An inverted composite wettability micro-cross pedestal structured surface for enhanced condensation heat transfer

Abstract

The present invention discloses an inverted composite wettability micro-cross pedestal structured surface for enhancing condensation heat transfer, which belongs to the field of enhancing condensation heat transfer. The present invention includes a cooling substrate and a micro-cross pedestal array thereon, wherein a plurality of grooves are formed between adjacent micro-cross pedestals; in addition, the top surface of each micro-cross pedestal is hydrophilic, and the side wall surface and the groove surface of the micro-cross pedestal are hydrophobic. The condensation heat transfer enhancement mechanism of the present invention is as follows: the hydrophilic top surface of the micro-cross pedestal preferentially condenses and nucleates, and the nucleated droplets quickly merge with the condensed droplets at the concave corners of the micro-cross pedestal side wall and then slide toward the top surface, promoting the detachment of the condensed droplets on the top surface, while the hydrophobic grooves effectively delay the accumulation of the condensed droplets into a liquid film on the cooling substrate. The surface makes full use of the synergistic effect of the composite wettability and the micro-cross pedestal structure to achieve an increase in the condensation nucleation density and the liquid shedding frequency, thereby enhancing the condensation heat transfer efficiency of the surface.

Description

Technical Field

[0001] The present invention relates to the technical field of enhanced condensation heat transfer, and more particularly to an inverted composite wettability micro-cross pillar structured surface for enhanced condensation heat transfer. Background Art

[0002] As electronic components become increasingly powerful and miniaturized, the heat flux density on their local surfaces increases dramatically. The resulting heat dissipation issues severely impact the stability, reliability, and operating life of electronic devices, becoming a bottleneck restricting their technological development. The condensation heat transfer process can release a large amount of latent heat under very small temperature differences, exponentially increasing the heat transfer performance of the heat transfer area and offering significant advantages in heat transfer technology.

[0003] In recent years, researchers at home and abroad have discovered that the condensation heat transfer performance of a surface can be enhanced by modifying the condensation surface. Modifying the hydrophilicity and microstructural characteristics of the condensation surface is a major approach and has broad application prospects. The condensation process produces a large number of droplets. When these droplets aggregate on a large scale during growth and cannot detach from the condensation surface in time, film condensation occurs. In the film condensation mode, the liquid film covering the condensation surface produces a large heat transfer resistance, which deteriorates the condensation heat transfer.

[0004] However, by rationally modifying the condensation surface, the condensation process can be maintained in a beaded condensation mode, where the droplet dynamics include growth, movement, coalescence, and shedding. Nucleation and growth of a large number of condensed droplets releases a large amount of latent heat of vaporization, and the heat transfer coefficient can be increased several times compared to film condensation. Therefore, how to rationally utilize the two surface properties of hydrophilicity and microstructure to maintain a continuous beaded condensation mode, and on this basis, further increase the condensation nucleation density and accelerate the droplet shedding frequency, has become the key to promoting the large-scale and efficient application of condensation surfaces. Summary of the Invention

[0005] The purpose of the present invention is to provide an inverted composite wettability micro-cross pedestal structured surface that can fully utilize the synergistic effect of composite wettability and micro-cross pedestal structure, improve the nucleation density of beaded condensation, increase the frequency of condensation droplet shedding, and effectively avoid the "flooding" phenomenon of the liquid film, thereby realizing the synergistic enhancement of condensation heat transfer and enhancing condensation heat transfer.

[0006] To achieve the above objectives, the present invention adopts a technical solution that includes a cooling substrate and a plurality of micro-cross pedestals arranged in an array on the surface of the cooling substrate, wherein a series of groove surfaces are formed between adjacent micro-cross pedestals; a hydrophobic surface layer is provided on the groove surfaces and all micro-cross pedestal sidewall surfaces of each micro-cross pedestal, and a hydrophilic surface layer is provided on the top surface of each micro-cross pedestal.

[0007] The central cross section of the top surface of the micro cross pedestal is a symmetrical plane, and the structural dimensions of each micro cross pedestal are the same.

[0008] The short side length of the micro cross pedestal is a, a=0.4-0.8 mm; the long side length of the micro cross pedestal is b, b=2.6a-3.4a; and the height of the micro cross pedestal is c, c=0.8-2.5 mm.

[0009] The groove surfaces are interconnected, and the narrowest spacing d of each micro-cross column is the same, d=0.8b~1.2b.

[0010] The static contact angles of the hydrophobic surface on the surface of the channel and the sidewall surfaces of all micro-cross pedestals of each micro-cross pedestal are the same.

[0011] The static contact angle is 110 degrees to 140 degrees.

[0012] The static contact angle of the hydrophilic surface layer is 30 degrees to 70 degrees.

[0013] Compared with the prior art, the present invention has the following beneficial technical effects:

[0014] The present invention fully utilizes the synergistic effects of composite wettability and microstructure to enhance condensation heat transfer. First, the hydrophilic top surface of the micro-cross pedestal with higher surface energy can reduce the energy barrier for condensation nucleation, thereby increasing the density of condensation nucleations on the top surface. Simultaneously, the structural effect of the concave angles on the sidewalls of the micro-cross pedestal can also reduce the energy barrier for condensation nucleation, further increasing the density of condensation nucleations on the surface. The large number of condensation droplets nucleated on the surface releases a large amount of latent heat of vaporization during the nucleation process, effectively increasing the amount of heat dissipated during the condensation process.

[0015] Secondly, the dynamic characteristics of the droplets on the micro-cross pedestal can significantly improve the frequency of droplet renewal on the condensation surface. The condensed droplets nucleate and grow on the hydrophilic top surface of the micro-cross pedestal. The growing droplets quickly merge with the condensed droplets at the concave corners of the micro-cross pedestal side walls and then slide to the top surface of the pedestal. At this time, the droplets have reached the droplet detachment radius and detach quickly. In addition, the cross-shaped top surface of the micro-pedestal can weaken the influence of the "pinning" effect of the three-phase contact line on the residual droplets during the droplet detachment stage, reducing the heat transfer resistance of the residual droplet attachment area. The above droplet dynamic behavior accelerates the droplets to reach the detachment size, increases the droplet shedding frequency, effectively refreshes the condensation surface, and thus achieves the enhancement of condensation heat transfer.

[0016] Furthermore, the hydrophobic channel surface, with its low surface energy, has a large condensation nucleation barrier, making it difficult for condensation nucleation to occur. The hydrophobic channel can effectively prevent the coalescence of condensate droplets at adjacent sidewall corners and significantly delay the accumulation of droplets into a liquid film. Therefore, the design of the hydrophobic channel surface enables the continuous maintenance of an efficient bead-like condensation pattern on the cooling substrate, achieving a synergistic enhancement of condensation heat transfer.

[0017] In addition, the microstructure modified surface of the present invention can be achieved through common commercial processing methods, is easy to operate and has the ability to be mass-produced, and has high industrialization potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 3D structural diagram of the inverted composite wettability micro-cross pedestal of the present invention;

[0019] Figure 2 It is a bottom view of the present invention;

[0020] Figure 3 is a side view of the present invention;

[0021] Figure 4 Schematic diagram of droplet growth on a single micro-cross pedestal of the present invention;

[0022] Figure 5 Schematic diagram of droplet merging on a single micro-cross column platform of the present invention;

[0023] Figure 6 Schematic diagram of a single micro-cross column platform of the present invention where a droplet is about to detach;

[0024] Among them, 1-cooling substrate; 2-micro cross pedestal; 3-groove surface; 4-side wall surface of micro cross pedestal; 5-top surface of micro cross pedestal; 6-side wall concave corner of micro cross pedestal; 7-top surface nucleated droplets; 8-side wall nucleated droplets; 9-merged droplets; 10-droplets about to detach. DETAILED DESCRIPTION

[0025] In order to make the technical solutions, objectives and advantages of the present invention more clear and explicit, the present invention is further described below with reference to the accompanying drawings and specific working processes.

[0026] See also Figure 1 The present invention includes a cooling substrate 1 and a plurality of micro-cross pedestals 2 arranged in an array on the cooling substrate 1. A plurality of groove surfaces 3 are formed between adjacent micro-cross pedestals 2. A hydrophobic surface layer is provided on each groove surface 3 and each micro-cross pedestal side wall surface 4 by a chemical modification method, and the static contact angles thereof are all 110 to 140 degrees. A hydrophilic surface layer is provided on the top surface 5 of each micro-cross pedestal, and the static contact angle thereof is 30 to 70 degrees.

[0027] See also Figure 2 and Figure 3 The micro-cross pedestal 2 and the groove surface 3 of the present invention are processed on the copper surface by micro-milling or wire cutting, and have the same structural dimensions. The short side length of each micro-cross pedestal 2 is a, a=0.4~0.8mm; the long side length is b, b=2.6a~3.4a; the height is c, c=0.8~2.5mm; the grooves formed between each micro-cross pedestal are interconnected, and the narrowest spacing is equal, both d, d=0.8b~1.2b.

[0028] The following combination Figure 4 、 Figure 5 and Figure 6 The specific working process of the present invention is described in detail:

[0029] When the present invention is working normally, the condensation nucleation points are mainly distributed at the top surface 5 of the micro-cross pedestal and the concave corners 6 of the side walls of the micro-cross pedestal.

[0030] See also Figure 4 When the substrate of the present invention is cooled, since the top surface 5 of the micro-cross pedestal is a hydrophilic surface and the condensation nucleation energy barrier is low, the top surface 5 of the micro-cross pedestal is condensed and nucleated first, and top surface nucleation droplets 7 are generated on its surface; then, due to the structural effect, the condensation nucleation energy barrier is reduced at the side wall concave corner 6 of the micro-cross pedestal, and condensation nucleation also occurs, and a number of side wall concave corner nucleation droplets 8 are generated at the side wall concave corner 6 of the micro-cross pedestal. For the top surface nucleation droplets 7 generated at the top surface 5 of the micro-cross pedestal, the top surface nucleation droplets 7 continue to grow until the three-phase contact line is pinned to the edge of the top surface 5 of the micro-cross pedestal. At the same time, a number of side wall concave corner nucleation droplets 8 at the side wall concave corner 6 of the micro-cross pedestal also grow rapidly until they contact with the top surface nucleation droplet 7 and coalesce to form coalesced droplets 9. See. Figure 5 Under the combined action of gravity and surface tension, the coalesced droplets 9 gradually slide downward until they detach from the cooling substrate 1 and converge on the top surface 5 of the micro-cross pedestal. Then, the three-phase contact line undergoes a "pinning-depinning" dynamic behavior. Figure 6 The coalesced droplet 9 has reached the droplet breakaway radius, gradually forming a droplet neck. This neck tapers over time, forming a droplet 10 on the verge of breakaway. Subsequently, the droplet 10 detaches from the top surface 5 of the micro-cross pedestal and begins to drip. Ultimately, a seed droplet remains on the top surface 5 of the micro-cross pedestal. It condenses again at the concave corner 6 of the micro-cross pedestal's sidewall, forming a nucleus and rapidly growing, thus entering the next cycle of "nucleation-growth-coalescence-breakaway-nucleation."

[0031] The present invention controls the structural dimensions and wettability of the micro-cross pedestal 2, allowing the top surface 5 of the micro-cross pedestal to preferentially condense and nucleate. The growing droplets gather and pull several condensed droplets at the concave corners 6 of the micro-cross pedestal to the top surface 5 of the micro-cross pedestal. These coalesced droplets 9 have reached their detachment radius and detached. Simultaneously, the hydrophobic channel surface 3 effectively prevents the accumulation of condensed droplets on the substrate into a liquid film. Compared to a composite wettability flat surface, the present invention increases the number of condensation nucleation points at the concave corners of the micro-cross pedestal's sidewalls, effectively increasing the condensation nucleation density through structural effects, significantly reducing the droplet detachment time, and achieving a significant increase in the latent heat of vaporization release and droplet drip rate. Compared to the composite wettability square pedestal surface, the concave corners of the micro-cross pedestal's sidewalls have lower condensation nucleation barriers, longer droplet three-phase contact lines, and faster coalescence and detachment dynamics than the sidewall edges of the micro-square pedestal. The cross-shaped top surface of the micro-cross pedestal also weakens the "pinning" effect of the three-phase contact line on residual droplets during the droplet detachment phase, resulting in a lower thermal resistance to residual droplet heat transfer. As a result, the present invention increases the amount of droplet condensation within a single cycle and shortens the droplet dripping period, effectively improving the droplet dripping rate and condensation heat transfer coefficient.

[0032] This invention leverages the synergistic effects of composite wettability and microstructure to increase condensation nucleation density, extend the length of the droplet three-phase contact line, accelerate the droplet coalescence and detachment process, and increase the droplet shedding frequency. This effectively refreshes the condensation surface, preventing droplet accumulation and film formation on the condensation surface, thereby enhancing condensation heat transfer. The invention boasts a simple structure, ease of fabrication, and reliable operating principle, and is widely applicable to microscale heat transfer applications such as electronic component cooling, demonstrating promising application prospects.

[0033] The present invention and its embodiments are described schematically above, and this description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by this and, without departing from the purpose of the present invention, designs structures and embodiments similar to this technical solution without inventive means, they shall fall within the scope of protection of the present invention.

Claims

1. An inverted composite wettability micro-cross pedestal structured surface for enhancing condensation heat transfer, characterized by: The invention comprises a cooling substrate (1) and a plurality of micro-cross pedestals (2) distributed on the surface of the cooling substrate (1) and arranged in an array form, wherein a series of channel surfaces (3) are formed between adjacent micro-cross pedestals (2); a hydrophobic surface layer having the same static contact angle is provided on the channel surface (3) and all micro-cross pedestal sidewall surfaces (4) of each micro-cross pedestal (2), wherein the static contact angle is 110 to 140 degrees; and a hydrophilic surface layer is provided on the top surface (5) of each micro-cross pedestal, wherein the static contact angle is 30 to 70 degrees.

2. The inverted composite wettability micro-cross pedestal structured surface for enhancing condensation heat transfer according to claim 1, characterized in that: The central cross section of the top surface (5) of the micro-cross pedestal is a symmetrical plane, and the structural dimensions of each micro-cross pedestal (2) are the same.

3. The inverted composite wettability micro-cross pedestal structured surface for enhancing condensation heat transfer according to claim 1, characterized in that: The short side length of the micro cross column (2) is a, a=0.4-0.8 mm; the long side length of the micro cross column (2) is b, b=2.6a-3.4a; the height of the micro cross column (2) is c, c=0.8-2.5 mm.

4. The inverted composite wettability micro-cross pedestal structured surface for enhancing condensation heat transfer according to claim 1, characterized in that: The groove surfaces (3) are interconnected, and the narrowest spacing d of each micro-cross column platform (2) is the same, d=0.8b~1.2b.

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