Gradient porous enhanced heat exchange plate with vertical micro-channels and preparation method of gradient porous enhanced heat exchange plate

Abstract

The invention discloses a gradient porous enhanced heat exchange plate with vertical microchannels and a preparation method thereof, and the preparation method comprises the following steps: stamping a substrate to form a required macroscopic flow channel; a metal gradient porous layer with the average pore diameter gradually decreasing from the side close to the base plate to the side away from the base plate is constructed on the surface of the base plate with the macroscopic flow channel through a thermal spraying technology; performing scanning etching on the surface of the metal gradient porous layer by adopting short pulse laser equipment to form a series of vertical micro-channels; and carrying out thermal diffusion treatment on the sheet in a protective atmosphere. According to the method, the process of stamping and then thermal spraying is combined with laser etching, high-temperature deformation of the substrate is avoided, capillary force and a steam escape path are optimized through a gradient aperture structure, and directional high-speed steam escape and interface metallurgical bonding are achieved through the vertical microchannel array and thermal diffusion treatment; therefore, the heat transfer coefficient, the critical heat flux and the structural reliability of the heat exchange plate are synergistically improved.

Description

Technical Field

[0001] This invention relates to the field of heat exchange plate technology, and in particular to a gradient porous reinforced heat exchange plate with vertical microchannels and its preparation method. Background Technology

[0002] With the increasing demands for energy conservation and emission reduction in the petroleum, chemical, coal chemical, and new energy industries, the development of high-efficiency heat exchange equipment has become an urgent need. Plate heat exchangers are widely used in these fields due to their compact structure and high heat transfer efficiency. However, traditional plate heat exchangers mostly use smooth plates that are stamped or etched with flow channels. During phase change heat transfer such as boiling and evaporation, a stable vapor film easily forms on the smooth surface, generating huge thermal resistance. This causes the heat transfer efficiency to decrease rather than increase under phase change conditions, severely limiting its application in high-efficiency phase change heat transfer applications.

[0003] To improve performance, sintering to prepare a porous metal layer on the surface of a heat exchanger plate is a known technical approach. However, this approach has inherent drawbacks: First, the sintering process requires prolonged high-temperature heating with a large heat input, which easily causes warping deformation of the thin plate substrate. This not only affects the flatness and sealing reliability of the plate but also leads to thermal stress concentration within the porous layer, impacting bonding strength and long-term stability. Second, the porous structure formed by sintering exhibits highly random pore size and pore distribution, making precise control difficult and hindering the synergistic optimization of capillary liquid supply and efficient vapor escape in physical space. Although the porous layer can increase vaporization nuclei, the random pore structure often results in a tortuous vapor escape path with high resistance, limiting further improvements in critical heat flux density and heat transfer coefficient, especially prone to localized drying under high heat flux conditions. Furthermore, the sintering process is complex and energy-intensive, hindering large-scale, low-cost manufacturing.

[0004] Therefore, there is an urgent need in this field for a novel method for preparing heat exchange plates that can avoid high-temperature deformation, achieve controllable design of porous structures, and thus significantly improve the phase change heat transfer coefficient and critical heat flux density. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a gradient porous reinforced heat exchange plate with vertical microchannels and its preparation method. This invention utilizes a "stamping followed by thermal spraying" process combined with laser etching. This avoids high-temperature deformation of the substrate while optimizing capillary force and vapor escape paths through a gradient aperture structure. Furthermore, the vertical microchannel array and thermal diffusion treatment respectively achieve directional high-speed vapor escape and interfacial metallurgical bonding, thereby synergistically improving the heat transfer coefficient, critical heat flux density, and structural reliability of the heat exchange plate.

[0006] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution: This invention provides a method for preparing a gradient porous enhanced heat exchange plate with vertical microchannels, comprising the following steps: S1. Substrate pretreatment and flow channel forming: Stamping the substrate to form the required macroscopic flow channels; S2. Construction of a metal gradient porous layer: On the surface of a substrate with macroscopic flow channels, a metal gradient porous layer with an average pore size that gradually decreases from the side closer to the substrate to the side farther away from the substrate is constructed by a thermal spraying process. S3. Laser etching to construct a vertical microchannel array: A short-pulse laser device is used to scan and etch the surface of the metal gradient porous layer to form a series of vertical microchannels. S4. Thermal diffusion strengthening treatment: The plate obtained after step S3 is subjected to thermal diffusion treatment under a protective atmosphere.

[0007] Furthermore, the metal gradient porous layer includes an intermediate porous layer and a surface porous layer arranged from the inside out; the average pore size of the intermediate porous layer is 50-200 μm; and the average pore size of the surface porous layer is 10-50 μm.

[0008] Furthermore, in step S2, the thermal spraying process is one of flame spraying, arc spraying, plasma spraying, high-speed flame spraying, and supersonic flame spraying; the substrate temperature is controlled below 300°C during the spraying process.

[0009] Furthermore, the thickness of the metal gradient porous layer is 0.05-0.5 mm, and the metal powder material used is at least one of carbon steel, low-temperature steel, heat-resistant steel, stainless steel, copper, copper-nickel alloy, nickel alloy and titanium.

[0010] Furthermore, in step S2, before constructing the metal gradient porous layer, a transition layer with a thickness of 10-50 μm is first sprayed onto the substrate surface. The transition layer material is nickel-aluminum, molybdenum-aluminum composite powder or metal powder of the same material as the substrate.

[0011] Furthermore, in step S3, the laser used is a picosecond or femtosecond pulsed laser with a laser power of 10-50W and a scanning speed of 100-500mm / s.

[0012] Furthermore, the substrate is a smooth plate with a thickness of 0.3-5.0 mm, and the plate is made of one of the following materials: carbon steel, low-temperature steel, heat-resistant steel, stainless steel, copper and copper-nickel alloys, nickel alloys, and titanium.

[0013] Another aspect of the present invention provides a gradient porous heat exchange plate with vertical microchannels prepared by the above-described preparation method, comprising a substrate and a metal gradient porous layer; the substrate has macroscopic flow channels formed by stamping; the metal gradient porous layer covers the surface of the macroscopic flow channels, the metal gradient porous layer is formed by thermal spraying, and its average pore size gradually decreases from the side closer to the substrate to the side farther away from the substrate; the metal gradient porous layer has an array of vertical microchannels formed by laser etching that penetrates a portion of the thickness of the metal gradient porous layer.

[0014] Furthermore, a transition layer formed by spraying is provided between the substrate and the metal gradient porous layer.

[0015] Furthermore, the distribution density of the vertical microchannel array is related to the geometry of the macrochannel, with the microchannel density in the ridge region of the macrochannel being higher than that in the valley region.

[0016] The beneficial effects of this invention are as follows: This invention achieves the following synergistic technical effects by innovatively combining the "stamping followed by thermal spraying" process with laser etching technology: In terms of structural reliability, this invention solves the problem of plate warping and deformation caused by high temperature in traditional sintering methods, ensuring excellent dimensional accuracy of the product; at the same time, metallurgical bonding between interfaces is achieved through subsequent thermal diffusion treatment, improving bonding strength and ensuring the long-term structural integrity of the heat exchange plate under complex working conditions. In terms of heat transfer performance, the metal gradient porous layer constructed by thermal spraying effectively increases the number of surface vaporization nuclei. The pore size gradient structure and the vertical microchannel array formed by laser etching have a synergistic strengthening effect: the gradient pore size optimizes capillary liquid supply, while the vertical microchannels provide a directional, low-resistance, and rapid channel for vapor escape. This physical separation of the gas-liquid transport path enables the heat exchange plate to achieve stable and efficient boiling with a small temperature difference under boiling conditions. Its boiling heat transfer coefficient is greatly improved compared to traditional smooth plates, and it also increases the critical heat flux density, significantly widening the efficient and safe operating range.

[0017] Furthermore, the present invention employs a thermal spraying process, which can better adapt to various complex flow channel shapes, while laser etching can precisely control the aperture, depth, density, and distribution of microchannels, and can achieve matching optimization with macroscopic flow channels.

[0018] Furthermore, the continuous vapor microjets generated by the vertical microchannels also endow the surface with self-cleaning capabilities, and combined with the low wall temperature operation maintained by efficient heat transfer, the equipment's anti-fouling performance is enhanced. Attached Figure Description

[0019] Figure 1The graph shows a comparison of the boiling heat transfer performance of the heat exchange plates in Example 1, Comparative Example 1, and Comparative Example 2.

[0020] Figure 2 This is a schematic diagram of the gradient porous reinforced heat exchange plate of the present invention. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] This invention provides a method for preparing a gradient porous enhanced heat exchange plate with vertical microchannels, comprising the following steps: S1. Substrate pretreatment and flow channel forming: The substrate is stamped to form the required macroscopic flow channel; wherein, the substrate is a smooth plate with a thickness of 0.3-5.0mm, and the preferred material of the plate is one of carbon steel, low temperature steel, heat-resistant steel, stainless steel, copper and copper-nickel alloy, nickel alloy, and titanium.

[0023] S2. Construction of a metal gradient porous layer: On the surface of a substrate with macroscopic flow channels, a metal gradient porous layer with an average pore size that gradually decreases from the side closer to the substrate to the side farther away from the substrate is constructed by a thermal spraying process. The metal gradient porous layer comprises an intermediate porous layer and a surface porous layer arranged from the inside out. The average pore size of the intermediate porous layer is 50-200 μm, while the average pore size of the surface porous layer is 10-50 μm. The surface micropores utilize strong capillary forces to ensure efficient liquid supply to the heated wall surface and prevent drying; the intermediate macropores provide a low-resistance collection and buffering space for vapor. This precise functional division enables ultra-high critical heat flux and heat transfer coefficient. In step S2, the thermal spraying process is preferably one of flame spraying, arc spraying, plasma spraying, high-speed flame spraying, and supersonic flame spraying; the substrate temperature is controlled below 300°C during the spraying process. The thickness of the metal gradient porous layer is 0.05-0.5 mm, and the metal powder material used is at least one of the following: carbon steel, low temperature steel, heat-resistant steel, stainless steel, copper, copper-nickel alloy, nickel alloy, and titanium.

[0024] In step S2, to improve the interfacial bonding strength, a transition layer with a thickness of 10-50 μm is first sprayed onto the substrate surface before constructing the metal gradient porous layer. This transition layer is made of nickel-aluminum, molybdenum-aluminum composite powder, or a metal powder of the same material as the substrate. As a functionally graded material, the transition layer can form excellent metallurgical bonds with both the substrate and the upper metal gradient porous layer, acting as a strong "intermediate bridge." This enhances the bonding strength between the metal gradient porous layer and the substrate, enabling it to withstand stamping stress and long-term thermal fatigue.

[0025] S3. Laser etching to construct a vertical microchannel array: A short-pulse laser device is used to scan and etch the surface of the metal gradient porous layer to form a series of vertical microchannels. In step S3, a picosecond or femtosecond pulsed laser is used, with a laser power of 10-50W and a scanning speed of 100-500mm / s. Short-pulse lasers (picosecond / femtosecond) can produce a cold working effect, instantly vaporizing the metal with minimal thermal impact on the surrounding material. This allows for the etching of high-quality vertical microchannels with regular pore shapes, neat edges, and no slag residue on a soft porous layer, avoiding channel blockage or performance degradation.

[0026] S4. Thermal diffusion strengthening treatment: The plate obtained after step S3 is subjected to thermal diffusion treatment under a protective atmosphere at a temperature of 500-650℃.

[0027] The gradient porous heat exchange plate with vertical microchannels prepared by the above method includes a substrate 1 and a metal gradient porous layer 2; the substrate 1 has macroscopic flow channels 3 formed by stamping; the metal gradient porous layer 2 covers the surface of the macroscopic flow channels 3, the metal gradient porous layer 2 is formed by thermal spraying, and its average pore size gradually decreases from the side close to the substrate to the side far away from the substrate; the metal gradient porous layer 2 has a vertical microchannel array formed by laser etching that penetrates part of the thickness of the metal gradient porous layer.

[0028] Furthermore, a transition layer 4 formed by spraying is provided between the substrate and the metal gradient porous layer.

[0029] The distribution density of the vertical microchannel array is related to the geometry of the macrochannel, with a higher microchannel density in the ridge region of the macrochannel than in the valley region. Increasing the density of escape channels in the ridge region of the channel, where steam generation is more concentrated, can more effectively prevent steam retention, thereby further improving the overall heat transfer efficiency and critical heat flux density.

[0030] This invention achieves a breakthrough synergistic effect through a combination of "stamping followed by thermal spraying + laser etching + thermal diffusion." First, it resolves the inherent process contradiction of traditional stamping-to-sintering processes, where the substrate is prone to warping due to high-temperature sintering. Second, the composite structure of "gradient-aperture porous layer + vertical microchannel" in this invention optimizes the separation of gas-liquid transport paths, and their synergistic effect improves the heat transfer coefficient (HTC) and critical heat flux density (CHF). Finally, the thermal diffusion treatment achieves metallurgical bonding within the porous layer and between interfaces at relatively low temperatures, ensuring high reliability and durability of the overall structure under long-term, intense thermal cycling.

[0031] The present invention will be further described below through specific embodiments.

[0032] Example 1

[0033] S1. Substrate pretreatment and flow channel forming A carbon steel plate with dimensions of 500mm×500mm×1.5mm was selected as the substrate. First, the substrate was cleaned and degreased, and then the designed macroscopic flow channels were stamped out using a die.

[0034] S2. Construction of Metal Gradient Porous Layers The stamped substrate is sandblasted to roughen it and enhance the surface adhesion. An oxyacetylene flame spraying system was employed. First, a layer of nickel-coated aluminum powder was sprayed onto the substrate surface as a transition layer. Then, 75% carbon steel powder (-100 mesh) and 25% boron powder (activating additive) were uniformly mixed and sprayed as an intermediate layer to form a porous intermediate layer. Next, carbon steel powder (-350 to -500 mesh) was sieved and sprayed as a surface layer to form a porous surface layer, thus constructing a gradient pore size structure with smaller pores at the top and larger pores at the bottom. The substrate temperature was controlled below 300℃ during the spraying process. The boron powder effectively reduced metal surface oxides, purified the interface, and promoted atomic diffusion between powder particles and between interfaces during the subsequent thermal diffusion treatment, thereby significantly enhancing the metallurgical bonding strength. The thickness of the transition layer was 20 μm, and the thickness of the metal gradient porous layer was 0.18 mm.

[0035] S3. Laser etching to construct vertical microchannel arrays Etching was performed using a picosecond pulsed laser with a wavelength of 1064 nm, an average power of 25 W, and a pulse width of less than 15 ps. The laser path was controlled by a galvanometer scanning system at a scanning speed of 300 mm / s. Vertical microchannels with a diameter of approximately 50 μm and a depth of approximately 120 μm were etched into the porous surface layer, with a designed density of 15 channels / cm². 2 .

[0036] S4. Thermal diffusion enhancement treatment The laser-etched plate is placed in a heat treatment furnace and subjected to thermal diffusion treatment at 550°C under a protective atmosphere of nitrogen and hydrogen in a volume ratio of 3:1. After holding at this temperature for a certain period of time, it is cooled to room temperature with the furnace.

[0037] Example 2

[0038] S1. Substrate pretreatment and flow channel forming A copper plate with dimensions of 200mm×300mm×1.5mm was selected as the substrate; after cleaning and drying, the required macroscopic flow channels were stamped out.

[0039] S2. Construction of Metal Gradient Porous Layers The substrate was sandblasted. Using a plasma spraying system, pure copper powder was first sprayed onto the substrate to form a transition layer, followed by spraying -150 mesh pure copper powder to form an intermediate porous layer. Then, 8% -350 mesh nickel powder, 72% -350 mesh copper powder, and 20% deoxidizer were mixed evenly as a surface layer spraying powder to form a surface porous layer. The thickness of the transition layer was 25 μm, and the thickness of the metal gradient porous layer was 0.23 mm.

[0040] S3. Laser etching to construct vertical microchannel arrays A femtosecond pulsed laser with a power of 15W was used. The etched vertical microchannels had a diameter of approximately 30μm, a depth of approximately 80μm, and a density of 25 microchannels / cm². 2 Furthermore, the distribution density of vertical microchannels was appropriately increased in the ridge region of the macrochannel.

[0041] S4. Thermal diffusion enhancement treatment Under a protective atmosphere of high-purity argon, the sample was heat-treated at 580°C for 3 hours, and then cooled in the furnace.

[0042] Comparative Example 1 Using the same carbon steel substrate and flow channel design as in Example 1, a uniform porous layer is prepared only on the surface of the flow channel after stamping by conventional thermal spraying of carbon steel powder with a single particle size. No laser etching is performed to construct vertical microchannels, nor is thermal diffusion treatment performed.

[0043] Comparative Example 2 The same carbon steel substrate as in Embodiment 1 of the present invention is selected, and macroscopic flow channels with the same design as in Embodiment 1 are stamped on the substrate.

[0044] Figure 1 The boiling heat transfer performance of the heat exchange plates in Example 1, Comparative Example 1, and Comparative Example 2 is compared. Figure 1It can be seen that the boiling heat transfer performance of Example 1 of the present invention is significantly better than that of Comparative Example 1 and Comparative Example 2. Its unique structure creates a synergistic effect: the gradient porous layer optimizes capillary liquid supply, while the vertical microchannels provide a high-speed path for the directional escape of vapor, thereby achieving extremely high heat transfer efficiency while increasing the upper limit of heat dissipation capacity (critical heat flux density) and exhibiting more stable performance under high heat flux. In contrast, the high performance of Comparative Example 1 is limited due to competition for gas-liquid transport paths, while Comparative Example 2 has the lowest performance due to the easy formation of vapor film on its smooth surface.

[0045] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0046] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a gradient porous enhanced heat exchange plate with vertical microchannels, characterized in that, Includes the following steps: S1. Substrate pretreatment and flow channel forming: Stamping the substrate to form the required macroscopic flow channels; S2. Construction of a metal gradient porous layer: On the surface of a substrate with macroscopic flow channels, a metal gradient porous layer with an average pore size that gradually decreases from the side closer to the substrate to the side farther away from the substrate is constructed by a thermal spraying process. S3. Laser etching to construct a vertical microchannel array: A short-pulse laser device is used to scan and etch the surface of the metal gradient porous layer to form a series of vertical microchannels. S4. Thermal diffusion strengthening treatment: The plate obtained after step S3 is subjected to thermal diffusion treatment under a protective atmosphere.

2. The method for preparing a gradient porous enhanced heat exchange plate with vertical microchannels according to claim 1, characterized in that, The metal gradient porous layer includes an intermediate porous layer and a surface porous layer arranged from the inside out; the average pore size of the intermediate porous layer is 50-200 μm; and the average pore size of the surface porous layer is 10-50 μm.

3. The method for preparing a gradient porous enhanced heat exchange plate with vertical microchannels according to claim 1, characterized in that, In step S2, the thermal spraying process is one of flame spraying, arc spraying, plasma spraying, high-speed flame spraying, and supersonic flame spraying; the substrate temperature is controlled below 300°C during the spraying process.

4. The method for preparing a gradient porous enhanced heat exchange plate with vertical microchannels according to claim 1, characterized in that, The thickness of the metal gradient porous layer is 0.05-0.5 mm, and the metal powder material used is at least one of carbon steel, low temperature steel, heat-resistant steel, stainless steel, copper, copper-nickel alloy, nickel alloy and titanium.

5. The method for preparing a gradient porous enhanced heat exchange plate with vertical microchannels according to claim 1, characterized in that, In step S2, before constructing the metal gradient porous layer, a transition layer with a thickness of 10-50 μm is first sprayed onto the substrate surface. The transition layer material is nickel-aluminum, molybdenum-aluminum composite powder or metal powder of the same material as the substrate.

6. The method for preparing a gradient porous enhanced heat exchange plate with vertical microchannels according to claim 1, characterized in that, In step S3, the laser used is a picosecond or femtosecond pulsed laser with a laser power of 10-50W and a scanning speed of 100-500mm / s.

7. The method for preparing a gradient porous enhanced heat exchange plate with vertical microchannels according to claim 1, characterized in that, The substrate is a smooth plate with a thickness of 0.3~5.0mm. The plate is made of one of the following materials: carbon steel, low-temperature steel, heat-resistant steel, stainless steel, copper, copper-nickel alloy, nickel alloy, and titanium.

8. A gradient porous enhanced heat exchange plate with vertical microchannels prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The invention includes a substrate and a metal gradient porous layer; the substrate has macroscopic flow channels formed by stamping; the metal gradient porous layer covers the surface of the macroscopic flow channels, the metal gradient porous layer is formed by thermal spraying, and its average pore size gradually decreases from the side closer to the substrate to the side farther away from the substrate; the metal gradient porous layer has a vertical microchannel array formed by laser etching that penetrates a portion of the thickness of the metal gradient porous layer.

9. The gradient porous enhanced heat exchange plate with vertical microchannels according to claim 8, characterized in that, A transition layer formed by spraying is also provided between the substrate and the metal gradient porous layer.

10. The gradient porous enhanced heat exchange plate with vertical microchannels according to claim 8, characterized in that, The distribution density of the vertical microchannel array is related to the geometry of the macrochannel, with the microchannel density in the ridge region of the macrochannel being higher than that in the valley region.

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