Patent Publication Number: US-2023139421-A1

Title: Optimized connection assembly between two portions of a supply line for a cryogenic fluid, including an additional thermal insulation chamber and a fluid expansion chamber

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of the French patent application No. 2111497 filed on Oct. 28, 2021, the entire disclosures of which are incorporated herein by way of reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a connection assembly between two portions of a supply line for a cryogenic fluid. The invention notably concerns a connection assembly for a liquid hydrogen line in aircraft systems. 
     BACKGROUND OF THE INVENTION 
     Liquid hydrogen is a cryogenic fluid that can be used as a power source for generating electricity. It is, therefore, for example possible to use a hydrogen cell to power all of the communication and flight control systems of an aircraft, as well as the on-board lighting and the different accessories used on board the aircraft. Liquid hydrogen can also be used as a power source to propel an aircraft, by feeding a fuel cell or by direct combustion, which has the advantage of only discharging water into the atmosphere. The use of hydrogen requires distribution systems between one or more production or storage tanks and consumer devices. Thus, lines are conventionally used to carry the liquid hydrogen between a storage tank and a consumer device, such as a hydrogen cell. The lines used most commonly have an inner tube, through which the supplied fluid flows, and an outer wall that is separated from the inner tube by one or more thermal insulation chambers placed under a vacuum. Such lines, thermally insulated under vacuum, are pairs of concentric tubes in which the walls of the inner and outer tubes are kept apart from one another. In lines suitable to transport a cryogenic fluid for distribution, storage and/or another purpose, the thermal insulation between the inner tube and the outer wall enables both the fluid to be kept at a temperature suitable for distribution (for example, −253° C. in liquid form) and to prevent the formation of ice about the outer wall, which would be liable to generate mechanical stresses on neighboring elements in the distribution installation on account of the gradual increase in the volume of accumulated ice about the line. 
     Cryogenic fluid distribution lines often comprise a succession of flexible or rigid pipes that are thermally vacuum insulated and assembled together using suitable connection elements. This is notably the case for lines used to supply liquid oxygen, liquid nitrogen, liquid argon, liquid hydrogen, and liquid helium, for example. The fittings (connections) between the different flexible or rigid pipes that make up the line are connected together using pairs of connectors. Each pair of connectors includes a male connector arranged at the end of a pipe and configured to be inserted into a female connector arranged at the end of the neighboring pipe, and to form a tight sliding mechanical link. The seal is achieved simply by using a very-low-expansion material (coefficient of expansion) for the male connector and a material with significantly greater expansion for the female connector so that, when a cryogenic fluid flows through the line, the female connector contracts onto the male connector to make the tight mechanical link from a sliding link. The seal is reinforced by using one or more ring gaskets placed between the connected ends of two neighboring pipes. A ring gasket can, for example, be arranged between two adjacent flanges set back from the male nozzle and at the end of the female nozzle respectively, or between the end of the male nozzle and the bottom of the female nozzle. This type of joint between two neighboring pipes of a given line nonetheless requires the male connector (or male nozzle) to be inserted over a significant length in relation to the diameter of the line (up to several tens of centimeters) into the female connector (or female nozzle). For such a joint to be sealed, the female and male connectors also have to be coupled over a significant length, and be rigid. Such a configuration is not practical if a line, and more generally a fluid distribution system, needs to be installed in a restricted space, as is often the case on board an aircraft. Furthermore, a significant insertion length of the male nozzle in the female nozzle requires an equal space about the line to enable separation of two neighboring pipes during disassembly operations. 
     The situation can be improved. 
     SUMMARY OF THE INVENTION 
     One objective of the present invention is to propose connection means between two portions of a supply line for a cryogenic fluid that does not have at least some of the drawbacks of the existing solutions. 
     For this purpose, a connection assembly between two portions of a supply line for a cryogenic fluid is proposed, the connection assembly including a first line portion and a second line portion, the first line portion including a male nozzle arranged to be at least partially inserted into a female nozzle of the second line portion, the male and female nozzles together forming a tight sliding mechanical link, the first line portion being made of a first material with a coefficient of expansion lower than the coefficient of expansion of a second material used to make the second line portion, the first line portion including a first thermal insulation chamber and the second line portion including a second thermal insulation chamber, the connection assembly also including at least one additional thermal insulation chamber that is separate from each of the first and second thermal insulation chambers and that extends between the first and second thermal insulation chambers, and also includes an expansion chamber for the cryogenic fluid arranged about the contact surfaces between the first line portion and the second line portion, the expansion chamber being linked to a housing configured to receive or connect a presence sensor for the cryogenic fluid. 
     Advantageously, this provides connection means that are less bulky and more flexible between two line portions for supplying cryogenic fluid, such as liquid hydrogen, without the need for a significant amount of free space to enable the connection to be disassembled. 
     The connection assembly according to the invention may also include the following features, taken individually or in combination: 
     The maximum insertion distance of the male nozzle into the female nozzle is equal to or less than 50 mm, preferably equal to or less than 20 mm. 
     The fluid expansion chamber includes an element made of an absorbent material, preferably a spongy material. 
     At least one of the first line portion and the second line portion is generally cylindrical and has inner and outer walls with corrugations, the corrugations of the inner wall extending over a length of line with corrugations on the outer wall. 
     The first material is invar. 
     The second material is stainless steel. 
     A vacuum is created in each of the thermal insulation chambers. 
     The housing is a terminal volume of a duct linking the expansion chamber to the outside of the line. 
     The end of the outer wall of each of the line portions is flared to form a terminal contact flange that is configured to be positioned opposite the terminal contact flange of the other line portion of the two line portions, and in which the housing is arranged at the base of one of the two terminal flanges. 
     The invention also relates to a liquid hydrogen distribution system including a connection assembly as described above. 
     The invention also relates to an aircraft including a connection assembly between two line portions as mentioned above or a hydrogen distribution system including such an assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The aforementioned and other features of the present invention are set out more clearly in the description given below of an example embodiment, the description being provided with reference to the attached drawings, in which: 
         FIG.  1    is an overall perspective view of a connection between two joined portions of a line, according to one embodiment, 
         FIG.  2    is a vertical cross section perspective view of the connection between two portions of a line, as shown in  FIG.  1   , 
         FIG.  3    is a vertical cross section perspective view of the details of the connection between two portions of a line, as shown in  FIGS.  1  and  2   , 
         FIG.  4    is a vertical cross section perspective view showing a maximum insertion distance of the male nozzle into the female nozzle of the connection between two portions of a line, as shown in  FIGS.  1 ,  2  and  3   , and 
         FIG.  5    is a top view of an aircraft including a connection assembly between two portions of a line, as shown in  FIGS.  1  to  4   . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG.  1    is a schematic overview of a connection assembly  10  between a first portion  10   a  of a line and a second portion  10   b  of the same line, according to one embodiment. Each of the line portions  10   a  and  10   b  has an inner tube portion for a fluid flow and a thermal insulation chamber (not shown in  FIG.  1   ). 
     According to one embodiment, the line shown is configured to supply a cryogenic fluid and has other line portions in addition to the portions  10   a  and  10   b.  In the example described, the line shown is configured to supply liquid hydrogen, and more specifically to distribute liquid hydrogen on board an aircraft. In the present description, the term “cryogenic fluid” refers to a liquefied gas kept at low temperatures, or to a gas obtained from such a liquid as a result of evaporation. Thus, for example, if the cryogenic fluid is hydrogen (or more specifically dihydrogen H2), the term cryogenic fluid refers to both the liquid hydrogen and the hydrogen gas, and the present invention therefore relates both to the liquid hydrogen and to the hydrogen gas when the cryogenic fluid is hydrogen. 
     The portions of the line other than the portions  10   a  and  10   b  are not shown here since the invention relates to a connection assembly between two neighboring portions of a single line that are connected together, and the description of just one of the connections between two neighboring portions of the line is required to understand the invention. 
     The term “connection” should be understood to be a synonym of sealed joint or link of two portions  10   a  and  10   b  of the liquid hydrogen distribution line. 
     According to one embodiment, the line portions  10   a  and  10   b  are tubular and comprise two concentric tubes kept apart from one another, for example by spacers positioned at regular intervals between the inner tube and the outer tubular wall of the line. More specifically, each of the line portions  10   a  and  10   b  has an inner fluid-supply tube surrounded by an annular thermal insulation chamber delimited by an outer wall with an overall tubular shape, the chamber including spacers for holding the inner tube in relation to the outer wall of the line. The line portion  10   a  therefore has a thermal insulation chamber  12   a  (not shown in  FIG.  1   ) and the line portion  10   b  has a thermal insulation chamber  12   b  (not shown in  FIG.  1   ). Corrugations  10   d  and  10   e  are respectively arranged on the outer wall of the portion  10   a  and of the portion  10   b  of the connection assembly  10  such as to make the connection assembly  10  flexible, along with corrugations in the inner tube that are positioned on the same lengths of line (shown in  FIGS.  2  and  3   ). The resulting flexibility facilitates assembly and disassembly operations of the connection of two portions  10   a  and  10   b  of the connection assembly  10 . A vacuum opening  13   a  enables a vacuum to be created in an additional thermal insulation chamber  13  (shown in  FIG.  2   ) that is configured to provide thermal insulation for the connection assembly about the connection of the portions  10   a  and  10   b.  According to one embodiment, a vacuum is created in the additional thermal insulation chamber  13  and the thermal insulation chambers  12   a  and  12   b  of the line portions  10   a  and  10   b  using a vacuum pump connected to the vacuum opening of each of the chambers, after which the opening is closed. 
       FIG.  2    is a vertical cross section of the connection assembly  10  of two line portions  10   a  and  10   b.  The vertical cutting plane contains the longitudinal axis of the vacuum opening  13   a.  The perspective cross section view in  FIG.  2    shows details of the connection assembly  10  of two line portions  10   a  and  10   b.  The line portion  10   a  includes an inner tube  10   f  intended to contain the liquid hydrogen to be distributed using the line. The inner tube  10   f  is concentric with the overall tubular outer wall of the line portion  10   a.  The line portion  10   b  includes an inner tube  10   g  intended to contain the liquid hydrogen to be distributed, that is provided and configured to ensure continuity of distribution with the inner tube  10   f  of the line portion  10   a.  The inner tube  10   g  of the line portion  10   b  is concentric with the overall tubular outer wall of the line portion  10   b.  The term “overall tubular wall” refers herein to a line wall having a general tubular shape, which may nonetheless include corrugations over certain lengths to provide a degree of flexibility. The diameter of the end of the inner tube  10   f  positioned on the side of the line portion  10   a  intended to be connected to the line portion  10   b  is slightly less than the diameter of the end of the inner tube  10   g  positioned on the side of the line portion  10   b  intended to be connected to the line portion  10   a.  Thus, during assembly of the connection between the line portions  10   a  and  10   b,  the end of the inner tube  10   f  is inserted into the end of the inner tube  10   g.  In other words, the end of the inner tube  10   f  is a male nozzle that is inserted into the end of the inner tube  10   g.  The ends of the inner tubes  10   f  and  10   g  together form a sealed tight sliding link. To do so, the coefficient of expansion of the material used to make the inner tube  10   f  is much lower than the coefficient of expansion of the material used to make the inner tube  10   g.  According to one embodiment of the invention, the material used to make the inner tube  10   f  is invar and the material used to make the inner tube  10   g  is stainless steel. Advantageously, when the liquid hydrogen is inside the inner tubes  10   f  and  10   g  of the line portions  10   a  and  10   b,  the very low temperature of the liquid hydrogen contracts the end of the tube  10   g  on the end of the tube  10   f  and reinforces the tight sliding link to obtain a sealed tight link with no play. The contact surfaces  10   c  between the two ends of the inner tubes  10   f  and  10   g  are pressed against one another with significant mechanical force, since the invar hardly contracts at all with the cold and the stainless steel of the female end contracts significantly on the male end, as a result of the difference between the thermal coefficients of expansion of the two materials used. 
     Furthermore, a male nozzle  11   a  is arranged in the extension of the thermal insulation chamber  12   a  of the portion  10   a  of the connection assembly  10 , and a female nozzle  11   b  is arranged in the extension of the thermal insulation chamber  12   b  of the portion  10   b  of the connection assembly  10 . These two nozzles  11   a  and  11   b  cooperate like the ends of the inner tubes  10   f  and  10   g,  i.e., the male nozzle  11   a  is made of a material with a coefficient of expansion considerably lower than the material used to make the female nozzle  11   b,  so that the female nozzle  11   b  contracts onto the male nozzle  11   a  to create a sealed tight link when there is a cryogenic liquid such as liquid hydrogen inside the line. According to one embodiment of the invention, the line portion  10   a  is made of invar and the line portion  10   b  is made of stainless steel. Advantageously, any line portion joining two neighboring connection assemblies together comprises two elements that are rigidly connected together, one of which is made of invar and the other of stainless steel, so that the cold contraction principle applied to obtain a sealed tight mechanical link can be used for several successive connection assemblies on a given line. 
     An intermediate partition  10   i  extends between the outer wall of the line portion  10   a  and the inner tube  10   f  of the line portion  10   a,  delimiting the thermal insulation chamber  12   a  between the inner tube and the outer wall of the line portion  10   a,  on the side of the line portion  10   a  with the connection assembly  10 . Similarly, an intermediate partition  10   j  extends between the outer wall of the portion  10   b  and the inner tube  10   g  of the line portion  10   b,  delimiting a thermal insulation chamber  12   b  between the inner tube and the outer wall of the line portion  10   b,  on the side of the line portion  10   b  with the connection assembly  10 . Each line portion, for example the portions  10   a  and  10   b,  has an intermediate inner partition at each end, close to the connection assembly, where necessary. The two partitions  10   i  and  10   j  of each of the line portions delimit an additional thermal insulation chamber  13  between the liquid-hydrogen supply inner tube and the outer wall, the outer surface of which is in contact with the environment immediately outside the distribution line. According to one embodiment, the end of the outer wall of each of the line portions  10   a  and  10   b  is flared to form a terminal contact flange that is arranged to be positioned opposite the terminal contact flange of the other line portion of the line portions  10   a  and  10   b.  The terminal contact flanges are arranged to be surrounded by a strap or a collar  15  to hold the connection between the two line portions  10   a  and  10   b.  At least one of the terminal contact flanges has a groove to receive a ring gasket  16  that is compatible with the very low temperatures of a cryogenic fluid such as liquid hydrogen. Cleverly, a cryogenic fluid expansion chamber  14  is arranged on each side of the contact surfaces between the male and female nozzles respectively disposed at the end of the inner tubes  10   f  and  10   g,  and an additional thermal insulation chamber  13  is arranged between the intermediate inner partitions  10   i  and  10   j  and the outer walls of the portions  10   a  and  10   b  such as to thermally insulate the line portion including the cryogenic fluid expansion chamber  14 . A duct  14   a  (shown in  FIG.  3   ) is arranged between the expansion chamber  14  and the outside of the line. According to one embodiment, the opening of the duct  14   a  that leads to the outside of the line comprises a housing for fastening a sensor for detecting the presence of hydrogen. In the example described, the opening of the duct  14   a  is configured for the housing or to fasten a sensor configured to detect the presence of liquid hydrogen in the expansion chamber  14 . Such a housing enables a hydrogen detection sensor to be assembled so that some or all of the sensor is inserted into the line and is able to detect hydrogen coming from the expansion chamber  14 . In one example, the outer wall of the line is machined and threaded to enable assembly of a liquid or gas hydrogen detection sensor. According to one embodiment, the assembly is advantageously a “gas assembly” to prevent any hydrogen leaks to the outside of the line. A duct  14   a  links the expansion chamber  14  and the housing provided for assembly of a hydrogen detection sensor. Advantageously, the housing is a terminal volume of the duct  14   a  linking the expansion chamber to the outside of the line (with no sensor). The presence of liquid hydrogen in the expansion chamber  14  of the hydrogen line indicates a leak in the connection of the inner tubes  10   f  and  10   g,  which is potentially detrimental to the correct operation of the systems and/or to safety. Advantageously, the ability to quickly detect a liquid hydrogen leak in the joint between the male and female nozzles of the inner tubes  10   f  and  10   g  using a hydrogen detection sensor enables immediate action to be taken on the hydrogen supply in the line. This, for example, makes it possible to order the closure of a valve positioned on the line upstream of the connection assembly  10  to limit the quantity of fluid distributed through the line, and consequently the quantity of fluid that could leak from the inner tube if there is a leak in the connection between the inner tubes  10   f  and  10   g  in the line. 
     According to one embodiment, the fluid expansion chamber  14  contains an absorbent element  17  (shown in  FIG.  3   ) that is made of an absorbent material, preferably a spongy material, to act as a buffer and to keep the fluid in the expansion chamber. 
     According to a variant of the embodiment, a hydrogen detection sensor is inserted directly into the expansion chamber  14 , and the housing arranged at the outlet of the duct  14   a  linking the expansion chamber with the outside of the line is then configured to receive electrical connection means for the sensor (electrical power supply to the sensor and signal from the sensor) or to pass cables through a sealed shutter. 
       FIG.  3    shows in detail the corrugations  10   d ′ and  10   d ″ respectively arranged on the intermediate inner wall  10   i,  and on the inner tube  10   f  of the line portion  10   a,  as well as the detail of corrugations  10   e ′ and  10   e ″ respectively arranged on the intermediate inner wall  10   j  and on the inner tube  10   g  of the line portion  10   b.  The corrugations  10   d,    10   d ′ and  10   d ″ extend over shared lengths of each of the walls of the line portion  10   a  (outer, intermediate inner, and inner) providing greater flexibility in the line portion  10   a  than with a bayonet fitting found in the prior art. The same is true of the corrugations  10   e,    10   e ′ and  10   e ″ that extend over shared lengths of each of the walls of the line portion  10   b  (outer, intermediate inner, and inner) providing greater flexibility in the line portion  10   b  than with a bayonet fitting found in the prior art. 
       FIG.  4    shows a maximum insertion distance d 1  of the male nozzle  11   a  into the female nozzle  11   b  inherent in the structure of these nozzles and more generally in the structure of the line portions  10   a  and  10   b.  Advantageously, on account of the use of an expansion chamber to contain and detect leaks, this maximum insertion distance d 1  of the male nozzle  11   a  into the female nozzle  11   b  can be equal to or less than 50 mm, and preferably equal to or less than 20 mm. Indeed, although the risk of leaks occurring is greater if the insertion distance of the tight sliding link is shorter than with a bayonet fitting, leaks can be detected immediately by a sensor housed in the end of the duct  14   a  and appropriate action can be taken without delay to deal with the leak. For example, a valve in the line can be closed and the liquid hydrogen can be supplied via another line in the hydrogen distribution system. 
       FIG.  5    shows an aircraft  1  including a hydrogen cell and a liquid hydrogen distribution system including the connection assembly  10  as well as other connection assemblies similar to the connection assembly  10 . Advantageously, the use of such connection assemblies, similar to the connection assembly  10 , enables the installation of a liquid hydrogen distribution system between a hydrogen storage tank and the fuel cell of the aircraft  1 , including in tight spaces, since the connection assemblies are flexible and the assembly and disassembly thereof does not require a lot of free space about each of the connection assemblies. This is particularly advantageous on board an aircraft. 
     The invention is not limited to the embodiments and examples described, but more broadly concerns any connection assembly between two portions of a line for supplying a cryogenic fluid, including a male nozzle arranged to be at least partially inserted in a female nozzle to together form a tight mechanical link, over a distance equal to or less than 5 cm, a thermal insulation chamber for each of the two line portions and an additional thermal insulation chamber to thermally insulate the connection zone of the two line portions, as well as an expansion chamber for the supplied cryogenic fluid that is configured to be linked to a cryogenic fluid sensor in the fluid expansion chamber, arranged about the connection zone of the two line portions. 
     While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.