Flexible heat pipe with high elastic composite film and preparation method

Abstract

The application discloses a flexible heat pipe with a high-elasticity composite film, which comprises a high-elasticity composite film shell, a liquid-absorbing core and a liquid working medium; the shell surrounds a closed cavity, and the liquid-absorbing core and the liquid working medium are arranged in the cavity; wherein the high-elasticity composite film comprises a polymer base and at least one corrugated metal layer arranged in the polymer base, and the corrugated metal layer has a corrugated structure extending along the axial direction of the flexible heat pipe. The application further discloses a preparation method thereof. The high-elasticity composite film is used as the shell of the flexible heat pipe, has outstanding sealing performance under the premise of meeting the bending performance of the flexible heat pipe, can realize large-angle bending of the flexible heat pipe, and can still maintain good sealing performance within a certain number of bending times. The application can solve the problems of high-molecular penetration of traditional polymer film materials and insufficient bending performance of polymer-metal foil composite film materials, guarantee the bending and heat transfer performance of the flexible heat pipe, and provide a solution for heat dissipation of high-heat-flow-density flexible electronic devices.

Description

Technical Field

[0001] This invention relates to the technical field of heat and mass transfer in flexible heat pipes, and particularly to a flexible heat pipe with a highly elastic composite film and its preparation method. Background Technology

[0002] As one of the mainstream directions derived from heat pipes since their birth a century ago, flexible heat pipes have a unique flexibility that makes their application scenarios wider, such as flexible electronic screens, VR glasses, and some irregularly shaped high-temperature integrated electronic objects. Compared with traditional heat pipes, flexible heat pipes are more difficult to select shell materials. Compared with the traditional heat pipe shell, which only needs to transfer heat and maintain vacuum, the flexible heat pipe shell also needs to meet the requirements of high flexibility and no damage after repeated bending.

[0003] During bending, flexible heat pipes experience stretching on the outer side and compression on the inner side, resulting in inconsistent film deformation between the two sides. The current selection of flexible film materials is limited. Based on different shell materials, flexible heat pipes can be classified into three categories: metal flexible heat pipes, polymer flexible heat pipes, and composite flexible heat pipes. While polymer films provide superior flexibility, the intermolecular permeation problem leads to poor sealing performance, causing the internal pressure to gradually increase, raising the boiling point of the working fluid until failure. Furthermore, the low thermal conductivity of polymer materials reduces the heat transfer performance of the heat pipe. Although metal films offer high density, the inherent properties of metals, as shown in the stress-strain curve, result in a small elastic deformation range during bending, leading to breakage after repeated bending. This makes it difficult to support the large-angle, small-radius bending conditions of flexible heat pipes. Single-material films are clearly insufficient to meet the requirements of flexible heat pipe shells. Although polymer-metal composite films have been applied to flexible heat pipes to give them certain comprehensive performance, existing composite films lack targeted design. They are generally planar composite films from other fields that are directly used in heat pipe manufacturing. Due to the insufficient elasticity of the metal foil, the bending performance is poor. The main way to enhance flexibility is to create a structural topology on the film. However, this process is complex, causes significant film loss, and results in a low yield. Therefore, there is an urgent need for a new flexible heat pipe shell material to further improve its comprehensive performance.

[0004] Another flexible heat pipe manufacturing process involves using different materials for the evaporation section, insulation section, and condensation section of the heat pipe. Although this can significantly improve heat transfer and bending capabilities, it is clear that this method is more difficult to process.

[0005] Therefore, it is necessary to develop a highly elastic composite membrane and a flexible heat pipe. Summary of the Invention

[0006] The core objective of this invention is to create a flexible heat pipe with a highly elastic composite film and its preparation method, based on overcoming the limitations of existing flexible heat pipe technology. The highly elastic composite film serves as a key component of the heat pipe shell, thereby solving problems such as insufficient flexibility and short bending life of flexible heat pipes.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A flexible heat pipe with a highly elastic composite film includes a highly elastic composite film shell, a liquid wick, and a liquid working fluid; the shell forms a closed cavity, and the liquid wick and the liquid working fluid are disposed within the cavity; wherein the highly elastic composite film includes a polymer substrate and at least one corrugated metal layer disposed in the polymer substrate, and the corrugated metal layer has a corrugated structure extending along the axial direction of the flexible heat pipe.

[0009] Optionally, the thickness of the highly elastic composite film is 0.1 mm to 1 mm, the thickness of the corrugated metal layer is 10 to 100 μm, and the inner and outer sides of the corrugated metal layer cover the polymer substrate.

[0010] Optionally, the corrugated structure is composed of periodically repeating units, and the corrugation shape is a sine wave, triangle, rectangle or semicircle, with a wave height of 50~500 μm.

[0011] Optionally, the material of the corrugated metal layer includes Cu, Al, Fe or aluminum-based composite materials, wherein the aluminum-based composite material includes TiC / Al, TiB2 / Al or TiB2 / Al-Li.

[0012] Optionally, the polymer substrate may include rubber, PDMS, polyethylene, or polypropylene.

[0013] Optionally, the polymer substrate has multiple corrugated metal layers, which are spaced apart by the polymer substrate material.

[0014] Optionally, the liquid suction core is one or more of the following: copper wire mesh liquid suction core, powder sintered liquid suction core, fiber sintered liquid suction core, and porous foam liquid suction core; the liquid working fluid is one or more of the following: deionized water, anhydrous ethanol, and acetone; and the vacuum degree value inside the cavity is 1×10⁻⁶. -3 pa~1×10 -6 pa.

[0015] Optionally, the flexible heat pipe with a highly elastic composite film has two layers of the highly elastic composite film, which are joined at the edges to form a closed cavity. The wick and the working fluid are disposed within the cavity, forming a structure in which the wick and the working fluid are sandwiched between the two layers of highly elastic composite film. The two layers of highly elastic composite film can be pre-bent into a specific shape, thereby forming a specific cross-sectional shape of the heat pipe after joining.

[0016] The above-mentioned method for preparing a flexible heat pipe with a highly elastic composite film includes the following steps:

[0017] 1) Cold pressing pre-shaping of the highly elastic composite film;

[0018] 2) Take two cold-pressed high-elasticity composite membranes and sandwich the liquid-absorbing core. Seal the edges of the upper and lower high-elasticity composite membranes together through a sealing process, leaving a liquid inlet. Fill the liquid working medium through the liquid inlet. Seal the liquid inlet in a vacuum environment or after vacuuming, so that the liquid-absorbing core and the liquid working medium are located in the closed cavity surrounded by the high-elasticity composite membrane.

[0019] Optionally, the cold-pressing pre-shaping is to form a non-planar shape of the high-elasticity composite film, so that the two cold-pressed high-elasticity composite films are combined to form a specific cross-sectional shape, such as forming a circular, square or other irregular shape.

[0020] Optionally, the sealing process includes welding, hot pressing, or adhesive bonding.

[0021] In applications where it serves as the outer shell of a flexible heat pipe, the highly elastic composite film can adapt to a wide range of bending deformations. When bent under external force, the corrugated metal structure experiences axial tensile force and elastically elongates along with the outer film. The elongation reaches its maximum at the bending center and gradually decreases towards both sides, effectively coordinating with the stretching and contraction properties of the polymer layer while maintaining the integrity and functional stability of the film. Due to their inherent flexibility, the inner and outer polymer layers deform along with the corrugated structure. The corrugated structure and polymer layer absorb or release the bending stress of the composite film, reducing film loss during bending and improving the bending limit and lifespan of the composite film. Furthermore, because the corrugated structure is made of metal, the composite film maintains both high flexibility and airtightness, preserving the vacuum inside the flexible heat pipe and achieving continuous heat transfer performance.

[0022] The polymer substrate provides high flexibility to expand the bending range of the heat pipe and supports and protects the internal metal layer to prevent it from breaking. The metal layer achieves gas barrier, maintains a low vacuum inside the heat pipe and a low boiling point of the working fluid, and enables efficient heat transfer. Its corrugated structure compensates for the elongation of the metal layer when bending, allowing the metal layer to follow the polymer layer to bend at high angles without breaking.

[0023] Optionally, the polymer substrate material can be tightly bonded to the corrugated structure inside the membrane through a certain processing technology, and the resulting composite membrane can be bent repeatedly at large angles and small radii.

[0024] Furthermore, the welding process is one or more of the following: precision micro-welding, diffusion welding, welding in a vacuum or inert gas environment, laser micro-welding, etc.

[0025] The beneficial effects of this invention are as follows:

[0026] 1) The highly elastic composite film obtained by combining the metal corrugated structure and the polymer substrate material has excellent flexibility and sealing performance. The corrugated structure applied to the metal film can significantly increase its flexibility. Combined with the polymer, which has a certain degree of flexibility, the flexibility of the composite film is further enhanced. Under the bending conditions of large angle and small radius, it can be bent many times without damage. This allows the heat pipe to adapt to complex or irregular space designs, such as heat management applications in curved surfaces or corners. It is the preferred flexible shell material.

[0027] 2) The corrugated structure enhances the mechanical stability of the outer shell. When bent, the metal corrugated tube can automatically compensate and deform synchronously with the polymer film during the bending process. The two share the bending stress during the entire bending process, and can maintain its structural integrity and sealing even after repeated bending. Compared with a single polymer film, the composite film has high sealing performance due to its internal metal layer, so there will be no air leakage problem. When used as a flexible heat pipe outer shell, it can always maintain a low vacuum inside the heat pipe, improve the heat transfer life of the heat pipe, and improve the overall durability and reliability of the heat pipe.

[0028] 3) The metal layer in the composite film provides an efficient heat conduction path, which helps to quickly and evenly distribute heat, which is especially important for high-performance thermal management systems and can better meet the increasing heat dissipation requirements.

[0029] 4) Due to its excellent flexibility, thermal conductivity and durability, the flexible heat pipe of the present invention is suitable for a variety of applications, including but not limited to heat dissipation of electronic products, temperature control systems of spacecraft and satellites, wearable devices and other occasions that require efficient thermal management. The application range of the highly elastic composite film is very impressive. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the longitudinal section of a flexible heat pipe with a highly elastic composite film, as shown in the embodiment.

[0031] Figure 2 This is a schematic diagram of the longitudinal section of the highly elastic composite membrane in the embodiment.

[0032] Figure 3This is a schematic diagram (longitudinal section) showing the compensation of the internal corrugated structure of the high-elasticity composite membrane on the outer side when the flexible heat pipe is bent, as described in the embodiment.

[0033] Figure 4 This is a schematic diagram (longitudinal section) showing the stress absorption of the internal corrugated structure of the highly elastic composite membrane on the inner side of the flexible heat pipe during bending, as described in the embodiment.

[0034] Figure 5 This is a schematic diagram of the longitudinal section of a highly elastic composite membrane according to another embodiment;

[0035] In the figure: 1-high elastic composite membrane, 2-liquid absorbent core, 11 / 13-corrugated metal layer, 12-polymer substrate. Detailed Implementation

[0036] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments. The accompanying drawings are merely illustrative to facilitate understanding of the invention, and their specific proportions can be adjusted according to design requirements. The vertical relationships of relative elements and the definitions of front / back in the graphics described herein should be understood by those skilled in the art to refer to the relative positions of the components; therefore, they can all be flipped to present the same component, and all of this should fall within the scope disclosed in this specification.

[0037] A flexible heat pipe using a highly elastic composite film as its outer shell has the following overall structure: Figure 1 As shown, the device includes a highly elastic composite membrane shell (1), a liquid absorbent core (2), and a liquid working medium. The highly elastic composite membrane 1 forms a closed cavity, and the liquid absorbent core (2) and liquid working medium are disposed within the cavity. Specifically, the shell 1 is formed by two upper and lower highly elastic composite membranes 1 joined together at their edges to form a closed cavity. The liquid absorbent core (2) and liquid working medium are sandwiched between the two high-elasticity composite membranes 1 to form a strip-shaped tubular structure. The two highly elastic composite membranes 1 can be pre-formed into curved shapes, such as those with arc-shaped cross-sections, through processes such as cold pressing, and then joined together to form a circular tubular structure.

[0038] High-elasticity composite film 1 Figure 2 As shown, the high-elasticity composite film includes a corrugated metal layer 11 and a polymer substrate 12. The corrugated metal layer 11 is disposed within the polymer substrate 12. As can be seen from the longitudinal section along the axial direction of the flexible heat pipe, the high-elasticity composite film includes at least three layers of materials: two outer polymer materials formed by the polymer substrate and one embedded metal material. The corrugated metal layer 11 has a corrugated structure extending along the axial direction of the flexible heat pipe, and is tightly bonded to the polymer substrate 12 without gaps. The surface of the high-elasticity composite film (i.e., the side of the inner and outer polymer material layers away from the metal layer) remains flat, maintaining the flatness and uniformity of the overall structure.

[0039] In this embodiment, the total thickness of the high-elasticity composite film 1 is 0.1 mm. The corrugated metal layer 11 is made of copper and has a uniform thickness of 0.01–0.02 mm. Its longitudinal cross-sectional shape along the axis of the flexible heat pipe is a sinusoidal corrugated shape with a wave height of 500 μm and a wavelength of 1 mm. Except for the corrugated metal layer 11, the rest of the high-elasticity composite film 1 is a polymer substrate 12, and the material of the polymer substrate 12 is, for example, polypropylene.

[0040] The wick 2, for example, is made of hydrophilically modified copper wire mesh. This wick itself possesses excellent flexibility and can be bent synchronously with the outer shell. The working fluid, for example, is deionized water, with a filling rate of 50%. Through vacuuming and sealing, the vacuum level inside the flexible heat pipe reaches 1×10⁻⁶. -3 pa~1×10 -6 A certain vacuum level can lower the boiling point of the liquid working fluid. When the heat pipe is bent, the polymer substrate 12 provides high flexibility, thereby expanding the bending angle range and supporting and protecting the internal corrugated metal layer 11 to prevent it from breaking. The corrugated metal layer 11 achieves sealing performance and maintains a low vacuum level inside the heat pipe. The corrugated structure gives the metal layer good extensibility, allowing it to undergo stretching and compression deformation when bending at large angles with the polymer layer, thus achieving high flexibility, long life, and high thermal conductivity of the composite film.

[0041] When the flexible heat pipe is bent, the compensation of the internal corrugated structure of the high-elasticity composite film located on the outer side of the bending direction is as follows: Figure 3 As shown: Under normal conditions, the corrugated metal layer 11 in the membrane has a uniformly distributed corrugated structure in a periodic manner. When a bending force is applied from the outside, the corrugated metal layer 11 deforms. The deformation of the corrugated structure near the bending center is the largest, the corrugated thickness decreases, and it stretches to both sides to compensate for the increase in length caused by the tension on the outside of the high elastic composite membrane 1 during bending. The deformation gradually decreases to both sides and can be ignored after reaching a certain distance, that is, it still maintains the original waveform. When it returns from the bent state to the normal state, the corrugated structure of the stretched corrugated metal layer 11 returns to its original state.

[0042] When the flexible heat pipe is bent, the stress absorption of the internal corrugated structure of the high-elasticity composite film located on the inside of the bending direction is as follows: Figure 4 As shown: When the composite membrane is subjected to pressure, the corrugated structure of the inner corrugated metal layer 11 absorbs the pressure, the wavelength decreases, and the closer to the bending center, the denser the peaks and troughs become. This design reduces the possibility of bending damage to the composite membrane and reduces bending damage on the membrane, effectively improving the bending life of the inner composite membrane.

[0043] Throughout the process, the polymer substrate 12 deforms along with the corrugated metal layer 11. The corrugated metal structure, which deforms with bending, can store energy, thereby buffering or absorbing bending stress. When returning to a planar state, the corrugated metal structure releases strain, which helps the composite membrane to return from a bent state to a planar state. This allows the composite membrane to be bent repeatedly at large angles and small radii, achieving large-angle bending of 0-180 degrees without affecting the sealing performance. It has high flexibility while ensuring good sealing performance of the composite membrane. Its working state is similar to the tension and compression state of a spring.

[0044] During the preparation of the high-elasticity composite film 1, the substrate material and the corrugated metal layer within the film are tightly bonded through one or more processing techniques such as casting, adhesive bonding, hot pressing, and surface modification. This ensures that the different film layers remain tightly bonded even after repeated bending, preventing detachment or film breakage. The corrugated structure of the corrugated metal layer is processed using one or more techniques such as laser micromachining, electron beam etching, photolithography, and hydroforming.

[0045] For example, when the material of the corrugated metal layer 11 is aluminum, femtosecond laser technology can be used to selectively etch the upper and lower surfaces of the flat aluminum metal. The maximum etching depth is the difference between the thickness of the flat plate and the thickness of the corrugated structure. Through subtractive manufacturing, a periodic corrugated metal layer structure with a certain thickness is finally retained. Then, a polypropylene layer is bonded to the upper and lower surfaces with an adhesive. The polypropylene layer model satisfies the requirement that the three-layer structure has a neat and flat shape after bonding, resulting in a highly elastic composite film.

[0046] The above-mentioned method for preparing a flexible heat pipe using a highly elastic composite membrane with an internal corrugated structure is achieved through the following steps:

[0047] (1) Preliminary preparation: The high elastic composite membrane 1 and the liquid absorbent core 2 are cut according to the size of the heat pipe designed for use. The high elastic composite membrane 1 is cold-pressed and pre-shaped. The high elastic composite membrane 1 is placed between the molds of the cold press. Through the pressure and action of the cold press, the planar high elastic composite membrane 1 is plastically deformed under the action of the mold to obtain the required shape to distinguish the heat pipe shell and the sealing edge. For example, the planar high elastic composite membrane 1 is bent into an arc structure with a semi-circular cross-section and a sealing edge is formed for sealing. The relative position of the liquid absorbent core 2 and the high elastic composite membrane 1 is initially fixed to solve the positioning problem in subsequent operations. At the same time, a piece of high elastic composite membrane 1 of the same size is cut for single composite membrane flexibility test.

[0048] (2) Processing and preparation: Two cold-pressed high-elasticity composite membranes 1 are used to sandwich the liquid absorber 2 with the assistance of a mold. Then, the three sides are sealed by welding and other sealing processes, so that the sealing edge areas of the two composite membrane shells close to the liquid absorber 2 are tightly connected. The internal heat pipe shell area is not deformed by the sealing process. Then, liquid working fluid is poured in through the fourth side opening. Finally, the fourth side is sealed in a vacuum environment or after vacuuming, so that the liquid absorber 2 and the liquid working fluid are located in the closed cavity inside the heat pipe, and at the same time, the interior reaches a certain degree of vacuum at room temperature.

[0049] In another embodiment, the polymer substrate 12 of the highly elastic composite film 1 is provided with a plurality of corrugated metal layers 13, the plurality of corrugated metal layers 13 being spaced apart and the spacer areas filling the polymer substrate 12, as referenced. Figure 5 Taking two corrugated metal layers 13 as an example, the two corrugated metal layers 13 are preferably the same corrugated metal layer. For example, in this embodiment, they are both periodic triangular waves, which can also enhance the bending performance of the composite film. The working principle of the two corrugated layers can be the same as that of one corrugated layer, that is, the two layers can achieve the same effect simultaneously. Figure 3 or Figure 4 The working principle can also be implemented separately, such as Figure 3 and Figure 4 How it works.

[0050] 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 flexible heat pipe with a highly elastic composite film, characterized in that: It includes a highly elastic composite membrane shell, a liquid absorbent core, and a liquid working fluid; the shell forms a closed cavity, and the liquid absorbent core and liquid working fluid are disposed within the cavity, with a vacuum level of 1×10⁻⁶ within the cavity. -3 pa~1×10 -6 pa; wherein the highly elastic composite film comprises a polymer substrate and at least one corrugated metal layer disposed in the polymer substrate, the corrugated metal layer having a corrugated structure extending along the axial direction of the flexible heat pipe, the wave height being 50~500μm; the thickness of the highly elastic composite film is 0.1mm~1mm, the thickness of the corrugated metal layer is 10~100μm, and the inner and outer sides of the corrugated metal layer cover the polymer substrate.

2. The flexible heat pipe with a highly elastic composite film according to claim 1, characterized in that: The corrugated structure is composed of periodically repeating units, and the corrugation shape is a sine wave, triangle, rectangle or semicircle.

3. The flexible heat pipe with a highly elastic composite film according to claim 1, characterized in that: The material of the corrugated metal layer includes Cu, Al, Fe or aluminum-based composite materials, and the aluminum-based composite materials include TiC / Al, TiB2 / Al or TiB2 / Al-Li.

4. The flexible heat pipe with a highly elastic composite film according to claim 1, characterized in that: The polymer substrate includes rubber, PDMS, polyethylene, or polypropylene.

5. The flexible heat pipe with a highly elastic composite film according to claim 1, characterized in that: The polymer substrate has multiple corrugated metal layers, which are separated by material spacers in the polymer substrate.

6. The flexible heat pipe with a highly elastic composite film according to claim 1, characterized in that: The liquid-absorbing core is one or more of the following: copper wire mesh liquid-absorbing core, powder sintered liquid-absorbing core, fiber sintered liquid-absorbing core, and foam porous liquid-absorbing core; the liquid working medium is one or more of the following: deionized water, anhydrous ethanol, and acetone.

7. The method for preparing the flexible heat pipe with a highly elastic composite film according to any one of claims 1 to 6, characterized in that, Includes the following steps: 1) Cold pressing pre-shaping of the highly elastic composite film; 2) Take two cold-pressed high-elasticity composite membranes and sandwich the liquid-absorbing core. Seal the edges of the upper and lower high-elasticity composite membranes together through a sealing process, leaving a liquid inlet. Fill the liquid working medium through the liquid inlet. Seal the liquid inlet in a vacuum environment or after vacuuming, so that the liquid-absorbing core and the liquid working medium are located in the closed cavity surrounded by the high-elasticity composite membrane.

8. The method for preparing a flexible heat pipe with a highly elastic composite film according to claim 7, characterized in that: The cold-pressing pre-shaping process is used to form a non-planar shape for the highly elastic composite film.

9. The method for preparing a flexible heat pipe with a highly elastic composite film according to claim 7, characterized in that: The sealing process includes welding, hot pressing, or adhesive bonding.

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