Taiyo Nippon Sanso has recently begun marketing neon gas as the coolant. It will be used to cool superconductive equipment to under minus 200°C.
The equipment includes superconducting magnetic energy storage systems, superconducting motors and high temperature superconducting cables. This marks the first time ever that a turbo freezer using neon as the coolant has been marketed.
Requirements are on the rise for freezers suitable for freezing superconductive power equipment which has entered into the research stage which will lead to practical use. Because liquid nitrogen is used for cooling the operational temperature of the freezer is in the vicinity of minus 200°C.
A freezing performance of 2-10kW is required. Freezers now on the market, however, have a performance of only under 1kW. Additionally, because helium is used as the coolant, the operational temperature is in the vicinity of minus 269°C, a specification of which is much too high.
NEDO (the New Energy and Industrial Technology Development Organisation) carried out a project during the financial year 2008-2012, called the ‘Development of Technology for Yttrium-based Superconductive Power Equipment’.
Taiyo Nippon Sanso participated in this project, and developed a freezer of 2kW with the temperature region suitable for liquid nitrogen freezing. The freezer which just went on the market was based on the technology of the prototype of this freezer.
The freezer being marketed combines a neon coolant and a turbo compressor so that the type of freezing is the Brayton cycle. Its most important feature is that it employs a ‘magnetic bearing’ for both the compressor and the expansion turbine which are main components. This is a technology which causes the axis of rotation and the bearings are not connected mechanically.
Regarding this maintenance free feature, Isamu Sagara, the manager of the business department of the equipment division and responsible for the cryogenic field, stated, “With the conventional Sterling cycle type refrigerator, once a year at the very least, the parts of the piston which can wear out are changed and contaminants are removed. Because of this, major maintenance and inspection to the extent of even dismantling the compressor is required. Out refrigerators do not require maintenance for several dozen years. I feel that this is a great advantage for freezing related superconductive equipment which cannot be shut down even temporarily.”
The company plans to market this refrigerator not only in Japan, but also in Korea, China, Germany and Russia.