Patent Application
20230324004
The present invention relates to an inner liner of a pressure vessel, a pressure vessel including the liner and a method of manufacture of, an inner liner of a pressure vessel, and a conformal pressure vessel.
In recent years, hydrogen has emerged as a promising candidate as a renewable energy source. In particular, its use in the transportation industry has received significant interest because of its inherent advantages over battery technologies. For example, compared to battery technologies, hydrogen storage systems offer faster refuelling times and reduced weight.
Hydrogen can be stored in the solid state using adsorbing or absorbing materials, in the liquid state at cryogenic temperatures, or in the gaseous state under elevated pressure. In the field of mobile applications, amongst other things, a high volumetric and gravimetric energy density are desirable. In solid-state storage devices and liquid state storage devices, temperature management and control systems are often required. These systems add complexity and weight to the system, reducing the effective energy density of the storage system. For this reason, compressed hydrogen gas systems are the preferred choice in industry.
Compressed hydrogen gas systems are stored under extremely high pressure. For example, the ISO14687-2 and ISO12619-1:2014 standard define a gauge pressure of 700 bar. Other defined standard pressures are 300 bar, 350 bar and 500 bar. High pressures naturally result in an improvement in the volumetric and gravimetric energy density of the compressed gas. However, at these elevated pressures, the pressure vessels, containing the compressed gas, require additional reinforcement to ensure that that the vessel is mechanically robust. Often, this reinforcement results in increasing the thickness of the vessel, which leads to an increase in weight and overall volume, which may lead to a reduction in the energy density of the pressure vessel as a whole.
Notwithstanding the fact that hydrogen is extremely flammable, elevated pressures in general pose a significant safety risk. In the field of transportation, this risk is compounded by the proximity of these pressure vessels to passengers. Furthermore, conventional pressure vessels are based on cylindrical or spherical designs, which are cumbersome to handle, and have a tendency to roll. As such, pressure vessel designs of these geometries often require supportive elements to secure the pressure vessels in place.
US-A-2016061381 discloses a pressure vessel with an internal supportive structure to reduce the pressure applied to the external shell of the pressure vessel. The internal bonds of the supportive structure are mostly connected to a central supporting element. US-A-2016061381 discloses a compartmental or cellular design, which reduces the risk of explosions resulting from external damage to the vessel because the flow capacity is restricted by holes that connect each hole to the central supporting element.
US2006/0261073 discloses a pressure vessel liner, which includes a tubular trunk and head plates to close opposing ends of the trunk. Inside the liner there are reinforcing walls to improve resistant strength against longitudinal forces.
According to a first aspect of the present invention, there is provided a sectional inner liner of a pressure vessel comprising the sectional inner liner and an outer layer disposed around the sectional inner liner, the sectional inner liner comprising: at least two inner liner sections, wherein each inner liner section comprises an internal network structure; and at least two cap sections, wherein, the at least two cap sections and at least two inner liner sections are configured to assemble into a sectional inner liner.
The at least two inner liner sections may comprise an interlocking portion at each opposing open-end, which are either the same or complementary in shape; and the at least two cap sections may comprise an interlocking portion, which is either the same or complementary in shape to the interlocking portion of the at least two inner liner section. The cap sections and inner liner sections may therefore be configured to assemble via the interlocking portions. Adhesive bonding and/or welding may be used to secure the interlocking portions in place.
Each inner liner section and cap section may be a single moulding.
The cross-sectional shape of the sectional inner liner, defined by the outer surface of the inner liner section, maybe one of a square or a rounded square. Other shapes are possible.
The internal network structure of the sectional inner liner may comprise: a first set of support members comprising a plurality of first support members, wherein each of the first support members extend across an internal corner of the inner liner section. Optionally further comprising: a second set of support members comprising a plurality of second support members, wherein each of the second support members extend between two of the first support members that extend across adjacent corners of the inner liner section. Optionally further comprising: a third set of support members comprising a plurality of third support members, wherein each of the third support members extends between two adjacent second support members to form a square, or rounded square in cross section. Optionally further comprising: a fourth set of support members comprising a plurality of fourth support members, wherein each of the fourth support members extend radially between a face defined by the internal surface of the inner liner section and a vertex of the square, or rounded square formed by the third set of support members. Optionally, wherein each of the support members in the fourth set of support members bisects one or more of the second support members. Optionally further comprising: a fifth set of support members comprising a plurality of fifth support members, wherein each of the fifth support members extend radially between an internal corner of the inner liner section and one or more of the first support members. Optionally, wherein each of the support members in the fifth set of support members bisects one or more of the first support members.
The internal network structure of the sectional inner liner may be integrally formed within the thickness of the inner liner section wall and optionally, wherein the thickness of the inner liner section wall is largest along its corner edges and smallest along the centre of each of its faces. The variation in thickness of the inner liner section wall may define an internal volume with a shape, in cross section, substantially similar to the outer surface of the inner liner section wall. The internal network structure may comprise one or more holes located along each corner edge of the inner liner section. Optionally, the one or more holes are partially circumferential.
According to a first aspect of the present invention, there is provided a pressure vessel comprising: the sectional inner liner described above and an outer layer disposed around the sectional inner liner.
The outer layer may comprise a woven carbon-fibre cloth infused with resin, or a carbon-fibre winded overwrap.
According to a first aspect of the present invention, there is provided a method for manufacturing the sectional inner liner described above, comprising: injection moulding or casting the at least two inner liner sections and the at least two cap sections; and assembling said sections together. Assembling the sections together may comprise adhesive bonding or welding.
The sectional inner liner may, for example, be produced by additive manufacturing. The sectional inner liner may be represented digitally in the form of a design file. A design file, or computer aided design (CAD) file, is a configuration file that encodes one or more of the surface or volumetric configuration of the shape of the product. That is, a design file represents the geometrical arrangement or shape of the product.
Once obtained, a design file may be converted into a set of computer executable instructions that, once executed by a processer, cause the processor to control an additive manufacturing apparatus to produce a product according to the geometrical arrangement specified in the design file. The conversion may convert the design file into slices or layers that are to be formed sequentially by the additive manufacturing apparatus. The instructions (otherwise known as geometric code or “G-code”) may be calibrated to the specific additive manufacturing apparatus and may specify the precise location and amount of material that is to be formed at each stage in the manufacturing process.
The additive manufacturing apparatus may be controlled according to the computer executable instructions, and the additive manufacturing apparatus may therefore be instructed to print out one or more parts of the inner liner. These may be printed either in assembled or unassembled form. For instance, different sections of the inner liner may be printed separately (as a kit of unassembled parts) and then subsequently assembled. Alternatively, the different parts may be printed in assembled form.
Some embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:
The present invention provides a liner and pressure vessel, which address one or more of the aforementioned problems in the prior art. The present invention also provides a sectional inner liner and sectional pressure vessel.
The inner liner 200 of the present invention has plural functions. The outer surface 202 of the inner 200 serves the function of being substantially impermeable to the contained gas in the pressure vessel, while, the internal network structure 204 of the inner liner 200 serves the function of providing support to the pressure vessel walls 202, 302. In this way, the inner liner 200 of the present invention is able to contain pressurised gas and, at the same time, reduces the stress in the pressure vessel walls 202, 302 compared to conventional designs, such as the inner liner of
The internal network 204 of the inner liner 200 and outer surface 202 define a volume 206, which is configured to hold a fluid. Preferably, the volume 206 is interconnected. In some examples, the fluid comprises a pressurised gas, such as hydrogen, nitrogen, oxygen, bio gas, natural gas, ammonia or any other gas, as would be appreciated by the skilled person. In other examples, the fluid comprises a pressurised liquid, such as liquid hydrogen, liquid nitrogen, liquid oxygen, liquid bio gas, liquid ammonia liquid natural gas or any other pressurised liquid, as would be appreciated by the skilled person. For the latter, it is implicit that liquid stored gas can be generated at an arbitrary pressure and temperature, as defined by the corresponding pressure-temperature phase diagram.
The outer surface 202 of the inner liner 200 comprises a material that is configured to contain the contained fluid with only negligible leaking. That is, the material is, practically speaking, impermeable to the contained fluid. For example, if the fluid is pressurised hydrogen gas, then the inner liner is impermeable to hydrogen gas. As such, the function of the outer surface is similar, but not the same, as the inner liner 102 in the conventional pressure vessel.
Preferably, the internal network 204 and the outer surface 202 are integral. That is to say, the internal network 204 and outer surface 202 are formed as a single component. In other examples, the internal network 204 and outer surface 202 may be formed separately and combined in a joining step.
The internal network structure 204 shown in
The internal network of interconnected support members 204 provides structural reinforcement to the pressure vessel 300 which offers a route for increasing the gauge pressure of the pressure vessel whilst, at the same time, potentially improving the gravimetric and/or volumetric energy density of the pressure vessel. In particular, in a hydrogen storage vessel in mobile applications. During operation, or when the pressure vessel 300 is at least partially filled with pressurised gas, the pressurised gas exerts a hydrostatic pressure against the pressure vessel walls 202, 302. Generally speaking, the hydrostatic pressure is larger than the external pressure (pressure outside of the pressure vessel) and therefore acts to force the pressure vessel outwards. According to Newton's third law, in equilibrium, the pressure vessel must exert an equal and opposite force to compensate for this internal hydrostatic overpressure. This restoring force is generated by an elastic strain, which in turn, induces an internal stress in the walls of the pressure vessel 202, 302. This elastic strain, provided that the gauge pressure is greater than zero, is tensile. If the internal pressure increases, the tensile stress in the pressure vessel walls 202, 302 increases until the material comprising the pressure vessel wall 202, 302 fails plastically or otherwise. In the technical field of pressure vessels, especially in containing highly flammable gases such as hydrogen, plastic formation and failure is not an option. For this reason, pressure vessels only operate in the elastic regime and for the remainder of this application, it is implied that the outer skin 302 operates in the elastic regime.
As described above, the internal network 204 comprises a first and second set of one or more members 208 bonded, or otherwise in permanent mechanical contact, with the outer surface 202 at a first and second set of contact points and a continuous path is defined between the first and second set of contact points via mechanical connections with a third set of members 208. In this case, the hydrostatic pressure exerted by the pressurised gas also applies against the internal network 104. For regions of the internal network 204 distal from the outer surface 202 of the inner liner 200 (i.e., where edge effects can be discounted), the internal pressure exerts a hydrostatic compressive stress on the members 208, which form the internal network 204. However, at the same time, the internal pressure exerts a force on the pressure vessel walls 202, 302 to expand and the internal structure 204 must also expand via an elastic strain. Depending on the magnitude of the internal pressure and the structure of the internal network 204, the components of the stress tensor may be in overall tension. In this way, the effective stiffness of the pressure vessel walls 202, 302 increases. Accordingly, the elastic strain induced in the pressure vessel walls 202, 302 decreases as a portion of the elastic strain is “taken up” by the internal network structure 204. In turn, as the stiffness of the pressure vessel walls 202, 302 can be assumed constant (in the elastic regime), the induced stress within the pressure vessels walls 202, 302, for a given internal pressure, decreases. In this way, the internal pressure of the pressure vessel 300 can be increased without increasing the thickness of the outer skin 302.
It is emphasised that in order to induce elastic strain and stress in the members 208 of the internal network structure 204, the members 208 are constrained in some way relative to the outer skin 302 of the pressure vessel. That is to say, there exists a continuous path 304 between at least one point from the first set of contact points on the outer surface 202 of the inner liner 200 and at least one point from the second set of contact points.
The pressure vessel 300 depicted in
The feasibility study was a simulation in the ANSYS software package. The following assumptions were made:
In the feasibility study, the following parameters were taken as constant:
In the feasibility study, different configurations of pressure vessel 300 were generated by varying the following parameters:
The parametric values for each configuration is shown in Table 1.
The contribution of component mass and volume for each modelled pressure vessel configuration is shown in Table 2 and Table 3.
The calculated maximum radial deformation, and average hoop stresses in the outer surface 202 of the inner liner 200 and the outer skin 302 at 35 MPa gauge pressure are shown in Table 4.
By comparing the results shown in Table 2 to 4 of X1 with X0 and of X3 with X7, the effect of the internal network structure 204 on the gravimetric and volumetric energy density can be determined. For clarity, X0 and X7 denote the conventional type “IV” composite pressure vessels, and X1 and X3 have respectively equivalent physical properties, except they also include the diamond lattice structure of
X1 is approximately 70 percentage points heavier than X0. X1 has approximately 9 percentage points less volume 206 for filling with gas than X0. X1 has approximately 2.4, 2.3 and 1.8 percentage point reduction in radial deformation, and hoop stress in the outer surface 202 and outer skin 302 respectively.
X3 is approximately 70 percent heavier than X7. X3 is only capable of storing 91 percent of the volume of gas in X7. The radial deformation, and hoop stress in the outer surface 202 and outer skin 302 are approximately 3, 8.5 and 6.8 percent lower than of X7 respectively.
Accordingly, the results of the feasibility study confirm that the inner liner 200 leads to a reduction in stress and strain induced in the pressure vessel walls 202, 302. However, preliminary results show that, in the exemplary internal network structure 204 shown in
The internal network structure 500 comprises a plurality of radially extending support members 502. In some embodiments, the number of the radially extending support members 502 increase with distance from a centre point 504 of the pressure vessel. Nodes 512 in the internal network structure 500 are disposed in the structure for this purpose. In some examples, the centre point 504 of the pressure vessel is the centre of volume 504 of the pressure vessel. In some examples, the centre point 504 is the centre of mass of the pressure vessel. Depending on the overall geometry of the pressure vessel, the centre of mass and centre of volume may be coincident.
In the exemplary internal network structure 500 shown in
At each node 512, the supporting members “generated” by the multiplication factor are separated by an angle. In some examples, the supporting members are spaced evenly in angular space. In an example, if the multiplication factor is four, the angle between each supporting member may be 109.5 degrees.
As shown in
In some examples, each volume 506, 508, 510 may comprise essentially a periodic structure internal network structure 204 as shown in
The motivation behind this internal network structure 500 is that the inventors have recognised that the stress and strain induced in the outermost support members 208 in a periodic internal network structure 204 is larger than the stress and strain induced in the more inner members 208. This is caused at least in part by the formation of local stress concentrations that form at the contact points between the support members 208, 502 and the outer surface 202 of the inner liner 200. Accordingly, in the structure shown in
In this light, increasing the number density of the support members 502 in regions proximal to the outer surface 202 of the inner line 200 is a way of reducing stress concentration in these regions. Graded or hierarchical structures are a way of achieving this. In a graded structure, the number density of the support members may be varied continuously throughout the internal network structure. In hierarchical structures, the number density of the support members may be varied in discrete steps in the internal network structure. Generally speaking, a variation in number density of the support members can be adopted to accommodate for high stress regions where failure is most likely to occur. The number density can be varied in a number of different ways to generate either a graded or a hierarchical structure.
As alluded to above, an option for increasing the number density of support members is to include nodes with a multiplication factor of greater than one. A gradient in the number density of support members can then be generated by increasing the multiplication factor with increasing distance from the centre point 504. In this way, a “tree-like” structure results whereby the support members 502 (branches) become increasingly complex and finely distributed. Another option is to reduce the length of the support members 502, which decreases the distance between adjacent nodes, thereby increasing the local node density. By decreasing the length of the support members with increasing proximity to the outer surface 202 of the inner liner 200, a gradient in the number density of support members can be generated. Phrased differently, reducing the length of the support members 502 increases the number of nodes and therefore points for branching that can arise between the centre point 504 and the outer surface 202 of the inner liner 200. Another option is to increase the node density. Another option is to increase the angle between adjacent support members 502 that emerge from a given node 512. By varying this angle, the number of nodes points from the centre point 506 and outer surface 202 of the inner liner 200 increases because the continuous path that the support members 502 define is longer and more convoluted. These options (in the preceding paragraph) also increase the local support member density. In addition, the cross section (width and/or height) of the support member 502 may be varied to generate a gradient in the local support member density. This option can be used to generate a graded structure in a periodic internal network structure 204. In some examples, a gradient in local support member density may be generated by decreasing the cross-section of the support members 502 towards the outer surface 202 of the inner liner 200. Any of the above options for increasing the number and/or local support member density may be combined in any combination. For example, if the support member 502 cross section decreases proximal to the outer surface 202 of the inner liner 200, then the node density may accordingly be increased proximal to that surface 202.
It is proposed that a stress concentration profile, at the contact points between the support members 208 and the outer surface 202 of the inner liner 200, exists in the internal network structure 204, 500. Accordingly, in periodic internal network structures 204, failure is most likely to occur at these locations of stress concentration (the contact points with the outer surface 202 of the inner liner 200). Therefore, the interior regions of the internal network, at a lower overall stress, are less likely to fail. The interior regions of the internal network structure are therefore, at least partially, structurally redundant. By adopting a graded or hierarchical structure, some of this structural redundancy can be removed. This could lead to potential improvements in both volumetric and gravimetric energy densities of the pressure vessel 300. Improvements in volumetric and gravimetric energy densities of stored gas, such as compressed hydrogen are desirable in the field of mobile applications, such as for hydrogen powered vehicles. The graded or hierarchical structures defined above may be particularly effective in improving these energy densities.
In general, the stress-strain distribution may be a function of at least the following factors: the variation of the number density or volumetric density (the local density) of support members; the length of the support members 208, 502; the cross section (width and height) of the support members 208, 502; and the geometrical shape of those support members 208, 502 relative to the shape of the outer surface 202.
In summary, using a hierarchical or graded structure has at least the following possible advantages over a periodic structure such as that shown in
In other examples, the “virtual” stress-strain distribution may also be “flattened” at the outer edges of the internal network structure 204, 500 of the inner liner 200 by spatially varying the stiffness, or other mechanical property, of the material comprising the internal network structure 204, 500. Just as the number of support members 502 is increased towards the outer surface 202 of the inner liner 200 in
In
In
In
It is envisaged that other shapes of central portion 610, 620 are possible. For example, ellipsoids or variants of cylinders. Such generic variations in the shape of the central portion 610, 620 are all within the scope of the knowledge of the skilled person.
In
By using non-periodic internal network structure can accommodate stress concentrations, non-conventional shaped pressure vessels 700 are possible. These non-conventional shaped pressure vessels 700 may therefore be tailored to operating environment requirement and so, the pressure vessels 700 can be conformal. Conventional wisdom of the skilled person teaches against including “corner-like” 702 features, which act to introduce unacceptable stress concentrations that would lead to catastrophic failure. However, as described above, the non-periodic internal network structure can accommodate these stress concentrations and allow conformal pressure vessels, which may include pressure vessels with irregular shapes, for example to fit into the internal space of a vehicle. As described above, increasing the number density of support members 502 in proximity to these regions of high stress can accommodate for this stress concentration. Generally speaking, these stress concentrations are located around regions of lowest effective radius of curvature. As such, increasing the number density of support members 502 in proximity to regions of lower effective radius of curvature is a plausible route to mitigate the effects of stress concentrations. However, the stress concentrations may, as for example shown later in
By definition, a cuboid containing a cylindrical pressure vessel necessarily is larger in volume. An additional volume for containing pressurised gas is therefore available for cuboidal conformal pressure vessels 700. In practice, the corners of the pressure vessels 700 may be rounded to reduce stress concentrations, which reduces the overall increase in volume. However, the increase in volume afforded to cuboidal shaped conformal pressure vessels is not negligible. By way of example, a rectangular cuboid with cross section of nominal length 1 by 1, and nominal length of 3 is able to contain 38% more volume than the largest cylindrical pressure vessel, capped with hemispherical shells at each end, which fits inside that cuboid. These conformal pressure vessels therefore provide a plausible way to increase the gravimetric and volumetric energy densities of the pressure vessel in the technical field of energy storage.
The internal network structure 204, 500 may also improve safety in the case of catastrophic failure, e.g., during a vehicle crash. In conventional pressure vessels 100, if the outer skin 104 is compromised, the pressurised gas is rapidly released from the vessel in an explosion. This rapid release generates very large forces, which act on the pressure vessel, often causing the pressure vessel to become mobile. In effect, the pressure vessel acts as a ballistic. However, in a pressure vessel with an internal network structure 204, 500, the release rate of the pressurised gas is reduced because the volume contained within the internal network structure is interconnected and defines a convoluted path, acting to reduce the release rate of the pressurised gas. In this way, the gas is released more slowly from the compromised pressure vessel. By increasing the overall time in which gas is released, the overall force generated in this process can be decreased and the pressure vessel is less likely to cause damage. Furthermore, in catastrophic failure events, the fracture mechanism in a conventional cylindrical pressure vessel differs from pressure vessels 300, 700 described in this application. In conventional cylindrical pressure vessels, the fracture surface in the outer skin 104 is usually directly along the longitudinal axis of the vessel, and propagation of the fracture surface is rapid. This occurs in a single explosive event. Conversely, in a pressure vessel with an inner liner 200 comprising an internal network structure 204, 500, failure occurs in more controller manner—in sequential stages, where gas is released. Just as a car crumple zone dissipates energy by plastic deformation, the internal network structure 204, 500 acts to dissipate some of the stored elastic/plastic energy in the outer skin 302 after initial fracture occurs. In this way, fracture propagation is slower (possibly even stable, as the pressure in the vessel is released) and the energy released per sequential fracture “event” is lower than in the conventional case. This therefore provides a further safety improvement of the inner liner of the present invention.
Conformal pressure vessels have at least the following advantages over conventional cylindrical or spherical pressure vessels:
Generally speaking, the internal network structure in the conformal pressure vessel 700 is graded. In other examples, the grading may be in discrete steps, defining a hierarchical structure. The number density, angle, width, length and geometry of the support members 502 in regions 703 proximal to the corner-like 702 features is different to that of regions 704 more distal from such features 702. It is envisaged that a third region between these regions 702, 703 could be used to ensure that these regions 702, 703 “match up” if necessary. These regions may define the hierarchical levels of the hierarchical system. In some examples, there may be a continuous variation in the aforementioned properties across the regions 702, 703. In other examples, the aforementioned properties are constant in regions 702, 703 and a connecting region between these regions 702, 703 connects the two together which comprises the continuous variation instead.
In some examples, the location of the roots 612, 622 are disposed on the central portion disc/sphere 611, 621 to direct the hierarchical non-periodic structure towards the region 702 of local higher stress/strain.
It is envisaged that these regions 703, 704 are defined by stress thresholds. That is, the stress distribution in a “virtual” periodic structure 202 for a given gauge pressure can be calculated. Portions of the “virtual” periodic structure that are above a stress greater than a given threshold define region 703. In some examples, the stress may be the Von Mises stress or Tresca stress and the threshold is the yield stress of the material comprising the “virtual” periodic structure 202. Furthermore, if the stress is below a second threshold (e.g., a predetermined fraction of the yield stress), then this may define another region. In some examples, the stress in region 704 is lower than the first threshold. In other examples, the stress in region 704 is lower than the first and second threshold. According to these defined regions of stress, the structure of the non-periodic structure 500 can be modified to better accommodate for this higher stress. For example, the inventors envisage that the non-periodic structure 500 can be adopted to achieve this effect. The exact form and structure of the non-periodic structure 500 can be optimised by iteratively calculating these stress regions 703, 704 and adapting the structure accordingly. It is envisaged that the optimisation will be to be minimise the mass or volume for a given external shape and gauge pressure.
Referring to
It will be evident to the skilled person that there are potentially an infinite number of possible internal network structures 204 and that the “actual” design that will be accommodated is a complex function depending on the operating conditions, environment, manufacturing route and the commercial cost of these routes. It is impractical to cover all of these in writing because they are necessarily variable. The general purpose and effect of the internal network structure 204 has been described in detail above, and the skilled person, in view of this document, would appreciate that the specific designs shown are not limiting.
The internal network structure 800, 900 are modifications of the internal network structure 500. In these non-periodic structures, the support member density increases in regions proximal to the outer surface 202 of the inner liner 200. In internal network structures 800, 900 the support member density increases by varying the length of the support member 502. In this way, convoluted, interconnected structures can be generated. The internal network structure 900, in particular, illustrates the effect of reducing the length of the support member 502 on the local density of the support members. As shown in these structures 800, 900, the local density of the support members increases with increasing proximity to the outer surface 202 of the inner liner 200. Or equivalently, increases with distance from the centre point 504 of the inner liner.
In exemplary internal network structure 1000 the support members 502 are reinforced at each node 512. The motivation behind the reinforcements at each node 512 is to prevent premature failure at these nodes 512. It is evident that each node connects one support member 502 of a given stress state with another 502, and therefore the nodes 512 may be under a more complex and large overall stress state (Von Mises stress). By reinforcing the support members 502 in the internal network structure 1000, larger stresses can be accommodated by these nodes 512. Some of the nodes 512 may be in contact with the outer surface 202 of the inner liner 200. In some examples, the reinforcement may comprise varying the thickness and/or width of the support members can be adopted in any of the other internal network structure 204, 500, 800, 900 described above. In other examples, the material comprising the reinforced node regions may be stiffer and/or have a larger yield stress than the remainder of the support member 502. The material of the reinforced node region may therefore be different, or, may comprise a different fraction of reinforcing filler in these regions.
The internal network structure 1100 is an alternative example to the network structures 204, 502, 800, 900, 1000, 1200. In this example, the interconnected volumes 206 are defined by a series of “bubbles” 1101, or interconnected holes in an internal body 1102, rather than being defined by the support members 502. The bubbles 1101 are formed within an internal body 1102. The internal body 1102 can replace the internal network structure 204 in
The bubble internal network structures 1100 have one or more of the following characteristics:
In some examples, the internal network structure 1100 may comprise a foam-like structure. The foam-like structure may preferably be open-celled. That is, each of the one or more bubbles 1101 in the internal network structure 1100 are interconnected.
The internal network structure 1200 is another exemplary support structure design. The internal network structure 1200 comprises one or more radially extending support members 502, which comprises one or more holes 1201. These holes 1201 ensure that the volume of gas contained between the support members 502 are interconnected. In some examples, the radially extending support members 502 may be a fin, plate, strut or panel. Any of the central support structures of
In any of the internal network structures 204, 500, 800, 900, 1000 described above, an optimised structure can be determined using at least one or more of the following procedural steps. The optimised structure may maximise the gravimetric energy density, volumetric energy density or the mass of the pressure vessel for a given gauge pressure. In the example below an iterative method is adopted for minimising the mass of an optimised internal network structure.
The invention may be summarised by the following numbered clauses:
As the local number density of support members may be controllable, the number of contact points on the surface of the inner liner is controllable. The number of contact points may determine the magnitude of the stress concentration which forms at these contact points for a given gauge pressure.
The present invention further relates to a sectional inner liner, and sectional pressure vessel comprising the sectional inner liner.
The overall size and shape of the sectional pressure vessel 100 may be varied according to operation requirements. In general, the size of the sectional pressure vessel 100 may be in the range 50 to 2000 mm and the shape of the sectional pressure vessel 100 can be, for example, configured to fit an arbitrary space in a vehicle, or, configured in shape to allow stackable arrangements. The sectional pressure vessel 100 can therefore be described as a “conformal pressure vessel”.
The sectional pressure vessel 1300 comprises an outer skin 102, and a plurality of interlocking inner liner sections 1302, 1304, 1306 that, when connected, form an outer surface 202 of the sectional inner liner 1300 disposed inside the outer skin 102. There are three types of inner liner section: a central section 1302; a cap section 1306; and an intermediate section 1304.
Each of these inner liner sections 1302, 1304, 1306 comprises at least one interlocking portion 1308, 1310, which is configured to engage with a complementary interlocking portion 1308, 1310 of an adjacent inner liner section 1302, 1304, 1306, such that inner liner sections 1302, 1304, 1306 can be mated with one another. In an example, the complementary interlocking portions 1308, 1310 respectively comprise complimentary collars/flanges portions that interlock. Other examples include tongue and groove, or teeth arrangements, or any other latching mechanism, as the skilled person would appreciate. More generally, the interlocking portions 1308, 1310 can either be described as “male” type or “female” type.
The central and intermediate inner liner sections 1302, 1304 comprise two opposing open ends, whereas the cap section 1306 comprises an open-end and a closed-end. The closed-end defines one of the sectional inner liner faces 1312. The central liner section 1302 may comprise the same type of interlocking portion 1308, 1310 (i.e., male-male or female-female) at each of its open-ends. The intermediate inner liner section 1304 comprises opposite (or complementary) types of interlocking portion 1308, 1310 (i.e., female-male or male-female) at each of its open-ends. The cap section 1306 comprise a single interlocking portion 1308, 1310 (i.e., male or female) located at its open-end. Hence, a sectional inner liner 1300 may be constructed from a central inner section 1302, two cap sections 1306 and, optionally, one or more intermediate inner liner sections 1304.
Each inner liner section 1302, 1304, 1306 comprises an internal network structure, which may be any of the structures shown in
In another example (not shown), the sectional inner liner 1300 comprises two end sections 1306 without any intermediate or central inner liner section 1302, 1304. In this arrangement, the sectional inner liner 1300 resembles a split “clamshell”. The split line between each end section 1306 can either be parallel the longitudinal axis of the inner liner or orthogonal to it. Optionally, each end section 1306 comprises an internal network structure described in more detail below with reference to
In
Compared to conventional cylindrical or spherical pressure vessel designs, non-circular cross-sections (such as the rounded-square cross-section shown in
Referring now to
In the example shown in
In
The second set of support members 1516 therefore constrain the first support members 1504, thereby reducing their tendency to bow outwards (in a similar way to shown in
On the other hand, including further support members to the internal network structures reduces the total volume within which fluid may be stored under pressure. There is an optimisation to the number of support member sets, which maximises the gravimetric efficiency of the sectional pressure vessel.
In the example shown in
The fourth and fifth set of support members 1522, 1524 provide radial support to the second and first set of support members respectively. As has already been noted, the first 1504 and second support members 1506a, 1506b have a tendency to bow outwards (although this tendency is reduced by the second set of support members and third set of support members respectively). For the first and second support members 1504, 1506a, 1506b to bow outwardly, the radially extending support members 1512, 1514 must be compressed. Hence the fourth and fifth set of support members 1522, 1524 constrain the second and first set of support members respectively to reduce the maximum stress in the first and second set of support members 1514, 1516. In this way, the stress and strain are distributed more evenly over a larger area.
Referring now to
In
The (sectional) inner liner 200, 1300 may comprise a thermoplastic or thermoset polymer. For example, high density polyethylene (HDPE), polyaryletherketone (PAEK), polyether ether ketone (PEEK), nylon (e.g., PA6, PA12), an epoxy, or a blend thereof.
In some examples, the internal network structure 204, 500, 800, 900, 1000, 1100, 1200, 1500, 1510, 1520 of the (sectional) inner liner 200, 1300 may comprise additives. These additives, or fillers, may be functional and/or structural. In an example, nano-fillers such as graphene, carbon fibre (e.g., in the form of short, “chopped” fibres), and/or carbon nano-tubes are added to improve the stiffness and yield stress of the internal structure 204, 500, 800, 900, 1000, 1100, 1200, 1500, 1510, 1520. In some examples, the internal network structure may comprise additives of lightweight metals such as Aluminium, or aluminium alloys, titanium or titanium alloys, or ceramics e.g. alumina. In this way, the internal network structure may comprise a polymer-metal composite or a polymer-ceramic composite. As described above, in some examples, a gradient in stiffness can be engineered by varying the stiffness of the support members 208, 502. One option for generating this varying stiffness is to vary the volume or mass fraction of this structural additive.
In other examples, the internal network structure 204, 500, 1500, 1510, 1520 may be a lightweight metal or ceramic. A non-exhaustive list of possible metals includes aluminium and aluminium alloys. A non-exhaustive list of possible ceramics includes alumina.
In other examples, hydrogen absorbing, or adsorbing additives can be added to the internal network structure 204, 500, 800, 900, 1000, 1100, 1200, 1500, 1510, 1520. In this way, the effective volume 206 for containing pressurised gas can be increased. In response to a pressure drop, these hydrogen absorbing/adsorbing additives are configured to controllably release hydrogen.
In some examples, the outer surface 202 of the (sectional) inner liner 200, 1300 also comprises structural additives. It is envisaged that the outer surface 202 of the inner liner 200 is thin and therefore preferably the additive does not affect the permeability of the outer surface 202 of the inner liner 200 to the contained gas.
In examples where the pressurised gas is hydrogen, the material comprising the (sectional) inner liner 200, 1300 is not susceptible to hydrogen embrittlement. More generally, the material of choice may depend on a combination of additional factors, such as: material cost, density, stiffness and yield stress of the material. The use of an Ashby chart for selecting a material based on the optimisation of specific stiffness or equivalent, is known to the skilled person.
In the bubble or foam internal network structure 1100, the internal body 1102 may comprise a foamed thermoset, or a metal foam, or a ceramic foam. The thermoset may be an epoxy. The metal may be a lightweight alloy of aluminium or titanium. The ceramic may be alumina, zirconia, or other lightweight ceramic. In the above examples, complimentary foaming agents for each material may be included to facilitate the foaming process.
The outer skin 302 of the pressure vessel 300, 700 may comprise a filament or tape wound thermoset fibre reinforced composite (FRC), compression moulded FRC or a resin infusion or vacuum assisted resin transfer moulding (VARTM) of a thermoset in a carbon fibre pack. The filament or tape may comprise carbon fibre (e.g., pitch-based carbon fibre, or T1000), aramid or boron fibres. The resins may comprises any of epoxies, cyanate esters, polyurethane, polyester, vinyl ester, phenolics, furans or polyamides.
The mode of manufacture of the pressure vessel 200, 700 comprises four main steps. The sectional pressure vessel 1300 further comprises a joining step, as set out below.
i) Structural Optimisation
The first step is simulation-based optimisation of the internal network structure to minimise the mass for a given shape and internal operating gauge pressure. The optimisation may be based on iterative techniques. Other forms of optimisation are possible, e.g., gravimetric and volumetric energy densities. Equivalently, as set out in detail above, a structurally optimised internal network structure improves redistribution of stress from areas of “higher” stress in the internal network structure to areas of “lower” stress, thereby homogenising the stress in the inner liner elements to avoid premature failure at stress concentrations. The stress imposed in the overwrap and surface of the inner liner are thereby reduced.
ii) Manufacture of Inner Liner 200 or Inner Liner Sections 1302, 1304, 1306
In the second step, the optimised inner liner 200 (with internal network structure 204, 500, 800, 900, 1000, 1100, 1200) may be manufactured by a method of additive manufacturing. In other examples, the method of manufacture may be a conventional process such as net-shape forming. In other examples, the method of manufacture may be a subtractive method. In some of these examples, the method of manufacture may comprise a foaming agent.
The inner liner sections 1302, 1304, 1306 may be manufactured by additive manufacturing, injection moulding or casting. One or more valve ports may be added to each inner liner end section 1306, using manufacturing techniques known to the skilled person.
The exact choice of additive manufacturing is at least partially dependent on the material selection of the inner liner 200. A non-exhaustive list includes: stereolithography methods (Vat photopolymerisation), material jetting, binder jetting, powder bed fusion (Direct metal laser sintering (DMLS), selective laser sintering (SLS), selective laser melting (SLM), multi jet fusion (MJF), electron beam melting (EBM)), filament extrusion processes (fused deposition modelling (FDM). A non-exhaustive list of net-shaped manufacturing methods includes injection moulding, lost-wax casting or investment casting.
In some examples, the internal network structure may be manufactured using injection moulding. This mode of manufacture may be particularly advantageous for large internal network structures 204, 500, 800, 900, 1000, 1200 where additive manufacturing routes are impractical, or time consuming. A large internal network structure 204, 500, 800, 900, 1000, 1200 is one comprising dimensions greater than 500 mm. For example, in FDM, the size of the component is limited by the range of the rastering device and the size of the heated bed, which is typically less than 500 mm. The sectional inner liner sections 1302, 1304, 1306 may also be produced by injection moulding. In particular, using split moulding techniques.
In some examples, the intermediate and/or central inner liner sections may be formed by extrusion. The interlocking portions 1308, 1310 may then be produced by any subtractive manufacturing technique known to the skilled person.
The internal network structures 1200 may be produced by selectively removing material, rather than through additive manufacturing routes. In some examples, the internal network structure 1200 may be manufactured by drilling holes in plates 502 which are produced by an injection moulding process. Such subtractive manufacturing methods include CNC (computer numeric control) of drills, lathes, and the like.
In some examples, the internal network structure 1100 may form a foam. The foam may be manufactured by a foaming process route, which results in an open celled structure. The foaming process route may include a foaming agent. For polymeric materials, the foaming agent may be a chemical agent. The chemical agent may be used both to synthesis the polymer and to generate gas as a by-product in the reaction. In other examples, the foaming agent may comprise an inert gas such as Argon. In the latter, the local flow rate of the gas may be controlled spatially to generate regions of increasing or decreasing bubble density, such that the foam density varies from low density, or larger bubble diameters, at the core and decreases towards the outer surface 202 of the inner liner 200 to produce progressively smaller bubbles. The foaming agents may be included in combination with any applicable additive manufacturing route. Furthermore, the foam may be generated in a moulding process and therefore may also form a preparation step in a subtractive manufacturing method.
iii) Joining the Inner Liner Section to Form a Sectional Inner Liner
In the sectional inner liner approach, the manufactured inner liner sections 1302, 1304, 1306 are joined by mating complementary interlocking portions 1308, 1310 and sealing the sealing surface 1702 using adhesive bonding or welding. Adhesive bonding is applicable to both polymer-based and metal-based inner liner sections 202, 204, 206, 400. Welding is applicable for metallic inner liner sections 202, 204, 206, 400. Other joining methods known to the skilled person are also applicable.
iv) Applying Outer Skin (the Overwrap) 302
In the third step, the outer skin 302 of the inner liner 200 or sectional inner liner is overwrapped with a carbon fibre reinforced resin composite, or other reinforcing fibre. In some examples, the carbon fibre reinforced resin is applied using a filament winding method. The wind angle and tension can be controlled using appropriate machinery known to the skilled person. Alternatively, the outer skin 302 may be applied by braiding the filaments, infusing the braid with resin and curing under vacuum. Automated fibre placement may also be used to apply the overwrap. Options include: filament wound dry fibre/tape preform for resin impregnation, or pre-impregnated fibre/tape towpreg.
In other examples, pre-prepared woven carbon fibre cloth can be applied and bonded with the outer surface 202 of the (sectional) inner liner 200, 1300 using a resin infusion process or a low temperature compression moulding process. In the latter, an autoclave is used to bond two pre-impregnated skins of the pre-prepared woven carbon fibre cloth together in a curing process. In some examples, the carbon fibre cloth may be replaced with any of the filament or tape materials described above.
An advantage of the sectional inner liner approach is that the length of the sectional inner liner 1300 can be tuned according to operational requirements, and is not (unlike conventional inner liner) limited to the physical size of manufacturing equipment. Furthermore, for casting and injection moulding routes, only a finite number of moulds are required to produce an inner liner 1300 of arbitrary length.
v) Gas Valve Integration
During manufacture of the inner liner by injection moulding or additive manufacturing, a metallic valve port, such as a polar boss for a gas inlet/outlet, may be included by over-moulding or insert moulding.
One or more valves can be integrated into the end sections 1306 of the pressure vessel 300, 700, 1300. In the sectional approach, the one or more valves are optionally moulded-in with the end sections 1306 during injection moulding. Alternatively, the one or more valves can be fitted prior to or after the overwrapping step stage, using methods known to the skilled person.
The contained fluid in the pressure vessel may be hydrogen, nitrogen, oxygen, methane, natural gas, ammonia, biogas, liquid hydrogen, liquid nitrogen, liquid nitrogen, liquid natural gas, liquid ammonia, liquid methane, or liquid biogas.
The invention has been described in detail with reference to the exemplary embodiments; modifications may be made without departing from the scope of the invention as defined by the claims. Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014170.1 | Sep 2020 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/074865 | 9/9/2021 | WO |
