Abstract:
A cryogenic material transfer line has an inner tubular member and a coaxially disposed outer tubular member that together define an annular volume. Within the annular volume is a flow enhancing feature that increases the residence time and path length of a gas flowing within the annulus. The gas flowing inside the annulus thermally interacts with a fluid outside of the transfer line to provide a more consistent gas temperature and flow rate for use in scientific experiments.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119 to U.S. provisional patent application Ser. No. 62/011,070, titled “SINGLE PHASE COLD HELIUM TRANSFER LINE FOR CRYOGENIC HEAT TRANSFER APPLICATIONS”, and filed Jun. 12, 2014, which is hereby incorporated by reference in its entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
       [0002]    This invention was made with government support under Contract No. DE-AC05-00OR22725 awarded by the U.S. Department of Energy. The government has certain rights in the invention. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present disclosure relates to cryogenic materials and more particularly to apparatuses and methods for transferring such materials from a storage dewar to another location for use in research experiments and other uses. 
         [0005]    2. Description of the Related Art 
         [0006]    Heat transfer experiments near liquid helium temperatures, approximately 5 degrees Kelvin, provide representative evaluation of new configurations where thermal properties of materials under test are important. Experiments using liquid helium work from a temperature standpoint, but the two-phase nature of boiling or forced flow results in temperature fluctuations that can impact characterization and complicate modeling. Helium gas forms above liquid helium in storage dewars that can range in size from 30 liters up to 50000 liters. 
         [0007]    A conventional helium gas transfer line will function, but availability of full liquid helium dewars can be limited. The use of a conventional helium gas transfer line without flow enhancements results in helium gas flow with higher flow temperatures that impacts experimental test results and test duration. For heat transfer applications at or near liquid helium temperatures, heat loads applied to the devices under test can increase pressure in the liquid helium system and prevent consistent transfer of liquid from the storage dewar, thus affecting the results of the test and wasting liquid helium. Improvements to cryogenic material transfer lines are needed. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    Disclosed are examples of a cryogenic gas transfer line and methods of transferring a cryogenic gas from a storage dewar to a location outside of the storage dewar. For example, the outside location may be a characterization experiment. 
         [0009]    A cryogenic gas transfer line includes an inner wall that defines an inner tubular member that is disposed coaxially inside of an outer wall that defines an outer tubular member. An annulus is defined between the coaxial tubular members and the outer tubular member is sealed at a lowest end. An inlet aperture in the outer tubular member is located at a height that is in a gas region of a storage dewar when the transfer line is inserted into a storage dewar. A flow enhancing feature is disposed inside of the annulus. A gas stored at a cryogenic temperature in the gas region of a storage dewar will: enter the annulus through the inlet aperture; flow downward through the flow enhancing feature that is disposed within a liquid region located below the gas region of a storage dewar; reverse direction at the lowest end; and flow upward through the inner tubular member and out of a storage dewar when the transfer line is inserted into a storage dewar. In other examples, a storage dewar is provided with the transfer line as an assembly. 
         [0010]    A method for transferring a gas stored at a cryogenic temperature from inside a storage dewar to a location outside of the storage dewar comprises the steps of: a) inserting into a storage dewar a transfer line that has an inner wall that defines an inner tubular member disposed coaxially inside of an outer wall that defines a tubular member. The transfer line having an annulus defined between the coaxial tubular members and the outer tubular member is sealed at a lowest end. An inlet aperture in the outer tubular member is located at a height that is in a gas region of a storage dewar when the transfer line is inserted into a storage dewar, and a flow enhancing feature is disposed inside of the annulus; b) opening a cryogenic valve that controls the flow of a gas within the inner tubular member; and c) transferring a cryogenic gas from the gas region inside of the storage dewar to the location outside of the storage dewar. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
         [0011]    The exemplary apparatuses and methods may be better understood with reference to the following drawings and detailed description. Non-limiting and non-exhaustive descriptions are described with reference to the following drawings. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating principles. In the figures, like referenced numerals may refer to like parts throughout the different figures unless otherwise specified. 
           [0012]      FIG. 1  illustrates an exemplary cryogenic gas transfer line as assembled with a storage dewar and a device under test; 
           [0013]      FIG. 2  illustrates a detailed view of the transfer line of  FIG. 1 ; 
           [0014]      FIG. 3  illustrates a schematic view of the flow direction of cryogenic gas at the lower end of the transfer line of  FIG. 1 ; 
           [0015]      FIG. 4  illustrates a detailed view of an exemplary flow enhancing feature; 
           [0016]      FIG. 5  illustrates non-exhaustive examples of various flow enhancing features; 
           [0017]      FIG. 6  is a chart illustrating measured gas temperatures with and without flow enhancing features as liquid helium level changes; 
           [0018]      FIG. 7  is a chart illustrating measured gas temperatures with flow enhancing features of different lengths as liquid helium level changes; 
           [0019]      FIG. 8  is a chart illustrating measured inlet and outlet gas temperatures in the gas transfer line over time; and 
           [0020]      FIG. 9  illustrates tables of average outlet temperature at various mass flow rates for transfer lines with (top) and without (bottom) flow enhancing features. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    With reference first to  FIGS. 1-3 , an exemplary single-phase helium gas transfer line  10 , which overcomes the issues that two-phase liquid helium flow present in cryogenic heat transfer characterization is provided. The transfer line  10  can be joined to a storage dewar  12  for storing a material such as helium at cryogenic temperatures includes a lower liquid region  14  and an upper gas region  16 . The liquid region  14  of a standard 250 liter liquid helium dewar extends approximately  70  centimeters from the bottom of the dewar when full and, as the material is used, the level of the liquid region  14  decreases while the gas region  16  increases. An internal pressurization control heater  18  is used to maintain the proper pressure in the dewar  12 . A flexible vacuum jacketed line  20  is disposed between a gas flow control valve  22  and a device  24  under test. A heater  26  and flow meter  28  complete a typical experimental setup. 
         [0022]    The transfer line  10  intakes pressurized gas, for example helium gas, from the gas region  16  of the dewar  12  and passes it through a coaxial tube structure  30  that is at least partially immersed in the liquid region  14  within the dewar  12 . In this configuration, the gas flows with more consistent temperatures, between approximately 5 K and 10 K, and delivery pressures, between approximately 1.2 bar and 1.6 bar. These consistent flow conditions are desirable for prototype application development related to the production of cryogenic pellets for fusion fueling and plasma shutdown as well as cryopump development for fusion vacuum systems as well as other applications. 
         [0023]    The coaxial tubular structure  30  includes an inner wall  32  that defines an inner tubular member  34  and an outer wall  36  that defines an outer tubular member  38 . The inner tubular member  34  is disposed coaxially inside of the outer tubular member  38  with an annulus  40  defined between the coaxial members  34 ,  38 . A lower end  42  of the outer tubular member  38  is sealed with a disc  44 . One or more spacers  46  space the inner  34  and outer  38  tubular members apart and keep the annulus  40  area consistent. An inlet aperture  48  is defined by the outer wall  36  and is positioned at a height that is above the liquid region  14  when the transfer line  10  is inserted into a storage dewar  12 . For example, a 0.25 inch aperture  48  may be positioned at a height of 75 cm from the lower end  42  of the outer tubular member  38  to ensure that it is in the gas region of a full, 250 liter dewar of liquid helium. For smaller or larger sized dewars, the aperture  48  is suitably positioned in the gas regions  16 . 
         [0024]    In order to improve the heat exchange between the gas and the liquid while minimizing the gas temperature with continuously lowering liquid region  14  level, a flow enhancing feature  50  is disposed in the annulus  40  area. The flow enhancing feature  50  forces the gas to flow circuitously around the inner tubular member  34  and within the outer tubular member  38 , increasing the path length and residence time of the gas while it&#39;s flowing within the liquid region  14 . The extent of the flow enhancing features  50 , which are designed to increase the surface area within the transfer line and/or change the flow direction to increase the thermal transfer length and residence time, determine the outlet temperature of the transfer line  10  and can be adjusted for different flow rates, outlet temperatures, and test durations. 
         [0025]    Several examples of flow enhancing features  50  are shown in  FIGS. 4-5 . Details of a spiral  52  example include a fin spacing of between 3-10 fins per inch of length, a fin thickness of 0.010-0.050 inches, fin height of between 0.25-0.75 inches and a flow enhancing length of 30 cm-60 cm for example. In another example, a plurality of discs  54  extends from the inner  34  and outer  38  tubular members in an alternating pattern. In yet another example, a wool structure  56  fills the annulus  40 , and in yet another example, a plurality of convolutions  58  are formed in the outer wall  32 , the inner wall  36 , or both walls. While these examples are not exhaustive, they illustrate just a few of the flow enhancing features  50  that would work for this application. Other examples are contemplated. 
         [0026]    Flow enhancing features  50  could be present inside the inner tubular member  34  alone, in the annulus  40  alone, or in both. In the examples tested, a commercially available, continuous spiral fin feature  52  was affixed about the inner tubular member  34  and extended outward to the outer tubular member  38 . The function will next be described in greater detail. 
         [0027]    With respect to the present example, the section of transfer line  10  that was inserted into a 250 liter storage dewar  12  comprised a 65 inch long, 0.75 inch outer diameter stainless steel outer tubular member  38  coaxially disposed around a 30 inch long, 0.25 inch outer diameter stainless steel inner tubular member  34 . Within this 30 inch length, a 12 inch section of continuous spiral fin  52  was affixed to the inner tubular member  34 . This creates a spiral path in the annulus  40  for the gas to flow through, increasing its conduction path length and residence time, before exiting the dewar  12  through the inner tubular member  34  of the transfer line  10 . 
         [0028]    The upper portion of the outer tube  38  includes a vacuum jacketed space shared with the control valve  22  and the 90″ long flexible vacuum jacketed  20  transfer line. The transfer line  10  was terminated into a vacuum jacketed, 18 inch long, 0.50 inch OD dip tube that was inserted into the device  24  under test. These dimensions can be adjusted for adapting the transfer line  10  to other standard liquid helium dewars (100-liter or 500-liter) that are part of a liquid helium liquefier or separately. 
         [0029]    In operation, gas enters the inlet aperture  48  in the outer tubular member  38  at a position within the gas region  16  and exchanges heat with the liquid material (e.g., helium) bath within the liquid region  14  as it flows downward through the circuitous flow enhancing feature  50  in the annulus  40 . At the bottom or lower end  42  of the outer tubular member  38 , the gas reverses its direction and flows upward through the inner tubular member  34 . The inner flow path is separated from the annular flow path by the inner wall  32 . The longer effective length of the flow enhancing feature  50  increases significantly the residence time and the transfer of heat from the gas to the liquid bath thereby lowering the outlet temperature of the gas as it exits the dewar  12 . 
         [0030]    This provides a lower and more consistent gas temperature even as the level of liquid region  14  falls in the dewar  12 . 
         [0031]    The performance of the transfer line  10  was examined through a series of experiments, with the results shown in  FIGS. 6-9 , where the outlet temperature of the transfer line  10  was characterized with respect to the measured flow rate &amp; pressure in the dewar  12 . The effectiveness of the spiral features  52  was judged through experimental comparison to a co-axial, gas transfer line that was fabricated according to U.S. Pat. No. 5,406,594, which does not include a flow enhancing feature. 
         [0032]    While this disclosure describes and enables several examples of a cryogenic material transfer line, other examples and applications are contemplated. Accordingly, the invention is intended to embrace those alternatives, modifications, equivalents, and variations as fall within the broad scope of the appended claims. The technology disclosed and claimed herein may be available for licensing in specific fields of use by the assignee of record.