Heat-storing medium

Abstract

Normally granulates of rare earth compounds are used as a heat-storing medium for a low-temperature range below 15 Kelvin. The material costs for rare earths are high. Further, rare earths are magnetic and thus not suitable for all applications. The present heat-storing medium for a very low temperature range is composed of a set ( 22 ) of pourable and gastight sealed hollow bodies ( 30 ). Each hollow body ( 30 ) contains a fill ( 34 ) of a low-boiling gas as a storing medium. The hollow body wall ( 32 ) is made of metal or ceramic. Thus a relatively inexpensive heat-storing medium is provided whose physical, chemical, magnetic and mechanical properties can be adapted to the respective use by corresponding material selection.

1 . A heat-storing medium for a low-temperature range, comprising: 
 a set of pourable bodies, the bodies being gastight sealed hollow bodies, each hollow body containing a fill of a low-boiling gas as a storage medium, and having hollow body wall made of metal.    
   
   
       2 . The heat-storing medium according to  claim 1 , wherein the hollow body wall is made of copper.  
   
   
       3 . The heat-storing medium according to  claim 1 , wherein the material and the wall thickness of the hollow body wall are selected such that the thermal penetration depth equals at least the wall thickness.  
   
   
       4 . The heat-storing medium according to  claim 1 , wherein the storing medium is a fill of helium.  
   
   
       5 . The heat-storing medium according to  claim 4 , wherein the helium fill has a pressure of more than 0.5 bar at a temperature of 4 K.  
   
   
       6 . The heat-storing medium according to  claim 4 , wherein the helium fill has a pressure of approximately 200 bar at room temperature.  
   
   
       7 . The heat-storing medium according to  claim 1 , wherein the wall thickness of the hollow body wall is smaller than 1.0 mm.  
   
   
       8 . The heat-storing medium according to  claim 1 , wherein the hollow body is of approximately spherical configuration.  
   
   
       9 . The heat-storing medium according to  claim 8 , wherein the hollow body has a diameter of less than 3.0 mm.  
   
   
       10 . The heat-storing medium for a low-temperature range, comprising: 
 a set of pourable, gastight sealed hollow bodies, each hollow body containing a fill of a low-boiling gas as a storing medium, and having a hollow body wall is made of ceramic material.    
   
   
       11 . A regenerator for a low-temperature refrigerator, comprising: 
 a housing filled with the heat-storing medium according to  claim 1 .    
   
   
       12 . A low-temperature refrigerator comprising: 
 a regenerator according to  claim 11 , and being configured as a Gifford-McMahon, Stirling, or pulse tube refrigerator, and    helium gas used as a working fluid.    
   
   
       13 . A regenerator for a low-temperature refrigerator, comprising: 
 a housing filled with the heat-storing medium according to  claim 10 .    
   
   
       14 . A regenerator for a low temperature refrigerator comprising: 
 a housing;    a plurality of hollow, gas sealed bodies disposed in the housing, each body including: 
 a body wall made of one of metal and ceramic material, which defines an interior cavity,  
 a gas which boils at or below 30° K. disposed in the cavity.  
   
   
   
       15 . The regenerator according to  claim 14  wherein the gas includes at least one of helium, hydrogen, and neon.  
   
   
       16 . The regenerator according to  claim 14  wherein the body wall is thicker than:  
     
       
         
           
             
               2 
               ⁢ 
               
                 a 
                 
                   f 
                   mod 
                 
               
             
           
         
       
       where a is a thermal conductivity of the material at a working temperature below 15° K. and f mod  is a modulation frequency at which a working gas alternately flows through the housing.  
     
   
   
       17 . The regenerator according to  claim 14  wherein the material includes one of copper, aluminum, silver, brass, steel, and alloys thereof.  
   
   
       18 . The regenerator according to  claim 14  wherein the bodies are less than 3 mm in diameter and a body wall thickness less than 0.2 mm.  
   
   
       19 . The regenerator according to  claim 14  wherein the gas in the cavity has a pressure of at least 7.25 psi at 4° K.