Abstract:
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.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 62/187,936, filed on Jul. 2, 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]    The main purpose of a cryogenic nitrogen plant is to provide a customer with high purity gaseous nitrogen (GAN). In addition, liquid nitrogen (LN) is produced simultaneously and is typically 10% of the gas production. LN produced by cryogenic plants is stored in a local tank and used as a strategic reserve. 
         [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 a means for users of cryogenic fluid to overcome the challenge of obtaining purified (ideally sterile) cryogenic fluid. These systems and methods are particularly beneficial to cryogenic preservation facilities such as in vitro fertilization facilities and labs which were often not able to afford to implement filtering techniques to purify commercial grade cryogenic fluid (i.e., liquid nitrogen). 
         [0007]    These systems and methods use a cryogenic fluid such as commercial grade liquid nitrogen to generate highly purified liquid nitrogen from the commercial grade liquid nitrogen and/or from nitrogen in the air. The systems and methods promote the condensation of nitrogen while specifically preventing the condensation of oxygen from source air. 
         [0008]    The condensation can be achieved in an open system or a closed system. Condensation can be assisted by utilizing the pressure/temperature relationships of fluidic/gaseous systems&#39; characteristics (i.e. drawing a vacuum lowers the boiling temperature). 
         [0009]    In one aspect, a cryogenic fluid purification device includes: 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. Embodiments can include one or more of the following features. 
         [0010]    In some embodiments, the second container is sized and configured to be received at least partially in the interior region of the first container. In some cases, the device includes a manifold extending from an outlet of the first container to an inlet of the second container. The manifold can include an oxygen rejecting filter. In some cases, the device includes a pump operable to reduce pressure in the interior region of the first container. 
         [0011]    In some embodiments, the device includes a filter disposed in a path providing fluid communication between the interior region of the second container and the interior region of the first container. 
         [0012]    In some embodiments, the first container comprises a spout configured to engage a port of the second container. In some cases, the device includes a third container defining an interior region, wherein the second container is sized and configured to be received at least partially in the interior region of the third container. 
         [0013]    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 
         [0014]      FIG. 1  is a schematic view of a cryogenic fluid purification device. 
           [0015]      FIGS. 2A and 2B  show a pressure-temperature phase diagram for nitrogen. 
           [0016]      FIG. 3  is a schematic view of a cryogenic fluid purification device. 
           [0017]      FIG. 4  is a schematic view of a cryogenic fluid purification device. 
           [0018]      FIG. 5  is a schematic view of a cryogenic fluid purification device. 
       
    
    
       [0019]    Like reference symbols in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0020]    The systems and methods described in this disclosure provide a means for users of cryogenic fluid to overcome the challenge of obtaining purified (ideally sterile) cryogenic fluid. These systems and methods are particularly beneficial to cryogenic preservation facilities such as in vitro fertilization facilities and labs which were often not able to afford to implement filtering techniques to purify commercial grade cryogenic fluid (i.e., liquid nitrogen). 
         [0021]    These systems and methods use a cryogenic fluid such as commercial grade liquid nitrogen to generate a highly purified cryogenic fluid (e.g., highly purified liquid nitrogen) from the commercial grade cryogenic fluid and/or from gases in the air. In some embodiments, the systems and methods promote the condensation of nitrogen while specifically preventing the condensation of oxygen from source air. 
         [0022]    The condensation can be achieved in an open system or a closed system. Condensation can be assisted by utilizing the pressure/temperature relationships of fluidic/gaseous systems&#39; characteristics (i.e. drawing a vacuum lowers the boiling temperature). 
         [0023]      FIG. 1  shows a device  100  that provides for purification of commercial grade liquid nitrogen as well as for production of liquid nitrogen from air around the device. The device  100  includes a first container (e.g., outer container  110 ), a second (e.g., inner container  112 ), and a manifold  114 . The manifold  114  provides a fluid flow path connecting the outer container  110  and the inner container  112  such that gas formed by evaporation of cryogenic fluid in the outer container  110  can flow into the inner container  112 . 
         [0024]    The outer container  110  is an insulated container which limits the transfer of heat from the environment into the outer container  110 . In the device  100 , the outer container  110  includes polystyrene foam as an insulating material. In some embodiments, the outer container  110  includes other materials characterized by low heat conductivity such as other foams or “vacuum-based-insulation” in which two layers are separated by a gap which is partially evacuated of air, creating a near-vacuum instead or in addition to the polystyrene foam. The insulation provided by the outer container helps maintain the contents of the outer container (e.g., the commercial grade liquid nitrogen) at low temperature for a longer period than would be possible without the insulating effect of the outer container  110 . The outer container  110  is generally cylindrical in shape. In some embodiments, outer containers are formed in other shapes. 
         [0025]    A lid  116  extends across an open end of the outer container  110  with a seal  118  limiting (e.g., preventing) fluid flow between the outer container  110  and the lid  116 . A first port (e.g., filling port  120 ) extends through the lid  116  and can be used to introduce cryogenic fluid into the outer container  110 . The device  100  includes a funnel  122  with a valve  124  that facilitates adding cryogenic fluid to the outer container  110 . Some devices include other mechanisms for adding cryogenic fluid to the outer container. For example, a reservoir (e.g., a storage tank) of commercial grade liquid nitrogen can be connected to the device by permanently installed piping. However, it is anticipated that manually filled devices such as the device  100  will be appropriate for small-scale facilities with limited needs for highly purified cryogenic fluid. 
         [0026]    As discussed above, the manifold  114  provides a fluid flow path connecting the outer container  110  and the inner container  112 . The manifold  114  is attached to the lid  116  with an open side of the manifold  114  extending across a second port (e.g., evaporation port  126 ) and a third port (e.g., condensation port  128 ). The inner container  112  is inserted through the third port  128  into the chamber defined by the outer container  110  and the lid  116 . 
         [0027]    The inner container  112  has a flange which rests on a gasket extending around the third port  128 . The gasket limits (e.g., prevents) the flow of liquid out of the outer container  110  through gaps between the inner container  112  and the lid  116 . In some embodiments, other seals provide this function. For example, some lids include an elastic member extending around an inner perimeter of the third port. In addition, some devices include closures which may be movable between closed positions limiting fluid flow through the ports  120 ,  126 ,  128  and open positions allowing substantially free fluid flow through the ports  120 ,  126 ,  128 . The closures can be, for example, secondary lids or corks. 
         [0028]    In contrast to the outer container  110 , the inner container  112  has thin walls made of materials characterized by high thermal conductivity which facilitate heat transfer through the walls. In the device  100 , the walls of the inner container are made of 1 mm thick aluminum. In some devices, the walls of the inner container are made of other materials characterized by high thermal conductivity, such as steel, copper, glass, or high density plastic. The term “walls” refers to the boundary structures (e.g. side-walls, bottom walls, and top walls). The inner container  112  is generally cylindrical in shape. In some embodiments, inner containers are formed in other shapes. 
         [0029]    The lid  116  also includes a lock engageable to hold the inner container  112  in place relative to the lid and a lock engageable to hold the lid  116  in place relative to the outer container  110 . This limits upward movement of the inner container  112 /lid  116  due to buoyancy forces when the level of liquid in the space between the inner container  112  and the outer container  110  is higher than the level of liquid within the inner container  112 . 
         [0030]    A first filter  129  extends across the condensation port  128 . The first filter  129  can limit (e.g., prevent) unwanted materials such as particulate matter, bacteria, etc. from entering the inner container  112  through the condensation port  128 . The first filter  129  can be, for example, a mechanical filter or a membrane filter. In some embodiments, the first filter  129  comprises a High Efficiency Particulate Air (HEPA) filter. Additionally or alternatively, some filters  129  comprise a porous filter (e.g., a porous filer is characterized by a pore size smaller or equal to 0.22 micrometer), porous paper, a hydrophobic filter (e.g., a Polytetrafluoroethylene (PTFE) or Gore-Tex filter), an absorbing filter (e.g., a filter configured to absorb dust and/or water vapor) comprising an absorbing material, such as an activated carbon, or paper, or any other absorbing material appropriate for the case. In some embodiments, the filter  129  comprises a combination of several sub-filters. 
         [0031]    The manifold  114  also defines an atmospheric inlet port  130  that allows gases from the environment surrounding the device  100  to enter the manifold  114 . The atmospheric inlet port  130  is an optional feature that is omitted from some devices. 
         [0032]    The atmospheric inlet port  130  is optionally covered by a second filter  132 . The second filter  132  can be, for example, a mechanical filter or a membrane filter as described above with respect to the first filter. The second filter  132  can limit (e.g., prevent) unwanted materials such as particulate matter, bacteria, etc. from entering the manifold through the atmospheric inlet port  130 . The device  100  includes an oxygen rejecting filter such that the device  100  can be used to generate liquid nitrogen from the atmosphere in addition to purifying commercial grade liquid nitrogen. By excluding oxygen to produce liquid nitrogen rather than liquid air which includes both oxygen and nitrogen, the device  100  provides a purified cryogenic fluid that avoids the potential issues of flammability/explosiveness that are associated with oxygen rich gases. 
         [0033]    Alternatively, the atmospheric inlet port  130  is optionally covered by a second filter  132 . The second filter  132  can be, for example, a filter resistive to all gas passage (e.g. inhibits free flow) such that atmospheric gas is not freely entering the manifold space nor is evaporated nitrogen (e.g. from container  110  or  112 ) freely exiting the manifold to atmosphere. This resistive filter may filter particulate. This filter may be designed so as to release if any undue pressure builds up (e.g. as a safety relief). Alternatively or additionally, the manifold can include pressure relief valve. 
         [0034]    The device  100  produces purified cryogenic fluids by passively cooling gases inside the inner container  112 . The term “passive cooling” refers to bringing a first object into thermal contact with a second object, which is colder than the first object, thereby facilitating passive heat transfer from the first object to the second object. 
         [0035]    In operation, a user assembles the device  100 . After assembly, the user at least partially fills the outer container  110  with a cryogenic fluid to be purified (e.g., commercial grade liquid nitrogen). Initially, the inner container  112  will be filled with gas (e.g., filtered air or filtered nitrogen gas) and the fluid between the inner container  112  and the outer container  110  will exert a buoyancy force on the inner container. Heat transfer into the liquid nitrogen in the outer container  110  causes formation of nitrogen gas through evaporation. At the same time, the liquid nitrogen between the inner container  112  and the outer container  110  cools the gas in the inner container  112  causing condensation forming, for example, liquid nitrogen. The condensation reduces the volume formerly occupied by the gas phase materials and draws additional gas into the inner container  112  through the first filter  129 . Thus, evaporated nitrogen passes through the manifold  114  and the first filter  129  into the inner container  112 . As the air surrounding the device  100  is predominantly oxygen and nitrogen gas, the gas drawn through the second filter  132  is mostly nitrogen which then passes through the first filter  129  into the inner container. 
         [0036]    The inner container  112  and the chamber between the inner container  112  and the outer container  110  are coupled to the air around the device  100  by the atmospheric inlet port  130  of the manifold  114 . This connection keeps the pressure in these regions at approximately atmospheric pressure. 
         [0037]      FIGS. 2A and 2B  show the state of nitrogen at relative temperatures and pressures. Most in vitro fertilization (IVF) labs use liquid nitrogen as a cryogenic fluid for deep freezing of tissues. The liquid nitrogen is used at standard atmospheric pressure (1 Atm), which means it will boil when its temperature reaches 196° C.  FIG. 2B  shows the region near the boiling point of liquid nitrogen at standard pressure at larger scale than  FIG. 2A . Path  1  shows that if a slight vacuum is drawn on the liquid nitrogen (i.e., container pressure is slightly under 1 Atm.), the boiling temperature of the liquid nitrogen drops. If the gas pulled off during the vacuum drawing process is released to 1 Atm., as shown in path  2 , is allowed to cool, it will return to a liquid state, as shown in path . 3   
         [0038]      FIG. 3  shows an open system device  100  that is generally similar to the device  100  shown in  FIG. 1  with the addition of a pump  134  operable to induce a vacuum to the chamber between the outer container  110  and the inner container  112 . This pressure reduction reduces the temperature of the liquid nitrogen in the chamber between the outer container  110  and the inner container  112 . This reduction in temperature increases the temperature differential that drives the purification and production of liquid nitrogen. 
         [0039]      FIG. 4  shows a closed system device  100 ′. The closed system device  100 ′ is substantially similar to the open system device  100  but does not include an atmospheric inlet port so the interior of the device  100 ′ is not exposed to ambient gases during use. The closed system device is operable to purify cryogenic fluids such as liquid nitrogen but does not generate cryogenic fluids from the atmosphere. 
         [0040]    The first and second containers are not necessarily outer and inner containers.  FIG. 5  illustrates a system  200  in which a first container  210  has a filling port  212  and an evaporation port  214 . A spout  216  extends from the evaporation port  214  to a condensation port  217 . Optionally, the spout  216  includes a filter  218 . The condensation port  217  is configured to engage with a port in the side of a second container  220 . The second container  220  also has a spout  222  with a check valve  224 . The spout  222 /valve  224  combination can be used both as a pressure relief mechanism and as a discharge mechanism for pouring out purified cryogenic fluid from the second container  220 . A third container  226  is sized to receive the second container  220  and hold it immersed in cryogenic fluid. The first and second containers  210 ,  220  are thin-walled containers conducive to heat transfer while the third container  226  is insulated to be resistant to heat transfer. In some embodiments of the system  200 , the third container  226  includes a lid to limit the escape of gas phase nitrogen out of the third container. 
         [0041]    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.