Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
  • F25D3/00—Devices using other cold materials; Devices using cold-storage bodies
  • F25D3/10—Devices using other cold materials; Devices using cold-storage bodies using liquefied gases, e.g. liquid air
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
  • F25D29/00—Arrangement or mounting of control or safety devices
  • F25D29/001—Arrangement or mounting of control or safety devices for cryogenic fluid systems

Definitions

• the present invention relates to the operation of a cryogenic device in a gaseous environment, and more particularly relates to a method and device for providing a gaseous environment at a temperature equal or close to liquid coolant temperature.
• cryogenic cooling of cryogenic devices has been provided by immersing the cryogenic device in a liquid coolant such as liquid nitrogen or liquid helium, thus maintaining the temperature of the cryogenic device at or below the boiling temperature of the liquid coolant.
• a liquid coolant such as liquid nitrogen or liquid helium
• the use of liquid nitrogen provides for cryogenic operation at or below 77.3K
• the use of liquid helium provides for cryogenic operation at or below 4.2K.
• cryogenic devices have been designed which rely on movement of the device for operation.
• Such a device is set out in International Patent Publication No. WO 2004/015435 by CSIRO and Tilbrook, the content of which is incorporated herein by reference, which teaches rotation of one or more SQUIDs or superconducting field sensors in order to obtain information about a magnetic field.
• SQUIDs and superconducting field sensors must be maintained below the critical temperature T 0 of the superconducting material in order to achieve proper superconducting operation.
• T 0 critical temperature
• mechanical stress will be placed on the often delicate device by viscous drag and/or mechanical vibrations.
• the present invention is an apparatus for providing a cryogenic gaseous environment, the apparatus comprising: a chamber for containing the cryogenic gaseous environment and for excluding external liquid coolant; a liquid inlet for selectively flooding the chamber with liquid coolant; and a chamber gas port for selectively permitting egress of gas from the chamber during liquid flooding of the chamber, and for selectively containing gas within the chamber.
• the present invention is a method of providing a cryogenic gaseous environment, the method comprising: flooding a chamber with liquid coolant; and causing cryogenic gas to occupy the chamber and displace liquid coolant from the chamber.
• the chamber gas port may comprise a gas injection port for purging the chamber with gas to evacuate liquid from the chamber.
• the gas injection port may itself permit egress of gas during liquid flooding of the chamber.
• the chamber may comprise a gas outflow port for permitting egress of gas from the chamber during liquid flooding of the chamber.
• the chamber gas port may comprise a gas vent having open and closed positions, such that the gas vent when open allows egress of gas from the chamber during liquid flooding of the chamber, and such that the gas vent when closed contains gas within the chamber.
• the present invention is an apparatus for providing a gaseous environment for operation of a cryogenic device, the apparatus comprising: a chamber for housing the cryogenic device; a port in the chamber allowing the chamber to be flooded by liquid coolant; and a gas vent for allowing escape of gas from the chamber; wherein the chamber is configured such that, when the gas vent is closed, gas boiled off liquid coolant within the chamber will accumulate in the chamber and force liquid coolant out of the port.
• the present invention provides a method for providing a gaseous environment for operation of a cryogenic device; comprising: flooding a chamber with liquid coolant; and causing gas boiled off the liquid coolant to accumulate in the chamber, such that liquid coolant is forced out of the chamber.
• the present invention provides for the chamber to be flooded with liquid coolant, followed by evacuation of the liquid coolant while maintaining the interior of the chamber at cryogenic temperatures. Flooding of the chamber is of value in order to provide for rapid and thorough cooling of the interior and contents of the chamber. During such a cooling phase, gas boiled off the liquid coolant is allowed to exit the chamber and thus the chamber remains flooded.
• evacuation of the liquid coolant from the chamber can be initiated by closing the gas vent of the chamber. When the gas vent is closed, gas boiled off the liquid coolant will accumulate within the chamber, and displace the liquid coolant from the chamber via the port.
• the pressure of the gas within the chamber will equal or exceed hydrostatic pressure of the liquid coolant in the chamber and thus displace the liquid coolant.
• gas will escape out the under port at a rate equal to gas accumulating in the chamber, thus providing a quiescent state in which devices within the chamber are provided within a gaseous environment at substantially liquid coolant temperatures.
• the chamber is preferably positioned within a dewar, and is partially immersed or more preferably substantially immersed within liquid coolant held in the dewar, while maintaining a gaseous environment within the chamber. Immersing the chamber within a liquid coolant substantially eliminates transmission of heat to the chamber, such that the temperature of the gaseous environment within the chamber will remain substantially at the boiling temperature of the liquid coolant used.
• Heat may of course be generated within the chamber by operation of the cryogenic device(s), and/or by friction of any moving parts required for moving operation of the cryogenic device(s).
• the liquid coolant surrounding the chamber will act as a heat sink for such heat, as it will be carried away from the device and/or moving parts via conduction and/or convection in the gaseous environment and through the chamber walls and/or port to the liquid coolant.
• the chamber walls are preferably formed of a heat conductive material.
• the port of the .chamber is, in use, preferably positioned at or proximal to a lower extremity of the chamber, such that the chamber can be substantially wholly evacuated when the gas vent is closed.
• positioning of the port away from a lower extremity of the chamber, in use, providing for partial evacuation of the chamber may suffice in some embodiments.
• the presence of liquid coolant in a lower portion of the chamber may assist in maintaining suitably low temperatures within the gaseous environment in the upper part of the chamber.
• the port may be a hole through a wall of the chamber.
• the port may comprise a valve to enable selective closing or sealing of the port.
• the chamber can be sealed in order to allow control of pressure within the chamber, for instance by use of a pressure valve.
• a device to be operated within the chamber has pressure dependent characteristics.
• Such embodiments may further comprise a standpipe having an inlet within the chamber, and an outlet external to the chamber and above an external liquid level, for permitting liquid coolant to flow from the chamber when under hydrostatic pressure generated by gas within the chamber.
• the inlet of the standpipe is preferably proximal to a lower extremity of the chamber.
• a dewar containing the external liquid coolant and the chamber is preferably sealed to nevertheless provide for pressure control of the gaseous environment within the chamber.
• Figures IA to ID illustrate a dewar and chamber in accordance with an embodiment of the present invention
• Figure 2 illustrates a chamber, gas vent and drive shaft in accordance with a second embodiment of the present invention
• Figure 3 illustrates an apparatus for providing a cryogenic gaseous environment in accordance with a third embodiment of the present invention
• Figure 4 illustrates an apparatus for providing a cryogenic gaseous environment in accordance with a fourth embodiment of the present invention
• Figure 5 is a flowchart illustrating the process of cooling and evacuation of the chamber of the apparatus of Figure 4.
• Figures IA to ID illustrate a dewar 100 and chamber 120 in accordance with an embodiment of the present invention.
• Figure IA illustrates the dewar 100 and chamber 120 in an unused state, to illustrate the under port 122 and gas vent 124 of chamber 120.
• a cool-down mode of operation is shown in Figure IB.
• liquid coolant 102 is introduced to dewar 100, and gas vent 124 serving as a chamber gas port is held open by valve 126, thus allowing coolant 102 to enter the chamber 120 through the under port 122 so as to flood chamber 120.
• gas vent 124 serving as a chamber gas port is held open by valve 126, thus allowing coolant 102 to enter the chamber 120 through the under port 122 so as to flood chamber 120.
• Introduction of coolant 102 to flood chamber 120 allows the interior and contents of chamber 120 to be rapidly and thoroughly cooled.
• Boiled coolant from chamber 20 exits as gas through gas vent 124.
• a chamber evacuation step commences as illustrated in Figure 1C.
• the temperature of chamber 120 may be assessed by monitoring the gas flow through vent 124, and determining that the interior and contents of chamber 120 are sufficiently cool once the gas flow reduces below a threshold rate.
• gas vent 124 is closed by use of valve 126.
• gas 104 boiled off coolant 102 accumulates in chamber 120, and continued boiling generates sufficient pressure to counteract the hydrostatic pressure of the coolant 102 within chamber 120 so as to force coolant 102 out of chamber 120 through under port 122.
• Figure ID illustrates the quiescent state for operation of one or more cryogenic devices within a gaseous environment 104 provided within chamber 120.
• Valve 126 holds gas vent 124 closed.
• Liquid coolant 102 is maintained within dewar 100.
• Gas pressure within chamber 120 is equal to the head of liquid outside the chamber 120 and thus holds liquid coolant out of chamber 120. As chamber 120 is entirely immersed in liquid coolant, very little heat is able to enter chamber 120 and thus the interior and contents of chamber 120 remain substantially at the boiling temperature of the liquid coolant.
• FIG. 2 illustrates a dewar insert 200 comprising a chamber 220, gas vent 224 serving as a chamber gas port, and drive chain 240, 242 in accordance with a second embodiment of the present invention.
• a dewar insert 200 comprising a chamber 220, gas vent 224 serving as a chamber gas port, and drive chain 240, 242 in accordance with a second embodiment of the present invention.
• Such an embodiment provides for operation of a moving cryogenic device in a gaseous environment.
• a superconducting gradiometer mounted on a flexible substrate for example of the type set out in International Patent Publication No. WO 2004/015435 or International Patent Publication No. WO
• a stator device mount 232 is provided with an under port 222 to enable liquid from a dewar to flood, cool and evacuate chamber 220 in the manner described above with reference to Figs IA to ID.
• a cavity 226 is provided outside under port 222 in order to create a further gaseous region within cavity 226. Altering the dimensions of cavity 226 will enable the dewar insert and dewar to be placed on an angle such that drive shaft 242 is off-vertical. Such a configuration may be desirable where the dewar insert is for use as one of a plurality of rotating gradiometers having orthogonally positioned axes. Such a configuration is set out in Figure 2 of WO 2004/015435, and in conjunction with which the embodiment of Figure 2 may be applied.
• FIG. 3 illustrates an apparatus 300 for providing a cryogenic gaseous environment in accordance with a third embodiment of the present invention.
• Apparatus 300 comprises a dewar 302, and a dewar insert 304.
• Dewar insert 304 comprises a chamber 320, gas vent 324 serving as a chamber gas port and a drive chain 340, 342.
• a superconducting gradiometer mounted on a flexible substrate may be mounted on the lower curved portion of rotor device mount 330, which is driven by lower drive shaft 340.
• Lower drive shaft 340 is in turn driven by upper drive shaft 342.
• a stator device mount 332 is provided, for example to support a stationary SQUID to be flux coupled to a rotating gradiometer mounted on rotor 330.
• Chamber 320 further comprises an under port 322 to enable liquid 306 from dewar 302 to flood, cool and evacuate chamber 320 in the manner described in the preceding with reference to Figs IA to ID.
• a cavity 326 is provided outside under port 322 in order to create a further gaseous region within cavity 326. Altering the dimensions of cavity 326 will enable the dewar insert 304 and/or dewar 302 to be placed on an angle such that drive shaft 342 is off-vertical. Such a configuration may be desirable where the dewar insert 304 is for use as one of a plurality of rotating gradiometers having orthogonally positioned axes. Such a configuration is set out in Figure 2 of WO 2004/015435, and in conjunction with which the present embodiment may be applied.
• FIG. 4 illustrates an apparatus 400 for providing a cryogenic gaseous environment in accordance with a fourth embodiment of the present invention.
• Apparatus 400 comprises a dewar 402 being a glass vacuum flask refill, a chamber 420, valve 424 and a drive shaft 440.
• Apparatus 400 may be housed in a PVC tube (not shown), which may be coated on both inside and outside surfaces with silver paint in order to effect RF interference shielding, for example where a magnetic field detection device is to be operated within chamber 420.
• a superconducting device may be mounted on rotor device mount 430, which is driven by drive shaft 440.
• Drive shaft 440 may for example be driven by hand or by motor.
• Dewar 402 holds liquid coolant 406 immersing chamber 420.
• Apparatus 400 further comprises a standpipe 428 having an inlet within chamber 420 and proximal to a lower extremity of chamber 420 allowing liquid coolant within chamber 420 to be drawn down to level 452.
• the outlet of standpipe 428 is external to chamber 420 and above a level 450 to which liquid 406 initially fills dewar 402.
• a valve 462 can be opened and closed, to selectively allow liquid flow into or out of chamber 420.
• Valve 464 can be opened to allow gas or liquid to be bled out of dewar 402.
• Valve 466 and pressure regulator 468 allow gas pressure within chamber 420 to be held at or below a level defined by pressure regulator 468.
• Burst disc 470 provides a failure mechanism should pressure within dewar 402 exceed the bursting pressure of the burst disc 470.
• Stator device mount 432 is provided, for example to support a stationary SQUID to be flux coupled to a rotating gradiometer mounted on rotor 430. To maximise flux coupling, it may be desirable to minimise a gap between the rotor 430 and stator 432.
• rotor 430 and stator 432 are preferably constructed of material(s) having low thermal expansion coefficient(s), such that temperature variations do not undesirably affect the physical gap between the rotor 430 and stator 432, for example by avoiding contact between rotor 430 and stator 432.
• FIG. 5 is a flowchart illustrating the process 500 of cooling and evacuation of the chamber 420 of the apparatus 400 of Figure 4.
• the process begins.
• valves 464, 462 and 424 are opened, and valve 466 is closed.
• liquid coolant in this instance liquid nitrogen
• the liquid coolant freely travels between chamber 420 and dewar 402, due to valve 462 being open. Entry of the liquid nitrogen through valve 424 displaces the atmosphere within the chamber 420 and dewar 402, which is allowed to exit through valve 464.
• Liquid nitrogen injection continues until the liquid level is substantially at level 450.
• a sensor (not shown) may be provided within dewar 402 to determine the liquid level.
• Such flooding of both the chamber 420 and dewar 402 with liquid nitrogen provides for thorough and effective cooling of all components within the dewar 402 and chamber 420.
• the liquid nitrogen will boil and produce nitrogen gas, which is also allowed to exit through valve 464.
• Liquid nitrogen is preferably introduced throughout this stage to maintain the liquid level substantially at level 450.
• the flow rate of gas out of valve 464 during this stage substantially corresponds to a boiling rate of liquid nitrogen within the chamber, which in turn is indicative of the temperature of the contents of the chamber.
• monitoring the gas flow rate out of valve 464 can give an indication of the temperatures of the components within the chamber 420 and dewar 402.
• valve 462 may be closed, at step 508.
• nitrogen gas is then pumped into chamber 420 through valve 424.
• the nitrogen gas is preferably at a temperature close to the boiling temperature of nitrogen to avoid the introduction of excessive heat into chamber 420. Due to the gas entering through valve 424, and the likely production of nitrogen gas from the boiling of liquid nitrogen within the chamber 420, and due to valve 462 being closed, liquid nitrogen within chamber 420 is forced out of chamber 420 through standpipe 428 under hydrostatic pressure, such that a liquid level in dewar 402 may rise above level 450, for example to the level shown in Figure 4. Gas is injected into and accumulated within chamber 420 until a liquid level in chamber 420 falls to substantially level 452.
• Level 452 may be monitored by positioning a liquid level sensor within chamber 420.
• level 452 may be configured to be level with a lower extremity of standpipe 428, such that continued accumulation of gas within chamber 420 would cause gas to pass up standpipe 428 rather than liquid.
• valves 420 Once the liquid within chamber 420. has fallen substantially to level 452, valves
• step 512 a pressure seal of dewar 402 and chamber 420.
• Valve 466 is opened, such that a gas pressure within chamber 420 is regulated by pressure regulator 468. Maintaining constant gas pressure will improve the sensitivity of devices with pressure dependent characteristics which may be operated within the gaseous environment of chamber 420. Having achieved the desired cryogenic gaseous operating environment within chamber 420, the process ends at step 514. It has proven possible to maintain suitable cryogenic conditions within such a gaseous environment for around 3 hours.
• the device to be operated within the gaseous environment of any one of chambers 120, 220, 320 or 420 may be a magnetic sensor.
• all materials of the apparatus 100, 200, 300, 400 are preferably non-magnetic.
• moving parts of the embodiments of Figures 1 to 4 should be self-lubricating at cryogenic temperatures, and should generally have matching and/or low coefficients of thermal expansion.
• the dewar insert 200 may comprise a number of sections each formed from epoxy impregnated woven fibreglass, each section having lapped faces to mate with the adjacent section.
• Such a modular construction is advantageous in permitting interchanging of sections, for example interchanging of chamber section 220 should a different device be used.
• Nylon screws hold the sections together and application of a small amount of silicone grease on the faces effectively seals the sections together for the purpose of gas containment.
• Each rotor 230, 330, 430 may be formed of machinable ceramic, while the drive shaft 240, 340, 440 may be a ground Pyrex glass spindle.
• the Pyrex spindle drive shaft 340 runs in a graphite bearing 344 pressed into the housing of chamber 320, with a fibreglass driving dog 346 pressed onto the spindle 340 on the outer side of the bearing 344.
• the running faces between the dog 346 and the bearing 344 govern the vertical clearance of the rotor 330 from the stator 332 and pre-load can be applied by a plastic spring between the rotor 330 and the bearing 344.
• a thin- walled cupro-nickel tube 304 carrying a graphite bearing 348 at its upper end and pressed into the upper portion of chamber 320 at its lower end, transmits rotation via a long thin ground Pyrex glass rod 342 to a sliding coupling 350 which engages the driving dog 346.
• variations in the length of the drive spindle 342 due to thermal effects do not affect the separation of the rotor 330 and stator 332, and thus do not alter the tape-to-SQUID separation where such devices are mounted upon the rotor 330 and stator 332.
• a paddle-wheel type air motor is used to drive the spindle 342 via a single-stage epicyclic plastic gearbox. Rotation angle is monitored by an optical shaft encoder mounted on the spindle.
• a patterned superconducting thin-film magnetic shield may be mounted on the module immediately below the stator device, for example a SQUID, to attenuate the vertical field component seen by the SQUID .
• the modular mounting allows fine tilt and positioning of the shield by means of three differential screws, adjustable by thin rods taken out to the room-temperature environment.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Physics & Mathematics (AREA)
• Mechanical Engineering (AREA)
• Thermal Sciences (AREA)
• General Engineering & Computer Science (AREA)
• Containers, Films, And Cooling For Superconductive Devices (AREA)
• Filling Or Discharging Of Gas Storage Vessels (AREA)

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Cited By (4)

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Citations (8)

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• 2005
  • 2005-06-28 CA CA002572842A patent/CA2572842A1/en not_active Abandoned
  • 2005-06-28 WO PCT/AU2005/000945 patent/WO2006002461A1/en active Application Filing
  • 2005-06-28 EP EP05754588A patent/EP1782006A1/en not_active Withdrawn
  • 2005-06-28 CN CNB200580026575XA patent/CN100498147C/zh not_active Expired - Fee Related
  • 2005-06-28 US US11/631,596 patent/US20070245748A1/en not_active Abandoned
  • 2005-06-28 JP JP2007519559A patent/JP2008505300A/ja not_active Withdrawn
• 2007
  • 2007-01-25 ZA ZA200700725A patent/ZA200700725B/xx unknown

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