CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 62/237,026, filed on Oct. 5, 2015, the entire contents of which is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    This disclosure relates to devices and methods for purifying cryogenic fluids. 
       BACKGROUND 
       [0003]    Nitrogen, as an element of great technical importance, can be produced in a cryogenic nitrogen plant. Air inside a distillation column is separated at cryogenic temperatures (about 100K/−173° C.) to produce high purity nitrogen with 1 ppm of impurities. The process is based on the air separation, which was invented by Dr. Carl von Linde in 1895. 
         [0004]    Liquid nitrogen is widely used in the pharmaceutical, biopharmaceutical, and life sciences industries for lyophilization and quick-freezing of pharmaceutical preparations and storage of cells and microbial cultures. However, liquid nitrogen can act as a vehicle for transmitting contaminants such as microorganisms. 
         [0005]    Liquid nitrogen is a compact and readily transported source of nitrogen gas without pressurization. Further, its ability to maintain temperatures far below the freezing point of water makes it extremely useful in a wide range of applications, primarily as an open-cycle refrigerant. 
       SUMMARY 
       [0006]    The systems and methods described in this disclosure provide an approach to generating purified (ideally sterile) cryogenic fluid. These systems and methods can facilitate filtering liquid nitrogen in small volumes which can increase its affordability for many cryogenic preservation facilities (e.g., IVF facilities/labs) 
         [0007]    Some cryogenic fluid purification devices include: a first container including a wall or walls with a heat transfer coefficient of between 0.01 W/(m·K) and 310 W/(m·K) (e.g., less than 100 W/(m·K), less than 50 W/(m·K), less than 25 W/(m·K), less than 10 W/(m·K), less than 5 W/(m·K), less than 1 W/(m·K), less than 0.5 W/(m·K), less than 0.25 W/(m·K), less than 0.2 W/(m·K)), the wall or walls defining an interior region of the first container; a second container defining a reservoir; and a filter disposed below the reservoir of the second container, wherein the filter provides fluid communication between the reservoir of the second container and the interior region of the first container. Embodiments of these devices can include one or more of the following features. 
         [0008]    In some embodiments, an outer wall of the inner container and a corresponding inner wall of the outer container have the same shape with the outer wall of the inner container being slightly smaller. In some cases, engagement between the outer wall of the inner container and the corresponding inner wall of the outer container  110  provides a friction fit and seal which limits the flow of fluids out of the outer container between these walls. 
         [0009]    In some embodiments, cryogenic fluid purification devices include a lid with a heat transfer coefficient of between 0.01 W/(m·K) and 20 W/(m·K) (e.g., less than 10 W/(m·K), less than 5 W/(m·K), less than 1 W/(m·K), less than 0.5 W/(m·K), less than 0.25 W/(m·K), less than 0.2 W/(m·K)). In some cases, the lid is configured to seal an opening in the inner container such that such that movement of gases out of the inner container other than through the filter are substantially prevented. In some cases, the lid comprises a pressure relief valve. In some cases, when the lid is attached to the first container, a spout of the first container provides the only pathway through thermal insulation provided by the outer container and the lid. In some cases, the lid includes a surface coating or arrangement of texture to inhibit the buildup of ice. In some cases, the lid includes a platinum and activated carbon element that inhibits condensation of oxygen. 
         [0010]    Some cryogenic fluid purification devices include: a body having a heat transfer coefficient of between 0.01 W/(m·K) and 10 W/(m·K) (e.g., less than 5 W/(m·K), less than 1 W/(m·K), less than 0.5 W/(m·K), less than 0.25 W/(m·K), less than 0.2 W/(m·K)); a top portion removably attached to the body, the top portion having with a heat transfer coefficient of between 0.01 W/(m·K) and 10 W/(m·K) (e.g., less than 5 W/(m·K), less than 1 W/(m·K), less than 0.5 W/(m·K), less than 0.25 W/(m·K), less than 0.2 W/(m·K)); and a conduit with an inline filter. 
         [0011]    In some embodiments, a top wall of the body defines at least one opening which allows fluid to pass between a reservoir defined by the body and a space defined between the body and the top portion when the top portion is attached to the body. In some cases, cryogenic fluid purification devices include a sealing mechanism operable to close the at least one opening. The sealing mechanism can be a plunge seal. 
         [0012]    In some embodiments, cryogenic fluid purification devices include a heating element operable to accelerate the development of the vaporization pressure necessary to dispense a liquid cryogenic fluid from reservoir defined by the body. In some cases, the body comprises a section in which the insulation can be controllably removed and reset (e.g., wherein the section is hinged to the remainder of the body). In some cases, a control which operates both the heating element and a sealing mechanism operable to close the at least one opening simultaneously. 
         [0013]    In some embodiments, the heating element comprises a heat transfer element that provides heat transfer into the liquid cryogen bath. In some cases, the heat transfer element has a first position in which a portion of the heating element is disposed in the reservoir and second position in which less of the heating element is disposed in the reservoir. In some cases, the heating element comprises an electric heater operable to heat fluid in the reservoir. In some cases, the electric heater includes a switch that is closed when a sealing mechanism operable to close the at least one opening is closed. 
         [0014]    In some embodiments, the conduit extends from an inlet disposed in the reservoir near a bottom of the reservoir and extends through the top wall of the body to an outlet disposed in a dispensing spout. 
         [0015]    In some embodiments, cryogenic fluid purification devices a pump operable to compress environmental air into the cryogenic fluid purification device. In some cases the top portion comprises a pressure relief valve to avoid over pressurization of the system. 
         [0016]    In some embodiments, cryogenic fluid purification devices include a pump operable to compress fluid in a space defined between the body and the top portion when the top portion is attached to the body into a reservoir defined by the body. 
         [0017]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0018]      FIGS. 1A-1C  show a cryogenic fluid purification device in use. 
           [0019]      FIG. 2  shows a cryogenic fluid purification device. 
           [0020]      FIG. 3  shows a cryogenic fluid purification device. 
           [0021]      FIG. 4  shows a cryogenic fluid purification device. 
           [0022]      FIG. 5  shows a cryogenic fluid purification device. 
           [0023]      FIG. 6  shows a cryogenic fluid purification device. 
       
    
    
       [0024]    Like reference symbols in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0025]    The systems and methods described in this disclosure purify cryogenic fluids (e.g., liquid nitrogen) utilizing inexpensive filter technologies. These systems and methods include filling devices with supplied cryogenic fluid, containing the cryogenic fluid in a safe and insulated manner, processing the cryogenic fluid to remove impurities (e.g., filtering), and decanting the cryogenic fluid safely and in a controlled manner. Some devices are disposable while others are reusable. 
         [0026]    Some systems use gravity and/or pressure to feed a liquid cryogen (e.g., liquid nitrogen) through a particulate filter for the purpose of purification. A clean (and possibly sterile) insulated container is fitted with a clean inner conduit (also possibly sterile) which forms a barrier and creates a space and reservoir. A clean (again possibly sterile) filtering member is placed in position below the reservoir so that the cryogenic fluid will enter the filter from the reservoir due to gravity. 
         [0027]      FIGS. 1A-1C  show a cryogenic fluid purification device  100  that includes a first or outer container  110 , a second or inner container  112 , and a lid  114 . The outer container  110  defines an inner chamber  116  as well as a spout  118  and an opening  120  which extend through the walls of the outer container  110 . The inner chamber  116  and the opening  120  of the outer container are sized and configured to receive the inner container  112 . The outer container has a steel or polymer shell filled with a vacuum or insulative material which reduces heat transfer through the outer container  110 . The aggregate heat transfer coefficient of the container  110  would ideally be between 0.01 W/(m·K) and 0.20 W/(m·K). 
         [0028]    The inner container  112  has an upper portion  122  and a filter  124 . In the cryogenic fluid purification device  100 , the upper portion  122  and the filter  124  are separate components with the filter  124  inserted through an opening in the bottom of the upper portion  122 . A gasket material  125  provides a seal between the upper portion  122  and the filter  124  that limits the flow of fluids through the interface between the upper portion  122  and the filter  124 . This configuration facilitates replacement of the filter. Some devices use inner containers in which the upper portion  122  and the filter  124  are a single integrated component. 
         [0029]    The upper portion  122  of the inner container  112  is above the filter as shown in the  FIGS. 1A-1C  when the cryogenic fluid purification device  100  is being used. The upper portion  122  defines a reservoir chamber  126  in fluid communication with the filter  124 . The reservoir  126  has an inlet  128  through which fluid to be purified is introduced into the reservoir  126  and the filter  124  has an outlet  130  through which purified fluid is discharged from the filter  124  into the outer container  110 . 
         [0030]    In the cryogenic fluid purification device  100 , the outer wall of the upper portion  122  of the inner container  112  and the corresponding inner wall of the outer container  110  have the same shape with the outer wall of the upper portion  122  of the inner container  112  being slightly smaller. When the inner container  112  is inserted into the outer container  110 , the outer wall of the upper portion  122  of the inner container  112  engages the corresponding inner wall of the outer container  110 . In some devices, this engagement provides a friction fit and seal which limits the flow of liquids and/or gases out of the outer container  110  between these walls. 
         [0031]    The outer wall of the upper portion  122  of the inner container  112  and the inner wall of the outer container  110  extend slightly above the surrounding portions of the outer container  110 . This extension provides a rim that engages a corresponding groove on the lid  114 . In the cryogenic fluid purification device  100 , a laterally extending ridge on the extension engages a detent on the lid  114  to provide a snap-lock engagement between the extension and the lid. A gasket material within the groove provides a seal between the lid  114  and the extension which limits the flow of liquids and/or gases out of the outer container  110  between the lid  114  and the extension. This seal limits the escape of vapor phase cryogenic fluid. As the liquid cryogenic fluid vaporizes, the pressure in the inner container  112  increases and provides an additional force driving the liquid phase cryogenic fluid out of the inner container  112  through the filter  124 . In some devices, the lid  114  includes a pressure relief valve that limits pressure buildup due evaporation of the liquid cryogen in the inner container. 
         [0032]    Like the outer container  110 , the lid  114  has a steel or polymer shell filled with a vacuum or insulative material which reduces heat transfer through the lid  114 . When the lid  114  is attached to the other components of the cryogenic fluid purification device  100 , the spout  118  provides the only pathway through the thermal insulation provided by the outer container  110  and the lid  114 . This configuration limits the heat transfer associated with components such as, for example, pump inlets that extend through the walls of some other cryogenic fluid storage and/or purification devices. Lowering the heat transfer can slow the rate of evaporation of the liquid cryogenic fluid. Some devices include a closure mechanism such as, for example, a plug, a cap, or a valve limiting the escape of vapor phase cryogenic fluid through the spout. 
         [0033]    In some devices, the lid  114  is a surface coating or arrangement of texture to inhibit the buildup of ice. In some devices, the lid  114  is configured to seal out atmospheric gases from chamber  126  which inhibits the condensation of undesirable elements such as, for example, oxygen in the device, but permits the escape of vaporized gas from the chamber via a limiting valve feature. 
         [0034]    In use, the cryogenic fluid purification device  100  is assembled by inserting the inner container  112  into the outer container  110  until the inner container  112  is firmly seated. The cryogenic fluid (e.g., liquid nitrogen) to be purified is poured or otherwise transferred into the reservoir  126  is shown in  FIG. 1A . As shown in  FIG. 1B , gravity pulls the cryogenic fluid in the reservoir  126  through the filter  124  into the inner chamber  116  of the outer container  110 . As discussed above, the vaporization pressure generated by the evaporation of the cryogenic fluid in the upper portion  122  of the inner container  112  can provide an additional force driving the liquid phase cryogenic fluid out of the inner container  112  through the filter  124 .  FIG. 1C  shows the system after most of the cryogenic fluid has passed through the filter  124  into the inner chamber of the outer container  110 . A user can then decant the cryogenic fluid through the spout  118  into working vessels. 
         [0035]    Some cryogenic fluid purification devices use gas pressure to cause the cryogenic fluid (e.g., liquid nitrogen) to flow from a reservoir to an outlet through a conduit that includes a filter. 
         [0036]      FIG. 2  shows a cryogenic fluid purification device  200  that includes a body  210 , a top portion  212 , and a conduit  214  with a filter  216  inline. The top portion  212  is removably attached to the body  210 . Both the body  210  and the top portion  212  are insulated to limit thermal transfer through these components of the cryogenic fluid purification device  200 . The top wall of the body  210  defines opening(s)  224  which allow(s) fluid to pass between a reservoir  218  defined by the body  210  and a space  226  defined between the body  210  and the top portion  212  when the top portion  212  is attached to the body  210 . The fluid can be, for example, liquid cryogen being introduced into the reservoir  218  or gas moving between the space  226  and the reservoir  218 . 
         [0037]    The conduit  214  extends from an inlet  220  disposed in the reservoir  218  to an outlet  222 . The conduit  214  is positioned with its inlet  220  near the bottom of the reservoir  218  and extends through the top wall of the body  210  to a dispensing spout  228  which houses the outlet  222 . In the cryogenic fluid purification device  200 , the filter  216  is an integrated in-line filter. The filter may be above, partially submerged in, or fully submerged in the liquid cryogen depending on the level of the liquid cryogen in the reservoir  218 . Systems configured to keep the filter in a position where it stays at sub-zero temperatures can limit liquid water ingress. In some systems, the conduit  214  and the filter  216  are removable. 
         [0038]    The top portion  212  includes a pump  230  operable to compress environmental air into the cryogenic fluid purification device  200 . In the cryogenic fluid purification device  200 , the pump is a positive displacement pump operated by pushing the handle of the pump  230  downward. Some devices use other pressurizing mechanisms such as, for example, bellows or diaphragm systems. An increase in pressure in the reservoir  218  induces flow of the cryogenic liquid through the conduit  214 . The top portion  212  includes a pressure relief valve  232  to avoid over pressurization of the system. 
         [0039]    In some devices, the pump  230  uses a retained portion of evaporated cryogenic fluid rather environmental air as the pressurizing fluid. This avoids introducing oxygen into the system with the environmental air. For example, liquid nitrogen in reservoir boiling off due to natural heat transfer can be at least partially collected in the space  226 . Operation of the pump  230  pressurizes the nitrogen gas in the space  226  back into reservoir  218  thus inducing flow of the liquid nitrogen through the conduit  214 . These devices may include controls such as, for example, check valves or pressure relief valves between the space  226  and the reservoir  218  to selectively isolate the space  226  and the reservoir  218  from each other. 
         [0040]      FIG. 3  shows a cryogenic fluid purification device  250  that is substantially similar to the cryogenic fluid purification device  250 . However, the cryogenic fluid purification device  250  pressurizes the reservoir  218  by simply sealing the reservoir  218  except for the conduit  214 . This allows vaporization pressure to build-up due to gradual, and natural, heat transfer from ambient conditions around the cryogenic fluid purification device  250 . Once adequate pressure is reached, the cryogenic fluid is biased to flow from the reservoir  218 , through the filter  216 , and out the outlet  222 . 
         [0041]    The cryogenic fluid purification device  250  includes sealing mechanism  260  operable to close the opening  224  in the upper wall of the body  210 . In cryogenic fluid purification device  250 , the sealing mechanism  260  is a plunge seal but other cryogenic fluid purification devices use other sealing mechanisms such as, for example, rotary valves. The opening  224  is left unobstructed until a user wants to dispense purified cryogenic fluid. The sealing mechanism  260  is then operated to close the opening  224 . When not dispensing, the evaporation pressure of the liquid cryogenic fluid is released through opening  224  and then through pressure relief valve  232 . 
         [0042]      FIGS. 4-6  show cryogenic fluid purification devices that are generally similar to the devices described above but that include heating elements to accelerate the development of the vaporization pressure necessary to dispense the liquid cryogenic fluid. 
         [0043]      FIG. 4  shows a cryogenic fluid purification device  270  that is similar to the cryogenic fluid purification device  200  with an additional feature which increases the heat transfer rate. The cryogenic fluid purification device  270  includes a section  272  in which the insulation can be controllably removed and reset. In the illustrated device, the section  272  is hinged to expose a portion of the inner wall of the body  210 . In other devices, the section can slide or be extracted be to expose a portion of the inner wall of the body  210 . 
         [0044]    As the heat transfer rate increases, the evaporation rate of the cryogenic fluid also increases. If this feature was synchronized to a sealing mechanism (e.g., the sealing mechanism  260  shown in cryogenic fluid purification device  250 ) so that there was single path through the spout, the increasing rate and magnitude of vaporization pressure can cause faster, higher volume flows. When the seal was released, venting the vapor pressure build-up, the fluid flowing through the spout would stop. When the insulation is replaced, the rate of heat transfer will decrease reducing the volume of nitrogen boiling off and lost to atmospheric venting. 
         [0045]      FIG. 5  shows a cryogenic fluid purification device  270  with an element that provides heat transfer into the liquid cryogen bath. The cryogenic fluid purification device  270  includes a heat transfer element  274  that can be inserted directly into the liquid cryogenic fluid after or during sealing of the reservoir  218 . The flow of the cryogenic liquid can be arrested by releasing the seal (not shown). The rate of heat transferred to the liquid nitrogen can be reduced by drawing the heat-sink out from the reservoir  218  of cryogenic fluid. 
         [0046]      FIG. 6  also shows a cryogenic fluid purification device  280  with an element that provides heat transfer into the liquid cryogen bath. The cryogenic fluid purification device  280  includes an electric heater  282  operable to heat fluid in the reservoir  218 . The electric heater includes a switch  284  that is closed when the seal or valve over opening  224  is closed by depressing the handle  231 . Closing the switch  284  completes a circuit and conduct energy from a power source  286  to a heating element  288  placed in the liquid nitrogen chamber thereby increasing the evaporation rate. Releasing the handle  231  vents the reservoir  218  and opens the switch  284 . 
         [0047]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.
A cryogenic fluid purification device comprising: a first container defining an interior region; a second container defining an interior region in fluid communication with the interior region of the first container; and a cryogenic fluid in contact with an exterior of the second container.