Heat exchanger graphene coating processing method and heat exchanger

Abstract

The application discloses a graphene coating processing method for a heat exchanger and the heat exchanger. The processing method comprises the following steps: cleaning and converting the heat exchanger, mixing and dispersing graphene material with a large piece of layer and an organic solution to prepare a negative graphene dispersion liquid, then immersing a cathode part and the heat exchanger as an anode part into the graphene dispersion liquid, applying a constant voltage with a voltage range of 25V-30V for 8-10 seconds, so that a surface of the heat exchanger is deposited with an oxidized graphene deposition film with a thickness range of 16um-17um, and the oxidized graphene deposition film is subjected to freeze-drying, finally, the heat exchanger is subjected to heat reduction treatment for 0.5-12 hours in a vacuum space or an inert gas atmosphere space and in an environment with a temperature range of 300-500 DEG C, so that the oxidized graphene deposition film is converted into a reduced graphene oxide deposition film, and a graphene coating with the effects of uniform density, strong bonding force and uniform coverage is formed on the surface of the heat exchanger, so that the heat conduction efficiency of the heat exchanger is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of heat exchanger technology, and more particularly to a method for processing graphene coatings for heat exchangers and a heat exchanger thereof. Background Technology

[0002] Existing air conditioning heat exchangers mainly come in two forms: copper tube aluminum finned heat exchangers and aluminum alloy microchannel heat exchangers. Pure copper has a thermal conductivity of approximately 380-420 W / (m·K) and is a commonly used high thermal conductivity material in industry, widely used in radiator applications. However, the thermal resistance of copper tubes and aluminum finned heat exchangers increases due to the extrusion bonding method, resulting in a significant reduction in heat exchange efficiency. Pure aluminum has a thermal conductivity of approximately 170-220 W / (m·K). Although its thermal conductivity is lower than that of copper, its advantages such as low density, low cost, and ease of processing often make it a substitute for copper in applications requiring lightweight heat dissipation. However, aluminum alloy microchannel heat exchangers also suffer from a significant reduction in heat exchange efficiency due to the easy formation of an oxide layer on the fin surface.

[0003] Graphene is a two-dimensional carbon nanomaterial composed of carbon atoms arranged in a hexagonal honeycomb lattice with sp2 hybrid orbitals. The inherent stability of graphene's unique internal structure and the two-dimensional honeycomb lattice structure formed by carbon atoms give it excellent thermal conductivity, extremely high thermal conductivity coefficient, and directional thermal conductivity. Graphene is one of the best-known materials in terms of thermal conductivity; the theoretical thermal conductivity of a single layer of graphene can reach 5300 W / (m·K), making it one of the materials with the highest thermal conductivity known to date, far exceeding metals such as gold, silver, copper, and aluminum. Its thermal conductivity is approximately 14 times that of copper and 26 times that of aluminum. It can be used as an additive in composite materials to improve the heat exchange performance and corrosion resistance. Furthermore, through specific preparation methods, the thermal conductivity of graphene can exhibit a significant directionality. A complete, ideal single-layer graphene can conduct heat extremely efficiently within its two-dimensional plane (i.e., the horizontal direction), while its thermal conductivity perpendicular to the plane (i.e., the thickness direction) is very weak. This can be understood as "two-dimensional planar superconductivity, vertical insulation."

[0004] Graphene possesses excellent thermal conductivity properties, including extremely high thermal conductivity and tunable thermal conductivity directionality, making it a promising candidate for widespread application in air conditioning heat exchangers. Nano-graphene, by filling the contact gaps between copper tubes and aluminum fins in copper-tube aluminum-fin heat exchangers, can reduce thermal resistance and improve overall heat exchange efficiency. Nano-graphene, by covering the surface of aluminum alloy microchannel heat exchangers, prevents aluminum foil surface oxidation from reducing thermal conductivity, thus maintaining high heat exchange efficiency in practical applications. The thermal conductivity directionality of graphene allows for extremely efficient heat conduction within its two-dimensional plane (i.e., the horizontal direction), facilitating faster heat transfer across the surfaces of copper tubes and aluminum fins and increasing heat dissipation capacity.

[0005] Currently, there are two processes for applying graphene materials to the surface of air conditioning heat exchangers: spraying and immersion. The spraying process involves atomizing a graphene solution and spraying it onto a preheated substrate surface. This process is relatively simple, easy to implement for continuous operation and large-scale production, and is suitable for large-area, continuous production scenarios such as heat exchanger fins. It has good adaptability to the shape of the substrate. However, the uniformity, thickness, and adhesion of the resulting graphene coating are difficult to control, resulting in the inability to guarantee the thermal conductivity of the heat exchanger. The immersion process involves immersing the entire substrate in a graphene dispersion for coating. The equipment is simple and easy to operate, and it can process complex structural workpieces in one go. However, it has problems such as uneven thickness of the resulting graphene coating and material waste.

[0006] Air conditioning heat exchangers have complex structures, and some application scenarios require higher thermal conductivity. Spraying and immersion processes cannot produce heat exchangers with uniform and dense coatings, strong adhesion, and uniform coverage on complex surface structures. Summary of the Invention

[0007] The purpose of this invention is to provide a method for processing graphene coatings on heat exchangers, which can form a uniform, dense, and strongly bonded graphene coating that is evenly covered on the surface of the heat exchanger, thereby effectively improving the thermal conductivity of the heat exchanger and thus enhancing its performance.

[0008] Another objective of this invention is to provide a heat exchanger in which a uniform, dense, and strongly bonded graphene coating is formed on the surface of the heat exchanger, which can effectively improve the thermal conductivity of the heat exchanger and thus enhance its performance.

[0009] To achieve the above objectives, this invention discloses a method for processing a graphene coating on a heat exchanger, the method comprising: The heat exchanger was subjected to degreasing cleaning and chemical conversion treatment in sequence. Large sheets of graphene material are mixed and dispersed with an organic solution to prepare a negatively charged graphene dispersion. The cathode and the heat exchanger, which has been treated as an anode, are immersed in the graphene dispersion, and a constant voltage of 25V to 30V is applied to the heat exchanger and the cathode for 8 to 10 seconds to deposit a graphene oxide deposition film with a thickness of 16µm to 17µm on the surface of the heat exchanger. The heat exchanger after deposition was freeze-dried; The freeze-dried heat exchanger is subjected to thermal reduction treatment for 0.5 to 12 hours in a vacuum space or inert gas atmosphere and in an environment with a temperature range of 300°C to 500°C, so that the graphene oxide deposited film is converted into a reduced graphene oxide deposited film.

[0010] Furthermore, the "sequential degreasing and cleaning and chemical conversion treatment of the heat exchanger" includes: The heat exchanger is cleaned using an alkaline degreasing agent; The heat exchanger is then subjected to phosphating or chromating treatment after cleaning to form a conversion film on its surface.

[0011] Furthermore, prior to the step of "cleaning the heat exchanger with an alkaline degreasing agent," the process also includes: The surface of the heat exchanger is ground or sandblasted. The heat exchanger is then cleaned using alcohol or acetone.

[0012] Furthermore, the graphene material is graphene, and the organic solution includes an isopropanol solution. Furthermore, the graphene material is graphene oxide, the organic solution includes isopropanol solution, and before the step of "mixing and dispersing the large-scale graphene material with the organic solution," the process further includes: The graphene oxide was modified using a silane coupling agent, and the modified graphene oxide was used as the graphene material.

[0013] Furthermore, the concentration of the graphene material in the graphene dispersion ranges from 0.6 mg / mL to 10 mg / mL.

[0014] Furthermore, the step of "mixing and dispersing large-sheet graphene material with an organic solution to prepare a negatively charged graphene dispersion" includes: A negatively charged graphene dispersion is prepared by mixing and dispersing large-scale graphene material, organic solution and anodic electrophoretic paint.

[0015] Furthermore, before the step of "immersing the cathode element and the treated heat exchanger as the anode element into the graphene dispersion" is completed, the following steps are also included: A high-intensity magnetic field perpendicular to the surface of the heat exchanger is applied to the heat exchanger.

[0016] Furthermore, the distance between the heat exchanger and the cathode immersed in the graphene dispersion ranges from 1 cm to 2 cm.

[0017] To achieve the other objective mentioned above, the present invention discloses a heat exchanger comprising: a heat exchanger body, wherein the surface of the heat exchanger body is provided with the reduced graphene oxide deposition film generated using the heat exchanger graphene coating processing method described above.

[0018] Compared with existing technologies, this invention deposits graphene onto the surface of a heat exchanger via electrophoretic deposition. First, the heat exchanger is cleaned and converted, and large sheets of graphene material are mixed and dispersed with an organic solution to prepare a negatively charged graphene dispersion. Next, the cathode and the heat exchanger (acting as the anode) are immersed in the graphene dispersion, and a constant voltage of 25V to 30V is applied for 8 to 10 seconds to deposit a graphene oxide film with a thickness of 16µm to 17µm on the surface of the heat exchanger. This film is then freeze-dried. Finally, the heat exchanger undergoes thermal reduction treatment for 0.5 to 12 hours in a vacuum or inert gas atmosphere at a temperature range of 300°C to 500°C to convert the graphene oxide film into a reduced graphene oxide film. This achieves the formation of a uniform, dense, strongly bonded, and evenly covering graphene coating on the surface of the heat exchanger, effectively improving the heat exchanger's thermal conductivity and thus enhancing its performance. Attached Figure Description

[0019] Figure 1 This is a flowchart of a graphene coating processing method for a heat exchanger according to an embodiment of the present invention. Detailed Implementation

[0020] To illustrate the technical content, structural features, objectives, and effects of the present invention in detail, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0021] Please see Figure 1 This invention discloses a method for processing a graphene coating on a heat exchanger, the method comprising: 101. The heat exchanger is subjected to degreasing cleaning and chemical conversion treatment in sequence; Furthermore, "the heat exchanger is subjected to degreasing cleaning and chemical conversion treatment in sequence" includes: 1011. Clean the heat exchanger using an alkaline degreasing agent; The above-mentioned degreasing and cleaning can effectively remove the oil and impurities remaining in the heat exchanger during the stamping and transportation process, so as to ensure the cleanliness of the surface of the base heat exchanger.

[0022] 1012. After cleaning, the heat exchanger is subjected to phosphating or chromating treatment to form a conversion film on the surface of the heat exchanger.

[0023] The aforementioned micron-scale conversion film layer not only enhances the adhesion between the heat exchanger as the substrate and the subsequent graphene coating, preventing the graphene coating from peeling off, but also further improves the corrosion resistance of the heat exchanger.

[0024] Furthermore, in some embodiments, prior to "cleaning the heat exchanger with an alkaline degreasing agent," the following steps are also included: 11. Grind or sandblast the surface of the heat exchanger; 12. Clean the heat exchanger after treatment using alcohol or acetone.

[0025] The above-mentioned pretreatment operation of mechanically removing impurities such as oil, dust, and oxide layer from the surface of heat exchanger fins, combined with the use of solvent to clean the pretreated heat exchanger, can ensure that the surface of the heat exchanger fins is clean and flat, thereby effectively improving the adhesion of the graphene coating.

[0026] 102. Large sheets of graphene material are mixed and dispersed with an organic solution to prepare a negatively charged graphene dispersion. The above-mentioned operation of charging graphene sheets can enhance their responsiveness to external fields (electric field, magnetic field), which is beneficial for controlling the orientation of graphene through external force in subsequent processes. It is understandable that large-scale graphene or graphene oxide sheets have large diameters, resulting in long in-plane thermal conduction paths and less phonon scattering. When combined with the thorough and uniform dispersion of graphene in an organic solution, a stable dispersion can be formed, effectively preventing any graphene agglomeration from forming thermal resistance points.

[0027] Furthermore, the concentration of graphene material in the graphene dispersion ranges from 0.6 mg / mL to 10 mg / mL.

[0028] Furthermore, in some embodiments, the graphene material is graphene, and the organic solution includes an isopropanol solution. The graphene itself has high quality and purity, few defects, and good intrinsic thermal conductivity, which is beneficial to improving the thermal conductivity of heat exchangers.

[0029] Furthermore, in some embodiments, the graphene material is graphene oxide, and the organic solution includes an isopropanol solution. Before "mixing and dispersing the large-scale graphene material with the organic solution," the process further includes: 1020. Graphene oxide was modified using a silane coupling agent, and the modified graphene oxide was used as a graphene material.

[0030] By modifying the surface of graphene oxide with silane coupling agents as described above, the dispersion stability of graphene oxide in solution can be improved, resulting in a more uniform distribution.

[0031] Furthermore, in some embodiments, "mixing and dispersing large-sheet graphene material with an organic solution to prepare a negatively charged graphene dispersion" includes: 1021. A negatively charged graphene dispersion is prepared by mixing and dispersing large-scale graphene material, organic solution and anodic electrophoretic paint.

[0032] It should be noted that in this embodiment, the anodic electrophoretic paint includes acrylic resin, which helps graphene to form a more stable three-dimensional structure during deposition and enhances its bonding force with the substrate (heat exchanger).

[0033] Furthermore, before "immersing the cathode and the treated heat exchanger as the anode in the graphene dispersion," the process also includes: 1030. Apply a high-strength magnetic field perpendicular to the surface of the heat exchanger.

[0034] It is understandable that electrophoretic deposition generally achieves induced orientation by setting an electric field. In this embodiment, a DC electric field is set to cause the charged graphene sheet to move in a directional manner and deposit towards the electrode. During this process, the graphene sheet tends to be laid out with its large plane parallel to the electrode substrate, thereby forming an in-plane oriented structure.

[0035] Understandably, since graphene is diamagnetic, an external strong vertical magnetic field is applied during the deposition of graphene oxide film to induce the graphene coating, so as to force all the graphene sheets to be horizontally aligned with the magnetic field direction. By precisely controlling the voltage, current density and deposition time during the deposition process through steps 103 to 105, a dense and uniformly oriented film is obtained, so that the graphene coating on the heat exchanger surface has high thermal conductivity and high thermal conductivity directionality, which is beneficial to improving the heat exchanger's directional heat transfer efficiency.

[0036] 103. Immerse the cathode and the treated heat exchanger (which serves as the anode) in a graphene dispersion, and apply a constant voltage of 25V to 30V to the heat exchanger and cathode for 8 to 10 seconds to deposit a graphene oxide film with a thickness of 16µm to 17µm on the surface of the heat exchanger. Under the influence of an electric field, graphene is directionally deposited onto a conductive substrate (the surface of the heat exchanger), which can significantly improve the thermal conductivity of the heat exchanger. Furthermore, the prepared dense graphene coating has both thermal conductivity and anti-corrosion functions, effectively preventing water vapor and corrosive media from contacting the heat exchanger and effectively extending the service life of the heat exchanger in harsh environments.

[0037] Furthermore, the distance between the heat exchanger and the cathode immersed in the graphene dispersion ranges from 1 cm to 2 cm.

[0038] It is understood that in this embodiment, the parameters in the deposition operation are controlled very precisely according to step 103 so that the charged graphene particles can move in a direction and be deposited on the substrate (heat exchanger). At the same time, during the deposition process, the changes in current or voltage during electrophoretic deposition are monitored to indirectly determine the formation of the graphene deposition layer. Thus, an ultrathin graphene oxide deposition film with a thickness of about 15 micrometers is obtained by precise control, which makes it easy to achieve precise control of the coating thickness.

[0039] 104. Freeze-dry the heat exchanger after deposition; It should be noted that after the electrophoretic deposition operation, the graphene film on the heat exchanger surface will contain solvent and will not be firmly bonded to the heat exchanger surface. Therefore, freeze-drying is required to remove the solvent and effectively maintain the porous structure of the graphene film.

[0040] 105. In a vacuum space or inert gas atmosphere and in an environment with a temperature range of 300℃ to 500℃, the freeze-dried heat exchanger is subjected to thermal reduction treatment for 0.5 hours to 12 hours to convert the graphene oxide deposited film into a reduced graphene oxide deposited film.

[0041] The above conversion process can significantly improve the thermal and electrical conductivity of graphene-deposited films.

[0042] Understandably, graphene coatings possess a unique two-dimensional sheet structure and excellent phonon transport capabilities, which can significantly improve the thermal conductivity of heat exchangers. Inside the coating, graphene nanosheets can overlap to form a highly efficient three-dimensional heat-conducting network. When heat is conducted in the substrate (heat exchanger), the graphene nanosheets allow phonons, which are the main heat carriers, to pass through smoothly, thereby greatly reducing thermal resistance. At the same time, the graphene nanocoating also has an infrared radiation heat dissipation effect, which can further improve the heat dissipation performance of the heat exchanger.

[0043] In performance testing, compared with traditional heat exchangers with hydrophilic coatings, the heat exchanger of the present invention has a 5%-8% increase in heat exchange capacity and a 20%-30% increase in the equivalent thermal conductivity of the heat exchanger material.

[0044] Compared with existing technologies, this invention deposits graphene onto the surface of a heat exchanger via electrophoretic deposition. First, the heat exchanger is cleaned and converted, and large sheets of graphene material are mixed and dispersed with an organic solution to prepare a negatively charged graphene dispersion. Next, the cathode and the heat exchanger (acting as the anode) are immersed in the graphene dispersion, and a constant voltage of 25V to 30V is applied for 8 to 10 seconds to deposit a graphene oxide film with a thickness of 16µm to 17µm on the surface of the heat exchanger. This film is then freeze-dried. Finally, the heat exchanger undergoes thermal reduction treatment for 0.5 to 12 hours in a vacuum or inert gas atmosphere at a temperature range of 300°C to 500°C to convert the graphene oxide film into a reduced graphene oxide film. This achieves the formation of a uniform, dense, strongly bonded, and evenly covering graphene coating on the surface of the heat exchanger, effectively improving the heat exchanger's thermal conductivity and thus enhancing its performance.

[0045] Please see Figure 1 The present invention discloses a heat exchanger, comprising: a heat exchanger body, wherein a reduced graphene oxide deposition film generated by the aforementioned heat exchanger graphene coating processing method is disposed on the surface of the heat exchanger body.

[0046] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for processing a graphene coating on a heat exchanger, characterized in that, The processing method includes: The heat exchanger was subjected to degreasing cleaning and chemical conversion treatment in sequence. Large sheets of graphene material are mixed and dispersed with an organic solution to prepare a negatively charged graphene dispersion. The cathode and the heat exchanger, which has been treated as an anode, are immersed in the graphene dispersion, and a constant voltage of 25V to 30V is applied to the heat exchanger and the cathode for 8 to 10 seconds to deposit a graphene oxide deposition film with a thickness of 16µm to 17µm on the surface of the heat exchanger. The heat exchanger after deposition was freeze-dried; The freeze-dried heat exchanger is subjected to thermal reduction treatment for 0.5 to 12 hours in a vacuum space or inert gas atmosphere and in an environment with a temperature range of 300°C to 500°C, so that the graphene oxide deposited film is converted into a reduced graphene oxide deposited film.

2. The method for processing graphene coating on a heat exchanger according to claim 1, characterized in that, The phrase "performing sequential degreasing cleaning and chemical conversion treatment on the heat exchanger" includes: The heat exchanger is cleaned using an alkaline degreasing agent; The heat exchanger is then subjected to phosphating or chromating treatment after cleaning to form a conversion film on its surface.

3. The method for processing graphene coatings on heat exchangers according to claim 2, characterized in that, Before the step of "cleaning the heat exchanger with an alkaline degreasing agent", the following steps are also included: The surface of the heat exchanger is ground or sandblasted. The heat exchanger is then cleaned using alcohol or acetone.

4. The method for processing graphene coatings on heat exchangers according to claim 1, characterized in that, The graphene material is graphene, and the organic solution includes isopropanol solution.

5. The method for processing graphene coating on a heat exchanger according to claim 1, characterized in that, The graphene material is graphene oxide, the organic solution includes isopropanol solution, and before the step of "mixing and dispersing the large-scale graphene material with the organic solution", the process further includes: The graphene oxide was modified using a silane coupling agent, and the modified graphene oxide was used as the graphene material.

6. The method for processing graphene coating on a heat exchanger according to claim 1, characterized in that, The concentration of the graphene material in the graphene dispersion ranges from 0.6 mg / mL to 10 mg / mL.

7. The method for processing graphene coating on a heat exchanger according to claim 1, characterized in that, The phrase "mixing and dispersing large-sheet graphene material with an organic solution to prepare a negatively charged graphene dispersion" includes: A negatively charged graphene dispersion is prepared by mixing and dispersing large-scale graphene material, organic solution and anodic electrophoretic paint.

8. The method for processing graphene coating on a heat exchanger according to claim 1, characterized in that, Before the step of "immersing the cathode and the heat exchanger, which has been treated as an anode, into the graphene dispersion", the method further includes: A high-strength magnetic field perpendicular to the surface of the heat exchanger is applied to the heat exchanger.

9. The method for processing graphene coating on a heat exchanger according to claim 1, characterized in that, The distance between the heat exchanger and the cathode immersed in the graphene dispersion ranges from 1 cm to 2 cm.

10. A heat exchanger, characterized in that, include: A heat exchanger body, wherein the surface of the heat exchanger body is provided with the reduced graphene oxide deposition film generated by the heat exchanger graphene coating processing method according to any one of claims 1 to 9.

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