Porous wick with fractal grooves, preparation method of porous wick and phase change heat transfer device

Abstract

The invention relates to a porous wick with fractal grooves, a preparation method of the porous wick and a phase change heat transfer device, the porous wick comprises a powder sintering type porous matrix and fractal groove structures, the fractal groove structures are formed on the surface or in the porous matrix, and the fractal groove structures are through in the liquid flowing direction of the wick; the preparation method comprises the steps of manufacturing of a fractal filament mold, assembling of the fractal filament mold and a graphite mold, filling of sintering powder, sintering and demolding. The phase change heat transfer device comprises a vapor chamber shell and a porous liquid absorption core fixed to the inner side of the vapor chamber shell. The structural shape of the micro groove in the phase change heat transfer device is optimized, the comprehensive capillary performance of the micro groove-sintered powder composite wick is improved, then the heat transfer performance of the phase change heat transfer device is improved, an improved sintering mold is provided, and the manufacturing cost and the machining difficulty of the wick are reduced.

Description

Technical Field

[0001] The invention belongs to the field of phase-change heat transfer liquid wicks, and in particular relates to a porous liquid wick with fractal grooves, a preparation method thereof, and a phase-change heat transfer device. Background Art

[0002] Phase change heat transfer devices (heat pipes and vapor chambers) have extremely high thermal conductivity and are widely used in the cooling system of high-performance electronic devices. The heat transfer performance of phase change heat transfer devices is mainly limited by the capillary properties of the wick structure and the boiling heat transfer performance. Powder sintered wicks have the advantages of strong capillary force, simple manufacturing process and low cost, and have been widely used in phase change heat transfer devices. However, in the context of the development of ultra-thin and lightweight phase change heat transfer devices, powder sintered wicks made by conventional processes are difficult to meet the requirements of ultra-thin phase change heat transfer devices for high capillary performance of wicks. Therefore, composite wick structures with good capillary properties, such as micro-groove-sintered powder composite wicks and micro-groove-sintered wire mesh composite wicks, have received widespread attention.

[0003] Micro-groove-sintered powder composite absorbent core has the advantages of high permeability, strong capillary performance and light weight, but the existing research lacks the optimization design of the micro-groove structure, and usually adopts a simple linear groove composite sintered powder absorbent core, which limits the further improvement of the comprehensive capillary performance of the micro-groove-sintered powder composite absorbent core. At the same time, the existing micro-groove-sintered powder composite absorbent core usually relies on a sintering mold with a special structure, or is made by wire cutting, laser processing or micro milling, which increases the manufacturing cost and processing difficulty of the absorbent core, limits the structural shape of the groove, and is not conducive to the large-scale application of the micro-groove-sintered powder composite absorbent core. Summary of the invention

[0004] The purpose of the present invention is to provide a porous wick with fractal grooves, a preparation method thereof and a phase change heat transfer device, optimize the structural shape of microgrooves in the phase change heat transfer device, improve the comprehensive capillary performance of the microgroove-sintered powder composite wick, thereby improving the heat transfer performance of the phase change heat transfer device, and propose an improved sintering mold to reduce the manufacturing cost and processing difficulty of the wick.

[0005] In order to achieve the above-mentioned purpose, the first technical solution adopted by the present invention is: a porous liquid-absorbing core with fractal grooves, including a powder sintered porous matrix and a fractal groove structure, wherein the fractal groove structure is formed on the surface or inside of the porous matrix, and both ends of the fractal groove structure are open to the end surface of the porous matrix, and the fractal groove structure is connected in the liquid flow direction of the liquid-absorbing core.

[0006] Furthermore, the porous matrix is ​​formed by sintering metal powder or non-metal powder.

[0007] The second technical solution proposed by the present invention is: a method for preparing a porous liquid-absorbing core having fractal grooves, comprising the following steps: Step 1, using filaments to make a fractal filament mold by repeatedly bending, weaving or splicing; Step 2, preparing a graphite mold, including a graphite plate and an annular graphite groove on the graphite plate, wherein the lower end surfaces of the opposite ends of the annular graphite groove are provided with mold grooves for the two ends of the fractal filament mold to extend out; Step 3, assembling the fractal filament mold and the graphite mold, and the two ends of the fractal filament mold extend out from the mold groove; Step 4: Filling the assembled annular graphite groove with sintered powder to form a porous matrix material layer; Step 5, placing the graphite mold filled with sintering powder in step 4 into a high-temperature atmosphere sintering furnace, sintering in a protective atmosphere, cooling to room temperature with the furnace under the protective atmosphere after sintering, and then taking out the graphite mold from the sintering furnace; Step six, demolding the porous substrate with the fractal filament mold obtained after sintering from the graphite mold, and finally using the exposed parts at both ends of the fractal filament mold to demold and separate it from the porous substrate to obtain the desired porous liquid absorbent core.

[0008] Specifically, in step 1, the material of the filament is selected according to the material of the sintering powder and the sintering temperature, to ensure that during the sintering process, the fractal filament mold can withstand the sintering temperature and does not react with the sintering powder.

[0009] Specifically, in step 1, the shape of the fractal filament mold is a tree-like fractal structure, a Koch fractal structure, a Minkowski fractal structure or a Peano fractal structure, and after the fractal filament mold is manufactured, a release agent is sprayed on its surface.

[0010] As an implementation mode, in step three, the fractal filament mold is placed on the surface of the graphite plate, and then the annular graphite groove is assembled.

[0011] As another embodiment, in step 2, the graphite mold further includes an annular graphite bottom groove, the annular graphite bottom groove is placed on the graphite plate, and the annular graphite groove is stacked on the annular graphite bottom groove.

[0012] Furthermore, in step three and step four, the annular graphite bottom groove is first placed on the graphite plate, and then the bottom layer of sintered powder is filled into it, the filling height is the same as the height of the annular graphite bottom groove, and then the fractal filament mold is placed on the bottom layer of sintered powder, and then the annular graphite groove is stacked on the annular graphite bottom groove, and finally a certain thickness of sintered powder is filled into the annular graphite groove, and the filling thickness completely covers the fractal filament mold.

[0013] As another embodiment, the graphite plate in the graphite mold is replaced by a heat spreader shell.

[0014] The present invention also proposes a third technical solution: a phase change heat transfer device, comprising a heat spreader shell and a porous absorbent core fixed on the inner side of the heat spreader shell, wherein the porous absorbent core adopts the porous absorbent core with fractal grooves described in the first technical solution, or adopts the porous absorbent core with fractal grooves prepared in the second technical solution.

[0015] The beneficial effects of the present invention are as follows: the present invention adopts a fractal micro-groove structure to reduce the flow resistance of the liquid working medium, thereby further enhancing the capillary performance of the micro-groove-powder sintered composite liquid absorbent core; more importantly, the present invention proposes an efficient manufacturing method for the micro-groove-powder sintered composite liquid absorbent core, using repeatedly bent or woven filaments as micro-groove templates, and the micro-groove-powder sintered composite liquid absorbent core can be manufactured by one high-temperature sintering, and even the fractal micro-grooves can be sintered inside the powder liquid absorbent core, thereby achieving the beneficial effects of enhancing the capillary performance of the composite liquid absorbent core and reducing its manufacturing difficulty. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 A schematic diagram of a fractal groove forming mold used in the method for preparing a porous liquid-absorbing core having fractal grooves described in Example 1; Figure 2 This is a schematic structural diagram of a sintering mold used in the method for preparing a porous liquid-absorbing core with fractal grooves described in Example 1; Figure 3 Schematic diagram of the preparation process of the porous liquid absorbent core when the fractal groove is located on the surface of the porous substrate in Example 1; Figure 4 Schematic diagram of the structure of the porous liquid-absorbing core prepared in Example 1; Figure 5 A schematic diagram of the structure of a graphite mold used in the method for preparing a porous liquid-absorbing core having fractal grooves described in Example 2; Figure 6 Schematic diagram of the preparation process of the porous liquid absorbent core when the fractal groove is located inside the porous substrate in Example 2; Figure 7A schematic diagram of a fractal groove forming mold used in the method for preparing a porous liquid-absorbing core having fractal grooves described in Example 3; Markings in the figure: 1, fractal filament mold, 11, primary fractal structure, 111, first straight line segment, 112, first bending segment, 12, secondary fractal structure, 121, second straight line segment, 122, second bending segment, 13, tertiary fractal structure, 131, third straight line segment, 132, third bending segment, 14, quaternary fractal structure; 2. porous base material layer, 21. bottom layer copper powder, 22. upper layer copper powder; 3. graphite mold, 31. graphite plate, 32. annular graphite groove, 321. mold groove, 33. annular graphite bottom groove; 4. Porous wick, 41. Porous matrix, 42. Fractal groove structure. DETAILED DESCRIPTION

[0018] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments, but they are not intended to limit the invention in any way.

[0019] Example 1: Figure 1-4 As shown, a method for preparing a porous liquid-absorbing core having fractal grooves comprises the following steps: Step 1: A fractal filament mold 1 for forming a fractal groove is made by repeatedly bending, weaving or splicing filaments with high strength and good flexibility; Step 2: Take the graphite plate 31 and the annular graphite groove 32 as the graphite mold 3 for sintering, and the lower end surfaces of the opposite ends of the annular graphite groove 32 are provided with mold grooves 321; Step three, such as Figure 3 As shown in (a), the fractal filament mold 1 is placed on the surface of the graphite plate 31; then the annular graphite groove 32 and the graphite plate 31 are assembled to form a graphite mold 3, and during the assembly process, the two ends of the fractal filament mold 1 can pass through the mold groove 321, as shown in FIG. Figure 3 (b) as shown; Step 4: Place sintered powder in the annular graphite groove 32 to form a porous matrix material layer 2, the thickness of the porous matrix material layer 2 is greater than the height of the fractal filament mold 1, such as Figure 3 (c) as shown; Step 5, placing the graphite mold 3 filled with sintering powder in step 4 into a high-temperature atmosphere sintering furnace, sintering in a protective atmosphere, cooling to room temperature with the furnace under the protective atmosphere after sintering, and then taking out the graphite mold 3 from the sintering furnace; Step 6: remove the annular graphite groove 32 to obtain Figure 3(d) shows a porous substrate 41 with a fractal filament mold 1, and the exposed portions at both ends of the fractal filament mold 1 are used to demould and separate it from the porous substrate 41, thereby obtaining Figure 3 (e) and Figure 4 The porous absorbent core 4 shown has a fractal groove structure 42 formed on the surface of the porous absorbent core 4 that matches the shape of the fractal filament mold 1 .

[0020] In step 1, the filaments should be made of a suitable material according to the sintering powder material and the sintering temperature to ensure that the fractal filament mold 1 can withstand the sintering temperature and does not react with the sintering powder during the sintering process. For example, stainless steel, silver, copper, molybdenum and carbon fiber can be selected. In this embodiment, stainless steel wire is selected to make the fractal filament mold 1.

[0021] Furthermore, the structure of the fractal filament mold 1 can be a tree-like fractal structure, a Koch fractal structure, a Minkowski fractal structure, a Peano fractal structure, etc. Figure 1 The tree-like fractal structure shown.

[0022] The following is an explanation of the process of making a fractal filament mold 1 with a tree-like fractal structure using stainless steel wire.

[0023] A fractal filament mold 1 with a tree-like fractal structure is made by folding four stainless steel wires with a diameter of 100 μm in half and then bending them: the total length of the mold is 120 mm, and it is divided into four levels of fractal structures along the length direction, namely, a primary fractal structure 11, a secondary fractal structure 12, a tertiary fractal structure 13, and a fourth fractal structure 14. The first three levels of fractal structures all include straight segments and bending segments. For example, the primary fractal structure 11 includes a first straight segment 111 and a first bending segment 112, the secondary fractal structure 12 includes a second straight segment 121 and a second bending segment 122, and the tertiary fractal structure 13 includes a third straight segment 131 and a third bending segment 132. Among them, the lengths of the first straight segment 111 and the first bending segment 112 are 40 mm and 20 mm respectively, the lengths of the second straight segment 121 and the second bending segment 122, and the lengths of the third straight segment 131 and the third bending segment 132 are all 10 mm, and the fourth fractal structure has only straight segments with a length of 20 mm. The first straight segment 111 of the primary fractal structure 11 is composed of 8 parallel stainless steel wires, and its width is about 800 μm. The first bending segment 112 is composed of 4 parallel stainless steel wires, and its width is about 400 μm. The width of the second straight segment 121 of the secondary fractal structure 12 is half of the width of the first straight segment 111 of the primary fractal structure 11, and the width of the second bending segment 122 of the secondary fractal structure 12 is half of the width of the first bending segment 112 of the primary fractal structure 11; the width of the third straight segment 131 of the tertiary fractal structure 13 is half of the width of the second straight segment 121 of the secondary fractal structure 12, and the width of the third bending segment 132 of the tertiary fractal structure 13 is half of the width of the second bending segment 122 of the secondary fractal structure 12. The above width is achieved by adjusting the number of parallel stainless steel wires. The stainless steel wires are bonded and fixed with 502 glue.

[0024] In this embodiment, four stainless steel wires are folded in half to reduce the number of stainless steel wires used in the fractal filament mold 1, simplify the manufacturing process of the fractal filament mold 1, and facilitate the removal of the fractal filament mold 1 from the porous matrix after sintering.

[0025] In the step 1, after the fractal filament mold 1 is manufactured, a release agent is sprayed on its surface so as to remove the fractal filament mold 1 after high-temperature sintering.

[0026] In the step 2, the thickness of the graphite plate 31 is 5 mm.

[0027] In the step three, the first straight line segment 111 of the primary fractal structure 11 and a portion of the fourth fractal structure 14 in the fractal filament mold 1 of the tree-like fractal structure pass through the mold groove 321 on the lower end surface of the annular graphite groove 32 .

[0028] In step 4, the sintering powder can be made of metal, such as copper, aluminum, and stainless steel, etc.; or non-metal, such as polytetrafluoroethylene, glass, and ceramics, etc. In this embodiment, 250 mesh spherical copper powder is used as the sintering powder, and the porous matrix 41 of the porous liquid wick is formed after sintering. A porous matrix material layer 2 with a thickness of about 0.3 mm is laid in the graphite mold 3.

[0029] In step 5, the protective atmosphere is a mixture of 95% N2 and 5% H2, the sintering temperature is 900°C and the temperature is kept for 30 minutes. When other sintering powder materials are selected, the sintering temperature and the temperature holding time are determined according to the properties of the selected material.

[0030] Example 2: The same fractal filament mold, sintering parameters and copper powder as those in Example 1 were used, and the structural design of the graphite mold was changed to obtain a porous liquid-absorbing core having tree-like fractal micro-grooves inside.

[0031] like Figure 5 As shown, in this embodiment, the graphite mold 3 is adjusted to consist of a graphite plate 31, an annular graphite groove 32 and an annular graphite bottom groove 33, the thickness of the annular graphite bottom groove 33 is 0.3 mm, the circumferential dimension of the annular graphite bottom groove 33 is the same as the circumferential dimension of the annular graphite groove 32, the annular graphite bottom groove 33 is placed on the graphite plate 31, the annular graphite groove 32 is stacked above the annular graphite bottom groove 33, and the inner side surfaces of the annular graphite groove 32 and the annular graphite bottom groove 33 are flush.

[0032] In this embodiment, the preparation method of the porous liquid absorbent core is as follows: Figure 6 As shown: 1. If Figure 6 As shown in (a), the annular graphite bottom groove 33 is first placed on the graphite plate 31, and then a layer of bottom copper powder 21 is laid in the annular graphite bottom groove 33, and the thickness of the bottom copper powder 21 is the same as the height of the annular graphite bottom groove 33; 2. If Figure 6 As shown in (b), the fractal filament mold 1 is placed on the bottom copper powder 21; 3. If Figure 6 As shown in (c), the annular graphite groove 32 is stacked on the annular graphite bottom groove 33, and the first straight line segment 111 of the primary fractal structure 11 of the fractal filament die 1 and a segment of about 10 mm in length of the fourth fractal structure 14 pass through the die groove 321 on the annular graphite groove 32; 4. If Figure 6 As shown in (d), the upper layer of copper powder 22 is filled into the annular graphite groove 32, and the thickness of the upper layer of copper powder 22 filled for the second time is controlled to be 0.3 mm to completely cover the fractal filament mold 1. At this time, the fractal filament mold 1 is located inside the filled copper powder; 5. Sintering and demoulding are performed according to the process of Example 1. The structure of the porous liquid-absorbing core 4 before demoulding of the fractal filament mold 1 is as follows: Figure 6 As shown in (e), the fractal filament mold 1 is pulled out from one end of the four-level fractal structure 14 to obtain a porous liquid-absorbing core 4 with tree-like fractal micro-grooves inside.

[0033] Example 3 The same sintering parameters, copper powder and graphite mold as those in Example 1 were used, the folding method of the fractal filament mold was changed, and a porous liquid-absorbing core with three-dimensional microgrooves was obtained by the preparation method described in Example 1 or Example 2.

[0034] like Figure 7 As shown, the fractal filament mold in this embodiment is obtained by stacking the fractal filament molds described in Example 1, so that the porous absorbent core finally prepared has two layers of micro grooves with tree-like fractal structures.

[0035] Example 4 The porous liquid absorbent core with fractal grooves prepared in Examples 1-3 needs to be fixed on a vapor chamber housing and further packaged when in use to obtain a phase change heat transfer device.

[0036] The difference between this embodiment and embodiment 1 is that a copper vapor chamber shell is used to replace the graphite plate 31 in the graphite mold 3, and the remaining steps are the same as those in embodiment 1. After sintering and demolding, the copper powder particles and the copper vapor chamber shell melt under high temperature and form a sintering neck, thereby forming a porous wick with a fractal groove structure attached to the surface of the copper vapor chamber shell, and the fractal groove structure 42 is located between the copper vapor chamber shell and the porous substrate. This embodiment can omit the step of fixing the porous wick to the vapor chamber shell, simplifying the preparation and assembly process of the phase change heat transfer device.

[0037] Example 5 A phase change heat transfer device comprises a vapor chamber shell and a porous liquid absorbent core fixed inside the vapor chamber shell, wherein the porous liquid absorbent core is the porous liquid absorbent core with fractal grooves prepared in Examples 1-3.

[0038] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Those skilled in the art should understand that the specific implementation modes of the present invention may be modified or replaced by equivalents with reference to the above embodiments. Any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention are within the scope of protection of the pending claims.

Claims

1. A porous absorbent core having fractal grooves, characterized in that: It comprises a powder sintered porous matrix and a fractal groove structure, wherein the fractal groove structure is formed on the surface or inside of the porous matrix, both ends of the fractal groove structure are open to the end surface of the porous matrix, and the fractal groove structure is connected in the flow direction of liquid in the liquid absorbent core.

2. The porous absorbent core with fractal grooves according to claim 1, characterized in that: The porous matrix is ​​formed by sintering metal powder or non-metal powder.

3. A method for preparing a porous liquid-absorbing core having fractal grooves, characterized in that: The steps include: Step 1, using filaments to make a fractal filament mold by repeatedly bending, weaving or splicing; Step 2, preparing a graphite mold, including a graphite plate and an annular graphite groove on the graphite plate, wherein the lower end surfaces of the opposite ends of the annular graphite groove are provided with mold grooves for the two ends of the fractal filament mold to extend out; Step 3, assembling the fractal filament mold and the graphite mold, and the two ends of the fractal filament mold extend out from the mold groove; Step 4: Filling the assembled annular graphite groove with sintered powder to form a porous matrix material layer; Step 5, placing the graphite mold filled with sintering powder in step 4 into a high-temperature atmosphere sintering furnace, sintering in a protective atmosphere, cooling to room temperature with the furnace under the protective atmosphere after sintering, and then taking out the graphite mold from the sintering furnace; Step six, demolding the porous substrate with the fractal filament mold obtained after sintering from the graphite mold, and finally utilizing the exposed parts at both ends of the fractal filament mold to demold and separate it from the porous substrate to obtain the desired porous liquid absorbent core.

4. The method for preparing a porous absorbent core having fractal grooves according to claim 3, characterized in that: In step one, the material of the filament is selected according to the material of the sintering powder and the sintering temperature, so as to ensure that during the sintering process, the fractal filament mold can withstand the sintering temperature and does not react with the sintering powder.

5. The method for preparing a porous liquid-absorbing core having fractal grooves according to claim 3, characterized in that: In step one, the shape of the fractal filament mold is a tree-like fractal structure, a Koch fractal structure, a Minkowski fractal structure or a Peano fractal structure, and after the fractal filament mold is manufactured, a release agent is sprayed on its surface.

6. The method for preparing a porous liquid-absorbing core having fractal grooves according to any one of claims 3 to 5, characterized in that: In step three, the fractal filament mold is placed on the surface of the graphite plate, and then the annular graphite groove is assembled.

7. The method for preparing a porous liquid-absorbing core having fractal grooves according to any one of claims 3 to 5, characterized in that: In step 2, the graphite mold further includes an annular graphite bottom groove, the annular graphite bottom groove is placed on the graphite plate, and the annular graphite groove is stacked on the annular graphite bottom groove.

8. The method for preparing a porous liquid-absorbing core having fractal grooves according to claim 7, characterized in that: In step three and step four, the annular graphite bottom groove is first placed on the graphite plate, and then the bottom layer of sintered powder is filled into it, and the filling height is the same as the height of the annular graphite bottom groove. Then, the fractal filament mold is placed on the bottom layer of sintered powder, and then the annular graphite groove is stacked on the annular graphite bottom groove. Finally, a certain thickness of sintered powder is filled into the annular graphite groove, and the filling thickness completely covers the fractal filament mold.

9. The method for preparing a porous liquid-absorbing core having fractal grooves according to claim 3, characterized in that: The graphite plate in the graphite mold is replaced by a heat spreader shell.

10. A phase change heat transfer device, comprising a vapor chamber housing and a porous liquid wick fixed inside the vapor chamber housing, characterized in that: The porous absorbent core is the porous absorbent core with fractal grooves as claimed in claim 1 or 2, or the porous absorbent core with fractal grooves prepared by any one of claims 3-9.

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