Regenerative refrigerator

Abstract

A regenerative refrigerator includes a cylinder; a displacer provided in the cylinder; a groove pattern formed on the exterior circumferential surface of the displacer or the interior circumferential surface of the cylinder to form a first gas passage connecting one end and the other end of the exterior or interior circumferential surface, and including a groove having at least part thereof extending along a direction to cross the axial directions of the displacer to cause gas flowing from the one end to the other end in the gap between the exterior and interior circumferential surfaces to actively exchange heat with the cylinder and the displacer; a second gas passage to and from an expansion space; and a regenerator material formed of bismuth granules and provided in at least part of the second gas passage, wherein the lowest attainable temperature is 5 K to 15 K in an unloaded state.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]The present application is based upon and claims the benefit of priority of Japanese Patent Application No. 2009-063608, filed on Mar. 16, 2009, the entire contents of which are incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates generally to regenerative refrigerators. The present invention more particularly relates to a regenerative refrigerator capable of attaining cryogenic temperatures with the reciprocating motions of a displacer filled with a regenerator material in a cylinder.[0004]2. Description of the Related Art[0005]Examples of refrigerators widely used in cryogenic ranges include a regenerative refrigerator. The regenerative refrigerator includes a regenerative heat exchanger called a regenerator. The regenerator contains a heat exchange material called a regenerator material in the container.[0006]A material having high specific heat at a target temper...

AI Technical Summary

Benefits of technology

[0012]As a regenerator material to replace lead, bismuth, which is also used as a material for cosmetics, is believed to be highly safe and free of concern for environmental pollution, and is also inexpensive. Bismuth, however, is lower in specific heat than lead. In particular, in a cryogenic environment at or below 15 K, the specific heat of bismuth is significantly reduced. Therefore, although bismuth has good characteristics in terms of safety and burdens on the environment as described above, it has been believed difficult to use bismuth as a regenerator material in regenerative refrigerators for achieving cryogenic temperatures.

[0090]Further, a groove pattern may be formed on the cylindrical exterior circumferential surface of a displacer, so that gas that diverges from a main gas passage containing a regenerator material flows along this groove pattern in a gap between the displacer and a cylinder. This groove pattern is formed to include a groove extending along a direction to cross the axial directions of the displacer so as to allow the gas flowing in the groove to actively exchange heat with the displacer and the cylinder.

[0032]According to one aspect of the present invention, a regenerative refrigerator may be provided that is capable of attaining cryogenic temperatures lower than or equal to 15 K while using bismuth as a regenerator material.

Problems solved by technology

In the member states of the European Union, however, due to its effect on the environment, the use of lead has been strictly restricted by the Restriction of Hazardous Substances Directive or RoHS, which took effect on Jul. 1, 2006.

Therefore, regenerative refrigerators using lead as a regenerator material may be subject to this restriction.

Indium, however, is a very soft metal and cannot be used as a regenerator material as it is.

Therefore, indium is made into an alloy with bismuth and another metal to have a hardness required for a regenerator material, but is still insufficient in hardness to be practically used as a regenerator material.

Further, there is also a problem in that indium, whose price is approximately three times the price of lead, is too expensive to be used as a regenerator material.

Therefore, although bismuth has good characteristics in terms of safety and burdens on the environment as described above, it has been believed difficult to use bismuth as a regenerator material in regenerative refrigerators for achieving cryogenic temperatures.

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