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.

1 . A regenerative refrigerator, comprising:
 a cylinder formed of a material having a low thermal conductivity and a high airtightness, the cylinder having a cylindrical interior circumferential surface;   a displace provided in the cylinder so as to be reciprocatable in axial directions thereof with an expansion space formed between one end of the cylinder and the displacer, the displacer having an exterior circumferential surface along a cylindrical shape of the interior circumferential surface of the cylinder, the exterior circumferential surface being slightly smaller in diameter than the interior circumferential surface;   a groove pattern formed on one of the exterior circumferential surface of the displacer and the interior circumferential surface of the cylinder so as to form a first gas passage connecting a first end and a second end of the one of the exterior circumferential surface of the displacer and the interior circumferential surface of the cylinder, the groove pattern including a groove having at least a part thereof extending along a direction to cross the axial directions of the displacer so as to cause a gas flowing from one to another of the first end and the second end of the one of the exterior circumferential surface of the displacer and the interior circumferential surface of the cylinder in a gap between the exterior circumferential surface of the displacer and the interior circumferential surface of the cylinder to actively exchange heat with the cylinder and the displacer;   a second gas passage through which the gas is supplied to and collected from the expansion space; and   a regenerator material formed of bismuth granules and provided in at least a part of the second gas passage,   wherein a lowest attainable temperature of the regenerative refrigerator is in a range of cryogenic temperatures higher than or equal to 5 K and lower than or equal to 15 K in an unloaded state.   
     
     
         2 . The regenerative refrigerator as claimed in  claim 1 , wherein the groove pattern has a helical shape. 
     
     
         3 . The regenerative refrigerator as claimed in  claim 2 , wherein the helical shape of the groove pattern is formed with multiple helixes arranged in parallel. 
     
     
         4 . The regenerative refrigerator as claimed in  claim 1 , wherein the displacer is hollow with an internal cavity, the internal cavity being filled with the regenerator material to form the second gas passage. 
     
     
         5 . The regenerative refrigerator as claimed in  claim 1 , wherein the gap between the exterior circumferential surface of the displacer and the interior circumferential surface of the cylinder is 0.01 mm to 0.03 mm. 
     
     
         6 . The regenerative refrigerator as claimed in  claim 1 , wherein the bismuth granules are greater than or equal to 0.14 mm and smaller than or equal to 1.6 mm in grain size.