Composite wick structure and preparation method thereof

Abstract

The application provides a composite wick structure and a preparation method thereof. The composite wick is composed of a multilayer metal mesh sleeve formed by rolling a metal mesh, and a plurality of metal wires are fixedly arranged on the outer side of the outermost metal mesh sleeve at uniform intervals along the circumference of the metal mesh sleeve. Through the composite structure of the multilayer metal mesh sleeve and the outer axial metal wire, the uniform capillary effect of the metal mesh pores and the strong capillary pumping effect of the axial deep groove formed between the metal wire and the tube wall are ingeniously combined. Under the premise of not excessively increasing the liquid flow resistance, the axial capillary driving force of the wick is greatly enhanced, which is particularly beneficial to improving the heat transfer capacity and the heat load limit of the heat pipe under the anti-gravity working condition.

Description

Technical Field

[0001] This invention relates to the field of absorbent core structure technology, and more specifically, to a composite absorbent core structure and its preparation method. Background Technology

[0002] With the increasing distances explored in deep space and the deep sea, traditional solar and chemical energy sources are insufficient to meet the needs of long-term energy supply. Nuclear power sources cooled by alkali metal high-temperature heat pipes (referred to as heat pipe reactors) have advantages such as compact structure, high energy density, long endurance, and inherent safety, making them a key research direction for long-endurance energy supply. A typical heat pipe reactor uses highly enriched UO2 or UN as fuel in its core. The core fission heat is directed to the energy conversion system for thermoelectric conversion via alkali metal high-temperature heat pipes. Excess heat during the energy conversion process is discharged through a waste heat emission system, enabling a continuous energy supply for more than five years. As the most important heat transfer component of the heat pipe reactor, the alkali metal high-temperature heat pipe's heat transfer characteristics are crucial for the reactor's thermoelectric conversion, waste heat emission, and residual heat removal. The unique high-temperature operating environment of alkali metal high-temperature heat pipes also makes their heat transfer characteristics more complex.

[0003] A heat pipe is a passive heat transfer device, and its working principle is as follows: Figure 1 As shown. A standard heat pipe structure is a closed cylinder filled with a certain amount of working fluid. The inner wall of the heat pipe has a porous capillary wick processed by sintering or welding. The inside of the pipe is under vacuum, with a vacuum level ranging from 10. -2 ~ 10 -6 mmHg. A heat pipe consists of three parts: an evaporation section, an adiabatic section, and a condensation section. When the heat pipe is working, heat is input from an external heat source to the evaporation section, where a stable phase change and a gas-liquid two-phase circulation mass transfer process are gradually established. The heat is then transferred to the condensation section and output mainly in the form of latent heat of phase change. Capillary heat pipes can operate under horizontal and anti-gravity conditions.

[0004] A typical heat pipe structure includes a sealed tube shell, a wick inside the shell, and a working medium encapsulated within the tube under vacuum (for high-temperature heat pipes, the working medium is often an alkali metal such as sodium, potassium, or lithium). The core function of the wick is to provide the capillary force that drives the working liquid back from the condensation section to the evaporation section, and to serve as a channel for the flow of the liquid phase. Therefore, the capillary performance, permeability, and structural stability of the wick are key factors determining the heat transfer limit, start-up characteristics, and long-term operational reliability of the heat pipe.

[0005] Traditional wicking mechanisms come in various forms, such as sintered metal powder structures, wire mesh, and grooved structures. Among these, metal wire mesh wicks are widely used due to their relatively mature manufacturing process, uniform structure, and high design flexibility. However, under the high-temperature and high-heat-flux-density conditions encountered by alkali metal heat pipes, the performance of traditional single-structure wire mesh wicks faces challenges: on the one hand, while the fine wire mesh provides significant capillary force, it also increases the resistance to liquid flow, limiting its permeability and maximum heat transfer capacity; on the other hand, under anti-gravity or long-distance transport conditions, stronger capillary force is required to overcome the gravitational pressure drop, which places higher demands on the wicking mechanism structure. Summary of the Invention

[0006] (a) Technical problems to be solved The technical problem this invention aims to solve is how to overcome the shortcomings of existing single-structure wire mesh wicks in achieving both capillary driving force and liquid flow capability under high temperature, high heat flux, or anti-gravity conditions, and to provide a composite wick structure that combines high capillary force and good permeability. Simultaneously, it provides a reliable and feasible preparation method that matches this structure, ensuring that the components of the composite structure are firmly connected at high temperatures and that the overall performance is stable.

[0007] (II) Technical Solution To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a composite wicking structure for fixedly mounting on the inner surface of a heat pipe, covering the evaporation section, insulation section, and condensation section of the heat pipe. The composite wicking structure is characterized by comprising a multi-layered metal wire mesh sleeve formed by rolling metal wire mesh, with multiple metal wires fixedly arranged at uniform intervals along the circumference of the outermost metal wire mesh sleeve on its outer side. Specifically, the tightly rolled multi-layered metal wire mesh sleeve constitutes the matrix of the wicking structure, providing a uniform, high-porosity capillary structure that ensures the lateral distribution and wetting of the working fluid. The metal wires attached to the outermost metal wire mesh sleeve and uniformly arranged circumferentially form deeper and more regular axial capillary channels (microchannels) with the inner wall of the heat pipe. These channels can generate capillary forces much greater than the pore size of the wire mesh itself, thereby significantly enhancing the "pumping" capability that drives the working fluid to axially flow back from the condensation section to the evaporation section. The two structures complement each other and work together to improve the overall performance of the absorbent core.

[0008] Preferably, the metal wire and the metal wire mesh sleeve, as well as the adjacent layers of the multi-layer metal wire mesh sleeve, are fixedly connected by spot welding. Specifically, spot welding results in a small heat-affected zone, a strong connection, and controllable weld size, effectively preventing clogging of the wire mesh pores and ensuring the integrity and long-term reliability of the composite structure at high temperatures.

[0009] Preferably, the inner diameter of the heat pipe is 10-80 mm, and the cross-sectional shape of the heat pipe is circular, rectangular, trapezoidal, or triangular. Specifically, the structure of the present invention can be adapted to heat pipes of different shapes by adjusting the shape of the rolled mandrel and the size of the metal wire mesh, thus exhibiting strong versatility.

[0010] Preferably, the material of the metal mesh includes at least one of stainless steel, copper, and nickel. The material of the metal wire includes at least one of stainless steel, copper, and nickel. Preferably, the metal wire and the metal mesh are made of the same or similar materials with similar coefficients of thermal expansion to reduce thermal stress and adapt to high-temperature operating conditions. Stainless steel (such as 304, 316L) is the preferred material for high-temperature heat pipes due to its excellent high-temperature strength and resistance to alkali metal corrosion.

[0011] Secondly, the present invention provides a method for preparing a composite liquid-absorbing core structure, characterized by comprising the following steps: S1. Clean and dry the metal wire mesh and wire to remove oil, oxides and other impurities from the surface to ensure the quality of subsequent welding. S2. Flatten the wire mesh. At the position corresponding to the outermost layer of the rolled wire mesh sleeve, arrange the wires at a predetermined spacing and fix them by spot welding. On one side of the wire mesh, corresponding to the position that will become the outermost layer of the rolled wire mesh sleeve, arrange multiple wires at a predetermined uniform spacing and fix one or both ends of these wires to the wire mesh by spot welding (spot welded at intervals along the length of the wire). This pre-bonds the axial wires with the planar wire mesh, laying the foundation for the subsequent rolling to form a composite structure.

[0012] S3. The metal wire mesh is wound using a mandrel to form a multi-layered metal wire mesh sleeve. During the winding process, adjacent layers of the metal wire mesh sleeve are fixed at the joint by spot welding. Specifically, a mandrel with a diameter matching the inner diameter and cross-sectional shape of the target heat pipe is used to wind the metal wire mesh obtained in step S2, which already has metal wires fixed to it. This winds the first layer (innermost layer) of the metal wire mesh sleeve. The second layer of wire mesh is then wound. During the winding process, when the edge of the second layer of wire mesh overlaps with the joint of the first layer of wire mesh, the two layers of wire mesh are immediately fixed at the joint by spot welding. This process is repeated, winding and fixing layer by layer to form a multi-layered metal wire mesh sleeve base.

[0013] S4. Continue rolling until the outermost metal wire mesh sleeve with metal wires completely covers the inner metal wire mesh sleeve, and fix the outermost metal wire mesh sleeve and the next outermost metal wire mesh sleeve by spot welding to obtain the composite liquid absorption core.

[0014] Preferably, the cleaning process in step S1 includes: performing alkaline washing, acid washing, and deionized water washing in sequence.

[0015] Preferably, the alkaline washing uses a 1-5 mol / L sodium hydroxide solution for 10-15 minutes to remove grease; the acid washing uses a 5-10 mol / L hydrochloric acid solution for 10-15 minutes to remove the oxide layer. Finally, it is rinsed clean with deionized water and dried. Specifically, the washing steps for the metal mesh and metal wire are: tap water washing, alkaline washing, tap water washing, acid washing, tap water washing, deionized water washing, and finally drying with hot inert gas; during the washing process, the sequence is: tap water washing for 5-10 minutes, alkaline washing for 10-15 minutes, tap water washing for 5-10 minutes, acid washing for 10-15 minutes, tap water washing for 5-10 minutes, and deionized water washing for 10-15 minutes. The metal mesh needs to be agitated with a tool during washing to ensure full contact between the mesh and the liquid.

[0016] Preferably, in step S2, the welding current for spot welding the metal wire is 3-4A, and the spacing between adjacent welding points is 1-5cm. This parameter ensures that the metal wire is firmly welded to the wire mesh and avoids burning through the wire mesh due to excessive current.

[0017] Preferably, in steps S3 and S4, the welding current for spot welding the metal wire mesh sleeve is 1-2.5A, and the spacing between adjacent weld points is 1-5cm. Because the wire mesh is thin, using a smaller current can form reliable weld points without causing excessive melting or perforation of the material, ensuring connection strength and maintaining the pore structure of the wire mesh.

[0018] (III) Beneficial Effects The above-described technical solution of the present invention has at least the following advantages: 1. Significantly Improved Heat Transfer Performance: Through a composite structure of multi-layered metal mesh sleeves and outer axial metal wires, the uniform capillary effect of the metal mesh pores is cleverly combined with the strong capillary pumping effect of the deep axial channels formed between the metal wires and the tube wall. Without excessively increasing the liquid flow resistance, the axial capillary driving force of the wick is greatly enhanced, which is particularly beneficial for improving the heat transfer capacity and heat load limit of the heat pipe under anti-gravity conditions.

[0019] 2. Stable and reliable structure: The metal wires and wire mesh, as well as the various layers of the wire mesh, are fixed by spot welding. The welded joints are strong, with low thermal resistance, ensuring that the composite structure can operate for a long time in the high-temperature environment of alkali metals without delamination or loosening, resulting in high reliability.

[0020] 3. The process is rational and highly feasible: The preparation method has clear steps. The process involves first pre-fixing the metal wire onto a flat wire mesh via spot welding, and then rolling it into shape. This solves the problem of accurately and firmly arranging and fixing the fine metal wire on the outside of a pre-formed cylindrical surface. This process is easy to operate and control, and is suitable for preparing liquid-absorbing cores of different sizes and specifications.

[0021] 4. Good versatility and adaptability: This structure and method can flexibly adjust the capillary force and permeability of the wick by selecting wire meshes of different mesh counts and metal wires of different diameters and spacings to adapt to different heat pipe sizes and working fluids. The structure can be adapted to various tube shapes such as circular and rectangular, and has a wide range of applications. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram illustrating the working principle of a heat pipe.

[0024] Figure 2 This is a schematic diagram of the radial cross-sectional structure of the composite liquid-absorbing core structure provided in the embodiment of the present invention; Figure 3 This is a schematic diagram of the preparation process of the composite liquid absorption core structure provided in the embodiment of the present invention; The labels for the attached figures are as follows: 1. Composite liquid suction core; 11. Inner metal wire mesh sleeve; 12. Outer metal wire mesh sleeve; 13. Metal wire; 2. Metal wire mesh; 21. Rolling start edge; 22. Rolling end edge; 3. Spot welding point; 4. Heat pipe; 41. Steam chamber; 111. Second welding point; 121. Third welding point; 131. First welding point; A. First edge area; B. Second edge area. Detailed Implementation

[0025] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0026] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be located directly on or indirectly on the other component. When a component is referred to as "connected to" another component, it can be directly or indirectly connected to the other component.

[0027] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate that the device or element must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0028] In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. The specific implementation of this invention will be described in more detail below with reference to specific embodiments: Example 1: like Figure 2 As shown in the embodiment of the present invention, this embodiment provides a composite wick 1 for a circular cross-section alkali metal high-temperature heat pipe. The composite wick structure 2 is used to tightly adhere to the inner wall of the heat pipe shell and cover the entire evaporation section, insulation section, and condensation section.

[0029] The composite absorbent core 1 is composed of a multi-layer metal wire mesh sleeve formed by rolling two layers of stainless steel wire mesh (200 mesh). This includes an inner metal wire mesh sleeve 11, an outer metal wire mesh sleeve 12, and at least one metal wire mesh sleeve between the inner and outer metal wire mesh sleeves 11 and 12. On the outer side of the outer metal wire mesh sleeve 12, 12 stainless steel wires 13 are fixedly arranged at uniform circumferential intervals of 5 mm. These wires 13 extend parallel to the heat pipe axis.

[0030] The metal wire 13 is connected to the outer metal wire mesh sleeve 12 by evenly distributed spot welding points 3 (specifically, the first welding point 131). At the same time, the inner metal wire mesh sleeve 11 and the outer metal wire mesh sleeve 12 are also fixedly connected at their overlapping joints (i.e., the overlap between the starting edge 21 and the ending edge 22 of the metal wire mesh 2) by spot welding points 3 (specifically, the second welding point 111 and the third welding point 121), thus forming a solid composite structure.

[0031] Example 2: This embodiment provides a method for preparing the above-mentioned composite liquid-absorbing core structure 1, combined with Figure 3 The explanation is as follows: S1. Pretreatment: Select metal wire mesh 2 (specifically stainless steel material) and metal wire 13 (specifically stainless steel material) of appropriate size. First, place them in a 3 mol / L sodium hydroxide solution and ultrasonically clean for 12 minutes to remove oil stains; then soak them in a 3 mol / L hydrochloric acid solution at room temperature for 12 minutes to remove the oxide film; finally, rinse repeatedly with deionized water and dry in an inert gas environment. Specifically, the pretreatment steps are as follows: tap water wash for 7 minutes, alkaline wash for 12 minutes, tap water wash for 7 minutes, acid wash for 12 minutes, tap water wash for 7 minutes, and deionized water wash for 12 minutes. During washing, use a tool to agitate the metal wire mesh to ensure full contact between the wire mesh and the liquid.

[0032] S2. Prefabricated Composite Wire Mesh: Flatten the cleaned and dried wire mesh 2. On one side of the first edge region A in the width direction of the wire mesh 2 (this region will be located on the outermost side after rolling), arrange 12 metal wires 13 parallel to each other in the length direction, maintaining a spacing of 5mm between adjacent metal wires 13. Using a micro spot welder with a welding current of 3.5A, weld a first weld point 131 every 2cm along the length direction of each metal wire 13, firmly fixing it to the wire mesh 2.

[0033] S3. Rolling and Layer Fixing: Take a mandrel with a diameter of 19.6mm (slightly smaller than the inner diameter of the heat pipe, leaving room for assembly). (The mandrel should be made of brass; before each use, it should be polished and cleaned with gauze soaked in acetone.) Temporarily fix the starting end of the composite wire mesh (with metal wire 13 facing outwards) obtained in step S2 to the mandrel with tape. Manually or using equipment, rotate the mandrel at a uniform speed to wind the metal wire mesh 2 onto the mandrel to form the first layer (inner layer) sleeve. The second edge area B of the metal wire mesh 2 forms the first layer (inner layer) sleeve. When the first layer is finished and the second layer is started, use a spot welder at a current of 1.8A at 3cm intervals to spot weld at the overlapping part of the two layers of wire mesh, forming the second weld point 111, and fix the two layers of wire mesh at this point.

[0034] S4. Completion of Composite and Final Fixation: Continue winding until the portion of the mesh containing metal wire 13 is wound to the outermost layer, completely covering the inner sleeve. At this point, metal wire 13 is naturally arranged on the outside of the outermost sleeve. At the seam overlap between the outermost and second outermost mesh layers, spot weld again with a current of 1.8A and a spacing of 3cm to form a second weld point 121. Remove the tape at the starting end and spot weld the overlapping portion between the starting and ending ends to finally obtain a complete, self-supporting composite liquid-absorbing core.

[0035] Finally, the mandrel with the composite wick 1 is inserted into the shell of the heat pipe 4. After placement, the mandrel is removed, leaving the composite wick 1 inside the shell of the heat pipe 4. The metal wire 13 is close to the inner wall of the shell of the heat pipe 4, forming an axial deep channel between the metal wire 13 and the inner wall of the shell of the heat pipe 4. A vapor chamber 41 is formed inside the multi-layer metal wire mesh sleeve. The multi-layer metal wire mesh sleeve, formed by tightly rolled metal wire mesh, constitutes the matrix of the wick, providing a uniform, high-porosity capillary structure that ensures the lateral distribution and wetting of the working fluid. The metal wires attached to the outermost metal wire mesh sleeve and evenly distributed circumferentially form deeper and more regular axial capillary channels (axial deep channels) between the metal wires and the inner wall of the shell of the heat pipe 4. These channels can generate capillary forces much greater than the pores of the wire mesh itself, thereby significantly enhancing the "pumping" ability to drive the working fluid to axially flow back from the condensation section to the evaporation section. The two structures complement each other and work together to improve the overall performance of the absorbent core.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite wick structure for fixing to the inner surface of a heat pipe and covering the evaporation section, insulation section, and condensation section of the heat pipe, characterized in that, The composite liquid-absorbing core is composed of a multi-layer metal wire mesh sleeve formed by rolling metal wire mesh, and multiple metal wires are fixedly arranged at uniform intervals along the circumference of the outermost metal wire mesh sleeve on the outside of the outermost metal wire mesh sleeve.

2. The composite liquid-absorbing core structure as described in claim 1, characterized in that, The metal wire and the metal wire mesh sleeve, as well as the adjacent layers of the multi-layer metal wire mesh sleeve, are fixedly connected by spot welding.

3. The composite liquid-absorbing core structure as described in claim 1 or 2, characterized in that, The heat pipe has an inner diameter of 10-80 mm and a cross-sectional shape of circular, rectangular, trapezoidal or triangular.

4. The composite absorbent core structure as described in claim 1, characterized in that, The material of the metal wire mesh includes at least one of stainless steel, copper, and nickel.

5. The composite liquid-absorbing core structure as described in claim 1, characterized in that, The material of the metal wire includes at least one of stainless steel, copper, and nickel.

6. A method for preparing a composite liquid-absorbing core structure as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Clean and dry the metal wire mesh and metal wire for pretreatment; S2. Flatten the wire mesh and arrange the wires at predetermined intervals at the position corresponding to the outermost layer of the rolled wire mesh sleeve, and fix them by spot welding. S3. The metal wire mesh is rolled using a mandrel to form a multi-layer metal wire mesh sleeve. During the rolling process, the metal wire mesh sleeves of adjacent layers are fixed at the joint by spot welding. S4. Continue rolling until the outermost metal wire mesh sleeve with metal wires completely covers the inner metal wire mesh sleeve, and fix the outermost metal wire mesh sleeve and the next outermost metal wire mesh sleeve by spot welding to obtain the composite liquid absorption core.

7. The preparation method according to claim 6, characterized in that, The cleaning process in step S1 includes: sequentially performing alkaline washing, acid washing, and deionized water washing.

8. The preparation method according to claim 7, characterized in that, The alkaline washing uses a sodium hydroxide solution with a concentration of 1-5 mol / L and washes for 10-15 min; the acid washing uses a hydrochloric acid solution with a concentration of 5-10 mol / L and washes for 10-15 min.

9. The preparation method according to claim 6, characterized in that, In step S2, the welding current for spot welding the fixing metal wire is 3-4A, and the spacing between adjacent welding points is 1-5cm.

10. The preparation method according to claim 6, characterized in that, In steps S3 and S4, the welding current for spot welding the metal wire mesh sleeve is 1-2.5A, and the spacing between adjacent weld points is 1-5cm.

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