Heat pipe capable of changing contact angle of wick and liquid metal working medium and additive manufacturing method of heat pipe

Abstract

The invention discloses a heat pipe with a variable liquid absorption core and liquid metal working medium contact angle and an additive manufacturing method thereof.The heat pipe is provided with a heat pipe shell with an inner cavity filled with a metal working medium, the inner wall of the heat pipe shell is provided with an integrally-formed liquid absorption core structure, and the liquid absorption core structures of an evaporation section, a heat insulation section and a condensation section are configured to be different in roughness; a first contact angle of the wick structure of the evaporation section to a metal working medium is smaller than a second contact angle of the wick structure of the condensation section to the metal working medium, and a third contact angle of the wick structure of the heat insulation section to the metal working medium is between the first contact angle and the second contact angle and is gradually increased from the evaporation section to the condensation section; the roughness difference is achieved by adopting different printing process parameters in different functional sections in the additive manufacturing process, so that different microtopographies are formed on the surface of the wick. The working medium backflow capacity and efficiency are effectively improved, the heat transfer performance of the heat pipe is improved, and the heat pipe has the advantages of being integrated in structure, high in reliability and high in customizability.

Description

Technical Field

[0001] This invention relates to heat pipes, and more specifically to a heat pipe with a variable contact angle between the wick and the liquid metal working fluid, and its additive manufacturing method. Background Technology

[0002] Currently, high heat flux density devices such as aircraft and electronic chips have placed higher demands on heat dissipation. High-temperature heat pipes are widely used due to their high thermal conductivity, high reliability, low cost, and passive operation. The operating temperature of high-temperature heat pipes is generally between 600 and 1500 K. Their working principle is as follows: the inner cavity of the heat pipe is under negative pressure. The internal metal working fluid absorbs heat from the external heat source in the evaporation section and changes phase to gas. Under pressure, the gas reaches the condensation section and condenses into liquid. The liquid metal flows through the adiabatic section and returns to the evaporation section under the capillary force of the wick, thus achieving efficient heat transport.

[0003] The wick is the core component of a high-temperature heat pipe. Its function is to generate capillary force for the reflux of the liquid metal working fluid, driving the condensed liquid metal working fluid from the condensation section back to the evaporation section. Traditional high-temperature heat pipes typically use a single-structure wick such as wire mesh or sintered metal powder, and the heat pipe shell and wick are fabricated separately, with the wick ultimately fixed to the inner surface of the shell by welding. While such heat pipes have a simple structure, the manufacturing process is complex, and the heat transfer performance is limited. During axial heat transport, the capillary properties and contact angle of the working fluid are fixed. However, high heat flux density devices place higher demands on the internal reflux of the working fluid in the heat pipe. In the evaporation section, strong capillary force is needed to rapidly draw in the liquid metal working fluid, forming a liquid film that absorbs heat and evaporates. In the condensation section, the condensed liquid metal working fluid needs to be able to detach from the condensation surface and flow rapidly. In the adiabatic section, a stable liquid supply needs to be maintained. Summary of the Invention

[0004] Objectives of the invention: The first objective of this invention is to provide a heat pipe with better heat transfer performance by varying the contact angle between the wick and the liquid metal working fluid; the second objective of this invention is to provide an additive manufacturing method for this heat pipe.

[0005] Technical Solution: The present invention discloses a heat pipe with a variable wick contact angle with liquid metal working fluid, comprising a heat pipe shell with an inner cavity filled with liquid metal working fluid, and an integrally formed wick structure on the inner wall of the heat pipe shell. The wick structures of the evaporation section, the adiabatic section, and the condensation section are configured with different roughnesses, such that the first contact angle of the wick structure of the evaporation section with the liquid metal working fluid is smaller than the second contact angle of the wick structure of the condensation section with the liquid metal working fluid, while the third contact angle of the wick structure of the adiabatic section with the liquid metal working fluid is between the first and second contact angles and gradually increases from the evaporation section to the condensation section.

[0006] Furthermore, the first contact angle is 10° to 20°, and the second contact angle is 120° to 130°.

[0007] Furthermore, the liquid-absorbing core structure adopts a channel or dot matrix structure.

[0008] Furthermore, the heat pipe shell and the wick structure are made of stainless steel, nickel-based alloys, or high-temperature alloys.

[0009] Furthermore, the working metal can be sodium, potassium, lithium, or cesium.

[0010] The additive manufacturing method of the heat pipe with variable contact angle between liquid absorber and liquid metal working fluid according to the present invention includes a powder cleaning and vacuum injection pipe connected to the inner cavity of the heat pipe shell.

[0011] The additive manufacturing method includes the following steps:

[0012] S1. Design a heat pipe model and import it into the additive manufacturing equipment, then fill the additive manufacturing metal powder into the powder supply system of the additive manufacturing equipment;

[0013] S2. Based on the roughness requirements of the wick structure for the evaporation section, the insulation section, and the condensation section, the additive manufacturing process parameters for different functional sections of the heat pipe are set differently, and the additive manufacturing equipment is used to print layer by layer and form a single piece.

[0014] S3. After printing, the unmelted metal powder remaining on the heat pipe sample is removed by using the powder cleaning and vacuum injection tube.

[0015] S4. Clean the heat pipe sample after powder removal to remove residual powder, oil and other impurities adhering to the inner and outer surfaces of the heat pipe sample.

[0016] S5. The metal working fluid is injected into the heat pipe through the powder cleaning and vacuum injection pipe, followed by vacuuming. Finally, the powder cleaning and vacuum injection pipe is laser sealed and welded in a high vacuum environment to obtain the finished heat pipe.

[0017] Furthermore, in step S2, the additive manufacturing process parameters include laser power, scanning speed, scanning spacing, and layer thickness;

[0018] The laser energy density used in the liquid wick structure of the evaporation section is higher than that used in the liquid wick structure of the condensation section, while the laser energy density used in the liquid wick structure of the adiabatic section is between that of the evaporation section and the condensation section.

[0019] The evaporation section uses a smaller scanning interval and a higher scanning speed to form a dense, low-roughness surface structure on the liquid absorption core; the condensation section uses a larger scanning interval and a lower scanning speed to form a high-roughness surface structure with large feature sizes; the adiabatic section uses gradient printing parameters between the evaporation and condensation sections.

[0020] Furthermore, in step S3, the powder cleaning process includes airflow rinsing, precision vibration, and flexible mechanical intervention.

[0021] Further, in step S4, ultrasonic cleaning is performed sequentially using acetone, anhydrous ethanol, and deionized water.

[0022] Furthermore, in step S5, the vacuuming includes: firstly, performing a rough vacuum to maintain the pressure inside the tube within a first set value; then, heating the heat pipe at a high temperature to achieve secondary exhaust, removing as much non-condensable gas as possible from the tube; and continuing the vacuuming process to maintain the pressure inside the tube within a second set value.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0024] This invention utilizes additive manufacturing technology to achieve the integrated forming and manufacturing of a heat pipe with varying wicking angles and liquid metal working fluid contact angles in different axial regions, avoiding the contact thermal resistance and reliability issues associated with traditional assembly processes. Additive manufacturing employs a layer-by-layer accumulation method, enabling the fabrication of structures with complex internal geometries. The printing parameters for each functional segment of the heat pipe can be precisely controlled, and the integrated design and manufacturing of the heat pipe is possible, offering greater design freedom compared to traditional processes.

[0025] The advantages of the differential contact angle wick heat pipe structure designed in this invention are as follows: In the evaporation section of the heat pipe, the heat flux density is high, the gas-liquid phase transition is intense, and the demand for fluid supply is large. Therefore, the contact angle between the working fluid and the wick is designed to be as small as possible to form a large surface area liquid film and efficient liquid supply. The hydrophilic evaporation section enhances capillary force. In the condensation section of the heat pipe, the liquid metal working fluid needs to quickly detach from the surface for reflux. Therefore, the contact angle is designed to be as large as possible to form a non-wetting state. The hydrophobic condensation section promotes the shedding and reflux of condensate droplets. In the adiabatic section of the heat pipe, the gradient transition of the adiabatic section achieves stable liquid metal working fluid transport. The synergistic effect of these three aspects significantly improves the reflux dynamics and efficiency of the liquid, thereby enhancing the heat transfer performance of the heat pipe, which is particularly crucial for gravity-fed heat pipe applications. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a heat pipe structure with a variable wick and liquid metal working fluid contact angle provided in an embodiment of the present invention;

[0027] Figure 2 This is a schematic diagram showing the change in the contact angle between the liquid-absorbing core and the liquid metal working fluid in an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of the channel liquid suction core structure in an embodiment of the present invention. Detailed Implementation

[0029] The invention will now be further described with reference to the accompanying drawings.

[0030] Appendix Figures 1 to 3 The accompanying figure labels are as follows:

[0031] 1. Heat pipe shell; 2. Evaporation section; 3. Insulation section; 4. Condensation section; 5. Metal working fluid; 6. Powder cleaning and vacuum injection pipe.

[0032] like Figure 1 As shown, this embodiment of the invention provides a heat pipe with a variable contact angle between the liquid absorber and the liquid metal working fluid, including a heat pipe shell 1 (typically 1-1.5 mm thick). The heat pipe shell 1 has a hollow, closed cavity (hereinafter referred to as the inner cavity), and the heat pipe shell 1 is filled with a metal working fluid 5. The heat pipe shell 1 maintains a vacuum state inside the heat pipe and prevents leakage of the fluid working fluid. A powder cleaning and vacuum injection pipe 6 is provided on the outer circumferential surface of the heat pipe shell 1 and communicates with the inner cavity. The powder cleaning and vacuum injection pipe 6 is used to clean the residual metal powder after printing, and at the same time, it is used to maintain the negative pressure inside the heat pipe and to fill the working fluid.

[0033] The inner wall of the heat pipe shell 1 has an integrally formed wick structure. The function of the wick structure is to contain the liquid metal working fluid and provide capillary force, and the space above the wick provides a flow channel for the vapor after the fluid phase change. The wick structures of the evaporation section 2, the adiabatic section 3, and the condensation section 4 are configured with different roughnesses (this roughness difference is achieved by using different printing process parameters in different functional sections during additive manufacturing, resulting in different microstructures on the surface of the wick, as detailed below), so that the first contact angle of the wick structure of the evaporation section 2 with the metal working fluid 5 is smaller than the second contact angle of the wick structure of the condensation section 4 with the metal working fluid 5, while the third contact angle of the wick structure of the adiabatic section 3 with the metal working fluid 5 is between the first and second contact angles and gradually increases from the evaporation section 2 to the condensation section 4.

[0034] Specifically, the first contact angle is 10° to 20°, and the second contact angle is 120° to 130°.

[0035] The liquid-absorbing core structure adopts a channel or dot matrix structure.

[0036] The heat pipe housing 1 and the liquid wick structure are made of stainless steel, nickel-based alloy or high-temperature alloy.

[0037] The working medium 5 is sodium, potassium, lithium or cesium metal.

[0038] This invention also provides an additive manufacturing method for a heat pipe with a variable contact angle between the wick and the liquid metal working fluid, comprising the following steps:

[0039] S1. Design a heat pipe model and import it into the additive manufacturing equipment, then fill the additive manufacturing metal powder into the powder supply system of the additive manufacturing equipment;

[0040] The heat pipe model was designed using 3D modeling software. Design parameters included heat pipe geometry, wall thickness, the ratio of evaporation, insulation, and condensation section lengths, wick structure parameters, and vapor chamber dimensions. Before loading, the additive manufacturing metal powder (i.e., stainless steel, nickel-based alloy, or high-temperature alloy powder) required vacuum drying pretreatment to remove moisture and ensure powder flowability and print quality.

[0041] S2. Based on the roughness requirements of the liquid absorption core structure for the evaporation section 2, the insulation section 3 and the condensation section 4, the additive manufacturing process parameters for different functional sections of the heat pipe are set differently. The additive manufacturing equipment is used to print layer by layer, and the entire heat pipe is integrally printed from the same metal material.

[0042] Additive manufacturing process parameters include laser power, scanning speed, scanning spacing, and layer thickness.

[0043] The laser energy density used in the liquid suction core structure of evaporation section 2 is higher than that used in the liquid suction core structure of condensation section 4, while the laser energy density used in the liquid suction core structure of adiabatic section 3 is between that of evaporation section 2 and condensation section 4. Evaporation section 2 uses a smaller scanning interval and a higher scanning speed to form a dense, low-roughness surface structure for the liquid suction core; condensation section 4 uses a larger scanning interval and a lower scanning speed to form a high-roughness, large-feature-size surface structure; the adiabatic section uses gradient printing parameters between evaporation section 2 and condensation section 4. Therefore, a structure is formed as follows... Figure 2 The results show the small contact angle (dark color) of the evaporation section, the gradual contact angle (gradient color) of the adiabatic section, and the large contact angle (light color) of the condensation section.

[0044] S3. After printing, the unmelted metal powder remaining on the heat pipe sample is removed by using the powder cleaning and vacuum injection tube 6.

[0045] The powder removal process includes methods such as airflow rinsing, precision vibration, and flexible mechanical intervention.

[0046] S4. After cleaning the powder, the heat pipe sample is ultrasonically cleaned in sequence with acetone, anhydrous ethanol and deionized water to remove residual powder, oil and other impurities adhering to the inner and outer surfaces of the heat pipe sample.

[0047] S5. A metallic working fluid 5 (such as sodium, potassium, lithium, or cesium) is injected into the heat pipe through the cleaning and vacuuming injection pipe 6. A rough vacuum is then performed to maintain the pressure inside the pipe below 10 Pa. The heat pipe is then heated at high temperature to achieve secondary venting, removing as much non-condensable gas as possible. Vacuuming continues to maintain the pressure inside the pipe at 10 Pa. -4 Within Pa; finally, the powder cleaning and vacuum injection tube 6 is laser sealed and welded in a high vacuum environment to ensure that the heat pipe is kept in a high vacuum state, thereby obtaining the finished heat pipe.

[0048] Here is a specific example.

[0049] See Figure 3 The liquid-absorbing core structure adopts a channel structure, which is composed of individual units arrayed along and perpendicular to the fluid flow direction. The channel liquid-absorbing core structure is configured as follows: channel width 0.5 mm, wall thickness 0.5 mm, and height 3 mm. The length ratio of the evaporation section, adiabatic section, and condensation section is 1:2:1. Stainless steel powder is used as the additive manufacturing material. Sodium is used as the working fluid.

[0050] In step S2 of the additive manufacturing method, the additive manufacturing process parameters are configured as follows: evaporation section laser power 120W, scanning speed 800mm / s, scanning spacing 0.08mm, layer thickness 0.03mm; condensation section laser power 250W, scanning speed 500mm / s, scanning spacing 0.12mm, layer thickness 0.03mm; adiabatic section laser power parameters increase linearly from 120 to 250W, scanning speed decreases linearly from 800mm / s to 500mm / s, and scanning spacing increases linearly from 0.08mm to 0.12mm.

Claims

1. A heat pipe with variable wick to liquid metal working substance contact angle, having a heat pipe shell (1) filled with a metal working substance (5) in the inner cavity, characterized in that, The inner wall of the heat pipe shell (1) has an integrated wick structure, wherein the wick structures of the evaporation section (2), the heat insulation section (3) and the condensation section (4) are configured with different roughnesses, so that the first contact angle of the wick structure of the evaporation section (2) to the metal working medium (5) is smaller than the second contact angle of the wick structure of the condensation section (4) to the metal working medium (5), and the third contact angle of the wick structure of the heat insulation section (3) to the metal working medium (5) is between the first contact angle and the second contact angle and gradually increases from the evaporation section (2) to the condensation section (4).

2. The heat pipe of claim 1, wherein, The first contact angle is 10°-20°, and the second contact angle is 120°-130°.

3. The heat pipe of claim 1, wherein, The wick structure adopts a channel or dot array structure.

4. The heat pipe of claim 1, wherein, The material of the heat pipe shell (1) and the wick structure is stainless steel, nickel-based alloy or high-temperature alloy.

5. The heat pipe of claim 1, wherein, The metal working medium (5) is sodium, potassium, lithium or cesium metal.

6. An additive manufacturing method of a heat pipe of claim 1 to 5, wherein, A powder cleaning and vacuum injection pipe (6) is arranged on the heat pipe shell (1) and communicates with the inner cavity thereof; The additive manufacturing method comprises the following steps: S1, design a heat pipe model and import it into an additive manufacturing device, and load additive manufacturing metal powder into a powder supply system of the additive manufacturing device; S2, according to the roughness requirements of the evaporation section (2), the heat insulation section (3) and the condensation section (4) for the wick structure, differentially set the additive manufacturing process parameters of different functional sections of the heat pipe, and integrally form by layer printing with the additive manufacturing device; S3, after printing is completed, the residual un-melted metal powder of the heat pipe sample is removed by a powder cleaning process through the powder cleaning and vacuum injection pipe (6); S4, the heat pipe sample after powder cleaning is washed to remove residual powder, oil stains and other impurities attached to the inner and outer surfaces of the heat pipe sample; S5, the metal working medium (5) is filled into the heat pipe through the powder cleaning and vacuum injection pipe (6), then vacuum is performed, and finally the powder cleaning and vacuum injection pipe (6) is laser sealed and welded in a high vacuum environment to obtain a heat pipe finished product.

7. The additive manufacturing method of claim 6, wherein, In step S2, the additive manufacturing process parameters include laser power, scanning speed, scanning interval and layer thickness; The laser energy density used by the wick structure of the evaporation section (2) is higher than that used by the wick structure of the condensation section (4), and the laser energy density used by the wick structure of the heat insulation section (3) is between that of the evaporation section (2) and that of the condensation section (4); The evaporation section (2) uses smaller scanning interval and higher scanning speed to form a low-roughness surface structure with dense wick surface; the condensation section (4) uses larger scanning interval and lower scanning speed to form a high-roughness surface structure with large feature size; and the heat insulation section uses gradient change printing parameters between the evaporation section (2) and the condensation section (4).

8. The additive manufacturing method of claim 6, wherein, In step S3, the powder cleaning process includes airflow flushing, precise vibration and flexible mechanical intervention.

9. The additive manufacturing method of claim 6, wherein, In step S4, acetone, anhydrous ethanol and deionized water are used in sequence for ultrasonic cleaning.

10. The method of additive manufacturing according to claim 6, wherein, In step S5, the vacuumizing includes: firstly, performing rough vacuumizing, maintaining the pressure in the pipe within a first set value; then, performing high-temperature heating on the heat pipe to realize secondary exhaust, and remove the non-condensable gas in the pipe as much as possible; and continuing vacuumizing, maintaining the pressure in the pipe within a second set value.

Images