Development and Fundamental Characteristics of a Prototype Magnetocaloric Heat Pump
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Development and Fundamental Characteristics of a Prototype Magnetocaloric Heat Pump
Tsuyoshi Kawanami1 and Shigeki Hirano2 1 Dept. of Mech. Eng., Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan 2 Hokkaido Research Organization, N19-W11, Kita-ku, Sapporo 060-0819, Japan
ABSTRACT The primary objective of this study is to discuss the optimum operating conditions of magnetocaloric heat pumps according to the fundamental heat transfer characteristics of an active magnetic regenerator (AMR) bed. The AMR cycle has four sequential processes: magnetization, heat exchange fluid flow, demagnetization, and heat exchange fluid blow. The fundamental heat transfer characteristics of each process of the AMR cycle is investigated minutely. Moreover, the cooling power and the overall system performance are evaluated when the system is running continuously. In addition to the aforementioned investigation, we have developed a prototype rotational magnetocaloric heat pump having a compact component arrangement and an uncomplicated control system. A performance evaluation has been conducted to obtain the optimum conditions for practical operation. The operation parameters such as the heat transfer fluid flow rate, rotational frequency, and initial temperature of the heat transfer fluid are examined, and the variations of the maximum temperature span between the inlet and outlet for the heat transfer fluid are discussed. As a result, the values of the optimum rotational frequency and flow rate are obtained to obtain the maximum temperature span between the inlet and outlet of the present magnetocaloric heat pump.
INTRODUCTION In recent years, global warming has become an international concern and there is a need to reduce emissions of greenhouse gases; however, F-gases, which have a significant greenhouse effect, are still commonly used as a refrigerant for heat pumps. It is crucial to develop a new alternative refrigerant, which has zero global warming potential and is environmentally friendly.
A magnetic heat pump cycle is based on the magnetocaloric effect (MCE), which is caused by an entropy change induced by a magnetic field change and observed in a particular type of material called magnetocaloric material (MCM). The magnetocaloric material generates and absorbs heat induced by the magnetic field change and functions as the working material. The magnetocaloric heat pump is based on the magnetocaloric refrigeration cycle, which does not depend on F-gases; thus, magnetocaloric refrigeration has a high potential for use as an alternative refrigeration method. In the past, the use of magnetic refrigeration was limited to creating an extremely low temperature region to be used as a cryogenic field. The reason for the magnetic refrigerator not being widely used at near room temperature is the difficulty in obtaining a sufficient temperature change by using MCMs. In the room temperature range, the temperature change in an MCM induced by the MCE is small because of the increase in the lattice heat capacity of the mater
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