Insulation tube optimization structure and method of superconducting cable

Abstract

The invention discloses an insulating tube optimization structure and method of a superconducting cable, and belongs to the technical field of superconducting cables. The concrete structure comprises an outer pipe, an inner pipe and a heat-insulating material layer, wherein the heat-insulating material layer comprises a heat-insulating material and spacing bars. The method specifically comprises the following steps: respectively selecting spacing bars with different shapes and diameters, and alternately stacking a heat insulating material of a heat insulating material layer of the insulating tube and the spacing bars; heat flow is calculated, and the shape and the diameter of the optimal spacing bar are obtained; heat insulation material layers of different heat insulation structures are constructed respectively, and the optimal heat insulation structure and the shape and diameter of the spacing bar are obtained; thermal insulation material layers of different numbers of thermal insulation materials are constructed respectively, the optimal thermal insulation material layer is obtained, and optimization of the insulation pipe of the superconducting cable is achieved. A middle spacing bar is replaced by a heat insulation material with the same thickness, a better heat insulation effect is achieved in a small space, the spacing bar with low heat conductivity is used as a supporting structure, solid heat conduction of the heat insulation material is reduced, evacuation of a vacuum interlayer is facilitated, and optimization of the insulation pipe is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of superconducting cables, and more specifically, relates to an insulation tube optimization structure and method for superconducting cables. Background Art

[0002] In view of the actual situation of the current urban underground integrated pipe gallery, the inner diameters of the cable pipes vary, which puts forward new requirements for the size of superconducting cables and requires research on the miniaturization of superconducting cables. The outer diameter of the superconducting cable is mainly restricted by the liquid nitrogen flow channel inside the superconducting cable and the thickness of the multi-layer insulation between the double-layer insulation pipes. Therefore, how to reduce the thickness of the multi-layer insulation pipe and reduce the heat leakage of the insulation layer has become the primary issue at present.

[0003] Prior art document 1 (CN113393971B) discloses a high vacuum multilayer flexible thermal insulation tube and a manufacturing method for high temperature superconducting cables. The disadvantage is that the thickness of the thermal insulation tube and the influence of different shapes of the spacer layer on the insulation tube are not considered, resulting in high heat leakage. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the present invention provides an optimized structure and method for the insulation tube of a superconducting cable, which achieves a better insulation effect in a smaller space by replacing the middle spacer with an insulation material of the same thickness, reducing the diameter of the insulation tube, eliminating the middle spacer and appropriately adding multiple layers of composite materials; using low thermal conductivity spacers as supporting structures in the insulation material reduces heat conduction, reduces the solid thermal conductivity of the insulation material, and facilitates the evacuation of the vacuum interlayer, thereby achieving optimization of the insulation tube.

[0005] The present invention adopts the following technical solution.

[0006] The first aspect of the present invention provides an optimized structure of an insulation tube of a superconducting cable, comprising: an outer tube, an inner tube and a thermal insulation material layer:

[0007] The heat insulating material layer is located between the outer tube and the inner tube, and comprises a heat insulating material and a plurality of spacer strips;

[0008] The spacer bars are located between the outer tube and the insulation material, and are evenly distributed between the outer tube and the insulation material. The spacer bars are in direct contact with the outer tube, and are close to the cold wall surface inside the outer tube. The spacer bars are in direct contact with the insulation material, and support the insulation material.

[0009] The heat insulating material is in direct contact with the inner tube, and the heat insulating material is in close contact with the hot wall surface of the inner tube.

[0010] Preferably, the thermal insulation material is a polyester aluminum-plated film with 20-32 layers, and the thickness ratio of the aluminum-plated layer in the polyester aluminum-plated film to the polyester non-woven fabric is 1:1.

[0011] Preferably, the spacer strip is in the shape of a circle or a five-pointed star, with a diameter of 2 mm to 4 mm;

[0012] Preferably, the spacer strip is made of polytetrafluoroethylene, which has a density of 2.14-2.2 g / m3, a thermal conductivity of 0.19-0.27 W / m·K, and a degassing rate of 2×10-9 mbar·l / s·cm2.

[0013] A second aspect of the present invention provides a method for optimizing an insulation tube of a superconducting cable, which is operated on the above-mentioned insulation tube optimization structure of a superconducting cable, and comprises:

[0014] Select spacers of different shapes and diameters respectively, alternately stack the insulation material of the insulation material layer of the insulating tube and the spacers, and record the shape and diameter data of the spacers;

[0015] According to the recorded data of the shape and diameter of the spacer bar, the heat flow is calculated to obtain the shape and diameter of the optimal spacer bar that minimizes the heat flow;

[0016] According to the obtained shape and diameter of the optimal spacer, insulation material layers of different insulation structures are constructed respectively, the heat flow is calculated, and the optimal insulation structure and shape and diameter of the spacer that minimize the heat flow are obtained;

[0017] According to the obtained optimal insulation structure and the shape and diameter of the spacer strips, insulation material layers with different numbers of insulation materials are constructed respectively, the heat flow is calculated, and the optimal insulation material layer that minimizes the heat flow is obtained to achieve the optimization of the insulation tube of the superconducting cable.

[0018] Preferably, the shapes of the spacer bars include circle and five-pointed star, and the diameter of the spacer bars ranges from 2 to 4 mm.

[0019] Preferably, the heat flow is expressed as follows:

[0020]

[0021] In the formula,

[0022] is the heat flow,

[0023] λ is the thermal conductivity,

[0024] A is the contact area between the spacer and the cold wall surface,

[0025] θ1-θ2 is the temperature difference between the cold wall and the hot wall,

[0026] h is the thickness of the insulation material.

[0027] Preferably, different insulation structures include an insulating material and spacer bar alternating structure containing intermediate spacer bars and an insulating material and spacer bar structure not containing intermediate spacer bars, wherein the insulating material and spacer bar structure not containing intermediate spacer bars is a structure in which the intermediate spacer bars in the insulating material and spacer bar alternating structure are replaced with insulation material of the same thickness.

[0028] Preferably, the number of layers of the thermal insulation material is selected in the range of 10-32 layers.

[0029] Preferably, the optimal insulation material layer structure includes insulation material without intermediate spacers close to the hot wall surface and circular spacers close to the cold wall surface, and the optimal number of insulation material layers ranges from 20 to 32 layers.

[0030] Compared with the prior art, the beneficial effects of the present invention include at least the following: the present invention replaces the middle spacer with an insulating material of the same thickness, because the thermal conductivity of the spacer is better than that of the polyester fiber in the multi-layer insulating material, and thus achieves a better insulating effect. At the same time, the thickness of the insulating pipe is reduced under the condition of the same amount of heat leakage, and a better insulation effect is achieved in a smaller space by reducing the diameter of the insulating pipe, eliminating the middle spacer and appropriately adding multiple layers of composite materials; low thermal conductivity spacers are used as supporting structures in the insulating material, and when the shapes of the spacer layers are considered to be circular and five-pointed stars, the use of thin spacers reduces the heat transfer area, reduces heat conduction, reduces the solid thermal conductivity of the insulating material, and helps to evacuate the vacuum interlayer, thereby optimizing the insulating pipe. The optimal insulating pipe structure is selected by experimentally calculating the range of the number of layers of the optimal insulating material and the optimal spacer layer shape, as well as the influence of the spacer layer diameter under this shape on the heat leakage. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic diagram of an optimized structure of an insulation tube of a superconducting cable provided in accordance with an embodiment of the present invention;

[0032] Figure 2 It is a schematic diagram of a multi-layer polyester aluminum-plated film composite layer and a thick five-pointed star spacer strip alternately provided according to an embodiment of the present invention;

[0033] Figure 3 It is a schematic diagram of a multi-layer polyester aluminum-plated film composite layer and thin five-pointed star spacer strips alternately provided according to an embodiment of the present invention;

[0034] Figure 4 is a schematic diagram of a multi-layer polyester aluminum-plated film composite layer and a thick circular spacer strip alternately provided according to an embodiment of the present invention;

[0035] Figure 5 is a schematic diagram of a multi-layer polyester aluminum-plated film composite layer and a thin circular spacer strip alternating according to an embodiment of the present invention;

[0036] Figure 6 is a schematic diagram of a test flow-time curve provided according to an embodiment of the present invention;

[0037] Figure 7 is a schematic diagram of a group 1 of experiments of intermediate spacer bars provided according to an embodiment of the present invention;

[0038] Figure 8 is a schematic diagram of two groups of experiments on intermediate spacer bars provided according to an embodiment of the present invention;

[0039] Fig. 9 Schematic diagram of three groups of experiments on intermediate spacers provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The described embodiments are only embodiments of a part of the present invention, not all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.

[0041] like Figure 1 As shown, embodiment 1 of the present invention provides an optimized structure of an insulation tube of a superconducting cable, comprising: an outer tube 1, an inner tube 2 and a thermal insulation material layer.

[0042] The heat insulating material layer is located between the outer tube 1 and the inner tube 2, and comprises a heat insulating material 4 and a plurality of spacer bars 5;

[0043] The spacer bars are located between the outer tube 1 and the insulation material 4, and are evenly distributed between the outer tube 1 and the insulation material 4. The spacer bars (5) are in direct contact with the outer tube 1, and are close to the cold wall surface inside the outer tube 1. The spacer bars 5 are in direct contact with the insulation material 4, and support the insulation material 4.

[0044] The heat insulating material 4 is in direct contact with the inner tube 2 , and the heat insulating material 4 is in close contact with the hot wall surface of the inner tube 2 .

[0045] The diameter of the inner tube 2 is 11 mm.

[0046] The thermal insulation material 4 is made of polyester aluminized film with 20-32 layers, and the thickness ratio of the aluminized layer in the polyester aluminized film to the polyester non-woven fabric is 1:1.

[0047] The spacer bar 5 is in the shape of a circle or a five-pointed star, with a diameter of 2mm-4mm;

[0048] The material used for the spacer bar 5 is polytetrafluoroethylene, which has a density of 2.14-2.2 g / m3, a thermal conductivity of 0.19-0.27 W / m·K, and a degassing rate of 2×10-9 mbar·l / s·cm2.

[0049] Embodiment 2 of the present invention provides a method for optimizing an insulation tube of a superconducting cable, and the method for optimizing an insulation tube of a superconducting cable described in Embodiment 1 includes:

[0050] Step 1: Select spacers of different shapes and diameters respectively, alternately stack the insulation material of the insulation material layer of the insulation tube and the spacers, and record the shape and diameter data of the spacers;

[0051] The shapes of the spacers in step 1 include circles and five-pointed stars, and the number of spacer layers ranges from 2 to 4 mm.

[0052] Step 2: Calculate the heat flux according to the shape and diameter data of the spacer bars recorded in step 1, and obtain the shape and diameter of the optimal spacer bars that minimize the heat flux;

[0053] The heat flow is expressed as follows:

[0054]

[0055] In the formula,

[0056] is the heat flow,

[0057] λ is the thermal conductivity,

[0058] A is the contact area between the spacer and the cold wall surface,

[0059] θ1-θ2 is the temperature difference between the cold wall and the hot wall,

[0060] h is the thickness of the insulation material.

[0061] Step 3: According to the shape and diameter of the optimal spacer obtained in step 2, thermal insulation material layers of different thermal insulation structures are constructed respectively, the heat flow is calculated, and the optimal thermal insulation structure and shape and diameter of the spacer that minimize the heat flow are obtained;

[0062] Different insulation structures include an insulation material and spacer bar alternating structure containing intermediate spacer bars and an insulation material and spacer bar structure not containing intermediate spacer bars, wherein the insulation material and spacer bar structure not containing intermediate spacer bars is a structure in which the intermediate spacer bars in the insulation material and spacer bar alternating structure are replaced with insulation material of the same thickness.

[0063] The number of layers of the thermal insulation material can be selected in the range of 10-32 layers, and the thickness of the thermal insulation structure formed in combination with the spacer strips can range from 101.5 mm to 105.2 mm.

[0064] Step 4: Based on the optimal insulation structure and the shape and diameter of the spacer obtained in step 3, insulation material layers with different numbers of insulation materials are constructed respectively, the heat flow is calculated, and the optimal insulation material layer that minimizes the heat flow is obtained to achieve the optimization of the insulation tube of the superconducting cable.

[0065] The optimal insulation material layer structure includes insulation material without intermediate spacers close to the hot wall surface and circular spacers close to the cold wall surface. The optimal number of insulation material layers ranges from 20 to 32 layers.

[0066] Compared with the prior art, the beneficial effects of the present invention include at least the following: the present invention replaces the middle spacer with an insulating material of the same thickness, because the thermal conductivity of the spacer is better than that of the polyester fiber in the multi-layer insulating material, and thus achieves a better insulating effect. At the same time, the thickness of the insulating pipe is reduced under the condition of the same amount of heat leakage, and a better insulation effect is achieved in a smaller space by reducing the diameter of the insulating pipe, eliminating the middle spacer and appropriately adding multiple layers of composite materials; low thermal conductivity spacers are used as supporting structures in the insulating material, and when the shapes of the spacer layers are considered to be circular and five-pointed stars, the use of thin spacers reduces the heat transfer area, reduces heat conduction, reduces the solid thermal conductivity of the insulating material, and helps to evacuate the vacuum interlayer, thereby optimizing the insulating pipe. The optimal insulating pipe structure is selected by experimentally calculating the range of the number of layers of the optimal insulating material and the optimal spacer layer shape, as well as the influence of the spacer layer diameter under this shape on the heat leakage.

[0067] In Example 3 of the present invention, a comparison test was conducted on spacers of different shapes through an appearance test bench to verify the performance of different spacers under the comparison test of the same material and the same number of layers. The material used for the spacers is polytetrafluoroethylene, with a density of 2.14-2.2g / m3, a thermal conductivity of 0.19-0.27W / m·K, a degassing rate of 2×10-9mbar·l / s·cm2, a diameter of 2mm for the round thin spacers and the small five-pointed star spacers, and a diameter of 4mm for the round thick spacers and the large five-pointed star spacers.

[0068] The control group of the experiment was carried out according to the "polyester aluminum-coated film composite layer + spacer strip + polyester aluminum-coated film composite layer", which are: Figure 2 As shown in the figure, 20 layers of polyester aluminum-plated film composite layer + thick five-pointed star spacer + 20 layers of polyester aluminum-plated film composite layer, such as Figure 3 As shown in the figure, 20 layers of polyester aluminum-plated film composite layer + thin five-pointed star spacer + 20 layers of polyester aluminum-plated film composite layer, such as Figure 4 As shown in the figure, 20 layers of polyester aluminum-plated film composite layer + thick round spacer + 20 layers of polyester aluminum-plated film composite layer, as shown in the figure, Figure 5The 20-layer polyester aluminized film composite layer + fine circular spacer + 20-layer polyester aluminized film composite layer, 10-layer polyester aluminized film composite layer + thick five-pointed star spacer + 10-layer polyester aluminized film composite layer, 10-layer polyester aluminized film composite layer + fine five-pointed star spacer + 10-layer polyester aluminized film composite layer, 10-layer polyester aluminized film composite layer + thick circular spacer + 10-layer polyester aluminized film composite layer, 10-layer polyester aluminized film composite layer + fine circular spacer + 10-layer polyester aluminized film composite layer, the schematic diagram of the apparent test group is as shown Figure 2 shown.

[0069] Test data such as Figure 6 As shown in the figure, when the number of layers is 20, the flow rate of the test group with round thick spacers and large five-pointed star spacers is greater than that of the test group with thin and small spacers. The larger the material diameter, the larger the contact surface with the cold wall surface, and the greater the heat transfer caused by heat conduction. The heat leakage of the test group with round thick spacers is 0.512W, the heat leakage of the test group with large five-pointed star spacers is 0.506W, the heat leakage of the test group with round thin spacers is 0.492W, and the heat leakage of the test group with small five-pointed star spacers is 0.490W.

[0070] The test flow curve is as follows: Figure 6 The test results are shown in Table 1. When there are more layers, the heat leakage caused by thin spacers will be smaller. When there are more layers, the pressure will be greater. The contact surface of thick spacers will be larger after being pressed, so the heat loss caused by heat conduction will be greater. When there are fewer layers, the heat loss caused by thick spacers will be smaller. This is because when there are fewer layers, the pressure on the support bars is smaller, so the thick spacers play a supporting role, reducing the pressure between layers and reducing the heat leakage. And when there are fewer layers, the heat leakage will be smaller overall than when there are more layers. This is because under the same vacuum processing time, more materials will lead to higher material leakage, so the heat loss caused by convective heat transfer will be greater.

[0071] Table 1 Heat leakage of each group of tests

[0072] 20+20 10+10 Thick five-pointed star spacer 0.506W 0.439W Thin pentagonal spacer 0.490W 0.482W Thick round spacer 0.512W 0.449W Thin round spacer 0.492W 0.472W

[0073] According to the above test results, in the process of miniaturization of insulated pipes, fine spacers should be used after controlling the wrapping tension to reduce the heat transfer area and reduce heat conduction.

[0074] Embodiment 4 of the present invention: Since the thermal conductivity of the spacer is better than that of the polyester fiber in the multi-layer thermal insulation material, the middle spacer is replaced by a thermal insulation material of the same thickness. Figure 7 The experimental group 1 and Fig. 9 The insulation performance of the three experimental groups shown in the figure is improved by 7.6%. Figure 8 The experimental groups shown in Figure 2 and Fig. 9In the experimental group 3 tests shown, the heat leakage loss caused by radiation heat transfer and solid heat conduction has been saturated for the 32-layer composite layer compared to the 20-layer composite layer. However, the vacuum degree of the 32-layer material will be significantly improved under the same evacuation time, which is caused by the degassing performance of the material.

[0075] Table 2 Short sample test study of the intermediate spacer

[0076]

[0077] Therefore, in the miniaturized design of the insulation pipe, in order to reduce the diameter of the insulation pipe, it is considered to remove the middle spacer and appropriately add multiple layers of composite materials, so as to achieve better insulation effect in a smaller space.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. An optimized structure of an insulation tube of a superconducting cable, comprising: The outer tube (1), the inner tube (2) and the thermal insulation material layer are characterized by: The heat insulating material layer is located between the outer tube (1) and the inner tube (2), and comprises a heat insulating material (4) and a plurality of spacer strips (5); The spacer bars are located between the outer tube (1) and the heat insulating material (4), and are evenly distributed between the outer tube (1) and the heat insulating material (4). The spacer bars (5) are in direct contact with the outer tube (1) and are closely attached to the cold wall surface inside the outer tube (1). The spacer bars (5) are in direct contact with the heat insulating material (4) and support the heat insulating material (4). The heat insulating material (4) is in direct contact with the inner tube (2), and the heat insulating material (4) is in close contact with the hot wall surface of the inner tube (2).

2. The optimized structure of the insulation tube of a superconducting cable according to claim 1, characterized in that: The heat insulating material (4) is made of polyester aluminum-plated film, the number of layers is 20-32, and the thickness ratio of the aluminum-plated layer in the polyester aluminum-plated film to the polyester non-woven fabric is 1:

1.

3. The optimized structure of the insulation tube of a superconducting cable according to claim 1, characterized in that: The spacer bar (5) is in the shape of a circle or a five-pointed star, and has a diameter of 2 mm to 4 mm.

4. The optimized structure of the insulation tube of a superconducting cable according to claim 1, characterized in that: The material used for the spacer bar (5) is polytetrafluoroethylene, which has a density of 2.14-2.2 g / m3, a thermal conductivity of 0.19-0.27 W / m·K, and a gas release rate of 2×10-9 mbar·l / s·cm2.

5. A method for optimizing an insulation tube of a superconducting cable, operating on the insulation tube optimization structure of a superconducting cable according to claim 1, comprising: Select spacers of different shapes and diameters respectively, alternately stack the insulation material of the insulation material layer of the insulating tube and the spacers, and record the shape and diameter data of the spacers; According to the recorded data of the shape and diameter of the spacer bar, the heat flow is calculated to obtain the shape and diameter of the optimal spacer bar that minimizes the heat flow; According to the obtained shape and diameter of the optimal spacer, insulation material layers of different insulation structures are constructed respectively, the heat flow is calculated, and the optimal insulation structure and shape and diameter of the spacer that minimize the heat flow are obtained; According to the obtained optimal insulation structure and the shape and diameter of the spacer strips, insulation material layers with different numbers of insulation materials are constructed respectively, the heat flow is calculated, and the optimal insulation material layer that minimizes the heat flow is obtained to achieve the optimization of the insulation tube of the superconducting cable.

6. The method for optimizing the insulation tube of a superconducting cable according to claim 1, characterized in that: The shapes of the spacers include circle and five-pointed star, and the diameter of the spacers ranges from 2 to 4 mm.

7. The method for optimizing the insulation tube of a superconducting cable according to claim 1, characterized in that: The heat flow is expressed as follows: In the formula, is the heat flow, λ is the thermal conductivity, A is the contact area between the spacer and the cold wall surface, θ1-θ2 is the temperature difference between the cold wall and the hot wall, h is the thickness of the insulation material.

8. The method for optimizing the insulation tube of a superconducting cable according to claim 1, characterized in that: Different insulation structures include an insulation material and spacer bar alternating structure containing intermediate spacer bars and an insulation material and spacer bar structure not containing intermediate spacer bars, wherein the insulation material and spacer bar structure not containing intermediate spacer bars is a structure in which the intermediate spacer bars in the insulation material and spacer bar alternating structure are replaced with insulation material of the same thickness.

9. The method for optimizing the insulation tube of a superconducting cable according to claim 1, characterized in that: The number of layers of the thermal insulation material can be selected in the range of 10-32 layers, and the thickness of the thermal insulation structure formed in combination with the spacer strips can range from 101.5 mm to 105.2 mm.

10. The method for optimizing the insulation tube of a superconducting cable according to claim 1, characterized in that: The optimal insulation material layer structure includes insulation material without intermediate spacers close to the hot wall surface and circular spacers close to the cold wall surface. The optimal number of insulation material layers ranges from 20 to 32 layers.

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