19-04-2012, 12:49 PM
Development of Room Temperature Magnetic Refrigerator - Overall Plan
[attachment=20351]
INTRODUCTION
The development of environmentally-friendly freezing and refrigerating technologies that do not use fluorocarbons or alternative fluorocarbons has accelerated in view of global warming countermeasures. From among these, in order to promote the development of high-efficiency non-fluorocarbon refrigeration and air conditioning systems, a magnetic refrigeration technology that is completely different from the conventional gas refrigeration method has been under development, utilizing the phenomenon in which a certain magnetic material changes temperature when a change is made to the magnetic field. Although the idea is to apply this refrigeration technology to air conditioners or refrigerators, it was at one time considered difficult to put magnetic refrigeration technology into practical application, since the temperature variation range of the magnetic material caused by one magnetic change is small. Recently, due to progress made in the development of refrigerating cycles and magnetic materials that are suitable for magnetic refrigeration, the development of a magnetic refrigeration system that operates at near room temperature has been promoted both domestically and abroad. In Japan, this has been chosen as a national project, and positive results have been achieved. In this report, the development of a room temperature magnetic refrigerator will be introduced.
DEVELOPING ROOM TEMPERATURE MAGNETIC REFRIGERATOR R&D
has been conducted on the use of magnetic refrigeration technology as a special technology to create ultra-low temperatures. In order to use this technology within the room temperature range, the following technical issues need to be resolved:
(1) The temperature change caused by the magneto-caloric effect is small at room temperature. When the temperature is 20 ºC or higher, the influx and efflux of heat caused by the magneto-caloric
- 2 -2010 International Symposium on Next-generation Air Conditioning and Refrigeration Technology,
17 – 19 February 2010, Tokyo, Japan
effect is absorbed by the lattice system, due to the lattice-specific heat being greater than the magnetic-specific heat. As a result, the temperature variation range obtained will be as small as several degrees Celsius. (2) Heat exchange is difficult due to the magnetic working material being solid. In general, it can be said regarding magnetic refrigerators that the amount of heat absorption and the caloric value per magnetic working material is large, giving them the merit of having the ability to be made compact. However, at the same time, it is difficult to improve upon the heat exchange efficiency, since a sufficient heat transfer area cannot be secured. In addition, there is a long history of R&D on refrigerators that operate at room temperature, due to the need for them. However, in circumstances where gas refrigerators are available at moderate prices, they are not attractive unless their performance dramatically improves. For this reason, magnetic refrigeration at room temperature has been considered less possible than magnetic refrigeration at ultra-low temperatures, and, therefore, insufficient R&D has been conducted regarding the aspect of materials. This can be stated as one of the reasons why magnetic refrigeration at room temperature has not put into application.
DEVELOPMENT STATUS
State of development domestically and abroad
Due to growing concern regarding global environmental problems and the progress in R&D of room temperature magnetic refrigerators, active efforts have been made domestically and abroad. In September 2005, the first international conference on room temperature magnetic refrigerators was held by the International Institute of Refrigeration (IIR) in Montreux, Switzerland. In this conference, a presentation was given on the results of the operation of a magnetic refrigerator developed by the same research group[1] which stated that a maximum refrigerating capacity of 50 W was obtained at room temperature using an La-based magnetic material. Although this value is slightly smaller than the maximum refrigerating capacity of the magnetic refrigeration system we have developed (60 W)[2], the weight of the magnetic material they used was approximately 1/20 that of the system we developed and the entire system was very compact, showing that engineering developments have been steadily progressing. The international conference on room temperature magnetic refrigerators was held even in 2007 and 2009, and will be held in China in 2010. As for domestic developments, the Tohoku University and Kyushu University groups are respectively working on the development of magnetic work materials, and they drew a high degree of attention at the international conference mentioned above. Concerning the system development, the development of a refrigerator in which a permanent magnet rotates is currently being promoted in the national project, which will be described hereinafter.
Rotary magnetic refrigeration system using permanent magnet
In 2000, it was verified that it is possible to cool items down even to room temperature utilizing magnetic refrigeration by use of the strong magnetic field of a superconducting magnet[3]. However, as long as a superconducting magnet is used, power is required to generate the magnetic field. Therefore, a compact system using a permanent magnet that does not require power to generate a magnetic field is necessary, in order to put magnetic refrigeration into practical application.
[attachment=20351]
INTRODUCTION
The development of environmentally-friendly freezing and refrigerating technologies that do not use fluorocarbons or alternative fluorocarbons has accelerated in view of global warming countermeasures. From among these, in order to promote the development of high-efficiency non-fluorocarbon refrigeration and air conditioning systems, a magnetic refrigeration technology that is completely different from the conventional gas refrigeration method has been under development, utilizing the phenomenon in which a certain magnetic material changes temperature when a change is made to the magnetic field. Although the idea is to apply this refrigeration technology to air conditioners or refrigerators, it was at one time considered difficult to put magnetic refrigeration technology into practical application, since the temperature variation range of the magnetic material caused by one magnetic change is small. Recently, due to progress made in the development of refrigerating cycles and magnetic materials that are suitable for magnetic refrigeration, the development of a magnetic refrigeration system that operates at near room temperature has been promoted both domestically and abroad. In Japan, this has been chosen as a national project, and positive results have been achieved. In this report, the development of a room temperature magnetic refrigerator will be introduced.
DEVELOPING ROOM TEMPERATURE MAGNETIC REFRIGERATOR R&D
has been conducted on the use of magnetic refrigeration technology as a special technology to create ultra-low temperatures. In order to use this technology within the room temperature range, the following technical issues need to be resolved:
(1) The temperature change caused by the magneto-caloric effect is small at room temperature. When the temperature is 20 ºC or higher, the influx and efflux of heat caused by the magneto-caloric
- 2 -2010 International Symposium on Next-generation Air Conditioning and Refrigeration Technology,
17 – 19 February 2010, Tokyo, Japan
effect is absorbed by the lattice system, due to the lattice-specific heat being greater than the magnetic-specific heat. As a result, the temperature variation range obtained will be as small as several degrees Celsius. (2) Heat exchange is difficult due to the magnetic working material being solid. In general, it can be said regarding magnetic refrigerators that the amount of heat absorption and the caloric value per magnetic working material is large, giving them the merit of having the ability to be made compact. However, at the same time, it is difficult to improve upon the heat exchange efficiency, since a sufficient heat transfer area cannot be secured. In addition, there is a long history of R&D on refrigerators that operate at room temperature, due to the need for them. However, in circumstances where gas refrigerators are available at moderate prices, they are not attractive unless their performance dramatically improves. For this reason, magnetic refrigeration at room temperature has been considered less possible than magnetic refrigeration at ultra-low temperatures, and, therefore, insufficient R&D has been conducted regarding the aspect of materials. This can be stated as one of the reasons why magnetic refrigeration at room temperature has not put into application.
DEVELOPMENT STATUS
State of development domestically and abroad
Due to growing concern regarding global environmental problems and the progress in R&D of room temperature magnetic refrigerators, active efforts have been made domestically and abroad. In September 2005, the first international conference on room temperature magnetic refrigerators was held by the International Institute of Refrigeration (IIR) in Montreux, Switzerland. In this conference, a presentation was given on the results of the operation of a magnetic refrigerator developed by the same research group[1] which stated that a maximum refrigerating capacity of 50 W was obtained at room temperature using an La-based magnetic material. Although this value is slightly smaller than the maximum refrigerating capacity of the magnetic refrigeration system we have developed (60 W)[2], the weight of the magnetic material they used was approximately 1/20 that of the system we developed and the entire system was very compact, showing that engineering developments have been steadily progressing. The international conference on room temperature magnetic refrigerators was held even in 2007 and 2009, and will be held in China in 2010. As for domestic developments, the Tohoku University and Kyushu University groups are respectively working on the development of magnetic work materials, and they drew a high degree of attention at the international conference mentioned above. Concerning the system development, the development of a refrigerator in which a permanent magnet rotates is currently being promoted in the national project, which will be described hereinafter.
Rotary magnetic refrigeration system using permanent magnet
In 2000, it was verified that it is possible to cool items down even to room temperature utilizing magnetic refrigeration by use of the strong magnetic field of a superconducting magnet[3]. However, as long as a superconducting magnet is used, power is required to generate the magnetic field. Therefore, a compact system using a permanent magnet that does not require power to generate a magnetic field is necessary, in order to put magnetic refrigeration into practical application.