A flat heat pipe, its preparation method and a heat exchanger

Abstract

The present invention discloses a flat heat pipe, a preparation method thereof, and a heat exchanger. The flat heat pipe includes an upper shell and a lower shell. The upper shell and the lower shell are hermetically connected to form a flat shell with a sealed cavity, and a phase change working medium is filled in the sealed cavity. A capillary wick is arranged in the flat shell, and the surface of the capillary wick has a micro-nano structure. Through the arrangement of the capillary wick with the micro-nano structure on the surface, the flat heat pipe of the present invention has excellent heat conduction performance, strong anti-gravity ability, and flexible use and arrangement methods.

Description

Technical Field

[0001] The present invention relates to the technical field of two-dimensional rapid heat conduction devices, and particularly to a flat heat pipe, a preparation method thereof, and a heat exchanger. Background Art

[0002] With the increasing development of technology, technologies in many frontier fields have been popularized and improved. For example, the performance of new-generation information and communication (ICT) technologies such as 5G communication, big data, cloud computing, and AI has been rapidly improved; new energy vehicles have been rapidly popularized, and their power and endurance performance have been enhanced; high-energy frontier devices such as radars and laser instruments have been widely used. Along with the progress of these technologies, the devices therein are characterized by high integration and high energy density. Therefore, there will inevitably be problems such as small and complex heat dissipation space, small heat dissipation area, and high heat flux density of the devices. The traditional heat dissipation methods of air cooling and liquid cooling are difficult to meet the heat dissipation requirements of high heat flux density devices. The performance and reliability of these components generally decrease sharply as the temperature rises, and the heat dissipation problem has become an important factor restricting the further development of a series of scientific and technological fields.

[0003] The working principle of a heat pipe is as follows: In a vacuum state, when the evaporation section of the heat pipe is heated, the liquid in the evaporation section quickly evaporates. The vapor flows to the condensation section under the action of a pressure difference, releases heat, and then condenses back into a liquid. The liquid returns to the evaporation section by means of the capillary suction of the wick. The vapor gradually increases in the evaporation section and reaches the maximum at the edge of the evaporation section, and then gradually decreases, reaching the minimum at the end of the condensation section. The liquid is just the opposite, being the most in the condensation section and the least in the evaporation section. Evaporation causes the radius of the meniscus formed by the surface tension in the evaporation section to be the smallest, and the capillary suction of the wick to be the largest, while condensation causes the radius of the meniscus formed by the surface tension in the condensation section to be the largest, and the capillary suction of the wick to be the smallest.

[0004] Traditional heat pipe technology is based on the phase change heat transfer of a fluid working medium. Its application solves the problem of one-dimensional high heat flux density and heat dissipation. The working principle of a vapor chamber is similar to that of a heat pipe, but different from traditional heat pipes, a flat heat pipe (or vapor chamber) is two-dimensional heat conduction, which can transfer a concentrated point heat source to a larger area and has a better heat transfer effect. However, at present, the capillary cores in vapor chambers are mostly of a single structure, or several porous media are simply combined as the capillary core, and their liquid absorption performance is weak, which limits the reflux speed of the phase change working medium, restricts the heat transfer performance, and even the heat pipes based on the above capillary core structures have very poor anti-gravity ability, and they fail when working against gravity and cannot transfer heat efficiently. In order to solve the problem of poor liquid absorption performance of a single capillary core, patent application CN101848629A discloses a vapor chamber with a composite capillary structure of foam metal and copper powder. Although this capillary core can increase the capillary force on the working medium, due to the filling of copper powder, the porosity of the capillary core is greatly reduced, and the flow and penetration resistance of the working medium increases sharply, and its overall capillary liquid absorption performance is limited, thus restricting its heat transfer efficiency. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a flat plate heat pipe and a preparation method thereof and a heat exchanger.

[0006] The technical solution adopted by the present invention is:

[0007] According to a first aspect of the present invention, a flat-plate heat pipe is provided, comprising an upper shell and a lower shell, wherein the upper shell and the lower shell are connected to form a flat-plate shell having a sealed cavity, wherein the sealed cavity is filled with a phase-change medium; a capillary core is provided in the flat-plate shell, and a surface of the capillary core has a first micro-nano structure.

[0008] The flat-plate heat pipe of the embodiment of the present invention has at least the following beneficial effects: the surface of the capillary wick in the flat-plate heat pipe has a first micro-nano structure, which can enhance the capillary driving effect on the phase change medium, improve the liquid absorption capacity of the capillary wick, and improve the gas-liquid circulation efficiency; in addition, through the setting of the first micro-nano structure on the surface of the capillary wick, in the heat exchange area of ​​the flat-plate heat pipe, the phase change can be enhanced to a certain extent, the phase change efficiency can be improved, thereby improving the thermal conductivity and temperature uniformity of the flat-plate heat pipe; and under the action of the above capillary wick, the flat-plate heat pipe is less affected by gravity when in use, has strong anti-gravity ability, and is flexible in use and arrangement.

[0009] According to some embodiments of the present invention, the capillary core includes a capillary core structure layer and / or a capillary chip layer; the capillary core structure layer is arranged on the inner wall of the flat shell, and the capillary chip layer is sandwiched between the upper shell and the lower shell; the surface of the capillary core structure layer and the surface of the capillary chip layer have the micro-nano structure.

[0010] According to some embodiments of the present invention, the capillary core includes the capillary chip layer, and the inner wall surface of the flat shell has a second micro-nano structure.

[0011] According to some embodiments of the present invention, the flat shell includes a heat exchange section, the heat exchange section includes an evaporation section and a condensation section, the evaporation section and the condensation section are sequentially distributed along the heat transfer direction of the flat heat pipe. According to some embodiments of the present invention, the capillary wick includes the capillary chip layer, the capillary chip layer is provided with a long gap along the heat transfer direction of the flat heat pipe; the width of the long gap increases from the evaporation section to the condensation section of the flat shell, and / or the thickness of the capillary wick increases from the evaporation section to the condensation section of the flat shell.

[0012] According to some embodiments of the present invention, the flat shell is a flexible flat shell; the capillary chip layer is sandwiched between the upper shell and the lower shell.

[0013] According to some embodiments of the present invention, the flat shell is a rigid flat shell, and a shell support is provided between the upper shell and the lower shell.

[0014] According to some embodiments of the present invention, the capillary core includes the capillary chip layer, and a capillary core support is further provided in the flat shell, and the capillary core support is used to press and fix the capillary chip layer against the inner wall surface of the flat shell.

[0015] In a second aspect of the present invention, there is provided a flat heat pipe, including an upper shell and a lower shell, the upper shell and the lower shell are hermetically connected to form a flat shell with a sealed cavity, and a phase change working fluid is filled in the sealed cavity; a capillary core is provided in the flat shell, and the inner surface of the flat shell has a second micro-nano structure.

[0016] The flat heat pipe according to the embodiment of the present invention has at least the following beneficial effects: the inner surface of the flat shell in the flat heat pipe has a second micro-nano structure, which can form an ultrathin gas-liquid interface, form a phase change enhanced surface, improve the phase change efficiency, and further improve the thermal conductivity and uniformity of the flat heat pipe.

[0017] According to some embodiments of the present invention, the capillary core includes a capillary core structure layer and / or a capillary chip layer; the capillary core structure layer is provided on the inner wall surface of the flat shell, and the surface of the capillary core structure layer has the second micro-nano structure; the capillary chip layer is clamped between the upper shell and the lower shell.

[0018] According to some embodiments of the present invention, the capillary core includes a capillary chip layer, and the surface of the capillary chip layer has a first micro-nano structure.

[0019] In a third aspect of the present invention, there is provided a preparation method for any one of the flat heat pipes provided in the first aspect of the present invention, including the following steps:

[0020] S1. Prepare an upper shell and a lower shell to cooperate to form a flat shell;

[0021] S2. Set a capillary core in the flat shell and perform surface micro-nano treatment on the capillary core so that a first micro-nano structure is formed on the surface;

[0022] S3. Hermetically connect the edges of the upper shell and the lower shell to form a flat shell with a sealed cavity, and then evacuate the sealed cavity and fill it with a phase change working fluid.

[0023] The preparation method of the flat heat pipe according to the embodiment of the present invention has at least the following beneficial effects: By arranging a capillary core in the flat shell and performing surface micro-nano treatment on the capillary core, a first micro-nano structure is formed on the surface of the capillary core, which can enhance the capillary driving effect on the working medium, improve the liquid absorption capacity of the capillary core, and enhance the gas-liquid circulation efficiency. In addition, through the arrangement of the first micro-nano structure on the surface of the capillary core, phase change can be strengthened in the heat exchange area of the flat heat pipe, the phase change efficiency can be improved, thereby improving the thermal conductivity and temperature uniformity of the flat heat pipe, and the flat heat pipe prepared has strong anti-gravity ability and flexible use and layout methods.

[0024] In step S2, the surface micro-nano treatment includes at least one of thermal oxidation treatment, electrochemical deposition, physical vapor deposition, femtosecond laser processing, and controlled sputtering.

[0025] In the fourth aspect of the present invention, there is provided a preparation method of any flat heat pipe provided in the second aspect of the present invention, including the following steps:

[0026] S1. Prepare an upper shell and a lower shell to cooperate to form a flat shell;

[0027] S2. Arrange a capillary core in the flat shell and perform surface micro-nano treatment on the inner wall surface of the flat shell to form a second micro-nano structure on the surface;

[0028] S3. Sealingly connect the edges of the upper shell and the lower shell to form a flat shell with a sealed cavity, and then evacuate and fill the sealed cavity with a phase change working medium.

[0029] The preparation method of the flat heat pipe according to the embodiment of the present invention has at least the following beneficial effects: By performing surface micro-nano treatment on the inner wall surface of the flat shell to form a second micro-nano structure on its surface, an ultra-thin gas-liquid interface can be formed, a phase change enhanced surface can be formed, the phase change efficiency can be improved, and further the thermal conductivity and uniformity of the flat heat pipe can be improved.

[0030] According to the fifth aspect of the present invention, there is provided a heat exchanger including any flat heat pipe provided in the first aspect or the second aspect of the present invention.

[0031] The heat exchanger according to the embodiment of the present invention has at least the following beneficial effects: Since the heat exchanger includes any flat heat pipe provided in the first aspect or the second aspect of the present invention, based on the beneficial effects of the above flat heat pipe, the heat exchanger has high heat transfer performance. Description of the Drawings

[0032] Figure 1 is a schematic structural diagram of a flat heat pipe according to an embodiment of the present invention;

[0033] Figure 2 is Figure 1SEM diagram of the capillary chip layer in the flat heat pipe shown;

[0034] Figure 3 It is a partial schematic cross-sectional view of the upper shell of the flat heat pipe in another embodiment of the present invention along the direction perpendicular to the long axis of the flat heat pipe;

[0035] Figure 4 It is a schematic diagram of the micro-nano structure on the inner wall surface of the upper flat shell of the flat heat pipe in another embodiment of the present invention;

[0036] Figure 5 It is a schematic diagram of the structure of the capillary chip layer on the flat heat pipe in another embodiment of the present invention;

[0037] Figure 6 It is a schematic diagram of the structure of the capillary chip layer on the flat heat pipe in another embodiment of the present invention;

[0038] Figure 7 It is a schematic diagram of the structure of the capillary chip layer on the flat heat pipe in another embodiment of the present invention;

[0039] Figure 8 It is along Figure 7 Cross-sectional schematic diagram of line A-A in

[0040] Figure 9 It is the test result of the liquid absorption performance of different capillary cores. Specific embodiments

[0041] The following will clearly and completely describe the concept and technical effects generated by the present invention in combination with embodiments to fully understand the purpose, features, and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative efforts shall fall within the scope of protection of the present invention.

[0042] In the description of the embodiments of the present invention, if it involves orientation description, such as "upper", "lower", "front", "rear", "left", "right", etc., the orientation or positional relationship indicated is based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0043] In the description of the embodiments of the present invention, if a certain feature is referred to as "arranged", "fixed", "connected", or "installed" on another feature, it can be directly arranged, fixed, connected, or installed on the other feature, or indirectly arranged, fixed, connected, or installed on the other feature. In the description of the embodiments of the present invention, if "several" is involved, it means more than one; if "multiple" is involved, it means more than two; if "greater than", "less than", or "exceeding" is involved, it should be understood as not including the number itself; if "above", "below", or "within" is involved, it should be understood as including the number itself. If "first" or "second" is involved, it should be understood as being used to distinguish technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence relationship of the indicated technical features.

[0044] Please refer to Figure 1 , Figure 1 which shows a schematic structural diagram of a flat heat pipe according to an embodiment of the present invention. As Figure 1 shown, the flat heat pipe includes an upper housing 11 and a lower housing 12. The upper housing 11 and the lower housing 12 are covered and connected to form a flat housing 10 with a sealed cavity. A phase change working fluid (not shown in the figure) is filled in the sealed cavity. A capillary core 20 is provided in the flat housing 10, and the surface of the capillary core 20 has a first micro-nano structure. The capillary core 20 covers the entire flat heat pipe. In this embodiment, the flat heat pipe further includes a liquid filling pipe 30, and the liquid filling pipe 30 is connected to the flat housing 10 and communicates with the sealed cavity.

[0045] The flat plate housing 10 can be made of different materials and designed as a rigid flat plate housing or a flexible flat plate housing according to the needs of the application scenario. Specifically, the materials of the upper housing 11 and the lower housing 12 can be metals, including but not limited to copper, aluminum, aluminum alloy, steel, and stainless steel, etc.; they can also be non-metals, including but not limited to polymethyl methacrylate (PMMA), polycarbonate (PC), polyethylene (PE), polyethylene terephthalate (PET), glass, etc.; or they can be composite materials, including but not limited to laminated composite materials (such as aluminum plastic film, composite film of plastic and metal foil, etc.), doped composite materials (such as ceramic matrix composite materials, resin matrix composite materials, etc.). The material selection of the upper housing 11 and the lower housing 12 is determined according to the usage requirements. For example, for high-power and high-temperature heat transfer scenarios, materials with good thermal conductivity are required (such as copper, aluminum, stainless steel, etc.); or, corresponding ultra-thin flexible materials are used according to the usage requirements, so that the flat heat pipe can be bent and deformed, so that it can not only transfer heat with high performance on a plane, but also its heat transfer path is more flexible and can transfer heat along the bent path. The flat plate housing 10 can be designed into different shapes according to actual application needs, such as rectangular, square, trapezoidal, circular, cylindrical shell, conical shell, etc., or it can be designed into a special-shaped configuration according to needs. The thickness of the flat plate housing 10 can be 0.05 - 100 mm. In this embodiment, the flat plate housing 10 is a rectangular rigid flat plate housing, the materials of the upper housing 11 and the lower housing 12 are aluminum alloy, and the heat transfer direction of the flat heat pipe is the long axis direction of the flat plate housing 10.

[0046] The heat transfer direction of the flat heat pipe can be designed according to actual needs. For example, the flat heat pipe can be designed as a circular flat heat pipe, the flat plate housing is circular, the heat source can be set at the center of the circular flat heat pipe, and the heat transfer direction of the flat heat pipe is from the center to the surrounding; or, the flat heat pipe can be designed as a trapezoidal flat heat pipe, its flat plate housing corresponds to a trapezoid, the heat source can be set on the side close to the upper base of the trapezoidal flat heat pipe, and the heat transfer direction of the flat heat pipe is from the upper base to the lower base; or, the flat heat pipe can be designed as a square flat heat pipe, its flat plate housing corresponds to a square, the heat source can be set at the center of the square flat heat pipe, and the heat transfer direction of the flat heat pipe is from the center to the surrounding.

[0047] As Figure 1 shown, in this embodiment, the flat plate housing 10 serves as a protective shell, and a capillary wick 20 is provided inside the flat plate housing 10. Specifically, the capillary wick 20 is a capillary chip layer sandwiched between the upper housing 11 and the lower housing 12, and the capillary chip layer completely fills the inner plane of the entire flat plate housing 10. In this embodiment, the capillary chip layer is made of foam metal material, specifically foam copper, and the surface of the capillary chip layer is subjected to thermal oxidation micro-nano treatment so that the surface has a first micro-nano structure, and this first micro-nano structure has super-hydrophilic properties. Using an electron scanning microscope to observe this capillary chip layer, the obtained results Figure 2As shown, where (a) is the SEM image of the capillary chip layer in the flat heat pipe of this embodiment, and (b) is the 3000-fold enlarged view of the area framed in (a).

[0048] In other embodiments, the capillary core can adopt other porous medium materials. For example, when applied at low temperature or normal temperature, any one of metal wire mesh, sintered powder, and 3D printing materials can be used. When preparing high-temperature heat pipes, foam ceramics, porous ceramics, etc. can be used, and surface micro-nano treatment is carried out to form the first micro-nano structure on the surface. The surface micro-nano treatment can specifically be thermal oxidation treatment, electrochemical deposition, physical vapor deposition, femtosecond laser processing, controlled sputtering, etc. By performing surface micro-nano treatment on the above capillary chip layer to form the first micro-nano structure on its surface, it can have superhydrophilic characteristics, enhance the capillary driving effect on the phase change working medium, and improve the gas-liquid circulation efficiency.

[0049] In order to improve the stability of the heat pipe, in this embodiment, a housing support 13 is provided between the upper housing 11 and the lower housing 12. The housing support 13 is specifically fixed on the inner surface of the lower housing 11. By setting the housing support 13, it is used to support the flat housing 10 to prevent the inner cavity of the flat heat pipe from collapsing. In addition, in order to fix the capillary chip layer, a capillary core support 14 can also be provided in the flat housing 10, which is used to press and fix the capillary chip layer against the inner wall surface of the flat housing 10. In this embodiment, the capillary core support 14 is also provided on the inner surface of the lower housing 12. Specifically, the capillary chip layer is pressed against the inner surface of the upper housing 11 through the capillary core support 14. In addition, in order to ensure the support effect of the housing support 13 and further ensure the installation stability of the capillary chip layer, an installation through hole 21 for installing the housing support 13 can be provided on the capillary chip layer. The housing support 13 abuts against the upper housing 11 through the installation through hole 21 of the capillary chip layer for support. The housing support 13 and the capillary core support 14 can be designed as cylindrical, square columnar, prismatic, elliptical cylindrical, etc. If the flat housing 10 is a flexible flat housing, the above housing support 13 and capillary core support 14 can be not added.

[0050] In other embodiments, a capillary core structure layer can also be directly provided on the inner wall surface of the flat housing 10, and the surface of the capillary core structure layer is subjected to surface micro-nano treatment (such as thermal oxidation treatment, electrochemical deposition, physical vapor deposition, femtosecond laser processing, controlled sputtering, etc.) to form a capillary core structure layer with the first micro-nano structure on the surface on the inner wall surface of the flat housing 10 to serve as the capillary core 20, and the capillary core 20 can penetrate the entire planar heat plate. Or, a capillary core structure layer provided on the inner wall surface of the flat housing 10 and having the first micro-nano structure on the surface can be combined with a capillary chip layer sandwiched between the upper housing 11 and the lower housing 12 and having the first micro-nano structure on the surface as the capillary core 20. The above capillary core structure layer and capillary chip layer are generally cooperatively connected and covered on the entire planar heat pipe.

[0051] The basic structure of the capillary core structure layer on the inner wall surface of the flat plate housing 10 can adopt a basic structure similar to the above-mentioned capillary chip layer, or can be designed as a microchannel capillary structure. If the basic structure of the capillary structure layer on the inner wall surface of the flat plate housing 10 adopts a microchannel capillary structure, the microchannel capillary structure generally extends along the heat transfer direction of the corresponding flat heat pipe, and the microchannel capillary structure on the inner wall surface of the flat plate housing 10 can be designed into different shapes. For example, as Figure 3 shown Figure 3 Figure 5 shows a partial schematic cross-sectional view of the upper housing of the flat heat pipe in another embodiment of the present invention along the direction perpendicular to the long axis of the flat plate housing Figure 3 which specifically shows a microchannel capillary structure with microchannels of different shapes, such as Figure 3 in (a) is a square groove, (b) is a triangular groove, (c) is a circular groove, and (d) is a trapezoidal groove. In addition, the microchannel capillary structures on the inner wall surface of the flat plate housing 10 can be arranged parallel and uniformly along the heat transfer direction of the corresponding flat heat pipe; or, the widths of the microchannel capillary structures are arranged unevenly along the heat transfer direction of the corresponding flat heat pipe.

[0052] On the basis of the basic structure of the above-mentioned capillary core structure layer, its surface is further subjected to surface micro-nano treatment to make its surface have a first micro-nano structure. The method of surface micro-nano treatment of the inner wall surface of the flat plate housing 10 can be the same as or different from the method of surface micro-nano treatment for preparing the capillary chip layer. As Figure 4 shown, in some embodiments, the inner wall surface of the flat plate housing 10 can be subjected to surface micro-nano treatment to form different-shaped first micro-nano structures on the surface. For example, as Figure 4 in (a) is a cylindrical array micro-nano structure, (b) is an elliptical cylinder array micro-nano structure, (c) is a frustum of a cone array micro-nano structure, (d) is an elliptical frustum array micro-nano structure, (e) is a conical array micro-nano structure, and (f) is a square pyramid array micro-nano structure. By arranging the capillary structure layer on the inner wall surface of the flat plate housing 10 and performing surface micro-nano treatment as above, an ultrathin gas-liquid phase change interface is formed, and a phase change enhanced surface is formed, which can improve the phase change efficiency.

[0053] In addition, in some embodiments, the wick 20 may include a wick chip layer sandwiched between the upper housing 11 and the lower housing 12 and having a first micro-nano structure on its surface. The area corresponding to the wick chip layer on the inner wall surface of the flat housing 10 may also be subjected to surface micro-nano treatment to form a second micro-nano structure. For example, the wick 20 is a wick chip layer covering the entire flat heat pipe and having a first micro-nano structure on its surface. The inner wall surface of the flat housing 10 may be subjected to surface micro-nano treatment to form a second micro-nano structure. By setting the first micro-nano structure on the above-mentioned wick chip layer, the liquid absorption capacity of the wick can be improved, and the gas-liquid circulation efficiency can be enhanced; by setting the second micro-nano structure on the inner wall of the flat housing 10, the phase change can be strengthened, the phase change efficiency can be improved, so as to improve the thermal conductivity and temperature uniformity of the flat heat pipe, and improve the anti-gravity ability of the flat heat pipe.

[0054] In some embodiments, the wick 20 in the flat housing 10 may also adopt a conventional or special wick, and the inner surface of the flat housing 10 (specifically, the upper housing 11 and / or the lower housing 12) is subjected to surface micro-nano treatment to form a second micro-nano structure on its surface, that is, the inner surface of the flat housing 10 has a second micro-nano structure, so that the inner surface of the flat housing 10 can form an ultra-thin gas-liquid interface, form a phase change enhanced surface, improve the phase change efficiency, and further improve the thermal conductivity and uniformity of the flat heat pipe. Generally, at least the inner surface of the heat exchange section of the flat housing is subjected to surface micro-nano treatment to strengthen the phase change. The wick 20 may specifically be a wick structure layer, a wick chip layer, or a combination of both. The wick structure layer is provided on the inner wall surface of the flat housing 10, and the surface of the wick structure layer has a second micro-nano structure; the wick chip layer is sandwiched between the upper housing 11 and the lower housing 12. Adopting a wick structure layer with a second micro-nano structure can simultaneously play the role of strengthening the phase change and improving the liquid absorption capacity of the wick, and enhancing the gas-liquid circulation efficiency. In some embodiments, the wick includes a wick chip layer. In order to improve the liquid absorption capacity of the wick, the surface of the wick chip layer may also be subjected to surface micro-nano treatment to form a first micro-nano structure, that is, the surface of the wick chip layer has a first micro-nano structure.

[0055] In some embodiments, the wick 20 includes a wick chip layer sandwiched between the upper housing 11 and the lower housing 12. A long strip gap may be designed on the wick chip layer along the heat transfer direction of the flat heat pipe (as Figure 5 shown, its heat transfer direction is the long axis direction of the flat housing). The wick chip layer may be attached to the flat housing 10 so that the space formed by the long strip gap on the wick chip layer and the flat housing 10 serves as a sealing cavity or a part of the sealing cavity. According to the calculation of multiphase fluid mechanics theory, the gap ratio on the wick chip layer is generally designed to be 1-100. Through the design of the above structure, the wick chip layer can be used as a support between the upper housing 11 and the lower housing 12, and the arrangement of additional supports or ribs can be cancelled, which can meet the requirements for the thin and light design of the device.

[0056] Especially for the problem that heat needs to be dissipated from high heat flux density devices in restricted spaces and complex irregular spaces in many application scenarios, heat pipes are expected to be ultra-thin and flexible and deformable. However, traditional heat spreaders or heat pipes require additional vapor chamber space inside and need to have a certain mechanical strength to maintain the cavity shape. Therefore, reinforcing ribs need to be arranged inside the existing heat spreaders or heat pipes, and the thickness of the stamped outer shell is relatively large and rigid, making it difficult to be flexibly applied in restricted spaces and complex irregular spaces, which restricts the application of flat heat pipes in the field of heat dissipation of highly integrated and complex irregular devices.

[0057] For the above special application scenarios of restricted spaces and complex spaces, in some embodiments of the present application, the flat heat pipe can be designed as an ultra-thin flexible flat heat pipe. Specifically, a flexible flat shell can be used as the outer shell. The capillary wick 20 includes a flexible capillary chip layer clamped between the upper shell 11 and the lower shell 12. And in combination with the graphic design and processing method, a long strip gap 22 is arranged on the capillary chip layer along the long axis direction of the flat shell 10. The space gap between the upper shell 11 and the lower shell 12 (including the space formed by the cooperation of the long strip gap on the capillary chip layer and the shell) serves as a sealed cavity, so that there is no need to increase the additional cavity height in the thickness direction. With the support of the capillary chip layer, there is no need to additionally set shell support members or reinforcing ribs; and the vapor flow resistance can be reduced, and the gas-liquid entrainment interference can be avoided; at the same time, the capillary chip layer has excellent flexibility, so that the preparation of an ultra-thin flexible flat heat pipe can be realized. It can be in close contact with the device, is flexible to use, improves its scope of application, and is suitable for heat dissipation of devices in highly integrated and high-power complex systems.

[0058] In some embodiments, the flat plate housing 10 may include a heat exchange section, the heat exchange section including an evaporation section and a condensation section, and the evaporation section and the condensation section being sequentially distributed along the heat transfer direction of the flat heat pipe. Additionally, in some embodiments, the flat plate housing 10 may also be designed to include a heat exchange section and an adiabatic section, the heat exchange section including an evaporation section and a condensation section, and the evaporation section, the adiabatic section, and the condensation section being sequentially distributed along the heat transfer direction of the flat heat pipe. A capillary core structure layer with a micro-nano structure on its surface may be provided on the inner wall surface of the heat exchange section of the flat plate housing 10, and a capillary chip layer with a micro-nano structure on its surface may be provided within the adiabatic section of the flat plate housing. The capillary core structure layer and the capillary chip layer are connected to cooperate as the capillary core 20 of the flat heat pipe, forming a gas-liquid circulation system. By providing a capillary core structure layer with a micro-nano structure on the inner wall surface of the heat exchange section, an ultra-thin gas-liquid phase change interface can be formed, creating a phase change enhanced surface, improving the phase change efficiency, and simultaneously having a strong liquid absorption capacity; and by providing a capillary chip layer with a micro-nano structure within the adiabatic section, due to the presence of the surface micro-nano structure, it has super-hydrophilic characteristics, enabling the capillary chip layer to greatly enhance the capillary driving effect on the phase change working fluid with little change in the penetration resistance, significantly improving the gas-liquid circulation efficiency, and thereby significantly enhancing the heat conduction performance and temperature uniformity of the flat heat pipe. Moreover, under the action of the above capillary core 20, the flat heat pipe is minimally affected by gravity during use.

[0059] The shape of the capillary core 20 can be designed differently according to different application scenarios. Specifically, it can be designed to have an equal thickness, or, the thickness of the capillary core 20 can be designed to be unequal (such as Figure 7 and Figure 8 ). Specifically, the shape of the capillary core 20 can be designed according to application requirements to gradually thicken from the evaporation section to the condensation section of the flat plate housing 10, that is, the thickness of the capillary core increases from the evaporation section to the condensation section of the flat plate housing 10, the cross-section of the capillary core 20 along the direction perpendicular to the long axis of the flat plate housing 10 continuously increases, and the outer surface of the capillary core 20 forms a certain angle with the inner wall surface of the upper housing 11 of the flat plate housing 10, such as 0.5 to 5°, and can exceed this range under extreme conditions. When the heat pipe is working, generally, the vapor amount in the evaporation section is the largest and the liquid amount is the least, while the vapor amount in the condensation section is the smallest and the liquid amount is the largest; and due to the influence of surface tension and the interaction between the gas-liquid interface, the gas-liquid interface in the evaporation section is sunken on the surface of the capillary core 20, forming a very small contact angle, resulting in the largest capillary suction force of the capillary core 20, while in the condensation section, the gas-liquid spreads flat on the surface of the capillary core 20, forming a larger contact angle, resulting in the smallest capillary suction force of the capillary core 20; through the above structural design of the capillary core 20, a thin capillary core structure is adopted in the evaporation section with less liquid and high capillary force area, and a thick capillary core structure is adopted in the condensation section with more liquid and low capillary force area, which can not only ensure the reflux of the liquid but also smooth the vapor flow channel, thereby improving the capillary limit power of the heat pipe.

[0060] In addition, such as Figure 5As shown, in some embodiments, the width of the long strip gap on the capillary chip layer may also be set to be equal along the gas-liquid circulation direction (or the long axis direction of the flat shell 10); or, as Figure 6 shown, according to the usage, it can be designed that the width of the long strip gap is unequal. Specifically, it can be designed that the width of the long strip gap increases from the evaporation section to the condensation section of the flat shell 10 to further improve the heat transfer efficiency of the heat pipe. For example, for a circular parallel heat pipe with a heat transfer direction from the center to the surrounding, if its capillary chip layer is correspondingly circular, the long strip gap on its capillary chip layer can be designed to gradually increase from the center to the surrounding of the capillary chip layer. Or, for a trapezoidal flat heat pipe with a heat transfer direction from the upper bottom edge to the lower bottom edge, if its capillary chip layer is correspondingly trapezoidal, the long strip gap on its capillary chip layer can be designed to gradually increase from the upper bottom edge to the lower bottom edge of the capillary chip layer.

[0061] The phase change working fluid in the sealed cavity of the flat shell 10 can be selected according to different application scenarios of the flat heat pipe. For example, low-temperature phase change working fluids can be selected, including but not limited to helium, ammonia, nitrogen, pentane, Freon-21 (CHCI2F), Freon-11 (CCI3F), and Freon-113 (CCI2F.CCIF2), etc.; or, normal-temperature phase change working fluids can be selected, including but not limited to deionized water, acetone, methanol, heptane, ethanol, or methanol after degassing treatment, etc.; or, high-temperature phase change working fluids can be selected, including but not limited to potassium, potassium salts, lithium, mercury, cesium, lithium, etc. The ratio of the volume of the phase change working fluid injected into the sealed cavity of the flat shell 10 to the volume of the sealed cavity can be set according to actual design requirements, generally 5% - 80%.

[0062] The surface of the capillary core 20 in the above flat heat pipe has a micro-nano structure, which can enhance the capillary driving effect of the phase change working fluid, improve the liquid absorption capacity of the capillary core 20, and enhance the gas-liquid circulation efficiency; through the setting of the micro-nano structure on the surface of the capillary core 20, phase change can be enhanced in the heat exchange area of the flat heat pipe, improving the phase change efficiency, thereby improving the thermal conductivity and temperature uniformity of the flat heat pipe; and under the action of the capillary core 20 with the above-mentioned micro-nano structure on the surface, the flat heat pipe is less affected by gravity during use and has strong anti-gravity ability. Through infrared measurement, when the heating power of the flat heat pipe in this embodiment is 100W, the maximum temperature difference is less than 1°C, and the temperature uniformity is excellent. Its effective thermal conductivity is 6.67×10 5 W / (m·K), which is 1755 times that of copper, and its thermal conductivity is excellent. And when the flat heat pipe is placed horizontally and vertically along the gravity direction, the difference in the heat transfer performance of the effective thermal conductivity is very small. When placed against the gravity direction, the heat transfer capacity of the flat heat pipe is slightly weaker than when placed along the gravity direction, but its thermal conductivity is still very excellent, indicating that the flat heat pipe can operate against gravity, making its use and layout methods very flexible; and it is simple to process and has low cost.

[0063] The present invention also provides a preparation method for the above flat heat pipes, which may include the following steps:

[0064] S1. Prepare an upper housing 11 and a lower housing 12 to cooperate as a flat housing 10. For a rigid flat housing, housing support members 13 and / or wick support members 14 may be arranged on the lower housing 12, and then an organic cleaning solution (such as isopropyl alcohol or acetone, etc.) can be used to clean and remove grease, and then the surface can be cleaned with dilute hydrochloric acid to remove the oxide layer. For a flexible flat housing, the setting of the above support members can be cancelled.

[0065] S2. Arrange a wick in the flat housing 10 and perform surface micro-nano treatment on the wick so that a first micro-nano structure is formed on its surface. Specifically, a wick structure base layer can be arranged on the inner wall surface of the upper housing 11 and / or the lower housing 12, and surface micro-nano treatment is performed on its surface to form a wick structure layer with a first micro-nano structure on the surface; and / or, a wick base layer is prepared by using a porous medium material, and an organic cleaning solution such as isopropyl alcohol or acetone can be used to clean and remove grease, and then the surface is cleaned with dilute hydrochloric acid to remove the oxide layer, and then surface micro-nano treatment is performed on the wick base layer to form a wick chip layer with a first micro-nano structure on the surface, and the wick chip layer is clamped between the upper housing 11 and the lower housing 12. In addition, for the case where the wick 20 includes a wick chip layer, surface micro-nano treatment can be performed on the corresponding area of the wick chip layer on the inner wall surface of the flat housing to form a second micro-nano structure to strengthen the phase change.

[0066] Alternatively, a wick is arranged in the flat housing 10, and surface micro-nano treatment is performed on the inner surface of the flat housing 10 so that a second micro-nano structure is formed on the surface; the wick 20 can be the above wick or a conventional wick, and generally, surface micro-nano treatment is at least performed on the inner surface of the heat exchange section of the flat housing 10.

[0067] S3. Hermetically connect the edges of the upper housing 11 and the lower housing 12 to form a flat housing with a sealed cavity, and evacuate and fill the sealed cavity with a phase change working fluid. Among them, the hermetic connection can specifically adopt a welding method, and the vacuum range for evacuation is generally 10 -5 ~10 4 Pa, and the volume ratio of the filled phase change working fluid to the volume of the sealed cavity is generally 5% - 80%.

[0068] In the above preparation method, a capillary wick is arranged inside the flat shell. If the surface of the capillary wick is subjected to surface micro-nano treatment so that the surface of the capillary wick 20 has a first micro-nano structure, it can enhance the capillary driving effect on the working fluid, improve the liquid absorption capacity of the capillary wick, and enhance the gas-liquid circulation efficiency. In addition, through the setting of the first micro-nano structure on the surface of the capillary wick, in the heat exchange area of the flat heat pipe, phase change can be strengthened and the phase change efficiency can be improved, thereby improving the thermal conductivity and temperature uniformity of the flat heat pipe. The prepared flat heat pipe has strong anti-gravity ability and flexible use and layout methods. If the inner surface of the flat shell is subjected to surface micro-nano treatment so that its inner surface has a second micro-nano structure, the phase change can also be strengthened and the phase change efficiency can be improved.

[0069] The inventor of the present invention Figure 1 conducted capillary wick liquid absorption performance experiments on the capillary wicks used in the flat heat pipes shown and the different capillary wicks used in existing flat heat pipes. Among them, the capillary wick used in the flat heat pipe shown in the present invention Figure 1 was taken as an experimental example, which was a foam copper capillary chip layer modified with a super-hydrophilic micro-nano structure by a surface oxidation process; the capillary wick of Comparative Example 1 was a foam nickel capillary chip layer; the capillary wicks in Comparative Example 2 and Comparative Example 4 were capillary chip layers with a capillary structure of square micro-channels arranged in parallel and uniformly, and porous particles sintered in the micro-channels; the capillary wick of Comparative Example 3 was a capillary chip layer in which copper particles were sintered into a foam shape. The liquid absorption performance of the above capillary wicks was tested respectively, and the obtained results are as Figure 9 shown. It can be seen from Figure 9 that the capillary chip layer used in the flat heat pipe of the present invention has been subjected to surface micro-nano treatment so that the surface has a first micro-nano structure, and its liquid absorption height has been significantly improved, which is 2 to 3 times that of the capillary wicks of the existing comparative examples.

[0070] The above flat heat pipe can be further applied to the preparation of heat exchangers. Therefore, the present invention also provides a heat exchanger, including any one of the above flat heat pipes. In addition, in order to enhance the heat exchange efficiency, according to application requirements, heat exchange enhancement components (such as fins, water-cooling blocks, radiation enhancement coatings, etc.) can be coupled and connected to some areas or the entire surface of the flat shell of the flat heat pipe to form an efficient heat exchanger, which can then be used in various heat dissipation or heating scenarios, including but not limited to base station chips, computer CPUs, automotive power batteries and fast charging, rapid preheating of automotive power batteries and power modules, efficient heat exchange of power generation devices, and heat dissipation of high heat flux densities such as lasers and radars.

Claims

1. A flat heat pipe, characterized in that, The flat heat pipe includes an upper shell and a lower shell. The upper shell and the lower shell are hermetically connected to form a flat shell with a sealed cavity, and a phase change working fluid is filled in the sealed cavity. A capillary wick is provided in the flat shell, and the capillary wick includes a capillary chip layer and a capillary wick structure layer. The capillary chip layer is made of foam metal, and the surface of the capillary chip layer is subjected to surface micro-nano treatment so that its surface has a first micro-nano structure. The capillary wick structure layer adopts a micro-channel capillary structure, and the surface of the capillary wick structure layer is subjected to surface micro-nano treatment so that its surface has a first micro-nano structure. The flat shell includes a heat exchange section and a heat insulation section. The heat exchange section includes an evaporation section and a condensation section, and the evaporation section, the heat insulation section, and the condensation section are sequentially distributed along the heat transfer direction of the flat heat pipe. The capillary chip layer is clamped and arranged between the upper shell and the lower shell. A long strip gap is arranged on the capillary chip layer along the heat transfer direction of the flat heat pipe, and the width of the long strip gap increases from the evaporation section to the condensation section of the flat shell. The capillary wick structure layer is arranged on the inner wall surface of the flat shell.

2. The flat heat pipe according to claim 1, characterized in that, The thickness of the capillary wick increases from the evaporation section to the condensation section of the flat shell.

3. The flat heat pipe according to any one of claims 1 to 2, characterized in that, The flat shell is a flexible flat shell.

4. The preparation method of the flat heat pipe according to any one of claims 1 to 3, comprising the following steps: S1. Prepare an upper shell and a lower shell to cooperate to form a flat shell. S2. Set a capillary wick in the flat shell and perform surface micro-nano treatment on the capillary wick so that a first micro-nano structure is formed on the surface. S3. Hermetically connect the edges of the upper shell and the lower shell to form a flat shell with a sealed cavity, and then evacuate the sealed cavity and fill it with a phase change working fluid.

5. A heat exchanger, characterized in that, Including the flat heat pipe according to any one of claims 1 to 3.

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