggested that a composite layer material of MnFe(PGe) would show excellent cooling capacity in the temperature span of 20 K. INTRODUCTION In recent years, environmental aspects have been becoming an important issue. New technologies are preferred if they are energy-efficient and environmentally friendly. Magnetic refrigeration based on the magnetocaloric effect (MCE) has recently attracted increased attention as an alternative technology to the conventional gas compression cycle for room temperature applications, because it does not take a lot of energy to operate and uses no environmentally hazardous chemicals. Since the pioneer work by Ames Laboratory and Astronautics in 1997 [1], various prototype magnetic refrigerators have been proposed [2]. We have been involved in a five-year national project of "Development on Room Temperature Magnetic Refrigeration" supported by New Energy and Industrial Technology Development Organization (NEDO) in Japan, together with Chubu Electric Power Co. Inc., Tokyo Institute of Technology and Kobe University since 2005. During this project, Chubu Electric Power Co. Inc. and Tokyo Institute of Technology group have developed a rotary-type magnetic refrigerator with permanent magnets and they obtained the Coefficient of Performance (COP) of 2.6 in the temperature span of 5 ºC (from 24 ºC to 19 ºC). Moreover, a maximum temperature difference of 20 ºC was achieved by using Gd metals and alloys as magnetic refrigerant materials [3]. These results strongly suggest high performance of magnetic refrigeration near room temperature. However, for the practical application, COP of 7.5 or higher is necessary in the temperature span of 15 ºC for a 100 W class refrigerator. If this is achieved, we expect COP of 12 or greater for a 10 kW class refrigerator, which exceeds the COP of the conventional gas refrigerator. Recently, Hirano et al. simulated the cooling power of their magnetic refrigerator and concluded that COP of 3 in the temperature span of 15 ºC is possible, if the heat exchange mechanism is improved [3]. Their calculations are based on the performance of a magnetic refrigerator equipped with Gd metals and alloys. Therefore, in order to realize COP > 7.5, we have to develop new magnetic refrigerant materials of which cooling capacity is 2.5 times higher
than that of Gd. Such a large cooling capacity co
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