A method for preparing a porous wick of a stainless steel heat pipe

Abstract

The application discloses a preparation method of a stainless steel heat pipe porous liquid absorbing core. The specific process steps are as follows: after cleaning, the stainless steel pipe is vacuum dried for standby; polyvinyl butyral is dissolved in ethanol, and after adding Tween-20, glycerol and polyethylene glycol, magnetic stirring is carried out; after impurities are removed, stainless steel powder is added and uniformly stirred to obtain a stainless steel slurry; the prepared stainless steel pipe is uniformly covered with the stainless steel slurry by using a pulling method; after drying, the stainless steel coating is covered; then, the pipe is filled with aluminum oxide powder, assembled to a graphite clamp, and sintered in a vacuum furnace; after the furnace is cooled to room temperature, the assembly is removed to complete the preparation, and the stainless steel heat pipe porous liquid absorbing core is obtained. The liquid absorbing core preparation method provided by the application can be applied to various stainless steel pipe heat conduction grooves with complex shapes, has a simple and controllable process flow, a short preparation period, is green, pollution-free, safe and reliable, and is suitable for batch production.

Description

Technical Field

[0001] This invention relates to phase change heat transfer technology in the field of heat dissipation, specifically a method for preparing a porous liquid wick for a stainless steel heat pipe.

[0002] Nuclear power is a clean energy source with advantages such as economy, reliability, safety, and cleanliness. One source of nuclear leak accidents is the failure to effectively cool the reactor core and spent fuel when the facility loses power or is damaged. Therefore, research on passive cooling systems in the nuclear power field is crucial. Passive cooling systems can ensure the smooth dissipation of heat sources even when equipment loses power. Among existing technologies, heat pipes rely on the phase change of the working fluid inside the pipe for heat transfer, dissipating large amounts of heat without the need for additional power. They also have advantages such as high thermal conductivity, good temperature uniformity, and high reliability, and have received widespread attention and practical applications in the field of temperature control.

[0003] A heat pipe, as a highly efficient phase change heat transfer element, mainly consists of a shell, a wick, and a working fluid. The wick, as the core component, plays a crucial role in transferring the liquid working fluid, and its performance determines the heat transfer performance of the heat pipe. Generally, heat pipes can be classified into wire mesh, grooved, fiber, and sintered types. Grooved wicks have the advantage of low flow resistance but poor gravity resistance; wire mesh wicks have a simple structure and high porosity, but their radial thermal resistance is relatively high, capillary force is low, they are easily damaged, and their production efficiency is low; fiber wicks have a large specific surface area and high permeability, but their thermal resistance is high and capillary pressure is low; while sintered wicks have a rough surface morphology and advantages such as large specific surface area, light weight, high capillary force, and good gravity resistance. Therefore, sintered heat pipes are the most widely used type of high-efficiency heat pipe in commercial applications.

[0004] On the other hand, considering material factors, copper heat pipes are currently the most widely used in the market. However, given the harsh environment of nuclear power plants, characterized by high temperature, high pressure, strong radiation, and strong corrosion, higher requirements are placed on heat pipe materials. Stainless steel, with its characteristics of high temperature resistance, corrosion resistance, radiation resistance, oxidation resistance, and high strength, is more suitable as a heat pipe material in the nuclear power field. Summary of the Invention

[0005] This invention discloses a method for preparing a porous liquid-absorbing core for a stainless steel heat pipe, characterized by the following steps:

[0006] a. Pretreatment: Clean the inner wall of the seamless 304 stainless steel tube of the required length with acetone, then place it in ethanol for ultrasonic cleaning for 30 minutes, and then dry it in a vacuum drying oven.

[0007] b. Slurry preparation: Weigh the required mass of 304 stainless steel powder, dissolve 3-6% of polyvinyl butyral powder relative to the powder mass in ethanol at a certain ratio, then add 3%-4% of Tween-20, glycerol and polyethylene glycol relative to the ethanol mass, place it under magnetic stirring until the solution is clear and free of impurities, add the weighed stainless steel powder and stir evenly to obtain stainless steel slurry.

[0008] c. Coating Covering: The stainless steel coating of the required thickness is uniformly covered on the inner wall of the stainless steel tube by multiple lifting methods. The lifting method is as follows: The prepared stainless steel tube is completely immersed in the prepared stainless steel slurry in a vertical direction. After being lifted out at a uniform speed, it is placed in a vacuum drying oven in a vertical direction for 15 minutes to dry the slurry inside the tube. After that, the stainless steel tube is vertically rotated 180° to complete one lifting method.

[0009] d. Assembly: After the coating is completed, the stainless steel tube is filled with 40-60 mesh alumina powder, and screen sleeves are put on both ends of the stainless steel tube and pressed tightly. The screen sleeves are then tightened with clamps. After assembly into the graphite fixture, the tube is placed in a vacuum furnace.

[0010] e. Sintering: Start the vacuum furnace for heating, with a vacuum level of not less than 2×10⁻⁶. -2 Pa, the sintering process is as follows: (1) Heat from room temperature to 300℃ at a heating rate of 4℃ / min and hold for 120min; (2) Heat to 700℃ at a heating rate of 2℃ / min and hold for 60min; (3) Heat to 900℃ at a heating rate of 2℃ / min and hold for 60min; (4) Heat to 1020℃ at a heating rate of 5℃ / min and hold for 20min.

[0011] f. Finally, after cooling to room temperature in the furnace, the assembly is removed to complete the preparation, and the porous liquid-absorbing core of the stainless steel heat pipe is obtained.

[0012] In step b, the particle size of the 304 stainless steel powder is 20-30 μm.

[0013] In step b, the viscosity of the polyvinyl butyral powder is 15-18s.

[0014] In step b, the dissolution ratio of polyvinyl butyral powder is 1:10-1:15.

[0015] This invention discloses a method for preparing a porous liquid-absorbing core for a stainless steel heat pipe, the advantages of which are:

[0016] (1) This method can be used with internal wall heat conduction grooves of different complex shapes to prepare various composite stainless steel heat pipes;

[0017] (2) The prepared porous liquid wick has a large specific surface area, good anti-gravity performance, high permeability, and strong capillary driving force, which is conducive to improving the heat transfer performance of the heat pipe. It also has a stable structure and controllable thickness.

[0018] (3) Using stainless steel as raw material, the heat pipes are lightweight, high temperature resistant, corrosion resistant, radiation resistant, oxidation resistant and high strength. They have a wide range of applications, can be used for a long time under harsh working conditions, and have high stability.

[0019] (4) The process is simple and controllable, the preparation cycle is short, and it is green and pollution-free, safe and reliable, and suitable for mass production. Attached Figure Description

[0020] Figure 1 This is a cross-sectional schematic diagram of the porous wick of a stainless steel heat pipe.

[0021] Figure 2 This is a scanning electron microscope image of the porous liquid-absorbing core of the stainless steel heat pipe in Example 1.

[0022] Figure 3 This is a backscattered image of the porous liquid wick of the stainless steel heat pipe in Example 1. Detailed Implementation Plan

[0023] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to these embodiments.

[0024] Example 1

[0025] a. Pretreatment: Clean the inner wall of the seamless 304 stainless steel tube of the required length with acetone, then place it in ethanol for ultrasonic cleaning for 30 minutes, and then dry it in a vacuum drying oven.

[0026] b. Slurry preparation: Weigh the required mass of 304 stainless steel powder with a particle size of 25μm. Dissolve 3% (relative to the powder mass) of polyvinyl butyral powder with a viscosity of 15s in ethanol at a ratio of 1:12.5. Then add 3% (relative to the ethanol mass) of Tween-20, glycerol, and polyethylene glycol. Stir magnetically until the solution is clear and free of impurities. Add the weighed stainless steel powder and stir evenly to obtain the stainless steel slurry.

[0027] c. Coating Covering: The stainless steel coating of the required thickness is evenly covered on the inner wall of the stainless steel tube by a two-stage lifting method. The lifting method is as follows: The prepared stainless steel tube is completely immersed in the prepared stainless steel slurry in a vertical direction. After being lifted out at a uniform speed, it is placed in a vacuum drying oven in a vertical direction for 15 minutes to dry the slurry inside the tube. Then, the stainless steel tube is vertically rotated 180° to complete the first lifting method.

[0028] d. Assembly: After the coating is completed, the stainless steel tube is filled with 40-mesh alumina powder, and screen sleeves are put on both ends of the stainless steel tube and pressed tightly. The screen sleeves are then tightened with clamps. After being assembled into the graphite fixture, it is placed in a vacuum furnace.

[0029] e. Start the vacuum furnace heating, ensuring a vacuum level of not less than 2×10⁻⁶. -2 Pa, the sintering process is as follows: (1) Heat from room temperature to 300℃ at a heating rate of 4℃ / min and hold for 120min; (2) Heat to 700℃ at a heating rate of 2℃ / min and hold for 60min; (3) Heat to 900℃ at a heating rate of 2℃ / min and hold for 60min; (4) Heat to 1020℃ at a heating rate of 5℃ / min and hold for 20min.

[0030] f. Finally, after cooling to room temperature in the furnace, the assembly is removed to complete the preparation, and the porous liquid-absorbing core of the stainless steel heat pipe is obtained.

[0031] The suction performance of the obtained stainless steel heat pipe porous wick was tested. The working fluid was ethanol, and the time taken was 7 minutes and 46 seconds when the capillary rise height was 10 cm.

[0032] Example 2

[0033] a. Pretreatment: Clean the inner wall of the seamless 304 stainless steel tube of the required length with acetone, then place it in ethanol for ultrasonic cleaning for 30 minutes, and then dry it in a vacuum drying oven.

[0034] b. Slurry preparation: Weigh the required mass of 304 stainless steel powder with a particle size of 25μm. Dissolve 3% (relative to the powder mass) of polyvinyl butyral powder with a viscosity of 15s in ethanol at a ratio of 1:15. Then add 3% (relative to the ethanol mass) of Tween-20, glycerol, and polyethylene glycol. Stir magnetically until the solution is clear and free of impurities. Add the weighed stainless steel powder and stir evenly to obtain stainless steel slurry.

[0035] c. Coating Covering: The stainless steel coating of the required thickness is evenly covered on the inner wall of the stainless steel tube by a two-stage lifting method. The lifting method is as follows: The prepared stainless steel tube is completely immersed in the prepared stainless steel slurry in a vertical direction. After being lifted out at a uniform speed, it is placed in a vacuum drying oven in a vertical direction for 15 minutes to dry the slurry inside the tube. Then, the stainless steel tube is vertically rotated 180° to complete the first lifting method.

[0036] d. Assembly: After the coating is completed, the stainless steel tube is filled with 40-mesh alumina powder, and screen sleeves are put on both ends of the stainless steel tube and pressed tightly. The screen sleeves are then tightened with clamps. After being assembled into the graphite fixture, it is placed in a vacuum furnace.

[0037] e. Start the vacuum furnace heating, ensuring a vacuum level of not less than 2×10⁻⁶. -2Pa, the sintering process is as follows: (1) Heat from room temperature to 300℃ at a heating rate of 4℃ / min and hold for 120min; (2) Heat to 700℃ at a heating rate of 2℃ / min and hold for 60min; (3) Heat to 900℃ at a heating rate of 2℃ / min and hold for 60min; (4) Heat to 1020℃ at a heating rate of 5℃ / min and hold for 20min.

[0038] f. Finally, after cooling to room temperature in the furnace, the assembly is removed to complete the preparation, and the porous liquid-absorbing core of the stainless steel heat pipe is obtained.

[0039] The suction performance of the obtained stainless steel heat pipe porous wick was tested. The working fluid was ethanol, and the time taken was 7 minutes and 58 seconds when the capillary rise height was 10 cm.

[0040] Example 3

[0041] a. Pretreatment: Clean the inner wall of the seamless 304 stainless steel tube of the required length with acetone, then place it in ethanol for ultrasonic cleaning for 30 minutes, and then dry it in a vacuum drying oven.

[0042] b. Slurry preparation: Weigh the required mass of 304 stainless steel powder with a particle size of 20μm. Dissolve 3% (relative to the powder mass) of polyvinyl butyral powder with a viscosity of 15s in ethanol at a ratio of 1:12.5. Then add 3% (relative to the ethanol mass) of Tween-20, glycerol, and polyethylene glycol. Stir magnetically until the solution is clear and free of impurities. Add the weighed stainless steel powder and stir evenly to obtain the stainless steel slurry.

[0043] c. Coating Covering: The stainless steel coating of the required thickness is evenly covered on the inner wall of the stainless steel tube by a two-stage lifting method. The lifting method is as follows: The prepared stainless steel tube is completely immersed in the prepared stainless steel slurry in a vertical direction. After being lifted out at a uniform speed, it is placed in a vacuum drying oven in a vertical direction for 15 minutes to dry the slurry inside the tube. Then, the stainless steel tube is vertically rotated 180° to complete the first lifting method.

[0044] d. Assembly: After the coating is completed, the stainless steel tube is filled with 40-mesh alumina powder, and screen sleeves are put on both ends of the stainless steel tube and pressed tightly. The screen sleeves are then tightened with clamps. After being assembled into the graphite fixture, it is placed in a vacuum furnace.

[0045] e. Start the vacuum furnace heating, ensuring a vacuum level of not less than 2×10⁻⁶. -2 Pa, the sintering process is as follows: (1) Heat from room temperature to 300℃ at a heating rate of 4℃ / min and hold for 120min; (2) Heat to 700℃ at a heating rate of 2℃ / min and hold for 60min; (3) Heat to 900℃ at a heating rate of 2℃ / min and hold for 60min; (4) Heat to 1020℃ at a heating rate of 5℃ / min and hold for 20min.

[0046] f. Finally, after cooling to room temperature in the furnace, the assembly is removed to complete the preparation, and the porous liquid-absorbing core of the stainless steel heat pipe is obtained.

[0047] The suction performance of the obtained stainless steel heat pipe porous wick was tested. The working fluid was ethanol, and the time taken was 8 minutes and 10 seconds when the capillary rise height was 10 cm.

[0048] Example 4

[0049] a. Pretreatment: Clean the inner wall of the seamless 304 stainless steel tube of the required length with acetone, then place it in ethanol for ultrasonic cleaning for 30 minutes, and then dry it in a vacuum drying oven.

[0050] b. Slurry preparation: Weigh the required mass of 304 stainless steel powder with a particle size of 30μm. Dissolve 4% (relative to the powder mass) of polyvinyl butyral powder with a viscosity of 18s in ethanol at a ratio of 1:15. Then add 4% (relative to the ethanol mass) of Tween-20, glycerol, and polyethylene glycol. Stir magnetically until the solution is clear and free of impurities. Add the weighed stainless steel powder and stir evenly to obtain stainless steel slurry.

[0051] c. Coating Covering: The stainless steel coating of the required thickness is evenly covered on the inner wall of the stainless steel tube by a four-stage lifting method. The lifting method is as follows: The prepared stainless steel tube is completely immersed in the prepared stainless steel slurry in a vertical direction. After being pulled out at a uniform speed, it is placed in a vacuum drying oven in a vertical direction for 15 minutes to dry the slurry inside the tube. Then, the stainless steel tube is vertically rotated 180° to complete one lifting method.

[0052] d. Assembly: After the coating is completed, the stainless steel tube is filled with 40-mesh alumina powder, and screen sleeves are put on both ends of the stainless steel tube and pressed tightly. The screen sleeves are then tightened with clamps. After being assembled into the graphite fixture, it is placed in a vacuum furnace.

[0053] e. Start the vacuum furnace heating, ensuring a vacuum level of not less than 2×10⁻⁶. -2 Pa, the sintering process is as follows: (1) Heat from room temperature to 300℃ at a heating rate of 4℃ / min and hold for 120min; (2) Heat to 700℃ at a heating rate of 2℃ / min and hold for 60min; (3) Heat to 900℃ at a heating rate of 2℃ / min and hold for 60min; (4) Heat to 1020℃ at a heating rate of 5℃ / min and hold for 20min.

[0054] f. Finally, after cooling to room temperature in the furnace, the assembly is removed to complete the preparation, and the porous liquid-absorbing core of the stainless steel heat pipe is obtained.

[0055] The suction performance of the obtained stainless steel heat pipe porous wick was tested. The working fluid was ethanol, and the time taken was 7 minutes and 52 seconds when the capillary rise height was 10 cm.

[0056] Example 5

[0057] a. Pretreatment: Clean the inner wall of the seamless 304 stainless steel tube of the required length with acetone, then place it in ethanol for ultrasonic cleaning for 30 minutes, and then dry it in a vacuum drying oven.

[0058] b. Slurry preparation: Weigh the required mass of 304 stainless steel powder with a particle size of 30μm. Dissolve 3% (relative to the powder mass) of polyvinyl butyral powder with a viscosity of 15s in ethanol at a ratio of 1:15. Then add 3% (relative to the ethanol mass) of Tween-20, glycerol, and polyethylene glycol. Stir magnetically until the solution is clear and free of impurities. Add the weighed stainless steel powder and stir evenly to obtain stainless steel slurry.

[0059] c. Coating Covering: The stainless steel coating of the required thickness is evenly covered on the inner wall of the stainless steel tube by a four-stage lifting method. The lifting method is as follows: The prepared stainless steel tube is completely immersed in the prepared stainless steel slurry in a vertical direction. After being pulled out at a uniform speed, it is placed in a vacuum drying oven in a vertical direction for 15 minutes to dry the slurry inside the tube. Then, the stainless steel tube is vertically rotated 180° to complete one lifting method.

[0060] d. Assembly: After the coating is completed, the stainless steel tube is filled with 60-mesh alumina powder, and screen sleeves are put on both ends of the stainless steel tube and pressed tightly. The screen sleeves are then tightened with clamps and assembled into graphite fixtures and placed in a vacuum furnace.

[0061] e. Start the vacuum furnace heating, ensuring a vacuum level of not less than 2×10⁻⁶. -2 Pa, the sintering process is as follows: (1) Heat from room temperature to 300℃ at a heating rate of 4℃ / min and hold for 120min; (2) Heat to 700℃ at a heating rate of 2℃ / min and hold for 60min; (3) Heat to 900℃ at a heating rate of 2℃ / min and hold for 60min; (4) Heat to 1020℃ at a heating rate of 5℃ / min and hold for 20min.

[0062] f. Finally, after cooling to room temperature in the furnace, the assembly is removed to complete the preparation, and the porous liquid-absorbing core of the stainless steel heat pipe is obtained.

[0063] The suction performance of the obtained stainless steel heat pipe porous wick was tested. The working fluid was ethanol, and the time taken was 7 minutes and 53 seconds when the capillary rise height was 10 cm.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the scope of the technical solution of the present invention.

Claims

1. A method for producing a porous wick of a stainless steel heat pipe, characterized by Specific is completed according to the following steps: a. Pretreatment: the inner wall of the seamless 304 stainless steel pipe of the required length is cleaned with acetone and then placed in ethanol for ultrasonic cleaning for 30 min, and dried in a vacuum drying oven; b. Slurry preparation: weigh the required mass of 304 stainless steel powder, dissolve 3-6% polyvinyl butyral powder relative to the mass of the powder in ethanol at a certain ratio, then add 3%-4% Tween-20, glycerol, and polyethylene glycol relative to the mass of the ethanol, place in a magnetic stirrer until the solution is clear and free of impurities, add the weighed stainless steel powder and stir uniformly to obtain a stainless steel slurry; c. Coating covering: evenly cover the required thickness of the stainless steel coating on the inner wall of the stainless steel pipe by multiple pull-up methods, and after each pull-up method is completed, the stainless steel pipe is vertically turned over 180° for the next pull-up, the pull-up method is as follows: the prepared stainless steel pipe is completely immersed in the prepared stainless steel slurry in the vertical direction, pulled out at a uniform speed, and then placed vertically in a vacuum drying oven for 15 min, and the pull-up method is completed after drying the slurry in the pipe; d. Assembly: fill the stainless steel pipe after coating covering with 40-60 mesh alumina powder, and tightly wrap the screen sleeve on both ends of the stainless steel pipe, tighten the screen sleeve with a clamp, assemble to a graphite clamp, and place in a vacuum furnace; e. Sintering: Start vacuum furnace heating, vacuum degree is not less than 2x10 -2 Pa, sintering process is: (1) with 4 ℃ / min heating rate, from room temperature to 300 ℃, then keep 120 min; (2) with 2 ℃ / min heating rate, to 700 ℃, then keep 60 min; (3) with 2 ℃ / min heating rate, to 900 ℃, then keep 60 min; (4) with 5 ℃ / min heating rate, to 1020 ℃, then keep 20 min; f. Finally, after cooling to room temperature, remove the assembly parts to complete the preparation, and obtain the stainless steel heat pipe porous wick.

2. The preparation method of the stainless steel heat pipe porous wick according to claim 1, wherein the particle size of the 304 stainless steel powder in step b is 20-30 μm.

3. The preparation method of the stainless steel heat pipe porous wick according to claim 1, wherein the viscosity of the polyvinyl butyral powder in step b is 15-18 s.

4. The preparation method of the stainless steel heat pipe porous wick according to claim 1, wherein the dissolving ratio of the polyvinyl butyral powder in step b is 1:10-1:15.

Images