A gradient wetting microstructure that promotes the sustained and stable occurrence of microbubble jet boiling

Abstract

The present invention relates to a gradient wetting microstructure that promotes the continuous and stable occurrence of microbubble jet boiling, belonging to the technical field of heat dissipation structures, comprising: a heat exchange substrate and a plurality of microcolumns, wherein the plurality of microcolumns are fixed on the top surface of the heat exchange substrate in an array, the volume of the plurality of microcolumns gradually increases from the center of the top surface of the heat exchange substrate to the edge of the top surface of the heat exchange substrate, the gap between two adjacent microcolumns is a communicating channel, and the channel width of the plurality of channels gradually increases from the center of the top surface of the heat exchange substrate to the edge of the top surface of the heat exchange substrate, the smoothness of the top surface A of the plurality of microcolumns is greater than the smoothness of the side surface B of the plurality of microcolumns and the plurality of channels, and the wettability of the top surface A of the plurality of microcolumns is less than the wettability of the side surface B of the plurality of microcolumns and the plurality of channels. The above structure utilizes the smoothness of the top surface of the microcolumns and the roughness of the side surface of the microcolumns and the channel surface to form a wettability difference in the vertical direction, significantly enhancing the detachment of the bottom bubble and the formation of the top air film, and in addition, the existence of the wetting gradient promotes the replenishment of the supercooled fluid. The gradient wetting microstructure surface designed in the present invention is conducive to the continuous and stable occurrence of microbubble jet boiling, while reducing the surface temperature and improving the uniformity of the surface temperature.

Description

Technical Field

[0001] The invention relates to the technical field of heat dissipation structures, and in particular to a gradient wetting microstructure that enables microbubble jet boiling to occur continuously and stably. Background Art

[0002] With the rapid increase in the integration and local heat flux of advanced equipment and systems such as semiconductor chips, electric vehicle inverters and fusion reactors, heat dissipation has become one of the important factors restricting their development. Therefore, the demand for more efficient heat dissipation technology is also growing. Boiling heat transfer technology can effectively utilize the latent heat of phase change of the working fluid to achieve efficient heat dissipation and has great potential. Traditional boiling heat transfer mainly relies on the high heat transfer coefficient maintained in the nucleate boiling stage to achieve efficient heat dissipation. Once the heat flux density of the heat source exceeds the critical heat flux density, the boiling state will quickly transform into film boiling, causing the equipment temperature to soar and even burn the device. Therefore, how to avoid boiling deterioration has become the key to effectively and safely utilizing its heat transfer performance.

[0003] Microbubble jet boiling is a special boiling phenomenon that often occurs in the transition boiling stage of supercooled pool boiling. When this phenomenon occurs, a layer of air film that continuously covers the surface and changes periodically in volume will be formed, accompanied by the collapse of the air film in the local area and the ejection of microbubbles, thereby providing a heat exchange capacity several times that of nucleate boiling, and effectively avoiding the occurrence of film boiling. It has good application prospects in the field of heat dissipation of high heat flux devices. However, the conditions for microbubble jet boiling are very harsh, and there are strict requirements on the supercooling degree of the working fluid, surface size, surface structure and wettability. It is generally believed that at a higher supercooling degree (greater than 25K), a small-sized (side length less than 15mm) hydrophilic surface can trigger the microbubble jet boiling phenomenon.

[0004] At present, the research on microbubble jet boiling phenomenon is mostly focused on smooth hydrophilic surfaces, and mainly promotes its occurrence by increasing the supercooling of the working fluid. However, how to stably and continuously trigger microbubble jet boiling is still a difficult problem. Enhancing the replenishment of the supercooled fluid to the surface is one of the keys to solving this problem. In traditional boiling heat transfer technology, modifying the heat exchange surface is an effective method to enhance the surface boiling heat transfer performance and has been widely used.

[0005] Therefore, how to design a gradient wetting microstructure that promotes continuous and stable microbubble jet boiling is an urgent problem to be solved by technicians in this field. Summary of the invention

[0006] The purpose of the present invention is to provide a gradient wetting microstructure hydrophilic surface that promotes the microbubble jet boiling phenomenon to occur continuously and stably, so as to solve the problems of boiling deterioration and insufficient heat exchange performance that are easy to occur in pool boiling heat dissipation technology. Based on the goal of promoting the microbubble jet boiling phenomenon to occur stably and continuously, the present invention improves and optimizes the heat exchange substrate by using a surface modification method. The design of the wettability difference in the vertical direction can effectively reduce the minimum triggering supercooling of the microbubble jet boiling phenomenon, and the wetting gradient that gradually changes from the edge of the heat exchange substrate to the center area can make the occurrence of the microbubble jet boiling phenomenon more stable and continuous; the present invention is particularly suitable for pool boiling high heat flux heat dissipation solutions using microbubble jet boiling, which can improve heat exchange performance while avoiding boiling deterioration.

[0007] The technical solution of the present invention to solve the above technical problems is as follows: a gradient wetting microstructure that promotes continuous and stable microbubble jet boiling, comprising: a heat exchange substrate and a plurality of microcolumns,

[0008] The plurality of micro-pillars are fixed in an array on the top surface of the heat exchange substrate (the top surface of the heat exchange substrate is processed by laser etching to form a plurality of micro-pillars distributed in an array), the volume of the plurality of micro-pillars gradually increases from the center of the top surface of the heat exchange substrate to the edge of the top surface of the heat exchange substrate, the gaps between two adjacent micro-pillars are interconnected grooves, and the groove widths of the plurality of grooves gradually increase from the center of the top surface of the heat exchange substrate to the edge of the top surface of the heat exchange substrate, the smoothness of the top surfaces A of the plurality of micro-pillars is greater than the smoothness of the side surfaces B of the plurality of micro-pillars and the plurality of grooves, and the wettability of the top surfaces A of the plurality of micro-pillars is less than the wettability of the side surfaces B of the plurality of micro-pillars and the plurality of grooves.

[0009] The beneficial effects of the present invention are:

[0010] 1. Designed by Multiple micropillars and multiple grooves distributed in an array can expand the effective heat exchange area under the condition of the same surface size of the heat exchange substrate; at the same time, the smooth micropillar top surface and the rough micropillar side surface and groove form a wettability difference in the vertical direction, which significantly enhances the detachment of the bottom bubbles and the formation of the top air film, which is conducive to the occurrence of microbubble jet boiling;

[0011] 2. Since the volume of multiple micro-columns and the width of multiple grooves gradually increase from the center of the top surface of the heat exchange substrate to the edge of the top surface of the heat exchange substrate, this change in micro-column density obtains a gradient wetting surface, making it easier for the supercooled fluid to be replenished to the central dry area, which is conducive to the continuous and stable occurrence of microbubble jet boiling;

[0012] 3. Compared with ordinary smooth hydrophilic surfaces, the gradient wetting microstructure surface has the advantages of low minimum supercooling when triggering microbubble jet boiling, low surface temperature, and small surface temperature fluctuation;

[0013] 4. By etching micro-pillars and grooves on the heat exchange substrate, the difference in wettability in the vertical direction is obtained. At the same time, a gradient wetting surface is obtained by adopting reasonable micro-pillar and groove sizes that change from the edge of the top surface of the heat exchange substrate to the center, which promotes the growth and detachment of the bottom bubbles and the formation of the top air film, and enhances the replenishment of the supercooled fluid from the edge of the surface to the central area, thereby reducing the minimum supercooling degree of microbubble jet boiling and ensuring its continuous and stable triggering, effectively avoiding the deterioration of surface boiling and improving the heat transfer performance.

[0014] Based on the above technical solution, the present invention can also be improved as follows.

[0015] Furthermore, the size of the heat exchange substrate is less than or equal to 15 mm.

[0016] Furthermore, the plurality of micro-pillars are all prisms.

[0017] Furthermore, the top surfaces and bottom surfaces of the plurality of prism bodies are both square structures.

[0018] Furthermore, the side length a of the top surfaces of the plurality of prism bodies is 0.2-0.4 mm, the side length b of the bottom surfaces is 0.1-0.2 mm, and the height d is 0.032-0.06 mm.

[0019] The above further beneficial effects are: compared with simple square microcolumns, microcolumns with prism structures have larger column spacing, which is more conducive to the replenishment of supercooled fluid to the central area, thereby ensuring the continuous and stable occurrence of microbubble jet boiling; at the same time, because the side of the microcolumn is inclined upward and the formed groove is narrow at the bottom and wide at the top, the growth of small bubbles at the bottom is not restricted, avoiding local overheating caused by large accumulation of bubbles and improving the uniformity of surface temperature distribution.

[0020] Furthermore, the longitudinal sections of the plurality of grooves are all isosceles trapezoidal structures.

[0021] Furthermore, the top groove width c of the plurality of grooves is 0.2-0.4 mm, and the bottom groove width e is 0.1-0.2 mm.

[0022] The further beneficial effect of adopting the above is that the narrow bottom and wide top structure of the groove promotes the growth and separation of small bubbles, while avoiding heat concentration caused by the structure. 。

[0023] Furthermore, the static contact angles of the top surfaces A of the plurality of micropillars are 70° to 100°, and the static contact angles of the side surfaces B of the plurality of micropillars and the static contact angles of the plurality of grooves are both 20° to 30°.

[0024] Furthermore, the static contact angles of the top surfaces A of the plurality of micropillars, the side surfaces B of the plurality of micropillars and the local areas formed by the plurality of grooves gradually increase from the center of the top surface of the heat exchange substrate toward the edge of the top surface of the heat exchange substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of the three-dimensional structure of a gradient wetting microstructure that promotes continuous and stable microbubble jet boiling according to the present invention;

[0026] Figure 2 A schematic diagram of a top view of a gradient wetting microstructure for promoting continuous and stable microbubble jet boiling according to the present invention;

[0027] Figure 3 for Figure 2 A local enlarged structural diagram;

[0028] Figure 4 A schematic diagram of a side view of a gradient wetting microstructure for promoting continuous and stable microbubble jet boiling according to the present invention;

[0029] Figure 5 for Figure 4 A schematic diagram of the local enlarged structure at point B;

[0030] Figure 6 A schematic diagram of bubble growth in each region of a gradient wetting microstructure that promotes continuous and stable microbubble jet boiling according to the present invention;

[0031] Figure 7 A schematic diagram of a heat transfer enhancement process of microbubble jet boiling occurring in a gradient wetting microstructure that causes microbubble jet boiling to occur continuously and stably according to the present invention;

[0032] Figure 8 A schematic diagram of the principle of realizing directional movement of fluid in a gradient wetting microstructure that promotes continuous and stable microbubble jet boiling according to the present invention;

[0033] Fig. 9 This is a schematic diagram of the replenishment of supercooled fluid from the surface edge to the center in a gradient wetting microstructure of the present invention that promotes continuous and stable microbubble jet boiling.

[0034] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0035] 1 is the heat exchange substrate, 2 is the microcolumn, 3 is the top surface A, 4 is the side surface B, 5 is the groove, 6 is the bubble generated at the top of the microcolumn, 7 is the bubble generated at the bottom of the groove, 8 is the bubble generated at the side of the microcolumn, 9 is the bubble covering the groove, the side and top of the microcolumn, 10 is the bubble generated at the side and top of the microcolumn, 11 is the air film covering almost the entire surface, 12 is the collapsed area at the edge of the air film, 13 is the small bubbles sprayed from the edge, 14 is the collapsed area at the top of the air film, 15 is the small bubbles sprayed from the top, 16 is the groove wetted by fluid, 17 is the groove covered by bubbles, and 18 is the droplets on the surface. DETAILED DESCRIPTION

[0036] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0037] like Figure 1 As shown, a gradient wetting microstructure that promotes continuous and stable microbubble jet boiling comprises: a heat exchange substrate 1 and a plurality of microcolumns 2,

[0038] A plurality of micropillars 2 are fixed on the top surface of the heat exchange substrate 1 in an array, and the volume of the plurality of micropillars 2 gradually increases from the center of the top surface of the heat exchange substrate 1 toward the edge of the top surface of the heat exchange substrate 1, the gap between two adjacent micropillars 2 is a communicating groove 5, and the groove width of the plurality of grooves 5 gradually increases from the center of the top surface of the heat exchange substrate 1 toward the edge of the top surface of the heat exchange substrate 1, the smoothness of the top surface A3 of the plurality of micropillars 2 is greater than the smoothness of the side surfaces B4 of the plurality of micropillars 2 and the plurality of grooves 5, and the wettability of the top surface A3 of the plurality of micropillars 2 is less than the wettability of the side surfaces B4 of the plurality of micropillars 2 and the plurality of grooves 5.

[0039] Specifically, the size of the heat exchange substrate 1 is less than or equal to 15 mm.

[0040] Specifically, the plurality of micro-pillars 2 are all prism-shaped.

[0041] In some specific embodiments, the top surfaces and bottom surfaces of the plurality of prism-shaped bodies may both be square structures.

[0042] Specifically, the side length a of the top surfaces of the plurality of prism bodies may be 0.2 to 0.4 mm, the side length b of the bottom surfaces may be 0.1 to 0.2 mm, and the height d may be 0.032 to 0.06 mm.

[0043] Specifically, the longitudinal sections of the plurality of grooves 5 may all be isosceles trapezoidal structures.

[0044] Specifically, the top groove width c of the plurality of grooves 5 may be 0.2-0.4 mm, and the bottom groove width e may be 0.1-0.2 mm.

[0045] Specifically, the static contact angle of the top surface A3 of the plurality of micro-pillars 2 is 70° to 100°, and the static contact angle of the side surface B4 of the plurality of micro-pillars 2 and the static contact angle of the plurality of grooves 5 are both 20° to 30°.

[0046] Specifically, the static contact angles of the local areas formed by the top surfaces A3 of the micropillars 2 , the side surfaces B4 of the micropillars 2 and the grooves 5 all increase gradually from the center of the top surface of the heat exchange substrate 1 toward the edge of the top surface of the heat exchange substrate 1 .

[0047] like Figure 6 As shown, when the gradient wetting microstructure of the present invention that promotes the continuous and stable occurrence of microbubble jet boiling is heated, since the top surface A3 of the microcolumn is less hydrophilic, bubbles 6 are generated earlier in this area, and the bubble volume is smaller and the detachment is slower; then bubbles 7 and 8 appear on the side B4 of the microcolumn and the surface of the channel 5. Since the hydrophilicity of this area is stronger and the cross section of the channel 5 is narrow at the bottom and wide at the top, the generated bubble volume is larger and easier to detach; the bubbles 7 and 8 generated on the side B4 of some microcolumns and the surface of the channel 5 before detachment are aggregated with the bubbles 6 generated on the top surface A3 of the microcolumn to form large bubbles 9 covering a part of the area; the bubbles generated on the side B4 of some microcolumns are aggregated with the bubbles generated on the top surface A3 of the microcolumn during the upward detachment to form bubbles 10. The bubble growth mechanism formed by the difference in wettability in the vertical direction makes it easier for bubbles in the channel to detach, avoiding local overheating, and also facilitates the formation of an air film on the entire surface, thereby promoting the occurrence of microbubble jet boiling.

[0048] like Figure 7 As shown, in a gradient wetting microstructure of the present invention that promotes continuous and stable microbubble jet boiling, when microbubble jet boiling occurs, there is a gas film 11 that almost covers the entire surface, and the gas film oscillates periodically and is accompanied by the collapse of local areas and the ejection of microbubbles; when the edge of the gas film collapses 12, the ejected microbubbles 13 are small in size and fast in speed; when the top of the gas film collapses 14, the ejected microbubbles 15 are large in size and slow in speed; the arrows in the figure show the convection process of the supercooled fluid near the gas film when microbubble jet boiling occurs. Since the edge area is close to the supercooled fluid and the temperature is relatively low, the grooves are mostly in a state of fluid infiltration 16, while the temperature in the central area of ​​the surface is relatively high, the fluid replenishment is relatively slow, and it is more likely to dry out, so that the grooves are covered by bubbles 17.

[0049] like Figure 8 As shown, when the droplet 18 covers part of the surface, the unbalanced surface tension can be written as F d =∫γ(cosθ a -cosθ r )dl, where γ is the surface tension of the droplet, θ a With θ ris the dynamic contact angle, dl is the integral variable along the droplet contact line. Since the surface wettability is better as it approaches the center, the dynamic contact angle is smaller, that is, θ a <θ r , F d >0, the direction of droplet movement is r→a as shown by the arrow, that is, the droplet moves toward the central area.

[0050] like Fig. 9 As shown, in the gradient wetting microstructure of the present invention that promotes continuous and stable microbubble jet boiling, when microbubble jet boiling occurs, drying occurs in the center and other local areas, causing the temperature of some areas to rise. At the same time, the air film covering the surface ejects microbubbles and collapses. At this time, the supercooled fluid is replenished to the edge of the surface, and flows toward the center and other dried-up areas in the direction indicated by the arrow under the action of the wetting gradient, avoiding the occurrence of continuous drying out. At the same time, the air film also expands again, promoting the continuous occurrence of microbubble jet boiling, maintaining a high heat exchange performance and a low surface temperature, and improving the surface temperature uniformity.

[0051] The present invention controls the growth and detachment of regional bubbles through the wettability difference in the vertical direction obtained by physical polishing and laser etching, and at the same time changes the size of the microcolumn 2 and the groove 5 along the surface edge toward the center to promote the replenishment of the supercooled fluid to the burn-dry area.

[0052] Compared with ordinary smooth hydrophilic surfaces, the present invention effectively forms a regionalized bubble growth and detachment mechanism, which promotes the formation of the air film required for microbubble jet boiling while accelerating the bubble detachment rate, which is more conducive to the triggering of microbubble jet boiling, reduces the minimum supercooling threshold for the occurrence of microbubble jet boiling, and avoids the occurrence of boiling deterioration.

[0053] Compared with ordinary structural surfaces, the present invention avoids the occurrence of continuous drying out of some areas, enhances the continuous replenishment of supercooled fluid, thereby ensuring the stable occurrence of microbubble jet boiling, while reducing the occurrence of local overheating areas, maintaining good surface temperature uniformity, and improving heat exchange performance.

[0054] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A gradient wetting microstructure that promotes continuous and stable microbubble jet boiling, characterized in that: include: Heat exchange substrate (1), A plurality of micro-pillars (2), wherein the plurality of micro-pillars (2) are fixed in an array on the top surface of the heat exchange substrate (1), and the volume of the plurality of micro-pillars (2) gradually increases from the center of the top surface of the heat exchange substrate (1) toward the edge of the top surface of the heat exchange substrate (1), the gaps between two adjacent micro-pillars (2) are interconnected grooves (5), and the groove widths of the plurality of grooves (5) gradually increase from the center of the top surface of the heat exchange substrate (1) toward the edge of the top surface of the heat exchange substrate (1), the smoothness of the top surface A (3) of the plurality of micro-pillars (2) is greater than the smoothness of the side surfaces B (4) of the plurality of micro-pillars (2) and the plurality of grooves (5), and the wettability of the top surface A (3) of the plurality of micro-pillars (2) is less than the wettability of the side surfaces B (4) of the plurality of micro-pillars (2) and the plurality of grooves (5); The plurality of micropillars (2) are all prisms; the top and bottom surfaces of the plurality of prisms are all square structures; the side length a of the top surface of the plurality of prisms is 0.1 to 0.2 mm, the side length b of the bottom surface is 0.2 to 0.4 mm, and the height d is 0.032 to 0.06 mm; The size of the heat exchange substrate (1) is less than or equal to 15 mm; the static contact angle of the top surface A (3) of the plurality of micro-pillars (2) is 70° to 100°, and the static contact angle of the side surface B (4) of the plurality of micro-pillars (2) and the static contact angle of the plurality of grooves (5) are both 20° to 30°.

2. The gradient wetting microstructure for promoting continuous and stable microbubble jet boiling according to claim 1, characterized in that: The longitudinal sections of the plurality of grooves (5) are all isosceles trapezoidal structures.

3. The gradient wetting microstructure for promoting continuous and stable microbubble jet boiling according to claim 1, characterized in that: The top groove width c of the plurality of grooves (5) is 0.2-0.4 mm, and the bottom groove width e is 0.1-0.2 mm.

4. The gradient wetting microstructure for promoting continuous and stable microbubble jet boiling according to claim 1, characterized in that: The static contact angles of the local areas formed by the top surfaces A (3) of the plurality of micro-pillars (2), the side surfaces B (4) of the plurality of micro-pillars (2) and the plurality of grooves (5) all gradually increase from the center of the top surface of the heat exchange substrate (1) toward the edge of the top surface of the heat exchange substrate (1).

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