Non-uniform structured material for enhancing boiling heat transfer and preparation method of non-uniform structured material

Abstract

The invention provides a non-uniform structured material for strengthening boiling heat transfer and a preparation method of the non-uniform structured material, and belongs to the technical field of strengthening phase change heat transfer. The millimeter-level porous column comprises a first stepped porous coating layer, the porosity of the first stepped porous coating layer is gradually increased from bottom to top, and a super-hydrophobic coating layer is locally arranged at the top of the first stepped porous coating layer; the mini-porous column comprises a second stepped porous coating, the porosity of the second stepped porous coating is gradually increased from bottom to top, and the top of the second stepped porous coating is subjected to super-hydrophilic treatment; and gaps between the millimeter-scale porous columns and the mini-porous columns form channels. The number of gasification cores of the non-uniform structured material is effectively increased, the superheat degree of the surface is reduced, and therefore the boiling heat transfer coefficient of the surface under the low heat flux density is increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of enhanced phase change heat transfer, in particular to a non-uniform structured material for enhancing boiling heat transfer and a preparation method thereof. BACKGROUND

[0002] As a highly efficient heat transfer mode, boiling heat transfer has attracted attention and application in the field of high-integration chip or high heat flux electronic device thermal management due to its superior heat transfer performance and inherent advantage of effectively controlling the temperature of the boiling surface. However, with the development of production and technological innovation, the heat dissipation demand of highly integrated chips and high-power electronic devices is also increasing, and the operation stability and safety of electronic devices are facing unprecedented challenges. Therefore, in order to further meet the heat dissipation demand of high heat flux electronic devices, it is necessary to simultaneously enhance the boiling heat transfer coefficient and the critical heat flux density of the surface to meet the operation stability of electronic devices under extreme working conditions.

[0003] In recent years, porous coating surfaces have attracted widespread attention in the field of boiling heat transfer enhancement due to their large specific surface area and strong liquid replenishment capacity. The stepped porous coating surface can better balance the contradictory relationship between coating thermal resistance and liquid replenishment capacity, and the stepped pore structure conforms to the growth law of bubbles and promotes the rapid detachment of bubbles, so it exhibits superior boiling heat transfer performance. However, under high heat flux density, the stepped porous surface cannot effectively regulate the bubble behavior, making it difficult to further improve the critical heat flux density (CHF).

[0004] With the development of subtractive material manufacturing technology, by machining columnar structures on the porous surface and regulating the geometric size of the structured surface, the liquid replenishment capacity can be improved to further improve the CHF of the wall surface. However, the porous structured surface cannot effectively separate the gas-liquid path, thereby limiting the further improvement of the boiling heat transfer performance under high heat flux density. SUMMARY

[0005] In view of the technical problems in the background art, the present application provides a non-uniform structured material for enhancing boiling heat transfer and a preparation method thereof, aiming to solve the technical problem that the porous structured surface cannot effectively separate the gas-liquid path, thereby limiting the further improvement of the boiling heat transfer performance under high heat flux density.

[0006] In a first aspect, the embodiments of the present application provide a non-uniform structured material for enhancing boiling heat transfer, comprising: a heat transfer substrate; a millimeter-level porous column, a plurality of millimeter-level porous columns are uniformly arranged on the heat transfer substrate, the plurality of millimeter-level porous columns are arranged in a square array, and the millimeter-level porous column comprises a first stepped porous coating, the porosity of the first stepped porous coating gradually increases from bottom to top, and a super-hydrophobic coating is locally arranged on the top of the first stepped porous coating. The mini porous column is arranged between two adjacent millimeter porous columns, and the mini porous column comprises a second gradient porous coating, the porosity of the second gradient porous coating gradually increases from bottom to top, and the top of the second gradient porous coating is subjected to super-hydrophilic treatment. The gap between the millimeter porous column and the mini porous column forms a channel.

[0007] In some embodiments, the millimeter porous column is a cuboid, the length and width of the millimeter porous column are 4.1-4.3 mm, and the height is 0.45-0.75 mm.

[0008] In some embodiments, the mini porous column comprises a strip-shaped column and a square column, and a channel is arranged between the square column and the strip-shaped column.

[0009] In some embodiments, the width of the strip-shaped column is 0.6-1.0 mm, the length is 4.1-4.3 mm, and the height is 0.45-0.75 mm.

[0010] In some embodiments, the length and width of the square column are 0.6-1.0 mm, and the height is 0.45-0.75 mm.

[0011] In some embodiments, the width of the channel is 0.2-0.6 mm.

[0012] In some embodiments, the millimeter porous column and the mini porous column have the same height.

[0013] In some embodiments, the first gradient porous coating comprises, from bottom to top, a 30%-40% porosity copper porous coating, a 50%-60% porosity copper porous coating, and a 70%-80% porosity copper porous coating, the thicknesses of the 30%-40% porosity copper porous coating, the 50%-60% porosity copper porous coating, and the 70%-80% porosity copper porous coating are the same, and each is 0.15-0.25 mm.

[0014] In some embodiments, the second gradient porous coating comprises, from bottom to top, a 30%-40% porosity copper porous coating, a 50%-60% porosity copper porous coating, and a 70%-80% porosity copper porous coating, the thicknesses of the 30%-40% porosity copper porous coating, the 50%-60% porosity copper porous coating, and the 70%-80% porosity copper porous coating are the same, and each is 0.15-0.25 mm.

[0015] In some embodiments, the super-hydrophobic coating accounts for 15%-20% of the upper surface area of the millimeter porous column.

[0016] In some embodiments, the super-hydrophobic coating is formed by heat treatment of polytetrafluoroethylene powder, and the thickness of the super-hydrophobic coating is 2-3 mm.

[0017] In some embodiments, the super-hydrophilic coating is obtained by wet etching.

[0018] In a second aspect, the embodiments of the present application provide a preparation method of a non-uniform structured material for enhancing boiling heat transfer, comprising the following steps: S1, coating 900-1000 mesh atomized copper particles on a heat exchange substrate, heating to 950-1000℃ under nitrogen protection for 1-2h, then coating 200-300 mesh atomized copper particles and 100-200 mesh electrolytic copper particles on the surface in sequence, heating to 800-850℃ under nitrogen protection for 1-2h, to obtain a hierarchical porous coating; S2, cutting the hierarchical porous coating into a plurality of uniformly distributed millimeter porous columns and mini porous columns, the gap between the millimeter porous columns and the mini porous columns forming a channel, to obtain a non-uniform structured material blank; S3, performing local super-hydrophobic modification on the surface of the millimeter porous column by water transfer printing, to obtain a super-hydrophobic coating; S4, covering the millimeter porous column after super-hydrophobic modification with a hydrophobic film, and performing super-hydrophilic modification on the mini porous column by wet etching, to obtain a super-hydrophilic coating, thereby obtaining the non-uniform structured material for enhancing boiling heat transfer.

[0019] In some embodiments, the water transfer printing in step S3 comprises the following steps: Adding polytetrafluoroethylene powder with a particle size of 1μm into deionized water, stirring uniformly to obtain a water transfer printing solution, and forming a thin layer of polytetrafluoroethylene powder on the surface of the water transfer printing solution; Covering a mask plate on the surface of the hierarchical porous coating, immersing it in the water transfer printing solution, and then lifting it upwards, so that the thin layer of polytetrafluoroethylene powder is attached to the surface of the millimeter porous column; Removing the mask plate, drying, and then heating to 325℃ under nitrogen protection for 1h, to obtain a super-hydrophobic coating.

[0020] In some embodiments, the wet etching for super-hydrophilic modification in step S4 comprises the following steps: Dispersing sodium hydroxide and potassium persulfate in water to obtain a mixed solution; Immersing the non-uniform structured material blank after super-hydrophobic modification in the mixed solution, heating to 40℃, and reacting for 16min, then washing and drying after the reaction is completed, to obtain a super-hydrophilic coating.

[0021] In a third aspect, the embodiments of the present application provide an application of the non-uniform structured material for enhancing boiling heat transfer in the field of heat exchangers.

[0022] Compared with the prior art, the beneficial effects of the present application include: 1. The application provides a non-uniform structured material for enhancing boiling heat transfer, which is characterized by the following steps: firstly, the top of the millimeter porous column is locally modified by super-hydrophobic modification, which effectively increases the number of gasification cores of the non-uniform structured material, reduces the surface superheat, and thus improves the boiling heat transfer coefficient of the surface under low heat flux density; secondly, the mini porous column with near super-hydrophilic modification promotes liquid supplement and increases the critical heat flux density of the surface, thus delaying the occurrence of film boiling and effectively exerting the synergistic enhancement of hydrophobic and hydrophilic modification on boiling heat transfer.

[0023] 2. The millimeter porous column and the mini porous column are both composed of a gradient porous coating, the porosity of which gradually increases from bottom to top, and the gradient porosity of the gradient porous coating reduces the wall thermal resistance while improving the wicking capacity of the wall surface, which is helpful to further reduce the wall superheat. Moreover, the gradient pore size of the gradient porous coating conforms to the bubble growth rule, which is conducive to reducing the bubble detachment resistance, improving the bubble detachment frequency, and promoting the rewetting of the wall surface.

[0024] 3. The combination of the millimeter porous column and the mini porous column effectively regulates the surface behavior, the top of the millimeter porous column with local super-hydrophobic modification is the main nucleation area, the mini porous column with near super-hydrophilic modification is used to block bubble coalescence and promote liquid supplement from the top of the porous column to the channel, thus realizing the separation of gas-liquid paths, effectively reducing the wall superheat under medium and high heat flux density, and delaying the occurrence of film boiling.

[0025] 4. The application provides a non-uniform structured material for enhancing boiling heat transfer, which is made of pure copper powder with different particle sizes, has low material cost and high reliability, and can realize long-term safe and stable operation of the thermal management system.

[0026] The above description is only a summary of the technical scheme of the application, in order to more clearly understand the technical means of the application, the specific embodiments of the application can be implemented according to the content of the specification, and in order to make the above and other purposes, characteristics and advantages of the application more obvious and easy to understand, the following will specifically describe the embodiments of the application. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical scheme of the application, the drawings used in the application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creating laborious work.

[0028] Figure 1 The structure of the non-uniform structured material in the embodiment 1 of the application is shown in the figure.

[0029] Figure 2Scanning electron microscope cross-sectional view of the hierarchical porous coating in Example 1 of the present application.

[0030] Figure 3 Scanning electron microscope view of the superhydrophobic coating in Example 1 of the present application.

[0031] Figure 4 Scanning electron microscope view of the superhydrophilic coating in Example 1 of the present application.

[0032] Figure 5 Comparison chart of boiling curves in Example 1 and Comparative Examples 1-3.

[0033] Figure 6 Comparison chart of boiling curves of Example 1 and coatings with different porosities.

[0034] BRIEF DESCRIPTION OF DRAWINGS: 1, heat exchange base; 2, millimeter scale porous column; 3, mini porous column; 31, strip column; 32, square column; 4, superhydrophobic coating; 5, channel; 6, 30%-40% porosity copper porous coating; 7, 50%-60% porosity copper porous coating; 8, 70%-80% porosity copper porous coating; 9, polytetrafluoroethylene powder. DETAILED DESCRIPTION

[0035] The embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying drawings. The following examples are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above description of drawings are intended to cover non-exclusive inclusion.

[0037] In order to solve the technical problem that the porous structured surface cannot effectively separate the gas-liquid path, thereby limiting the further improvement of the boiling heat transfer performance under high heat flux, the present application proposes a non-uniform structured material for enhancing boiling heat transfer.

[0038] Please refer to Figure 1In a first aspect, the embodiments of the present application provide a non-uniform structured material for enhancing boiling heat transfer, comprising: a heat transfer substrate, wherein millimeter-scale porous columns are uniformly arranged on the heat transfer substrate in a square array, mini porous columns are arranged between two adjacent millimeter-scale porous columns, the mini porous columns comprise strip-shaped columns and square columns, the square columns are located at the centers of the four mini porous columns, the gaps between the millimeter-scale porous columns and the mini porous columns form channels, the widths of the channels are consistent, and the widths of the channels are 0.2-0.6 mm. By arranging the millimeter-scale porous columns and the mini porous columns, a non-uniform porous structured surface is formed on the surface of the heat transfer substrate, which can effectively regulate the bubble dynamics behavior, realize gas-liquid path separation, and improve the boiling heat transfer coefficient under medium and high heat fluxes; the channels are macro liquid supplement paths in the boiling heat transfer process of the non-uniform porous structured surface.

[0039] The millimeter-scale porous column comprises a first gradient porous coating layer, and the porosity of the first gradient porous coating layer gradually increases from bottom to top, serving as a main nucleation area in the boiling process of the non-uniform porous structured surface.

[0040] The millimeter-scale porous column is a cube, and the sizes of the millimeter-scale porous columns are consistent, the length and the width of the millimeter-scale porous column are the same, and are 4.1-4.3 mm, and the height is 0.45-0.75 mm. Preferably, as shown in Figure 2 The first gradient porous coating layer comprises a 30%-40% porosity copper porous coating layer, a 50%-60% porosity copper porous coating layer, and a 70%-80% porosity copper porous coating layer from bottom to top, and the thicknesses of the 30%-40% porosity copper porous coating layer, the 50%-60% porosity copper porous coating layer, and the 70%-80% porosity copper porous coating layer are consistent, and the size range is 0.15-0.25 mm. The gradient porous structure reduces the thermal resistance of the porous coating layer and conforms to the bubble growth law to promote the detachment of bubbles.

[0041] As shown in Figure 3 A super-hydrophobic coating layer is arranged on the top of the first gradient porous coating layer, and the super-hydrophobic coating layer is distributed in the four corners of the non-uniform structured material for enhancing boiling heat transfer. The super-hydrophobic coating layer is formed by heat treatment of polytetrafluoroethylene powder, the thickness of the super-hydrophobic coating layer is 2-3 μm, and the super-hydrophobic coating layer accounts for 15%-20% of the upper surface area of the millimeter-scale porous column. The super-hydrophobic modification of the millimeter-scale porous column can effectively improve the vaporization core density of the wall surface, thereby reducing the wall surface superheat under medium and low heat fluxes.

[0042] The mini porous column is arranged between two adjacent millimeter-scale porous columns, and the mini porous column comprises a second gradient porous coating layer, the porosity of the second gradient porous coating layer gradually increases from bottom to top, serving as an auxiliary liquid supplement channel in the boiling process of the non-uniform porous structured surface, and blocking the coalescence of bubbles under high heat fluxes.

[0043] The mini porous columns include strip columns and square columns. The dimensions of the strip columns are consistent, with a width of 0.6mm~1.0mm, a length of 4.1mm~4.3mm, and a height of 0.45mm~0.75mm. The dimensions of the square columns are consistent, with the length and width of the square columns being the same, with a length and width of 0.6mm~1.0mm and a height of 0.45mm~0.75mm. Preferably, the second-stage porous coating includes, from bottom to top, a 30%~40% porosity copper porous coating, a 50%~60% porosity copper porous coating, and a 70%~80% porosity copper porous coating. The thickness of the 30%~40% porosity copper porous coating, the 50%~60% porosity copper porous coating, and the 70%~80% porosity copper porous coating are all 0.15mm~0.25mm. The stepped pore structure reduces the thermal resistance of the porous layer and conforms to the growth law of bubbles, thereby promoting the detachment of bubbles.

[0044] The millimeter-scale porous columns have the same height as the mini porous columns.

[0045] like Figure 4 As shown, a super-hydrophilic coating is provided on the top of the second-stage porous coating, and the super-hydrophilic coating is obtained by wet etching. Super-hydrophilic modification of the mini porous column can effectively improve the capillary rehydration capacity of the wall, thereby greatly improving the critical heat flux density of the wall. However, the effect of single wettability modification of the heat exchange material on the enhancement of boiling heat transfer is limited, and it is impossible to improve the nucleation density and rehydration capacity at the same time. The present invention performs local wettability modification on the surface, and the local super-hydrophobic area increases the surface vaporization core density and reduces the wall superheat under low heat flux density, and the near-super-hydrophilic area promotes rehydration and increases the critical heat flux density of the surface. Thereby, the synergistic enhancement of the boiling heat transfer performance of the porous structured surface is achieved.

[0046] The present invention is based on a stepped porous coating. By processing non-uniformly sized millimeter-scale porous columns and mini porous columns on the stepped porous coating and performing local composite wettability modification on them, the combination of stepped porous coating, non-uniform structural arrangement and composite wettability is achieved. While improving the surface nucleation density, the wall's liquid replenishment capacity is enhanced. The non-uniformly distributed structured surface is used to regulate the bubble behavior, separate the gas-liquid flow path, and promote the detachment of bubbles, thereby achieving a synergistic enhancement of the boiling heat transfer performance.

[0047] In a second aspect, an embodiment of the present application provides a method for preparing a non-uniform structured material for enhancing boiling heat transfer, comprising the following steps: S1, coating 900-1000 mesh atomized copper particles on the heat exchange substrate, heating to 950-1000℃ under nitrogen protection for 1-2h, then coating 200-300 mesh atomized copper particles and 100-200 mesh electrolytic copper particles on the surface in sequence, heating to 800-850℃ under nitrogen protection for 1-2h, to obtain a gradient porous coating; S2, cutting the gradient porous coating into a plurality of uniformly distributed millimeter porous columns and mini porous columns, the gap between the millimeter porous columns and the mini porous columns forming a channel, to obtain a non-uniform structured material blank; S3, performing local super-hydrophobic modification on the surface of the millimeter porous column by using a water transfer printing method, to obtain a super-hydrophobic coating; S4, covering the millimeter porous column after super-hydrophobic modification with a hydrophobic film, and performing super-hydrophilic modification on the mini porous column by using a wet etching method, to obtain a super-hydrophilic coating, thereby obtaining a non-uniform structured material for enhancing boiling heat transfer.

[0048] In some embodiments, the water transfer printing method in step S3 includes the following steps: adding polytetrafluoroethylene powder with a particle size of 1μm into deionized water, stirring uniformly to obtain a water transfer printing solution, and forming a thin layer of polytetrafluoroethylene powder on the surface of the water transfer printing solution; covering a mask plate on the surface of the gradient porous coating, immersing it in the water transfer printing solution, and then lifting it upwards, so that the thin layer of polytetrafluoroethylene powder is attached to the surface of the millimeter porous column; removing the mask plate, drying, and then heating to 325℃ under nitrogen protection for 1h, to obtain a super-hydrophobic coating.

[0049] In some embodiments, the wet etching method for super-hydrophilic modification in step S4 includes the following steps: dispersing sodium hydroxide and potassium persulfate in water to obtain a mixed solution; immersing the non-uniform structured material blank after super-hydrophobic modification in the mixed solution, heating to 40℃, and reacting for 16min, then washing and drying after the reaction is completed, to obtain a super-hydrophilic coating.

[0050] In a third aspect, the embodiments of the present application provide an application of a non-uniform structured material for enhancing boiling heat transfer in the field of heat exchangers.

[0051] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. If the specific technology or condition is not specified in the embodiments, it is performed according to the technology or condition described in the literature in the art or according to the product manual. If the reagent or instrument is not specified by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0052] I. Preparation method Example 1 A preparation method of a non-uniform structured material for enhancing boiling heat transfer, comprising the following steps: S1, a two-step sintering method is used to prepare a stepped porous coating, 1000 mesh atomized copper particles are uniformly coated on the heat transfer substrate, and then heat preservation is carried out at 1000°C for 2 hours under nitrogen protection. Subsequently, 300 mesh atomized copper particles and 200 mesh electrolytic copper particles are coated on the surface layer in turn, and heat preservation is carried out at 850°C for 2 hours under nitrogen protection. A stepped porous coating surface with a specific thickness is obtained, as shown in Figure 2 .

[0053] S2, a slow wire cutting is used to prepare a non-uniform structured material on the basis of the stepped porous coating, the stepped porous coating surface is placed in the area to be processed, and an anti-electrolysis pulse power source is used to avoid the oxidation corrosion of the copper porous surface. A 0.3 mm diameter pure copper wire is used as the electrode wire, and deionized water is used for cooling during the processing. After processing, a millimeter-level porous column and a mini porous column are obtained, the millimeter-level porous column has a width of 4.3 mm, a height of 0.6 mm, the mini porous column has a width of 0.6 mm, a length of 4.3 mm / 0.6 mm, and a height of 0.6 mm, and the channel is 0.4 mm.

[0054] After the surface processing is completed, the remaining debris on the surface is cleaned with ultrasonic waves, and then the non-uniform structured material blank is placed in a vacuum drying box for room temperature drying, and then the non-uniform structured material blank is obtained.

[0055] S3, a water transfer printing method is used to locally modify the super-hydrophobicity of the non-uniform porous structured surface. First, a corresponding mask pattern is designed, and the mask is processed according to the designed mask size. Then, a water transfer printing solution is prepared, 1 μm polytetrafluoroethylene powder is added to deionized water, and magnetic stirring is carried out for 10 minutes. A uniform thin layer of polytetrafluoroethylene powder is formed on the surface of the water transfer printing solution. Then, the mask is covered on the non-uniform structured material blank and fixed, and then the surface is slowly lifted, so that the polytetrafluoroethylene powder thin layer is attached to the mask pattern area. Then, the mask is removed and placed in a vacuum drying box for room temperature drying. The non-uniform structured material blank after drying is placed in a nitrogen-protected tube furnace and heat treated at 325°C for 1 hour to enhance the adhesion strength of the polytetrafluoroethylene particles on the copper particle surface, and a super-hydrophobic coating is obtained. The distribution of polytetrafluoroethylene powder on the porous surface is shown in Figure 3 , and the local super-hydrophobic film layer has a width of 0.4 mm.

[0056] S4, after the water transfer printing process is completed, a wet etching process is performed, and the non-uniform structured material blank subjected to the super-hydrophobic modification is covered with a hydrophobic film to avoid being contaminated during processing. The non-uniform structured material blank is immersed in a solution containing 7.5 g / L of sodium hydroxide and 1.5 g / L of potassium persulfate, and heated in a water area at 40°C for 16 minutes, during which a nano-grass structure is formed on the surface, and a super-hydrophobic coating is obtained, as shown in Figure 4 After the reaction is completed, the surface is cleaned of residual solution using ultrasonic waves, and after completion, is placed in a vacuum drying oven for room temperature drying, and then the non-uniform structured material for strengthening boiling heat exchange using a hierarchical porous column and a composite wetting modification is obtained.

[0057] Comparative Example 1 Comparative Example 1 differs from Example 1 in that the millimeter-level porous column is not subjected to super-hydrophobic modification, and the other steps are the same as in Example 1.

[0058] Comparative Example 2 Comparative Example 2 differs from Example 1 in that the millimeter-level porous column is not subjected to super-hydrophobic modification, and the mini porous column is not subjected to super-hydrophilic modification, and the other steps are the same as in Example 1.

[0059] Comparative Example 3 In Comparative Example 3, the heat exchange substrate is provided with a copper coating having a smooth surface.

[0060] II. Test Methods 1. Boiling heat transfer performance detection method: The boiling heat transfer performance of the test surface is tested by using a saturated pool boiling experiment platform with deionized water as the working medium. During the experiment, the heating power of the platform is gradually increased to adjust the heat flux through the test surface. In addition, a thermocouple arranged on the back of the test surface is used to monitor the temperature change of the test surface. The difference between the measured wall temperature and the boiling point of saturated water is the wall superheat. By adjusting the heating power of the test platform, the wall superheat corresponding to the surface at a certain heat flux can be read, and then the boiling curve of the test surface can be drawn. Due to the differences between the boiling surfaces, the boiling curves also present various forms.

[0061] 2. Critical heat flux (CHF) monitoring: By gradually increasing the heating power of the test platform, a working condition point before the occurrence of film boiling is reached, and the corresponding heat flux is the critical heat flux.

[0062] III. Analysis of Test Results of Each Example and Comparative Example (1) The cross section of the non-uniform structured material for strengthening boiling heat exchange prepared in Example 1 is scanned using a scanning electron microscope, and the obtained Figure 2 Figure 2 ​It can be seen that the present application realizes the preparation of the stepped porous coating.

[0063] (2) In addition, through experimental determination, compared with the smooth flat surface, the unmodified non-uniform structured surface with the same size, and the near super-hydrophilic modified non-uniform structured surface with only the mini-column, the critical heat flux of the composite porous surface is improved, and the wall superheat is lower under the same heat flux, as shown in Figure 5 .

[0064] In addition, through experimental determination, compared with the non-uniform structured surface for boiling heat transfer synergistically enhanced by the stepped porous column and the composite wettability modification, the porous surface with 30% uniform porosity, the porous surface with 53% uniform porosity, and the porous surface with 72% uniform porosity, the composite porous surface synergistically utilizes the advantages of porous coatings with different porosities, realizes the improvement of the boiling heat transfer coefficient and the critical heat flux, as shown in Figure 6 .

[0065] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications of the embodiments that can be thought of by those skilled in the art, and other ways constructed by combining part of the constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. A non-uniform structured material for enhancing boiling heat transfer, characterized in that: include: heat exchange substrate; Millimeter-scale porous columns, several of which are evenly disposed on the heat exchange substrate, and are arranged in a square array. The millimeter-scale porous columns include a first stepped porous coating, wherein the porosity of the first stepped porous coating gradually increases from bottom to top, and a super-hydrophobic coating is partially provided on the top of the first stepped porous coating; A mini porous column is disposed between two adjacent millimeter-scale porous columns, the mini porous column comprising a second stepped porous coating, the porosity of the second stepped porous coating gradually increasing from bottom to top, and the top of the second stepped porous coating being subjected to a super-hydrophilic treatment; The gaps between the millimeter-scale porous columns and the mini porous columns form channels.

2. The heterogeneous structured material for enhancing boiling heat transfer according to claim 1, characterized in that: The millimeter-scale porous column is a cube, and the length and width of the millimeter-scale porous column are both 4.1-4.3 mm, and the height is 0.45-0.75 mm.

3. The heterogeneous structured material for enhancing boiling heat transfer according to claim 1, characterized in that: The mini porous column includes a strip column and a square column, and a groove is provided between the square column and the strip column; The strip column has a width of 0.6-1.0 mm, a length of 4.1-4.3 mm, and a height of 0.45-0.75 mm; The length and width of the square column are 0.6-1.0 mm, and the height is 0.45-0.75 mm; The width of the groove is 0.2~0.6mm; The millimeter-scale porous columns have the same height as the mini porous columns.

4. The heterogeneous structured material for enhancing boiling heat transfer according to claim 1, characterized in that: The first step porous coating comprises, from bottom to top, a copper porous coating with a porosity of 30% to 40%, a copper porous coating with a porosity of 50% to 60%, and a copper porous coating with a porosity of 70% to 80%, and the thickness of the copper porous coating with a porosity of 30% to 40%, the copper porous coating with a porosity of 50% to 60%, and the copper porous coating with a porosity of 70% to 80% is the same, which is 0.15 to 0.25 mm; The second-step porous coating includes, from bottom to top, a 30%-40% porosity copper porous coating, a 50%-60% porosity copper porous coating, and a 70%-80% porosity copper porous coating. The thickness of the 30%-40% porosity copper porous coating, the 50%-60% porosity copper porous coating, and the 70%-80% porosity copper porous coating are the same, all of which are 0.15-0.25 mm.

5. The heterogeneous structured material for enhancing boiling heat transfer according to claim 1, characterized in that: The super-hydrophobic coating occupies 15% to 20% of the upper surface area of ​​the millimeter-scale porous column.

6. The heterogeneous structured material for enhancing boiling heat transfer according to claim 1, characterized in that: The super-hydrophobic coating is formed by heat-treating polytetrafluoroethylene powder, and the thickness of the super-hydrophobic coating is 2-3 μm; The super-hydrophilic coating is obtained by wet etching.

7. A method for preparing a non-uniform structured material for enhancing boiling heat transfer according to any one of claims 1 to 6, characterized in that: The steps include: S1. Coating 900-1000 mesh atomized copper particles on a heat exchange substrate, heating to 950-1000° C. under nitrogen protection for 1-2 hours, then coating 200-300 mesh atomized copper particles and 100-200 mesh electrolytic copper particles on the surface in sequence, heating to 800-850° C. under nitrogen protection for 1-2 hours to obtain a stepped porous coating; S2. Cutting the stepped porous coating into a plurality of evenly distributed millimeter-sized porous columns and mini-porous columns, wherein the gaps between the millimeter-sized porous columns and mini-porous columns form channels, thereby obtaining a non-uniform structured material blank; S3, using a water transfer method to perform local super-hydrophobic modification on the surface of the millimeter porous column to obtain a super-hydrophobic coating; S4. After covering the super-hydrophobic modified millimeter-scale porous column with a hydrophobic film, the mini porous column is subjected to super-hydrophilic modification by wet etching to obtain a super-hydrophilic coating, thereby preparing a non-uniform structured material for enhancing boiling heat transfer.

8. The method for preparing a non-uniform structured material for enhancing boiling heat transfer according to claim 7, characterized in that: The water transfer method in step S3 includes the following steps: Adding polytetrafluoroethylene powder with a particle size of 1 μm into deionized water and stirring evenly to obtain a water transfer solution, wherein a thin layer of polytetrafluoroethylene powder is formed on the surface of the water transfer solution; Covering the surface of the stepped porous coating with a mask, immersing it in the water transfer solution and then lifting it upward, so that a thin layer of polytetrafluoroethylene powder adheres to the surface of the millimeter-scale porous column; The mask was removed, dried, and then heated to 325° C. under nitrogen protection for 1 hour to obtain a super-hydrophobic coating.

9. The method for preparing a non-uniform structured material for enhancing boiling heat transfer according to claim 7, characterized in that: The super-hydrophilic modification by wet etching in step S4 includes the following steps: dispersing sodium hydroxide and potassium persulfate in water to obtain a mixed solution; The super-hydrophobic modified non-uniform structured material body was immersed in the mixed solution, heated to 40°C, and reacted for 16 minutes. After the reaction was completed, it was washed and dried to obtain a super-hydrophilic coating.

10. Use of the heterogeneous structured material for enhancing boiling heat transfer according to any one of claims 1 to 6 in the field of heat exchangers.

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