CN112129146A

CN112129146A - Directional microchannel and disordered porous composite heat pipe and preparation method thereof

Info

Publication number: CN112129146A
Application number: CN202010853793.7A
Authority: CN
Inventors: 刁开侃
Original assignee: Wuhan Hanwei New Material Technology Co ltd
Current assignee: Wuhan Hanwei New Material Technology Co ltd
Priority date: 2020-08-24
Filing date: 2020-08-24
Publication date: 2020-12-25

Abstract

The invention discloses a directional microchannel and a disordered porous composite heat pipe, wherein the directional microchannel heat pipe comprises an outer pipe and a metal core layer fixedly laid on the inner wall of the outer pipe, the metal core layer is uniformly laid along the axial direction of the outer pipe, a plurality of continuous microchannels penetrating through the whole metal core layer are arranged in the metal core layer along the axial direction of the outer pipe, and a plurality of micropores are formed among the microchannels. The invention also discloses a preparation method of the directional microchannel and the disordered porous composite heat pipe, and the heat pipe is prepared by the steps of pulping, wire embedding, coating, drying, presintering, sintering reduction, final packaging and the like. The invention has simple integral preparation process and lower manufacturing cost, and the prepared capillary core of the heat pipe has continuous micro-channels and micro-holes inside and extremely excellent heat dissipation performance.

Description

Directional microchannel and disordered porous composite heat pipe and preparation method thereof

Technical Field

The invention relates to the technical field of heat pipe heat dissipation, in particular to a directional microchannel and disordered porous composite heat pipe and a preparation method thereof.

Background

The heat pipe (heatpipe) has the heat transfer performance far higher than that of other solid heat transfer materials by utilizing a phase change heat transfer technology, and is widely applied to the industries of aerospace, military industry and the like. With the rapid development of the computer industry, heat pipe heat dissipation is also introduced into the heat sink manufacturing industry in large quantities, especially in the field of microelectronics, so that people change the design idea of the traditional heat sink, get rid of the single heat dissipation mode of obtaining better heat dissipation effect by only depending on a high-air-volume motor, utilize the heat transfer characteristic of the heat pipe material close to superconductivity, solve the problems that the common solid heat transfer and heat dissipation material needs high energy consumption, high-rotating-speed motor assistance, high noise, poor heat dissipation effect and the like, and are widely used in the chip heat dissipation of computers and mobile phones.

The traditional heat pipe consists of a pipe shell, a liquid absorption core and an end cover, wherein phase-change liquid is sealed in the pipe shell and undergoes heat absorption evaporation at a heated end (a heat absorption part contacting a heat source) and heat release condensation at a heat dissipation section (a heat dissipation part far away from the heat source), and the condensed liquid is refluxed to the heated end again through capillary pressure of the liquid absorption core, so that the circulation is carried out, and the efficient heat transfer without external force drive from the heated end to the heat dissipation end is realized. However, the conventional heat pipe has some inherent defects, which limit the promotion of its heat transfer capability and the popularization of its application: first, conventional heat pipes are limited in their orientation and length of use. The capillary core in the common heat pipe is influenced by gravity, and when the capillary pressure cannot overcome the gravity to enable liquid in the condensation section to flow back to a heat source, the heat pipe can be disabled; meanwhile, the heat transfer length of the traditional heat pipe is also limited by capillary pressure, and the traditional heat pipe cannot be used for long-distance heat transfer. Secondly, the gas-liquid contact and the channel sharing in the traditional heat pipe are realized, but the flow directions are opposite, so that the two parts can be subjected to larger resistance when moving directionally, and the heat dissipation performance is seriously influenced. Finally, conventional heat pipes are limited in size and degree of bending, which is not conducive to use in complex installation environments.

As a modification, the loop heat pipe is constituted by an evaporator, a condenser, a reservoir, and vapor and liquid lines. And the vapor and the condensed liquid are separated through the directional gas-liquid channel, and the condensed liquid is pushed to return to the evaporation end again by utilizing the vapor generated by heat absorption, so that circulation and heat transfer are formed. The method overcomes the limitation of the traditional heat pipe, overcomes the influence of gravity and realizes long-distance heat transfer. However, the loop heat pipe has a complex internal structure and high manufacturing cost, and the combination of multiple structures makes the loop heat pipe bulky, which affects the range of the loop heat pipe.

The directional microchannel heat pipe is characterized in that a directional microchannel is designed and prepared in a metal core of a common heat pipe, so that evaporation gas is transmitted to a condensation section through the microchannel in the metal core, gas and liquid in the heat pipe are separated, the gas and liquid flowing resistance is reduced, circulation is accelerated, and an internal directional channel without external force drive is formed. However, the directional microchannel heat pipe in the prior art has limited length due to the limitation of the preparation process, the occupation ratio and distribution of microchannels are difficult to control, the heat dissipation performance is improved limitedly, the preparation process of the heat pipe is complex, and the preparation cost is extremely high.

Disclosure of Invention

The invention provides a directional microchannel and disordered porous composite heat pipe and a preparation method thereof, aiming at least one technical problem in the prior art, the integral preparation process is simple, the manufacturing cost is low, the prepared heat pipe capillary core is internally provided with continuous microchannels and micropores, and the heat dissipation performance is extremely excellent.

The technical scheme for solving the technical problems is as follows: the utility model provides a directional microchannel and porous composite heat pipe of unordered, directional microchannel heat pipe includes the outer tube and fixes the metal core layer of laying on the outer tube inner wall, the metal core layer is evenly laid along the axial direction of outer tube be provided with a plurality of continuous microchannels that link up whole metal core layer along the outer tube axial in the metal core layer, still be provided with a plurality of micropores between a plurality of microchannels.

On the basis of the technical scheme, the invention can be further improved as follows.

Further, the plurality of micro channels are communicated with each other through the micro holes.

Furthermore, the aperture of the micro-channel is 50-1000 μm.

Preferably, the pore diameter of the micro-channel is 100-800 μm.

Furthermore, the volume ratio of the micro-channel accounts for 30-70% of the metal core layer.

Preferably, the volume ratio of the micro-channel accounts for 40-60% of the metal core layer.

Further, the metal core layer is made of a heat-conducting metal material.

Preferably, the metal core layer is made of copper, nickel-based alloy or steel.

Furthermore, the aperture of the micropore is 50-1000 μm.

Preferably, the pore diameter of the micropores is 10-500 μm.

Furthermore, the volume of the micropores accounts for 20-70% of that of the metal core layer.

Preferably, the micropore volume accounts for 30-60% of the metal core layer.

The invention also designs a preparation method of the directional microchannel and the disordered porous composite heat pipe, which comprises the following steps:

s1 preparation of slurry: weighing the components according to the following volume percentage, and uniformly mixing, wherein 20-70% of metal or metal oxide powder, 20-70% of filling powder and 2-15% of binder are used for obtaining slurry;

s2 brushing slurry and filling wire: coating the slurry prepared in the step S1 on filling wires made of thermoplastic polymer materials, and directionally adhering the filling wires to the inner wall of the outer pipe along the direction of the outer pipe, wherein one end of the filling wires coated with the slurry is flush with the port of the outer pipe, and the other end of the filling wires is away from the port of the outer pipe, so that a heat pipe blank is prepared;

s3 drying and forming: drying and shaping the heat pipe blank prepared in the step S2 in the atmosphere to prepare a heat pipe blank;

s4 pre-sintering in atmosphere: pre-sintering the heat pipe blank prepared in the step S3 in an atmospheric environment, and cooling to room temperature after sintering to prepare an oxidized metal core blank with a directional micro-channel;

s5 sintering and reducing: sintering and reducing the oxidized metal core blank with the directional micro-channel prepared in the step S3 in vacuum or reducing atmosphere, and cooling to room temperature after sintering and reducing to prepare a heat pipe body;

s6, filling the phase-change liquid into the heat pipe body prepared in the step S5, and sealing to obtain the directional microchannel heat pipe.

Further, in step S1, the metal or metal oxide powder is a powder of a metal such as copper, nickel-based alloy, or steel, or an oxide powder thereof.

Further, the filler powder is a solid organic powder or an inorganic powder having a vaporization temperature not higher than a pre-sintering temperature, and in step S2, the filler filaments of the thermoplastic polymer material are filler filaments of the thermoplastic polymer material having a vaporization temperature not higher than the pre-sintering temperature.

Further, in the step S1, the metal or metal oxide powder is contained in an amount of 30 to 60% by volume.

Further, in the step S1, the particle size of the metal or metal oxide powder is 20 to 300 μm.

Further, in the step S1, the filling powder is selected from one or more of PLA, PP, acryl or urea.

Further, in the step S1, the filling powder is 30 to 60% by volume.

Further, in the step S1, the filler powder has a particle size of 50 to 1000 μm.

Further, in the step S1, the binder is selected from alcohol, PVA, or vaseline, and the binder is 5 to 10% by volume.

Further, in step S2, the filling filament made of thermoplastic polymer material is a plastic filament made of PLA, PP, or ABS.

Further, in the step S2, the other end of the filling wire coated with the slurry is spaced from an outer pipe port by 1-2 cm, and the outer pipe may be made of a metal material such as copper, nickel-based alloy or steel.

Further, in the step S2, the volume percentage of the slurry and the filling yarn is 30-70% of the slurry and 30-70% of the filling yarn.

Further, in the step S2, the diameter of the filling wire is 50-1000 μm.

Preferably, in step S4, the pre-sintering is performed at a temperature increase rate of 10 ℃ per minute from room temperature to 400 ℃ to 600 ℃ for 1 hour or more.

Preferably, in the step S5, when the sintering reduction is performed in a vacuum atmosphere, the vacuum pressure is less than 10Pa, and the temperature is maintained for 5-7 hours from the room temperature to 800-950 ℃ at a heating rate of 10 ℃ per minute; the sintering reduction is carried out in a reducing atmosphere, the temperature is raised from room temperature to 500-950 ℃ at the rate of temperature rise of 10 ℃ per minute, and the temperature is kept for 0.5-3 h

Preferably, in step S5, when the sintering is performed in a reducing atmosphere, the reducing gas is pure hydrogen or a mixed gas of hydrogen and nitrogen; when the reducing gas is a mixed gas of hydrogen and nitrogen, the content of the hydrogen is 10-70%.

The invention has the following beneficial effects:

1) the heat pipe prepared by the invention has the advantages of no influence of gravity and small gas-liquid flow resistance, and is simple in manufacturing process and low in manufacturing cost.

2) The directional microchannel and the disordered porous composite heat pipe have simple internal structures and long heat transfer distance, solve the problem that other heat pipe materials are limited by using directions, lengths, installation and the like, and have good application prospects in various fields of miniature electronic equipment, solar heat transmission, spacecraft heat transfer and radiation and the like.

3) According to the oriented microchannel and the disordered porous composite heat pipe, the oriented microchannel in the heat pipe is a continuous channel, the proportion and the distribution of the microchannels can be controlled by adjusting the proportion of the filling wires and the coating mode according to the requirements, the heat pipe with densely arranged microchannels can be prepared, the preparation process is very convenient, and the overall heat dissipation performance is extremely excellent.

4) The micro-pores are arranged among the micro-channels, so that the micro-channels can be continuously supplemented with the heat dissipation medium through the micro-pores by utilizing the capillary phenomenon of the capillary pores, dry burning in a heat dissipation area is avoided, and the continuous and stable work of the heat pipe is effectively ensured.

Drawings

FIG. 1 is a schematic structural view of the present invention;

FIG. 2 is a schematic structural view of a metal core layer of the present invention;

FIG. 3 is a schematic cross-sectional view of a metal core layer of the present invention;

FIG. 4 is a schematic view of the phase change heat exchange of the present invention;

FIG. 5 is a microscope photograph of the internal structure of the present invention;

in the drawings, the components represented by the respective reference numerals are listed below:

1. capillary core, 2, micro-channel, 3, outer tube.

Detailed Description

The principles and features of this invention are described below in conjunction with the following drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention.

The gasification in the invention refers to the transformation from solid state to gas state, including physical or chemical transformation such as pyrolysis gasification and sublimation.

As shown in fig. 1 to 5, the directional microchannel and disordered porous composite heat pipe designed by the invention comprises an outer pipe 3 and a metal core layer 1 fixedly laid on the inner wall of the outer pipe. The metal core layer 1 is uniformly laid along the axial direction of the outer tube 3, a plurality of continuous micro-channels 2 penetrating through the whole metal core layer 1 are arranged in the metal core layer 1 along the axial direction of the outer tube, and a plurality of micropores are further arranged among the micro-channels 2.

Preferably, the plurality of microchannels 2 are communicated with each other through micropores.

In a more preferred embodiment of the present invention, the pore diameter of the microchannel 2 is 50 to 1000 μm.

Preferably, the pore diameter of the micro-channel 2 is 100-800 μm.

In a more preferred embodiment of the present invention, the volume ratio of the micro-channel 2 is 30-70% of the metal core layer 1.

Preferably, the volume ratio of the micro-channel 2 is 40-60% of the metal core layer 1.

In a preferred embodiment of the present invention, the metal core layer is made of a heat conductive metal material.

In a more preferred embodiment of the present invention, the pore diameter of the micropores is 50 to 1000 μm.

Preferably, the pore diameter of the micropores is 10-500 μm.

In a more preferred embodiment of the present invention, the volume of the micropores accounts for 20 to 70% of the metal core layer.

Preferably, the micropore volume accounts for 30-60% of the metal core layer.

The metal or metal oxide powder of the present invention may be selected from powders of metals such as copper, nickel-based alloys, or steel, or oxide powders thereof. Copper, which is excellent in thermal conductivity, is preferably used as a material for preparing the outer tube 3. The thermal conductivity of copper in all metals is 403W/mK, 429W/mK second only to silver, and much higher than 237W/mK of aluminum. Whereas the price of copper $ 6.52/kg is only 1.3% of $ 510.71/kg for silver in terms of cost. The choice of copper as the production material is clearly the best choice.

In the heat pipe of the present invention, the metal core layer 1 mainly depends on the heat dissipation medium in the heat pipe to perform phase change heat transfer in the micro-channels 2 of the metal core layer 1, so that the material of the metal core layer 1 does not need to have an excessively high requirement on the heat conductivity of the material. Copper, nickel-based alloy or steel can be adopted, and other metal materials which are low in price and easy to sinter and form can also be adopted.

In the existing heat pipe, the metal core is made of copper or other high heat-conducting metal materials. The heat pipe is characterized in that the metal core of the existing heat pipe is sintered in a powder metallurgy mode or a metal mesh is adopted, the existing heat pipe has a certain specific surface area, a medium can be sucked in through capillary action, and heat is dissipated by means of phase change heat transfer. However, in actual manufacturing, if a metal material with poor thermal conductivity is used, the influence on the heat dissipation performance is large. Therefore, in the art, it is widely believed that the material of the metal core has an influence on the heat dissipation performance of the heat pipe, and when the heat pipe dissipates heat, the metal core itself needs to conduct heat to a certain extent.

The inventor of the invention finds that the heat exchange of the metal core can be ignored when the heat pipe radiates and the radiation can be realized by completely depending on the radiation medium by adopting a specific structure after research and experiments on the invention. The inventor reasonably speculates through experimental data that the existing heat pipe does not have the directional microchannel 2, gas generated by evaporation during phase change heat transfer cannot be discharged directionally, local overheating phenomenon can be formed by local aggregation, and at the moment, a heat dissipation medium in an overheating area is insufficient, so that heat needs to be conducted to other areas through heat conduction of the metal core. The inventor also speculates that although the existing metal core has a certain specific surface area, the internal pores are small and discontinuous, gas is easy to block capillary pores in an evaporation section, a heat dissipation medium cannot enter the evaporation section, cavity areas are formed at local fine positions, and heat of the cavity areas needs to be transferred to other areas through heat conduction of the metal core.

In the heat pipe, the metal core layer 1 is provided with a directional microchannel 2 for exhausting air, and micropores are designed at the same time. The inventor believes that the invention not only increases the specific surface area of the metal core layer 1, but also can increase micropores outside the capillary pores formed by sintering to guide gas and enhance capillary action. Therefore, the generation of the local overheating area and the generation of the cavity area are completely avoided, the heat conduction circulation is formed in the heat pipe by completely utilizing the heat dissipation medium, the dependence on the heat conduction performance of the metal core layer 1 is eliminated, the purpose of preparing the metal core layer 1 by adopting other metal materials with lower cost is realized, and the technical bias of the traditional technology in the field is overcome.

s1, preparing slurry: weighing the components according to the following volume percentage, and uniformly mixing, wherein 20-70% of metal or metal oxide powder, 20-70% of filling powder and 2-15% of binder are used for obtaining slurry;

s2, brushing slurry and filling wires: coating the slurry prepared in the step S1 on a filling wire made of a thermoplastic polymer material, and directionally adhering the filling wire to the inner wall of the outer tube 3 along the axial direction of the outer tube 3, wherein one end of the filling wire coated with the slurry is flush with the port of the outer tube 3, and the other end of the filling wire is away from the port of the outer tube 3, so that a heat pipe blank is prepared;

s3, drying and forming: drying and shaping the heat pipe blank prepared in the step S2 in the atmosphere to prepare a heat pipe blank;

s4, pre-sintering in the atmosphere: pre-sintering the heat pipe blank prepared in the step S3 in an atmospheric environment, and cooling to room temperature after sintering to prepare an oxidized metal core blank with a directional micro-channel;

s5, sintering and reducing: sintering and reducing the oxidized metal core blank with the directional micro-channel prepared in the step S3 in vacuum or reducing atmosphere, and cooling to room temperature after sintering and reducing to prepare a heat pipe body;

s6, filling the phase-change liquid into the heat pipe body prepared in the step S5, and sealing to prepare the directional microchannel heat pipe.

At present, the main preparation methods for preparing the microchannel of the metal core of the directional microchannel heat pipe are metal powder sintering, metal mesh filling, micro milling in the pipe, 3D printing and a metal-gas eutectic directional solidification method. Sintering metal powder and filling metal nets are main preparation methods of heat pipe inner cores, phase-change liquid can flow back to an evaporation section from a condensation section through capillary phenomenon by means of capillary holes in the sintered metal powder or capillary holes among the metal nets, but the two inner cores cause large resistance of gas from the evaporation end to the condensation section, and the phenomenon of dry burning of a heat pipe is caused when the evaporation gas cannot be transmitted to the condensation section in time, so that heat dissipation efficiency is influenced. The micro milling in the pipe can process single layer on the inner surface of the heat pipe, which reduces the resistance of the evaporated gas from the evaporation end to the condensation section, but reduces the relative capillary phenomenon, the condensed liquid returns to the evaporation section mainly by gravity, and the gravity factor must be considered for installation. The metal-gas eutectic directional solidification method can prepare a multi-layer straight microchannel structure in the material, greatly increases the number of channels and the heat dissipation specific surface area, and can control the diameter of the microchannel to a certain extent, but has the defects that the length of the channels is limited, generally not more than 20mm, the channels cannot be arranged in a controllable way, the distribution randomness is large, the port of each channel is closed, and the channels must be separated by using a wire cutting technology before being used as a heat pipe. Moreover, for the heat pipe, the metal core is thin, and an axial micro-channel needs to be formed, and the preparation by the metal-gas eutectic directional solidification method is extremely difficult and extremely high in cost (at present, the method can only be used for preparing the heat pipe). The existing mature 3D printing technology still needs to break through the preparation precision of micropores and microchannels, when the laser 3D printing is used for preparing the microchannels, powder in the microchannels is partially sintered together due to a laser heat affected zone to block the channels, and meanwhile, it is quite difficult to take out the filling metal powder from the microchannels formed after laser cladding. The prior art does not adopt an ablation method to prepare the micro-channel, mainly because the thermoplastic polymer ablation material is gasified basically at 300 ℃, and at the temperature, the metal powder cannot be sintered and molded and can collapse in a sintering furnace.

Although the metal-gas eutectic directional solidification method can theoretically prepare the directional microchannel loop heat pipe, the prepared heat pipe has serious defects. The length of the directional microchannel heat pipe prepared by the method has serious limitation. Due to the principle and existing problems of the metal-gas eutectic directional solidification method, the length of the heat pipe can not exceed 80mm generally. For example, in the case of the "GASAR porous Cu-Cr alloy prepared by metal-hydrogen eutectic directional solidification", the length of the finally prepared micro-channel is about 60mm, and in the case of the "research on preparing lotus-shaped porous metal by metal-hydrogen eutectic directional solidification", the cast ingot prepared by finally taking Mg as a base material is only 40mm high. Although theoretically, the metal core can be prepared in sections by adopting a metal-gas eutectic directional solidification method to prepare the heat pipe, and then the metal core and the heat pipe are spliced into a whole. However, in the preparation process, the position of the holes is difficult to accurately control, so that the micro-channels of the finally prepared metal core have the problem of staggered distribution, the flow of a heat-radiating medium is blocked, unsmooth air exhaust is also caused, and the heat-radiating effect is influenced.

In the present invention, the inventors have found that when pre-sintering, the metal is first oxidized in the presence of oxygen to form an oxide, and at a temperature of 200 ℃ to 300 ℃, weak connection between metal oxide powders is formed, and the blank can maintain its shape without collapsing. The above findings allow the inventors to use ablation to prepare directional microchannel heat pipes. The size, the aperture of the microchannel 2, the volume ratio of the microchannel 2 and the like of the directional microchannel heat pipe prepared by the method can be accurately controlled, even the distribution of the microchannel 2 can be accurately controlled, and the preparation cost and the preparation difficulty are far lower than those of a metal-gas eutectic directional solidification method. Meanwhile, the metal core layer 1 with the directional microchannel 2 can be directly prepared in the outer tube 3 of the heat pipe, which cannot be realized by a metal-gas eutectic directional solidification method.

In a more preferred embodiment, in step S1, the filler powder is a solid organic powder or an inorganic powder having a vaporization temperature equal to or lower than a pre-sintering temperature; in step S2, the thermoplastic polymer material filling yarns are thermoplastic polymer material filling yarns whose vaporization temperature is lower than or equal to the pre-sintering temperature.

In principle, any solid organic or inorganic powder having a vaporization temperature below the pre-sintering temperature, as well as filled filaments of thermoplastic polymer material, can be used in the present invention.

However, considering environmental protection, cost, instantaneous internal pressure during gasification, and other factors, the cost is low in order to ensure better environmental protection, and the instantaneous internal pressure during gasification can ensure a weak bonding force lower than that of the metal oxide powder and can ensure that the metal oxide powder does not collapse during pre-sintering. Thus, the filler powder is preferably selected from one or a combination of more than one of PLA, PP, acryl or urea. The filling silk of the thermoplastic high polymer material is preferably selected from plastic silk of PLA, PP or ABS, etc.

In a more preferred embodiment, in the step S1, the metal or metal oxide powder is 30 to 60 volume%.

In a more preferred embodiment, in the step S1, the filling powder is 30 to 60 volume percent.

The gasifiable powder is mixed into the slurry to prepare the slurry, so that the better slurry can be ensured firstly, and the finally prepared metal core layer 1 belongs to the foamed metal and has more excellent specific surface area. However, it has been found through experimental studies that the strength of the pre-sintered oxidized metal core blank gradually decreases as the content of the metal or metal oxide powder decreases, and when the content of the metal or metal oxide powder is less than 20%, the pre-sintered oxidized metal core blank partially collapses or collapses. Meanwhile, after the heat dissipation performance of the finally manufactured heat pipe is tested, the heat dissipation performance is gradually reduced when the content of the metal or metal oxide powder is gradually increased from 20%, the reduction trend is not uniform, and an inflection point exists at about 70%. When the content of the metal or metal oxide powder is gradually increased from 20% to 70%, the heat dissipation performance is uniformly reduced, and when the content of the metal or metal oxide powder exceeds 70%, the heat dissipation performance is reduced at a very rapid speed. Therefore, the combination of the factors of manufacturing difficulty, heat dissipation performance and cost is considered, and the content of the metal or metal oxide powder is preferably controlled to be 30-60%. The inventor speculates through experimental data that the heat dissipation performance and the content of the metal or metal oxide powder are in the above-mentioned correlation relationship, and should be that when the content of the metal is low, the micro-channels 2 can be better communicated through the micro-pores due to the large number of the micro-pores, the capillary action is strong, and the heat dissipation medium can be rapidly supplemented into the evaporation section; when the content of the metal or metal oxide powder exceeds 70%, the number of micropores between the microchannels 2 is small, the connectivity is also reduced, the efficiency of the heat dissipation medium supplemented by the capillary action is greatly reduced, and therefore the heat dissipation performance is greatly reduced.

In the research process of the invention, the inventor chooses to introduce non-metal powder to prepare the micropores, and the starting point is to increase the specific surface area of the metal core layer 1, increase the specific surface area to improve the evaporation efficiency, obtain more efficient phase change efficiency and improve the heat dissipation performance. The improvement of the heat dissipation efficiency finally obtained is completely unexpected by the inventor. The above-mentioned theories of the present invention, such as the increase of capillary action, are presumed to be based on the rational analysis of experimental data after the inventors have intensively studied based on the completely unexpected technical effects of the present invention.

Correspondingly, the content of the filling powder in percentage by volume is preferably controlled to be 30-60%.

In a more preferred embodiment, in step S1, the binder is preferably selected from alcohol, PVA, or vaseline, and the binder is 5 to 10% by volume. The adhesive has good bonding effect and is easy to remove. When the content of the binder is less than 5%, the bonding effect is extremely poor, and the removal difficulty is increased due to the excessive addition amount of the binder, so that the volume percentage content of the binder is preferably controlled to be 5-10%.

In a more preferred embodiment, in the step S1, the particle size of the metal or metal oxide powder is 20 to 300 μm.

The core of the invention is that the metal oxide powder can generate enough weak binding force when being sintered at low temperature, so as to ensure that other substances except the metal oxide powder can be removed when being pre-sintered, and simultaneously ensure that the oxidized metal core blank cannot collapse. According to the analysis of the experimental research results by the inventors, when the particle size of the powder exceeds 1mm, the heat dissipation performance is poor. The inventors speculate that the powder particles have too large a size, so that large gaps exist among the powder particles during sintering, the size of the gaps exceeds the diameter of the microchannel 2, an effective capillary micropore structure cannot be formed on the microchannel wall, and the solid-liquid contact area and the heat dissipation area of the material are greatly reduced. The inventors reasonably speculate that the solid-liquid contact area and the heat dissipation area have a relatively large correlation with the powder particle size, and that the larger the powder particle size, the smaller the area. The smaller the particle size is, the higher the cost is, and the particle size is preferably controlled to be 20-300 mu m based on the comprehensive consideration of cost and bonding force.

In a more preferred embodiment, in the step S1, the filler powder has a particle size of 50 to 1000 μm.

Preferably, the particle size of the filler powder is 100 to 500 μm.

The particle size can obtain micropores with corresponding pore diameters, and the micropores in the pore diameter range can have better capillary action.

In a more preferred embodiment, in step S2, the other end of the filling wire coated with the slurry is spaced from an end of the outer tube by 1 to 2cm, and the outer tube may be made of a metal material such as copper, nickel-based alloy, or steel.

The heat pipe prepared by the invention can finish the condensation of a heat dissipation medium by reserving a distance of 1-2 cm at the condensation end.

In a more preferred embodiment, in the step S2, the volume percentage of the slurry and the filling yarn is 30 to 70% of the slurry and 30 to 70% of the filling yarn.

In a more preferred embodiment, in the step S2, the diameter of the filler wire is 50 to 1000 μm.

Preferably, the diameter of the filling wire is 100-800 μm.

The larger the content of the filling wires is, the denser the micro-channels are, and the higher the heat dissipation efficiency is. However, it is found through experimental studies that the strength of the pre-sintered oxidized metal core blank is gradually reduced with the increase of the content of the filler wire, and when the content of the filler wire is higher than 70%, the pre-sintered oxidized metal core blank is locally collapsed or collapsed. If the content of the filler wire is too low, the heat dissipation performance is reduced. Therefore, the content of the filler filaments is preferably controlled to be 30 to 70%. Just because the special preparation process of the invention can realize that the micro-channel accounts for more than 60 percent, the preparation of the over-dense micro-channel is difficult to realize by other methods.

And the diameter of the filler wire determines the pore size of the final microchannel. The aperture is too small, the self adhesion of the heat dissipation medium can cause the steam at the evaporation end to be unable to pass through the micro-channel, and the flow rate of the heat dissipation medium can be influenced if the aperture is too large. After comprehensive consideration, the diameter of the filling wire is preferably 50-1000 μm.

In a more preferred embodiment, in step S4, the pre-sintering is performed at a temperature increase rate of 10 ℃ per minute from room temperature to 400 ℃ to 600 ℃ for 1 hour or more.

The core of the invention lies in the pre-sintering step, whether the metal core layer 1 with better quality can be prepared depends on whether the non-metallic oxide material can be completely removed in the pre-sintering process, and the shape of the oxidized metal core blank can be maintained. The control of the presintering temperature is therefore particularly critical and is the core of the invention. After repeated experimental research by the inventor, the oxidized metal core blank with the best quality can be obtained by adopting the better pre-sintering parameters, the impurity removal rate can reach 100%, and meanwhile, the shape can be kept to be 100% intact.

In a more preferred embodiment, in the step S5, when the sintering reduction is performed in a vacuum atmosphere, the vacuum pressure is less than 10Pa, and the temperature is maintained for 5 to 7 hours from the room temperature to 800 to 950 ℃ at a temperature rise rate of 10 ℃ per minute; and when the sintering reduction is carried out in a reducing atmosphere, the temperature is raised from room temperature to 500-950 ℃ at the heating rate of 10 ℃ per minute, and the temperature is kept for 0.5-3 h.

In a more preferred embodiment, in step S5, when the sintering is performed in a reducing atmosphere, the reducing gas is pure hydrogen or a mixed gas of hydrogen and nitrogen; when the reducing gas is a mixed gas of hydrogen and nitrogen, the content of the hydrogen is 10-70%.

In a more preferred embodiment, in step S6, the final step of preparing the heat pipe is as follows: firstly, sealing the heated evaporation end of the heat pipe, then vacuumizing and filling phase-change liquid in the heat pipe, and finally sealing the heated evaporation end of the heat pipe.

Preferably, the phase-change liquid is selected from vaporizable liquids such as distilled water, alcohol, ether and/or ammonia water.

After the vacuum pumping, the heat dissipation medium with a lower boiling point is configured, so that the phase change generation speed in the heat dissipation process can be accelerated, and the heat dissipation efficiency is effectively improved.

The following is a specific embodiment of the invention, the embodiment of the invention completely adopts the metal outer pipe 3, and when the metal core layer 1 is prepared, slurry is coated and a distance of 1-2 cm is reserved between the slurry and the outer pipe port.

Example 1

The embodiment provides a copper heat pipe with a directional microchannel and a disordered porous composite structure

Preparing slurry: weighing copper powder, urea powder and a binder PVA white glue according to the following volume percentage, and uniformly mixing the components, 60 percent of copper powder (with the average particle diameter of 100 mu m), 30 percent of urea powder (with the average particle diameter of 50 mu m) and 10 percent of binder PVA white glue to obtain slurry.

Filling the slurry and filling wires into the heat pipe: filling filaments PLA filaments (diameter 1000 μm) were embedded in the mixed slurry in a directional direction and coated on the inner wall of the outer tube 3. The volume percentages of the size and the filling yarn were as follows, 70% size, 30% filling yarn.

Drying and forming: and filling the slurry and the filling wire into the heat pipe, and drying and solidifying the slurry and the filling wire in the atmosphere to form a blank.

Pre-sintering in the atmosphere: drying the formed blank, placing the blank in a muffle furnace, and preserving heat for one hour from room temperature to 500 ℃ at a heating rate of 10 ℃ per minute in an atmospheric environment, wherein copper powder can be oxidized by heating in an air environment, the oxidized copper powder can form weak connection before the filling material is decomposed, the filling material urea powder and PLA filaments start to be decomposed when the temperature reaches 200 ℃, and a stable copper oxide blank can be formed by preserving heat for one hour at 500 ℃.

Sintering and reducing: reducing the copper oxide blank in vacuum, keeping the temperature of 850 ℃ for 5-7 hours from the room temperature at the temperature rising rate of 10 ℃ per minute with the vacuum pressure of less than 10Pa, and cooling the copper oxide blank to the room temperature along with the furnace.

Sealing the heated evaporation end of the heat pipe, then vacuumizing the heat pipe and filling alcohol, and finally sealing the heated evaporation end of the heat pipe.

The outer pipe 3 of the heat pipe in the embodiment is a copper pipe, the diameter of the directional microchannel of the metal core layer 1 is 1000 μm, the volume ratio of the microchannel is 30%, the average pore size of the disordered porous is 50 μm, and the volume ratio of the disordered porous is 30%.

According to the heat pipe of the embodiment, cooling liquid can be sucked into the metal core layer 1 through the micropores, the cooling liquid is evaporated at the evaporation section, gas is discharged from the directional microchannel 2 to the condensation section in a directional mode, heat is rapidly transferred to a position far away from a heat source, and the heat exchange performance of the heat pipe is greatly enhanced.

Example 2

Preparing slurry: weighing copper oxide powder, PP powder and vaseline serving as a binder according to the following volume percentage, and uniformly mixing the components, wherein the copper oxide powder accounts for 30 percent (the average particle diameter is 20 mu m), the PP powder accounts for 60 percent (the average particle diameter is 100 mu m), and the vaseline accounts for 10 percent to obtain slurry.

Coating the slurry and the filling wire: an ABS filament (800 μm in diameter) as a filler wire was embedded in the mixed slurry in the orientation direction and coated on the inner wall of the outer tube 3. The volume percentages of the size and the filling yarn were as follows, 40% size, 60% filling yarn.

Drying and forming: after the slurry and the filling wire are filled into the outer tube 3, the outer tube is dried and solidified in the atmosphere to form a blank.

Pre-sintering in the atmosphere: and (3) placing the dried and formed blank in a muffle furnace, wherein copper oxide powder can form weak connection under an air ring before the filler material is decomposed, the filler PP powder and the ABS wire start to be decomposed when the temperature reaches above 200 ℃, and the blank is subjected to heat preservation at 500 ℃ for one hour to form a stable copper oxide blank.

Sintering and reducing: and (3) reducing and sintering the copper oxide blank in an atmosphere reducing furnace, wherein the reducing gas is hydrogen content of 50% in hydrogen-nitrogen mixed gas, and the temperature is increased from room temperature to 700 ℃ at a temperature rise rate of 10 ℃ per minute. Keeping the temperature for 2 hours, and then cooling the mixture to room temperature along with the furnace.

And sealing the heated evaporation end of the heat pipe, vacuumizing the heat pipe and filling water into the heat pipe, and finally sealing the heated evaporation end of the heat pipe.

The outer pipe 3 of the heat pipe in this embodiment is a copper pipe, the diameter of the directional microchannel of the metal core layer 1 is 800 μm, the volume ratio of the microchannel is 60%, the average pore size of the disordered porous is 100 μm, and the volume ratio of the disordered porous is 60%.

Example 3

The embodiment provides a nickel-based alloy composite heat pipe with a directional microchannel and a disordered porous composite structure

Preparing slurry: weighing nickel-based alloy or nickel oxide-based alloy powder, acrylic powder and binder alcohol according to the following volume percentage, and uniformly mixing, wherein the slurry is obtained by 70% of nickel-based alloy or nickel oxide-based alloy powder (with the average particle diameter of 500 microns), 20% of acrylic powder (with the average particle diameter of 100 microns) and 10% of binder alcohol.

Filling the slurry and filling wires into the heat pipe: filling filaments PLA filaments (diameter 100 μm) were embedded in the mixed slurry in a directional direction and coated on the inner wall of the outer tube 3. The volume percentages of the size and the filling yarn were as follows, 30% size and 70% filling yarn.

Pre-sintering in the atmosphere: and (2) placing the dried and formed blank in a muffle furnace, wherein the nickel-based alloy or nickel oxide-based alloy powder can form weak connection under an air ring before the filler is decomposed, the filler acrylic powder and the PLA wire start to be decomposed when the temperature reaches 200 ℃, and the stable nickel oxide-based alloy blank can be formed after heat preservation for one hour at 650 ℃.

Sintering and reducing: reducing and sintering the nickel oxide base alloy blank in an atmosphere reducing furnace, wherein the reducing gas is hydrogen, and the temperature is increased from room temperature to 1200 ℃ at the temperature increase speed of 10 ℃ per minute. Keeping the temperature for 1 hour, and then cooling to room temperature along with the furnace.

And sealing the heated evaporation end of the heat pipe, vacuumizing the heat pipe and filling ammonia water in the heat pipe, and finally sealing the heated evaporation end of the heat pipe.

The outer tube 3 of the heat pipe in the embodiment is a nickel-based alloy tube, the diameter of the oriented micro-channel of the metal core layer 1 is 100 μm, the volume ratio of the micro-channel is 70%, the average pore size of disordered pores is 500 μm, and the volume ratio of disordered pores is 20%.

Example 4

The embodiment provides a directional microchannel and disordered porous composite structure steel composite heat pipe

Preparing slurry: weighing steel or oxidized steel powder, urea powder and a binder PVA white glue according to the following volume percentage, and uniformly mixing, wherein 20% of the steel or oxidized steel powder (with the average particle diameter of 300 microns), 70% of the urea powder (with the average particle diameter of 1000 microns) and 10% of the binder PVA white glue to obtain slurry.

Filling the slurry and filling wires into the heat pipe: filling filaments PLA filaments (diameter 50 μm) were embedded in the mixed slurry in a directional direction and coated on the inner wall of the outer tube 3. The volume percentages of the size and the filling yarn were as follows, 60% size, 40% filling yarn.

Pre-sintering in the atmosphere: drying the formed blank, placing the blank in a muffle furnace, forming weak connection between steel or oxidized steel powder under an air ring before the filler is decomposed, decomposing the filler urea powder and PLA filaments when the temperature reaches 200 ℃, and preserving the heat at 650 ℃ for 30 minutes to form a stable oxidized steel blank.

Sintering and reducing: reducing and sintering the oxidized steel blank in an atmosphere reducing furnace, wherein the reducing gas is hydrogen, and the temperature is increased from room temperature to 900 ℃ at the temperature increase speed of 10 ℃ per minute. Keeping the temperature for 2 hours, and then cooling the mixture to room temperature along with the furnace.

The outer pipe 3 of the heat pipe in the embodiment is a steel pipe, the diameter of the directional micro-channel of the metal core layer 1 is 50 μm, the volume ratio of the micro-channel is 40%, the average pore size of disordered pores is 1000 μm, and the volume ratio of disordered pores is 70%.

Example 5

Preparing slurry: weighing copper powder, PLA powder and a binding agent PVA white glue according to the following volume percentage, and uniformly mixing, 40% of copper powder (with the average particle diameter of 150 mu m), 50% of PLA powder (with the average particle diameter of 300 mu m) and 10% of binding agent PVA white glue to obtain slurry.

Filling the slurry and filling wires into the heat pipe: a filler wire PP (500 μm in diameter) was embedded in the mixed slurry in the orientation direction and coated on the inner wall of the outer tube 3. The volume percentages of the size and the filling yarn are as follows, 50% size and 50% filling yarn.

Pre-sintering in the atmosphere: and (2) drying the formed blank, placing the blank in a muffle furnace, and preserving heat for one hour from room temperature to 500 ℃ at a heating rate of 10 ℃ per minute in an atmospheric environment, wherein copper powder can be oxidized by heating in an air environment, the oxidized copper powder can form weak connection before the filling material is decomposed, the filling material PLA powder and PP wire begin to decompose when the temperature reaches 200 ℃, and a stable copper oxide blank can be formed by preserving heat for one hour at 500 ℃.

The outer tube 3 of the heat pipe in this embodiment is a copper tube, and the diameter of the directional microchannel of the metal core layer 1 is 500 μm, the volume ratio of the microchannel is 50%, the average pore size of the disordered porous is 300 μm, and the volume ratio of the disordered porous is 50%.

Example 6

The embodiment provides a copper-zinc alloy composite heat pipe with a directional microchannel and a disordered porous composite structure

Preparing slurry: weighing copper-zinc alloy or copper-zinc oxide alloy powder, PP powder and binder vaseline according to the following volume percentage, and uniformly mixing, wherein 50% of copper-zinc alloy or copper-zinc oxide alloy powder (with the average particle diameter of 180 mu m), 40% of PP powder (with the average particle diameter of 700 mu m) and 10% of binder vaseline are used for obtaining slurry.

Filling the slurry and filling wires into the heat pipe: an ABS filament (diameter 400 μm) as a filler wire was embedded in the mixed slurry in the orientation direction and coated on the inner wall of the outer tube 3. The volume percentages of the size and the filling yarn were as follows, 450% size, 55% filling yarn.

Pre-sintering in the atmosphere: and (3) placing the dried and formed blank in a muffle furnace, wherein the copper-zinc alloy or copper-zinc oxide alloy powder can form weak connection under an air ring before the filler is decomposed, the filler PP powder and the ABS wire start to be decomposed when the temperature reaches 200 ℃, and the stable copper-zinc oxide alloy blank can be formed after heat preservation at 650 ℃ for 30 minutes.

Sintering and reducing: reducing and sintering the copper oxide zinc alloy blank in an atmosphere reducing furnace, wherein the reducing gas is hydrogen, and the temperature is increased from room temperature to 890 ℃ at the temperature rising speed of 10 ℃ per minute. Keeping the temperature for 2.5 hours, and then cooling to room temperature along with the furnace.

The outer tube 3 of the heat pipe in the embodiment is a copper-zinc alloy tube, the diameter of the oriented micro-channel of the metal core layer 1 is 400 μm, the volume ratio of the micro-channel is 55%, the average pore size of disordered pores is 700 μm, and the volume ratio of disordered pores is 40%.

The heat pipes of the existing copper powder sintered core, copper mesh core and inner wall slotted metal core structure mentioned in the background art are taken as comparative examples 1, 2 and 3, the examples 1 and 2 of the invention are taken as examples, the heat dissipation performance of the heat pipes under different power conditions is tested, and the obtained results are shown in table 1.

TABLE 1 different heat pipe heat dispersion parameters table

As can be seen from the results in table 1, in the embodiment of the present invention, due to the special heat dissipation structure of the micro holes cooperating with the micro channels 2, the heat dissipation medium can be efficiently supplemented through the micro holes, and the heat dissipation efficiency is significantly improved by directionally exhausting and dissipating heat through the micro channels 2. Through the parameter comparison result, compared with the prior art, the heat pipe has the advantage that the heat dissipation performance is remarkably improved.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims

1. A directional microchannel and disordered porous composite heat pipe is characterized in that: the directional microchannel heat pipe comprises an outer pipe (3) and a metal core layer (1) fixedly laid on the inner wall of the outer pipe, wherein the metal core layer (1) is uniformly laid along the axial direction of the outer pipe (3), a plurality of continuous microchannels (2) penetrating through the whole metal core layer (1) are axially arranged in the metal core layer (1) along the outer pipe, and a plurality of micropores are formed among the microchannels (2).

2. The micro-channel and disordered porous composite heat pipe of claim 1, wherein: the plurality of micro channels (2) are communicated with each other through micropores.

3. The micro-channel and disordered porous composite heat pipe of claim 1, wherein: the pore diameter of the micro-channel (2) is 50-1000 mu m.

4. A directional microchannel and random porous composite heat pipe as claimed in claim 3, wherein: the pore diameter of the micro-channel (2) is 100-800 mu m.

5. The micro-channel and disordered porous composite heat pipe of claim 1, wherein: the volume ratio of the micro-channel (2) accounts for 30-70% of the metal core layer (1).

6. The micro-channel and disordered porous composite heat pipe of claim 5, wherein: the volume ratio of the micro-channel (2) accounts for 40-60% of the metal core layer (1).

7. The micro-channel and disordered porous composite heat pipe of claim 1, wherein: the metal core layer (1) is made of a heat-conducting metal material.

8. A directional microchannel and random porous composite heat pipe as claimed in claim 7, wherein: the metal core layer (1) is made of copper, nickel-based alloy or steel.

9. The micro-channel and disordered porous composite heat pipe of claim 1, wherein: the aperture of the micropores is 50-1000 mu m.

10. A directional microchannel and random porous composite heat pipe as claimed in claim 9, wherein: the aperture of the micropore is 10-500 mu m.

11. The micro-channel and disordered porous composite heat pipe of claim 1, wherein: the volume of the micropores accounts for 20-70% of that of the metal core layer (1).

12. A directional microchannel and random porous composite heat pipe as set forth in claim 11, wherein: the volume of the micropores accounts for 30-60% of that of the metal core layer (1).

13. A method for preparing the oriented microchannel and disordered porous composite heat pipe according to claims 1 to 12, which is characterized by comprising the following steps:

s2 brushing slurry and filling wire: coating the slurry prepared in the step S1 on a filling wire made of a thermoplastic polymer material, and directionally adhering the filling wire to the inner wall of the outer tube (3) along the direction of the outer tube (3), wherein one end of the filling wire coated with the slurry is flush with the port of the outer tube (3), and the other end of the filling wire is away from the port of the outer tube (3), so that a heat pipe blank is prepared;

14. The method for preparing a directional microchannel and a disordered porous composite heat pipe according to claim 13, wherein: in step S1, the metal or metal oxide powder is a powder of a metal such as copper, nickel-based alloy, or steel, or an oxide powder thereof.

15. The method for preparing a directional microchannel and a disordered porous composite heat pipe according to claim 13, wherein: the filling powder is solid organic powder or inorganic powder with a vaporization temperature below the pre-sintering temperature, and in step S2, the filling filament of the thermoplastic polymer material is a filling filament of a thermoplastic polymer material with a vaporization temperature below the pre-sintering temperature.

16. The method for preparing a directional microchannel and a disordered porous composite heat pipe according to claim 13, wherein: in the step S1, the metal or metal oxide powder is 30 to 60% by volume.

17. The method for preparing a directional microchannel and a disordered porous composite heat pipe according to claim 13, wherein: in the step S1, the particle size of the metal or metal oxide powder is 20 to 300 μm.

18. The method for preparing a directional microchannel and a disordered porous composite heat pipe according to claim 13, wherein: in the step S1, the filling powder is selected from one or more of PLA, PP, acryl or urea.

19. The method for preparing a directional microchannel and a disordered porous composite heat pipe according to claim 13, wherein: in the step S1, the filling powder is 30-60% by volume.

20. The method for preparing a directional microchannel and a disordered porous composite heat pipe according to claim 13, wherein: in the step S1, the particle size of the filler powder is 50 to 1000 μm.

21. The method for preparing a directional microchannel and a disordered porous composite heat pipe according to claim 13, wherein: in the step S1, the binder is selected from alcohol, PVA or vaseline, and the volume percentage content of the binder is 5-10%.

22. The method for preparing a directional microchannel and a disordered porous composite heat pipe according to claim 13, wherein: in the step S2, the filling filament made of thermoplastic polymer material is a plastic filament such as PLA, PP, or ABS.

23. The method for preparing a directional microchannel and a disordered porous composite heat pipe according to claim 13, wherein: in the step S2, the distance of 1-2 cm is reserved between the other end of the filling wire coated with the sizing agent and the port of the outer pipe, and the outer pipe can be made of metal materials such as copper, nickel-based alloy or steel.

24. The method for preparing a directional microchannel and a disordered porous composite heat pipe according to claim 13, wherein: in the step S2, the volume percentage of the slurry and the filling yarns is 30-70% of the slurry and 30-70% of the filling yarns.

25. The method for preparing a directional microchannel and a disordered porous composite heat pipe according to claim 13, wherein: in the step S2, the diameter of the filling wire is 50-1000 μm.

26. The method for preparing a directional microchannel and a disordered porous composite heat pipe according to claim 14, wherein: in the step S4, the pre-sintering is carried out for heat preservation for more than 1h from room temperature to 400-600 ℃ at a heating rate of 10 ℃ per minute.

27. The method for preparing a directional microchannel and a disordered porous composite heat pipe according to claim 14, wherein: in the step S5, when the sintering reduction is carried out in a vacuum atmosphere, the vacuum pressure is less than 10Pa, and the temperature is kept for 5-7 h from the room temperature to 800-950 ℃ at the heating rate of 10 ℃ per minute; and when the sintering reduction is carried out in a reducing atmosphere, the temperature is raised from room temperature to 500-950 ℃ at the heating rate of 10 ℃ per minute, and the temperature is kept for 0.5-3 h.

28. The method of claim 27, wherein the method comprises the steps of: in the step S5, when the sintering reduction is performed in a reducing atmosphere, the reducing gas is pure hydrogen or a mixed gas of hydrogen and nitrogen; when the reducing gas is a mixed gas of hydrogen and nitrogen, the content of the hydrogen is 10-70%.