Heat exchanger with surface having multi-stage micro-nano structure and preparation method thereof

Abstract

This invention belongs to the field of heat exchanger technology, and particularly relates to a heat exchanger with a multi-level micro / nanostructure on its surface and its fabrication method. The multi-level micro / nanostructure includes: micron-sized pits, as the first-level structure, distributed on the inner surface of the metal material, with a diameter between 1 and 600 μm; submicron-sized etch pits, as the second-level structure, distributed on or around the micron-sized pits, with a diameter between 0.1 and 1 μm; and nanosheets, as the third-level structure, covering the surface of the submicron-sized etch pits or filling the spaces between them, with a thickness between 100 and 500 nm. This invention modifies the surface of the metal material in the heat exchanger through the synergistic effects of physical processing, chemical corrosion, and hydrothermal synthesis, constructing a multi-level micro / nanostructure with "micron-sized pits-submicron-sized etch pits" on the inner surface of the metal material in the heat exchanger, thus achieving ultra-low thermal resistance start-up and high critical heat flux density in the phase change heat exchanger.

Description

Technical Field

[0001] This invention belongs to the field of heat exchanger technology, and particularly relates to a heat exchanger with a multi-level micro-nano structure on its surface and its preparation method. Background Technology

[0002] As a core component of energy conversion and utilization systems, the thermal efficiency of heat exchangers directly determines the energy economy and environmental sustainability of industrial processes. Improving heat exchange efficiency hinges on enhancing the heat transfer process, which can be achieved by optimizing fluid flow patterns, expanding heat exchange area, and improving material thermal conductivity and surface wetting properties. Optimizing fluid flow patterns focuses on improving fluid dynamics through innovative flow channel structures. A typical technique is replacing traditional bow-shaped baffles with helical baffles, allowing the fluid to flow in a helical pattern, thereby reducing dead zones, enhancing turbulence, and improving heat exchange efficiency. However, this approach can easily lead to increased pressure drop, decreased flow stability, and increased design complexity. Expanding the heat exchange area relies on structural innovation, such as microchannel heat exchangers that reduce channel size to the millimeter level, resulting in increased heat exchange area per unit volume and a significantly higher volumetric heat transfer coefficient compared to traditional shell-and-tube heat exchangers. However, this approach brings drawbacks such as increased cost, increased risk of fouling accumulation, increased flow resistance, and weakened structural strength. In recent years, material improvement and surface treatment technologies have provided new directions for efficient heat exchange. In terms of new materials with high thermal conductivity, high thermal conductivity materials such as graphite have thermal conductivity that is several to tens of times that of carbon steel and have good corrosion resistance, performing excellently in heat exchange processes in corrosive media. Nanofluid technology can improve the thermal conductivity of fluids by adding metal or oxide nanoparticles to the base fluid. However, current material improvement and surface treatment technologies often suffer from drawbacks such as high material modification and surface treatment costs, complex processes, high environmental pressure, and limited applicability.

[0003] Furthermore, compared to heat transfer methods such as conduction, convection, and radiation, phase change heat transfer is a highly efficient heat transfer method that achieves heat transfer by absorbing or releasing latent heat during a phase change. Its core principle is that during a phase change, such as liquid → gas → liquid, a large amount of latent heat is released or absorbed, while the temperature remains relatively stable. For example, water absorbs 2260 kJ / kg of latent heat when it evaporates, and releases the same amount of heat when it condenses. This characteristic makes its heat transfer efficiency far exceed that of single-phase heat transfer. Commonly used heat exchangers based on phase change heat transfer mainly include: (1) heat pipe heat exchangers, which consist of three parts: tube shell, capillary wick, and working fluid, and are usually operated in a high vacuum environment; (2) loop thermosiphons, which consist of an evaporation section, a condensation section, a rising section, and a falling section forming a closed loop, which can break through the traditional heat pipe length limitation and realize long-distance heat transfer; (3) steam heat exchangers, which use steam as a heat source and realize heat exchange through phase change heat transfer. The core mechanisms include direct steam-water mixing and indirect phase change heat exchange. Heat transfer, composite enhanced heat transfer, etc., have the advantages of high thermal efficiency, strong adaptability and significant energy saving effect; (4) VC heat exchange plate, which is composed of a metal shell, capillary core and working fluid. It operates in a high vacuum environment. It relies on the working fluid in the evaporation zone to absorb heat and vaporize. The vapor diffuses into the condensation zone in the cavity and releases latent heat in the condensation zone to condense into liquid. Then the liquid returns to the evaporation zone through the capillary force of the capillary core to achieve heat transfer. It has the advantages of strong heat flux density carrying capacity, compact structure and long service life. Overall, compared with traditional single-phase heat transfer, phase change heat transfer has the following advantages: (1) High heat transfer efficiency: latent heat transfer makes the heat carried by a unit mass of working fluid much higher than that of sensible heat transfer. (2) Near isothermal heat transfer: The temperature fluctuation during the phase change process is small, which can avoid local overheating or overcooling and the system has high stability; (3) Simple and compact structure: Under the same heat exchange power, the volume of the phase change heat exchanger is significantly reduced compared with the traditional heat exchange equipment, which can save installation space. At the same time, the treatment method of the relatively extended surface is simpler and more economical.

[0004] Currently, phase change heat exchangers are widely used in industrial waste heat recovery, such as flue gas waste heat recovery in industries like steel, metallurgy, chemicals, and power; heat dissipation for high heat flux density components in electronic devices such as CPUs, GPUs, and IGBTs; and heat exchange under low temperature and special operating conditions. While phase change heat exchangers offer advantages such as high heat transfer efficiency and compact structure, with technological advancements, such as the continuous increase in the power density of electronic chips, traditional phase change heat exchangers are no longer sufficient to meet application demands, necessitating further improvements in heat exchanger efficiency.

[0005] As a highly efficient two-phase heat transfer device, the core performance of a phase change heat exchanger depends on the boiling heat transfer efficiency of the evaporator. To improve the boiling heat transfer efficiency of phase change heat exchangers, various methods have been employed to modify the inner surface of the heat exchanger, such as machining grooves or single sandblasting. While these methods can increase bubble nuclei to some extent, improper selection of the sandblasting mesh can lead to excessive roughness, wasting substrate and causing bubble retention and increased dust accumulation. Furthermore, under high heat flux, bubble coalescence can easily occur, leading to burn-out, resulting in a low critical heat flux (CHF). Therefore, subsequent chemical treatment and hydrothermal synthesis can further weaken excessively rough spots, forming smaller microstructures that improve both heat exchanger heat dissipation performance and operational stability. Furthermore, existing technologies also use chemical methods to modify the surface structure of heat exchangers, such as chemical oxidation or anodizing to improve surface wettability. However, the nanostructures formed in this way often inhibit bubble nucleation due to the lack of attachment sites, leading to poor heat exchange performance under low loads and primarily improving the corrosion resistance of the metal. In addition, alkaline etching processes for aluminum alloys are prone to producing smut, which, if not properly handled, can severely affect coating adhesion and system reliability. Existing high-performance surfaces, such as sintered copper powder, generally involve complex processes, high costs, and often require strong acid descaling, resulting in high process complexity, poor environmental performance, and inconsistencies with green manufacturing trends.

[0006] In view of this, the present invention provides a surface modification method based on the synergistic effect of physical processing, chemical corrosion and hydrothermal synthesis, in order to construct a micro-morphology with multi-level micro-nano structures on the surface of metal materials in heat exchangers, thereby achieving ultra-low start-up superheat and high critical heat flux density of phase change heat exchangers, so as to achieve efficient thermal management of heat sources within the stable operating power range and obtain relatively lower and more stable operating temperatures. Summary of the Invention

[0007] This invention aims to provide a heat exchanger with a multi-level micro / nano structure on its surface and its preparation method. The method modifies the surface of the metal material in the heat exchanger through the synergistic effects of physical processing, chemical corrosion and hydrothermal synthesis, and constructs a micro-morphology with a multi-level micro / nano structure on the surface of the metal material. This achieves ultra-low start-up superheat and high critical heat flux density of the phase change heat exchanger, so as to realize efficient thermal management of the heat source within the stable operating power range and obtain a relatively lower and more stable operating temperature.

[0008] In view of this, the present invention provides a heat exchanger with a multi-level micro / nano structure on its surface, wherein the inner surface of the metal material in the heat exchanger has a multi-level micro / nano structure, wherein the multi-level micro / nano structure includes: Micrometer pits, as a first-order structure, are distributed on the inner surface of metallic materials, and the diameter of the micrometer pits is between 1 and 600 μm. Submicron-sized etch pits, as a secondary structure, are distributed on or around the surface of micron-sized pits, and the diameter of the submicron-sized etch pits is between 0.1 and 1 μm. Nanosheets, as a tertiary structure, cover the surface of submicron etch pits or fill the spaces between them, with the thickness of the nanosheets ranging from 100 to 500 nm.

[0009] Furthermore, the heat exchanger is a phase change heat exchanger.

[0010] Furthermore, the heat exchanger is a heat pipe heat exchanger, a loop thermosiphon, a steam heat exchanger, or a VC heat exchanger plate.

[0011] Furthermore, the heat exchanger is made of the metal material or a composite material with a metal inner side.

[0012] Furthermore, the nanosheet layer is a layered structure with two-dimensional nanosheet structures as basic units.

[0013] Furthermore, the nanosheets are boehm nanosheets.

[0014] Furthermore, the metal material is pure aluminum or an aluminum alloy.

[0015] This invention also provides a method for fabricating a heat exchanger with a multi-level micro / nano structure on its surface. The method is used to fabricate the aforementioned heat exchanger and includes the following steps: S1, Physical configuration treatment: The surface of the metal substrate is mechanically treated to form micron-sized pits on the surface of the metal substrate; wherein the metal substrate is pure aluminum or an aluminum alloy; S2, Chemical Reconstruction Processing: The workpiece after physical configuration processing is immersed in acidic or alkaline etching solution for chemical etching to create submicron-sized pits on the surface of the metal substrate. S3, Descaling: Remove the workpiece from the etching solution and clean it to remove ash; S4, Hydrothermal Synthesis Treatment: The workpiece after ash removal treatment is immersed in deionized water, and boehmite nanosheets are grown in situ on the surface of the workpiece using the hydrothermal synthesis method. S5, Heat exchanger preparation: The heat exchanger is prepared using the metal substrate processed in step S4.

[0016] Furthermore, in step S1, after mechanical processing, the metal substrate is ultrasonically cleaned.

[0017] Furthermore, in the hydrothermal synthesis process, the metal substrate is first immersed in boiling deionized water or distilled water at a temperature greater than 95°C, and the pH of the water is adjusted to 8-9 using an alkaline solution. Then, the immersion is maintained for 60-180 minutes. By utilizing the reaction between the aluminum substrate and the high-temperature water, a layer of boehmite nanosheets with a thickness of 100-500 nm is grown in situ.

[0018] Compared with existing technologies, the heat exchanger with a multi-level micro / nano structure on its surface and its preparation method described in this invention have the following advantages: In the heat exchanger with multi-level micro-nano structures on the surface described in this invention, the dual micro-nano structure of "micron pits + submicron etch pits" formed by mechanical processing and chemical etching can serve as nucleation sites for micron, submicron, or even nanobubbles during the heat exchange process. It can significantly reduce the nucleation energy barrier, enabling the system to start boiling at extremely low superheat (2-3℃).

[0019] In the heat exchanger with a multi-level micro-nano structure on the surface described in this invention, the "nanopump" composed of boehmite nanosheet structure can continuously replenish liquid to the heating surface during the bubble growth and detachment process by utilizing strong capillary force, effectively suppressing the expansion of dry spots and significantly improving the critical heat flux density.

[0020] 3. This invention uses mechanical ash removal to replace traditional nitric acid / chromic acid chemical ash removal, which significantly reduces waste liquid treatment costs and environmental risks. Moreover, the process flow is short and suitable for large-scale industrial production.

[0021] In summary, this invention provides a heat exchanger with a multi-level micro / nano structure on its surface. Through the synergistic effects of physical processing, chemical corrosion, and hydrothermal synthesis, the surface of the metal material in the heat exchanger is modified. A multi-level micro / nano structure with "micron-micron pits-nano sheets" is constructed on the inner surface of the metal material in the heat exchanger. This achieves ultra-low thermal resistance start-up and high critical heat flux density of the phase change heat exchanger, and realizes efficient thermal management of the heat source within the stable operating power range, resulting in a relatively lower and more stable operating temperature. Detailed Implementation

[0022] The technical solutions in the embodiments of this application will be clearly described below with reference to specific examples. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0023] It should be noted that all directional and positional terms used in this invention, such as "up," "down," "left," "right," "front," "back," "vertical," "horizontal," "inner," "outer," "top," "lower," "lateral," "longitudinal," and "center," are only used to explain the relative positional relationships and connections between components in a specific state. They are merely for the convenience of describing the invention and do not require the invention to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. Furthermore, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0024] In the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0025] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0026] This invention provides a heat exchanger with a multi-level micro-nano structure on its surface. The surface of the metal material in the heat exchanger is modified by the synergistic effect of physical processing, chemical corrosion and hydrothermal synthesis. The microstructure of the multi-level micro-nano structure with "micron pits-submicron etch pits-nano sheets" is constructed on the inner surface of the metal material in the heat exchanger, so as to realize the ultra-low thermal resistance start-up and high critical heat flux density of the phase change heat transfer heat exchanger.

[0027] Specifically, the inner surface of the metal material in the heat exchanger of the present invention has a multi-level micro / nano structure, wherein the multi-level micro / nano structure includes: Micrometer pits, as a first-order structure, are distributed on the inner surface of metallic materials, and the diameter of the micrometer pits is between 1 and 600 μm. Submicron-sized etch pits, as a secondary structure, are distributed on or around the surface of micron-sized pits, and the diameter of the submicron-sized etch pits is between 0.1 and 1 μm. Nanosheets, as a tertiary structure, cover the surface of submicron etch pits or fill the spaces between them. The thickness of the nanosheets is between 100 and 500 nm, and the thickness of the nanosheets is their lateral thickness in a two-dimensional plane parallel to the surface of the metal substrate.

[0028] As some examples of the present invention, the diameter of the micron-sized pits can be 1µm, 5µm, 10µm, 15µm, 30µm, 50µm, 80µm, 100µm, 150µm, 200µm, 230µm, 260µm, 300µm, 400µm, 470µm, 520µm, 590µm, or 600µm.

[0029] As some examples of the present invention, the diameter of the submicron etch pit can be 0.1um, 0.2um, 0.3um, 0.5um, 0.7um, 0.9um, or 1um.

[0030] As some examples of the present invention, the thickness of the nanosheets is 100nm, 150nm, 160nm, 180nm, 200nm, 230nm, 250nm, 270nm, 295nm, 300nm, 400nm, 460nm, and 500nm.

[0031] As a preferred example of the present invention, the nanosheet layer is a layered structure with two-dimensional nanosheet structures as basic units.

[0032] As some examples of the present invention, the nanosheets are boehmite nanosheets.

[0033] As a preferred example of the present invention, the metal material is pure aluminum or an aluminum alloy.

[0034] As some examples of the present invention, the aluminum alloy may be 1060 aluminum alloy, 3003 aluminum alloy, 4343 aluminum alloy, 5052 aluminum alloy, 6061 aluminum alloy, 6063 aluminum alloy, etc.

[0035] Preferably, the aluminum alloy is a 6-series aluminum alloy, such as 6061 aluminum alloy, 6063 aluminum alloy, etc.

[0036] As some examples of the invention, the heat exchanger may be made entirely or partially of metallic materials.

[0037] As some examples of the present invention, the heat exchanger can be made directly from the metal material or from a composite material with a metal inner side.

[0038] As a preferred example of the present invention, the heat exchanger is a phase change heat exchanger, specifically a gas-liquid phase change heat exchanger or a gas-solid phase change heat exchanger.

[0039] As some specific examples of the present invention, the heat exchanger is a heat pipe heat exchanger, a loop thermosiphon, a steam heat exchanger, or a VC heat exchanger.

[0040] As some examples of the present invention, the heat exchanger with a multi-level micro-nano structure on the surface is a loop thermosiphon aluminum alloy evaporator, which is used for heat dissipation of high heat flux density electronic devices.

[0041] Furthermore, the present invention also provides a method for fabricating a heat exchanger with a multi-level micro / nano structure on its surface, comprising the following steps: S1, Physical configuration treatment: The surface of the metal substrate is mechanically treated to form micron-sized pits of 1~600um on the surface of the metal substrate, which form the basis of the re-entrant nucleation cavity; wherein the metal substrate is pure aluminum or aluminum alloy. S2, Chemical Reconstruction Processing: The workpiece after physical configuration processing is immersed in acidic or alkaline etching solution for chemical etching to create a large number of micron to nanon submicron etch pits on the surface of the metal substrate, thereby significantly increasing the specific surface area of ​​the substrate. S3, Descaling: Remove the workpiece from the etching solution and immerse it in water for ultrasonic cleaning to remove ash. S4, Hydrothermal Synthesis Treatment: The workpiece after ash removal is immersed in deionized water, and boehmite nanosheets are grown in situ on the surface of the workpiece using hydrothermal synthesis.

[0042] As some examples of the present invention, in step S1, the specific methods for mechanically treating the surface of the metal substrate can be sandblasting, laser texturing, laser shock wave treatment, electrical discharge machining, ball end milling, shot pressing, etc. The present invention does not limit the specific implementation process of the mechanical treatment, as long as it ensures that micron-sized pits of a set size can be formed on the surface of the metal substrate.

[0043] As a preferred example of the present invention, in step S1, the micron-sized pits are formed on the surface of the metal substrate by sandblasting.

[0044] As some examples of the present invention, in step S1, after mechanical processing, the metal substrate can be cleaned by ultrasonic cleaning to remove any grease or fingerprints that may remain during the mechanical processing, ensuring uniform etching in the subsequent process, and then the metal substrate is rinsed with clean water.

[0045] As some examples of the present invention, in step S2, the process of treating with an alkaline etching solution can be as follows: immersing the workpiece treated in step S1 in a sodium hydroxide aqueous solution with a concentration of 7-15 wt%, controlling the solution temperature at 35-65°C, and treating for 3-5 minutes. Specifically, it is preferable to be able to etch a large number of submicron or even nanometer-sized submicron pits onto the metal substrate to significantly increase the specific surface area.

[0046] As a preferred example of the present invention, in step S2, the process of using an alkaline etching solution for treatment can be as follows: immersing the workpiece treated in step S1 into a 10wt% sodium hydroxide aqueous solution, controlling the solution temperature at 50±2℃, and the treatment time at 3~5min.

[0047] As a preferred example of the present invention, in step S2, the etching rate can be controlled at 1-3 μm / min by adjusting parameters such as the concentration and temperature of the etching solution, and the etching time can be strictly controlled at 3-5 min. This rate can effectively remove the surface deformation layer caused by the previous mechanical treatment, and avoid the surface deformation layer from hindering the subsequent boehmite growth due to too many lattice defects. It can also create micropores through intergranular etching to form submicron etch pits, while avoiding completely smoothing out the sandblasting texture.

[0048] During the etching process in step S2, because elements such as Si, Fe, and Mg in the metal material are insoluble, the surface of the metal material will quickly be covered with a layer of black / dark gray smut. This is a normal phenomenon and can be removed through subsequent smut removal. It is important to note that after the etching time reaches the set time, the plate must be immediately removed and quickly immersed in a large amount of cold water for quenching to stop the reaction.

[0049] As a preferred example of the present invention, in the chemical etching process, the water used to prepare the etching solution can be deionized water, distilled water or purified water, and high-hardness tap water should be avoided as much as possible to prevent calcium and magnesium precipitation from clogging the micropores on the surface of the metal substrate.

[0050] In addition, during the chemical etching process, heating devices such as electric heating plates and water baths can be used, and alkali-resistant containers such as stainless steel basins or polypropylene (PP) plastic buckets should be used to hold the alkaline etching solution. Glass or aluminum containers are strictly prohibited.

[0051] As some examples of the present invention, in step S3, in addition to ultrasonic cleaning, dry compressed air, high-pressure water guns and other equipment can also be used to remove the dust on the surface of the metal material.

[0052] As a preferred example of the present invention, in step S3, the workpiece after chemical etching is removed and immediately immersed in deionized water for ultrasonic cleaning. This utilizes the cavitation effect of ultrasound to physically remove the black, loose residual layer formed by insoluble impurities such as Fe and Si, exposing a clean, highly active metal substrate surface without damaging the microstructure formed by the etching. This step avoids the use of strong acid reagents such as concentrated nitric acid and employs physical methods to treat the ash layer, making it more environmentally friendly.

[0053] It should be noted that the ash layer on the surface of the metal substrate actually consists of two parts: the outer layer is loosely attached oxides and metal particles, and the inner layer is intermetallic compound protrusions that are bonded to the base metal. Here, we need to remove the outer layer to prevent it from falling off and contaminating the working fluid when the heat exchange medium boils during subsequent use, but we need to retain the inner layer to increase roughness and heterogeneous nucleation sites.

[0054] As a preferred example of the present invention, in step S3, the ultrasonic cleaning process is as follows: the etched metal substrate is subjected to ultrasonic treatment in an ultrasonic cleaner with warm water at 40~50°C for 10~15 minutes, so as to effectively break and peel off loose silica ash and magnesium hydroxide precipitates on the surface by utilizing the cavitation effect of ultrasonic waves.

[0055] It should be noted that the surface of the metal substrate after cleaning and dust removal in step S3 will not be as bright and silvery as it was initially, but will instead appear as a uniform dark gray or matte gray, which is acceptable. In step S3, the standard for the cleaning feel is: touching the surface of the metal substrate with a finger should not result in any noticeable black powder flakes off.

[0056] This invention uses mechanical ash removal to replace traditional nitric acid / chromic acid chemical ash removal, which significantly reduces waste liquid treatment costs and environmental risks. Moreover, the process is short and suitable for large-scale industrial production.

[0057] As some examples of the present invention, in step S4, the hydrothermal synthesis process is as follows: the cleaned and de-dusted metal substrate is immersed in boiling deionized water or distilled water at a temperature greater than 95°C and kept for 60-180 minutes. By utilizing the reaction between the aluminum substrate and the high-temperature water, a layer of boehmite nanosheets with a thickness of 100-500 nm is grown in situ. The boehmite nanosheets exhibit a porous network structure and can impart superhydrophilic properties to the surface of the metal substrate. Tests have shown that the static water contact angle of the metal substrate surface is <5°.

[0058] As some preferred examples of the present invention, in step S4, during the hydrothermal synthesis process, an alkaline solution can be used to adjust the pH of the water to 8-9. This weakly alkaline water environment is more conducive to boehmite growth. However, since trace amounts of NaOH may remain on the surface of the metal substrate in the preceding steps, directly immersing it in boiling water can usually naturally form a weakly alkaline environment. Therefore, it may not be necessary to add additional reagents. In specific cases, the pH value of the water needs to be tested and then adjusted accordingly.

[0059] Growth kinetics studies of boehmite nanosheets showed that the boehmite layers grew rapidly in the first 10 minutes of the hydrothermal synthesis process, but with low coverage; a dense layer formed after 30 minutes; and the thickness and density of the nanosheets reached equilibrium between 45 and 60 minutes, sufficient to provide superhydrophilicity. Therefore, the optimal hydrothermal synthesis time is 60–100 minutes.

[0060] As some examples of the present invention, the preparation method further includes step S5, preparing a heat exchanger: After hydrothermal synthesis treatment, the metal substrate can be taken out and placed in a dry, anhydrous device, such as a drying oven, or dried with clean hot air and then stored in a dry environment. The heat exchanger is then prepared using the metal substrate. It should be noted that during the preparation of the heat exchanger, the multi-level micro / nano structures already formed on the surface of the metal substrate should be avoided as much as possible. Therefore, when processing the metal substrate to form multi-level micro / nano structures on its surface, the shape of the metal substrate can be determined as needed, such as a plate-like, tubular, or other irregular shape.

[0061] Experimental Example 1: After being processed using different processes, multiple aluminum alloy plates with different surface conditions were installed into a loop thermosiphon system and tested under different heat loads. The test results are shown in Table 1 below. The temperature drop rate (%) of each sample compared with the bare plate sample 1 under different heat loads is calculated as follows: 100% * (measured temperature of bare plate sample 1 - measured temperature of each sample) / measured temperature of bare plate sample 1. Among them, aluminum alloy plate sample 1 is a plain plate without any treatment, aluminum alloy plate sample 2 has only undergone chemical etching treatment (alkaline etching), aluminum alloy plate sample 3 has only undergone sandblasting treatment (80-mesh sandblasting), aluminum alloy plate sample 4 has only undergone sandblasting treatment (180-mesh sandblasting), and aluminum alloy plate sample 5 (180-mesh sandblasting) has undergone sandblasting treatment + chemical etching treatment + dust removal treatment + hydrothermal synthesis treatment in sequence according to steps S1~S4. The specific process used for the same treatment process is the same for different aluminum alloy plates.

[0062] Table 1. Test Results The experiment revealed that compared with aluminum alloy plate sample 1 and samples 2-4, aluminum alloy plate sample 5 showed a significant performance improvement, which reduced the target heat dissipation temperature by 19.83-23.37%.

[0063] Analysis suggests that in the heat exchanger with multi-level micro-nano structures on the surface described in this invention, the dual micro-nano structure of "micron pits + submicron etch pits" formed by mechanical and chemical etching processes can serve as nucleation sites for micron, submicron, or even nanobubbles during the heat exchange process. This can significantly reduce the nucleation energy barrier, enabling the system to start boiling at extremely low superheat (e.g., 2-3°C).

[0064] Based on this, the "nanopump" composed of boehmite nanosheet structure can continuously replenish liquid to the heating surface during the growth and detachment of bubbles by utilizing strong capillary force, effectively inhibiting the expansion of dry spots and significantly improving the critical heat flux density.

[0065] The embodiments of this application have been described above. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A heat exchanger with a multi-level micro / nano structure on its surface, characterized in that, The inner surface of the metallic material in the heat exchanger has a multi-level micro / nano structure, wherein the multi-level micro / nano structure includes: Micrometer pits, as a first-order structure, are distributed on the inner surface of metallic materials, and the diameter of the micrometer pits is between 1 and 600 μm. Submicron-sized etch pits, as a secondary structure, are distributed on or around the surface of micron-sized pits, and the diameter of the submicron-sized etch pits is between 0.1 and 1 μm. Nanosheets, as a tertiary structure, cover the surface of submicron etch pits or fill the spaces between them, with the thickness of the nanosheets ranging from 100 to 500 nm.

2. The heat exchanger with a multi-level micro / nano structure on its surface according to claim 1, characterized in that, The heat exchanger is a phase change heat exchanger.

3. The heat exchanger with a multi-level micro / nano structure on its surface according to claim 2, characterized in that, The heat exchanger is a heat pipe heat exchanger, a loop thermosiphon, a steam heat exchanger, or a VC heat exchanger plate.

4. The heat exchanger with a multi-level micro / nano structure on its surface according to claim 1, characterized in that, The heat exchanger is made of the aforementioned metal material or a composite material with a metal inner side.

5. The heat exchanger with a multi-level micro / nano structure on its surface according to claim 1, characterized in that, The nanosheet layer is a layered structure with two-dimensional nanosheet structures as basic units.

6. The heat exchanger with a multi-level micro / nano structure on its surface according to claim 5, characterized in that, The nanosheets are boehmite nanosheets.

7. The heat exchanger with a multi-level micro / nano structure on its surface according to claim 1 or 6, characterized in that, The metal material is pure aluminum or an aluminum alloy.

8. A method for fabricating a heat exchanger with a multi-level micro / nano structure on its surface, characterized in that, The preparation method is used to prepare the heat exchanger according to any one of claims 1 to 7, and the preparation method includes the following steps: S1, Physical configuration treatment: The surface of the metal substrate is mechanically treated to form micron-sized pits on the surface of the metal substrate; wherein the metal substrate is pure aluminum or an aluminum alloy; S2, Chemical Reconstruction Processing: The workpiece after physical configuration processing is immersed in acidic or alkaline etching solution for chemical etching to create submicron-sized pits on the surface of the metal substrate. S3, Descaling: Remove the workpiece from the etching solution and clean it to remove ash; S4, Hydrothermal Synthesis Treatment: The workpiece after ash removal treatment is immersed in deionized water, and boehmite nanosheets are grown in situ on the surface of the workpiece using the hydrothermal synthesis method. S5, Heat exchanger preparation: The heat exchanger is prepared using the metal substrate processed in step S4.

9. The method for preparing a heat exchanger with a multi-level micro / nano structure on its surface according to claim 8, characterized in that, In step S1, after mechanical processing, the metal substrate is ultrasonically cleaned.

10. The method for preparing a heat exchanger with a multi-level micro / nano structure on its surface according to claim 8, characterized in that, In the hydrothermal synthesis process, the metal substrate is first immersed in boiling deionized water or distilled water at a temperature greater than 95°C, and the pH of the water is adjusted to 8-9 using an alkaline solution. Then, the immersion is maintained for 60-180 minutes. By utilizing the reaction between the aluminum substrate and the high-temperature water, a layer of boehmite nanosheets with a thickness of 100-500 nm is grown in situ.

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