A flexible heat transfer device with a channel-hemispherical composite topology and its preparation method

Abstract

This invention provides a method for fabricating a flexible heat transfer device with a channel-hemispherical composite topology structure. The method includes the following steps: Step 1: Designing a channel topology and a hemispherical topology arranged at intervals as the topological structure, with multiple hemispherical topologies between adjacent channel topologies; Step 2: Optimizing the design profile curve, design height, design period T1 of the channel topology, the design radius of the hemispherical topology, the design spacing T2 between multiple hemispherical topologies between adjacent channel topologies, and the design spacing T3 between two adjacent rows of hemispherical topologies based on fluid flow resistance, maximum bending stress, effective cross-sectional area, and maximum structural support force, and selecting the optimized channel topology and hemispherical topology; Step 3: Fabricating a flexible heat transfer device with the optimized channel topology and hemispherical topology from Step 2. The flexible heat transfer device fabricated using the topology optimization design of this invention can maintain high-efficiency heat transfer performance even after multiple bends.

Description

Technical Field

[0001] This invention relates to the field of flexible heat transfer technology, and in particular to a flexible heat transfer device with a channel-hemispherical composite topology and its preparation method. Background Technology

[0002] Flexible heat transfer technology refers to heat transfer based on the absorption and release of latent heat during the phase change of a liquid working medium, and it is applicable to various shapes, surfaces, and bending scenarios. Currently, flexible heat transfer technology is widely used in flexible heat transfer devices. As a type of flexible device with high heat transfer efficiency, high stability, long bending life, and low cost, flexible heat transfer devices typically consist of a flexible shell, a flexible wick, and a liquid working medium.

[0003] Common flexible outer shells include metal films, polymer films, and polymer-metal composite films, which can be bent at large angles and with small radii under external force. Common flexible liquid-absorbing cores include woven metal mesh, foam metal mesh, 3D printed hydrogel porous structures, and powder sintered porous structures, which have capillary suction properties to achieve liquid working fluid reflux.

[0004] Traditional flexible heat transfer devices consist of three main parts: the outer shell, the steam channel, and the liquid wick. On the one hand, traditional flexible heat transfer devices have large bending moments during uneven bending, which can cause stress concentration and damage. On the other hand, their internal structure is complex, resulting in high manufacturing costs and low integration.

[0005] Therefore, flexible heat transfer devices still face significant technical bottlenecks in manufacturing technology, mechanical performance, and stability. Related research has proposed a segmented flexible heat transfer scheme, designing a flexible heat transfer device capable of operating at a certain bending angle. Specifically, a polymer shell is used in the flexible bending section, with an internal powder-sintered absorbent core. However, in most applications, such as foldable screen phones, flexible electronic devices, and aerospace systems, the corresponding heat transfer devices require multiple bending cycles. This scheme suffers from problems such as shell breakage, absorbent core powder shedding, and vapor channel blockage after repeated bending. Furthermore, this scheme has a relatively small bending angle, which cannot meet the requirements of current highly flexible electronic products. Another approach proposes using precision manufacturing processes to process flexible materials, thereby meeting the requirements for mechanical bending and long-term stability, but this method incurs high production costs.

[0006] Therefore, it is necessary to develop a flexible heat transfer device that can meet the requirements of mechanical bending and long-term stability, and has low manufacturing cost and simple manufacturing method. Summary of the Invention

[0007] The main technical problem to be solved by the present invention is to provide a flexible heat transfer device with a channel-hemispherical composite topology and its preparation method, which can avoid the problems of flexible shell damage and steam channel blockage caused by excessive flexible bending moment and stress concentration after multiple bends, thereby improving the heat transfer performance, bending life and working stability of the flexible heat transfer device.

[0008] To address the aforementioned technical problems, this invention provides a method for preparing a flexible heat transfer device with a channel-hemispherical composite topology, the method comprising the following steps:

[0009] Step 1: Design a topology of channel and hemispherical topology arranged at intervals as the topology structure, with multiple hemispherical topologies between adjacent channel topologies;

[0010] Step 2: Optimize the design profile curve, design height, design period T1, design radius of the hemispherical topology, design spacing T2 between multiple hemispherical topologies between adjacent channel topologies, and design spacing T3 between two adjacent columns of hemispherical topologies based on fluid flow resistance, maximum bending stress value, effective area of ​​cross section, and maximum support force index of structure, and select the optimized channel topology and hemispherical topology;

[0011] Step 3: Fabricate a flexible shell with the optimized channel topology and hemispherical topology from Step 2. Assemble the flexible shell with a flexible wicking core and a liquid working fluid to form a flexible heat transfer device. The material of the flexible wicking core is not limited; as long as it achieves the purpose of this invention, one or more of the following can be selected: woven metal mesh, foam metal mesh, 3D-printed hydrogel porous structure, and powder sintering porous structure. The woven metal mesh is formed by weaving metal wires into a mesh with a square or rhomboid cross-section; the metal wire material can be one or more of aluminum alloy, stainless steel, and copper; the woven metal mesh has a distinct pore size characteristic, with a pore size of 100–400 mesh.

[0012] In some embodiments, the channel topology in step 2 adopts a periodic profile curve, and the design profile curve is adjusted to one of the following: trigonometric function, polynomial function, exponential function, logarithmic function, and inverse trigonometric function. The design height is adjusted within the range of 0.1-1mm, and the T1 is adjusted within the range of 0.2-2mm.

[0013] In some embodiments, the radius of the hemispherical topological profile design is adjusted in the range of 0.1-1mm, T2 is adjusted in the range of 0.2-2mm, and T3 is adjusted in the range of 1-5mm.

[0014] In some of these embodiments, T2 is equal to twice T1, and T3 is equal to T1.

[0015] In some embodiments, the channel topology design contour curve optimized in step 2 is fitted with trigonometric functions, T1 is 1 mm, the design height is 0.5 mm, the design radius of the hemispherical topology optimized in step 2 is 0.45 mm, T2 is 2 mm, and T3 is 1 mm.

[0016] In some embodiments, step 3 involves hot-pressing the flexible material using a channel topology mold to obtain a channel topology shell, hot-pressing the flexible material using a hemispherical topology mold to obtain a hemispherical topology shell, and then stacking the channel topology shell and the hemispherical topology shell together to obtain the flexible shell. The type of flexible material is not limited; as long as it achieves the purpose of the invention, it can be one or more of a metal film, a polymer film, or a polymer-metal composite film. The types of metal and polymer materials are not limited; as long as they achieve the purpose of the invention, the metal material can be one of copper, aluminum, stainless steel, etc., and the polymer material can be one or more of PP (polypropylene), PE (polyethylene), PET (low-density polyethylene terephthalate), etc.

[0017] To address the aforementioned technical problems, the present invention also provides a channel-hemispherical composite topology flexible heat transfer device, wherein the flexible heat transfer device is prepared by the preparation method of any of the above embodiments.

[0018] In some embodiments, the flexible outer shell includes an upper shell and a lower shell, the flexible liquid-absorbing core is placed between the upper shell and the lower shell, the liquid working fluid is transported in the flexible liquid-absorbing core inside the shell, the upper shell and the lower shell include flexible sections and non-bending sections, the optimized channel topology and the hemispherical topology constitute the flexible section, and the thickness of the upper shell and the lower shell is between 0.05-0.2 mm.

[0019] In some embodiments, the flexible absorbent core is provided with a hollow structure corresponding to the topology. The hollow structure includes multiple hollow units arranged in an array, with a spacing of 0.5-3mm between the hollow units.

[0020] In some embodiments, the hollowed-out unit is shaped as a grid, strip, or snake.

[0021] To address the aforementioned issues, this embodiment also provides a flexible heat transfer device heat pipe with a composite topology, including the aforementioned channel-hemispherical composite topology flexible heat transfer device.

[0022] Compared with the prior art, the beneficial effects of the present invention include:

[0023] 1. This invention utilizes topology optimization design to create an optimized channel-hemispherical composite topology flexible shell for fabricating a flexible heat transfer device. The channel topology is subjected to stretching and contraction, compensating for displacement caused by bending and reducing bending moment. At the same time, the hemispherical topology has strong support capacity, ensuring smooth steam flow and preventing the flexible shell from breaking under repeated bending cycles and the steam channel from becoming blocked, which would otherwise result in a short lifespan and high thermal resistance for the flexible heat transfer device.

[0024] 2. The present invention adopts a flexible liquid-absorbing core with a hollow structure, which can effectively optimize the flexibility of the flexible liquid-absorbing core. On the one hand, it can reduce stress concentration during bending, and on the other hand, it provides the liquid return capillary suction force required for the operation of the flexible heat transfer device, reducing the impact of the decrease in capillary suction force caused by material removal. This further enables the flexible heat transfer device to operate in multiple cycles, extends the life of the flexible heat transfer device, and improves its performance. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the overall structure of the flexible heat transfer device;

[0026] Figure 2 This is a schematic diagram of a flexible outer shell;

[0027] Figure 3 This is a schematic diagram of a flexible liquid-absorbing core.

[0028] Figure label:

[0029] 1. Upper shell; 2. Flexible absorbent core; 3. Lower shell; 1-1. Non-bending section upper shell; 1-2. Flexible section upper shell; 1-2a. Flexible section channel topology upper shell; 1-2b. Flexible section hemispherical topology upper shell; 1-2c. Flexible section channel-hemispherical composite topology upper shell; 2-1. Non-bending section absorbent core; 2-2. Bending section absorbent core; 2-2a. Flexible section transverse strip structure absorbent core; 2-2b. Flexible section vertical strip structure absorbent core; 2-2c. Flexible section serpentine structure absorbent core. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in more detail below with reference to the accompanying drawings and specific embodiments. However, the scope of protection of this invention is not limited to these embodiments. The same reference numerals throughout the text always represent the same elements, and similar reference numerals represent similar elements.

[0031] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "horizontal", "vertical", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the perspective view in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0032] Example 1

[0033] Reference Figures 1-3 This embodiment provides a flexible heat transfer device with a channel-hemispherical composite topology, including a flexible shell and a flexible liquid-absorbing core 2. The flexible shell is divided into an upper shell 1 and a lower shell 3. The flexible liquid-absorbing core 2 is placed between the upper shell 1 and the lower shell 3. The liquid working fluid is transferred in the flexible liquid-absorbing core inside the shell.

[0034] like Figure 2 As shown, in this embodiment, the upper shell 1 includes a flexible upper shell 1-2 and a non-bending upper shell 1-1. The channel topology after topology optimization and the hemispherical topology constitute the flexible segment 1-2. The flexible segment 1-2 is obtained by overlapping the flexible channel topology upper shell 1-2a and the flexible hemispherical topology upper shell 1-2b. The lower shell 3 has the same structure as the upper shell 1, and the thickness of both the upper shell 1 and the lower shell 3 is 0.113 mm.

[0035] like Figure 3 In this embodiment, the flexible absorbent core 2 includes a non-bending absorbent core 2-1 and a flexible absorbent core 2-2. The flexible absorbent core 2 has a perforated structure corresponding to the topological structure as the flexible absorbent core 2-2. The perforated structure includes multiple perforated units arranged in an array, with a 2mm interval between units. The perforated units are in the shape of a grid. As a simple alternative to this embodiment, the perforated unit shape can also be a strip structure or a serpentine structure.

[0036] The flexible heat transfer device with a channel-hemispherical composite topology in this embodiment is manufactured through the following steps:

[0037] Step 1: Design a reasonable topology.

[0038] Since flexible heat transfer devices need to provide internal channels or cavities to allow the working fluid to flow during operation, and stress concentration during bending needs to be reduced in order to improve the flexibility life, a reasonable topology needs to be designed to meet the requirements.

[0039] In this embodiment, a channel topology and a hemispherical topology arranged at intervals are designed as the topological structure according to the above requirements. The adjacent channel topologies include multiple hemispherical topologies. The channel topology design can provide a channel for the flow of working fluid, and at the same time, it can reduce stress concentration in the bending section, while the hemispherical topology can further provide support for the internal cavity.

[0040] Step 2: Optimize the topology.

[0041] Based on fluid flow resistance, maximum bending stress, effective cross-sectional area, and maximum structural support force, the design profile curve, design height, design period T1, design radius of the hemispherical topology, design spacing T2 between multiple hemispherical topologies between adjacent channel topologies, and design spacing T3 between two adjacent columns of hemispherical topologies are optimized, and the optimized channel topology and hemispherical topology are selected.

[0042] Specifically, in this embodiment, the channel topology adopts a periodic profile curve, and the designed profile curve is adjusted to one of the following: trigonometric function, polynomial function, exponential function, logarithmic function, and inverse trigonometric function. The design height is adjusted within a range of 0.1-1 mm, and T1 is adjusted within a range of 0.2-2 mm. The hemispherical topology profile design radius is adjusted within a range of 0.1-1 mm, T2 within a range of 0.2-2 mm, and T3 within a range of 1-5 mm. Wherein, T2 is equal to twice T1, and T3 is equal to T1.

[0043] By observing the index values ​​of fluid flow resistance, maximum bending stress, effective cross-sectional area, and maximum structural support force, the channel topology and hemispherical topology are continuously optimized within the above adjustment range. Specifically, the smaller the fluid flow resistance and maximum bending stress, the better the optimization effect of the topology; the larger the effective cross-sectional area and the maximum structural support force, the better the optimization effect.

[0044] After optimization, the optimized channel topology and hemispherical topology are obtained. Specifically, the design contour curve of the optimized channel topology in step 2 is fitted with trigonometric functions, T1 is 1mm, the design height is 0.5mm, the design radius of the optimized hemispherical topology in step 2 is 0.45mm, T2 is 2mm, and T3 is 1mm.

[0045] Step 3: Fabricate a flexible outer shell with the optimized channel topology and hemispherical topology from Step 2, and assemble the flexible outer shell with a flexible wicking core and a liquid working fluid to form a flexible heat transfer device. Specific steps include:

[0046] (1) Fabrication of the outer shell. In this embodiment, an aluminum-polymer composite film is selected as the flexible material for the flexible outer shell and cut to size to obtain an upper shell 1 and a lower shell 3 of 30mm × 120mm, wherein the thickness of both the upper shell 1 and the lower shell 3 is 0.113mm. The cut aluminum-polymer composite film is hot-pressed using a mold with an optimized channel topology to obtain a flexible channel topology upper shell 1-2a, and hot-pressed using a mold with an optimized hemispherical topology to obtain a flexible hemispherical topology upper shell 1-2b. The flexible channel topology upper shell 1-2a and the flexible hemispherical topology upper shell 1-2b are stacked to obtain a flexible channel-hemispherical composite topology upper shell 1-2c. The same steps are used to fabricate a flexible channel-hemispherical composite topology lower shell.

[0047] As a simple alternative to this embodiment, the flexible material used as the flexible shell can also be a metal film, a polymer film, or other polymer-metal composite film. The metal material can be one of copper, aluminum, stainless steel, etc., and the polymer material can be one of PP (polypropylene), PE (polyethylene), PET (low-density polyethylene terephthalate), etc.

[0048] In this embodiment, the flexible shell of the channel-hemispherical composite topology is manufactured using hot pressing technology. As a simple alternative to this embodiment, it can also be manufactured using other manufacturing technologies, including but not limited to micromachining technology and sintering process.

[0049] (2) Fabrication of a flexible absorbent core. A 250-mesh copper braided mesh is cut to an appropriate size to obtain a 25mm × 100mm flexible absorbent core 2. Using laser processing technology, an array of mesh cutout units is fabricated on the 250-mesh copper braided mesh to form a hollow structure, which serves as the flexible section 2-2 of the absorbent core. The flexible absorbent core 2 is obtained by low-temperature sintering of multiple layers of copper braided mesh, wherein the mesh cutout units are spaced 2mm apart.

[0050] As a simple alternative to this embodiment, it is also possible to process products such as Figure 3 The flexible segment transverse strip structure liquid absorption core 2-2a, the flexible segment vertical strip structure liquid absorption core 2-2b, and the flexible segment serpentine structure liquid absorption core 2-2c are shown.

[0051] As a simple alternative to this embodiment, the flexible absorbent core 2 can also be made of foam metal mesh, 3D printed hydrogel porous structure, or powder sintering porous structure. When woven metal mesh is used as the flexible absorbent core 2, the woven mesh can also be made of aluminum alloy or stainless steel, and the pore size can be any size between 100 and 400 mesh.

[0052] In this embodiment, the hollow structure of the flexible segment 2-2 of the flexible liquid-absorbing core 2 is formed by laser technology. As a simple alternative to this embodiment, it can also be formed by laser technology, milling technology, micro-carving technology, etc.

[0053] (3) Assemble the flexible outer shell (upper shell 1, lower shell 3) with the flexible liquid-absorbing core 2 and the liquid working medium to form a flexible heat transfer device. The upper shell 1 and lower shell 3 made in (1) and the flexible liquid-absorbing core 2 made in (2) are sealed by hot pressing welding process. Then, the flexible heat transfer device of the channel-hemispherical composite topology of this embodiment is prepared by the encapsulation process of vacuuming, filling with liquid working medium and resealing.

[0054] In this embodiment, a hot-press welding process is used to seal the upper shell 1, lower shell 3, and flexible liquid-absorbing core 2. As a simple alternative to this embodiment, one or more welding processes such as low-temperature diffusion welding and ultrasonic welding can also be used for sealing. Welding can provide a sealed space to ensure the vacuum level required for operation. The vacuum level is achieved by extracting and venting internal air using relevant machines and then sealing the joints with welding. The vacuum level is 4-6 Pa.

[0055] In this embodiment, the liquid working medium is one of anhydrous ethanol, deionized water, acetone, etc.

[0056] To verify the optimization results of the flexible heat transfer device with a channel-hemispherical composite topology obtained after topology optimization design in this embodiment, referring to "GB / T 14812-2008 Test Method for Heat Transfer Performance of Heat Pipe", a point heat source was arranged at one end of the prepared flexible heat transfer device, and thermocouples were arranged at equal intervals through the sample. The temperature distribution law of the flexible heat transfer device was tested under a stepped heat load input. The flexible heat and mass transfer device was fixed at one end and free at the other end. The bending life of the device was tested under the operation of the bending test device with a bending radius of 5 mm and a bending angle of 0° to 180°.

[0057] After verification, the total mass of the flexible heat transfer device in this embodiment is ≤5g; the heat transfer flux density of the flexible heat transfer device in this embodiment is ≥4W / cm³. 2 The temperature difference between the evaporation end and the condensation end is ≤4℃, and the thermal resistance of the flexible heat transfer device is ≤1℃ / W;

[0058] The flexible heat transfer device in this embodiment can withstand ≥50,000 bends and its thermal performance decays by ≤10%. After more than 50,000 free bends, the flexible outer shell of the flexible heat transfer device is not damaged and the internal vacuum level does not decrease significantly.

[0059] Under a working temperature of 90°C, the flexible heat transfer device of this embodiment can work continuously for ≥1000 hours with a thermal performance degradation of ≤10%.

[0060] From an initial 0° angle, the bending radius of the flexible heat transfer device in this embodiment is ≤5mm, and the bending moment is ≤15N·mm.

[0061] This embodiment features a flexible heat transfer device with a channel-hemispherical composite topology designed with topology optimization. The flexible upper shell 1 and lower shell 3 of the composite topology provide a combination of functions, such as supporting the vapor channel and reducing bending moment. The flexible liquid absorbing core 2 provides a combination of functions, such as capillary suction force for liquid reflux and reducing stress concentration. Experiments have shown that this flexible heat transfer device with a channel-hemispherical composite topology designed with topology optimization still has high heat transfer performance after bending at large angles, small radii, and multiple times.

[0062] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a flexible heat transfer device with a channel-hemispherical composite topology, characterized in that, The preparation method includes the following steps: Step 1: Design a topology of channel and hemispherical topology arranged at intervals as the topology structure, with multiple hemispherical topologies between adjacent channel topologies; Step 2: Optimize the design profile curve, design height, design period T1, design radius, design spacing T2 between multiple hemispherical topologies between adjacent channel topologies, and design spacing T3 between two adjacent columns of hemispherical topologies based on fluid flow resistance, maximum bending stress value, effective area of ​​cross section, and maximum structural support force index. Select the optimized channel topology and hemispherical topology. The channel topology adopts a periodic profile curve, and the design profile curve is adjusted to a trigonometric function. Step 3: Fabricate a flexible shell with the optimized channel topology and hemispherical topology of Step 2, and assemble the flexible shell with the flexible liquid wick and liquid working fluid to form a flexible heat transfer device.

2. The method for preparing the flexible heat transfer device with channel-hemispherical composite topology according to claim 1, characterized in that, The design height adjustment range in step 2 is 0.1-1mm, and the T1 adjustment range is 0.2-2mm.

3. The method for preparing the flexible heat transfer device with a channel-hemispherical composite topology according to claim 2, characterized in that, The radius adjustment range for the hemispherical topological profile design is 0.1-1mm, the adjustment range for T2 is 0.2-2mm, and the adjustment range for T3 is 1-5mm.

4. The method for preparing the flexible heat transfer device with channel-hemispherical composite topology according to claim 3, characterized in that, T2 equals twice T1, and T3 equals T1.

5. The method for preparing the flexible heat transfer device with channel-hemispherical composite topology according to claim 4, characterized in that, The optimized channel topology design contour curve in step 2 is fitted with trigonometric functions, T1 is 1mm, the design height is 0.5mm, the design radius of the optimized hemispherical topology in step 2 is 0.45mm, T2 is 2mm, and T3 is 1mm.

6. The method for preparing the flexible heat transfer device with a channel-hemispherical composite topology according to claim 5, characterized in that, Step 3 involves using a channel topology mold to hot-press the flexible material to obtain a channel topology shell, using a hemispherical topology mold to hot-press the flexible material to obtain a hemispherical topology shell, and then stacking the channel topology shell and the hemispherical topology shell together to obtain the flexible shell.

7. A flexible heat transfer device with a channel-hemispherical composite topology, characterized in that, The flexible heat transfer device is prepared by the preparation method according to any one of claims 1-6.

8. The flexible heat transfer device with channel-hemispherical composite topology according to claim 7, characterized in that, The flexible outer shell includes an upper shell and a lower shell, and the flexible liquid-absorbing core is placed between the upper shell and the lower shell. The liquid working fluid is transported in the flexible liquid-absorbing core inside the shell. The upper shell and the lower shell include a flexible section and a non-bending section. The optimized channel topology and the hemispherical topology constitute the flexible section.

9. The flexible heat transfer device with channel-hemispherical composite topology according to claim 8, characterized in that, The flexible absorbent core has a hollow structure corresponding to the topological structure. The hollow structure includes multiple hollow units, which are arranged in an array.

10. The flexible heat transfer device with channel-hemispherical composite topology according to claim 9, characterized in that, The hollowed-out unit can be one of the following shapes: grid, strip, or serpentine.

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