CN111964500B - Method for preparing flexible micro heat pipe by laser-induced reduction sintering of copper oxide ink - Google Patents

Method for preparing flexible micro heat pipe by laser-induced reduction sintering of copper oxide ink Download PDF

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CN111964500B
CN111964500B CN202010653892.0A CN202010653892A CN111964500B CN 111964500 B CN111964500 B CN 111964500B CN 202010653892 A CN202010653892 A CN 202010653892A CN 111964500 B CN111964500 B CN 111964500B
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heat pipe
laser
cuo
preparing
flexible
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CN111964500A (en
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谢小柱
黄亚军
龙江游
任庆磊
张宇梁
张家发
徐美芳
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Guangdong University of Technology
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D15/00—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies
    • F28D15/02—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes
    • F28D15/04—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with tubes having a capillary structure
    • F28D15/046—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with tubes having a capillary structure characterised by the material or the construction of the capillary structure

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  • General Engineering & Computer Science (AREA)
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Abstract

The invention relates to the technical field of heat dissipation of electronic devices, in particular to a method for preparing a flexible micro heat pipe by reducing and sintering copper oxide ink under the induction of laser, which comprises the following steps: s10, preparing CuO nano ink from precursor material CuO NP, dispersing agent PVP and reducing agent EG, wherein mCuO NP：mEG＝1.33～2.28，mCuO NP：mPVP1.85-3.08; s20, spin-coating the CuO nano ink prepared in the step S10 on a polymer substrate film, and drying to obtain a CuO nano coating; s30, inducing the CuO nano coating dried in the step S20 to be reduced and sintered by adopting a femtosecond laser processing system to obtain a Cu array, and rinsing the surface of the polymer substrate membrane to remove the residual CuO NP in the unprocessed area to obtain a flexible liquid absorption core; and S40, packaging to obtain the flexible micro heat pipe. According to the invention, the CuO nano coating is reduced and sintered by adopting the femtosecond laser processing system to obtain the flexible liquid absorption core, so that a Cu array with a loose structure, a small line width and more gaps and holes can be obtained, the Cu array is used as the liquid absorption core to prepare the hot heat pipe, the backflow resistance of liquid in the heat pipe is small, the heat pipe has high heat transfer efficiency, and the heat pipe has good heat conduction performance.

Description

Method for preparing flexible micro heat pipe by laser-induced reduction sintering of copper oxide ink
Technical Field
The invention relates to the technical field of heat dissipation of electronic devices, in particular to a method for preparing a flexible micro heat pipe by reducing and sintering copper oxide ink under the induction of laser.
Background
The development trend of high power, high integration, miniaturization and flexibility of modern electronic equipment puts an urgent need on advanced thermal management materials and thermal management technologies. A heat pipe technology based on gas-liquid phase change is an efficient heat management means, however, the traditional rigid heat pipe cannot meet the high-performance heat dissipation requirements of miniature electronic components and foldable electronic devices with complex structures and narrow spaces. The wick is used as a core component of the heat pipe and determines the heat transfer performance of the micro heat pipe, the wicks commonly used at present comprise a cutting groove type wick, a sintering type wick and a wire mesh type wick, wherein the wick prepared by a cutting and sintering forming processing method cannot be made into a wick with non-linearity, multiple scales and a complex structure, cannot be microscopically controlled in structure and shape, and is difficult to prepare on a flexible substrate; although wicks can be made on flexible substrates using metallic copper mesh or sintered copper powder, the capillary structures obtained therefrom have poor hydrophilic and mechanical properties.
Chinese patent CN104759627A is a method for manufacturing a miniature high-porosity sintered copper heat pipe by using millimeter, micron or nanometer copper oxide powder, which is different from the method for manufacturing the heat pipe by using the required high-porosity sintered copper as a liquid absorption core through adding the copper oxide powder or the copper oxide powder mixed with different particle sizes and performing hydrogen reduction and sintering treatment. Although the method can obtain the liquid absorption core by reduction sintering on the flexible base material, the method has complex process and high manufacturing cost, and is difficult to be suitable for preparing the liquid absorption core of the micro heat pipe; in addition, when the liquid absorption core obtained by the method is used for the micro heat pipe, the hydrophilic performance and the mechanical performance of the capillary structure are poor, and the internal capillary structure is easily damaged when the micro heat pipe is bent, so that the heat transfer performance of the heat pipe is reduced.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides a method for preparing a flexible micro heat pipe by reducing and sintering copper oxide ink under the induction of laser, which can obtain a Cu array with a loose structure, small line width and more gaps and holes, and has the advantages of small backflow resistance of liquid in the heat pipe, high heat transfer efficiency of the heat pipe and good heat conducting property of the heat pipe.
In order to solve the technical problems, the invention adopts the technical scheme that:
the method for preparing the flexible micro heat pipe by reducing and sintering the copper oxide printing ink under the induction of the laser comprises the following steps:
s10, preparing CuO nano ink from precursor material CuO NP, dispersing agent PVP and reducing agent EG, wherein mCuO NP：mEG＝1.33～2.28，mCuO NP：mPVP＝1.85～3.08；
S20, preparing a CuO nano coating: spin-coating the CuO nano ink prepared in the step S10 on a polymer substrate film, and drying to obtain a CuO nano coating;
s30, preparing a flexible liquid absorption core: reducing and sintering the dried CuO nano coating obtained in the step S20 by adopting a femtosecond laser processing system to obtain a Cu array, and rinsing the surface of the polymer substrate film to remove the residual CuO NP in the unprocessed area to obtain a flexible liquid absorption core;
s40, preparing a flexible micro heat pipe: cleaning the polymer flexible membrane and the metal pipe, and packaging the flexible liquid absorption core in the step S30 by using the polymer flexible membrane to obtain the flexible micro heat pipe; the interior of the flexible micro heat pipe is vacuumized by adopting a liquid filling pipe, two ends of the flexible micro heat pipe are connected with metal pipes, and a condensation section of each metal pipe is connected with a condenser.
The invention relates to a method for preparing a flexible micro heat pipe by reducing and sintering copper oxide ink under the induction of laser, which comprises the following steps: the CuO nano coating is reduced and sintered by adopting a femtosecond laser processing system to obtain a flexible liquid absorption core, so that a Cu array which is loose in structure, small in line width and contains a plurality of gaps and holes can be obtained, the Cu array can reduce the backflow resistance of liquid in the heat pipe, improve the heat transfer efficiency and enhance the heat conduction performance of the heat pipe; the femtosecond laser induced reduction sintering is adopted, the process is simple, the control accuracy is high, and the prepared flexible liquid absorption core is suitable for the micro heat pipe; compared with noble metal nanoparticles and Cu nanoparticles, the CuO NP is used as a raw material, so that the production cost can be reduced to a greater extent; the micro heat pipe is endowed with good flexibility by taking the polymer substrate film as a substrate and the polymer flexible film as a packaging material, thereby better realizing the repeatable bending performance and having better practicability; the metal pipe is connected with the evaporation section and the condensation section, so that the thermal resistance between a heat source and the working liquid can be reduced, the thermal resistance of the whole heat dissipation system is reduced, and the heat conduction performance is improved.
Preferably, in step S10, the CuO nanoink is formulated as follows:
s11, under the combined action of heating, magnetic stirring and ultrasonic oscillation, uniformly mixing PVP and EG in batches for multiple times to obtain a dispersing agent solution;
s12, uniformly dispersing the CuO NP in the dispersing agent solution in the step S11 by matching with mechanical vibration, magnetic stirring and ultrasonic oscillation to form the CuO nano ink.
The viscosity of the dispersant solution is controlled to facilitate dispersion of CuO NP when PVP and EG are used to prepare the dispersant solution, and the dispersion mixing method of PVP and EG and the dispersion method of CuO NP are not intended to be limiting, and other dispersion methods that can achieve uniform liquid-liquid dispersion and uniform solid-liquid dispersion may be applied to the present invention. In step S11, heating is performed in a water bath at 45 to 65 ℃ in order to facilitate sufficient mixing of the liquid and the liquid.
Preferably, in step S20, before the CuO nano ink is spin-coated, the surface of the polymer substrate film is subjected to oxygen plasma surface treatment; the polymer substrate film is selected from one of a PET film, a PEN film, a PC film, a PI film, a PES film and a PLLA film, but is not limited to the listed film types. In order to ensure the flatness of the polymer substrate film in the processing process, the surface of the polymer substrate film is subjected to oxygen plasma surface treatment, and after the surface treatment is finished, the CuO nano ink is spin-coated to the polymer substrate film according to the set rotating speed and time.
Preferably, in step S30, the laser parameters adopted by the femtosecond laser induction are: the laser pulse energy is 0.21 nJ-0.24 nJ, the laser scanning speed is 2 mm/s-7 mm/s, the laser scanning frequency is 1 time, and the laser pulse width, the repetition frequency and the laser wavelength are fixed values. The invention can obtain the flexible liquid absorption cores with different porosities, different line widths and complex structures according to the change of laser parameters and the thickness of the CuO nano coating, and has flexible controllability.
Preferably, the laser pulse width is 280fs, the repetition frequency is 76MHz, and the laser wavelength is 1030 nm.
Preferably, in step S30, the laser parameters adopted by the femtosecond laser induction are: the laser pulse energy was 0.21nJ, the laser scanning speed was 2mm/s, and the number of laser scans was 1.
Preferably, in step S30, the surface of the polymer substrate film is rinsed with ethanol and deionized water. CuO NP which is not induced to be reduced and sintered can be separated from the surface of the polymer substrate membrane after being rinsed by ethanol and deionized water.
Preferably, in step S40, the metal tube is placed in an acid solution to be soaked and cleaned to remove the surface oxide layer, then the surface of the metal tube is cleaned with clean water, and the polymer flexible membrane is soaked in a diluted solution of an organic detergent to be cleaned to remove organic stains on the surface. Wherein, the optional metal material that has better ductility and better heat conductivility simultaneously of tubular metal resonator, the optional membrane material that has better flexibility and encapsulation performance simultaneously of polymer flexible membrane.
Preferably, the femtosecond laser processing system includes a femtosecond laser, a first optical path transmission system, a second optical path transmission system, a display module, and a nano moving platform, the CuO nano coating dried in step S20 is sandwiched between the nano moving platform, the first optical path transmission system is disposed between the femtosecond laser and the nano moving platform, guides laser generated by the femtosecond laser to the CuO nano coating, and the second optical path transmission system is disposed between the nano moving platform and the display module.
Preferably, the first optical path transmission system comprises a dichroic mirror for changing the direction of the optical path and a microscope objective for focusing the light beam, and the microscope objective is positioned between the dichroic mirror and the nano moving platform.
Preferably, the second optical path transmission system comprises a reflecting mirror for reflecting the light beam and a CCD camera for imaging, the CCD camera is connected with the display module, and the reflecting mirror is positioned between the CCD camera and the nano moving platform.
Compared with the prior art, the invention has the beneficial effects that:
the method for preparing the flexible micro heat pipe by reducing and sintering the copper oxide ink through laser induction can obtain the Cu array which has a loose structure, small line width, large average capillary suction rate and more gaps and holes, the Cu array is used as a liquid absorption core to prepare the hot heat pipe, the backflow resistance of liquid in the heat pipe is small, the heat pipe heat transfer efficiency is high, and the heat pipe has good heat conduction performance.
Drawings
FIG. 1 is a schematic flow chart of a method for preparing a flexible micro heat pipe by reducing and sintering copper oxide ink under laser induction;
FIG. 2 is a schematic diagram of a femtosecond laser processing system;
FIG. 3 is a schematic representation of Cu array porosity characterization;
FIG. 4 is a schematic representation of Cu array wettability characterization;
FIG. 5 is a schematic structural diagram of a flexible micro heat pipe;
in the drawings: 1-a femtosecond laser; 2-a display module; 3-a nano mobile platform; 4-a dichroic mirror; 5-a microscope objective; 6-a reflector; 7-CCD camera; 8-Cu array; 9-a polymeric substrate film; 10-high molecular flexible membrane.
Detailed Description
The present invention will be further described with reference to the following embodiments.
Example one
Fig. 1 to 4 show an embodiment of a method for preparing a flexible micro heat pipe by laser-induced reduction sintering of copper oxide ink according to the present invention, comprising the following steps:
s10, preparing CuO nano ink from precursor material CuO NP, dispersing agent PVP and reducing agent EG, wherein mCuO NP：mEG＝1.33，mCuO NP：mPVP＝3.07；
S20, preparing a CuO nano coating: spin-coating the CuO nano ink prepared in the step S10 on the polymer substrate film 9, and drying to obtain a CuO nano coating; before the CuO nano ink is coated in a spin mode, oxygen plasma surface treatment is carried out on the surface of the polymer substrate film 9 so as to ensure the surface flatness of the polymer substrate film 9; in addition, when the surface of the polymer substrate film is subjected to oxygen plasma surface treatment, the oxygen plasma and the molecules on the surface of the polymer material directly or indirectly act, so that polar groups can be generated on the molecular chains on the surface of the polymer substrate film, the surface tension is obviously improved, the surface of the polymer substrate film is easy to accept a coating, and the adhesion of a Cu array is increased;
s30, preparing a flexible liquid absorption core: reducing and sintering the dried CuO nano coating in the step S20 by adopting a femtosecond laser processing system to obtain a Cu array 8, and rinsing the surface of the high polymer substrate film by adopting ethanol and deionized water to remove the residual CuO NP in the unprocessed area to obtain a flexible liquid absorption core;
s40, preparing a flexible micro heat pipe: cleaning the polymer flexible film and the metal pipe, and packaging the flexible liquid absorption core obtained in the step S30 by using the polymer flexible film 10 to obtain the flexible micro heat pipe, as shown in FIG. 5; the interior of the flexible micro heat pipe is vacuumized by adopting a liquid filling pipe, two ends of the flexible micro heat pipe are connected with metal pipes, and a condensation section of each metal pipe is connected with a condenser.
In step S10, PVP and EG are mixed evenly in batches for multiple times under the combined action of water bath heating at 50 ℃, magnetic stirring and ultrasonic oscillation to obtain a dispersant solution; and uniformly dispersing the CuO NP in the dispersing agent solution in the step S11 by matching with mechanical vibration, magnetic stirring and ultrasonic oscillation to form the CuO nano ink.
In step S30, the laser parameters adopted for femtosecond laser induction are: the laser pulse energy is 0.21nJ, the laser scanning speed is 2mm/s, the laser scanning times are 1 time, the laser pulse width is 280fs, the repetition frequency is 76MHz, and the laser wavelength is 1030 nm.
The femtosecond laser processing system comprises a femtosecond laser 1, a first optical path transmission system, a second optical path transmission system, a display module 2 and a nanometer moving platform 3, wherein the CuO nanometer coating dried in the step S20 is clamped on the nanometer moving platform 3, the first optical path transmission system is arranged between the femtosecond laser 1 and the nanometer moving platform 3 and guides laser generated by the femtosecond laser 1 to the CuO nanometer coating, and the second optical path transmission system is arranged between the nanometer moving platform 3 and the display module 2. The first optical path transmission system comprises a dichroic mirror 4 for changing the direction of an optical path and a microscope objective 5 for focusing light beams, wherein the microscope objective 5 is positioned between the dichroic mirror 4 and the nano mobile platform 3; the second optical path transmission system comprises a reflecting mirror 6 for reflecting the light beam and a CCD camera 7 for imaging, the CCD camera 7 is connected with the display module 2, and the reflecting mirror 6 is positioned between the CCD camera 7 and the nano moving platform 3. When the method is implemented, the femtosecond laser 1 outputs Gaussian light, the direction of the Gaussian light is changed by the dichroic mirror 4 to be right opposite to the nano moving platform 3, the Gaussian light is transmitted to the microscope objective 5, the microscope objective 5 focuses light beams on the surface of the CuO nano coating, and the CuO nano coating is induced to be reduced and sintered by controlling the heating temperature to form a Cu array; in the process, Cu array graphs of various tracks are prepared by controlling the laser and the nano moving platform 3 together; light rays on the surface of the CuO nano coating are reflected to a CCD camera 7 through a reflector 6 so as to observe the processing condition of the CuO nano coating on line in real time.
In step S40, a copper tube is selected as a metal tube, a polymer PDMS film is selected as a packaging material, and the packaging process can be a chemical bonding, mechanical sealing, or welding connection; when the copper tube is cleaned, the copper tube is soaked in a 10% dilute hydrochloric acid solution, and can also be soaked in other types of acid solutions with other concentrations, and the soaking time is based on completely removing an oxide layer on the surface of the metal; in order to accelerate the cleaning rate, the cleaning process of the embodiment can be matched with ultrasonic oscillation or mechanical stirring and other modes; in order to clean the residual acid solution on the metal surface, the acid solution is cleaned by clean water after the oxide layer is removed and is dried for standby. The surface of the polymer PDMS membrane often adsorbs some organic impurities, in the embodiment, the cleaning time is based on completely removing the organic impurities on the surface in a diluted solution of an organic cleaning agent; in order to accelerate the cleaning rate, the cleaning process of the embodiment can be matched with ultrasonic oscillation or mechanical stirring and other modes; in order to clean the organic solution remained on the surface of the macromolecular PDMS membrane, after organic impurities are removed, the organic solution is cleaned by clean water and dried for standby.
The thermal performance of the heat pipe is determined by the performance of the liquid absorption core, the porosity and the capillary suction rate of the liquid absorption core are increased, and the heat pipe is small in thermal resistance and good in heat transfer performance. Thus, this example tests the Cu array obtained in step S30 for porosity and average capillary suction rate:
when the porosity was measured, the Cu array surface was observed using a SU8010 field emission scanning electron microscope from HIRACHI, and the porosity was calculated using image J. The surface topography of the Cu array of this embodiment is shown in fig. 3, in which fig. 3(a) is a surface topography diagram of a cross-sectional view of the Cu array, fig. 3(b) is a surface topography diagram of an oblique view of the Cu array, and fig. 3(c) is a schematic view of calculating a porosity. As can be seen from fig. 3(a) and 3(b), the Cu array structure is loose and has numerous gaps and holes; from FIG. 3(c), the porosity of the Cu array of this example is 30.22%; the Cu array structure with high porosity can effectively enhance the axial heat transfer capacity of the heat pipe, can reduce the backflow resistance of liquid in the heat pipe by increasing the porosity, can improve the heat transfer efficiency and enhance the heat conduction performance of the heat pipe.
When the average capillary suction rate was measured, this example produced a Cu array 15mm long by 2.4mm wide consisting of 40 Cu wires each having a line width of 11 μm, a height of 17.695 μm and a Cu wire spacing of 50 μm. And (3) performing wettability characterization on the prepared Cu array, specifically: deionized water is selected as a working fluid of the heat pipe, a drop of deionized water is injected into the lowest end of the Cu array in the 3 rd s, the deionized water ascends along the axis at the moment of contacting the Cu array, and reaches the limit position in 8s, and the ascending height is 6.308 mm; throughout the process, the capillary suction rate gradually decreased as the liquid climb height increased, decreasing to zero at 8s, at which time the liquid climb height no longer changed, as shown in fig. 4 (a). The average capillary suction rate can be simply calculated by the ratio of the capillary suction distance to the capillary suction time, and the antigravity average capillary suction rate in this experiment was 1.26 mm/s. The liquid has substantially completely evaporated by 14s, 5s from the start of capillary suction until capillary suction reaches the upper height limit, and 6s from capillary suction until liquid has completely evaporated. At 2.5s, a drop of deionized water was injected into the rightmost end of the Cu array, and the liquid flowed rapidly from right to left along the axis of the Cu array, over a distance of 1mm for 0.6s, as shown in fig. 4(b), the calculated horizontal average capillary suction rate was 1.67mm/s, which was greater than the antigravity average capillary suction rate due to the absence of gravity. As can be seen from the test results, the liquid in the wick obtained in this embodiment has a lower reflux resistance, which can help to improve the thermal conductivity of the heat pipe.
When the micro heat pipe works, the liquid absorption core pumps working fluid on one hand and enables the working fluid to evaporate on the other hand. The wick may remain saturated when the evaporation rate < the capillary suction rate. When the evaporation rate > capillary pumping rate, the working fluid pumped to the wick is less than the working fluid evaporated from the wick, the saturation of the oil wick will decrease. As the saturation of the wick decreases, the evaporation rate decreases while the capillary suction rate increases until they are equal to each other, and then enters a new equilibrium.
Example two
The present embodiment is the same as the first embodiment, except that the femtosecond laser induction adopts laser parameters as follows: the laser pulse energy was 0.21nJ, the laser scanning speed was 5mm/s, and the number of laser scans was 1. The prepared Cu array was tested for porosity and horizontal average capillary suction rate in the same manner as in example one, where the porosity was measured to be 27% and the horizontal average capillary suction rate was 1.45. Therefore, the Cu array obtained under the laser parameters of the embodiment can effectively enhance the axial heat transfer capacity of the heat pipe, reduce the reflux resistance of liquid in the heat pipe, improve the heat transfer efficiency of the heat pipe and enhance the heat conduction performance of the heat pipe.
EXAMPLE III
The present embodiment is the same as the first embodiment, except that the femtosecond laser induction adopts laser parameters as follows: the laser pulse energy was 0.24nJ, the laser scanning speed was 3mm/s, and the number of laser scans was 1. The prepared Cu array was tested for porosity and horizontal average capillary suction rate in the same manner as in example one, where the porosity was measured to be 25% and the horizontal average capillary suction rate was 1.3. Therefore, the Cu array obtained under the laser parameters of the embodiment can effectively enhance the axial heat transfer capacity of the heat pipe, reduce the reflux resistance of liquid in the heat pipe, improve the heat transfer efficiency of the heat pipe and enhance the heat conduction performance of the heat pipe.
Example four
The present embodiment is the same as the first embodiment, except that the femtosecond laser induction adopts laser parameters as follows: the laser pulse energy was 0.24nJ, the laser scanning speed was 7mm/s, and the number of laser scans was 1. The prepared Cu array was tested for porosity and horizontal average capillary suction rate in the same manner as in example one, where the porosity was measured to be 22% and the horizontal average capillary suction rate was 1.15. Therefore, the Cu array obtained under the laser parameters of the embodiment can effectively enhance the axial heat transfer capacity of the heat pipe, reduce the reflux resistance of liquid in the heat pipe, improve the heat transfer efficiency of the heat pipe and enhance the heat conduction performance of the heat pipe.
EXAMPLE five
This embodiment is the same as the first embodiment except that mCuO NP：mEG＝1.48，mCuO NP：mPVP3.08. The prepared Cu array was tested for porosity in the same manner as in example one, which was found to be 28.38%. Therefore, the Cu array obtained under the laser parameters of the embodiment can effectively enhance the axial heat transfer capacity of the heat pipe, reduce the reflux resistance of liquid in the heat pipe, improve the heat transfer efficiency of the heat pipe and enhance the heat conduction performance of the heat pipe.
EXAMPLE six
This embodiment is the same as the first embodiment except that mCuO NP：mEG＝2.28，mCuO NP：mPVP1.85. The prepared Cu array was tested for porosity in the same manner as in example one, and the porosity measured in this example was 26.05%. Therefore, the Cu array obtained under the laser parameters of the embodiment can effectively enhance the axial heat transfer capacity of the heat pipe, reduce the reflux resistance of liquid in the heat pipe, improve the heat transfer efficiency of the heat pipe and enhance the heat conduction performance of the heat pipe.
Comparative example 1
The comparative example is the same as the first example, except that the femtosecond laser induction adopts laser parameters as follows: the laser pulse energy was 0.17nJ, the laser scanning speed was 15mm/s, and the number of laser scans was 1. The prepared Cu array was tested for porosity and horizontal average capillary suction rate in the same manner as in example one, which measured 9.89% porosity and 0.35 horizontal average capillary suction rate. It can be seen that, under the laser parameters selected in this comparative example, the porosity of the Cu array is small, the improvement of the heat transfer capability of the heat pipe is limited, and the performance of the Cu array is more suitable for being used as a Cu circuit and not suitable for being used as a wick and manufacturing the heat pipe.
Comparative example No. two
This comparative example is the same as example one except that mCuO NP：mEG＝0.68，mCuO NP：mPVP18.5. The prepared Cu array was tested for porosity in the same manner as in example one, and the porosity measured in this example was 13.1%. Therefore, under the condition of the composition ratio of the CuO nano ink selected in the comparative example, the porosity of the Cu array is small, the improvement on the heat transfer capacity of the heat pipe is limited, and the performance of the Cu array is more suitable for being used as a Cu circuit and is not suitable for being used as a wick and manufacturing the heat pipe.
It should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.

Claims (9)

1. The method for preparing the flexible micro heat pipe by reducing and sintering the copper oxide printing ink under the induction of the laser is characterized by comprising the following steps of:
s10, preparing CuO nano ink from precursor material CuO NP, dispersing agent PVP and reducing agent EG, wherein mCuONP：mEG＝1.33～2.28，mCuONP：mPVP＝1.85～3.08；
S20, preparing a CuO nano coating: spin-coating the CuO nano ink prepared in the step S10 on a polymer substrate film, and drying to obtain a CuO nano coating;
s30, preparing a flexible liquid absorption core: reducing and sintering the dried CuO nano coating obtained in the step S20 by adopting a femtosecond laser processing system to obtain a Cu array, and rinsing the surface of the polymer substrate film to remove the residual CuO NP in the unprocessed area to obtain a flexible liquid absorption core; the femtosecond laser induction adopts laser parameters as follows: the laser pulse energy is 0.21 nJ-0.24 nJ, the laser scanning speed is 2 mm/s-7 mm/s, the laser scanning frequency is 1 time, and the laser pulse width, the repetition frequency and the laser wavelength are fixed values;
s40, preparing a flexible micro heat pipe: cleaning the polymer flexible membrane and the metal pipe, and packaging the flexible liquid absorption core in the step S30 by using the polymer flexible membrane to obtain the flexible micro heat pipe; the interior of the flexible micro heat pipe is vacuumized by adopting a liquid filling pipe, two ends of the flexible micro heat pipe are connected with metal pipes, and a condensation section of each metal pipe is connected with a condenser.
2. The method for preparing a flexible micro heat pipe by laser-induced reduction sintering of copper oxide ink according to claim 1, wherein in step S10, CuO nano ink is prepared according to the following steps:
s11, under the combined action of heating, magnetic stirring and ultrasonic oscillation, uniformly mixing PVP and EG in batches for multiple times to obtain a dispersing agent solution;
s12, uniformly dispersing the CuO NP in the dispersing agent solution in the step S11 by matching with mechanical vibration, magnetic stirring and ultrasonic oscillation to form the CuO nano ink.
3. The method for preparing a flexible micro heat pipe by laser-induced reduction sintering of copper oxide ink according to claim 1, wherein in step S20, before the coating of CuO nano ink, the surface of the polymer substrate film is subjected to oxygen plasma surface treatment; the polymer substrate film is selected from one of a PET film, a PEN film, a PC film, a PI film, a PES film and a PLLA film.
4. The method for preparing a flexible micro heat pipe by laser-induced reduction sintering of copper oxide ink according to claim 1, wherein the pulse width of the laser is 280fs, the repetition frequency is 76MHz, and the wavelength of the laser is 1030 nm.
5. The method for preparing a flexible micro heat pipe by laser-induced reduction sintering of copper oxide ink according to claim 1, wherein in step S30, the surface of the polymer substrate film is rinsed with ethanol and deionized water.
6. The method for preparing a flexible micro heat pipe by laser-induced reduction sintering of copper oxide ink according to claim 1, wherein in step S40, the metal pipe is immersed in an acid solution to clean and remove a surface oxide layer, then the surface of the metal pipe is cleaned with clean water, and the polymer flexible film is immersed in a diluted solution of an organic cleaning agent to clean and remove organic stains on the surface.
7. The method for preparing a flexible micro heat pipe by laser-induced reduction sintering of copper oxide ink according to any one of claims 1 to 6, wherein the femtosecond laser processing system comprises a femtosecond laser, a first optical path transmission system, a second optical path transmission system, a display module and a nano moving platform, the CuO nano coating dried in the step S20 is clamped on the nano moving platform, the first optical path transmission system is arranged between the femtosecond laser and the nano moving platform and guides laser generated by the femtosecond laser to the CuO nano coating, and the second optical path transmission system is arranged between the nano moving platform and the display module.
8. The method for preparing the flexible micro heat pipe by using the copper oxide ink through laser-induced reduction sintering according to claim 7, wherein the first optical path transmission system comprises a dichroic mirror for changing the direction of the optical path and a microscope objective for focusing the light beam, and the microscope objective is positioned between the dichroic mirror and the nano moving platform.
9. The method for preparing the flexible micro heat pipe by laser-induced reduction sintering of the copper oxide ink according to claim 8, wherein the second optical path transmission system comprises a reflector for reflecting the light beam and a CCD camera for imaging, the CCD camera is connected with the display module, and the reflector is positioned between the CCD camera and the nano moving platform.
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