Magnetocaloric effect: From materials research to refrigeration devices

The active magnetic regenerator (AMR) is an alternative refrigeration cycle with a potential gain of energy efficiency compared to conventional refrigeration techniques. The AMR poses a complex problem of heat transfer, fluid dynamics and magnetic field, which requires detailed and robust modeling. This paper reviews the existing numerical modeling of room temperature AMR to date. The governing equations, implementation of the magnetocaloric effect (MCE), fluid flow and magnetic field profiles, thermal conduction etc. are discussed in detail as is their impact on the AMR cycle. Flow channeling effects, hysteresis, thermal losses and demagnetizing fields are discussed and it is concluded that more detailed modeling of these phenomena is required to obtain a better understanding of the AMR cycle.

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Review on numerical modeling of active magnetic regenerators for room temperature applications

Application of an electric or magnetic field can significantly affect the freezing characteristics of water. A DC electric field will tend to induce ice nucleation at a lower degree of supercooling, and there is evidence to show that an AC electric field delays the onset of ice nucleation. Industrial research has shown that a magnetic field can be used to delay nucleation and to induce small, unclustered ice. Smaller ice crystals are essential in the preservation of the structure or bioavailability of frozen materials, particularly biological or food products. On the other hand, larger ice crystals facilitate faster freeze drying because it results in less vapor mass transfer resistance. The end part of this review introduces another application of magnetic field in the form of magnetocaloric freezers. This technology is a potential alternative to heat pump drying for commercial freezing and refrigeration.

Effects of Electric and Magnetic Field on Freezing and Possible Relevance in Freeze Drying

Numerical analysis of a reciprocating active magnetic regenerator made of gadolinium wires

A room-temperature magnetic refrigerator, consisting of permanent magnet, active magnetic refrigeration (AMR) cycle bed, pumps, hydraulic circuit, active magnetic double regenerator cycle (AM2RC) and control subsystems, has been designed. The magnetic field is supplied by NdFeB permanent magnets. The AMR bed made by stainless steel 304 encloses gadolinium particles as the magnetic working substance. Each part of the refrigerator is controlled by the programmable controller. The different standard heat exchangers are employed to expel heat. The cycle performance of this self-designed facility is analyzed using Langevin theory. The results provide useful data for future design and development of room-temperature magnetic refrigeration.

Design and performance study of the active magnetic refrigerator for room-temperature application.

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 10 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 0.9 T, 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.

/pdf/optimization-of-a-magnetic-refrigerator-at-room-temperature-48ex96brwz.pdf

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

The cooling characteristics of a room temperature magnetic refrigerator using an active magnetic regenerator (AMR) is presented. The AMR system, which is based on a combination of a thermal storage process and a regeneration process, is widely applied for room temperature magnetic refrigerator. And the system has four sequential processes : adiabatic magnetization, fluid flow, adiabatic demagnetization, and fluid flow. We devise the appropriate simulation model of the heat transfer process inside the AMR particle bed. In addition, the temperature profile inside the AMR bed and the cooling characteristics of the room temperature magnetic regenerator using AMR are performed analytically. In this research, the validity of the analytical model is verified by comparing the experimental results with the analytical results. The results show the larger the fluid transfer volume, the larger the temperature difference between the hot and the cold ends. Also we can observe when the higher magnetic field is applied to the magnetocaloric material, the large temperature span is obtained.

https://www.jstage.jst.go.jp/article/kikaib1979/73/735/73_735_2323/_pdf

Cooling Performance of Room-temperature Magnetic Refrigerator with Active Magnetic Regenerator (Numerical Analysis on Cooling Performance)

The purpose of this study was to understand the optimum operation condition of magnetic refrigerator at room temperature for direct air cooling. The basic components of the target system were a magnetic circuit including two permanent magnets, a test section, an air blower, and an associated instrumentation. The test section consisted of ten test cells which enclosed gadolinium chips as a magnetic working substance in prescribed packing factor. In order to change the applied magnetic field from 0 to 0.9 T, the magnetic circuit was installed on an electric slider which generated reciprocating motion. The system performances were widely investigated both experimentally and analytically for the variety of operation conditions such as a volumetric flow rate of air, a packing mass of magnetic working substance, and a heat exchange cycle. The results reveal that the maximum value of the cooling capacity of the present magnetic refrigerator is obtained in a certain operating condition.

Kohei Sakurai

Papers

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

Cooling Performance of Room-temperature Magnetic Refrigerator with Active Magnetic Regenerator (Numerical Analysis on Cooling Performance)

Cooling Characteristics of a Magnetic Refrigerator at Room Temperature for Air Cooling Systems