CRYOGENIC STORAGE SYSTEM WITH IMPROVED TEMPERATURE STABILITY

Abstract

The present disclosure relates to devices and methods for the storage of material at cryogenic temperatures. Such devices may be useful for storing materials in the vapor space of a cryogenic dewar at a stable temperature and for preventing temperature excursions that may otherwise occur during refilling of a dewar with liquid cryogen. In some implementations, the devices may include a cryogen space holding liquid cryogen and gas, a separate storage space containing only gas, and a separate path for gas to leave the cryogen space during cryogen refills without passing through or substantially disturbing the temperature of the storage space. Some implementations further provide for passage of gas from the cryogen space to the storage space between cryogen refills to improve cryogen utilization efficiency.

Claims

1-56. (canceled)

57. A device for storing material at a cryogenic temperature, comprising a dewar having inner walls and outer walls; a storage space within the dewar configured to store materials; a cryogen space within the dewar containing liquid cryogen and cryogen gas; a barrier between the storage space and cryogen space permitting substantially no exchange of gas or liquid between them; one or more first conduits configured to carry liquid cryogen from the external environment outside the dewar to fill the cryogen space without penetrating the storage space or releasing cryogen into the storage space; one or more second conduits configured to carry gas from the cryogen space to either the storage space or the external environment outside the dewar, or both by bifurcation; and one or more valves configured such that actuation of the valves during cryogen refilling causes gas leaving the cryogen space through the second conduits to mostly or entirely flow to the external environment outside the dewar, and such that alternative actuation of the valves after refilling causes most or all gas evolved from evaporation of cryogen in the cryogen space to flow into the storage space.

58. The device of claim 57, wherein the one or more valves are electronically actuated and configured such that application of electric power to the valves is required for gas from the cryogen space to flow to the external environment, and such that the default power-off state of the valves results in most or all gas generated within the cryogen space flowing into the storage space.

59. The device of claim 57 or 58, wherein the one of more valves include a three-port valve configured to switch between directing gas from the cryogen space entering a common port of the three-port valve to the storage space and directing gas from the cryogen space entering the common port to the external environment outside the dewar.

60. The device of claim 57 or 58, wherein the one or more valves comprise a plurality of valves, and the plurality of valves are configured to be synchronized such that gas from the cryogen space flows to either the cryogen space or the external environment without simultaneously flowing to both or neither.

61. The device of claim 57 or 58, wherein: each second conduit carrying gas from the cryogen space is bifurcated into two conduit branches, a first conduit branch leading to the storage space, and a second conduit branch leading to the external environment outside the dewar; wherein the one or more valves include a valve connected to the second conduit branch configured to, when open, allow gas from the cryogen space to leave the dewar and, when closed, prevent gas from the cryogen space from leaving the dewar so that the gas must flow into the storage space; and wherein the flow resistance of the first conduit branch differs from the flow resistance of the second conduit branch such that, when the valve connected to the second conduit branch is open, more gas leaving the cryogen space flows through the second branch than the first branch.

62. The device of claim 61, wherein the first conduit branch has an adjustable gas flow resistance.

63. The device of claim 57 or 58, wherein second conduits leading to the storage space have a higher flow resistance than second conduits leading to the external environment such that, when the latter conduits are open, more gas from the cryogen space flows to the external environment outside the dewar than to the storage space.

64. The device of claim 63, wherein the second conduits leading to the storage space have an adjustable gas flow resistance.

65. The device of any one of claim 57 or 58 wherein the one or more valves are located outside the dewar.

66. The device of claim 61, wherein the one or more valves are located outside the dewar.

67. The device of claim 62, wherein the one or more valves are located outside the dewar.

68. The device of claim 63, wherein the one or more valves are located outside the dewar.

69. The device of claim 64, wherein the one or more valves are located outside the dewar.

70. A method of reducing temperature disturbance within the storage space of a dewar during refilling of liquid cryogen, consisting of operating the valves of any one of the devices of claim 57 or 58 during refilling such that most or all gas that is introduced, generated, or displaced from the cryogen space leaves the dewar without entering the storage space during refilling.

71. A method of reducing temperature disturbance within the storage space of a dewar during refilling of liquid cryogen, consisting of operating the valves of the device of claim 59 during refilling such that most or all gas that is introduced, generated, or displaced from the cryogen space leaves the dewar without entering the storage space during refilling.

72. A method of reducing temperature disturbance within the storage space of a dewar during refilling of liquid cryogen, consisting of operating the valves of the device of claim 60 during refilling such that most or all gas that is introduced, generated, or displaced from the cryogen space leaves the dewar without entering the storage space during refilling.

73. A method of reducing temperature disturbance within the storage space of a dewar during refilling of liquid cryogen, consisting of operating the valves of the device of claim 61 during refilling such that most or all gas that is introduced, generated, or displaced from the cryogen space leaves the dewar without entering the storage space during refilling.

74. A method of reducing temperature disturbance within the storage space of a dewar during refilling of liquid cryogen, consisting of operating the valves of the device of claim 62 during refilling such that most or all gas that is introduced, generated, or displaced from the cryogen space leaves the dewar without entering the storage space during refilling.

75. A method of reducing temperature disturbance within the storage space of a dewar during refilling of liquid cryogen, consisting of operating the valves of the device of claim 63 during refilling such that most or all gas that is introduced, generated, or displaced from the cryogen space leaves the dewar without entering the storage space during refilling.

76. A method of reducing temperature disturbance within the storage space of a dewar during refilling of liquid cryogen, consisting of operating the valves of the device of claim 64 during refilling such that most or all gas that is introduced, generated, or displaced from the cryogen space leaves the dewar without entering the storage space during refilling.

77. A method of reducing temperature disturbance within the storage space of a dewar during refilling of liquid cryogen, consisting of operating the valves of the device of claim 65 during refilling such that most or all gas that is introduced, generated, or displaced from the cryogen space leaves the dewar without entering the storage space during refilling.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0191] The drawings show schematic connections between spaces, conduits, and valves. The drawings are not to scale.

[0192] Whenever drawings show symmetrical duplicates of conduits and valves on the left and right sides of a drawing, it is to be understood that the conduits and valves shown can exist either singularly or as a plurality with no symmetry or number requirement for the device to operate as disclosed.

[0193] The drawings generally use liquid nitrogen as an example, but the liquid shown could be any suitable cryogen.

[0194] FIG. 1 shows a dewar 10 for storing materials in a cryogenic environment.

[0195] FIG. 2 shows a dewar 10A having increased temperature stability during cryogen refilling, according to some embodiments of the present disclosure.

[0196] FIG. 3 shows another dewar 10B having increased temperature stability during cryogen refilling, according to some embodiments of the present disclosure.

[0197] FIG. 4 shows yet another dewar 10C having increased temperature stability during cryogen refilling, according to some embodiments of the present disclosure.

[0198] FIG. 5 shows a fourth dewar 10D having increased temperature stability during cryogen refilling, according to some embodiments of the present disclosure.

[0199] FIG. 6 shows a fifth dewar 10E having increased temperature stability during cryogen refilling, according to some embodiments of the present disclosure.

[0200] FIG. 7 shows a sixth dewar 10F having increased temperature stability during cryogen refilling, according to some embodiments of the present disclosure.

[0201] FIG. 8 shows a seventh dewar 10G having increased temperature stability during cryogen refilling, according to some embodiments of the present disclosure.

[0202] FIG. 9 shows an eighth dewar 10H having increased temperature stability during cryogen refilling, according to some embodiments of the present disclosure.

DETAILED DESCRIPTION

[0203] FIG. 1 shows a dewar 10 used for storage of materials in a low temperature gas environment inside the dewar. As known in the art, vacuum space 11 containing layers of reflective insulation (not shown) thermally insulates the interior space 12 of dewar 10 from the ambient temperature of the environment external to the dewar. The vacuum space 11 is contained between a cylindrical inner dewar wall 17 and cylindrical outer dewar wall 18. A removable foam lid 13 thermally insulates the top of the dewar, and provides access to the interior space 12 for addition and removal of stored materials. A cryogen conduit 14 is used to periodically refill a pool of liquid cryogen 15, such as liquid nitrogen, at the bottom of the interior space 12. Continuous evaporation of the cryogen maintains the cold temperature of the interior space. The liquid cryogen is kept at a level sufficiently low to retain a large gas-filled space above it suitable for storage of materials in a racking system (not shown). Gas produced by cryogen filling and evaporation passes from inside the dewar through the interior space 12 and then to the external environment through openings 16 of the loose-fitting dewar lid 13.

[0204] In one embodiment of the present disclosure, FIG. 2 shows a dewar 10A in which the interior space inside dewar 10A has been divided by a gas-impermeable barrier 20 into a storage space 21 containing gas, and a cryogen space 22 containing liquid cryogen and gas. As depicted in FIG. 2, the storage space 21 is bounded by dewar lid 13, inner walls 17, and barrier 20. Above the barrier 20, the storage space 21 contains no liquid nitrogen, instead having containers or materials placed for storage at a cryogenic temperature. The storage space 21 is accessible via removable dewar lid 13.

[0205] The barrier 20 separating the two spaces is substantially impenetrable by gas or liquid. For example, the barrier 20 may have a permeance of 0.1 ng/(s.Math.m.sup.2.Math.Pa) or less. Liquid nitrogen (or other cryogen liquid(s)) is added and replenished by a fill tube 14 passing through the vacuum space 11 and entering the cryogen space 22 near or at its bottom. The barrier 20 prevents gas produced by cryogen filling and evaporation from entering the storage space 21, instead forcing gas from the cryogen space 22 to exit the dewar through one or more gas vent conduits 23.

[0206] Accordingly, in the embodiment depicted in FIG. 2, instead of displacing gas through the entire interior space of the dewar, gas generated by boiling or evaporation of liquid nitrogen (or other liquid cryogen) in the cryogen space 22 displaces only gas in the cryogen space. This displaced gas may exit the dewar through a gas vent tube or conduit 23 connected near the top of the cryogen space 22, passing through the vacuum space 11, which leaves gas in the storage space 21 undisturbed. Advantageously, by using tube or conduit 23, the temperature of the storage space may not be disturbed by excess cold gas moving through it when the liquid nitrogen is refilled. Dewar 10A may include only one gas vent conduit 23, but in some embodiments additional conduits may be added for redundancy and/or to prevent undesired buildup of pressure in the cryogen space 22 during filling.

[0207] Generally, during operation of traditional dewars, such as the dewar of FIG. 1, the liquid nitrogen (or other liquid cryogen) in the dewar 10 contributes to keeping the dewar cold in two stages. First, the liquid nitrogen absorbs 199 kJ/kg of heat in the process of boiling/evaporating into a gas. Second, as the gaseous nitrogen rises through the interior space 12 of the dewar 10, and especially as it warms while moving between the dewar lid 13 and inner wall 17 to exit the dewar at exhaust 16, it may absorb an additional 200 kJ/kg of heat during warming to ambient temperature. Accordingly, modifications to the embodiment shown in FIG. 2 may be made to retain the latter cooling mechanism.

[0208] In another embodiment of the present disclosure, FIG. 3 shows another dewar 10B in which the interior space has been divided by a gas-impermeable barrier 20 into a storage space 21 containing gas, and a cryogen space 22 containing liquid cryogen and gas. In this embodiment, each gas vent conduit 23 is connected to the common port of a three-port valve 30 that diverts the gas flow from the cryogen space 22 to either an interior gas vent conduit 31 leading to the storage space 21, or an exterior gas vent conduit 32 leading to the exterior environment outside the dewar.

[0209] In the embodiment of FIG. 3, during refilling of liquid nitrogen (or other liquid cryogen), the valve 30 may send gas from the cryogen gas vent tube 23 to an exterior gas vent tube 32. Advantageously, this may avoid disturbing the temperature of the storage space 21 during filling, similar to the embodiment of FIG. 2. Moreover, in the embodiment of FIG. 3, when filling stops, the valve 30 may send gas from the cryogen gas vent tube 23 into a path 31 leading to the storage space 21 instead of the external environment. Advantageously, this may allow the cold gas from the cryogen space 22 to contribute to cooling the storage space 21 by exiting the dewar between the dewar lid 13 and interior wall 17, similar to traditional dewars. Accordingly, the embodiment of FIG. 3 (and other embodiments described below) may have the advantage of not substantially disturbing the temperature of stored material during liquid nitrogen refilling while still utilizing liquid nitrogen with increased efficiency.

[0210] In one embodiment of the dewar, FIG. 4 shows another dewar 10C in which the interior space has been divided by a gas-impermeable barrier 20 into a storage space 21 containing gas, and a cryogen space 22 containing liquid cryogen and gas. In the embodiment of FIG. 4, there are separate interior gas vent conduits 31 and exterior gas vent conduits 32 able to vent gas from the cryogen space 22. Each interior gas vent conduit 31 may be opened or closed by an interior gas vent conduit valve 41 to release gas from the cryogen space 22 into the storage space 21. In addition, each exterior gas vent conduit 32 may be opened or closed by an exterior gas vent conduit valve 42 to release gas from the cryogen space 22 to the exterior environment outside the dewar. A pressure relief value 43 opens the exterior gas vent conduit 32 if any valve malfunction or blockage causes pressure to build in the cryogen space 22.

[0211] For ease of construction and maintenance, it may be desirable to avoid placement of valves inside the vacuum space of the dewar. Accordingly, in the embodiment of FIG. 4 there are separate types of gas vent tubes emerging from the cryogen space. There is a type of gas vent tube 32 that leads directly outside the dewar 10C, and another type of gas vent tube 31 that leads directly to the storage space 21. Gas flow paths leading to the storage space and gas flow paths leading outside the dewar are respectively controlled by separate valves 41 and 42 that may be opened or closed. During liquid nitrogen refilling, for example, valve(s) 41 may be closed, and valve(s) 42 may be opened, forcing gas from the cryogen space 22 to leave the dewar 10C without passing through the storage space 21. By way of further example, between liquid nitrogen refills, valve(s) 41 may be open, and valve(s) 42 may be closed, forcing gas from the cryogen space 22 to pass into the storage space 21. If pressure in the cryogen space 22 rises above a particular threshold, a relief valve 43 may provide a gas exit path to protect against any blockages or valve malfunctions. Advantageously, the embodiment of FIG. 4 may retain the advantages of the embodiment of FIG. 3 with a simplified construction design.

[0212] In yet another embodiment of the present disclosure, FIG. 5 shows dewar 10D in which the interior space has been divided by a gas-impermeable barrier 20 into a storage space 21 containing gas, and a cryogen space 22 containing liquid cryogen and gas. In this embodiment, each gas vent conduit 23 bifurcates into an exterior gas vent conduit 32 and a constricted interior gas vent conduit 51. The constricted interior gas vent conduit 51 may have a smaller diameter and/or smaller exit orifice than the exterior gas vent conduit 32 such that when the exterior gas vent conduit valve 42 is open, gas from the cryogen space 32 preferentially flows through the exterior gas vent conduit 32 rather than the interior gas vent conduit 51. When the exterior gas vent conduit valve 42 is closed, gas leaving the cryogen space 22 may flow into the storage space 21. A pressure relief value 43 may open the exterior gas vent conduit 32 if, for example, any valve malfunction or blockage causes pressure to build in the cryogen space 22.

[0213] Accordingly, in the embodiment of FIG. 5, only one type of gas vent tube 23 emerges from the cryogen space 22. Furthermore, in this embodiment, only the exterior vent tube 32 has a valve 42 that can be opened or closed. During liquid nitrogen (or other liquid cryogen) refilling, for example, the valve 42 may be opened. The interior vent tube 51 and/or its opening orifice may be designed so that the flow resistance of tube 51 and its opening are higher than the flow resistance of tube 32 and valve 42 when open. If valve 42 is opened during refilling, for example, gas from the cryogen space 22 may flow through the exterior vent tube 32 in preference to flowing through the interior vent tube 51. Accordingly, more gas may flow outside the dewar than into the storage space 21. On the other hand, the closure of valve 42 between refills may force gas from the cryogen space 22 into the storage space 21. Advantageously, the embodiment of FIG. 5 may minimize the number of valves (e.g., allowing for as few as one), and construction may be simplified via the placement of all valves are outside the dewar 10D.

[0214] In another embodiment of the present disclosure, FIG. 6 shows dewar 10E in which the interior space has been divided by a gas-impermeable barrier 20 into a storage space 21 containing gas, and a cryogen space 22 containing liquid cryogen and gas. In the embodiment of FIG. 6, separate exterior gas vent conduits 32 and constricted interior gas vent conduits 51 emerge from the cryogen space 22. The constricted interior gas vent conduit 51 may have a smaller diameter and/or smaller exit orifice than the exterior gas vent conduit 32 such that when the exterior gas vent conduit valve 42 is open, gas from the cryogen space 32 preferentially flows through the exterior gas vent conduit 32 rather than the interior gas vent conduit 51. For example, when the exterior gas vent conduit valve 42 is closed, gas leaving the cryogen space 22 may flow through the constricted interior gas vent conduit 51 into the storage space 21. A pressure relief value 43 may open the exterior gas vent conduit 32, for example, if any valve malfunction or blockage causes pressure to build in the cryogen space 22.

[0215] Accordingly, in the embodiment of FIG. 6, tubes 51 carrying gas directly from the cryogen space 22 to the storage space 21 are designed so that they exhibit greater resistance to flow of gas from the cryogen space than exterior vent tubes 32 with valves 42 in the open state. Therefore, if valve(s) 42 are opened during refilling of liquid nitrogen (or other liquid cryogen), for example, most gas that enters or is generated in the cryogen space 22 during refilling may flow outside the dewar via vent tube(s) 32. On the other hand, when valve 42 is closed, such as when not refilling with liquid nitrogen, cold gas generated in the cryogen space 22 from evaporating liquid nitrogen may flow through vent tube(s) 51 into the storage space 21 to assist in absorbing heat that leaks into the dewar from the external environment. Advantageously, this may increase the efficiency of dewar 10E with respect to the use of liquid nitrogen (or other liquid cryogen).

[0216] Opening orifice of interior gas vent tubes 51 in any of the disclosed embodiments may be adjustable such that the flow resistance of the path through vent tube 51 and its opening may be adjusted to improve diversion of gas to the dewar exterior during refilling, while still permitting adequate venting of the cryogen space between refills when valve 42 is closed.

[0217] In the embodiment of FIG. 7, the storage space 21 of dewar 10F further includes a temperature chamber. For example, the temperature chamber may include vertical dividers, walls, a floor, and/or a removable ceiling made of thermally conductive metal 71 that reduces temperature gradients within the temperature chamber used for storing materials. Part of the thermally conductive metal 71 may be in contact with temperature measurement probes and heating elements to achieve precise temperature control. Layers of foam insulation 72 above and below the temperature chamber may cause the temperature chamber to reach an equilibrium temperature between the temperature of the liquid cryogen and ambient temperature outside the dewar, with the equilibrium temperature determined by the thickness and insulation efficiency of each foam layer and the dewar lid 13. Additionally, the cryogen space 22 may include a platform 70 made of thermally conductive metal that reduces temperature gradients within the cryogen space, which may help keep the cryogen space 22 at a constant temperature nearly equal to the temperature of the liquid cryogen 15 regardless of cryogen level. Advantageously, this may keep the gas-impermeable barrier 20 and/or bottom of the storage space 21 containing the temperature chamber at a constant temperature independent of the cryogen level in the cryogen space 22.

[0218] It will be understood by those skilled in the art that the embodiments of the present disclosure for minimizing disturbance of the temperature of the storage space 21 during liquid nitrogen refilling may be combined with other mechanisms that reduce the temperature gradient of a storage space, and/or finely control the temperature of a storage space. For example, in some embodiments, the storage space 21 of the present disclosure might contain a thermally-conductive sleeve to reduce the vertical temperature gradient. Alternatively or concurrently, in some embodiments, the storage space 21 may include one or more temperature chambers, an example of which having two thermally-conductive vertical compartment dividers is shown in FIG. 7. The example of FIG. 7 further includes a thermally conductive platform 70 to increase the uniformity of the temperature inside the cryogen space and increase the independence of the temperature from the liquid nitrogen level.

[0219] Generally, most of the operating time of a dewar is spent in a relatively quiescent state between liquid nitrogen refills. Therefore, when solenoid valves or other electrically-controlled valves are used in embodiments, it may be preferable for the normal power-off (e.g., default) state of the valves to result in gas from the cryogen space 22 flowing into the storage space 21.

[0220] Although it is generally preferable to avoid influx of large amounts of cold gas into the storage space, sometimes it may be desired to flood the storage space, or space above a temperature chamber in the storage space, with dry, cold gas. For example, this may be desirable to accelerate cooling of a large warm mass placed into the storage space. By way of further example, it may be desirable to displace warm, moist air introduced into the storage space by opening the dewar lid. Such cold gas flow may help clear condensed fog out of the storage space to improve visibility, and maintain cold temperatures in the storage space while the dewar lid is open.

[0221] In some embodiments, cold gas may flow into the storage space 21 by pushing either liquid nitrogen or dry gaseous nitrogen (or other cryogen) into the cryogen conduit 14, and refraining from valve actuation, leaving all valves in the default state that exists between refilling. Advantageously, this may result in excess gas in the cryogen space 22 flowing into the storage space 21 at a temperature similar to the temperature of liquid nitrogen. Alternatively, cold gas at a temperature warmer than liquid nitrogen may be made to flow into the storage space 21 by pushing dry gas into the external gas vent conduit 32 of the embodiments of, for example, FIGS. 4-9 (and optionally opening valve 41). Such methods for flushing the storage space with cold gas may expel moisture and improve visibility and may be useful when the storage space 21 contains a temperature chamber to protect stored materials from changes in the temperature of surrounding gas.

[0222] In another embodiment of the present disclosure, FIG. 8 shows a dewar 10G similar to the embodiment of FIG. 6 and with the interior gas vent conduits 51 running directly from the cryogen space 22 into the storage space 21. Each constricted interior gas vent conduit 51 may have a smaller diameter and/or smaller exit orifice than the exterior gas vent conduit 32 such that when the exterior gas vent conduit valve 42 is open, gas from the cryogen space 32 preferentially flows through the exterior gas vent conduit 32 rather than the interior gas vent conduit 51. When the exterior gas vent conduit valve 42 is closed, gas leaving the cryogen space 22 may flow through the constricted interior gas vent conduit 51 into the storage space 21. A pressure relief value 43 may open the exterior gas vent conduit 32 if, for example, any valve malfunction or blockage causes pressure to build in the cryogen space 22.

[0223] In another embodiment of the present disclosure, FIG. 9 shows a dewar 10H containing exterior gas vent conduits 32 without valve 42 of other embodiments. In this embodiment, the only valve on each exterior gas vent conduit 32 is a relief valve 43. The relief valve 43 may open automatically at a threshold pressure that occurs in the cryogen space 22 during cryogen refilling. Each constricted interior gas vent conduit 51 may have a smaller diameter and/or smaller exit orifice than the exterior gas vent conduit 32 such that when the exterior gas vent conduit relief valve 43 is open, gas from the cryogen space 22 preferentially flows through the exterior gas vent conduit 32 rather than the interior gas vent conduit 51. When the exterior gas vent conduit relief valve 43 is closed, gas leaving the cryogen space 22 may flow through the constricted interior gas vent conduit 51 into the storage space 21.

[0224] In some embodiments, no manual or electronic valve actuation may be necessary to divert gas from the cryogen space 22 to the dewar exterior during refilling with liquid nitrogen (or other liquid cryogen). For example, as depicted in FIG. 9, it is possible to equip the exterior gas vent conduit 32 solely with a pressure relief valve 43. The threshold pressure of this valve may be selected such that it only opens due to a pressure increase that occurs in the cryogen space 22 during liquid nitrogen refilling. When open, gas from the cryogen space 22 may preferentially flow through the exterior gas vent conduit 32 and relief valve 43 rather than through the constricted interior gas vent conduit 51. When liquid nitrogen is not being refilled, and pressure inside the cryogen space 22 is low, the relief valve 43 may close, and gas evaporating from liquid nitrogen in the cryogen space 22 may flow through interior conduits 51 to the storage space 21.

[0225] Although the present disclosure uses liquid nitrogen and nitrogen gas as examples, any other appropriate cryogen and its associated gas may be used.