Cryogenic gas circulation and heat exchanger

Abstract

A cryogenic system includes a housing of a cryogenic chamber, a cold source in the cryogenic chamber, and a gas circulation loop for circulating cryogenic gas between the cold source and material to be cooled in the cryogenic chamber. The circulation loop includes a gas pump, and a counter-flow heat exchanger connecting the gas pump to the cold source for cooling an in-flow of the cryogenic gas from the gas pump to the cold source with an out-flow of the cryogenic gas from the material to be cooled to the gas pump. In a preferred construction, the heat exchanger includes an outer tube and an inner tube nested within the outer tube, and a pair of three-port connector fittings attached to respective ends of the tubes.

What is claimed is: 
     
         1 . A cryogenic system comprising:
 a housing of a cryogenic chamber;   a cold source in the cryogenic chamber; and   a gas circulation loop for circulating cryogenic gas between the cold source and material to be cooled in the cryogenic chamber;   wherein the gas circulation loop includes a gas pump, and a counter-flow heat exchanger connecting the gas pump to the cold source for cooling an inlet flow of the cryogenic gas from the gas pump to the cold source with an outlet flow of the cryogenic gas from the material to be cooled in the cryogenic chamber to the gas pump.   
     
     
         2 . The cryogenic system as claimed in  claim 1 , wherein the gas pump is located outside of the cryogenic chamber. 
     
     
         3 . The cryogenic system as claimed in  claim 1 , which includes a cryocooler having a cold head in the cryogenic chamber, the cold source includes the cold head, and the gas circulation loop includes another heat exchanger, which is fastened to the cold head and coupled to the counter-flow heat exchanger for receiving the inlet flow of the cryogenic gas from the counter-flow heat exchanger. 
     
     
         4 . The cryogenic system as claimed in  claim 1 , which includes at least one cryocooler having a plurality of stages, the at least one cryocooler has a plurality of cold heads in the cryogenic chamber, the cold source includes at least two of the cold heads, and the counter-flow heat exchanger is coupled to the cold heads for progressively cooling the inlet flow of cryogenic gas from the counter-flow heat exchanger by heat transfer to a higher-temperature one of the cold heads and then to a lower-temperature one of the cold heads before passing to the material to be cooled in the cryogenic chamber. 
     
     
         5 . The cryogenic system as claimed in  claim 1 , wherein the counter-flow heat exchanger includes an outer tube and an inner tube nested within the outer tube, and a pair of three-port connector fittings attached to respective ends of the tubes so that the three-port connector fittings provide a sealed environment with independent access to each of the in-flow and out-flow of the cryogenic gas through the counter-flow heat exchanger while preventing mixing of the in-flow and out-flow of the cryogenic gas through the counter-flow heat exchanger. 
     
     
         6 . The cryogenic system as claimed in  claim 5 , wherein the outer tube is a stainless steel tube, and the inner tube is a copper tube. 
     
     
         7 . The cryogenic system as claimed in  claim 5 , wherein the tubes are wound into a helix. 
     
     
         8 . The cryogenic system as claimed in  claim 5 , wherein the three-port connector fittings are T-connector fittings, and each of the T-connector fittings has a first port, a second port opposite the first port, and a third port, and the inner tube passes through the first port of each of the T-connector fittings and the outer tube is attached to the first port of each of the T-connector fittings, and in each of the T-connector fittings, a first gas flow passage outside of the inner tube and inside the outer tube extends through the first port to the third port, and a second gas flow passage inside the inner tube extends to the second port. 
     
     
         9 . A method of cooling a material in a cryogenic chamber, said method comprising circulating cryogenic gas in a gas circulation loop between a cold source in the cryogenic chamber and the material in the cryogenic chamber, wherein the gas circulation loop includes a gas pump and a counter-flow heat exchanger, and said method further includes the gas pump pumping the cryogenic gas through the gas circulation loop, and the counter-flow heat exchanger cooling an inlet flow of the cryogenic gas from the gas pump to the cold source with an outlet flow of the cryogenic gas from the material in the cryogenic chamber to the gas pump. 
     
     
         10 . The method as claimed in  claim 9 , wherein the gas pump is operating in a room-temperature environment to circulate the cryogenic gas through the gas circulation loop. 
     
     
         11 . The method as claimed in  claim 9 , wherein the cold source is providing a temperature below 70 degrees Kelvin, and the material in the cryogenic chamber is cooled to below 70 degrees Kelvin. 
     
     
         12 . The method as claimed in  claim 9 , wherein the cold source is a cold head of a cryocooler, and the gas circulation loop includes another heat exchanger, which is fastened to the cold head and receiving the inlet flow of the cryogenic gas from the counter-flow heat exchanger. 
     
     
         13 . The method as claimed in  claim 9 , wherein the cold source includes at least two cold heads of at least one cryocooler having the cold heads in the cryogenic chamber, and the inlet flow of cryogenic gas from the counter-flow heat exchanger is progressively cooled by heat transfer to a higher-temperature one of the cold heads and then to a lower-temperature one of the cold heads before passing to the material to be cooled in the cryogenic chamber. 
     
     
         14 . The method as claimed in  claim 9 , wherein the counter-flow heat exchanger includes an outer tube and an inner tube nested within the outer tube, and a pair of three-port connector fittings attached to respective ends of the tubes so that the three-port connector fittings provide a sealed environment with independent access to each of the in-flow and out-flow of the cryogenic gas through the counter-flow heat exchanger while preventing mixing of the in-flow and out-flow of the cryogenic gas through the counter-flow heat exchanger. 
     
     
         15 . The method as claimed in  claim 14 , wherein the three-port connector fittings are T-connector fittings, and each of the T-connector fittings has a first port, a second port opposite the first port, and a third port, and the inner tube passes through the first port of each of the T-connector fittings and the outer tube is attached to the first port of each of the T-connector fittings, and in each of the T-connector fittings, a first gas flow passage outside of the inner tube and inside the outer tube extends through the first port to the third port, and a second gas flow passage inside the inner tube extends to the second port. 
     
     
         16 . The method as claimed in  claim 15 , wherein the in-flow of cryogenic gas through the counter-flow heat exchanger passes through the first gas flow passage, and the out-flow of cryogenic gas through the counter-flow heat exchanger passes through the second gas flow passage. 
     
     
         17 . A counter-flow heat exchanger comprising an outer tube and an inner tube nested within the outer tube, and a pair of three-port connector fittings attached to respective ends of the tubes so that the three-port connector fittings provide a sealed environment with independent access to a first flow of fluid and a second flow of fluid while preventing mixing of the first flow of fluid and the second flow of fluid, wherein the first flow of fluid flows between the three-port connector fittings inside the outer tube and outside the inner tube, and the second flow of fluid flows between the three-port connector fittings inside the inner tube. 
     
     
         18 . The counter-flow heat exchanger as claimed in  claim 17 , wherein the outer tube is a stainless steel tube, and the inner tube is a copper tube. 
     
     
         19 . The counter-flow heat exchanger as claimed in  claim 17 , wherein the tubes are wound into a helix. 
     
     
         20 . The counter-flow heat exchanger as claimed in  claim 17 , wherein the three-port connector fittings are T-connector fittings, and each of the T-connector fittings has a first port, a second port opposite the first port, and a third port, and the inner tube passes through the first port of each of the T-connector fittings and the outer tube is attached to the first port of each of the T-connector fittings, and in each of the T-connector fittings, a first gas flow passage outside of the inner tube and inside the outer tube extends through the first port to the third port, and a second gas flow passage inside the inner tube extends to the second port.