A surface structure for enhancing condensation heat transfer and its preparation method and application

Abstract

The present invention belongs to the field of heat transfer technology and relates to a surface structure for enhancing condensation heat transfer, a preparation method thereof, and an application thereof. The surface structure comprises, from top to bottom, a mesh structure layer and a wedge-shaped gradient channel structure layer; the wedge-shaped gradient channel structure layer comprises wedge-shaped fins and wedge-shaped grooves, the wedge-shaped fins and the wedge-shaped grooves being arranged adjacent to each other in sequence; the mesh structure layer is in contact with the wedge-shaped fins; the mesh diameter of the mesh structure layer is smaller than the channel width of the wedge-shaped gradient channel structure layer, the surfaces of the mesh structure layer and the wedge-shaped gradient channel structure layer are both covered with a nanostructure layer, and the nanostructure layer is covered with a hydrophobic coating. The present invention can achieve the technical effects of limiting the formation of pinned droplets and the overflow of surface condensate, realizing the reasonable separation of gas-liquid channels, and improving the heat transfer efficiency and heat transfer performance of condensation. It can be widely used in the enhanced condensation of condensation heat exchangers, steam chamber condensation ends, or seawater desalination water collection.

Description

Technical Field

[0001] The present invention belongs to the field of heat transfer technology, and in particular relates to a surface structure for enhancing condensation heat transfer, a preparation method thereof, and an application thereof. Background Art

[0002] With the continuous development of industries such as seawater desalination, power generation, and air conditioning, the associated equipment requires higher heat exchange efficiency. Condensation, as a highly efficient phase-change heat transfer method, is a primary heat transfer method in these industries. Therefore, improving condensation heat transfer efficiency, reducing energy consumption, and accelerating the integration and efficiency of energy systems have become key technological advancement goals in various industrial sectors.

[0003] The wettability and structural morphology of the heat transfer surface are key factors affecting the condensation heat transfer characteristics. Using micro-nanostructured surfaces to control the behavior of droplets / liquid films can significantly enhance condensation heat transfer. In recent years, many scholars have developed various types of micro-nanostructured surfaces and coating surfaces to accelerate the detachment of droplets and improve the condensation heat transfer performance by changing the surface structure and wetting characteristics. Currently, fins or grooved surfaces are commonly used to increase the condensation area and promote the sliding and detachment of droplets, but the grooves are mostly straight rectangular channels. The regulatory effect of such grooves on droplets / liquid films is relatively simple and limited, and the efficiency of removing condensate from the surface needs to be improved. Furthermore, the super-hydrophobic grooved surface with micro-nanostructures is prone to droplet pinning and condensate overflow at high supercooling degrees, resulting in increased surface heat transfer thermal resistance and worsened condensation heat transfer.

[0004] Therefore, how to prepare a surface structure to limit the formation of pinned droplets and the overflow of surface condensate, and improve the heat transfer efficiency and heat transfer performance of condensation, has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0005] In response to the defects of the prior art, the present invention provides a surface structure for enhancing condensation heat transfer, a preparation method and application thereof, so as to solve the technical problems of the prior art such as the increase in heat exchange thermal resistance and the deterioration of condensation heat transfer caused by the pinning of condensation droplets and the overflow of condensation, thereby achieving the technical effect of limiting the formation of pinned droplets and the overflow of surface condensation, realizing the reasonable separation of gas-liquid channels, and improving the heat transfer efficiency and heat transfer performance of condensation.

[0006] According to a first aspect of the present invention, a surface structure for enhancing condensation heat transfer is provided, which comprises, from top to bottom, a mesh structure layer and a wedge-shaped gradient channel structure layer; the wedge-shaped gradient channel structure layer includes wedge-shaped fins and wedge-shaped grooves, and the wedge-shaped fins and the wedge-shaped grooves are arranged adjacent to each other in sequence; the mesh structure layer is in contact with the wedge-shaped fins; the mesh diameter of the mesh structure layer is smaller than the channel width of the wedge-shaped gradient channel structure layer, and the surfaces of the mesh structure layer and the wedge-shaped gradient channel structure layer are both covered with a nanostructure layer, and the nanostructure layer is covered with a hydrophobic coating.

[0007] Preferably, the structure of the wedge-shaped fin is a wedge-shaped gradient-contracting fin structure, and the structure of the wedge-shaped slot is a wedge-shaped gradient-expanding slot structure.

[0008] Preferably, the mesh diameter of the mesh structure layer is 10 μm to 100 μm, the width of the mesh wire of the mesh structure layer is 10 μm to 80 μm, and the mesh number of the mesh structure layer is 100 to 250 meshes.

[0009] Preferably, the widths of the wedge-shaped fin structure and the wedge-shaped groove structure are independently selected from 0.2 mm to 1.4 mm, and the depth of the wedge-shaped groove structure is 0.2 mm to 1 mm.

[0010] Preferably, the materials of the mesh structure layer and the wedge-shaped gradient channel structure layer are selected from copper, aluminum, and titanium.

[0011] Preferably, the material of the nanostructure layer is one or more of copper oxide, aluminum oxide, titanium oxide, and silicon oxide, and the material of the hydrophobic coating is one or more of thiol, fluorosilane, polytetrafluoroethylene, polydimethylsiloxane, paraffin, or carbon nanotubes.

[0012] According to another aspect of the present invention, a method for preparing the surface structure for enhancing condensation heat transfer is provided.

[0013] (1) making a mesh structure layer;

[0014] (2) selecting a substrate and fabricating a wedge-shaped gradient channel structure on the surface of the substrate to form a wedge-shaped gradient channel structure layer;

[0015] (3) Covering the mesh structure layer on the wedge-shaped gradient channel of the wedge-shaped gradient channel structure layer to form a combination.

[0016] (4) immersing the combined body in an alkaline solution or an oxidizing solution that can oxidize the surface of the combined body to form a nano-metal oxide, thereby forming a nano-structured layer on the surface of the combined body by a chemical oxidation method;

[0017] or coating a suspension of a material containing a nanostructure layer on the combined body by a coating method to form a nanostructure layer on the surface of the combined body;

[0018] (5) Immersing the composite body having the nanostructure layer in a solution containing a hydrophobic molecular precursor, and forming a hydrophobic coating on the nanostructure layer by molecular self-assembly or physical deposition.

[0019] Preferably, the alkaline solution is selected from a mixed aqueous solution of NaClO2, NaOH and Na3PO4, or ammonia water; the oxidizing solution is selected from a H2O2 solution, or a mixed aqueous solution of K2S2O8 and KOH, or a mixed aqueous solution of (NH4)2S2O8 and NaOH;

[0020] Preferably, a pretreatment step is further included before step (3), and the pretreatment step specifically includes: polishing the surface of the wedge-shaped gradient channel structure layer, and cleaning the polished wedge-shaped gradient channel structure layer and the mesh structure layer.

[0021] According to another aspect of the present invention, an application of the surface structure for enhancing condensation heat transfer is provided, which is used for enhancing condensation in a condensing heat exchanger or a condensing end of a steam chamber or a desalination water collection device.

[0022] In general, the above technical solutions conceived by the present invention have the following technical advantages compared with the existing technology:

[0023] (1) The surface structure for enhancing condensation heat transfer of the present invention combines a mesh structure layer with a wedge-shaped gradient channel structure layer. The mesh structure layer can effectively limit the overflow of the condensate, so that the condensate is reasonably confined in the wedge-shaped grooves of the wedge-shaped gradient channel structure layer. At the same time, the wedge-shaped gradient channel structure promotes the downward transport process of the liquid film, so that the condensate can be quickly discharged downward in the wedge-shaped grooves. These provide good support for the structural surface to achieve efficient drip-film condensation heat transfer.

[0024] (2) The present invention combines wedge-shaped fins with wedge-shaped grooves to provide an asymmetric flow channel for the condensate. The condensate droplets or liquid columns are restricted by the wall surface in the groove to form an asymmetric curvature interface at the upper and lower ends. The generated Laplace pressure difference can drive the droplets or liquid columns to move in a self-driven manner, which is conducive to accelerating the separation of the condensate.

[0025] (3) The present invention utilizes a chemical oxidation method to oxidize the metal surface to produce a metal oxide with a nanostructure, or utilizes a coating method to deposit metal oxide nanoparticles or silicon oxide nanoparticles on the surface of the wedge-shaped gradient channel structure layer and the mesh structure layer as a nanostructure layer, providing nanoscale roughness, making the surface hydrophobic after subsequent hydrophobic treatment more hydrophobic, reducing the adhesion of condensate on the surface, and accelerating the flow of surface condensate.

[0026] (4) The present invention uses a molecular self-assembly method to form chemical bonds between hydrophobic molecules and oxygen atoms of surface oxides to form a hydrophobic coating with a single molecular thickness, or uses a physical deposition method to attach hydrophobic organic polymers or carbon nanotubes to the surface as a hydrophobic layer; the formed hydrophobic coating ensures that droplets are formed on the network structure layer during the condensation process, and liquid columns or discontinuous liquid films are formed in the wedge-shaped gradient channel structure, thereby avoiding the formation of a large-area continuous liquid film on the surface, thereby accelerating the renewal of the condensate and reducing the thermal resistance of the condensate.

[0027] (5) The mesh diameter of the mesh structure layer of the present invention is smaller than the channel width of the wedge-shaped gradient channel structure. The purpose is to ensure that the resistance that the condensate in the wedge-shaped gradient channel structure layer needs to overcome to pass through the mesh structure layer and overflow the channel is greater than the resistance of the condensate flowing along the channel, thereby confining the condensate in the wedge-shaped gradient channel structure within the channel and preventing the condensate from overflowing and flooding the mesh structure layer.

[0028] (6) The mesh diameter of the mesh structure layer of the present invention is 10 μm to 100 μm, which is smaller than the capillary size and can reduce the droplet detachment diameter and accelerate the condensate detachment. At the same time, the size cannot be too small to avoid the condensate clogging the mesh holes; the mesh wire width of the mesh structure layer is 10 μm to 80 μm, which size range can ensure that the mesh structure layer has good thermal conductivity and reliable strength of the structure; the width of the wedge-shaped fin structure and the wedge-shaped groove structure are independently selected from 0.2 mm to 1.4 mm, which is smaller than the capillary size and can limit the shape of the condensate in the channel, while ensuring that the flow resistance of the condensate is small. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic top view of a surface structure for enhancing condensation heat transfer according to the present invention.

[0030] Figure 2 It is a side view schematic diagram of a surface structure for enhancing condensation heat transfer according to the present invention.

[0031] Figure 3 This is a local SEM image of a surface structure for enhancing condensation heat transfer according to the present invention.

[0032] Figure 4 (a) is an SEM image of the copper oxide nanostructure layer formed on the surface of the copper-based wedge-shaped gradient channel of the surface structure for enhancing condensation heat transfer prepared in Example 1 of the present invention; (b) is an SEM image of the copper oxide nanostructure layer formed on the copper-based mesh structure layer.

[0033] Figure 5These are the images of the condensed liquid droplet-liquid film behavior on the surface of the hydrophobic wedge-shaped gradient channel structure of Comparative Example 1 at different degrees of supercooling, where (a) is a schematic diagram of the wedge-shaped gradient channel structure, (b) is an image of the condensed liquid droplet-liquid film behavior at a supercooling degree of 2K, (c) is an image of the condensed liquid droplet-liquid film behavior at a supercooling degree of 6K, and (d) is an image of the condensed liquid droplet-liquid film behavior at a supercooling degree of 10K.

[0034] Figure 6 These are images of the condensed liquid droplet-liquid film behavior on the surface of the single-layer copper mesh structure of Comparative Example 2 at different degrees of supercooling; (a) is a schematic diagram of the single-layer copper mesh structure, (b) is an image of the condensed liquid droplet-liquid film behavior when the supercooling degree is 2K, (c) is an image of the condensed liquid droplet-liquid film behavior when the supercooling degree is 6K, and (d) is an image of the condensed liquid droplet-liquid film behavior when the supercooling degree is 10K.

[0035] Figure 7 These are images of the condensed liquid droplet-liquid film behavior on the surface of the wedge-shaped gradient channel-copper mesh composite structure disclosed in Example 1 of the present application; wherein (a) is a schematic diagram of the wedge-shaped gradient channel-copper mesh composite structure, (b) is an image of the condensed liquid droplet-liquid film behavior at a supercooling degree of 2K, (c) is an image of the condensed liquid droplet-liquid film behavior at a supercooling degree of 6K, and (d) is an image of the condensed liquid droplet-liquid film behavior at a supercooling degree of 10K.

[0036] Figure 8 1 and 2 are curves showing the change of the condensation heat flux density q with the supercooling degree ΔT for the surface structures of Example 1, Comparative Example 1, and Comparative Example 2.

[0037] Figure 9 1 is a curve showing the change of the condensation heat transfer coefficient h of the surface structure of Example 1, Comparative Example 1, and Comparative Example 2 with the supercooling degree ΔT.

[0038] Figure 10 1 is a curve showing the change of the condensation heat flux density q with the supercooling degree ΔT of the surface structure of Example 1, Example 2, Example 3 and Comparative Example 2.

[0039] Figure 11 1 is a curve showing the change of the condensation heat transfer coefficient h of the surface structure of Example 1, Example 2, Example 3 and Comparative Example 2 with the supercooling degree ΔT.

[0040] In the figure, 100 is a mesh structure layer; 101 is a wedge-shaped gradient channel structure layer; 1002 is a nanostructure layer; 1003 is a hydrophobic coating; 1011 is a wedge-shaped fin; and 1012 is a wedge-shaped groove. DETAILED DESCRIPTION

[0041] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0042] According to a first aspect of the present invention, a surface structure for enhancing condensation heat transfer is provided, which comprises, from top to bottom, a mesh structure layer and a wedge-shaped gradient channel structure layer; the wedge-shaped gradient channel structure layer includes wedge-shaped fins and wedge-shaped grooves, and the wedge-shaped fins and the wedge-shaped grooves are arranged adjacent to each other in sequence; the mesh structure layer is in contact with the wedge-shaped fins; the mesh diameter of the mesh structure layer is smaller than the channel width of the wedge-shaped gradient channel structure layer, and the surfaces of the mesh structure layer and the wedge-shaped gradient channel structure layer are both covered with a nanostructure layer, and the nanostructure layer is covered with a hydrophobic coating.

[0043] Preferably, the structure of the wedge-shaped fin is a wedge-shaped gradient-contracting fin structure, and the structure of the wedge-shaped slot is a wedge-shaped gradient-expanding slot structure.

[0044] In some embodiments, the mesh diameter of the mesh structure layer is 10 μm to 100 μm, the width of the mesh wire of the mesh structure layer is 10 μm to 80 μm, and the mesh number of the mesh structure layer is 100 to 250 meshes.

[0045] In some embodiments, the widths of the wedge-shaped fin structure and the wedge-shaped groove structure are independently selected from 0.2 mm to 1.4 mm, and the depth of the wedge-shaped groove structure is 0.2 mm to 1 mm.

[0046] In some embodiments, the materials of the mesh structure layer and the wedge-shaped gradient channel structure layer are selected from copper, aluminum, and titanium.

[0047] In some embodiments, the material of the nanostructure layer is one or more of copper oxide, aluminum oxide, titanium oxide, and silicon oxide, and the material of the hydrophobic coating is one or more of thiol, fluorosilane, polytetrafluoroethylene, polydimethylsiloxane, paraffin, or carbon nanotubes.

[0048] In some embodiments, the mesh structure layer is manufactured by metal wire weaving or powder sintering.

[0049] In some embodiments, the wedge-shaped gradient channel structure layer is manufactured by machining or wire electric discharge cutting.

[0050] In some embodiments, the mesh structure layer and the wedge-shaped gradient channel structure layer are combined to form a combined body by vacuum sintering, protective gas sintering, or electroplating.

[0051] According to another aspect of the present invention, a method for preparing the surface structure for enhancing condensation heat transfer is provided.

[0052] (1) making a mesh structure layer;

[0053] (2) selecting a substrate and fabricating a wedge-shaped gradient channel structure on the surface of the substrate to form a wedge-shaped gradient channel structure layer;

[0054] (3) covering the mesh structure layer on the wedge-shaped gradient channel of the wedge-shaped gradient channel structure layer to form a combined body;

[0055] (4) immersing the combined body in an alkaline solution or an oxidizing solution that can oxidize the surface of the combined body to form a nano-metal oxide, thereby forming a nano-structured layer on the surface of the combined body by a chemical oxidation method;

[0056] or coating a suspension of a material containing a nanostructure layer on the combined body by a coating method to form a nanostructure layer on the surface of the combined body;

[0057] (5) Immersing the combination having the nanostructure layer in a solution containing a hydrophobic molecular precursor, and forming a hydrophobic coating on the nanostructure layer by molecular self-assembly or physical deposition.

[0058] In some embodiments, the alkaline solution is selected from a mixed aqueous solution of NaClO2, NaOH and Na3PO4, or aqueous ammonia; the oxidizing solution is selected from an aqueous solution of H2O2, or a mixed aqueous solution of K2S2O8 and KOH, or a mixed aqueous solution of (NH4)2S2O8 and NaOH;

[0059] In some embodiments, the material of the nanostructure layer is one or more of copper oxide, aluminum oxide, titanium oxide, and silicon oxide; when the material of the nanostructure layer is copper oxide, aluminum oxide, or titanium oxide, the nanostructure layer is formed by chemical oxidation; when the material of the nanostructure layer is copper oxide, aluminum oxide, titanium oxide, or silicon oxide, the nanostructure layer is formed by coating;

[0060] In some embodiments, the material of the hydrophobic coating is one or more of thiol, fluorosilane, polytetrafluoroethylene, polydimethylsiloxane, paraffin or carbon nanotubes. When the material of the hydrophobic coating is thiol, fluorosilane or polydimethylsiloxane, the hydrophobic coating is formed by molecular self-assembly; when the material of the hydrophobic coating is polytetrafluoroethylene, paraffin or carbon nanotubes, the hydrophobic coating is formed by physical deposition.

[0061] Example 1

[0062] like Figure 1-3A surface structure for enhancing condensation heat transfer is shown, comprising a mesh structure layer 100 and a wedge-shaped gradient channel structure layer 101. The mesh structure layer 100 is located on top of the wedge-shaped gradient channel structure layer 101 and is used to limit the overflow of condensate. A nanostructure layer 1002 is disposed on the surfaces of the mesh structure layer 100 and the wedge-shaped gradient channel structure layer 101.

[0063] The wedge-shaped gradient channel structure layer 101 is provided with a wedge-shaped gradient tapered fin structure 1011 and a wedge-shaped gradient gradually expanding groove structure 1012 to promote the self-transport of the liquid film in the groove. The number of the wedge-shaped gradient tapered fin structure 1011 and the wedge-shaped gradient gradually expanding groove structure 1012 are both 17, and they are arranged at intervals to allow droplets and liquid columns to separate, forming a fast channel for the separation of droplets and liquid columns.

[0064] The upper width of the wedge-shaped fin 1011 is larger than the lower width, and the upper width of the wedge-shaped channel structure 1012 is smaller than the lower width. The upper width of the wedge-shaped fin 1011 is 1.0 mm, and the lower width is 0.4 mm. The upper width of the wedge-shaped channel 1012 is 0.4 mm, and the lower width is 1.0 mm, and they change monotonically along the length direction. The height of the wedge-shaped fin is 0.4 mm. The mesh structure layer 100 is a copper mesh with a mesh size of 150. Figure 3 SEM image of the surface structure that enhances condensation heat transfer.

[0065] A method for preparing a surface structure for enhancing condensation heat transfer comprises the following steps:

[0066] S10. Weaving a single layer of copper mesh using a copper mesh weaving device, and cutting the copper mesh into a required size; importing the design drawing of the wedge-shaped gradient channel into a CNC milling machine, and processing the copper plate to form a wedge-shaped gradient channel structure.

[0067] S11 pretreatment: polishing the surface of the wedge-shaped gradient channel structure layer 101; cleaning the polished wedge-shaped gradient channel structure layer 101 and the network structure layer 100: using acetone, anhydrous ethanol, deionized water, dilute sulfuric acid and deionized water to clean the network structure layer 100 and the polished wedge-shaped gradient channel structure layer 101 in sequence. Among them, acetone is used to clean the oil stains on the surface of the network structure layer 100 and the wedge-shaped gradient channel structure layer 101, anhydrous ethanol is used to clean the acetone remaining on the surface of the network structure layer 100 and the wedge-shaped gradient channel structure layer 101, deionized water is used to clean the ethanol remaining on the surface of the network structure layer 100 and the wedge-shaped gradient channel structure layer 101, dilute sulfuric acid is used to remove oxides such as copper oxide on the surface of the network structure layer 100 and the wedge-shaped gradient channel structure layer 101, and deionized water is used to clean the residual dilute sulfuric acid; during the above cleaning process, the network structure layer 100 and the wedge-shaped gradient channel structure layer 101 can be immersed in a cleaning agent for 20 minutes, and the mass percentage of dilute sulfuric acid is selected to be 5%. Through the pretreatment step, burrs, oil stains and oxides on the surfaces of the network structure layer 100 and the wedge-shaped gradient channel structure layer 101 are removed, so that the network structure layer 100 can be more tightly bonded to the surface of the wedge-shaped gradient channel structure layer 101.

[0068] S20, using a clamp to fix the mesh structure layer 100 and the wedge-shaped gradient channel structure layer 101 together to form a combination; placing the combination into a vacuum high-temperature sintering furnace for sintering to bond the mesh structure layer 100 to the surface of the wedge-shaped gradient channel structure layer 101 to form a combination of the two

[0069] S30, preparing a nanostructured layer, immersing the combination of the mesh structure layer 100 and the wedge-shaped gradient channel structure layer 101 in a mixed solution of NaClO2, NaOH, Na3PO4·12H2O, and deionized water in a mass ratio of 3.75:5:10:100 at a temperature of 90°C for 20 minutes, and oxidizing the solution to prepare a nanostructured layer 1002 on the surface of the combination.

[0070] S40, cleaning the nanostructure layer, using deionized water to rinse the combination with the metal oxide nanostructure layer 1002 to remove the alkaline solution remaining on the surface of the combination;

[0071] S50, making a hydrophobic coating, soaking the conjugate in an ethanol solution of octadecyl mercaptan with a molar concentration of 0.0025 mol / L at a temperature of 70°C for 1 hour to perform a molecular self-assembly reaction, then taking out the conjugate, and rinsing it with ethanol and deionized water in sequence to form a hydrophobic coating 1003 on the nanostructure layer.

[0072] Figure 4As shown in (a), a layer of flaky copper oxide nanostructure is formed on the surface of the copper-based wedge-shaped gradient channel structure after alkaline chemical oxidation treatment. Figure 4 (b) shows the copper oxide nanostructure formed on the copper wire surface of the copper mesh. After chemical oxidation with alkaline solution, a dense nanostructure is formed on the surface of the copper mesh and the wedge-shaped gradient channel structure below.

[0073] Example 2

[0074] The difference from Example 1 is that the mesh number of the copper mesh used is 100 mesh.

[0075] Example 3

[0076] The difference from Example 1 is that the mesh number of the copper mesh used is 200 mesh.

[0077] Comparative Example 1

[0078] A surface structure for enhancing condensation heat transfer, which is different from Example 1 in that its surface structure is only a wedge-shaped gradient channel structure layer, and the structure of the wedge-shaped gradient channel structure layer is the same as that of Example 1.

[0079] Comparative Example 2

[0080] A surface structure for enhancing condensation heat transfer, which is different from Example 1 in that its surface structure is only a single-layer copper mesh structure, and the single-layer copper mesh structure is the same as Example 1.

[0081] In order to verify the effect of the surface structure for enhancing condensation heat transfer disclosed in the embodiments of the present application on enhancing heat transfer performance, condensation was taken as an example to conduct an experimental verification, and the wedge-shaped gradient channel-copper mesh composite structure surface in Example 1 was compared with the wedge-shaped gradient channel structure surface in Comparative Example 1 and the single-layer copper mesh structure surface in Comparative Example 2 to illustrate the effect.

[0082] Compare the dynamic behavior and heat transfer performance of condensed droplets / liquid films of the wedge-shaped gradient channel-copper mesh composite structure of Example 1, the wedge-shaped gradient channel structure surface of Comparative Example 1, and the single-layer copper mesh structure surface of Comparative Example 2. Figure 5 The distribution of condensate on the surface of the wedge-shaped gradient channel structure under different supercooling conditions in Comparative Example 1 is shown. The wedge-shaped gradient channel structure does promote the self-transport of condensate to a certain extent, but because condensate in adjacent channels merges to form large droplets that span multiple channels, the condensation heat transfer resistance is greatly increased.

[0083] Figure 6 The distribution of condensate on the surface of the single-layer copper mesh structure of Comparative Example 2 under different supercooling conditions is shown in FIG. Figure 6A liquid film appears on some areas of the single-layer copper mesh structure. This is because the condensation on the copper mesh surface is intense, and the narrow channel connecting the copper mesh to the substrate is insufficient to provide sufficient drainage channels for the generated condensate. As a result, the condensate overflows the copper mesh surface, forming a strip-shaped liquid film area (see the dotted line in the figure), along which the condensate flows downward. However, the removal rate of the condensate flowing downward along the liquid film area is slow, and the strip-shaped liquid film area persists during the condensation process.

[0084] Figure 7 The figure shows the distribution of condensate on the surface of the wedge-shaped gradient channel-copper mesh composite structure of Example 1 under different supercooling conditions. The wedge-shaped gradient channel-copper mesh composite structure in the figure shows no significant condensate overflow. Condensate only overflows from the copper mesh surface near the lower end, where it is about to leave the surface. This is because the opening of the wedge-shaped channel at the lower end is insufficient to quickly drain the condensate, while the mesh size is just right, allowing the condensate to overflow from the copper mesh surface just below the surface, achieving rapid removal. Liquid droplets condense on the copper mesh surface, enter the underlying copper mesh, and are drawn into the wedge-shaped gradient, gradually expanding channels, forming a thin liquid film in the channels. The channels act as drainage channels, allowing the condensate to flow downward, preventing the copper mesh surface from being covered by a large liquid film.

[0085] On the surface of the wedge-shaped gradient channel-copper mesh composite structure, steam rapidly condenses on the top of the copper mesh. The wedge-shaped grooves provide condensate removal channels, allowing condensate to drain from the grooves. This separates the paths for condensate generation and removal, thereby achieving efficient drip-film condensation heat transfer. Furthermore, the surface area occupied by condensate overflowing from the wedge-shaped gradient channel-copper mesh composite structure is relatively small. The proportion of surface area covered remains essentially unchanged at different degrees of supercooling, and is significantly smaller than the proportion of condensate covered on the surface of the wedge-shaped gradient channel structure or on the surface of a single layer of copper mesh.

[0086] The above-mentioned heat transfer performance experimental results show that the copper mesh restriction layer in the enhanced condensation heat transfer surface structure disclosed in the embodiment of the present application can effectively limit the overflow of the condensate, so that the condensate is reasonably confined in the groove. At the same time, with the help of the wedge-shaped gradient expansion channel, the downward transport process of the liquid film is promoted, so that the condensate can be quickly discharged downward in the groove. Moreover, the copper mesh has a good thermal conductivity coefficient, which can control the heat transfer thermal resistance of the surface structure at a reasonable level, thereby realizing efficient drip film condensation heat transfer.

[0087] Figure 8 The heat flux q of the three surfaces of Example 1, Comparative Example 1 and Comparative Example 2 varies with the degree of supercooling ΔT. Figure 8It can be seen that the heat flux density of the wedge-shaped gradient channel structure surface and the single-layer copper mesh structure surface shows similar trends as the supercooling degree increases. The heat flux density curves of the two surfaces basically overlap when the supercooling degree ΔT is less than 4 K. As the supercooling degree increases further, the heat flux density curve of the wedge-shaped gradient channel-copper mesh composite structure surface is significantly higher than that of the other two surfaces.

[0088] Figure 9 The heat transfer coefficient h of the three surfaces of Example 1, Comparative Example 1 and Comparative Example 2 varies with the degree of supercooling ΔT. Figure 9 It can be seen that when ΔT = 2K and 6K, the heat transfer coefficient h of the wedge gradient channel-copper mesh composite structure surface is 87.8kW / (m 2 ·K)、63.9kW / (m 2 K), h increased by 51% and 86% compared to the surface of the wedge-shaped gradient channel structure and the single-layer copper mesh surface, respectively. The aforementioned analysis of condensate droplet-liquid film behavior shows that the significant enhancement in condensation heat transfer performance on the wedge-shaped gradient channel-copper mesh composite surface is primarily due to its higher surface condensate removal efficiency. This effectively separates the channels for condensate generation and removal, allowing the condensate to be properly confined by the copper mesh confinement layer within the gradient-diverging microgrooves and drain downward along the grooves. The top copper mesh surface maintains efficient condensation, preventing large-scale condensate overflow.

[0089] Figure 10 The heat flux density q of the surface structure of Example 1, Example 2, Example 3 and Comparative Example 2 varies with the degree of supercooling ΔT. Figure 10 The 100-mesh copper mesh shown has too large pores to effectively limit the overflow of surface condensate, causing the surface copper mesh to be immersed in the liquid film. The 150-mesh and 250-mesh copper meshes have relatively small pore sizes and both effectively limit the overflow of surface condensate.

[0090] Figure 11 The heat transfer coefficient h of the surface structure of Example 1, Example 2, Example 3 and Comparative Example 2 varies with the degree of supercooling ΔT. Figure 11It can be seen that the heat flux density curve of the wedge-shaped gradient channel-copper mesh composite structure (100 mesh) is located below the surface of the single-layer copper mesh. Combined with the previous analysis of the condensation droplet-liquid film behavior on these two surfaces, it can be seen that the 100-mesh copper mesh as a restrictive layer cannot effectively limit the occurrence of liquid film overflow. Adding 150-mesh and 250-mesh copper meshes to the surface of the wedge-shaped gradient micro-groove can effectively limit the occurrence of surface condensate overflow. However, compared with the surface of the wedge-shaped gradient channel-copper mesh composite structure (150 mesh), the copper mesh pore size used on the surface of the wedge-shaped gradient channel-copper mesh composite structure (250 mesh) is smaller. At low supercooling (ΔT<1.6K), the copper mesh surface has a larger specific surface area, more nucleation sites, and a larger heat transfer coefficient; while at high supercooling (ΔT>1.6K), the narrow mesh of the 250-mesh copper mesh hinders the removal of condensate. The less efficient condensate removal also limits the utilization of the condensation area in the groove, resulting in a lower heat transfer coefficient on its surface than that of the wedge-shaped gradient channel-copper mesh composite structure (150 mesh).

[0091] It should be noted that the above description of the alkaline solution, chemical oxidation reaction temperature, chemical oxidation reaction time, mass percentage of dilute sulfuric acid, molar concentration of thiol, single molecule self-assembly temperature and single molecule self-assembly time is only an example in the embodiment of the present application and is not the sole limitation to the embodiments of the present application.

[0092] The preparation method of the enhanced condensation heat transfer surface structure disclosed in the embodiment of the present application has simple steps, reasonable design, easy implementation, strong operability, and is convenient for large-scale preparation and production, and has important practical value and promotion significance.

[0093] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A surface structure for enhancing condensation heat transfer, characterized in that: The invention discloses a method for preparing a nanostructured substrate for a nanostructured substrate. The method comprises, from top to bottom, a mesh structure layer (100) and a wedge-shaped gradient channel structure layer (101); the wedge-shaped gradient channel structure layer (101) comprises wedge-shaped fins (1011) and wedge-shaped grooves (1012), and the wedge-shaped fins (1011) and the wedge-shaped grooves (1012) are arranged adjacent to each other in sequence; the mesh structure layer (100) is in contact with the wedge-shaped fins (1011); the mesh diameter of the mesh structure layer (100) is smaller than the channel width of the wedge-shaped gradient channel structure layer (101); the surfaces of the mesh structure layer (100) and the wedge-shaped gradient channel structure layer (101) are both covered with a nanostructure layer (1002), and the nanostructure layer (1002) is covered with a hydrophobic coating (1003).

2. The surface structure for enhancing condensation heat transfer according to claim 1, characterized in that: The structure of the wedge-shaped fin (1011) is a fin structure with a wedge-shaped gradient gradually contracting, and the structure of the wedge-shaped groove (1012) is a groove structure with a wedge-shaped gradient gradually expanding.

3. The surface structure for enhancing condensation heat transfer according to claim 1, characterized in that: The mesh diameter of the mesh structure layer (100) is 10 μm to 100 μm, the width of the mesh of the mesh structure layer (100) is 10 μm to 80 μm, and the mesh number of the mesh structure layer (100) is 100 to 250 meshes.

4. The surface structure for enhancing condensation heat transfer according to claim 2, characterized in that: The widths of the wedge-shaped fins (1011) and the wedge-shaped grooves (1012) are independently selected from 0.2 mm to 1.4 mm, and the depth of the wedge-shaped grooves (1012) is 0.2 mm to 1 mm.

5. The surface structure for enhancing condensation heat transfer according to claim 1, characterized in that: The materials of the mesh structure layer (100) and the wedge-shaped gradient channel structure layer (101) are selected from copper, aluminum, and titanium.

6. The surface structure for enhancing condensation heat transfer according to claim 1, characterized in that: The material of the nanostructure layer (1002) is one or more of copper oxide, aluminum oxide, titanium oxide, and silicon oxide; the material of the hydrophobic coating (1003) is one or more of thiol, fluorosilane, polytetrafluoroethylene, polydimethylsiloxane, paraffin, or carbon nanotubes.

7. The method for preparing a surface structure for enhancing condensation heat transfer according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) making a mesh structure layer; (2) selecting a substrate and fabricating a wedge-shaped gradient channel structure on the surface of the substrate to form a wedge-shaped gradient channel structure layer; (3) covering the mesh structure layer on the wedge-shaped gradient channel of the wedge-shaped gradient channel structure layer to form a combined body; (4) immersing the combined body in an alkaline solution or an oxidizing solution that can oxidize the surface of the combined body to form a nano-metal oxide, thereby forming a nano-structured layer on the surface of the combined body by a chemical oxidation method; or coating a suspension of a material containing a nanostructure layer on the combined body by a coating method to form a nanostructure layer on the surface of the combined body; (5) Immersing the composite body having the nanostructure layer in a solution containing a hydrophobic molecular precursor, and forming a hydrophobic coating on the nanostructure layer by molecular self-assembly or physical deposition.

8. The method for preparing a surface structure for enhancing condensation heat transfer according to claim 7, characterized in that: The alkaline solution is selected from a mixed aqueous solution of NaClO2, NaOH and Na3PO4 or ammonia water; the oxidizing solution is selected from a H2O2 solution, a mixed aqueous solution of K2S2O8 and KOH, or a mixed aqueous solution of (NH4)2S2O8 and NaOH.

9. The method for preparing a surface structure for enhancing condensation heat transfer according to claim 7, characterized in that: Before step (3), a pretreatment step is also included, and the pretreatment step specifically includes: polishing the surface of the wedge-shaped gradient channel structure layer, and cleaning the polished wedge-shaped gradient channel structure layer and the mesh structure layer.

10. Use of a surface structure for enhancing condensation heat transfer according to any one of claims 1 to 6, characterized in that: Use it for enhanced condensation in condensing heat exchangers, at the condensing end of steam chambers or for desalination water collection.

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