JP5649312B2 - Vacuum insulation tube and superconducting cable - Google Patents

Description

  The present invention relates to a vacuum heat insulating tube capable of improving the degree of vacuum during vacuum evacuation and maintaining the degree of vacuum for a long time, and a superconducting cable including the vacuum heat insulating tube.

  A typical structure of a vacuum heat insulating tube is a double-structured tube consisting of an inner tube and an outer tube. The inner tube and the outer tube are maintained at a solid long spacer, and the inner tube and the outer tube are separated from each other. The thing which evacuated between pipes is mentioned. There is also a configuration in which a heat insulating material is wound around the outer periphery of the inner tube in order to further improve the heat insulating performance of the vacuum heat insulating tube.

  The degree of vacuum in the vacuum heat insulating tube must always be maintained at a degree that allows heat insulation to be maintained. The degree of vacuum is equal to or higher than the degree of vacuum (predetermined degree of vacuum) when maintaining the heat insulation property according to a prescribed standard. The higher the degree of vacuum, the better the heat insulation. If the vacuum heat insulating tube is used for a long period of time, the degree of vacuum decreases with time. Therefore, it is desirable that the initial degree of vacuum (attainment degree of vacuum) after evacuation is high. The degree of vacuum (stopping vacuum) that has decreased over time must be equal to or greater than the specified degree of vacuum.

  In the vacuum heat insulating tube, when evacuation is performed, outgas discharged from a structural member such as a double structure tube or a spacer, moisture (water vapor) attached to the structural member (hereinafter, simply referred to as “outgas”) If it exists, it takes time to reach the desired ultimate vacuum, and it is difficult to further improve the ultimate vacuum. In addition, if there is outgas released from the component during long-term use, the rate at which the degree of vacuum decreases from the ultimate degree of vacuum over time is large.

  In order to remove this outgas and increase the degree of vacuum, when performing evacuation, a heat treatment called baking is performed to activate and discharge the outgas component contained in the structural member by heating the heat insulating tube. Furthermore, during this baking process, by using the porous material adsorbent together with the exhaust in the double-structured tube, outgas is adsorbed, so that the vacuum can be increased to a high vacuum in a shorter time than when only exhaust is used. A heat insulating tube is disclosed in Patent Document 1. Further, Patent Document 1 discloses a vacuum heat insulating tube that can maintain the degree of vacuum for a long period of time by adsorbing an outgas released from a component member over a long period of time with an adsorbent such as a hydrogen storage alloy.

  These adsorbents are hermetically housed in a case in a vacuum state because their adsorption capacity decreases in a short time when left in the atmosphere. The case contains a rupture member that deforms at a predetermined temperature and breaks the vacuum inside the case. The rupture member deforms depending on the temperature during baking or when the vacuum insulation tube is used. The adsorbent can adsorb outgas.

JP 2006-153245 A

  Using the above-mentioned conventional technology, it is possible to achieve a high vacuum in a shorter time by adsorbing the outgas together with the exhaust in the double-structured tube, but the device for the adsorption (the case for storing the adsorbent and the case) The breaking member to be broken) is required. Further, when the vacuum heat insulating tube is long, in order to uniformly adsorb outgas over the entire length, it is necessary to disperse and install a great number of devices in the longitudinal direction. Moreover, it is conceivable that the apparatus causes outgas generation that lowers the degree of vacuum in the double structure tube. Therefore, it is desired to improve the structural members of the vacuum heat insulating tube that cause outgassing.

  The present invention has been made in view of the above circumstances, and one of its purposes is to provide a vacuum heat insulating tube capable of improving the degree of vacuum during vacuum evacuation and maintaining the degree of vacuum for a long period of time.

  Another object of the present invention is to provide a superconducting cable including the vacuum heat insulating tube.

  The present invention achieves the above object by forming at least a part of a spacer, which is one of constituent members of a vacuum heat insulating tube, from a porous material.

  The vacuum heat insulating tube of the present invention is formed between a double structure tube composed of an inner tube and an outer tube, a spacer for maintaining a space between the inner tube and the outer tube, and the inner tube and the outer tube. And at least a part of the spacer is formed of a porous material.

The porous material has innumerable minute pores inside, and at least a part of the plurality of pores is connected to form a structure having many exhaust passages each composed of minute pores. , It has the property of easily discharging outgas.

  By using this porous material for at least a part of the spacer, it is possible to discharge more outgas contained in the spacer when evacuating than in the past. Since the outgas from the spacer which is a constituent member of the vacuum heat insulating tube can be discharged more, the ultimate vacuum can be improved.

  In addition, when the vacuum heat insulating tube is used for a long time, the outgas is gradually released from the constituent members. However, since the outgas of the spacer is largely exhausted during evacuation, the outgas released over time is conventionally There are few compared. In addition, since the initial ultimate vacuum can be increased, it can be stopped compared to the prior art to prevent a decrease in vacuum, or the rate at which the vacuum decreases over time can be reduced, and the vacuum can be maintained for a long time. Can do.

  One aspect of the present invention is that the porosity of the porous material is 1% or more and 60% or less.

  When the porosity of the porous material is 1% or more, the surface area per unit volume of the spacer is increased, and the exhaust path is further increased accordingly, so that more outgas is contained in the spacer when evacuating. Can be discharged. Therefore, when the vacuum heat insulating tube is used for a long period of time, the outgas discharged from the spacer with time is also reduced. Since the initial ultimate vacuum can be increased and the stop vacuum can be prevented from being lowered, the vacuum can be maintained for a long time.

  Moreover, the mechanical strength requested | required as a spacer is maintained because the porosity of a porous material is 60% or less. For example, even if the vacuum insulation tube is bent, if the spacer has a certain degree of mechanical strength, it is not crushed between the double structure tubes, and the distance between them can always be kept constant. .

  One embodiment of the present invention is that the porous material is a fluororesin.

  Since the fluororesin has a smaller thermal conductivity than that of a metal, it is possible to suppress thermal conduction through a spacer between the inner tube and the outer tube. In addition, since the fluororesin has a high melting point, it has excellent heat resistance, does not harden even at extremely low temperatures, and does not become brittle, and can cope with a wide range of temperatures of the medium distributed in the vacuum heat insulating tube.

  Said vacuum heat insulation pipe | tube can be utilized for the superconducting cable characterized by providing the cable core accommodated in the inside.

  A typical configuration of a superconducting cable includes a cable core having a superconducting conductor, a vacuum heat insulating tube of the present invention that houses the cable core, and a refrigerant flow path that cools the superconducting conductor between the cable core and the inner tube. Things.

  When the vacuum heat insulating tube of the present invention is used for the superconducting cable, the vacuum heat insulating tube of the present invention can maintain high heat insulating properties, so that energy saving necessary for maintaining the temperature of the refrigerant flowing in the heat insulating tube can be expected.

  The vacuum heat insulating tube of the present invention improves the initial ultimate vacuum by preventing the lowering of the stop vacuum by forming at least a part of the spacer which is one of the components of the vacuum heat insulating tube with a porous material. Can maintain the vacuum for a long time.

  Moreover, the superconducting cable provided with the vacuum heat insulating tube of the present invention is expected to improve the heat insulating performance of the vacuum heat insulating tube and save energy necessary for maintaining the temperature of the refrigerant.

FIG. 1 is a schematic diagram of a vacuum heat insulating tube of the present invention according to an embodiment. FIG. 2 is a schematic diagram of the spacer used in the vacuum heat insulating tube of FIG. FIG. 3 is a cross-sectional view of a superconducting cable including the vacuum heat insulating tube of FIG.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same reference numerals denote the same members.

<Embodiment 1>
A vacuum heat insulating tube 1 according to the present invention will be described with reference to FIG. The vacuum heat insulating tube 1 includes a double-structure tube 2 composed of an inner tube 21 and an outer tube 22, a spacer 3 for maintaining a space between the inner tube 21 and the outer tube 22, and the inner tube 21 and the outer tube 22. And a vacuum layer 4 formed therebetween. In this example, in order to further improve the heat insulating performance, the heat insulating material layer 5 in which the heat insulating material is wound around the outer periphery of the inner tube 21 is formed. Hereinafter, each structure of the vacuum heat insulation pipe | tube 1 is demonstrated in detail.

[Vacuum insulation pipe]
(Double structure pipe)
The double-structure tube 2 is a stainless corrugated tube made of an inner tube 21 and an outer tube 22 and having a bellows shape in the longitudinal direction so as to be easily bent. In the inner tube 21, a normal fluid flows. The temperature of the fluid varies depending on the type of fluid and the intended use, and a wide range of temperatures from extremely low to high is used.

  As the material of the double structure tube 2, a metal such as flexible aluminum can be used in addition to stainless steel.

  In addition to the corrugated pipe, the double-structure pipe 2 can be a straight pipe having no irregularities on the surface for straight sections when it is not necessary to bend or when the distance of the vacuum heat insulating pipe is short.

  The thickness of each of the inner and outer tubes constituting the double structure tube 2 is determined by the pressure at which the double structure tube 2 expands in the circumferential direction due to the fluid flowing inside the inner tube 21, and the double structure tube 2 Is made to have a thickness capable of withstanding the tension applied in the longitudinal direction.

(Spacer)
A spacer 3 is installed in order to keep the distance between the inner tube 21 and the outer tube 22.

  By forming the spacer 3 with a porous material, the outgas emitted from the spacer 3 can be reduced. Hereinafter, the definition of the porosity of the porous material and the measurement method will be described.

≪Porosity≫
Porosity refers to the rate of mass loss relative to solid material. When the porosity is 1% or more, the surface area per unit volume of the spacer 3 is increased, and as a result, the number of exhaust paths during evacuation is increased, so that more outgas contained in the spacer 3 can be discharged. . On the other hand, if the porosity exceeds 60%, it is difficult to maintain the mechanical strength required for the spacer 3, so the porosity is preferably 60% or less. More preferably, the porosity is 20% or more and 40% or less.

≪Measurement method of porosity≫
The porosity is measured as follows.
(1) The mass M1 of a solid material having a constant volume (length) is measured.
(2) The mass M2 of the porous material having the same volume (length) as above is measured.
(3) Let {(M1-M2) / M1} × 100 (%) be the porosity of the porous material.

  By forming the porous material on at least a part of the spacer 3, it is possible to improve the initial ultimate vacuum, prevent the lowering of the stop vacuum, and maintain the vacuum for a long time. In particular, the more porous regions in the spacer 3, the more outgas contained in the spacer 3 can be discharged when evacuating. Examples of the configuration of the spacer 3 are given below. Here, the spacer 3 is made of a long material and is wound around the outer periphery of the inner tube 21 in a spiral shape.

  As a 1st form, the form by which the porous area | region was disperse | distributed to multiple places along the longitudinal direction of one elongate material is mentioned. Since the spacer 3 formed of a porous material can be disposed along the longitudinal direction of the vacuum heat insulating tube 1, the outgas of the spacer 3 can be discharged uniformly over the entire length of the vacuum heat insulating tube 1, and the outgas released over time can be Localization can be prevented.

  As a 2nd form, the part by which the one part of the radial direction center side of one elongate material is nonporous and the outer peripheral side remainder is porous is mentioned. As in the first embodiment, the outgas of the spacer 3 can be discharged uniformly over the entire length of the vacuum heat insulating tube 1, and the outgas released over time can be prevented from being localized.

  As a third form, in the case where a plurality of long materials are used, a form in which some of the long materials are porous and the rest is nonporous. As in the first embodiment, it is possible to prevent local outgas emitted from the spacer 3 with time, and to maintain the mechanical strength of the spacer 3 as a whole by using a plurality of long materials. Can do.

  As a fourth form, when a plurality of long materials are twisted together, a form in which several of the long materials are porous and the rest are nonporous is mentioned. As in the third embodiment, it is possible to prevent the outgas released from the spacer 3 from being localized over time, and to maintain the mechanical strength of the spacer 3 as a whole.

  As the material of the spacer 3, a fluororesin such as polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), ethylene-tetrafluoroethylene copolymer (ETFE) can be used. In addition to the fluororesin, a metal porous body can also be used. Moreover, those composite materials can also be used.

  As shown in FIG. 2, the shape of the spacer 3 is such that a plurality of long materials 31 are used, and each of the long materials 31 is held in parallel by connecting members 32 at equal intervals. Is preferred. The long material 31 is made of a porous material. The connecting member 32 may be the same material as the long material 31 or may be a wire such as polyamide. By winding this spacer 3 around the outer periphery of the inner tube 21 in a spiral manner, even if the spacer 3 is wound at a long pitch, a sufficient place to support the inner and outer tubes with the spacer 3 can be secured, and the number of turns can be reduced. . Further, by holding each of the long members 31 in parallel by the connecting member 32, the direction of the respective long members 31 and their adjacent intervals can be maintained. As a method of arranging the spacers 3, in addition to winding in a spiral shape, the spacers 3 may be vertically attached.

(Vacuum layer)
A vacuum is formed between the inner tube 21 and the outer tube 22 held by the spacer 3 to form a vacuum layer 4. The higher the degree of vacuum of the vacuum layer 4, the higher the heat insulation performance. Note that the double-structure tube 2 shown in FIG. 1 is shown with the left end open, but in practice it is sealed after evacuation.

(Insulation layer)
A heat insulating material layer 5 in which a heat insulating material is wound is formed on the outer periphery of the inner tube 21 on the inner side of the spacer 3 in order to further improve the heat insulating performance. Insulation layer 5 is super-insulated to prevent radiant heat from outside when the fluid temperature is lower than the outside temperature of the insulation tube, and to prevent radiant heat from the fluid when the fluid temperature is higher than the outside temperature of the insulation tube. Use a heat insulating material such as (trade name). This heat insulating material is wound around the entire outer circumference of the inner tube 21 to prevent the penetration of radiant heat into the inner tube 21 or the radiant heat from the inner tube 21. As an installation method of the heat insulating material, in addition to winding in a spiral shape, it may be added vertically.

[Function and effect]
By forming at least a part of the spacer 3 that is one of the constituent members of the vacuum heat insulating tube 1 with a porous material, more outgas contained in the spacer 3 can be discharged when evacuating, The ultimate vacuum can be improved. In addition, when the vacuum insulation tube 1 is used for a long time, the outgas from the spacer 3 is exhausted during evacuation, so the outgas released over time can be reduced, and the vacuum can be reduced by preventing the stop vacuum from being lowered. Can be maintained for a long time. In addition, a new component necessary for improving the degree of vacuum is not required.

<Embodiment 2>
Next, a schematic configuration of the superconducting cable 10 including the vacuum heat insulating tube 1 of the present invention will be described with reference to FIG. The superconducting cable 10 has a configuration in which a three-core cable core 11 is housed in the vacuum heat insulating tube 1. Hereinafter, each configuration of the superconducting cable 10 will be described in detail.

[Superconducting cable]
(Cable core)
The cable core 11 typically includes a former 12, a conductor layer 13, an electrical insulating layer 14, a magnetic shielding layer 15, and a protective layer 16 in order from the center. Of these layers, superconductors are used for the conductor layer 13 and the magnetic shielding layer 15.

  As the former 12, a solid one obtained by twisting metal wires or a hollow one using a metal pipe is used. When the hollow former 12 is used, the inside thereof can be used as a refrigerant flow path. The conductor layer 13 has a configuration in which a tape-like wire rod having an oxide superconductor, for example, a Bi2223 superconducting tape wire (Ag-Mn sheath wire) is spirally wound in a single layer or multiple layers. In addition, RE123-based thin film wires (RE: rare earth elements such as Y, Ho, Nd, Sm, and Gd) can also be used for the conductor layer 13. The electrical insulation layer 14 is formed by winding an insulating paper tape such as kraft paper, or a semi-synthetic insulating tape obtained by combining kraft paper and plastic, for example, a tape-like insulating material such as PPLP (registered trademark) manufactured by Sumitomo Electric Industries, Ltd. Configuration. The magnetic shielding layer 15 has a configuration in which the same superconducting wire as the conductor layer 13 is wound. The protective layer 16 may be configured by winding kraft paper or the like. An anticorrosion layer 18 made of polyvinyl chloride or the like is formed on the outer tube 22.

(Refrigerant flow path)
A refrigerant flow path 17 is formed between the inside of the vacuum heat insulating tube 1 and each cable core 11. A coolant for cooling the superconductor flows through the coolant channel 17.

  The refrigerant rises in temperature due to heat entering from the outside and affects the superconducting state of the conductor layer 13 and the magnetic shielding layer 15. However, since the vacuum heat insulating tube 1 according to the present invention uses the spacer 3 made of a porous material and can maintain a high heat insulating property, it is possible to reduce the heat of penetration from the outside.

[Function and effect]
The superconducting cable 10 provided with the vacuum heat insulating tube 1 of the present invention is expected to improve the heat insulating performance of the vacuum heat insulating tube 1 and save energy necessary for maintaining the temperature of the refrigerant.

<Test example>
The above-mentioned double structure tube 2 using spacers having different porosities was evacuated, and the degree of vacuum of the obtained vacuum heat insulating tube 1 according to Example and Comparative Example was measured over time. The measured degree of vacuum is an ultimate degree of vacuum (an initial degree of vacuum after evacuation) and a stop degree of vacuum (a degree of vacuum that decreases with time after the vacuum layer is sealed). Specific test conditions are shown below.

[Example 1]
Double structure tube Material: Stainless steel Shape: Corrugated tube Dimensions: Inner tube outer diameter 105mm, inner diameter 95mm
Outer tube outer diameter 129mm, inner diameter 119mm
1000mm length
Spacer Material: Polytetrafluoroethylene Porosity: 30%
Dimensions: Diameter 3mm, length 1000mm
Configuration: 15 long materials with the above materials, porosity, and dimensions are placed in a double-structured tube. Vacuum layer The conditions for the vacuum layer are described in [Measurement conditions] described later.

[Example 2]
A vacuum heat insulating tube similar to that of Example 1 except that the porosity of the long spacer material is 60%.

[Comparative example]
The configuration is the same as that of Example 1 except that the porosity of the long spacer material is 0%.

[Measurement condition]
Ultimate vacuum: Measured immediately after evacuation at room temperature (15 ° C) for 4 hours Stopped vacuum: Measured after leaving pump for 4 hours after closing the vacuum layer

[result]
The ultimate vacuum and stop vacuum are shown in Table 1. Table 1 also shows all outgas discharge amounts in the vacuum heat insulating tube 1 released over time from the time of measurement of the ultimate vacuum to the time of measurement of the stop vacuum. The outgas release amount is calculated by obtaining the number of moles of outgas (moisture) from the degree of vacuum using the gas equation of state.

As shown in Table 1, Example 1 improved the ultimate vacuum by about 96.2% and the stop vacuum by about 97.6% compared to the comparative example. Along with this, the amount of all outgas emission in the vacuum heat insulating tube 1 was reduced to about 1/100. In Example 2, the ultimate vacuum was improved by about 97.8% and the stop vacuum was improved by about 99.9% compared to the comparative example. Along with this, the amount of outgas emission in the vacuum insulation pipe 1 was reduced to about 1/1000 .

  After the measurement, the vacuum in the vacuum heat insulating tube 1 was broken, and the adhesion state of moisture on the spacer 3 was analyzed. This analysis was performed by comparing the mass of the spacer 3 before and after the test. As a result, moisture was not adsorbed in the pores of the spacer 3. Therefore, the improvement of the initial ultimate vacuum level and the long-term maintenance of the vacuum level by preventing the reduction of the stop vacuum level are due to the property that the outgas is easily discharged by the exhaust path constituted by the microscopic pores of the porous material. It is thought to be a thing.

  Conventionally, a porous material has a large surface area due to many pores, so there are many outgasses that lower the degree of vacuum, and moisture is easily adsorbed into the pores, which is considered inappropriate for the components of vacuum insulation tubes. However, it was found that by the exhaust path, moisture was adsorbed in the pores while being easily discharged, and the outgas was sufficiently discharged. When evacuating, it is possible to improve the ultimate vacuum by discharging more outgas from the spacer 3, and the amount of outgas released over time can be reduced. Long-term maintenance can be realized.

  The above-described embodiments can be appropriately changed without departing from the gist of the present invention, and the scope of the present invention is not limited to the above-described configuration.

  The vacuum heat insulation pipe of the present invention can be used as a fluid transport pipe that can widely cope with the temperature of the fluid flowing in the vacuum heat insulation pipe. The superconducting cable provided with the vacuum heat insulating tube of the present invention can be suitably used as a constituent member of a power transmission line.

1 Vacuum insulation tube
2 Double structure pipe
21 Inner pipe 22 Outer pipe
3 Spacer
31 Long material 32 Connecting member
4 Vacuum layer
5 Insulation layer
10 Superconducting cable
11 Cable core 12 Former
13 Conductor layer 14 Electrical insulation layer 15 Magnetic shielding layer 16 Protective layer
17 Refrigerant flow path 18 Anticorrosion layer

Claims (3)

A long double-structured tube consisting of an inner tube and an outer tube;
A long spacer for maintaining a distance between the inner tube and the outer tube;
A vacuum heat insulating tube comprising a vacuum layer formed between the inner tube and the outer tube,
The spacer is formed of a porous material over its entire length ,
The porous material is
Ri der porosity of 60% or less than 20%
Has innumerable fine pores inside, the vacuum thermal insulating pipe that have a myriad of exhaust path formed at least a part of the pores continuous.   The vacuum heat insulating tube according to claim 1, wherein the porous material is a fluororesin. The vacuum heat insulating tube according to claim 1 or 2,
A superconducting cable comprising a cable core housed inside the vacuum heat insulating tube.

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