Preparation method of heat exchange pipe with porous composite structure

Abstract

The invention discloses a preparation method of a heat exchange pipe with a porous composite structure, and relates to the technical field of heat exchange pipe preparation. The heat exchange efficiency and the service life of the heat exchange pipe can be improved. The method comprises the steps that a seamless metal pipe and metal powder are obtained, and the metal powder and the metal pipe are made of the same material; the metal powder is sprayed to the outer surface of the seamless pipe, and after a porous layer is formed on the outer surface of the seamless pipe, a pipe blank is obtained; and after the axial direction of the pipe blank is arranged to be perpendicular to the ground, the pipe blank is electrified under the protective atmosphere, so that after the pipe blank is heated, the metal powder and the metal pipe are subjected to metallurgical bonding, and the heat exchange pipe is obtained.

Description

Technical Field

[0001] This application relates to the technical field of heat exchange pipe preparation, and in particular to a preparation method for a heat exchange pipe with a porous composite structure. Background Art

[0002] Heat exchange pipes with a porous composite structure can be applied in industrial fields such as chemical engineering, petroleum, power, and medicine due to their special properties. Heat exchangers assembled with porous-dense composite structure heat exchange pipes as basic components can be used as heaters, coolers, condensers, evaporators, and reboilers, etc., and are widely used.

[0003] The following are the deficiencies of traditional heat exchange pipes: First, the specific surface area is low and the heat exchange area is small. Taking a smooth pipe as an example, the surface area that can contact the liquid medium is equal to its outer surface area. If the outer shape geometry is changed by machining means, its specific surface area can be increased, but this way of increasing the specific surface area is also limited. Second, the vaporization nuclei on the surface of the smooth pipe are uncertain, and cavitation will occur during vaporization, resulting in deformation and material erosion on the pipe surface. The broken microscopic surface is more likely to form vaporization nuclei, which will repeatedly aggravate, reducing the service life. Summary of the Invention

[0004] This application provides a preparation method for a heat exchange pipe with a porous composite structure, which can improve the heat exchange efficiency and service life of the heat exchange pipe.

[0005] To achieve the above object, this application adopts the following technical solutions:

[0006] In the first aspect of the embodiments of this application, a preparation method for a heat exchange pipe with a porous composite structure is provided, which is characterized in that the method includes:

[0007] Obtain a seamless metal pipe and metal powder, where the material of the metal powder is the same as that of the metal pipe;

[0008] Spray the metal powder onto the outer surface of the seamless pipe, and after forming a porous layer on the outer surface of the seamless pipe, obtain a pipe blank;

[0009] After setting the axial direction of the pipe blank perpendicular to the ground, under a protective atmosphere, energize the pipe blank to heat the pipe blank so that the metal powder and the metal pipe are metallurgically bonded to obtain a heat exchange pipe.

[0010] As a possible implementation, the outer diameter of the metal pipe is 10 - 100 mm, the wall thickness of the metal pipe is 1 - 10 mm, and the length of the metal pipe is 1000 - 3000 mm;

[0011] The particle size of the metal powder is 100 - 400 mesh, and the metal powder uses shaped powder.

[0012] As a possible implementation, spraying the metal powder onto the outer surface of the seamless pipe includes:

[0013] Using supersonic cold spraying technology, spraying and embedding the metal powder onto the outer surface of the seamless pipe.

[0014] As a possible implementation, spraying the metal powder onto the outer surface of the seamless pipe includes:

[0015] Dissolving the metal powder in an aqueous PVB solution to obtain a powder solution;

[0016] Using powder slurry spraying equipment to spray the powder solution onto the outer surface of the seamless pipe.

[0017] As a possible implementation, the mass fraction of the aqueous PVB solution is 2% - 20%.

[0018] As a possible implementation, after setting the axial direction of the pipe blank perpendicular to the ground, under a protective atmosphere, energizing the pipe blank includes:

[0019] Loading the pipe blank into a vacuum tube in an electric heating device and sealing it, with the axial direction of the pipe blank perpendicular to the ground;

[0020] After evacuating the vacuum tube, filling the vacuum tube with a protective gas;

[0021] Energizing the pipe blank to raise the temperature of the pipe blank.

[0022] As a possible implementation, energizing the pipe blank to raise the temperature of the pipe blank includes:

[0023] Applying voltage and current to the pipe blank to raise the temperature of the pipe blank;

[0024] After controlling the temperature rise of the pipe blank, enabling the metal powder and the metal pipe to undergo metallurgical bonding to obtain a heat exchange pipe.

[0025] As a possible implementation, the pipe blank is also connected to a temperature detection circuit and a controller, and controlling the temperature rise of the pipe blank includes:

[0026] Using the temperature detection circuit to collect the detected temperature of the pipe blank in real time and transmitting the detected temperature to the controller;

[0027] The controller is used to control the magnitudes of the voltage and current applied to the pipe blank according to the detected temperature.

[0028] As a possible implementation manner, the controlling the temperature rise of the pipe blank includes:

[0029] After controlling the temperature of the pipe blank to rise to 300 - 500 °C and keeping it warm for 5 - 25 min, then controlling the temperature of the pipe blank to rise to the sintering temperature of the metal powder again and keeping it warm for 5 - 20 min, the heat exchange pipe is obtained.

[0030] In the second aspect of the embodiments of the present application, a heat exchange pipe with a porous composite structure is provided, and the heat exchange pipe is prepared by using the preparation method of the heat exchange pipe with a porous composite structure in the first aspect of the embodiments of the present application.

[0031] The beneficial effects brought by the technical solutions provided in the embodiments of the present application at least include:

[0032] The preparation method of the heat exchange pipe with a porous composite structure provided in the embodiments of the present application includes obtaining a seamless metal pipe and metal powder, where the materials of the metal powder and the metal pipe are the same; spraying the metal powder onto the outer surface of the seamless pipe to form a porous layer on the outer surface of the seamless pipe, thus obtaining a pipe blank; after setting the axis of the pipe blank vertically to the ground, under a protective atmosphere, the pipe blank is energized to make the metal powder and the metal pipe undergo metallurgical bonding after the pipe blank is heated, and a heat exchange pipe is obtained.

[0033] The preparation method of the heat exchange pipe with a porous composite structure provided in the present application is to coat and metallurgically bond a metal porous layer on the outer surface of a conventional dense and smooth heat exchange pipe, forming a heat exchange pipe with a porous - dense composite structure. Compared with the conventional dense and smooth heat exchange pipe, the heat exchange pipe provided in the present application has a porosity of 20% - 35% on the surface of the pipe due to the porous layer, which can bring a specific surface area increase that cannot be compared by any mechanical processing means. In the unit projected area, the specific surface area increases geometrically, which is equivalent to the proportional increase of the heat exchange contact area, and the heat exchange efficiency increases proportionally. In addition, the porous layer helps to form vaporization nuclei. During the heat exchange process of the heat exchange pipe, since the dense metal particles in the porous layer can be used as vaporization nuclei, after the temperature and pressure on the surface environment of the heat exchange pipe reach the bubble point, the entire outer surface of the pipe can be regarded as vaporization nuclei, and voids can be formed, thus solving the problem that the cavitation phenomenon occurs locally on the surface of the conventional dense and smooth heat exchange pipe, resulting in the formation of preferential vaporization nuclei, and the repeated cycle aggravates, leading to the problem of structural failure. Description of the Drawings

[0034] Figure 1A flowchart of a preparation method for a heat exchange pipe with a hole composite structure provided by an embodiment of the present application;

[0035] Figure 2 A side microscopic image of a porous layer and a dense metal pipe in a heat exchange pipe provided by an embodiment of the present application;

[0036] Figure 3 A cross-sectional macroscopic image of a porous layer attached to the outer surface of a dense metal pipe provided by an embodiment of the present application. Detailed implementation manners

[0037] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0038] Hereinafter, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the embodiments of the present disclosure, unless otherwise stated, the meaning of "a plurality" is two or more.

[0039] In addition, the use of "based on" or "in accordance with" means open and inclusive, because a process, step, calculation, or other action "based on" or "in accordance with" one or more conditions or values may, in practice, be based on additional conditions or values beyond those.

[0040] An embodiment of the present application provides a preparation method for a heat exchange pipe with a porous composite structure, as Figure 1 shown, the method includes the following steps:

[0041] Step 101, obtain a seamless metal pipe and metal powder, where the material of the metal powder is the same as that of the metal pipe.

[0042] Optionally, the outer diameter of the metal pipe is 10 - 100 mm, the wall thickness of the metal pipe is 1 - 10 mm, and the length of the metal pipe is 1000 - 3000 mm; the particle size of the metal powder is 100 - 400 mesh, the metal powder uses shaped powder; and the thickness of the porous layer is 0.1 - 0.5 mm.

[0043] Optionally, the metal pipe can be stainless steel, titanium and its alloys, iron and its alloys, nickel and its alloys, etc. The embodiments of the present application do not specifically limit the material of the metal pipe, and can be specifically selected according to the heat exchange medium.

[0044] Step 102: Spray the metal powder onto the outer surface of the metal pipe. After forming a porous layer on the outer surface of the metal pipe, a pipe blank is obtained.

[0045] The preparation method of the heat exchange pipe with a porous composite structure provided by the present application is equivalent to coating and metallurgically bonding a metal porous layer on the outer surface of a conventional dense and smooth heat exchange pipe, forming a heat exchange pipe with a porous-dense composite structure. Compared with the conventional dense and smooth heat exchange pipe, the heat exchange pipe provided by the present application has a porosity of 20%-35% in the porous layer on the pipe surface, which can bring a specific surface area increase that cannot be compared by any mechanical processing means. In the unit projected area, the specific surface area increases geometrically, which is equivalent to an equal proportion increase in the heat exchange contact area, and the heat exchange efficiency increases in equal proportion. In addition, the porous layer helps to form vaporization nuclei. During the heat exchange process of the heat exchange pipe, since the dense metal particles in the porous layer can be used as vaporization nuclei, after the temperature and pressure on the surface environment of the heat exchange pipe reach the bubble point, the entire outer surface of the pipe can be regarded as vaporization nuclei, and voids can be formed, thereby solving the problem that the cavitation on the surface of the conventional dense and smooth heat exchange pipe causes cavitation erosion to become the preferred vaporization nuclei, and the repeated cycle aggravates, resulting in structural failure.

[0046] In addition, each metal particle in the porous layer of the heat exchange pipe with a porous composite structure of the present application can be regarded as a vaporization nucleus, thereby reducing local cavitation erosion. At the same time, the uniform vaporization phenomenon helps to break the laminar flow stability of the fluid close to the pipe wall with a slow flow rate, so that the fluid after heat exchange close to the pipe wall is disturbed and leaves the pipe wall, thereby improving the heat exchange efficiency.

[0047] As an implementation method, the supersonic cold spraying technology can be used to spray and embed the metal powder onto the outer surface of the seamless pipe.

[0048] It can be understood that the principle of the supersonic cold spraying technology is to use compressed gas to generate supersonic airflow through a converging-diverging Laval nozzle, send the metal powder axially into the supersonic airflow to form a gas-solid two-phase flow, and after acceleration, impact the seamless pipe substrate in a completely solid state, undergo plastic deformation, and be embedded and fixed on the outer surface of the dense pipe to obtain a pipe blank.

[0049] As another implementation method, the metal powder can be dissolved in an aqueous PVB solution to obtain a powder solution; the powder solution is sprayed onto the outer surface of the seamless pipe by using a powder slurry spraying device. Optionally, the mass fraction of the aqueous PVB solution is 2%-20%.

[0050] In the actual preparation process, the metal powder is placed in an aqueous solution of PVB (polyvinyl butyral ester, with a content of more than 99%) with a mass fraction of 2%-20%, fully wetted and stirred evenly, and then a powder slurry spraying device is used. Compressed air is used to atomize and eject the metal powder fluid through a nozzle, which is evenly attached to the outer surface of the metal pipe to obtain a pipe blank.

[0051] It should be noted that after spraying the metal powder onto the outer surface of the metal pipe by the above wet spraying method, the outer surface of the metal pipe also needs to be dried to dry the sprayed moisture, and the drying temperature can be 30-90°C.

[0052] Step 103: After setting the axis of the pipe blank perpendicular to the ground, under a protective atmosphere, the pipe blank is electrified so that after the pipe blank is heated, the metal powder and the metal pipe are metallurgically bonded to obtain a heat exchange pipe.

[0053] Optionally, the pipe blank is loaded into a vacuum tube in an electric heating device and sealed, and the axis of the pipe blank is perpendicular to the ground; after the vacuum tube is evacuated, a protective gas is filled into the vacuum tube; the pipe blank is electrified to heat the pipe blank.

[0054] Optionally, the electrifying the pipe blank to heat the pipe blank includes: after applying a voltage and a current to the pipe blank to heat the pipe blank; after controlling the temperature rise of the pipe blank, the metal powder and the metal pipe are metallurgically bonded to obtain a heat exchange pipe.

[0055] Among them, the voltage can be controlled at 30-50V, and the current can be controlled at 10-2000A.

[0056] Optionally, the pipe blank is also connected to a temperature detection circuit and a controller, and the controlling the temperature rise of the pipe blank includes:

[0057] Using the temperature detection circuit to collect the detected temperature of the pipe blank in real time and transmit the detected temperature to the controller; using the controller to control the magnitude of the voltage and current applied to the pipe blank according to the detected temperature.

[0058] It can be understood that during the process of applying a voltage and a current to the pipe blank to heat the pipe blank, the pipe blank can act as a resistor, but as the temperature of the pipe blank rises, the self-resistance of the pipe blank will change. Therefore, it is necessary to use the temperature detection circuit to collect the temperature of the pipe blank in real time and use the controller to control and adjust the magnitude of the voltage and current applied to the pipe blank in real time.

[0059] Optionally, controlling the temperature rise of the pipe blank includes: after controlling the temperature of the pipe blank to rise to 300 - 500 °C and keeping it for 5 - 25 min, then controlling the temperature of the pipe blank to rise to the sintering temperature of the metal powder and keeping it for 5 - 20 min, thus obtaining the heat exchange pipe.

[0060] In the actual preparation process, the pipe blank can be loaded vertically into the vacuum tube supporting the electric heating device. The two ends of the pipe blank are fixed with conductive chucks, and the gap between the vacuum tube and the chucks is sealed with insulating materials. The vacuum tube is pre-evacuated until the vacuum degree is less than 100 Pa, and then a protective atmosphere gas is filled. Argon is preferred for titanium and nickel alloys, and reducing atmospheres such as hydrogen can be selected for ferroalloys or stainless steels. Then, a voltage is applied to the pipe blank and current is passed. The voltage is controlled at 30 - 50 V, and the current is controlled at 10 - 2000 A. During the period when the pipe temperature is 300 - 500 °C, it is kept for 5 - 25 min to facilitate the volatilization and removal of the binder. Then, the current is continuously increased, and it is kept for 5 - 20 min within the suitable sintering temperature range of different metal materials to facilitate the growth of sintering necks between the powders and metallurgical bonding. During the energization process of the pipe blank, the tensile stress at both ends of the chuck is kept greater than 100 N. After the energization ends, the protective atmosphere is continuously passed for 10 - 30 minutes for cooling. After cooling to below 80 °C, the pipe is taken off and the two ends are machined to obtain a usable heat exchange pipe.

[0061] In this application, by applying direct current to the pipe blank and using the heating technical route of the current thermal effect, combined with the skin effect of the current, the temperature of the pipe rises rapidly and evenly. Then, through the ways of thermal radiation and heat conduction, the thermal energy is transferred to the interface where the metal powders attached to the surface are in contact. At the same time, there is also the thermal effect of the current at the contact interface, further increasing the temperature of the contact surface between the powders. The high temperature accelerates the diffusion between atoms, forms sintering necks, and achieves the purpose of metallurgical bonding.

[0062] In addition, under the action of the protective atmosphere, oxidation of the dense pipe and metal powders can be avoided, and at the same time, the flowing protective gas can take away the volatilized binder, and finally a porous layer is formed on the surface of the dense pipe, and a heat exchange pipe with a porous composite structure is finally prepared.

[0063] The preparation method of the heat exchange pipe with a porous composite structure provided by this application solves the problem of difficult interatomic diffusion and metallurgical bonding of metal powders during the preparation of conventional porous-dense composite structures. In addition, conventional atmosphere heating usually adopts methods such as continuous sintering furnaces, horizontal sintering furnaces, and vertical sintering furnaces. However, these methods all have the following problems. For horizontal sintering, the pipe must lie horizontally on the base, which will cause the metal powder on the surface of the pipe to contact the material rack. Under high temperature and the pressure of the pipe's own weight, the porous layer on the outer surface will have the situation of adhesive material rack shedding or compacting powder gaps. At the same time, high temperature will cause the straightened pipe substrate to anneal and recover, and it is difficult to guarantee the straightness.

[0064] If the suspended horizontal lying method is adopted to avoid the situation of porous layer adhesion and compaction, the strength of the pipe will decrease at high temperature, and it will inevitably bend downward in the middle due to its own gravity, and it is difficult to guarantee the straightness.

[0065] If the vertical furnace loading method is adopted, lifting the pipe for heating can avoid the straightness problem. However, the temperature difference between the upper and lower parts of the vertical furnace is generally large, which will leave hidden dangers for the consistency of its metallurgical bonding, and the production efficiency of the vertical furnace is low.

[0066] This application solves the above technical problems. This application adopts the technical route of vertical placement, clamping and electrifying. The clamping at both ends maintains tensile force, and while heating, the pipe substrate is straightened. While guaranteeing the straightness, due to its vertical loading method, the porous layer on the outer surface does not come into contact with the outside world, guaranteeing that the powder on its outer surface is not damaged. At the same time, because its heating mechanism is the thermal effect of current, there is no temperature difference brought by external heating at the upper and lower ends of the pipe during the heating process, and its heating efficiency is high and the production efficiency is high.

[0067] Based on the preparation method of the heat exchange pipe with a porous composite structure provided in the above embodiments. This application also provides some specific embodiments. The following embodiments more specifically describe the technical solutions of this application. These embodiments are only for illustrative purposes, because various modifications and changes within the scope of the disclosure of this application are obvious to those skilled in the art. The reagents and raw materials used in the embodiments can be obtained through commercial purchase or synthesized according to conventional methods, and can be directly used without further treatment, and the instruments and devices used in the embodiments can all be obtained through commercial purchase.

[0068] Example 1

[0069] 1. Select a seamless pure titanium tube obtained by rolling, with a specification of φ50mm, a wall thickness of 3mm, and a length dimension of 1000mm.

[0070] 2. Select shaped pure titanium powder obtained by hydrogenation and dehydrogenation, with a particle size range of 100-160 mesh.

[0071] 3. Place the metal powder in an aqueous solution of 2% by mass of PVB (polyvinyl butyral, with a content of over 99%), soak it thoroughly and stir evenly. Use a slurry spraying device to spray the metal powder onto the outer surface of the metal pipe. After obtaining a porous layer with a thickness of 0.2 - 0.4 mm attached to the surface, a composite structure pipe blank with a titanium dense pipe as the substrate is obtained.

[0072] 5. Place the above-mentioned pipe blank vertically into the vacuum tube used in the electric heating device, and seal the gap between the vacuum tube and the chuck with insulating materials.

[0073] 6. Pre-pump the vacuum tube. After the vacuum degree is less than 100 Pa, fill it with argon.

[0074] 7. Apply voltage and current. Control the voltage at 30 - 40 V, and control the current to gradually increase the temperature of the pipe. Keep it for 5 - 25 min during the pipe temperature of 400 - 500 °C to facilitate the volatilization and removal of the adhesive. Then continue to increase the current and keep it at the sintering temperature of 1100 °C ± 20 °C for 10 - 20 min to facilitate the growth of sintering necks and metallurgical bonding between titanium powders. The current is automatically adjusted by the temperature-current control module. During the heating process, keep the tensile stress at both ends of the chuck greater than 100 N.

[0075] 8. After the power is turned off, continue to pass the protective atmosphere for 10 - 30 min for cooling. After cooling to below 80 degrees, remove the pipe and perform machining and leveling treatment on both ends to obtain a porous-dense composite structure heat exchange titanium pipe.

[0076] Example 2

[0077] 1. Select a 316L stainless steel pipe obtained by rolling, with a specification of φ80 mm, a wall thickness of 8 mm, and a length dimension of 2000 mm.

[0078] 2. Select 316L stainless steel special-shaped powder of the same brand, with a particle size range of 100 - 160 mesh.

[0079] 3. Use a supersonic cold spraying device to spray and attach the stainless steel powder on the outer surface of the dense pipe. After obtaining a porous layer with a thickness of 0.2 - 0.5 mm, a pipe blank is obtained.

[0080] 5. Place the above-mentioned pipe blank vertically into the vacuum tube used in the electric heating device, and seal the gap between the vacuum tube and the chuck with insulating materials.

[0081] 6. Pre-pump the vacuum tube. After the vacuum degree is less than 100 Pa, fill it with hydrogen.

[0082] 7. Apply the load voltage and current. Control the voltage within 35 - 45V, and control the current to gradually increase the temperature of the pipe material. Maintain it at the sintering temperature of 1200°C ± 20°C for 10 - 20 minutes to facilitate the growth of sintering necks and metallurgical bonding between stainless steel powders. The current is automatically adjusted by the temperature - current control module. During the heating process, maintain the tensile stress at both ends of the chuck greater than 100N;

[0083] 8. After the power - on ends, continue to pass hydrogen for 20 - 30 minutes for cooling. After cooling to below 80°C, remove the pipe material and perform machining and leveling treatment on both ends to obtain a porous - dense composite - structure heat - exchange titanium pipe.

[0084] Example Three

[0085] 1. Select a 20# low - carbon steel pipe obtained by the rolling method, with a specification of φ30mm, a wall thickness of 2mm, and a length dimension of 3000mm;

[0086] 2. Select iron powder prepared by the atomization method, with a particle size range of 200 - 325 mesh;

[0087] 3. Place the powder in an aqueous solution of PVB (polyvinyl butyral, with a content of more than 99%) with a mass fraction of 10%, fully soak and stir evenly. Use a slurry spraying device to obtain a porous layer with an attached thickness of 0.3 - 0.5mm on the surface, and obtain a pipe blank with a composite structure having a titanium - dense pipe as the substrate;

[0088] 5. Place the above - mentioned pipe blank vertically into the vacuum tube supporting the electric heating device, and seal the gap between the vacuum tube and the chuck with insulating materials;

[0089] 6. Pre - evacuate the vacuum tube. After the vacuum degree is less than 100Pa, fill it with hydrogen;

[0090] 7. Apply the load voltage and current. Control the voltage within 30 - 40V, and control the current to gradually increase the temperature of the pipe material. Maintain it at 400 - 450°C for 10 - 20 minutes to facilitate the volatilization and removal of the binder. Then continue to increase the current and maintain it at the sintering temperature of 1100°C ± 20°C for 10 - 20 minutes to facilitate the growth of sintering necks and metallurgical bonding between iron powders. The current is automatically adjusted by the temperature - current control module. During the heating process, maintain the tensile stress at both ends of the chuck greater than 100N;

[0091] 8. After the power - on ends, continue to pass the protective atmosphere for 10 - 30 minutes for cooling. After cooling to below 80 degrees, remove the pipe material and perform machining and leveling treatment on both ends to obtain a porous - dense composite - structure heat - exchange pipe. As Figure 2 shown is the side microscopic image of the porous layer and the dense metal pipe in the heat - exchange pipe. As Figure 3 shown outside is the cross - sectional macroscopic photograph of the porous layer attached to the outer surface of the dense metal pipe.

[0092] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered that the scope described in this specification is covered.

[0093] The above embodiments only represent several implementation manners of the present application, and the description is relatively specific and detailed. However, it should not be construed as a limitation to the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A preparation method of a heat exchange pipe with a porous composite structure, characterized in that, The method includes: Obtaining a seamless metal pipe and metal powder, where the material of the metal powder is the same as that of the metal pipe; Spraying the metal powder onto the outer surface of the metal pipe, and after forming a porous layer on the outer surface of the metal pipe, obtaining a pipe blank; After setting the axial direction of the pipe blank perpendicular to the ground, under a protective atmosphere, applying electricity to the pipe blank to heat the pipe blank so that the metal powder and the metal pipe undergo metallurgical bonding to obtain a heat exchange pipe.

2. The method according to claim 1, wherein The outer diameter of the metal pipe is 10 - 100 mm, the wall thickness of the metal pipe is 1 - 10 mm, and the length of the metal pipe is 1000 - 3000 mm; The particle size of the metal powder is 100 - 400 mesh, and the metal powder uses special-shaped powder; The thickness of the porous layer is 0.1 - 0.5 mm.

3. The method according to claim 1, wherein The spraying the metal powder onto the outer surface of the metal pipe includes: Using supersonic cold spraying technology to spray and embed the metal powder onto the outer surface of the metal pipe.

4. The method according to claim 1, wherein The spraying the metal powder onto the outer surface of the metal pipe includes: Dissolving the metal powder in a PVB aqueous solution to obtain a powder solution; Using powder slurry spraying equipment to spray the powder solution onto the outer surface of the metal pipe.

5. The method according to claim 4, wherein The mass fraction of the PVB aqueous solution is 2% - 20%.

6. The method according to claim 1, wherein After setting the axial direction of the pipe blank perpendicular to the ground, under a protective atmosphere, applying electricity to the pipe blank includes: Loading the pipe blank into a vacuum tube in an electric heating device and sealing it, with the axial direction of the pipe blank perpendicular to the ground; After evacuating the vacuum tube, filling the vacuum tube with a protective gas; Applying electricity to the pipe blank to heat the pipe blank.

7. The method according to claim 6, wherein The applying electricity to the pipe blank to heat the pipe blank includes: Applying voltage and current to the pipe blank to heat the pipe blank; After controlling the pipe blank to heat up, enabling the metal powder and the metal pipe to undergo metallurgical bonding to obtain a heat exchange pipe.

8. The method according to claim 7, wherein The pipe blank is also connected to a temperature detection circuit and a controller, and the controlling the pipe blank to heat up includes: Using the temperature detection circuit to collect the detected temperature of the pipe blank in real time and transmitting the detected temperature to the controller; Using the controller to control the magnitudes of the voltage and current applied to the pipe blank according to the detected temperature.

9. The method according to claim 7, wherein The controlling the pipe blank to heat up includes: Controlling the pipe blank to heat up to 300 - 500 °C, keeping it warm for 5 - 25 min, and then controlling the pipe blank to heat up to the sintering temperature of the metal powder again and keeping it warm for 5 - 20 min to obtain the heat exchange pipe.

10. A heat exchange pipe with a porous composite structure, characterized in that, The heat exchange pipe is prepared by using the preparation method of the porous composite structure heat exchange pipe according to any one of claims 1 - 9.

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