FR3137739A1 - Cryogenic fluid storage unit - Google Patents

Abstract

Cryogenic fluid storage unit This cryogenic fluid storage unit comprises: a suspension (9) securing the internal tank (3) to the external tank (7). The suspension (9) comprises a connection (23) comprising: - an external tube (25), located inside the internal reservoir (3); - a bottom plate (31) sealingly closing the distal end of the outer tube (25);- an inner tube (33) extending inside the outer tube (25), the inner tube (33) having an inner distal end (61) attached to the bottom plate (31) ; the bottom plate (31) having a large internal face (46) facing the inside of the external tube (25) and carrying a rib with a closed contour (51) having a central axis (C) delimited by a edge (52) , the internal distal end (61) being fixed to said edge (52). Figure for abstract: 3

Description

Cryogenic fluid storage unit

The present invention generally relates to a cryogenic fluid storage unit.

Such a storage unit typically comprises an internal tank internally delimiting a storage volume of the cryogenic fluid, an external tank inside which the internal tank is housed, and a suspension fixing the internal tank to the external tank.

The suspension can include two connections, each having:
- an external tube having an external proximal end fixed to the internal reservoir, and an external distal end located inside the storage volume;

- a bottom plate sealingly closing the external distal end;

- an internal tube extending inside the external tube, the internal tube having an internal proximal end fixed to the external reservoir, and an internal distal end fixed to the bottom plate.

The bottom plate may include a central stud, engaged in the internal proximal end. The internal distal end is welded to a shoulder of the central stud.

In order to limit heat transfer by convection from the external tank to the internal tank, the space defined between the internal tank and the external tank is maintained under a high vacuum.

Transfers by radiation are limited by arranging a layer of insulating material on the internal reservoir.

Heat transfers by conduction from the external tank to the internal tank mainly pass through the suspension, in particular through the internal tube. They are relatively high with the arrangement described above.

In this context, the invention aims to propose a storage unit whose suspension is designed to minimize the heat flow circulating by conduction from the external tank to the internal tank.

To this end, the invention relates to a cryogenic fluid storage unit, the storage unit comprising an internal tank internally delimiting a cryogenic fluid storage volume, an external tank inside which the internal tank is housed, and a suspension fixing the internal tank to the external tank, the suspension comprising a connection comprising:

- an external tube, having an external proximal end fixed to the internal reservoir and an external distal end located inside the storage volume;

- a bottom plate sealingly closing the external distal end;

- an internal tube extending inside the external tube, the internal tube having an internal proximal end fixed to the external reservoir and an internal distal end fixed to the bottom plate;

the bottom plate having a large internal face facing the interior of the external tube and carrying a rib with a closed contour having a central axis delimited by a slice, the internal distal end being fixed to said slice.

Because the inner distal end is attached to the edge of the rib, heat transmission from the inner tube to the bottom plate is very reduced.

The internal distal end and the rib are arranged end to end, the contact zone between the internal distal end and the rib consequently being of very small section. This section is much smaller than when the internal distal end is welded to a shoulder provided on a central stud engaged in said end.

This helps to limit heat transfers from the external tank to the internal tank.

The cryogenic fluid storage unit may also have one or more of the characteristics below, considered individually or in all technically possible combinations:

• An edge of the inner distal end connected to the closed-contour rib has a wall of given thickness, the closed-contour rib having a rib thickness between the given thickness minus 10% and the given thickness plus 10% .
• The rib with a closed contour is delimited inwards by an internal surface connected to the large internal face by an arcuate surface of internal rib, for example having in section in planes containing the central axis a shape in the form of an arc of a circle or in portion of ellipse.
• The rib with a closed contour is delimited towards the outside by an external surface connected to the large internal face by an arcuate surface of external rib, for example having in section in planes containing the central axis a shape in the form of an arc of a circle or in portion of ellipse.
• The large internal face of the bottom plate has a raised peripheral edge delimited by a slice, the external distal end being fixed to said slice.
• The closed contour rib has a height greater than that of the erect peripheral edge.
• The outer distal end has a wall of given thickness, the erect peripheral edge having an edge thickness between the given thickness minus 10% and the given thickness plus 10%.
• The erect peripheral edge is delimited inwards by an internal surface connected to the large internal face by an arcuate surface of internal edge, for example having in section in planes containing the central axis an arc of a circle or portion shape of ellipse.
• The inner edge arcuate surface and the outer rib arcuate surface are directly connected to each other.
• The bottom plate comprising a flat wall, substantially perpendicular to the central axis, defining the large internal face and carrying the rib with a closed contour.

Other characteristics and advantages of the invention will emerge from the detailed description given below, for information only and in no way limiting, with reference to the appended figures, among which:

- There is an axial sectional view of the cryogenic fluid storage unit;

- There is an enlarged axial section view of the suspension of one end of the internal reservoir of the ;

- There is an enlarged axial sectional view of the distal ends of the inner and outer tubes and the bottom plate of the suspension of the ;

- There is a sectional view of a preferred alternative embodiment of the bottom plate;

- There is a schematic representation illustrating the stress level of the internal tube, for the bottom plate of the ;

- There is a schematic representation illustrating the stress level of the internal tube, for the bottom plate of the ; And

- There is a schematic representation illustrating the stress level in the bottom plate of the (top) and in the bottom plate of the (bottom), for loading along the central axis (left) and in a direction perpendicular to the central axis (right).

Storage unit 1 shown on the is intended to store a cryogenic fluid.

By cryogenic fluid we mean a fluid at a very low temperature, which is at least partially in the liquid state inside the storage unit.

This fluid is typically hydrogen. Alternatively, the fluid is helium, nitrogen, a natural gas such as methane CH ₄ , air, or any other suitable fluid.

This storage unit is typically intended to be on board a vehicle having an electric propulsion motor, for example a motor vehicle, a train, a boat or any other vehicle.

The motor vehicle is for example a car, a utility vehicle, a truck, etc.

The storage unit 1 is typically intended to power a fuel cell. The fuel cell is configured to generate electricity and power the vehicle's electric propulsion motor.

The cryogenic fluid storage unit 1 comprises an internal tank 3 internally delimiting a cryogenic fluid storage volume 5, an external tank 7 inside which the internal tank 3 is housed, and a suspension 9 fixing the internal tank 3 to the external tank 7.

In the example shown, the internal tank 3 has a horizontal central axis C.

The internal reservoir 3 comprises a shell 11, closed at its two axial ends by bases 13.

The ferrule 11 is cylindrical, centered on the central axis C.

The external tank 7 also has a horizontal axis.

It comprises a ferrule 15, closed at its two axial ends by bases 17.

The ferrule 15 is cylindrical, centered on the central axis C.

The internal tank 3 and the external tank 7 define between them an intermediate space 19, maintained under a high vacuum.

This vacuum is typically of the order of 10 ^-5 millibars, so as to strongly limit heat transfer by convection from the external tank 7 to the internal tank 3.

Thermal insulation 21 is interposed between the internal tank 3 and the external tank 7. The thermal insulation 21 is typically placed on the external surface of the internal tank 3. The thermal insulation 21 comprises for example a plurality of metal sheets superimposed on each other on the others, with interposition of layers of fibers.

The suspension 9 is arranged in such a way that the entire weight of the internal tank 3 is taken up by the external tank 7 via the suspension 9.

The weight of the internal tank 3 is understood here to include the weight of the cryogenic fluid stored in the internal tank 3.

The accelerations experienced by the internal tank 3 and the cryogenic fluid contained in the internal tank 3 are also transmitted to the external tank 7 via the suspension 9.

When the storage unit 1 is embedded in a vehicle, these accelerations result from changes in direction of the vehicle, braking applied to the vehicle or acceleration of the vehicle, as well as roughness or irregularities in the road, or even shocks. applied to the vehicle.

In the example shown, the suspension comprises two connections 23. The connections 23 each suspend one of the two opposite axial ends of the internal reservoir 3 to the external reservoir 7. These connections 23 are identical. Only one of these connections 23 will be described below.

As visible on the , connection 23 includes:

- an external tube 25, having an external proximal end 27 fixed to the internal reservoir 3 and an external distal end 29 located inside the storage volume 5;

- a bottom plate 31 sealingly closing the external distal end 29;

- an internal tube 33 extending inside the external tube 25.

The connection 23 comprises an internal ring 35 directly fixed to the internal surface of the internal reservoir 3.

The internal ring 35 is fixed to the bottom 13.

The internal ring 35 is annular. The internal ring 35 comprises an annular base 37, delimiting a front face 39.

The front face 39 is annular and extends in a plane perpendicular to the central axis C.

The annular base 37 is extended axially by a cylindrical neck 41, opposite the front face 39.

The annular base 37 and the neck 41 internally delimit a cylindrical passage 43, coaxial with the central axis C.

The annular base 37 and the neck 41 are externally connected to each other by a fillet 45, in the form of a torus portion.

A slice 44 connects the front face 39 to the fillet 45.

The annular base 37 is engaged in an orifice provided in the bottom 13 of the internal reservoir 3.

The internal reservoir 3 is fixed to the edge 44 of the annular base 37.

The external tube 25 is substantially cylindrical, and is coaxial with the central axis C.

It is located inside storage volume 5, typically entirely inside volume 5.

The external proximal end 27 of the external tube 25 extends axially the neck 41. It has a thickness substantially identical to that of the neck 41.

The external tube 25 has a wall of substantially constant thickness over its entire axial length.

The bottom plate 31 has a large internal face 46 facing the inside of the external tube 25.

The large internal face 46 carries a raised peripheral edge 47, delimited by a edge 48. The external distal end 29 is fixed to said edge 48, typically directly fixed to the edge 48.

The erect peripheral edge 47 extends over the entire circumference of the large internal face 46. It has a closed contour.

The erect peripheral edge 47 extends from the large internal face 46 axially towards the external tube 25. It is placed axially in the extension of the external distal end 29. It is fixed in a sealed manner, for example by welding, at the external distal end 29.

The edge 48 corresponds to the surface constituting the top of the erect peripheral edge 47. It is substantially annular, and extends in a plane perpendicular to the central axis C. It delimits the erect peripheral edge 47 opposite the large internal face 46.

The external distal end 29 is in contact only with the edge 48. It is not in contact with the radially internal and external surfaces of the erect peripheral edge 47.

The external distal end 29 has a wall of given thickness. The erect peripheral edge 47 has an edge thickness between the given thickness minus 10% and the given thickness plus 10%.

In other words, the erect peripheral edge 47 has substantially the same thickness as the external distal end 29.

A thermal insulation layer 49 is placed inside the outer tube 25, against the inner surface of the outer tube 25. This thermal insulation layer 49 extends over the entire length of the outer tube 25, crosses the passage 43 and extends beyond the front face 39.

The internal tube 33 is placed inside the thermal insulation layer 49, and is separated from it by a void 50.

The large internal face 46 carries a rib with a closed contour 51 delimited by a edge 52.

The closed contour rib 51 is cylindrical, and has a central axis.

This central axis coincides with the central axis C.

The internal tube 33 has an internal proximal end 59 fixed to the external reservoir 7 and an internal distal end 61 fixed to the bottom plate 31.

The internal distal end 61 is fixed to the edge 52 of the closed contour rib 51, typically directly fixed to the edge 52.

The internal tube 33 has a central section 63 connecting the internal proximal end 59 to the internal distal end 61.

The suspension 9 comprises a fixing ring 65 fixed to the external reservoir 7, the internal proximal end 59 of the internal tube 33 being directly fixed to the fixing ring 65.

In the example shown, the fixing ring 65 is fixed to a cup 67, itself fixed to the internal surface of the external tank 7 ( ). The cup 67 is placed axially opposite the bottom 13 of the internal reservoir 3. It has a central part 69 extended by a raised edge 71, rigidly fixed to the ferrule 15 of the external reservoir 7.

In the example shown, the fixing ring 65 is similar to the internal ring 35. It thus includes an annular base 73, defining a front face 75.

The front face 75 extends in a plane perpendicular to the central axis C. It has an annular shape.

The annular base 73 is extended axially opposite the front face 75 by a neck 77. The neck 77 is substantially cylindrical, centered on the axis C. The annular base 73 and the neck 77 internally delimit a substantially cylindrical passage 79 , centered on axis C. The annular base 73 and the neck 77 are connected externally to each other by a fillet 81, in the form of a torus portion.

A slice 82 connects the front face 75 to the fillet 81.

The annular base 73 is engaged in an orifice provided in the cup 67.

The cup 67 is fixed to the edge 82 of the annular base 73.

The internal tube 33 is substantially rectilinear and cylindrical. It is centered on the central axis C.

The central section 63 has a wall of given average thickness e.

Typically, the wall of the central section 63 has a substantially constant thickness over the entire length of the central section 63.

The internal distal end 61 has a thicker wall than that of the central section 63.

The internal distal end 61 comprises a first distal section 83 having a wall with a thickness greater than 150% of the given average thickness e.

Advantageously, the internal distal end 61 further comprises a second distal section 85 having a wall with a thickness greater than 250% of the given average thickness e.

The second distal section 85 is connected to the central section 63 by the first distal section 83.

The first distal section 83 has a thickness advantageously between 150% and 250% of the given average thickness e, more preferably between 175% and 225%, and worth for example 200% of the given average thickness e.

The second distal section 85 has a thickness of between 250% and 350% of the given average thickness e, preferably between 275% and 325% of the given average thickness e, and worth for example 300% of the thickness given average e.

According to a particularly advantageous embodiment, the internal tube 33 comprises a main sleeve 87 and a first distal sleeve 89 arranged in or around the main sleeve 87.

In the example shown, the first distal sleeve 89 is arranged in the main sleeve 87.

The internal tube 33 further comprises a second distal sleeve 91 arranged in or around the first distal sleeve 89 and the main sleeve 87.

In the example shown, the second distal sleeve 91 is arranged in the first distal sleeve 89.

The main sleeve 87 extends over the entire length of the internal tube 33.

The first distal sleeve 89 extends along the first distal section 83 but not along the central section 63.

The first distal sleeve 89 also extends along the second distal section 85.

The second distal sleeve 91 extends along the second distal section 85, but not along the first distal section 89 nor along the central section 63.

In other words, the central section 63 consists only of the main sleeve 87. The first distal section 83 has two thicknesses, and is formed from the superposition of the first distal sleeve 89 and the main sleeve 87.

The second distal section 85 has three thicknesses, and is formed from the superposition of the second distal sleeve 91, the first distal sleeve 89 and the main sleeve 87.

The main sleeve 87 and the first distal sleeve 89 are pressed against each other, without play.

Likewise, the second distal sleeve 91 and the first distal sleeve 89 are pressed against each other, without play.

Typically, the main sleeve 87 has a thickness of between 1 and 5 millimeters, preferably between 1 and 3 millimeters, and worth for example 1.5 millimeters.

The distal sleeves 89 and/or 91 advantageously have the same thickness as the main sleeve 87.

The rib with closed contour 51 extends from the large internal face 46 axially towards the internal tube 33. It is placed axially in the extension of the internal distal end 61. It is fixed in a sealed manner to the distal end internal 61.

The closed contour rib 51 is typically cylindrical, coaxial with the central axis C.

The edge 52 corresponds to the surface constituting the top of the rib with closed contour 51. It is substantially annular, and extends in a plane perpendicular to the central axis C. It delimits the rib with closed contour 51 on the opposite of the large internal face 46.

The internal distal end 61 is in contact only with the edge 52. It is not in contact with the radially internal and external surfaces of the closed contour rib 51.

An edge of the inner distal end 61 connected to the closed-contour rib 51 has a wall of given thickness, the closed-contour rib 51 having a rib thickness between the given thickness minus 10% and the given thickness plus 10%.

This edge is defined by the second distal section 85.

In other words, the closed-contour rib 51 has substantially the same wall thickness as the internal distal end 61.

The internal distal end 61 has a given external section, the closed contour rib 51 having substantially the same external section.

The internal proximal end 59 is directly fixed to the ring 65.

More precisely, it is attached to collar 77.

The internal proximal end 59 has a thicker wall than that of the central section 63.

The internal proximal end 59 comprises a first proximal section 103 having a wall thickness greater than 150% of the given average thickness e.

Advantageously, it also comprises a second proximal section 105 having a wall thickness greater than 250% of the given average thickness e.

The second proximal section 105 is connected to the central section 63 by the first proximal section 103.

The second proximal section 105 is directly connected to the fixing ring 65. It preferably has a wall thickness substantially equal to the thickness of the neck 77.

The first proximal section 103 has a thickness advantageously between 150% and 250% of the given average thickness e, more preferably between 175% and 225%, and worth for example 200% of the given average thickness e.

The second proximal section 105 has a thickness between 250% and 350% of the given average thickness e, preferably between 275% and 325% of the given average thickness e, and worth for example 300% of the thickness given average e.

The internal tube 33 advantageously comprises a first proximal sleeve 107 arranged in or around the main sleeve 87.

The first proximal sleeve 107, in the example shown, is arranged in the main sleeve 87.

The first proximal sleeve 107 extends along the first proximal section 103 but not along the central section 63.

The internal tube 33 further comprises a second proximal sleeve 109 arranged in or around the first proximal sleeve 107 and the main sleeve 87.

In the example shown, the second proximal sleeve 109 is arranged in the first proximal sleeve 107.

The first proximal sleeve 107 extends along the second proximal section 105.

The second proximal sleeve 109 extends along the second proximal section 105, but not along the first proximal section 103 nor along the central section 63.

The first proximal section 103 has two thicknesses, and is formed from the superposition of the first proximal sleeve 107 and the main sleeve 87.

The second proximal section 105 has three thicknesses, and is formed from the superposition of the main sleeve 87, the first proximal sleeve 107 and the second proximal sleeve 109.

As before, the main sleeve 87 and the first proximal sleeve 103 are pressed against each other, without play.

Likewise, the second proximal sleeve 109 and the first proximal sleeve 107 are pressed against each other without play.

The bottom plate 31 comprises a flat wall 110, substantially perpendicular to the central axis C and defining the large internal face 46. The flat wall 110 carries the rib with a closed contour 51.

The flat wall 110 also carries the erect peripheral edge 47.

The flat wall 110 has a portion of constant thickness 111, delimited by the closed contour rib 51. This thickness is between 6 and 2 mm, preferably between 5 and 4 mm and ideally equal to 4.5 mm.

The closed contour rib 51 is delimited inwardly by an internal surface 112 connected to the large internal face 46 by an arcuate surface of internal rib 113.

The internal surface 112 is the radially internal surface of the closed contour rib 51 relative to the central axis C.

The arcuate surface of internal rib 113, in section in planes containing the central axis C, preferably has sections in ellipse portion ( ) or alternatively has circular arc sections (Figures 2 and 3).

On the , the radius of curvature of the section gradually increases when said section is followed from the internal surface 112 to the large internal face 46. The arcuate surface of the internal rib 113 does not connect tangentially to the large internal face 46.

In Figures 2 and 3, the arcuate surface of internal rib 113 is a fillet. Considered in section in a radial plane containing the central axis C, it has a quarter-circle shape, connecting tangentially to the internal surface 112 and to the large internal face 46.

Likewise, the rib with closed contour 51 is delimited towards the outside by an external surface 115 connected to the large internal face 46 by an arcuate surface of external rib 117.

The external surface 115 is the radially internal surface of the closed contour rib 51 relative to the central axis C.

The arcuate surface of the external rib 117, in section in planes containing the central axis C, preferably has sections in an ellipse portion ( ) or alternatively has circular arc sections (Figures 2 and 3).

On the , the radius of curvature of the section gradually increases when said section is followed from the external surface 115 to the large internal face 46. The arcuate surface of the external rib 117 does not connect tangentially to the large internal face 46.

In Figures 2 and 3, the arcuate surface of external rib 117 is a fillet. Considered in section in a radial plane containing the central axis C, it has a quarter-circle shape, connecting tangentially to the external surface 115 and the large internal face 46.

Thus, the rib with closed contour 51 is connected to the large internal face 46 by a solid, annular part, of section increasing axially from the rib 51 towards the large internal face 46.

The erect peripheral edge 47 is delimited inwardly by an internal surface 119 connected to the large internal face 46 by an arcuate internal edge surface 121.

The internal surface 119 is the radially internal surface of the erect peripheral edge 47 relative to the central axis C.

In Figures 2 and 3, the arcuate inner edge surface 121 is a fillet. Considered in section in a radial plane containing the central axis C, it has a quarter-circle shape, connecting tangentially to the internal surface 119 and to the large internal face 46.

Likewise, on the , the arcuate inner edge surface 121 is a fillet.

According to a variant not shown, the arcuate surface of the external rib 117 has, in section in planes containing the central axis C, sections in ellipse portions.

Thus, the erect peripheral edge 47 is connected to the large internal face 46 by a solid, annular part, of section increasing axially from the erect peripheral edge 47 towards the large internal face 46.

The inner edge arcuate surface 121 and the outer rib arcuate surface 117 are directly connected to each other.

In Figures 2 and 3, they together form a half-torus surface.

In all alternative embodiments, the spacing between the external surface 115 and the internal surface 119 controls the radii of curvature of the arcuate surfaces of external rib 117 and internal edge 121. This distance corresponds to the thickness of the thermal insulation 49, increased by the void 50.

When the arcuate surfaces of external rib 117 and/or internal edge 121 are of circular sections, the radius is worth half of said spacing. When the arcuate surfaces of the external rib 117 and/or the internal edge 121 are of sections in the portion of an ellipse, the half-minor axis of the ellipse is worth half of said spacing.

Typically, the arcuate surface of the internal rib 113 has sections substantially symmetrical to those of the arcuate surface of the external rib 117. This contributes to obtaining a good distribution of forces in the bottom plate 31.

Thus, if the arcuate surface of the external rib 117 has sections in the form of an arc of a circle, the arcuate surface of the internal rib 113 also has sections in the form of an arc of a circle, of the same radius. If the arcuate surface of the external rib 117 has sections in the form of an ellipse, the arcuate surface of the internal rib 113 also has sections in the form of an ellipse, with the same half-minor axis.

Preferably, the height of the closed contour rib 51 is greater than the height of the erect peripheral edge 47. This height is taken axially from the large internal face 46.

This makes it easier to weld the internal distal end 61 to the closed contour rib 51.

The technical effect obtained due to the design of the bottom plate 31 is illustrated in Figures 5 to 7.

There illustrates the mechanical stress levels in the internal tube 33, for the bottom plate 31 of Figures 2 and 3.

Zones of increasing mechanical stress are materialized and referenced from a to i. The stress ranges, in MPa, corresponding to each zone are indicated on the . They vary between 40 and 200 MPa.

The connection between the internal tube 33 and the bottom plate 31 is subject to very high stresses, due to the significant overhang between the internal proximal end 59 of the internal tube 33 and the bottom plate 31.

Likewise, the overhang between the external proximal end 27 of the external tube 25, fixed to the internal reservoir 3, and the bottom plate 31 is very important, such that the stresses at the level of the fixing of the tube external 25 to the bottom plate 31 are elevated.

It appears that, due to the progressive variation in thickness of the wall of the internal tube 33 at the level of the internal distal end 61, the mechanical stresses at this internal distal end 61 are well controlled and are at a satisfactory level .

These constraints are greater in the central section 63, relatively less important at the level of the first distal section 83, and even less significant at the level of the second distal section 85, directly linked to the bottom plate 31.

It appears that the zone undergoing the maximum mechanical stresses is the portion of the central section 63 which adjoins the first distal section 83. In all cases, the stresses remain lower than the admissible limit, which here is 180 MPa.

These results were obtained by calculation, for a connection whose different elements are made of type 316L stainless steel. The mechanical calculations were made with an exterior temperature of 20°C and considering that the storage unit is at 20°C, corresponding to the most severe condition given that the resistance of type 316L stainless steel decreases. with the temperature.

The length of the inner tube is 560 millimeters and its diameter is 76 millimeters. The thickness of the different sleeves is 1.5 millimeters. The central section of the internal tube thus has a wall of 1.5 millimeters thickness, the first proximal section and the first distal section a wall thickness of 3 millimeters, the second proximal section and the second distal section a wall thickness of 4.5 millimeters.

The axial length of the first proximal sleeve and the first distal sleeve is 55 millimeters. The axial length of the second proximal sleeve and the second distal sleeve is 40 millimeters.

The calculation was carried out for an internal tank whose mass is 167 kg, storing 40 kg of hydrogen.

The heat flux passing by conduction along the internal tube 33 is approximately 1 W/m ² .K. This heat transfer by conduction is particularly low.

The complete heat transfer from the external reservoir to the internal reservoir, taking into account the flows by convection, by conduction and by radiation, is approximately 6.2 W, with approximately 1 W transmitted by each of the two links.

There shows illustrates the mechanical stress levels in the internal tube 33, for the bottom plate 31 of the .

Zones of increasing mechanical stress are materialized and referenced from a to i. The stress ranges, in MPa, corresponding to each zone are indicated on the . They vary between 40 and 200 MPa.

As previously, the maximum stress level is in the portion of the central section 63 which adjoins the first distal section 83. The maximum is 171.8 MPa, and remains below the admissible limit, which here is 180 MPa.

There , on the right, illustrates the levels of mechanical stresses in the bottom plate 31, for a loading case corresponding to an acceleration of 5 g, perpendicular to the central axis C. The illustration at the top corresponds to the alternative embodiment of the Figures 2 and 3, and the bottom illustration of the alternative embodiment of the .

Zones of increasing mechanical stress are materialized and referenced from a to i. The stress ranges, in MPa, corresponding to each zone are indicated on the . They vary between 2.2 and 108.4 MPa.

For the bottom plate 31 of Figures 2 and 3, the maximum is 108.4 MPa and remains acceptable. The variant of the allows the maximum to be lowered to 86.8 MPa.

There , on the left, illustrates the levels of mechanical stresses in the bottom plate 31, for a loading case corresponding to an acceleration of 6.6 g, along the central axis C. The illustration at the top corresponds to the alternative embodiment of Figures 2 and 3, and the bottom illustration to the alternative embodiment of the .

Zones of increasing mechanical stress are materialized and referenced from a to i. The stress ranges, in MPa, corresponding to each zone are indicated on the . They vary between 0 and 22.8 MPa.

For the bottom plate 31 of Figures 2 and 3, the maximum is 22.8 MPa and remains acceptable. The variant of the allows the maximum to be lowered below 20.3 MPa.

These different illustrations show that the highest stresses are not in the zone of the welding of the internal tube 33 to the bottom plate 31, nor in the junction between the edge 52 of the rib with closed contour 51 and the stack of main sleeves 87, first distal 89 and second distal 91. The stresses are quite low and in full material, in a zone without the beginning of rupture. These beginnings of rupture are generally located either in the weld or at the level of a sudden change in geometry.

The suspension architecture described above is particularly advantageous.

The fact that an edge of the internal distal end connected to the closed-contour rib has a wall of given thickness, the rib having a rib thickness between the given thickness minus 10% and the given thickness plus 10 %, contributes to ensuring that the contact surface between the closed-contour rib and the internal distal end is very limited, and therefore that heat transfer by conduction is reduced.

The fact that the closed contour rib is connected to the large internal face of the bottom plate by arcuate surfaces makes it possible to avoid stress concentrations at the connection between the internal distal end and the closed contour rib, and in the closed contour rib. This area is heavily loaded mechanically, due to the significant overhang from the attachment points to the internal tank and the external tank.

Therefore, it is possible to reduce the wall thickness of the closed-contour rib, and to reduce the wall thickness of the inner distal end. This helps to further reduce heat transfer by conduction towards the bottom plate.

The fact that the large internal face of the bottom plate has a raised peripheral edge delimited by a slice, the external distal end being fixed to said slice, also contributes to limiting heat transfer by conduction. In fact, the cryogenic fluid bathes the external surface of the external tube. The amount of heat radiated from the bottom plate into the outer tube is reduced because the contact area between the outer tube and the bottom plate is also reduced. This contact zone is limited to the edge of the erect peripheral edge.

The fact that the external distal end has a wall of given thickness, the erect peripheral edge having an edge thickness between the given thickness minus 10% and the given thickness plus 10%, contributes to ensuring that the surface of contact between the erect peripheral edge and the external distal end is very limited, and therefore heat transfer by conduction is reduced.

The fact that the erect peripheral edge is delimited towards the inside by an internal surface connected to the large internal face by an arcuate surface of the internal edge, makes it possible to avoid stress concentrations at the level of the connection between the external distal end and the erect peripheral edge and in the erect peripheral edge.

Therefore, it is possible to reduce the wall thickness of the erect peripheral edge, and to reduce the wall thickness of the outer distal end. This helps to further reduce heat transfer by conduction from the bottom plate to the external tube.

The fact that the inner edge arcuate surface and the outer rib arcuate surface are directly connected to each other and together form a half-torus surface makes it possible to obtain large radii for the inner edge arcuate surface and the arcuate surface of outer rib, with enough space between the inner tube and the outer tube to accommodate the thermal insulation layer and the vacuum.

The storage unit can have multiple variations.

The internal tank and the external tank are not necessarily horizontal axes but could be vertical axes.

The internal proximal end and/or the internal distal end are not necessarily of the type described above, that is to say with an extra thickness of material compared to the central section. Depending on the accelerations to be taken up, the mass of the internal reservoir, the method of attachment to the external reservoir, the internal proximal end and/or the internal distal end could also be of the same thickness as the central section.

The inner edge arcuate surface, the inner rib arcuate surface and the outer rib arcuate surface may not have circular arc or ellipse portion sections. Alternatively, they have sections in oval portions or any other suitable shape.

Claims (10)

Cryogenic fluid storage unit, the storage unit (1) comprising an internal tank (3) internally delimiting a volume (5) for storing the cryogenic fluid, an external tank (7) inside which the tank is housed internal (3), and a suspension (9) fixing the internal tank (3) to the external tank (7), the suspension (9) comprising a connection (23) comprising:
- an external tube (25), having an external proximal end (27) fixed to the internal reservoir (3) and an external distal end (29) located inside the storage volume (5);
- a bottom plate (31) sealingly closing the external distal end (29);
- an internal tube (33) extending inside the external tube (25), the internal tube (33) having an internal proximal end (59) fixed to the external reservoir (7) and an internal distal end (61) fixed to the bottom plate (31);
the bottom plate (31) having a large internal face (46) facing the inside of the external tube (25) and carrying a closed contour rib (51) having a central axis (C) delimited by a edge (52) , the internal distal end (61) being fixed to said edge (52). Storage unit according to claim 1, wherein an edge of the inner distal end (61) connected to the closed contour rib (51) has a wall of given thickness, the closed contour rib (51) having a thickness of rib between the given thickness minus 10% and the given thickness plus 10%. Storage unit according to any one of the preceding claims, in which the closed-contour rib (51) is delimited inwardly by an internal surface (112) connected to the large internal face (46) by an arcuate rib surface internal (113), for example having in section in planes containing the central axis (C) a shape in the form of an arc of a circle or a portion of an ellipse. Storage unit according to any one of the preceding claims, in which the closed-contour rib (51) is delimited outwardly by an external surface (115) connected to the large internal face (46) by an arcuate rib surface external (117), for example having in section in planes containing the central axis (C) a shape in the form of an arc of a circle or a portion of an ellipse. Storage unit according to any one of the preceding claims, in which the large internal face (46) of the bottom plate (31) carries a raised peripheral edge (47) delimited by a edge (48), the external distal end (29) being fixed to said slice (48). Storage unit according to claim 5, wherein the closed contour rib (51) has a height greater than that of the erect peripheral edge (47). Storage unit according to claim 5 or 6, wherein the outer distal end (29) has a wall of given thickness, the erect peripheral edge (47) having an edge thickness between the given thickness minus 10% and the given thickness plus 10%. Storage unit according to any one of claims 5 to 7, in which the erect peripheral edge (47) is delimited inwardly by an internal surface (119) connected to the large internal face (46) by an arcuate surface of internal edge (121), for example having in section in planes containing the central axis (C) a shape like an arc of a circle or a portion of an ellipse. A storage unit according to claim 8 combined with claim 4, wherein the inner edge arcuate surface (121) and the outer rib arcuate surface (117) are directly connected to each other. Storage unit according to any one of the preceding claims, in which the bottom plate (31) comprising a flat wall (111), substantially perpendicular to the central axis (C), defining the large internal face (46) and carrying the closed contour rib (51).