The present embodiments relate to insulated pipeline. 
     Insulated pipelines are known which may be externally insulated with lagging or vacuum jacketed. When a cryogenic substance is pressurized its temperature increases and, with cryogenics, an increase in temperature is not desirable. For example, liquid nitrogen (LIN) boils at atmospheric pressure (0 barg) 77.347K (−195.83° C.). However, when the pressure of the liquid nitrogen is increased to 30 barg in a pipline, the boiling temperature of the liquid increases to 126.30° K. (−146.85° C.), an increase of approximately 50° in temperature. This boiling temperature increase of the cryogen causes the cryogen to lose a large portion of its cooling efficiency and increases the risk of evaporation during transportation in the pipeline. Therefore, subcooling the liquid is used to solve the problem but unfortunately, existing pipeline design and construction still permits the liquid cryogen to vaporize after or downstream of the subcooler. 
     SUMMARY OF THE INVENTION 
     The present inventive embodiments maintain the liquid cryogen at a temperature as low as possible during transportation or delivery of the cryogen through the pipeline; increase cooling efficiency of the liquid cryogen so that same can be used for impingement cooling applications where high pressure LIN above 3 barg is used; and, when used with a vacuum pump, reduce the cryogenic temperature below temperatures of LIN at −1 barg at 63.148° K. (−210° C.) therefore increasing the LIN efficiency at impingement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       For a more complete understanding of the present embodiments, reference may be had to the following description taken in conjunction with the drawing Figures, of which: 
         FIG. 1  shows a perspective, transparent view of a cryogenic pipeline embodiment of the present invention; 
         FIG. 2  shows a cross-section of the pipeline embodiment taken along line  2 - 2  of  FIG. 1 ; and 
         FIG. 3  shows a cross-sectional side view of the cryogenic pipeline embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1-3 , a pipeline apparatus of the present embodiments is shown generally at  10 . The apparatus  10  includes a central pipe  12  through which a liquid cryogen such as for example nitrogen (N 2 ), Hydrogen (H), or Helium (He) will flow. The pipe  12  can be constructed from copper or copper alloy material. By way of example, reference to the cryogen will be liquid nitrogen (LIN), although it is understood that other fluids and other cryogenic liquids can flow through the pipe  12 . The central pipe  12  can be of any length and manufactured with turned or bent sections as the application requires. 
     Copper fins  14 , 15  or wings are mounted to the central pipe  12 . The fins  14 , 15  can be welded or brazed to an exterior surface of the central pipe  12 . The fins  14 , 15  provide an insulation effect and a pair of passageways  16 , 17  or channels along an exterior of the central pipe  12 . As shown, the fins  14 , 15  substantially extend along the central pipe  12  parallel to a longitudinal axis of said pipe and therefore the fins essentially conform to the shape of the central pipe. The fins  14 , 15  can be formed integral with the central pipe  12 . The combination of the central pipe  12  and the fins  14 , 15  provide a first insert  18 . 
     The apparatus  10  includes a tube member  20  having an interior  22  sized and shape to receive the first insert  18 . The tube member  20  can be vacuum jacketed or vacuum insulated, and may be formed from stainless steel, copper or other metallic material. The fins  14 , 15  coact with the tube member  20  to form the passageways  16 , 17  or channels. 
     An outer pipe  21  having a shape similar to the central pipe  12  and tube member  20  has a space  23  therein sized and shaped to receive the tube member, as shown for example in  FIG. 1 . The space  23  provides an insulation effect with air or a vacuum therein. Alternatively foam or other insulation material can fill the space  23  to provide insulation for the first inset  18 . The combination of the first inset  18  and the tube member  20  form a second insert  25  which is disposed in the space  23  provided by the outer pipe  21 . The outer pipe  21  may be formed from stainless steel, copper or other metallic material. 
     At least one spacer  27  and depending upon the length of the apparatus and the bends therein, a plurality of said spacers may be used to provide structural support and spatial arrangement between and among the central pipe  12 , the tube member  20  and the outer pipe  21 . The spacer(s)  27  can be welded into position as shown in  FIG. 1 . 
     One end  24  of the central pipe  12  is connected to a source (not shown) of high pressure sub-cooled liquid nitrogen at approximately greater than 3 barg. Another end  26  of the central pipe  12  extends through the end cap  30 . The first insert  18  does not consume the entire interior space  22  of the tube  20 . That is, end caps  28 , 30  seal opposed ends of the tube  20 , but provide an entry space  32  and a return space  34 , respectively at opposed ends of the tube member  20 . 
     A pipe  35  introduces a low pressure liquid nitrogen  36  for sub-cooling and circulation at less than approximately 1 barg to the entry space  32 . The liquid nitrogen flows in the passageway  16  along the length of the tube member  20  whereupon it reaches the return space  34  before the end cap  30 , at which point the flow turns and proceeds along the passageway  17 . The copper fins  14 , 15  coact to provide the separate passageways  16 , 17 . The flow  43  of the liquid cryogen continues back toward where it was introduced at the entry space  32  to be recirculated again back through the passageway  16 . The flow  43  keeps the temperature of the cryogen liquid in the central pipe  12  as low as possible to prevent vaporization of the liquid. 
     A circulation pump  40  and a vacuum pump  42  are in communication with the entry space  32  through a line  46  or conduit to circulate the low pressure LIN  36  along the fins  14 , 15 . A pressure control unit  44  includes relief valves and a pressure gauge and is disposed for communication with the line  46  for the circulating and vacuum pumps  40 , 42  respectively. Although the pressure control unit  44  in  FIG. 3  is shown used with the line  46  where the low pressure liquid nitrogen  36  is introduced, the pressure control can also be mounted for use at the return space  34 . The circulation of the LIN  36  is to increase convection from the cold liquid flow through the tube member  20 . It is necessary to only use either the circulation pump  40  or the vacuum pump  42 , depending upon temperature regeneration and the cooling medium (cryogen) being used. The setting at the pressure control unit  44  will therefore control and maintain the pressure in the entry space  32 . During operation, there will be evaporation of the LIN  36 , and any evaporated gas or vapor will have to be released from the apparatus  10  through relief valves at the pressure control unit  44 . For the circulation pump  40 , a set point at the pressure control unit  44  will determine when relief valves are to be opened to exhaust evaporated gas. For the vacuum pump  42 , a set point for the pressure control unit  44  will determine when the pump  42  is to continue to work to release extra pressure created by the evaporation so the set point does not change. 
     The sub-cooling LIN  36  is circulated over the fins  14 , 15  in most applications from the uppermost to the lowermost parts of the central pipe  12 , and any gas occurring therefrom will be vented through a pressure relief valve operationally associated with the pressure control  44 . 
     As an option, the sub-cooling LIN  36  can be applied under a vacuum to reduce its temperature. A cryogen&#39;s boiling point changes with changing pressure, i.e. increasing pressure will therefore increase the boiling temperature of the cryogen. Therefore, reducing the pressure below atmosphere pressure will lead to decreasing the boiling point of the cryogen for subcooling the liquid. Lower temperatures to create a larger difference between the cryogen&#39;s boiling temperature and the actual temperature when the cryogen is transported will be required. 
     Should the pressure of the sub-cooling LIN  36  exceed a pre-determined pressure, said pressure will be released by the pressure control unit  44  and vented external to the apparatus  10 . 
     The present embodiments provide for recycled low pressure liquid (the sub-cooling liquid) to therefore increase the convection of the liquid to correspondingly increase the efficiency of the subcooling. By controlling the pressure of the present embodiments one is able to strictly control the sub-cooling temperatures in the sub-cooling chamber. The sub-cooling liquid can be subjected to a vacuum to provide lower sub-cooling temperatures which would therefore enable more efficient sub-cooled transportation of the cryogens through the pipe. By increasing a surface area of sub-cooler with the fins it is therefore possible to increase the efficiency of the sub-cooling liquid. Finally, the embodiments provide for concurrent sub-cooling and transport of the cryogen. 
     It will be understood that the embodiments described herein are merely exemplary, and that one skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described and claimed herein. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result.
A pipeline apparatus for liquid cryogen includes a first assembly consisting of a first pipe having a first exterior surface and a first passageway for liquid cryogen, and a longitudinal member extending along a portion of the first exterior surface of the first pipe; a second pipe having a second passageway sized and shaped to receive the first assembly therein, the second pipe coacting with the longitudinal member to provide a pair of channels in the second passageway; and a third pipe having a third passageway sized and shaped to receive the second pipe therein, the third pipe spaced apart from the second pipe.