Press Release Back Number(2006)

Reliable Cryocooler Achieves World's Greatest Output

September 6, 2006
Chubu Electric Power Co., Inc.

Chubu Electric, in collaboration with Aisin Seiki Co., Ltd. (President: Yasuhito Yamauchi; address: 2-1, Asahi-machi, Kariya, Aichi, 448-8650) has successfully developed a pulse tube cryocooler with the world's greatest output.

Cryocoolers are freezers able to chill items to temperatures of -100°C or below using the principle that compressed helium gas removes heat as it expands. Major applications are in magnetic resonance imaging (MRI) equipment and linear motor cars, among others. Presently, applications for such coolers are growing more diverse, and there is a growing need for high-capacity, maintenance-free cryocoolers.

To ensure that the newly developed pulse tube cryocooler has greater refrigerating capacity than earlier cryocoolers, the developer changed the structure from a single cylinder to the world's first two-cylinder layout in the part of the cryocooler where the helium gas expands. This doubles the output and achieves top-class freezing efficiency. In addition, the cryocooler contains no components that will rub against the area that causes the enclosed helium gas to compress and expand, so wear does not cause the system to break down and the six-month maintenance interval, one of the biggest issues with earlier cryocoolers, can now be extended to 10 times that length.

The newly developed cryocooler has the following features.

1. Cryogenic refrigerating capacity with world's highest output

At -196°C, achieves 300W, double the output of earlier pulse tube cryocoolers

2. World's highest freezer efficiency

Delivers 6.7%* efficiency, 10% better than earlier pulse tube cryocoolers and the world's highest in its class

3. Longer maintenance interval

In the 150W freezer class, maintenance interval is 50,000 hours, or 10 times the interval of earlier systems

*The ratio of refrigerating capacity to work load (pressure inside container volume) in cryocooler's compression and expansion parts

This cryocooler was developed as part of the Superconducting Electric Power Network Control Technical Development project (Agency for Natural Resources and Energy, Ministry of Economy, Trade and Industry) and was commissioned by the New Energy and Industrial Technology Development Organization (NEDO). The newly developed cryocooler will be incorporated into a Superconducting Magnetic Energy Storage (SMES) system and will undergo endurance testing by FY2007.

The cryocooler will be on display at the 19th International Symposium on Superconductivity (ISS2006) at Nagoya Congress Center on October 31 and November 1.

Research period: June 2004 - March 2008


Development of Reliable Cryocooler

1. Background to development

Cryocoolers are used for cooling applications with superconducting magnets, magnetic resonance imaging (MRI) systems, linear motor cars and so on, and the number of applications is growing. Chubu Electric has been working to develop cryocoolers that are inexpensive and reliable and provide high output, long life and low vibration; these cryocoolers are intended to be used in the development of a Superconducting Magnetic Energy Storage (SMES) system at Chubu Electric.

2. About cryocoolers

Cryocoolers are freezers able to chill items to temperatures of -100°C or below using the principle that compressed fluid (helium) removes heat as it expands.

The major types of cryocoolers include Stirling cryocoolers, which compress and expand an enclosed gas, and Gifford-McMahon coolers, which convert a fluid compressed in a separate compressor to cause compression and expansion. These cryocoolers can liquefy nitrogen (-196°C or 77K), hydrogen (-253°C or 20K) or helium (-269°C or 4K). Cryocoolers have two basic parts: a compression unit that performs the work of isothermal compression, and an expansion / cold storage unit that collects the cold. The newly developed pulse tube cryocooler, which is a type of Stirling cryocooler, is compact because it combines these two basic parts into one.

3. Overview of the newly developed equipment

The newly developed pulse tube cryocooler uses a linear motor for the compression unit, and the reciprocating vibration unit is grasped with a coil spring. This construction eliminates friction and wear. Additionally, fluids are stored even in the freezer compartment, and with the use of a pressure phase adjustment device (the pulse tube) there are no components that undergo friction. The part that creates the cold, furthermore, consists of a multi-cylinder structure with two cold storage devices next to each other. By making a balance of these two, the new cryocooler has increased refrigerating capacity at -196°C (77K) to 300W, or twice the previous level (comparison made with Aisin Seiki product).

Also, the cryocooler offers the world's highest freezer efficiency at 6.7%*, a 10% improvement over earlier pulse tube freezers.

Moreover, since there are no rubbing parts, there is less vibration and noise during operation and no parts subject to structural deterioration. This can greatly extend the maintenance period (test interval 50,000 hours).

*The ratio of refrigerating capacity to work load (pressure inside container volume) in cryocooler's compression and expansion part

Fig. 1: Appearance of pulse tube cryocooler

Table 1: Cryocooler specifications

Item Specifications
Model Stirling pulse tube cryocooler
Refrigerating capacity 77K 300W and up
Energy consumption 9kW or below
Voltage used AC 200V 10%
Current used 65A or below
Power frequency 50 / 60Hz
Water requirement 1.0m3/h
Inlet temperature 30°C or less
Dimensions(units: mm) H800 W1,037 D700
Product weight Approx. 300kg

4. Looking ahead

The developers will perform endurance testing in a superconducting coil chilling application as part of superconducting storage system actual system connection tests in the Superconducting Electric Power Network Control Technical Development project. During this testing, the developers will re-examine problems in practical use and make improvements for them, also working to minimize loss in the linear drive and further enhance freezing efficiency.