Optimization of a magnetic refrigerator at room temperature for air cooling systems

Abstract

The purpose of this study is to understand the optimum operating condition of magnetic refrigerator at room temperature for direct air-cooling. The basic components of the target system are a magnetic circuit including two permanent magnets, a test section, an air blower, and an associated instrumentation. The test section consists of ten test cells which enclose gadolinium chips as a magnetic working substance in a prescribed packing rate. In order to change the applied magnetic field from 0 to 0.9T, the magnetic circuit is installed on an electric slider which generates reciprocating motion. The system performances are widely investigated both experimentally and analytically for the variety of conditions such as a volumetric flow rate of air, a packing length of magnetic working substance, and a heat exchange cycle. The results reveal that the present magnetic refrigerator has a maximum value of the cooling rate in an appropriate operating condition. Keywords IntroductionMagnetic refrigerators are capable of maintaining high efficiency at a range of extremely low temperatures at which operation is difficult for a conventional gas compression refrigerator. Such refrigeration devices are used to generate extremely low temperatures in the milli-Kelvin range. Accordingly because realization of a compact, low noise and low vibration refrigerator system is possible, it is expected that a magnetic refrigerator can be developed for a compact residential refrigeration system that can be operated in the room-temperature range.However, at room temperature, the heat capacity of the magnetic working substances -the refrigerants -becomes markedly larger than at the extremely low temperatures at which they are typically used. The temperature distribution of the magnetic working substance obtained by changing the magnetic field becomes smaller. Therefore, efficient heat transfer control is important for constructing a useful magnetic refrigeration system. Improvement of the refrigeration cycle and system miniaturization have been studied [1][2][3][4] to solve this problem and to put room-temperature magnetic refrigerators to practical use, but no technology has been established. Urgent studies are necessary to obtain a practical system. The performance of the magnetic refrigeration system depends on the magnetocaloric effect of the magnetic working substance. Therefore, research and development of magnetic substances [5,6] that can provide markedly higher magnetocaloric effects have been the subjects of great effort. Nevertheless, no examples exist of research and development from the perspective of promoting heat transfer of magnetic substances.Accordingly, the primary objective of the present study is to elucidate heat transfer characteristics between magnetic working substances used for magnetic refrigeration systems and heat transfer media under a variety of conditions. In this study, a magnetic room-temperature refrigeration system is constructed, and an experimental study is executed to explain the influences o...

Numerical study on the thermohydraulic performance of a reciprocating room temperature active magnetic regenerator

“…The AMR was splitted into two symmetrical cylinders (Figure 3), in order to enhance its heat transfer efficiency. These cylinders were designed according to the flow between the MCM particles configuration (Figure 4) presented by Kawanami et al [10]. The permanent magnet alternatively moves towards the left and right cylinders, inducing their alternative magnetisation and demagnetisation.…”

A review of magnetic refrigerator and heat pump prototypes built before the year 2010

“…This is the case when the temperature differences in the heat exchangers do not match the adiabatic temperature change of the magnetocaloric material. An (Kawanami et al, 2005;Kawanami, 2007). Fig.…”

“…15, another reciprocating magnetic refrigerator was built in 2005 at the Graduate School of Engineering of the Hokkaido University (Kawanami et al, 2005). Destilled water was chosen as heat transfer fluid.…”

Overview of Existing Magnetocaloric Prototype Devices

“…The heat-transfer fluid was water. At frequency of 0.167 Hz, the device produced a specific cooling power of 45.5 W kg −1 at a temperature span of 23 K. In a lower magnetic field of 1 T, a specific cooling power of 18.2 W kg −1 was obtained for a temperature span of 11 K. In 2005 researchers from Hokkaido University presented their first prototype in the article by Kawanami et al [12]. It was a Gd packed-bed AMR with a permanent-magnet assembly that produced a magnetic field of 0.9 T. The heat-transfer fluid was air.…”