Abstract:
A container for cryogenic liquids, comprising an evacuable outer container, wherein the outer container has a substantially flat base wall, a substantially flat ceiling wall and side walls. A support is arranged between inner containers, wherein the support is larger in the direction of the longitudinal axis of the inner container than in the direction between the inner containers and at right angles to the longitudinal axis of the inner container.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a container for cryogenic liquids, composed of an outer container and a number of inner containers, with a vacuum preferably prevailing in the space between the inner containers and the outer container in order to provide thermal insulation. Containers of said type are intended for installation in motor vehicles, aircraft or spacecraft. They contain liquefied gases which are extracted from the container for use either as a propellant or for other purposes (for example as a cooling medium). 
         [0002]    The vacuum insulation, usually improved using further measures, is intended to impede the introduction of heat and therefore an evaporation of the cryogenic liquids, and the associate pressure rise. The cryogenic liquid may however also be stored at high pressure. In this way, firstly, the stored quantity is increased for the same volume, but secondly, the container becomes heavier in order to withstand the pressure loading. 
         [0003]    As a result of the vacuum insulation, however, a pressure acts on the containers in any case. The outer container is loaded from the outside by atmospheric pressure, because the vacuum prevails in its interior. The inner containers are loaded by the full inner pressure because they are surrounded by a vacuum. Said pressures are manageable in the case of an entirely cylindrical container. 
         [0004]    The cylindrical container shape is however very impractical for use in vehicles for reasons of space. Development is therefore proceeding in the direction of luggage-space-shaped flat containers. In the case of a flat design, however, both the inner and outer containers are subjected to high loadings on account of the large planar and free surfaces, which loadings can only be absorbed by means of massive supports. This results in an increased weight (particularly negative in road vehicles and aircraft) and an increased introduction of heat into the interior of the container. 
         [0005]    It is therefore an object of the invention to develop a container which utilizes space effectively while simultaneously having a low weight. 
       SUMMARY OF THE INVENTION 
       [0006]    By definition, a longitudinal axis direction is to be understood to mean a direction substantially parallel to the direction of the longitudinal axes of the adjacent inner containers. Here, small deviations from a parallel alignment fall within the scope of protection. 
         [0007]    According to the invention, the container is a tank of flat design, but with certain deviations within the context of a slight curvature of the top, base and/or side surfaces of the outer tank being permitted and falling within the scope of protection. 
         [0008]    According to the invention, a plurality of inner containers are arranged in the outer container, with the longitudinal axes being arranged substantially parallel and in a plane. Slight deviations with regard to the parallel alignment of the longitudinal axes, or a slight axial offset of an inner container from a common plane, are however permitted and encompassed by the scope of protection. 
         [0009]    The expressions “substantially parallel” and “substantially in a plane” thereby encompass “parallel” and “in a plane” and insignificant deviations from these (for example as a result of production or design tolerances). 
         [0010]    By means of the support proposed according to the invention, the outer container can be stabilized against occurring compressive and tensile loadings from the inside and from the outside. Such compressive and tensile loadings may for example be brought about by an evacuation of the outer tank or by mechanical external loads on the outer tank. 
         [0011]    According to the invention, a design of a flat container is proposed which does not have the discussed disadvantages known from the prior art. Said design is intended to be as light and simple as possible while providing the best possible thermal insulation. According to one embodiment of the invention, this is achieved in that the inner containers are cylinders which are arranged adjacent to one another and have a base at both sides, and in that the planar wall parts of the outer container are supported with respect to one another by means of supports which are arranged between the cylinders. Thanks to the arrangement of a plurality of inner containers adjacent to one another (wherein it is not necessary for all the inner containers to be arranged strictly in a plane adjacent to one another), the cylindrical shape, which is particularly expedient in the case of an internal pressure, can be maintained. This makes it possible to store the cryogenic liquid under high pressure even in the case of a relatively small wall thickness. There is also the advantage that the cylinders can be used in a modular fashion, in different numbers and different configurations, for containers with different outer dimensions. 
         [0012]    According to one embodiment of the invention, the support is a compressive support, that is to say a support for providing support of/against compressive forces, and/or a tension support, for providing support of/against tensile forces. 
         [0013]    According to one embodiment of the invention, the inner containers are provided as separate containers, for example as structurally separate cylindrical tank containers which are filled and/or emptied by means of a suitable device, if appropriate together or separately. 
         [0014]    The support of the planar wall parts with respect to one another makes it possible for a plurality of inner containers to be surrounded by a common outer container, because atmospheric pressure which acts on the planar surfaces which are thereby created can be absorbed without subjecting the inner containers to any loading. Said support makes it possible to considerably reduce the wall thickness of the outer container, and permits a corresponding weight reduction 
         [0015]    According to one embodiment of the invention, the support has, as viewed in the section of the support with the plane of the longitudinal axes of the adjacent inner container, a maximum length extent measured in the longitudinal axis direction, and normally with respect thereto, a maximum width extent measured between the adjacent inner tanks. According to one particular embodiment of the invention, the ratio of maximum length extent to maximum width extent is at least 1.25:1. This results in particularly good stability of the container according to the invention. 
         [0016]    If the support between two inner containers is composed of a plurality of support elements arranged along the longitudinal axis, then the maximum length extents or maximum width extents of the support elements are added in order to determine the effective overall length extent or overall width extent of the support which acts between the inner containers. Here, overlaps of two or more compressive support elements in the longitudinal or width direction are counted only once in the determination of the effective overall length or the effective overall width of the support. The effective overall length or overall width of the support elements determined in this way is considered to be the dimension (length extent, width extent) of the support. 
         [0017]    According to a further embodiment of the invention, it is particularly advantageous if the support elements are arranged symmetrically or at approximately uniform intervals with respect to one another in the direction of the longitudinal axis of the inner container. In this way, it is ensured that the introduction of force via the outer container takes place uniformly without distortion of the container structure. 
         [0018]    According to a further embodiment of the invention, the ratio of maximum length extent to maximum width extent is at least 2:1. 
         [0019]    According to a further embodiment of the invention, the ratio of maximum length extent to maximum width extent is at least 5:1. 
         [0020]    According to a further embodiment of the invention, the top wall is supported with respect to the base wall between the at least two inner containers, in the longitudinal axis direction, over at least 10% of the length of the outer container by the support. 
         [0021]    According to a further embodiment of the invention, the top wall is supported with respect to the base wall between the at least two inner containers, in the longitudinal axis direction, over at least 25% of the length of the outer container by the support. 
         [0022]    According to a further embodiment of the invention, the compressive support has a minimum length of at least 10%, in particular of at least 25%, of the longitudinal dimension of the outer container. 
         [0023]    According to one particular embodiment, the compressive support has a minimum length of at least 10%, in particular of at least 25%, of the longitudinal dimension of the inner container. 
         [0024]    According to a further embodiment of the invention, the support which is arranged longitudinally between the at least two inner containers has a plurality of separate support elements. 
         [0025]    According to a further embodiment of the invention, the support extends over the entire length of the at least two inner containers. 
         [0026]    According to a further embodiment of the invention, the at least two inner containers are of cylindrical design. 
         [0027]    According to a further embodiment of the invention, the at least two inner containers are suspended at their ends on the side walls of the outer containers, such that thermal expansions in the longitudinal direction are absorbed. 
         [0028]    According to a further embodiment of the invention, the inner containers are composed of high-grade steel. 
         [0029]    According to a further embodiment of the invention, the inner containers are surrounded by carbon fibers embedded in a plastics matrix. 
         [0030]    According to a further embodiment of the invention, the inner containers are suspended at their bases, at both sides, on end walls of the outer containers, such that thermal expansions in the longitudinal direction are absorbed. 
         [0031]    According to a further embodiment of the invention, the inner containers are fixedly connected at one end to an end wall of the outer container, and at the other end are freely movable in the longitudinal direction. 
         [0032]    According to a further embodiment of the invention, the outer container is composed of thin sheet metal and is wrapped in fibers embedded in a plastics matrix. 
         [0033]    According to a further embodiment of the invention, the support may also be formed such that it at least partially supports the inner container transversely (that is to say transversely with respect to the longitudinal axis direction) either in the direction of the width of the outer container and/or in the direction of the height of the outer container, or at least partially holds the inner container in position in said directions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    The invention is described and explained below on the basis of exemplary schematic figures, in which: 
           [0035]      FIG. 1  shows an axonometric view of a container according to the invention, 
           [0036]      FIG. 2  shows a plan view of the same, 
           [0037]      FIG. 3  shows a side view of the same, 
           [0038]      FIG. 4  shows a section according to C-C in  FIG. 3 , 
           [0039]      FIG. 5  shows an alternative embodiment to  FIG. 4 , 
           [0040]      FIG. 6  shows a longitudinal section according to VI-VI in  FIG. 5 , 
           [0041]      FIG. 7  shows an alternative embodiment to  FIG. 2 , in section according to VII-VII in  FIG. 8 , and 
           [0042]      FIG. 8  shows a section according to VIII-VIII in  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0043]    In  FIGS. 1 to 4 , the outer container is denoted generally by  1 , and the inner containers which are arranged adjacent to one another in parallel in said outer container  1  are denoted by  2 ,  3  and  4 . The inner containers are cylindrical tubes, preferably composed of high-grade steel. The outer container  1  which surrounds said inner containers with a spacing can thereby have a flat design. Said outer container  1  is substantially a flat cuboid whose side surfaces may be rounded. In any case, however, said outer container has two planar wall parts  10 ,  11 . For thermal insulation, a vacuum prevails in the space  5  between the inner containers  2 ,  3 ,  4  and the outer container  1 , which vacuum, together with further measures, forms a so-called “super insulation” arrangement. As a result of the vacuum in the space  5 , the planar wall parts  10 ,  11  are pressed together by the atmospheric pressure. On the other hand, the inner containers  2 ,  3 ,  4  are pressed outward even with atmospheric pressure prevailing in them. If the cryogenic liquid in the inner containers  2 ,  3 ,  4  is stored at a relatively high pressure, the tensile loading of the cylindrical walls and of the bases  7 ,  8  of the inner containers  2 ,  3 ,  4  is correspondingly greater. 
         [0044]    To absorb the compressive forces acting on the planar wall parts  10 ,  11  of the outer container  1 , said wall parts  10 ,  11  are supported with respect to one another by supports  12 ,  13 . As can be seen in  FIG. 4 , said supports  12 ,  13  connect the two planar wall parts  10 ,  11 , with said supports  12 ,  13  extending between the inner containers  2 ,  3  and  3 ,  4 , preferably without coming into contact with the latter. In  FIG. 2 , the supports  12 ,  13  are individual supports. The inner containers  2 ,  3 ,  4  can, in a known way, be suspended on the side walls  14 ,  15  by means of suspension arrangements  17 ,  18 , which are known per se, at both sides. 
         [0045]    The modified embodiment of  FIGS. 5 and 6  differs from this in that the supports  22 ,  23  extend over the length of the inner containers  2 ,  3 ,  4  and in that the inner containers  2 ,  3 ,  4  are fastened only at one side, by means of heat-insulating feet  32 , to an end wall  33  of the outer container  1 , and are freely movable with their other end. As can be seen in  FIG. 5 , the supports  23 ,  24  are I-shaped profiles whose foot parts  24 ,  25  bear at the inside against the planar walls  10 ,  11  and whose web parts have reinforcement ribs  26  in order to increase their buckling resistance. With the inner containers  2 ,  3 ,  4  arranged at a sufficient distance, said inner containers  2 ,  3 ,  4  may be wrapped in carbon fibers  30  embedded in a plastics matrix in order to withstand high internal pressures while having the lowest possible weight. In a similar way, the outer container  1  may also be composed of a very thin metal sheet if it is likewise provided with fiber-reinforced wrapping  31 . 
         [0046]      FIG. 7  and  FIG. 8  illustrate a further possible embodiment of a container according to the invention for cryogenic liquid. Here, the container has an outer container  40  with a length L, a width B and a structural height H. 
         [0047]    The further possible embodiment according to  FIG. 7  and  FIG. 8  differs from other embodiments in that the support  34  has two separate, elongate support elements  35  and  36  which are arranged the along longitudinal axes  37  of the inner container  38 , that is to say in the longitudinal axis direction. Here,  FIG. 7  shows a section of the support along the plane through the two longitudinal axes  37  of the inner containers  38 . By adding the lengths of the cross sections of the support elements  35  and  36  in the longitudinal axis direction, it is found that the outer container  40  is supported between its base wall  41  and its top wall  42  over more than 50% of its longitudinal extent by the support  34 . It can also be seen that the longitudinal extent (along the longitudinal axis of the cylindrical inner container) of the support is, in cross section, a multiple of the width extent of said support. To determine the length extent or the width extent, the maximum length dimensions or maximum width dimensions of the cross section of the individual support elements, arranged in each case between two inner containers, are added. Portions of the cross section of the support elements which overlap in the direction of the longitudinal axis or in the direction of the width (section with the plane through the two longitudinal axes  37 ) are counted only once in said addition. 
         [0048]    In  FIG. 8 , it can be seen that the support  34  has an additional reinforcement  39  in the region of the base wall and of the top wall of the outer container  40 . In this way, the mutual introduction of force between the outer tank and the support can be improved. In  FIG. 7  and  FIG. 8 , it can be seen that, in the illustrated embodiment, the cumulative extent of the cross-sectional area of the support  34  in the direction of the longitudinal axis is significantly greater than in the direction between the inner containers and at right angles to the longitudinal axis, that is to say in the direction of the width of the outer container  40 . The outer container  40  is illustrated in each case only schematically in  FIG. 7  and  FIG. 8 .