Preparation method of tubular loop heat pipe capillary core evaporator

Abstract

The invention discloses a preparation method of a tubular loop heat pipe capillary core evaporator, and the evaporator prepared by the method mainly comprises a shell, a capillary core and a steam collecting cavity, and is mainly characterized in that the shell, a steam channel and the capillary core of the evaporator are integrally sintered and formed, so that the machining procedures of the capillary core and the steam channel of the traditional tubular evaporator are reduced; the preparation process is shortened; the structural integrity and the sealing performance of the capillary core of the evaporator are improved, and meanwhile the production efficiency of the loop heat pipe evaporator is improved. The performance of the capillary core evaporator can be regulated, controlled and optimized by changing the physical property parameters of the capillary core raw material powder, the length-diameter ratio of the evaporator and the size of the steam channel. The preparation method of the capillary core evaporator is simple and suitable for batch production.

Description

Technical Field

[0001] This invention relates to a method for preparing a tubular loop heat pipe capillary evaporator, belonging to the technical field of loop heat pipe capillary phase change circuits, and specifically to the preparation of a high-efficiency tubular loop heat pipe evaporator. Background Technology

[0002] A loop heat pipe (LHP) is a two-phase heat exchanger that utilizes capillary force generated by a capillary wick to drive the circulation of the working fluid. It achieves efficient passive heat exchange by absorbing heat and vaporizing at the evaporation end and releasing heat and liquefying at the condensation end, using capillary force within the capillary wick evaporator as the driving force. Through a gas-liquid separation design, the loop heat pipe enables long-distance, efficient heat transfer without gravity limitations, while also possessing high power density and precise temperature control capabilities. The evaporator, driven by a capillary pump, circulates the working fluid and efficiently absorbs heat source energy through phase change; it is the decisive component for the system's heat transfer dynamics and thermal control accuracy. In a tubular evaporator, a typical structure includes an evaporator shell, a tubular capillary wick, and liquid inlets. Its tubular capillary wick structure not only provides the interface for liquid evaporation and a continuous liquid supply but also effectively prevents vapor generated in the vapor chamber from back-permeating into the liquid storage chamber. With its unique geometry, mechanical strength, and long-distance heat transfer advantages, tubular evaporators can withstand high pressure, have strong load-bearing capacity, adapt to complex structures, and have high long-distance heat transfer efficiency, making them irreplaceable in aerospace and high-power electronic heat dissipation.

[0003] The structure and performance of the evaporator and capillary wick determine the heat transfer and stability of the loop heat pipe. When the loop heat pipe is running, if steam accumulates in the evaporator, a "heat leak" will occur, turning the liquid storage chamber into a secondary evaporator. The working fluid in the liquid storage chamber will generate a backflow of steam, colliding with the normal return liquid in the opposite direction. This interrupts the working fluid supply at the capillary wick inlet, causing the evaporation front to retract to the inner wall of the liquid storage chamber, resulting in a collapse in the system's heat transfer capacity and a "burn-out" phenomenon. Invention patent (CN202110610209) "A Steam Channel Loop Heat Pipe" discloses a tubular capillary wick evaporator structure. Through the design of the tubular capillary wick structure, the start-up speed of the evaporator system is improved; the use of a pore-forming agent increases the porosity and pore size of the capillary wick, thereby reducing the resistance during working fluid flow; the evaporation area is increased, facilitating steam overflow and improving the ultimate power of the heat pipe. Compared with traditional evaporators, the tubular capillary wick evaporator can transfer more heat with the same effective heat transfer area and can handle a wider range of heat loads. However, this type of evaporator has a relatively complex structure, and the capillary wick structure is prone to breakage and failure during assembly.

[0004] Typically, the tubular evaporator shell and tubular capillary wick require precision machining before assembly. A key step in this process is the complex secondary machining of the tubular capillary wick substrate. This involves machining specific forms of vapor channels, such as axial, spiral, or mesh-like channels, into its cylindrical surface or interior, ensuring close contact between the processed capillary wick vapor channel area and the inner wall of the tubular evaporator shell to guarantee effective heat transfer. However, this secondary machining of the fine porous capillary wick easily damages its pore structure, leading to pore blockage and ultimately weakening the capillary wick's liquid absorption and working fluid transport capabilities. The invention patent "A Method for Preparing a High Aspect Ratio, High Porosity Tubular Capillary Wick" (CN119910185A) discloses a method for preparing a tubular capillary wick. This method solves the sintering and forming problem of high aspect ratio tubular capillary wicks by using PMMA mandrel removal technology, thereby improving porosity and suction performance. However, this technology still has limitations. It only focuses on the preparation of tubular capillary wicks and does not solve the integration problem between the capillary wick and the evaporator shell. Precision machining and secondary positioning are still required during assembly. At the same time, this invention patent does not involve the synchronous sintering and forming of key structures such as evaporator steam channels, and cannot avoid the risk of pore damage. The system thermal resistance problem still exists.

[0005] To address the aforementioned problems, this invention provides a method for preparing a tubular loop heat pipe capillary evaporator. The core innovation of this method lies in the fact that the prepared evaporator consists of a shell, a capillary wick, and a steam collection chamber. Its main feature is that the evaporator shell, steam channels, and capillary wick are integrally sintered, reducing the machining steps required for the capillary wick and steam channels in traditional tubular evaporators. This improves the structural integrity and sealing of the evaporator capillary wick while simultaneously increasing the production efficiency of the loop heat pipe evaporator.

[0006] The key innovation of this invention lies in its proposed integrated sintering forming technology for the shell, capillary wick, and steam collection chamber with a steam channel structure. Compared to existing manufacturing techniques, its substantial improvement lies in solving the core processing pain point of requiring secondary machining of the evaporator shell, capillary wick, and steam channels, fundamentally avoiding the risk of pore blockage and capillary wick failure caused by secondary machining. The manufacturing method of the tubular loop heat pipe capillary wick evaporator provided by this invention significantly simplifies the assembly process of tubular evaporators and shortens the production cycle while ensuring consistent product quality. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a tubular loop heat pipe capillary evaporator, characterized in that the evaporator includes a liquid inlet (1), a lower end cap (2), a tubular shell (3), a liquid channel (4), a steam channel (5), a capillary wick (6), a steam collecting chamber (7), an upper end cap (8), and a steam outlet (9); the upper end cap (8), the tubular shell (3), and the lower end cap (2) are fixedly connected, forming an internal cavity, and the steam channel (5), the capillary wick (6), and the steam collecting chamber are also included. (7) Set in the cavity; the central hole of the capillary (6) is concentric with the liquid injection port (1) on the lower end cover (2); the space between the upper end cover (8) and the capillary (6) forms a steam collection chamber (7), and the steam channel (5) is connected to the steam collection chamber (7); when the loop heat pipe is working, the steam formed by the vaporization of the liquid working fluid in the capillary (6) flows out from the steam channel (5) and gathers in the steam collection chamber (7); the steam outlet (9) is connected to the external condenser pipeline and cooling device.

[0008] Furthermore, a method for preparing a tubular loop heat pipe capillary evaporator is characterized by the following preparation process:

[0009] Step 1: Based on the shape and dimensions of the tubular loop heat pipe capillary evaporator to be prepared, prepare the tubular shell (3), and mechanically grind the inner wall of the tubular shell (3) to remove the adhering substances and metal oxide film on the inner surface of the tubular shell (3); the dimensions of the tubular shell are...

[0010] Step 2: Attach a certain number of square polymethyl methacrylate (PMMA) rods, each 2mm × 1mm × 120mm in size, to the inner wall of the tubular shell (3), in a quantity of 16. Insert a core rod into the center hole of the lower end cap (2). The core rod is made of polymethyl methacrylate (PMMA) and has dimensions of [missing information]. The lower end cap (2) is connected to the tubular shell (3) by welding.

[0011] Step 3: Weigh out a certain amount of PMMA pore-forming agent, nickel powder and copper powder respectively, put them into a ball mill and mix them evenly to obtain a loosely packed mixed powder: the mass fraction of PMMA pore-forming agent is 15% and the particle size is 13μm; the median particle size of pure nickel powder is 1.3μm; the median particle size of pure copper powder is 5.5μm; the ball mill speed is 20 rpm and the mixing time is 20 min.

[0012] Step 4: Weigh a certain amount of the mixed powder from Step 3 and fill it into the tubular shell (3) from Step 2. Tap the outer surface of the shell to make the mixed powder inside the shell evenly distributed. During this process, it is necessary to ensure that the core rod is always located at the axial position of the shell.

[0013] Step 5: Place a compressed block on the surface of the mixed powder obtained in Step 4 inside the evaporator shell, and then place it in a vacuum furnace for sintering. After the room temperature is raised to 400℃, hold for 120 minutes at a heating rate of 2℃ / min. After the holding period, continue heating to the target sintering temperature of 675℃, hold for 180 minutes at a heating rate of 1℃ / min. The sintering atmosphere is a vacuum, with a vacuum degree better than 5×10⁻⁶. -2 Pa; finally, the furnace is cooled, the press block is removed, and a capillary evaporator semi-finished product is obtained.

[0014] Step six: Weld the steam outlet end of the evaporator semi-finished product obtained in step five to the upper end cover (8) with steam outlet (9) to obtain the finished tubular loop heat pipe capillary evaporator.

[0015] As an improvement, the tubular shell (3), steam channel (5) and capillary core (6) are integrally sintered, which reduces the machining steps of the capillary core and steam channel in traditional tubular evaporators and shortens the preparation process.

[0016] As an improvement, the steam channel (5) is pre-set by laying polymethyl methacrylate (PMMA) long rods inside the tubular shell of the evaporator, and the steam channel is formed after sintering; the cross section of the PMMA long rod can be rectangular and square, or semi-circular, elliptical, serrated, wavy, or triangular; the volume of the steam channel space can be controlled by adjusting the size and number of PMMA long rods.

[0017] As an improvement, a steam collecting chamber (7) is left between the upper end cover (8) and the capillary core (6), and the steam channel (5) is connected to the steam collecting chamber (7). The size of the steam chamber can be adjusted by adjusting the thickness of the pressure block. The thickness of the pressure block is in the range of 3 to 10 mm, and the diameter of the pressure block is consistent with the inner diameter of the tubular shell (3).

[0018] As an improvement, during the integral sintering process of the tubular shell (3), steam channel (5) and capillary core (6), the steam collection chamber (7) is formed by placing a pressure block on the top of the capillary core powder. At the same time, the purpose of introducing the pressure block is to provide pressure for the capillary core sintering during the sintering process and promote the sintering process. The pressure range of the pressure block is 0.1 to 10 kPa.

[0019] As an improvement, the sintering atmosphere of the tubular shell (3), steam channel (5) and capillary core (6) integral sintering process can be a vacuum, or a hydrogen or argon protective atmosphere. The sintering temperature range is 600-900℃, the holding time is 30-240min, and the heating rate is 0.5-5℃ / min. During the heating process, the temperature is held in the range of 300-450℃ to remove the PMMA core rod, PMMA steam channel long rod and PMMA pore-forming agent. The holding time is 30-180min.

[0020] As an improvement, the capillary core (6) is made of metal, and the corresponding raw material powder can be copper powder, nickel powder, stainless steel powder, or a mixture of two or three of the above powders; the particle size range of the capillary core metal powder is 0.3 to 30.0 μm.

[0021] As an improvement, the pore structure of the capillary wick (6) can be a single-pore structure or a dual-pore structure. When the pore structure of the capillary wick (6) is a dual-pore structure, it can be achieved by adjusting the particle size and content of the mixed powder, or by adding pore-forming agents with different contents and particle sizes to different metal powders. The pore-forming agent powder can be PMMA, NH4HCO3 (ammonium bicarbonate), PVA (polyvinyl alcohol), or NaCl (sodium chloride). The mass fraction of the pore-forming agent ranges from 5% to 30%, and the particle size ranges from 5 to 30 μm.

[0022] As an improvement, different specifications and irregularly shaped tubular evaporators can be prepared by adjusting the size and shape of the evaporator shell. The shape of the evaporator can be circular, square, rectangular, elliptical and U-shaped. The material of the evaporator shell can be the same as or different from the material of the capillary core (6). Before filling with metal powder, the inner wall of the evaporator shell should be mechanically polished to remove the attached substances and metal oxide film on the inner surface of the tubular shell, so as to ensure that the capillary core metal powder and the tubular shell achieve effective metallurgical bonding during the sintering process.

[0023] The key aspects of the preparation method involved in this invention are: (a) the integrated sintering forming technology of the shell, capillary wick, and steam collection chamber with steam channel structure solves the core processing pain point that the evaporator shell, capillary wick, and steam channel must undergo secondary machining, fundamentally avoiding the risk of pore blockage and capillary wick failure caused by secondary machining. (b) the shape and size of the pre-set steam channel inside the evaporator shell can be designed and modified according to actual needs, ensuring the effective contact area between the capillary wick and the evaporator shell, and guaranteeing the heat transfer capacity and heat load range that the evaporator can bear; (c) the capillary wick hole structure can be a single-diameter structure or a double-diameter structure.

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] Figure 1 Three-view diagram of the overall structure of the capillary evaporator;

[0026] Figure 2 A photograph of the tubular shell of a capillary evaporator after it has been filled with powder;

[0027] Figure 3 Photograph of the end section of the steam channel of a capillary evaporator;

[0028] Figure 4 Photograph of the liquid injection end cross-section of a capillary evaporator;

[0029] Figure 5 Liquid absorption performance curves of capillary evaporators prepared at different sintering temperatures;

[0030] Figure 6 The liquid absorption performance curves of capillary evaporators with different aspect ratios are shown.

[0031] In the accompanying drawings, the same reference numerals are used to denote the same components or structures, wherein: 1—liquid inlet, 2—lower end cap, 3—tubular shell, 4—liquid channel, 5—steam channel, 6—capillary wick, 7—steam collecting chamber, 8—upper end cap, 9—steam outlet. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] Example 1

[0034] This embodiment describes a tubular capillary evaporator with a length-to-diameter ratio of 7:1, prepared at different sintering temperatures. The specific implementation scheme is as follows:

[0035] First, prepare the tubular shell (3), and mechanically grind the inner wall of the tubular shell (3) to remove the attached substances and metal oxide film on the inner surface of the tubular shell (3); the dimensions of the tubular shell are... The second step involves attaching a certain number of square polymethyl methacrylate (PMMA) rods, each measuring 2mm × 1mm × 120mm, to the inner wall of the tubular shell (3), in a quantity of 16. A core rod is then inserted into the center hole of the lower end cap (2). The core rod is made of polymethyl methacrylate (PMMA) and has dimensions of [missing information]. The lower end cap (2) is connected to the tubular shell (3) by welding. In the third step, a certain mass of PMMA pore-forming agent, nickel powder, and copper powder are weighed and mixed evenly in a ball mill to obtain a loosely packed mixed powder: the mass fraction of PMMA pore-forming agent is 15%, and the particle size is 13 μm; the median particle size of nickel powder is 1.3 μm; the median particle size of copper powder is 5.5 μm; the ball mill speed is 20 rpm, and the mixing time is 20 min. In the fourth step, a certain mass of the mixed powder is weighed and filled into the tubular shell (3). The outer surface of the shell is tapped to ensure that the mixed powder inside the shell is evenly distributed. During this process, it is necessary to ensure that the mandrel is always located at the axial position of the shell. Fifth, a compact is placed on the surface of the mixed powder inside the evaporator shell obtained in step four, and then placed in a vacuum furnace for sintering. The room temperature is raised to 400℃ and held for 120 minutes at a heating rate of 2℃ / min. After holding, the temperature is further raised to the target sintering temperature of 675℃ and held for 180 minutes at a heating rate of 1℃ / min. The sintering atmosphere is a vacuum, with a vacuum degree better than 5×10⁻⁶. -2 Pa; Finally, cool with the furnace, remove the press block, and obtain the capillary evaporator semi-finished product. Step 6, weld the steam outlet end of the evaporator semi-finished product obtained in step 5 to the upper end cover (8) with steam outlet (9) to obtain the tubular loop heat pipe capillary evaporator finished product.

[0036] The cross-sectional structure of the capillary evaporator's steam channel end and liquid injection end is as follows: Figure 3 , Figure 4 As shown.

[0037] Repeating the above steps and changing the sintering temperature yields tubular capillary evaporators with a length-to-diameter ratio of 7:1 and different liquid absorption properties. Figure 5 ).

[0038] Example 2

[0039] This embodiment describes tubular capillary evaporators with different aspect ratios prepared by sintering at 675℃. The specific implementation scheme is as follows:

[0040] First, prepare the tubular shell (3), and mechanically grind the inner wall of the tubular shell (3) to remove the attached substances and metal oxide film on the inner surface of the tubular shell (3); the dimensions of the tubular shell are... The second step involves attaching a certain number of polymethyl methacrylate (PMMA) square rods, each measuring 2mm × 1mm × 120mm, to the inner wall of the tubular shell (3), in eight rods. A core rod, made of polymethyl methacrylate (PMMA) and measuring 120mm, is then inserted into the center hole of the lower end cap (2). The lower end cap (2) is connected to the tubular shell (3) by welding. In the third step, a certain mass of PMMA pore-forming agent, nickel powder and copper powder are weighed and mixed evenly in a ball mill to obtain loose mixed powder: the mass fraction of PMMA pore-forming agent is 15% and the particle size is 13μm; the median particle size of pure nickel powder is 1.3μm; the median particle size of pure copper powder is 5.5μm; the ball mill speed is 20 rpm and the mixing time is 20 min. In the fourth step, a certain mass of mixed powder is weighed and filled into the tubular shell (3), and the outer surface of the shell is tapped to make the mixed powder inside the shell evenly distributed. During this process, it is necessary to ensure that the mandrel is always located at the axial position of the shell. Fifth step: Place a compressed block on the surface of the mixed powder obtained in step four inside the evaporator shell, and then place it in a vacuum furnace for sintering. After the room temperature is raised to 400℃, hold for 120 minutes at a heating rate of 2℃ / min. After the holding period, continue heating to the target sintering temperature of 675℃, hold for 180 minutes at a heating rate of 1℃ / min. The sintering atmosphere is a vacuum, with a vacuum degree better than 5×10⁻⁶. -2 Pa; Finally, cool with the furnace, remove the press block, and obtain the capillary evaporator semi-finished product. Step 6, weld the steam outlet end of the evaporator semi-finished product obtained in step 5 to the upper end cover (8) with steam outlet (9) to obtain the tubular loop heat pipe capillary evaporator finished product.

[0041] Repeating the above steps and changing the length-to-diameter ratio of the evaporator shell yields tubular capillary evaporators with different liquid absorption properties after sintering at 675℃. Figure 6 ).

[0042] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A method for preparing a tubular loop heat pipe capillary evaporator, characterized in that... The evaporator includes a liquid inlet (1), a lower end cover (2), a tubular shell (3), a liquid channel (4), a steam channel (5), a capillary wick (6), a steam collection chamber (7), an upper end cover (8), and a steam outlet (9). The upper end cover (8), the tubular shell (3), and the lower end cover (2) are fixedly connected, forming a cavity inside. The steam channel (5), the capillary wick (6), and the steam collection chamber (7) are located in the cavity. The central hole of the capillary wick (6) is concentric with the liquid inlet (1) on the lower end cover (2). The space between the upper end cover (8) and the capillary wick (6) forms the steam collection chamber (7), and the steam channel (5) is connected to the steam collection chamber (7). When the loop heat pipe is working, the steam formed by the vaporization of the liquid working fluid in the capillary wick (6) flows out from the steam channel (5) and collects in the steam collection chamber (7). The steam outlet (9) is connected to the external condenser pipeline and cooling device. The preparation process of a tubular loop heat pipe capillary evaporator is as follows: Step 1: Based on the shape and dimensions of the tubular loop heat pipe capillary evaporator to be prepared, prepare the tubular shell (3), and mechanically grind the inner wall of the tubular shell (3) to remove the adhering substances and metal oxide film on the inner surface of the tubular shell (3); the dimensions of the tubular shell are... Step 2: Attach a certain number of square polymethyl methacrylate (PMMA) rods, each 2mm × 1mm × 120mm in size, to the inner wall of the tubular shell (3), in a quantity of 16. Insert a core rod into the center hole of the lower end cap (2). The core rod is made of polymethyl methacrylate (PMMA) and has dimensions of [missing information]. The lower end cap (2) is connected to the tubular shell (3) by welding. Step 3: Weigh out a certain amount of PMMA pore-forming agent, nickel powder and copper powder respectively, put them into a ball mill and mix them evenly to obtain a loosely packed mixed powder: the mass fraction of PMMA pore-forming agent is 15% and the particle size is 13μm; the median particle size of pure nickel powder is 1.3μm; the median particle size of pure copper powder is 5.5μm; the ball mill speed is 20 rpm and the mixing time is 20 min. Step 4: Weigh a certain amount of the mixed powder from Step 3 and fill it into the tubular shell (3) from Step 2. Tap the outer surface of the shell to make the mixed powder inside the shell evenly distributed. During this process, it is necessary to ensure that the core rod is always located at the axial position of the shell. Step 5: Place a compressed block on the surface of the mixed powder obtained in Step 4 inside the evaporator shell, and then place it in a vacuum furnace for sintering. After the room temperature is raised to 400℃, hold for 120 minutes at a heating rate of 2℃ / min. After the holding period, continue heating to the target sintering temperature of 675℃, hold for 180 minutes at a heating rate of 1℃ / min. The sintering atmosphere is a vacuum, with a vacuum degree better than 5×10⁻⁶. -2 Pa; finally, the furnace is cooled, the press block is removed, and a capillary evaporator semi-finished product is obtained. Step six: Weld the steam outlet end of the evaporator semi-finished product obtained in step five to the upper end cover (8) with steam outlet (9) to obtain the finished tubular loop heat pipe capillary evaporator.

2. The method for preparing a tubular loop heat pipe capillary evaporator according to claim 1, characterized in that... The tubular shell (3), steam channel (5) and capillary core (6) are integrally sintered, which reduces the machining steps of the capillary core and steam channel in traditional tubular evaporators and shortens the preparation process.

3. The method for preparing a tubular loop heat pipe capillary evaporator according to claim 1, characterized in that... The steam channel (5) is pre-set by laying polymethyl methacrylate (PMMA) long rods inside the tubular shell of the evaporator, and the steam channel is formed after sintering; the cross section of the PMMA long rod can be rectangular and square, or semi-circular, elliptical, sawtooth, wavy, or triangular; the volume of the steam channel space can be controlled by adjusting the size and number of PMMA long rods.

4. The method for preparing a tubular loop heat pipe capillary evaporator according to claim 1, characterized in that... A steam collecting chamber (7) is left between the upper end cap (8) and the capillary core (6). The steam channel (5) is connected to the steam collecting chamber (7). The size of the steam chamber can be adjusted by adjusting the thickness of the pressure block. The thickness of the pressure block is 3 to 10 mm, and the diameter of the pressure block is consistent with the inner diameter of the tubular shell (3).

5. The method for preparing a tubular loop heat pipe capillary evaporator according to claim 4, characterized in that... During the integral sintering process of the tubular shell (3), steam channel (5) and capillary core (6), the steam collection chamber (7) is formed by placing a pressure block on the top of the capillary core powder. At the same time, the purpose of introducing the pressure block is to provide pressure for the capillary core sintering during the sintering process and promote the sintering process. The pressure range of the pressure block is 0.1 to 10 kPa.

6. The method for preparing a tubular loop heat pipe capillary evaporator according to claim 5, characterized in that... The sintering process of the tubular shell (3), the vapor channel (5) and the capillary core (6) can be carried out in a vacuum atmosphere or a hydrogen or argon protective atmosphere. The sintering temperature range is 600-900℃, the holding time is 30-240min, and the heating rate is 0.5-5℃ / min. During the heating process, the temperature is held in the range of 300-450℃ to remove the PMMA core rod, the PMMA vapor channel long rod and the PMMA pore-forming agent. The holding time is 30-180min.

7. The method for preparing a tubular loop heat pipe capillary evaporator according to claim 1, characterized in that... The capillary core (6) is made of metal, and its corresponding raw material powder can be copper powder, nickel powder, stainless steel powder, or a mixture of two or three of the above powders; the particle size range of the capillary core metal powder is 0.3 to 30.0 μm.

8. The method for preparing a tubular loop heat pipe capillary evaporator according to claim 7, characterized in that... The pore structure of the capillary core (6) can be a single-pore structure or a dual-pore structure. When the pore structure of the capillary core (6) is a dual-pore structure, it can be achieved by adjusting the particle size and content of the mixed powder, or by adding pore-forming agents with different contents and particle sizes to different metal powders. The pore-forming agent powder can be PMMA, NH4HCO3 (ammonium bicarbonate), PVA (polyvinyl alcohol), or NaCl (sodium chloride). The mass fraction of the pore-forming agent ranges from 5% to 30%, and the particle size ranges from 5 to 30 μm.

9. The method for preparing a tubular loop heat pipe capillary evaporator according to claim 1, characterized in that... Different specifications and irregularly shaped tubular evaporators can be prepared by adjusting the size and shape of the evaporator shell. The shape of the evaporator can be circular, square, rectangular, elliptical and U-shaped. The material of the evaporator shell can be the same as or different from the material of the capillary core (6). Before filling with metal powder, the inner wall of the evaporator shell should be mechanically polished to remove the attached substances and metal oxide film on the inner surface of the tubular shell, so as to ensure that the capillary core metal powder and the tubular shell achieve effective metallurgical bonding during the sintering process.

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