Anti-scaling composite evaporating pipe and preparation method thereof

Abstract

The invention discloses an anti-scaling composite evaporating pipe and a preparation method thereof, and belongs to the technical field of evaporating pipes. The anti-scaling composite evaporating pipe comprises an inner wall layer, a middle layer and an outer wall layer which are sequentially arranged from inside to outside, a micro-arc oxidation porous structure is arranged on the inner surface of the inner wall layer, and a hydrophobic layer is arranged on the inner surface of the inner wall layer; the middle layer is of a honeycomb structure, the outer wall layer is a heat conduction layer, and the outer wall layer is fixedly connected with the outer wall layer through the middle layer. The pore diameter of the micro-arc oxidized porous structure of the inner wall layer is 100nm to 150nm, and the porosity is 30 percent to 40 percent. The contact angle between the hydrophobic layer and water is not less than 150 degrees, and the pore diameter of the honeycomb is 2-3mm. The invention further discloses a preparation method of the anti-scaling composite evaporating pipe. According to the anti-scaling composite evaporating pipe and the preparation method thereof, the problem that an existing evaporating pipe is poor in corrosion resistance and anti-scaling performance can be solved, and the anti-scaling composite evaporating pipe has the advantages of being high in strength and good in heat conductivity.

Description

Technical Field

[0001] This invention relates to the field of evaporator technology, and in particular to an anti-scaling composite evaporator and its preparation method. Background Technology

[0002] Evaporation tubes, as the core component of heat exchange equipment, are widely used in chemical, energy, and seawater desalination industries. Their heat exchange efficiency, structural strength, and anti-scaling performance directly affect the operational stability and service life of the equipment.

[0003] In actual operating conditions, the inner wall of the evaporator tube is in long-term contact with fluid media containing salt and hardness ions, which easily leads to scaling. The accumulation of scale will significantly reduce the heat transfer coefficient, increase energy consumption, and in severe cases, it can also cause pipe blockage and local overheating damage. At the same time, the thermal stress generated by fluid scouring, corrosive media erosion, and temperature changes will aggravate the wear, corrosion, and deformation of the evaporator tube, further shortening its service life.

[0004] Existing evaporator tubes mostly use a single metal material or a simple composite structure design, making it difficult to simultaneously meet core requirements such as anti-scaling, high strength, corrosion resistance, and high thermal conductivity. For example, although pure titanium alloy tubes have strong corrosion resistance, they are prone to scaling on the surface and have limited structural strength; aluminum alloy tubes have excellent thermal conductivity, but insufficient corrosion resistance and deformation resistance; traditional composite tubes have low interlayer bonding strength and are prone to peeling failure.

[0005] Furthermore, existing anti-scaling technologies mostly rely on coating spraying, which suffers from problems such as poor coating adhesion, easy peeling, and insufficient erosion resistance; while designs that enhance structural strength often sacrifice heat exchange efficiency, making it difficult to achieve comprehensive performance optimization. Therefore, developing a composite evaporator tube structure that combines high strength, anti-scaling, corrosion resistance, and high thermal conductivity has become an urgent technical problem to be solved. Summary of the Invention

[0006] The purpose of this invention is to provide an anti-scaling composite evaporator tube and its preparation method, thereby solving the problems of poor corrosion resistance and anti-scaling performance of existing evaporator tubes.

[0007] To achieve the above objectives, the present invention provides an anti-scaling composite evaporator tube, comprising an inner wall layer, a middle layer, and an outer wall layer arranged sequentially from the inside to the outside. The inner surface of the inner wall layer is provided with a porous structure of micro-arc oxidation and a hydrophobic layer. The middle layer has a honeycomb structure, and the outer wall layer is a heat-conducting layer. The outer wall layer is fixedly connected to the middle layer.

[0008] Preferably, the inner wall layer is a titanium alloy tube, and the pore size of the micro-arc oxidation porous structure of the inner wall layer is 100nm-150nm, and the porosity is 30%-40%.

[0009] Preferably, the contact angle between the hydrophobic layer and water is not less than 150°.

[0010] Preferably, the intermediate layer is a honeycomb nickel-titanium shape memory alloy with a pore size of 2mm-3mm and a wall thickness of 0.5mm-1mm.

[0011] Preferably, the outer wall layer is made of aluminum alloy.

[0012] The preparation method of the above-mentioned anti-scaling composite evaporator tube includes the following steps: S1. Micro-arc oxidation treatment is performed on the inner surface of the inner wall layer to form a porous structure on the inner surface of the inner wall layer; S2. A honeycomb-shaped intermediate layer structure is prepared by 3D printing, the intermediate layer is placed on the outer surface of the inner wall layer, and the intermediate layer and the inner wall layer are fixedly connected by diffusion welding. S3. Prepare the outer wall layer, put the outer wall layer on the outside of the intermediate layer, and fix the outer wall layer and the intermediate layer together by brazing. S4. Prepare a hydrophobic layer on the inner surface of the inner wall layer to complete the preparation of the evaporation tube.

[0013] Preferably, in step S1, the micro-arc oxidation process includes the following specific steps: S11. Treat the inner surface of the inner wall layer of the titanium alloy tube to remove the surface oxide layer and oil stains, and then pickle and activate the inner surface of the inner wall layer. Rinse with deionized water until neutral and then blow dry. S12. Fix the inner wall layer in the DC pulse micro-arc oxidation equipment. Insert a stainless steel cathode mesh into the tube of the inner wall layer. Inject an electrolyte at 35°C into the DC pulse micro-arc oxidation equipment, ensuring the electrolyte submerges the inner wall layer. Start the DC pulse micro-arc oxidation equipment to perform micro-arc oxidation treatment. The forward voltage is 300V-400V, the reverse voltage is 50V-100V, the frequency is 250Hz-500Hz, the duty cycle is 25%-35%, and the current density is 10-20. The processing time is 30-60 minutes; S13. After the micro-arc oxidation treatment is completed, rinse the inner wall layer with deionized water to remove the residual electrolyte on the surface, and then dry it.

[0014] Preferably, in step S12, the electrolyte comprises 8 -12 Sodium silicate, 3 -5 Sodium hexametaphosphate, 1 -3 Sodium hydroxide and a concentration of 5 -10 Glycerin, 0.4 -0.8 Carbon nanotube dispersion; The carbon nanotube dispersion was obtained by ultrasonic dispersion and ball milling of carbon nanotubes, TNWDIS dispersant and deionized water, with a mass ratio of carbon nanotubes to TNWDIS dispersant of 2:1. The carbon nanotubes have a diameter of 10nm-20nm and a length of 5μm-15μm.

[0015] Preferably, in step S2, the welding temperature for diffusion welding is 800℃-900℃, and the holding time is 1-2 hours; In S3, the brazing temperature is 550℃-650℃.

[0016] Preferably, in step S4, the process of preparing the hydrophobic layer includes: S41. Treat the inner surface of the inner wall layer with ultraviolet ozone for 15-30 minutes. S42. Immerse the treated inner wall layer in a PFOTS-ethanol solution preheated to 50°C for 30-60 minutes. S43. Remove the inner wall layer and dry it in an oven at 80℃-100℃ for 1-2 hours. The PFOTS-ethanol solution comprises 0.1%-0.5% glacial acetic acid and 0.5%-4% nano-silica by mass; the volume ratio of PFOTS to ethanol is 0.5-2:100.

[0017] The advantages and positive effects of the anti-scaling composite evaporator tube and its preparation method described in this invention are as follows: This invention, through micro-arc oxidation treatment on the inner surface of the inner wall layer and the addition of carbon nanotubes to the electrolyte, improves the corrosion resistance, wear resistance, and thermal conductivity of the evaporator tube, and enhances the bonding strength between the hydrophobic layer and the inner wall layer, thereby improving the anti-scaling effect of the evaporator tube. The nano-silica in the hydrophobic layer synergistically works with the porous structure of the micro-arc oxidation to improve the anti-scaling effect of the evaporator tube. The evaporator tube is a composite structure comprising an inner wall layer, a middle layer, and an outer wall layer. The honeycomb nickel-titanium shape memory alloy middle layer provides good support for the evaporator tube and reduces the impact of water flow on the evaporator tube, improving its resistance to deformation and extending its service life.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 This is a three-dimensional structural diagram of the evaporator tube according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the intermediate layer structure of the evaporator tube according to an embodiment of the present invention.

[0020] Figure Labels 1. Outer wall layer; 2. Inner wall layer; 3. Intermediate layer. Detailed Implementation

[0021] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use. They are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," and "connect" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] In this application, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. In case of any inconsistency, the meaning set forth in this specification or derived from the content described herein shall prevail. Furthermore, the terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit the scope of this application.

[0023] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0024] like Figure 1 , Figure 2 As shown, an anti-scaling composite evaporator tube includes an inner wall layer 2, a middle layer 3, and an outer wall layer 1 arranged sequentially from the inside to the outside. The inner surface of the inner wall layer 2 is provided with a porous structure of micro-arc oxidation, and a hydrophobic layer is provided on the inner surface of the inner wall layer 2. The middle layer 3 has a honeycomb structure. The outer wall layer 1 is a heat-conducting layer, and the outer wall layer 1 is fixedly connected to the middle layer 3.

[0025] The inner wall layer 2 is a titanium alloy tube. The porous structure of the micro-arc oxidation of the inner wall layer 2 has a pore size of 100nm-150nm and a porosity of 30%-40%.

[0026] The contact angle between the hydrophobic layer and water is not less than 150°.

[0027] By performing micro-arc oxidation treatment on the inner surface of inner wall layer 2, a ceramic oxide layer is formed on the titanium alloy surface. The hardness of the ceramic phase material is much higher than that of the titanium alloy substrate, which can directly resist mechanical wear such as fluid erosion and particle friction, reducing the wear of inner wall layer 2. Furthermore, the micro-arc oxidation layer has strong chemical stability, forming a physical barrier that blocks the contact between corrosive media such as water and electrolytes and the titanium alloy substrate, inhibiting substrate oxidation or electrochemical corrosion and improving the corrosion resistance of the evaporator tube. In addition, the porous structure provides an anchoring interface for the hydrophobic layer, improving the bonding strength between the hydrophobic layer and inner wall layer 2. The hydrophobic layer effectively improves the hydrophobic effect of inner wall layer 2, reducing scaling on the inner wall of the evaporator tube.

[0028] The intermediate layer 3 is a honeycomb-structured nickel-titanium shape memory alloy with a pore size of 2mm-3mm and a wall thickness of 0.5mm-1mm. The honeycomb structure possesses high structural strength and toughness, providing excellent support for the inner wall layer 2 and enhancing the strength of the evaporator tube. The nickel-titanium shape memory alloy exhibits high strain recovery and damping characteristics, effectively buffering energy impacts, reducing the impact on the evaporator tube, and enhancing its resistance to deformation, thus extending its service life.

[0029] The outer wall layer 1 is made of aluminum alloy. Aluminum alloy has a low melting point and high thermal conductivity, which is beneficial for improving the thermal conductivity of the evaporator tube and facilitates the production of the evaporator tube.

[0030] The preparation method of the above-mentioned anti-scaling composite evaporator tube includes the following steps: S1. Perform micro-arc oxidation treatment on the inner surface of the inner wall layer 2 to form a porous structure on the inner surface of the inner wall layer 2.

[0031] The micro-arc oxidation process includes the following specific steps: S11. The inner surface of the inner wall layer 2 of the titanium alloy tube is sanded to remove the surface oxide layer. Acetone ultrasonic cleaning is used to remove oil stains. The inner surface of the inner wall layer 2 is then acid-washed and activated using 10%-20% HF for 3-5 minutes; then rinsed with deionized water until neutral, and dried with cold air.

[0032] S12. Fix the inner wall layer 2 in the DC pulse micro-arc oxidation equipment. Insert a stainless steel cathode mesh into the tube of the inner wall layer 2. Inject an electrolyte at 35°C into the DC pulse micro-arc oxidation equipment, submerging the inner wall layer 2. Start the DC pulse micro-arc oxidation equipment to perform micro-arc oxidation treatment. The forward voltage is 300V-400V, the reverse voltage is 50V-100V, the frequency is 250Hz-500Hz, the duty cycle is 25%-35%, and the current density is 10-20. The processing time is 30-60 minutes.

[0033] The electrolyte includes 8 -12 Sodium silicate, 3 -5 Sodium hexametaphosphate, 1 -3 Sodium hydroxide and a concentration of 5 -10 Glycerin, 0.4 -0.8 Carbon nanotube dispersion.

[0034] The carbon nanotube dispersion was obtained by ultrasonic dispersion and ball milling of carbon nanotubes, TNWDIS dispersant, and deionized water, with a mass ratio of carbon nanotubes to TNWDIS dispersant of 2:1. The carbon nanotubes had a diameter of 10 nm-20 nm and a length of 5 μm-15 μm.

[0035] Adding carbon nanotubes to the electrolyte can prevent the formation of micropores in the ceramic layer during micro-arc oxidation due to uneven discharge. These pores can become channels for corrosive media such as water and electrolytes to penetrate into the titanium alloy matrix. The high aspect ratio of carbon nanotubes allows them to disperse uniformly in the electrolyte and, during micro-arc oxidation, grows along with the ceramic layer and embeds itself into the pores, forming physical blockages that prevent the contact path between the corrosive media and the matrix, thus improving the corrosion resistance of the inner wall layer 2. Carbon nanotubes themselves possess excellent chemical resistance and tensile strength, forming a three-dimensional support network within the ceramic layer, further increasing the hardness of the ceramic layer and contributing to improved corrosion resistance and strength of the inner wall layer 2. The high thermal conductivity of carbon nanotubes also helps improve the thermal conductivity of the evaporator tube.

[0036] S13. After the micro-arc oxidation treatment is completed, rinse the inner wall layer 2 with deionized water to remove the residual electrolyte on the surface, and dry it at a temperature of 60℃-80℃.

[0037] S2. A honeycomb-shaped intermediate layer 3 structure is prepared by 3D printing. The intermediate layer 3 is then placed on the outer surface of the inner wall layer 2, and the intermediate layer 3 is fixedly connected to the inner wall layer 2 by diffusion welding. The welding temperature for diffusion welding is 800℃-900℃, and the holding time is 1-2 hours.

[0038] S3. Prepare the outer wall layer 1, fit the outer wall layer 1 over the middle layer 3, and fix the outer wall layer 1 and the middle layer 3 together by brazing. The brazing temperature is 550℃-650℃.

[0039] S4. Prepare a hydrophobic layer on the inner surface of the inner wall layer 2 to complete the preparation of the evaporation tube.

[0040] The process of preparing a hydrophobic layer includes: S41. Treat the inner surface of the inner wall layer 2 with ultraviolet ozone for 15-30 minutes to enhance the hydroxylation of the inner surface and improve the adhesion of silane.

[0041] S42. Immerse the treated inner wall layer 2 in a 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFOTS)-ethanol solution preheated to 50℃ for 30-60 minutes. This ensures sufficient hydrolysis and adsorption of the silane.

[0042] S43. Remove inner wall layer 2 and dry it in an oven at 80℃-100℃ for 1-2 hours.

[0043] The PFOTS-ethanol solution comprises 0.1%-0.5% glacial acetic acid and 0.5%-4% nano-silica by mass; the volume ratio of PFOTS to ethanol is 0.5-2:100.

[0044] Glacial acetic acid is used to adjust the pH of the silane solution to 4-5, promoting silane hydrolysis. Nano-silica is added to the PFOTS-ethanol solution. The micro-arc oxidation porous structure of the inner wall layer 2 provides a submicron-level rough substrate, while the nano-silica provides a nano-level rough substrate, which is beneficial for improving the hydrophobic effect of the inner wall layer 2. The hydroxyl groups of the nano-silica undergo a condensation reaction with the siloxane groups to form stable covalent bonds, improving the erosion resistance of the hydrophobic layer. Furthermore, the nano-silica can be embedded in the micro-arc oxidation porous structure to further enhance the bonding strength between the hydrophobic layer and the inner surface of the inner wall layer 2.

[0045] Example 1 The inner wall layer 2 is made of TC4 titanium alloy with a wall thickness of 2mm; the middle layer 3 is made of NiTi-01 nickel-titanium shape memory alloy with a wall thickness of 1mm; and the outer wall layer 1 is made of 6061-T6 aluminum alloy with a wall thickness of 2mm.

[0046] The micro-arc oxidation process of inner wall layer 2 is as follows: the electrolyte includes 10 Sodium silicate, 5 Sodium hexametaphosphate, 2 Sodium hydroxide and a concentration of 10 Glycerin, 0.5 Carbon nanotube dispersion.

[0047] The carbon nanotube dispersion was obtained by ultrasonic dispersion and ball milling of carbon nanotubes, TNWDIS dispersant, and deionized water, with a mass ratio of carbon nanotubes to TNWDIS dispersant of 2:1. The carbon nanotubes had a diameter of 10 nm and a length of 10 μm.

[0048] The micro-arc oxidation process has a forward voltage of 400V, a reverse voltage of 100V, a frequency of 300Hz, a duty cycle of 30%, and a current density of 10. The processing time is 30 minutes.

[0049] The diffusion welding temperature is 850℃, and the holding time is 2 hours. The brazing temperature is 600℃.

[0050] The PFOTS-ethanol solution contains 0.3% glacial acetic acid and 2% nano-silica by mass; the volume ratio of PFOTS to ethanol is 1:100.

[0051] An evaporation tube with an outer diameter of 50 mm, a wall thickness of 5 mm, and a length of 2000 mm was prepared. The micro-arc oxidation porous structure of the inner wall layer has a pore size of 120 nm and a porosity of 34%, while the honeycomb pore size of the middle layer is 2 mm.

[0052] Example 2 The difference between this embodiment and Embodiment 1 is that the electrolyte in this embodiment includes 0.8... Carbon nanotube dispersion.

[0053] PFOTS-ethanol solution contains 4% nano-silica.

[0054] Example 3 The difference between this embodiment and Embodiment 1 is that the electrolyte in this embodiment includes 0.4... Carbon nanotube dispersion.

[0055] PFOTS-ethanol solution contains 0.5% nano-silica.

[0056] Comparative Example 1 The difference between this comparative example and Example 1 is that this comparative example does not contain a carbon nanotube dispersion in the electrolyte. Other components and preparation methods are the same as in Example 1.

[0057] Comparative Example 2 The difference between this comparative example and Example 1 is that this comparative example does not contain nano-silica in the PFOTS-ethanol solution. Other components and preparation methods are the same as in Example 1.

[0058] Comparative Example 3 The difference between this comparative example and Example 1 is that this comparative example only uses the method described in Example 1 to perform micro-arc oxidation treatment on the inner wall layer 2, without preparing a hydrophobic layer.

[0059] The evaporation tubes prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests. After continuous operation in a brine solution for 1000 hours, the scale thickness on the tube wall was measured. The brine solution contained 20... Sodium chloride, 3 Calcium chloride, 2 Magnesium chloride, 1 The solution contained sodium bicarbonate and the remainder deionized water, with a pH of 7, and was prepared at room temperature (25°C). The evaporation tubes were immersed in a 5% hydrochloric acid solution and left at room temperature for 30 days, during which surface corrosion was observed. The test results for Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0060] Table 1 Test results of Examples 1-3 and Comparative Examples 1-3

[0061] As can be seen from Table 1, the micro-arc oxidation treatment of the inner wall layer 2, the addition of carbon nanotubes to the electrolyte, and the addition of nano-silica to the hydrophobic layer in this invention are beneficial to improving the corrosion resistance of the evaporator tube and significantly reducing the scaling problem of the evaporator tube.

[0062] Therefore, the anti-scaling composite evaporator tube and its preparation method described in this invention can solve the problems of poor corrosion resistance and anti-scaling performance of existing evaporator tubes, and have the advantages of high strength and good thermal conductivity.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A composite evaporator tube with anti-scaling properties, characterized in that: It includes an inner wall layer, a middle layer and an outer wall layer arranged sequentially from the inside to the outside. The inner surface of the inner wall layer is provided with a porous structure of micro-arc oxidation and a hydrophobic layer. The middle layer has a honeycomb structure and the outer wall layer is a thermally conductive layer. The outer wall layer is fixedly connected to the middle layer.

2. The anti-scaling composite evaporator tube according to claim 1, characterized in that: The inner wall layer is a titanium alloy tube, and the porous structure of the micro-arc oxidation of the inner wall layer has a pore size of 100nm-150nm and a porosity of 30%-40%.

3. The anti-scaling composite evaporator tube according to claim 1, characterized in that: The contact angle between the hydrophobic layer and water is not less than 150°.

4. The anti-scaling composite evaporator tube according to claim 1, characterized in that: The intermediate layer is a honeycomb nickel-titanium shape memory alloy with a pore size of 2mm-3mm and a wall thickness of 0.5mm-1mm.

5. The anti-scaling composite evaporator tube according to claim 1, characterized in that: The outer wall layer is made of aluminum alloy.

6. A method for preparing an anti-scaling composite evaporator tube according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Micro-arc oxidation treatment is performed on the inner surface of the inner wall layer to form a porous structure on the inner surface of the inner wall layer; S2. A honeycomb-shaped intermediate layer structure is prepared by 3D printing, and the intermediate layer is placed on the outer surface of the inner wall layer. The intermediate layer and the inner wall layer are fixedly connected by diffusion welding. S3. Prepare the outer wall layer, place the outer wall layer on the outside of the intermediate layer, and fix the outer wall layer and the intermediate layer together by brazing. S4. Prepare a hydrophobic layer on the inner surface of the inner wall layer to complete the preparation of the evaporation tube.

7. The method for preparing an anti-scaling composite evaporator tube according to claim 6, characterized in that: In step S1, the micro-arc oxidation process includes the following specific steps: S11. Treat the inner surface of the inner wall layer of the titanium alloy tube to remove the surface oxide layer and oil stains, and then pickle and activate the inner surface of the inner wall layer. Rinse with deionized water until neutral and then blow dry. S12. Fix the inner wall layer in the DC pulse micro-arc oxidation equipment. Insert a stainless steel cathode mesh into the tube of the inner wall layer. Inject an electrolyte at 35°C into the DC pulse micro-arc oxidation equipment, ensuring the electrolyte submerges the inner wall layer. Start the DC pulse micro-arc oxidation equipment to perform micro-arc oxidation treatment. The forward voltage is 300V-400V, the reverse voltage is 50V-100V, the frequency is 250Hz-500Hz, the duty cycle is 25%-35%, and the current density is 10-20. The processing time is 30-60 minutes; S13. After the micro-arc oxidation treatment is completed, rinse the inner wall layer with deionized water to remove the residual electrolyte on the surface, and then dry it.

8. The method for preparing an anti-scaling composite evaporator tube according to claim 7, characterized in that: In S12, the electrolyte includes 8 -12 Sodium silicate, 3 -5 Sodium hexametaphosphate, 1 -3 Sodium hydroxide and a concentration of 5 -10 Glycerin, 0.4 -0.8 Carbon nanotube dispersion; The carbon nanotube dispersion was obtained by ultrasonic dispersion and ball milling of carbon nanotubes, TNWDIS dispersant and deionized water, with a mass ratio of carbon nanotubes to TNWDIS dispersant of 2:

1. The carbon nanotubes have a diameter of 10nm-20nm and a length of 5μm-15μm.

9. The method for preparing an anti-scaling composite evaporator tube according to claim 8, characterized in that: In step S2, the welding temperature for diffusion welding is 800℃-900℃, and the holding time is 1-2 hours. In S3, the brazing temperature is 550℃-650℃.

10. The method for preparing an anti-scaling composite evaporator tube according to claim 9, characterized in that: In step S4, the process of preparing the hydrophobic layer includes: S41. Treat the inner surface of the inner wall layer with ultraviolet ozone for 15-30 minutes. S42. Immerse the treated inner wall layer in a PFOTS-ethanol solution preheated to 50°C for 30-60 minutes. S43. Remove the inner wall layer and dry it in an oven at 80℃-100℃ for 1-2 hours. The PFOTS-ethanol solution comprises 0.1%-0.5% glacial acetic acid and 0.5%-4% nano-silica by mass; the volume ratio of PFOTS to ethanol is 0.5-2:100.

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