Closed-loop precooling of cryogenically cooled equipment

Abstract

Apparatus for pre-cooling cryogenically cooled apparatus housed within a cryogen vessel ( 26 ), comprising a first closed-loop cooling circuit ( 30 ) containing heat transfer fluid, a circulator ( 32 ) for causing the heat transfer fluid to circulate around the closed circuit and a heat extractor ( 34 ) arranged to extracts heat from the heat transfer fluid, wherein the circuit carries heat transfer fluid into and from an interior volume of the cryogen vessel ( 26 ).

1 . Apparatus for pre-cooling cryogenically cooled apparatus housed within a cryogen vessel, comprising a first closed-loop cooling circuit containing heat transfer fluid, a circulator for causing the heat transfer fluid to circulate around the closed circuit and a heat extractor arranged to extract heat from the heat transfer fluid, wherein the circuit carries heat transfer fluid into and from an interior volume of the cryogen vessel.  
     
     
         2 . Apparatus according to  claim 11  wherein the circulator comprises a compressor which acts to compresses a gaseous heat transfer fluid to a pressure in the range of 100-300 kPa absolute.  
     
     
         3 . Apparatus according to  claim 11 , wherein the heat extractor is an external mechanical active cryogenic refrigerator.  
     
     
         4 . Apparatus according to  claim 1 , wherein the heat extractor is a passive cryogenic refrigerator comprising a reserve of a cryogen in thermal contact with the closed-loop cooling circuit.  
     
     
         5 . Apparatus according to  claim 4  wherein the reserve of cryogen comprises a quantity of solid cryogen.  
     
     
         6 . Apparatus according to  claim 4 , wherein the reserve of cryogen provides cooling to a temperature of below 70K.  
     
     
         7 . Apparatus according to  claim 1 , wherein the heat extractor comprises both an active cryogenic refrigerator and a passive cryogenic refrigerators arranged such that passive cooling may be applied to the heat transfer fluid until the cryogenically cooled apparatus has cooled to a first temperature, with further cooling being provided by switching the flow of heat transfer fluid to the active refrigerator, to continue with cooling down to a desired temperature, below that obtainable from the passive refrigerator alone.  
     
     
         8 . Apparatus according to  claim 1 , wherein the circulator comprises a fan.  
     
     
         9 . Apparatus according to  claim 1 , wherein the heat extractor which extracts heat from the heat transfer fluid is a heat exchanger, itself cooled by a second closed-loop cooling circuit containing a second heat transfer fluid, a second circulator for causing the second heat transfer fluid to circulate around the second closed-loop cooling circuit and a second heat extractor arranged to extract heat from the second heat transfer fluid.  
     
     
         10 . Apparatus according to  claim 9  wherein the first and second heat transfer fluids are both gases, and the second heat transfer fluid in the second closed-loop cooling circuit is at a higher pressure than the pressure of the heat transfer fluid in the first closed-loop cooling circuit.  
     
     
         11 . Apparatus according to  claim 9 , wherein the second heat transfer fluid in the second closed-loop cooling circuit is of a different material than the heat transfer fluid in the first closed-loop cooling circuit.  
     
     
         12 . Apparatus according to  claim 9 , wherein the second heat extractor is an external mechanical active cryogenic refrigerator.  
     
     
         13 . Apparatus according to  claim 9 , wherein the second heat extractor is a passive cryogenic refrigerator comprising a reserve of a cryogen in thermal contact with a pipe carrying the second heat transfer fluid around the second closed-loop cooling circuit.  
     
     
         14 . Apparatus according to  claim 13  wherein the reserve of cryogen comprises a quantity of solid cryogen.  
     
     
         15 . Apparatus according to  claim 9 , wherein the second heat extractor comprises both an active cryogenic refrigerator and a passive cryogenic refrigerators arranged such that passive cooling may be applied to the second heat transfer fluid until the cryogenically cooled apparatus has cooled to a first temperature, with further cooling being provided by switching the flow of second heat transfer fluid to the active refrigerator, to continue with cooling down to a desired temperature, below the temperature obtainable using the passive refrigerator alone.  
     
     
         16 . Apparatus according to  claim 13 , wherein the reserve of cryogen provides cooling to a temperature of below 70K.  
     
     
         17 . Apparatus according to  claim 9 , wherein the second circulator comprises a fan.  
     
     
         18 . Apparatus according to  claim 9 , wherein the heat exchanger comprises a volume of liquid or solid nitrogen; or water ice.  
     
     
         19 . A method for pre-cooling a cryogenically cooled apparatus within a cryogen vessel, comprising circulating a heat transfer fluid through a first closed-loop cooling circuit by operation of a circulator causing the heat transfer fluid to circulate around the first closed-loop cooling circuit and extracting heat from the heat transfer fluid by use of a heat extractor in thermal connection with the first closed-loop cooling circuit, wherein the heat transfer fluid flows into and from an interior volume of the cryogen vessel.  
     
     
         20 . A method according to  claim 19  wherein the circulator comprises a compressor compressing gaseous heat transfer fluid to a certain pressure in the range of 100-300 kPa absolute.  
     
     
         21 . A method according to  claim 15 , wherein heat extractor comprises an external mechanical active cryogenic refrigerator.  
     
     
         22 . A method according to  claim 19 , wherein heat extractor comprises a passive cryogenic refrigerator, being a reserve of cryogen in thermal contact with the first closed-loop cooling circuit.  
     
     
         23 . A method according to  claim 19 , wherein heat extraction is initially performed by passive cooling employing a reserve of cryogen until the cryogenically cooled equipment has cooled to a first temperature, being no lower than the temperature of the sacrificial cryogen, with further heat extraction then being performed by an active refrigerator, to continue with cooling down to a desired pre-cool temperature.  
     
     
         24 . A method according to  claim 19 , wherein the heat extractor is a heat exchangers and the heat exchanger is itself cooled by a second closed-loop cooling circuit which cools the heat exchanger by circulating a second heat transfer fluid by operation of a circulator causing the second heat transfer fluid to circulate around the second closed-loop cooling circuit and extracting heat from the second heat transfer fluid by use of a second heat extractor in thermal connection with the second closed-loop cooling circuit.  
     
     
         25 . A method according to  claim 24  wherein the second closed loop cooling circuit is brought into operation to cool the heat exchanger before the first closed loop cooling circuit is brought into operation.  
     
     
         26 . A method according to  claim 24 , wherein the second heat extractor is an external mechanical active cryogenic refrigerator.  
     
     
         27 . A method according to  claim 24 , wherein the second heat extractor comprises a passive cryogenic refrigerator, being a reserve of cryogen in thermal contact with the first closed-loop cooling circuit.  
     
     
         28 . A method according to  claim 24 , wherein heat extraction by the second closed-loop cooling circuit is initially performed by passive cooling employing a reserve of cryogen until the cryogenically cooled equipment has cooled to a first temperature, being no lower than the temperature of the reserve of cryogen, with further heat extraction then being performed by an active refrigerator, to continue with cooling down to a desired pre-cool temperature, below the temperature obtainable by use of the reserve of cryogen alone.  
     
     
         29 . A method according to  claim 24 , wherein the second circulator comprises a fan.  
     
     
         30 . A method according to  claim 24 , wherein the first and second heat transfer fluids are both gases, and the second heat transfer fluid in the second closed-loop cooling circuit is at a higher pressure than the pressure of the heat transfer fluid in the first closed-loop cooling circuit.  
     
     
         31 . A method according to  claim 24 , wherein the second heat transfer fluid in the second closed-loop cooling circuit is of a different material than the heat transfer fluid in the first closed-loop cooling circuit.  
     
     
         32 . A method according to  claim 24 , wherein heat extraction from the second closed-loop cooling circuit is performed by an external mechanical active cryogenic refrigerator.  
     
     
         33 . A method according to  claim 24 , wherein heat extraction from the second closed-loop cooling circuit is performed by a passive cryogenic refrigerator comprising a reserve of cryogen in thermal contact with the second closed-loop cooling circuit.  
     
     
         34 . A method according to  claim 24 , wherein heat extraction from the second closed-loop cooling circuit is performed by both an active cryogenic refrigerator and a passive cryogenic refrigerator, arranged such that passive cooling is applied to the second heat transfer fluid until the cryogenically cooled apparatus has cooled to a first temperature, with further cooling being provided by switching the flow of second heat transfer fluid to an active refrigerator, to continue with cooling down to a desired pre-cool temperature.  
     
     
         35 . A method according to  claim 24 , wherein the second circulator comprises a fan.  
     
     
         36 . A method according to  claim 24 , wherein the heat exchanger is formed of a volume of liquid or solid nitrogen; or water ice.  
     
     
         37 . A method according to  claim 24 , wherein the heat exchanger is cooled to a certain cryogenic temperature before operation of the first closed-loop cooling circuit.  
     
     
         38 . Apparatus or a method according to  claim 1 , wherein in the first closed-loop cooling circuit, the circulator acts on cooled first heat transfer fluid from the heat extractor on its way to the apparatus to be cooled.  
     
     
         39 . Apparatus or a method according to  claim 1 , wherein in the second closed-loop cooling circuit, the circulator acts on cooled first heat transfer fluid from the second heat extractor on its way to the heat exchanger.