Patent Application
20240183482
The present invention relates to a thermal insulation structure and a structure including the thermal insulation structure.
Since a propellant tank for storing a cryogenic fluid such as a national flagship launch system is required to be lightweight, a foam thermal insulation material is used as a thermal insulation material surrounding the propellant tank. However, the foam thermal insulation material has a low thermal insulation performance, and has a problem in that an evaporation rate of a cryogenic propellant such as liquid hydrogen cannot be suppressed. On the other hand, a cryogenic storage tank on the ground in which the evaporation rate is suppressed has a structure in which multilayer insulation (MLI) is provided in a vacuum double container.
In the conventional MLI, thermal insulation performance is secured by stacking a plurality of thermal insulation films in layers to lessen heat transfer due to radiation, and reducing a contact portion between the thermal insulation films with a nonwoven fabric or a mesh to reduce heat transfer due to heat conduction. For example, in the technique of Patent Document 1, a thick thermal insulation film is adopted to maintain the structure in order to maintain the interval between the thermal insulation films. In addition, Patent Document 2 discloses an MLI in which heat conduction is reduced by installing a spacer instead of a nonwoven fabric or a mesh.
Patent Document 3 discloses a technique related to a lightweight thermal insulation material for cryogenic storage intended for use in space. In the technique of Patent Document 3, the MLI is kept in a vacuum state even in the atmosphere by covering the thermal insulation material with a vacuum pack. In this technique, when moving to a vacuum environment such as in orbit, external pressure such as atmospheric pressure disappears, and a spring mechanism installed in the MLI expands to reduce heat conduction, by which thermal insulation performance is further improved.
However, in the MLI using a nonwoven fabric or a mesh as disclosed in Patent Document 1 or the MLI using a spacer as disclosed in Patent Document 2, there is a problem in that the contact state of the thermal insulation film changes according to an error at the time of construction, an acceleration environment, or an operation situation of the propellant tank, and the thermal insulation performance cannot be managed. In a case where the thermal insulation performance is low, it is conceivable to increase the total number of thermal insulation films (the number of layers) of MLI as a countermeasure, but when the total number of thermal insulation films is increased, MLI becomes thicker by an amount corresponding to the total number of thermal insulation films, by which a force to press the layers is generated in the bent portion due to a difference between the inside and the outside of the layer, and the thermal insulation performance is deteriorated. Furthermore, the possibility of contact between the thermal insulation films increases due to the increased weight load of the thermal insulation films. Therefore, increasing the total number of MLIs is not a direct countermeasure against performance deterioration due to contact between the thermal insulation films particularly in an environment receiving acceleration. In addition, the structure as disclosed in Patent Document 3 is a mechanism that partially breaks a component under atmospheric pressure, and focuses on thermal insulation performance when a pressurized environment is shifted to a vacuum environment.
In view of the above circumstances, an object of the present invention is to provide a lightweight thermal insulation structure having high thermal insulation performance, and a structure including the thermal insulation structure.
When the MLI is used as a thermal insulation material of a cryogenic propellant tank of a space transportation vehicle, a load environment changes due to its own weight due to acceleration such as engine thrust, or due to expansion or contraction of the tank due to pressurization or a change in surface temperature. At these times, the present inventors have focused on the fact that since the interval between the thermal insulation films held by a nonwoven fabric, a mesh, or a spacer is narrowed, contact occurs between the thermal insulation films, and heat transfer due to heat conduction increases.
As a result, the present inventors have found that it is possible to realize a lightweight thermal insulation structure having high thermal insulation performance by supporting the thermal insulation film by an elastically deformable support member in a state where tension is applied to the thermal insulation film forming the MLI. The present invention has been made based on such findings, and the gist is as follows.
(1) A thermal insulation structure according to one aspect of the present invention includes:
(2) In the thermal insulation structure according to (1),
(3) In the thermal insulation structure according to (1) or (2),
(4) In the thermal insulation structure according to any one of (1) to (3),
(5) In the thermal insulation structure according to any one of (1) to (4),
(6) In the thermal insulation structure according to any one of (1) to (5),
(7) In the thermal insulation structure according to any one of (1) to (6),
(8) A structure according to one aspect of the present invention includes: a thermal insulation structure according to any one of (1) to (7); and a base body.
According to the present invention, it is possible to provide a lightweight thermal insulation structure having high thermal insulation performance, and a structure including the thermal insulation structure.
Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited only to the configuration disclosed in the present embodiments, and various modifications can be made without departing from the gist of the present invention. In the following description, specific numerical values and materials may be exemplified, but other numerical values and materials may be applied as long as the effect of the present invention can be obtained. In addition, components of the following embodiments can be combined with each other. In addition, the numerical limit range in the following embodiments includes a lower limit value and an upper limit value. A numerical value indicated as “more than” or “less than” is not included in the numerical range.
The thermal insulation film 200 is supported by the support member 300 in a state where tension is applied in an in-plane direction of the thermal insulation film 200.
The thermal insulation film 200 is a low-emissivity film capable of suppressing heat transfer due to radiation. The thermal insulation film 200 is not particularly limited, but is formed by depositing a metal such as aluminum, gold, germanium, or conductive indium tin oxide (ITO) on a resin film such as polyimide or polyester. The thermal insulation film 200 is not limited to this, and can be made of any other suitable material as long as it can withstand the tension applied to the thermal insulation film 200. The thickness of the thermal insulation film 200 is preferably 6 μm or more, and more preferably 12 μm or more from the viewpoint of preventing damage to the thermal insulation film 200 such as elongation and breakage due to application of tension. In addition, the thickness of the thermal insulation film 200 is preferably 200 μm or less, and more preferably 25 μm or less, from the viewpoint of realizing a lightweight structure and suppressing the weight of the thermal insulation film 200. The thickness of the thermal insulation film 200 is an average value (arithmetic average value) of thicknesses measured at four arbitrary points by a dial gauge.
The thermal insulation film 200 is laminated with the support member 300 to be described later interposed between. In the example of
The thermal insulation film 200 may have, for example, a triangular shape as illustrated in
Next, the support member 300 will be described. As illustrated in
The first portion 310 has the upper surface 311, a lower surface 312 provided on the opposite side of the upper surface 311, and a side portion 313 connecting the upper surface 311 and the lower surface 312. The upper surface 311 is a surface in contact with the thermal insulation film 200 when the thermal insulation structure 100 is formed. The lower surface 312 faces an upper surface 321 of the second portion 320 to be described later.
The convex portion 314 is provided on the upper surface 311 of the first portion 310. The convex portion 314 is inserted into hole portion 210 of the thermal insulation film 200. In addition, the convex portion 314 may be engaged with a concave portion (not illustrated) provided in the second portion 320 to be described later.
The second portion 320 has an upper surface 321, a lower surface 322 provided on the opposite side of the upper surface 321, and a side portion 323 connecting the upper surface 321 and the lower surface 322. The lower surface 322 is a surface in contact with the thermal insulation film 200 when the thermal insulation structure 100 is formed. The upper surface 321 faces the lower surface 312 of the first portion 310.
The second portion 320 may be provided with a concave portion (not illustrated) that engages with the convex portion 314 provided on the upper surface 311 of the first portion 310. Thus, the support members 300 can be coupled to each other in the direction along the axis c of the support member 300. The convex portion 314 may be provided with a protruding portion 314a protruding in the outer diameter direction of the convex portion 314. In a case where the concave portion provided in the second portion 320 penetrates from the upper surface 321 toward the lower surface 322 of the second portion 320, the protruding portion 314a may be configured to be in contact with the upper surface 321 of the second portion 320 of the support member 300 to be coupled in a state where the convex portion 314 is inserted into the concave portion. In addition, the concave portion provided in the second portion 320 may be provided with a recess portion corresponding to the protruding portion 314a, and the protruding portion 314a and the recess portion may be configured to be engaged with each other.
The third portion 330 connects the first portion 310 and the second portion 320. In the example of
In the support member 300, the length of the third portion 330 in the extending direction thereof is longer than the distance between the first portion 310 and the second portion 320. Here, the distance between the first portion 310 and the second portion 320 is a distance D between the lower surface 312 of the first portion 310 and the upper surface 321 of the second portion 320 in a direction parallel to the axis c as illustrated in
In the example of
The support member 300 is elastically deformable in a direction intersecting a surface of the thermal insulation film 200. Thus, the thermal insulation film 200 can be supported by the support member 300 in a state where tension is applied in an in-plane direction of the thermal insulation film 200. More specifically, since the support member 300 is elastically deformable in a direction parallel to axis c, the support member 300 is elastically deformable in a direction intersecting a surface of the thermal insulation film 200 when the thermal insulation structure 100 is formed. Since the support member 300 has a structure in which the first portion 310 and the second portion 320 are connected by the third portion 330 as described above, in a case where a compressive force in a direction parallel to the axis c is received, a part or the whole of the third portion 330 is deformed to reduce the interval between the first portion 310 and the second portion 320, and the support member 300 as a whole contracts in a direction parallel to the axis c. In addition, in a case where a tensile force is applied in a direction parallel to the axis c, a part or the whole of the third portion 330 is deformed, by which the interval between the first portion 310 and the second portion 320 increases, and the support member 300 as a whole extends in a direction parallel to the axis c. In addition, when these compressive forces or tensile forces are no longer applied, the restoring force of the third portion 330 returns the interval between the first portion 310 and the second portion 320 to the initial state.
The height of the support member 300 in the direction parallel to the axis c is preferably 1 mm or more because it is necessary and sufficient to prevent contact between the thermal insulation films 200. In addition, the height is preferably 5 mm or less since this allows the support member 300 to easily maintain a shape parallel to the axis c. In addition, an outer diameter of the support member 300 on a plane orthogonal to axis c is preferably 3 mm to 20 mm in order to ensure a contact surface sufficient for the thermal insulation film 200 and the support member 300 to transmit a compressive force or a tensile force. The height of the support member 300 means a distance h between the upper surface 311 of the first portion 310 and the lower surface 322 of the second portion 320 in a direction parallel to the axis c as illustrated in
The support member 300 is preferably made of a resin material such as polyether ether ketone (PEEK), polycarbonate (PC), polyethylene terephthalate (PET), or polyimide (PI). For example, the support member 300 is manufactured by injection molding raw materials of these resin materials. The configuration of the support member 300 is not limited to this, and may be made of any other appropriate material. Polyether ether ketone is the most preferable material as the support member 300 from the viewpoints of high heat resistance, low temperature embrittlement resistance, a small amount of outgas in a vacuum, and ultraviolet resistance required in a thermal insulation material for space transportation vehicles.
As illustrated in
In order to efficiently transmit the force applied to the support member 300 to the base body 10, the support member 300 is preferably attached to the base body 10 such that a perpendicular line of the surface 11 of the base body 10 at a position where the support member 300 is attached coincides with the axis c of the support member 300. Therefore, in a case where the surface 11 of the base body 10 is a curved surface or a spherical surface, the axis c of the support member 300 is inclined with respect to the axis c of the adjacent support member 300.
In the support member 300, as illustrated in
The shape of the base body 10 is not particularly limited, but for example, a part of it may be a curved surface or a spherical surface. The base body 10 is, for example, a propellant tank for storing a cryogenic fluid such as a national flagship launch system, a structure such as an artificial satellite, or an inner wall of a vacuum tank on the ground. Since the thermal insulation structure 100 according to the present embodiment has high thermal insulation performance and is lightweight, the thermal insulation structure 100 according to the present embodiment can be preferably applied to these base bodies.
In order to apply tension to the thermal insulation film 200, when the thermal insulation structure 100 is installed on the base body 10, the support member 300 is compressed or stretched in a direction parallel to the axis c. In order to realize such a state, the interval between the hole portions 210 of the thermal insulation film 200 as described above is appropriately designed. For example, in a case where the thermal insulation structure 100 according to the present embodiment is provided at a position where the surface 11 of the base body 10 becomes convex toward the outside of the base body 10, the support member 300 is contracted as compared with the initial state by designing the distance between the adjacent hole portions 210 to be small. When the height of the support member 300 in the direction parallel to the axis c in the initial state is h and the height of the support member 300 in the contracted state is hc, h>hc is satisfied. In this case, tension is applied in the in-plane direction of the thermal insulation film 200 by a restoring force of the support member 300 to return to the initial state. Specifically, assuming that an elastic coefficient in a direction parallel to the axis c of the support member 300 is k, in a state where the support member 300 is contracted, a stress of σc=k (h−hc) is generated in a direction parallel to the axis c of the support member 300 and in which the first portion 310 and the second portion 320 are separated from each other. Since the axis c of the support member 300 is inclined with respect to the axis c of the adjacent support member 300, a component of the stress σc acts in the in-plane direction of the thermal insulation film 200, and tension is applied to the thermal insulation film 200 between the adjacent support members 300.
In addition, in a case where the thermal insulation structure 100 according to the present embodiment is provided at a position where the surface 11 of the base body 10 becomes concave toward the inside of the base body 10, the support member 300 is elongated as compared with the initial state by designing the distance between the adjacent hole portions 210 to be small. When the height of the support member 300 in the initial state is h and the height of the support member 300 in the elongated state is he, h>he is satisfied. In this case, tension is applied in the in-plane direction of the thermal insulation film 200 by the restoring force of the support member 300 to return to the initial state. Specifically, assuming that an elastic coefficient in a direction parallel to the axis c of the support member 300 is k, in a state where the support member 300 is elongated, a stress of σe=k (he−h) is generated in a direction parallel to the axis c of the support member 300 and in which the first portion 310 and the second portion 320 approach each other. Since the axis c of the support member 300 is inclined with respect to the axis c of the adjacent support member 300, a component of the stress σe acts in the in-plane direction of the thermal insulation film 200, and tension is applied to the thermal insulation film 200 between the adjacent support members 300.
Note that the position of the hole portion 210 is designed on condition that the thermal insulation structure 100 and the base body 10 are at room temperature)(25° ° C. under atmospheric pressure. For example, the arrangement of the support member 300 and the length of compression or stretching are appropriately designed such that the interval between the thermal insulation films 200 can be kept in a state of not being in contact with each other, and the arrangement of the thermal insulation film 200 and the hole portions 210 of the thermal insulation film 200 is determined in consideration of the temperature at the time of using each thermal insulation film layer, the temperature difference from room temperature, the deformation due to degassing in a vacuum state, the dimensional change when exposed to high temperature, and the like.
From the above, the thermal insulation structure 100 according to the present embodiment can be preferably used for the base body 10 having a part or the whole formed in a curved surface or a spherical surface. Note that the thermal insulation structure 100 may be installed in a sealed space in a vacuum state.
In the thermal insulation structure 100 according to the present embodiment, since the thermal insulation film 200 is supported by the support member 300 in a state where tension is applied in the in-plane direction of the thermal insulation film 200, deflection of the thermal insulation film 200 is suppressed. Therefore, contact between the laminated thermal insulation films 200 can be suppressed, and thermal insulation performance can be improved. In addition, since the length in the extending direction of the third portion 330 is longer than the distance between the first portion 310 and the second portion 320, the route through which heat is transferred in the support member 300 becomes longer, the heat conduction amount of the support member 300 can be reduced, and the thermal insulation performance of the thermal insulation structure 100 can be improved.
In addition, in the thermal insulation structure 100 according to the present embodiment, since the contact between the laminated thermal insulation films 200 can be suppressed only by the support member 300, a member such as a nonwoven fabric or a mesh is unnecessary, and the mass of the thermal insulation structure 100 can be reduced. In addition, since the support member 300 is elastically deformable in the direction intersecting the surface of the thermal insulation film 200, even in a case where the thermal insulation film 200 having a small thickness is used, an appropriate tension can be applied to the thermal insulation film 200, and the mass of the thermal insulation structure 100 can be reduced.
In a case where the thermal insulation structure 100 according to the above embodiment is applied to a propellant tank of a national flagship launch system, the outer surface has a high temperature due to the influence of sunlight and the like, and the inner surface has a relatively low temperature due to a fluid in the propellant tank. The fluid temperature in the propellant tank changes due to the remaining amount of the propellant and the pressure in the tank. Therefore, the temperature of the propellant tank itself or the thermal insulation structure 100 changes, and thermal distortion corresponding to each temperature difference occurs. In addition, in a case where the pressure in the propellant tank is changed, the tank expands. By further providing the following structure, it is possible to preferably maintain the interval between the laminated thermal insulation films 200 against such a change in temperature environment and a dimensional change of the propellant tank (base body).
In the thermal insulation structure 100 according to the above embodiment, at least a part of the thermal insulation film 200 may be bent or a cut portion may be provided in the thermal insulation film 200 such that the thermal insulation film 200 can be extended between the support members 300.
The state in which at least a part of the thermal insulation film 200 is bent means that a part of the thermal insulation film 200 is bent in the in-plane direction as illustrated in
In addition, as illustrated in
The bent portion 230 or the cut portion 250 is provided between the adjacent support members 300. The number of the bent portions 230 or the cut portions 250 is not particularly limited, but it is more preferable that the bent portions 230 or the cut portions 250 be provided on a line segment connecting the support member 300 and the support member 300. It is not necessary to provide the bent portion 230 or the cut portion 250 in the entire range of the thermal insulation structure 100, and it is preferable to appropriately set the arrangement of the bent portion 230 or the cut portion 250.
In the thermal insulation structure 100 according to the above embodiment, as illustrated in
In the thermal insulation structure according to the above embodiment, a net spacer or an embossed film may be further provided between the thermal insulation films 200. Since the embossed film is superior in rigidity to a normal flat film, the arrangement interval of the support members 300 can be lengthened, and it is effective for both reducing the influence of contact between the thermal insulation films 200 and preventing contact. To reduce costs, the use of embossed films may be partial.
In the thermal insulation structure according to the above embodiment, a conductor layer may be provided on the surface of the support member 300. Such a conductor layer may be formed by nickel plating or aluminum vapor deposition. Thus, it is possible to reduce a potential difference between the thermal insulation films 200 (between the thermal insulation film layers) to be laminated, and it is possible to satisfy a bonding requirement required for a spacecraft. In addition, the emissivity of the surface of the support member 300 can be reduced, and thermal insulation performance can be further improved by suppressing radiation heat transfer from the surface of the support member 300. In order to reduce the cost, the above conductor layer may be provided only on some of the support members 300.
Next, an example of the present invention will be described, but the conditions in the example are examples relating to one condition adopted to confirm the feasibility and effects of the present invention, but the present invention is not limited to this example. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.
In the present example, the thermal insulation structure described in the above embodiment was attached to a surface of a tank installed in a vacuum container, liquid nitrogen (LN2) was stored in the tank, and a mass flow rate of vapor generated from the inside of the tank was measured to evaluate heat entering from the thermal insulation structure. In the present example, a guard tank that individually removes heat by evaporation was set not to be affected by heat entering through a portion other than the thermal insulation structure such as a pipe. In addition, it was verified in advance that a corresponding evaporation amount could be obtained when a known heat input was applied by a heater installed on the surface of the tank in advance. The outline of the test apparatus is illustrated in
In this test apparatus, a mechanism for controlling the temperature of the side surface of the thermal insulation structure 1013 was provided, and the thermal insulation performance at three outer layer temperatures of 276K, 300K, and 353K was acquired using the difference in outer layer temperature as a parameter. Note that each configuration of the apparatus in
Note that, in
In addition,
In addition, Table 1 illustrates the results of comparing the performance of the thermal insulation structure (Example 1) according to the present invention at an outer layer temperature of 300 K with a thermal insulation structure of Comparative Example 1, which was a multilayer thermal insulation material having 20 layers of radiation films, and a thermal insulation structure of Comparative Example 2 including a foam thermal insulation material having a thickness of 25 mm. The thermal insulation structure used in Comparative Example 1 was different from that of Example 1 in that the members that support the radiation films are not elastically deformed. In the thermal insulation structure used in Comparative Example 2, a plurality of foam thermal insulation materials was stacked to form a thermal insulation structure.
From the results in Table 1, it was found that since the heat flux of Example 1 was smaller than the heat flux of Comparative Example 1 or Comparative Example 2, the thermal insulation material performance as a thermal insulation structure was high, and the evaporation amount could be suppressed.
In addition, Table 1 illustrates the results of calculation of the evaporation rate and evaporation amount of liquid nitrogen and the total mass as the insulation structure when each thermal insulation structure was applied to a spherical tank having a diameter of 2 m. Generally, in order to reduce the heat flux passing through the thermal insulation material, it is necessary to increase the area density of the thermal insulation material. However, since the thermal insulation structure of Example 1 had high thermal insulation performance, the thermal insulation performance could be secured without increasing the area density. Therefore, it can be seen that in a case where the thermal insulation structure of Example 1 was applied to a spherical tank, the evaporation amount of a substance (liquid nitrogen in this example) stored in the tank could be suppressed, and the mass as the thermal insulation structure could also be reduced.
According to the present invention, it is possible to provide a lightweight thermal insulation structure having high thermal insulation performance, and a structure including the thermal insulation structure. Therefore, the industrial value is extremely high.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/013988 | 3/31/2021 | WO |
