The late twenties of this century, scientists found the magnetic material in the magnetic field under the effect of temperature, the phenomenon of magnetocaloric effect. Subsequently, many scientists and engineers carried out a great deal of research and development work on magnetocaloric materials, magnetic refrigeration technology and devices. So far, low temperature magnetic refrigeration devices below 20K have been put into practical use in some fields, and room temperature magnetic refrigeration technology is still continuing to tackle the problem and has not yet reached the practical level.
Magnetically-cooled materials are materials that have a magnetocaloric effect for magnetic refrigeration systems. Magnetically cooled first is to add a magnetic field to the magnet, so that the magnetic moment in the direction of the magnetic field neatly arranged, and then remove the magnetic field so that the direction of the magnetic moment becomes cluttered, then the magnet absorbs heat from the surrounding heat exchanger to make the surrounding temperature lower , To achieve the purpose of cooling. Magnetically-chilled materials refer to a class of materials that have a magnetocaloric effect for magnetic refrigeration systems. Magnetically-chilled materials are the core of magnetic refrigerators, commonly known as refrigerants or refrigerants.
Due to the widespread use of cryogenic superconductivity, liquid helium is required to cool cryogenic superconducting magnets, but liquid helium is expensive, so it is desirable to have a small, high efficiency cryogenic refrigerator capable of reliquefying helium gasified with liquid helium. If the previous gas compression - expansion refrigerator miniaturization, the compressor must be smaller, this will greatly reduce the cooling efficiency. Therefore, in order to meet the need of liquefied helium, people have been accelerating the development of low temperature (4~20K) magnetic refrigeration materials and devices. After years of efforts, the low temperature magnetic refrigeration technology has been put into practical use. Magnetically-cooled materials used for cryogenic magnetic refrigeration are mainly rare earth garnet Gd3Ga5O12 (GGG) and Dy3Al5O12 (DAG) single crystals. The use of GGG or DAG and other materials made of low temperature magnetic refrigerator is a Kano magnetic refrigeration cycle type, the initial cooling temperature of 16K and 20K.
Low-temperature magnetic refrigeration devices have the unique advantages of miniaturization and high efficiency. They are widely used in the fields of cryogenic physics, magnetic resonance imaging, particle accelerator, space technology, far-infrared detection and microwave receiving. Some special electronic systems are widely used in low temperature Environment, its reliability and sensitivity can be significantly improved.
Magnetic refrigeration is the use of harmless, non-polluting rare earth materials as refrigerants, refrigerators, freezers and air conditioners that use Freon refrigerators instead of refrigerators, refrigerators and freezers can be eliminated as a result of the production and use of Freon refrigeration The environmental pollution caused by the agents and the destruction of the atmospheric ozone layer can therefore protect the human environment and have significant environmental and social benefits.
The Montreal Protocol on Substances that Deplete the Ozone Layer signed in 1987 by more than 80 countries stipulates that in order to prevent atmospheric ozone depletion caused by the production and use of CFCs by the year 2000, freon refrigeration will be restricted and banned in the world by 2000 Our country acceded to this international convention in June 1991 and stipulated that by 2010 China will ban the production and use of CFCs and HFCs such as Freon. Therefore, there is a need to expedite the research and development of harmless new refrigerants or other types of refrigeration technologies that do not use Freon refrigerants. So far, in the research and development in this area, it has been found that magnetic refrigeration is one of the refrigeration methods with high refrigeration efficiency, low energy consumption and no pollution. From the current research on the development of room temperature magnetic refrigeration technology in the United States, it is possible that within 3 to 5 years, room temperature magnetic refrigeration technology may be applied in automobile air conditioning systems and further development of magnetic refrigeration devices such as air conditioners and refrigerators .
Refrigeration materials used in magnetic refrigeration are basically alloys or compounds with rare earth metal as the main component, especially magnetic refrigeration at room temperature almost entirely using rare earth metal Gd or Gd-based alloys.
At present, the research and development of magnetically-cooled materials, technologies and devices and the advanced level in the United States and Japan have all listed the research and development of magnetic refrigeration technology as the key research project in the early 21st century by the end of this century, and have invested a large amount of funds and manpower And material and material resources, extremely competitive, all want to preempt the high-tech fields.
Article from NdFeB Industry Network