Composite microstructure based on multidirectional Laplace pressure gradient reinforced bead condensation

Abstract

The invention belongs to the technical field of condensation and heat and mass transfer, and relates to a composite microstructure surface based on multidirectional Laplace pressure gradient reinforced bead condensation, which comprises a super-hydrophobic substrate with an axis and a super-hydrophobic three-dimensional composite microstructure distributed on the top surface of the super-hydrophobic substrate, the super-hydrophobic three-dimensional composite microstructure comprises a plurality of wedge-shaped column structures arranged in the horizontal direction, the wedge-shaped column structures are distributed on the super-hydrophobic substrate in a multi-column mode, each wedge-shaped column structure is provided with a wide end and a narrow end, and the wide ends and the narrow ends of the wedge-shaped column structures in each column are sequentially and alternately arranged. The wedge-shaped column structures in every two adjacent columns are symmetrical in the axis direction of the super-hydrophobic substrate, a gap is formed between every two wedge-shaped column structures which are symmetrically arranged in every two adjacent columns, and a V-shaped groove structure with a V-shaped longitudinal section is formed between every two adjacent wedge-shaped column structures in each column. According to the invention, the probability of liquid drop bounce is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of condensation and heat and mass transfer, and in particular relates to a composite microstructure based on multi-directional Laplace pressure gradient to enhance bead condensation. Background Art

[0002] As one of the most common forms of heat transfer, condensation heat transfer is widely used in fields such as high-efficiency heat transfer equipment, seawater desalination, and air water extraction. During the condensation process, the condensation heat transfer process can be divided into film condensation and bead condensation, depending on the wetting properties of the condensation surface. Compared with film condensation, in bead condensation, the condensate exists on the condensation surface in the form of discrete droplets, which has a lower heat transfer resistance and higher heat transfer efficiency. Therefore, how to achieve stable bead condensation on the condensation surface is currently the focus of research on enhancing condensation heat transfer.

[0003] During bead condensation, the accumulation of condensate eventually leads to overflow, manifesting as a coexistence of film condensation and bead condensation on the condensation surface. To promptly remove condensate droplets, a class of micron-scale structures that can induce Laplace pressure gradients within the droplets, prompting their spontaneous motion, has been extensively experimentally studied. Typical structural forms include micron pillars, micron cones, and micron pyramids. Existing surface microstructures designed based on Laplace pressure gradients are mostly simple geometric arrays, with insufficient condensate droplet removal capabilities. There is a lack of composite microstructured surfaces that can further exploit this mechanism. To address these issues, the present invention proposes a composite microstructure based on multi-directional Laplace pressure gradients to enhance bead condensation. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a composite microstructure based on multi-directional Laplace pressure gradient to enhance bead condensation, which increases the probability of droplet bouncing and thereby improves the ability to remove condensed droplets.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions: The present invention provides a composite microstructure based on multi-directional Laplace pressure gradient enhanced bead condensation, comprising a super-hydrophobic substrate with an axis and a super-hydrophobic three-dimensional composite microstructure distributed on the top surface of the super-hydrophobic substrate, wherein the super-hydrophobic three-dimensional composite microstructure comprises a plurality of wedge-shaped column structures arranged in a horizontal direction, and the plurality of wedge-shaped column structures are distributed in multiple columns on the super-hydrophobic substrate, the wedge-shaped column structures have a wide end and a narrow end, and the plurality of wedge-shaped column structures in each column are alternately arranged with the wide end and the narrow end in sequence, each wedge-shaped column structure in two adjacent columns is symmetrical along the axis direction of the super-hydrophobic substrate, and a gap is provided between the two symmetrically arranged wedge-shaped column structures in the two adjacent columns, and a V-shaped groove structure with a V-shaped longitudinal section is formed between the two adjacent wedge-shaped column structures in each column.

[0006] Preferably, the width P1 of the gap is 30 μm to 60 μm.

[0007] Preferably, the height H of the wedge-shaped column structure is 30 μm to 50 μm, the wedge angle α of the wedge-shaped column structure is 16° to 28°, the length L of the wedge-shaped column structure is 100 μm to 150 μm, and the width W of the wedge-shaped column structure is 40 μm to 60 μm.

[0008] Preferably, the half-open angle β of the V-shaped groove structure is 0°<β≤25°, and the width P2 of the V-shaped groove structure is 30 μm to 60 μm.

[0009] Preferably, when the half-opening angle β of the V-groove structure is ≤7°, the condensed liquid droplets self-bounce in the V-groove structure; when the half-opening angle β of the V-groove structure is greater than 7°, the condensed liquid droplets self-propel in the V-groove structure.

[0010] Preferably, a plurality of the wedge-shaped column structures are symmetrically arranged in the order of wide end to wide end and narrow end to narrow end on the top surface of the superhydrophobic substrate, which can promote the merging and bouncing of condensed droplets through the self-driving behavior of droplets on the wide-end wedge-shaped columns.

[0011] Preferably, the surface contact angles of the super-hydrophobic substrate and each wedge-shaped column structure are both θ, and θ>160°.

[0012] Preferably, the surface contact angle θ values ​​of the super-hydrophobic substrate and each wedge-shaped column structure are both 165.8°.

[0013] The present invention also provides a method for preparing a composite microstructure based on multi-directional Laplace pressure gradient enhanced bead condensation, comprising the following steps: A plurality of wedge-shaped column structures are processed on a copper substrate using a laser direct writing method, and the plurality of wedge-shaped column structures are distributed in multiple columns on the top surface of the copper substrate, wherein the wedge-shaped column structures have a wide end and a narrow end, and the plurality of wedge-shaped column structures in each column are arranged alternately with the wide end and the narrow end, and each wedge-shaped column structure in two adjacent columns is symmetrical along the axis direction of the super-hydrophobic substrate, and a gap is provided between the two symmetrically arranged wedge-shaped column structures in the two adjacent columns, and a V-shaped groove structure with a V-shaped longitudinal section is formed between the two adjacent wedge-shaped column structures in each column; Cleaning the surfaces of the copper substrate and the plurality of wedge-shaped column structures; A nano-blade-shaped oxide substrate is processed on the surface of a copper substrate and multiple wedge-shaped column structures by chemical etching, and then a layer of coating is covered on the surface of the nano-blade-shaped oxide substrate by molecular self-assembly method to form a super-hydrophobic substrate and a super-hydrophobic three-dimensional composite microstructure.

[0014] Preferably, the copper substrate and the surfaces of the multiple wedge-shaped column structures are cleaned one by one using acetone, anhydrous ethanol and dilute hydrochloric acid.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The composite microstructure based on multi-directional Laplace pressure gradient to enhance bead condensation proposed in the present invention achieves enhanced removal of condensed droplets through multi-directional Laplace pressure gradient, wherein: The condensed droplets will undergo self-driving behavior on the top surface of the wedge-shaped column structure where the contact width with the condensed droplets increases along the direction approaching the gap, which is used to induce the generation of a Laplace pressure gradient inside the condensed droplets, thereby promoting the condensed droplets to merge and bounce at the gap.

[0016] A V-shaped groove structure with a V-shaped longitudinal section is formed between two adjacent wedge-shaped column structures in each column. The gradually widening geometric structure of the V-shaped groove structure can cause the condensed liquid droplets nucleated and grown in the V-shaped groove to deform under the constraint of the gradually widening geometric structure of the V-shaped groove, resulting in a curvature difference between the upper and lower surfaces, and then generating a vertically upward Laplace pressure gradient inside, which prompts the condensed liquid droplets to self-propel during the growth process, pushing the droplets to spontaneously move in the vertical direction upward, promoting the removal of the condensed liquid, and when the half-opening angle is less than 7°, the droplets can self-bounce, thereby enhancing the removal of the condensed liquid.

[0017] The larger the wedge angle α is within this value range, the faster the droplet moves during self-driving, and the shorter the time required for the droplet to merge and bounce.

[0018] The arrangement pattern of multiple wedge-shaped column structures on the superhydrophobic substrate can enable self-driven droplets on the wedge-shaped columns to contact at the center, merge and bounce off the surface, significantly increasing the probability of droplets merging and bouncing. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the overall structure of a composite microstructure based on multi-directional Laplace pressure gradient enhanced bead condensation, where Figure a is a structural illustration and Figure b is a geometric parameter illustration.

[0020] Figure 2 A front view of a composite microstructure based on multi-directional Laplace pressure gradient-enhanced bead condensation.

[0021] Figure 3 This is a schematic diagram of the principle of the wedge-shaped column structure driving the spontaneous motion of droplets, where Figure a is the overall structure diagram, Figure b is the x1 cross-sectional diagram, and Figure c is the x2 cross-sectional diagram.

[0022] Figure 4 Schematic diagram of the principle of V-groove structure driving the spontaneous motion of droplets.

[0023] Figure 5This is an electron microscope photograph of a composite microstructure based on multi-directional Laplace pressure gradient enhanced bead condensation before superhydrophobic treatment, where Figure a is the overall structure diagram and Figure b is a local magnified diagram.

[0024] Figure 6 This is an electron microscope photograph of a composite microstructure based on multi-directional Laplace pressure gradient-enhanced bead condensation after superhydrophobic treatment, where Figure a is the overall structure diagram and Figure b is a local magnified diagram.

[0025] Reference numerals 1. Superhydrophobic substrate; 2. Wedge-shaped column structure; 3. V-shaped groove structure; 4. Sidewall of wedge-shaped column structure; 5. Droplets merging and bouncing on opposing wedge-shaped columns; 6. Condensation droplets; 7. Condensation droplets self-propelled on the wedge-shaped column structure; 8. Condensation droplets self-bouncing on the V-shaped groove. DETAILED DESCRIPTION

[0026] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited by the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The experimental methods described in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0027] like Figures 1 to 4 As shown, the present invention provides a composite microstructure based on multi-directional Laplace pressure gradient enhanced bead condensation, comprising a super-hydrophobic substrate 1 with an axis and a super-hydrophobic three-dimensional composite microstructure distributed on the top surface of the super-hydrophobic substrate 1, wherein the super-hydrophobic three-dimensional composite microstructure comprises a plurality of wedge-shaped column structures 2 arranged in a horizontal direction, and the plurality of wedge-shaped column structures 2 are distributed in multiple columns on the super-hydrophobic substrate 1, the wedge-shaped column structures 2 having a wide end and a narrow end, and the plurality of wedge-shaped column structures 2 in each column are arranged alternately with the wide end and the narrow end in sequence, each wedge-shaped column structure 2 in two adjacent columns is symmetrical along the axis direction of the super-hydrophobic substrate 1, and there is a gap between the two symmetrically arranged wedge-shaped column structures 2 in two adjacent columns, and a V-shaped groove structure 3 with a V-shaped longitudinal section is formed between the two adjacent wedge-shaped column structures 2 in each column. The wedge-shaped column structure sidewalls 4 of the wedge-shaped column structures 2 on both sides of the V-shaped groove structure 3 are inclined wall surfaces.

[0028] Working principle: When steam condenses in the form of beads on the surface of a composite microstructure based on multi-directional Laplace pressure gradient enhanced bead condensation, the condensed droplets 6 will nucleate and grow on the super-hydrophobic substrate 1, the wedge-shaped column structure 2 and the V-shaped groove structure 3. As the condensed droplets 6 continue to grow, the condensed droplets 6 will undergo self-driving behavior on the top surface of the wedge-shaped column structure 2 where the contact width with the condensed droplets increases along the direction close to the gap, enabling the droplets to collide at the center of the gap, promoting the occurrence of merging and bouncing, while the condensed droplets 8 in the V-shaped groove can undergo self-bouncing behavior. Under the combined action of the two mechanisms, the removal efficiency of the condensed droplets 6 on the surface of the composite microstructure based on multi-directional Laplace pressure gradient enhanced bead condensation is significantly improved.

[0029] Specifically, the width P1 of the gap is 30 μm to 60 μm. When the width P1 of the gap is 30 μm to 60 μm, the droplet bounces, and when the width P1 of the gap is outside this range, the droplet cannot bounce.

[0030] Specifically, the height H of the wedge-shaped column structure 2 is 30 μm to 50 μm, the wedge angle α of the wedge-shaped column structure 2 is 16° to 28°, the length L of the wedge-shaped column structure 2 is 100 μm to 150 μm, and the width W of the wedge-shaped column structure 2 is 40 μm to 60 μm. The larger the wedge angle α is within this value range, the faster the movement speed of the droplet self-drive process, and the shorter the time required for the droplet to merge and bounce. The numerical ranges of the height of the wedge-shaped column structure 2, the length L of the wedge-shaped column structure 2, and the width W of the wedge-shaped column structure 2 are all set to make the droplet bounce. When the numerical ranges are exceeded, the droplet cannot bounce.

[0031] Specifically, the half-open angle β of the V-groove structure 3 is 0° < β ≤ 25°, and the width P2 of the V-groove structure 3 is 30 μm to 60 μm. The half-open angle β and the width of the V-groove structure 3 are both set to enable droplets to bounce. When the values ​​exceed the above range, the droplets cannot bounce.

[0032] Specifically, when the half-opening angle β of the V-shaped groove structure 3 is ≤7°, the condensed liquid droplets 6 self-bounce in the V-shaped groove structure 3; when the half-opening angle β of the V-shaped groove structure 3 is greater than 7°, the condensed liquid droplets 6 self-propel in the V-shaped groove structure 3.

[0033] Specifically, the surface contact angles of the super-hydrophobic substrate 1 and each wedge-shaped column structure 2 are both θ, and θ>160°, so as to ensure the occurrence of self-driving behavior of the droplets.

[0034] Specifically, the surface contact angle θ values ​​of the super-hydrophobic substrate 1 and each wedge-shaped column structure 2 are both 165.8°.

[0035] like Figure 5~Figure 6The present invention provides a method for preparing a composite microstructure surface based on multi-directional Laplace pressure gradient-enhanced bead condensation, comprising the following steps: A plurality of wedge-shaped column structures 2 are processed on a copper substrate by a laser direct writing method, and the plurality of wedge-shaped column structures 2 are distributed in multiple columns on the top surface of the copper substrate, wherein the wedge-shaped column structures 2 have a wide end and a narrow end, and the plurality of wedge-shaped column structures 2 in each column are arranged alternately with the wide end and the narrow end, and each wedge-shaped column structure 2 in two adjacent columns is symmetrical along the axis direction of the super-hydrophobic substrate 1, and a gap is provided between the two symmetrically arranged wedge-shaped column structures 2 in the two adjacent columns, and a V-shaped groove structure 3 with a V-shaped longitudinal section is formed between the two adjacent wedge-shaped column structures 2 in each column; Cleaning the surfaces of the copper substrate and the plurality of wedge-shaped column structures 2; A nano-blade-shaped oxide substrate is processed on the surface of a copper substrate and multiple wedge-shaped column structures 2 by chemical etching, and then a coating is covered on the surface of the nano-blade-shaped oxide substrate by molecular self-assembly method to form a super-hydrophobic substrate 1 and a super-hydrophobic three-dimensional composite microstructure.

[0036] Specifically, the surfaces of the substrate and the plurality of wedge-shaped column structures 2 are cleaned one by one using acetone, anhydrous ethanol and dilute hydrochloric acid.

[0037] Example 1 An embodiment of the present invention provides a composite microstructure for enhancing beaded condensation based on a multi-directional Laplace pressure gradient, comprising a super-hydrophobic substrate 1 having an axis and a super-hydrophobic three-dimensional composite microstructure distributed on the top surface of the super-hydrophobic substrate 1, wherein the super-hydrophobic three-dimensional composite microstructure comprises a plurality of wedge-shaped column structures 2 arranged in a horizontal direction, and the plurality of wedge-shaped column structures 2 are distributed in multiple columns on the super-hydrophobic substrate 1, and the plurality of wedge-shaped column structures 2 in each column are alternately arranged in sequence, and each wedge-shaped column structure 2 in two adjacent columns is symmetrical along the axis of the super-hydrophobic substrate 1, and there is a gap between the two symmetrically arranged wedge-shaped column structures 2 in two adjacent columns, and the condensed droplets 6 will self-drive on the top surface of the wedge-shaped column structure 2 where the contact width with the condensed droplets increases in the direction close to the gap, so as to induce a Laplace pressure gradient inside the condensed droplets 6 so that the condensed droplets 6 merge and bounce at the gap; a V-shaped groove structure 3 with a V-shaped longitudinal section is formed between the two adjacent wedge-shaped column structures 2 in each column, and the V-shaped groove structure 3 is used to cause the condensed droplets 6 to self-bounce within the V-shaped groove structure 3. The wedge-shaped column structures 2 on either side of the V-shaped groove structure 3 have inclined sidewalls 4. The wedge-shaped column structures 2 have a height H of 50 μm, a wedge angle α of 24°, a length L of 130 μm, a width W of 60 μm, and a wedge-shaped column gap P1 of 30 μm. The V-shaped groove structure 3 has a half-opening angle β of 7° and a groove width P2 of 40 μm.

[0038] The composite microstructure surface based on multi-directional Laplace pressure gradient to enhance bead condensation proposed in the present invention achieves enhanced removal of condensed droplets through multi-directional Laplace pressure gradient: (1) the oppositely arranged wedge-shaped column structures 6 can impose constraints on the bottom of the condensed droplets 6, triggering the self-propelled behavior of the droplets and promoting the occurrence of merging and bouncing phenomena; (2) the V-shaped groove structure 3 can promote the self-propulsion and self-bouncing behavior of the condensed droplets 6 through the gradually widening geometric structure. The design principle of the present invention is further explained below based on the above two action mechanisms:

[0039] (1) The oppositely arranged wedge-shaped pillars can induce the self-propulsion behavior of the droplets and promote the occurrence of merging and bouncing phenomena Refer to the attached Figure 3 When the condensation droplet 6 nucleates and grows on the wedge-shaped column structure 2, the contact width δ(x) between the condensation droplet 6 and the top surface of the wedge-shaped column will continue to increase along the positive direction of the x-axis, that is, δ(x2)>δ(x1), which will trigger the generation of a Laplace pressure gradient from δ(x1) to δ(x2) inside the condensation droplet 6, driving the condensation droplet 6 to spontaneously move from δ(x1) to δ(x2) of the wedge-shaped column structure 2, thereby improving the fluidity of the condensation droplet 6 on the surface of the wedge-shaped column structure. In addition, the opposite arrangement pattern of the wedge-shaped column structure 2 can make the condensation droplets 6 at both ends of the wedge-shaped column structure 2 self-driven to contact each other at the center, thereby causing the condensation droplets 6 to merge and bounce 5, and the condensation droplets 6 will quickly detach from the microstructure surface.

[0040] (2) The V-shaped groove structure 3 can promote the self-propulsion and self-bounce of the condensed liquid droplets 6 through the gradually widening geometric structure. Reference Figure 4 When condensate droplets 8 nucleate and grow within the V-groove structure 3, they deform due to the constraints of the V-groove's gradually widening geometry. This creates a curvature difference between the upper and lower surfaces of the condensate droplet 8, which in turn generates a vertically upward Laplace pressure gradient within the droplet, driving the condensate droplet 8 to spontaneously move upward in the vertical direction. When the half-open angle of the V-groove structure 3 is ≤7°, the surface curvature difference within the V-groove structure 3 is large, allowing the condensate droplet 8 to self-bounce. When the half-open angle is greater than 7°, the V-groove structure 3 provides insufficient constraints on the condensate droplet 8, resulting in only self-propulsion. Therefore, the V-groove structure 3 provides the driving force for the droplet's spontaneous upward motion, facilitating its removal.

[0041] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims and their equivalents, the present invention is intended to include such modifications and variations.

Claims

1. A composite microstructure based on multi-directional Laplace pressure gradient enhanced bead condensation, characterized in that: The invention comprises a super-hydrophobic substrate (1) having an axis and a super-hydrophobic three-dimensional composite microstructure distributed on the top surface of the super-hydrophobic substrate (1), wherein the super-hydrophobic three-dimensional composite microstructure comprises a plurality of wedge-shaped column structures (2) arranged in a horizontal direction, and the plurality of wedge-shaped column structures (2) are distributed in multiple columns on the super-hydrophobic substrate (1), the wedge-shaped column structures (2) have a wide end and a narrow end, and the plurality of wedge-shaped column structures (2) in each column are arranged alternately with the wide end and the narrow end in sequence, each wedge-shaped column structure (2) in two adjacent columns is symmetrical along the axis direction of the super-hydrophobic substrate (1), and there is a gap between the two symmetrically arranged wedge-shaped column structures (2) in the two adjacent columns, and a V-shaped groove structure (3) with a V-shaped longitudinal section is formed between the two adjacent wedge-shaped column structures (2) in each column.

2. The composite microstructure based on multi-directional Laplace pressure gradient enhanced bead condensation according to claim 1, characterized in that: The width P1 of the gap is 30 μm to 60 μm.

3. The composite microstructure based on multi-directional Laplace pressure gradient enhanced bead condensation according to claim 1, characterized in that: The height H of the wedge-shaped column structure (2) is 30 μm to 50 μm, the wedge angle α of the wedge-shaped column structure (2) is 16° to 28°, the length L of the wedge-shaped column structure (2) is 100 μm to 150 μm, and the width W of the wedge-shaped column structure (2) is 40 μm to 60 μm.

4. The composite microstructure based on multi-directional Laplace pressure gradient enhanced bead condensation according to claim 1, characterized in that: The half-open angle of the V-shaped groove structure (3) is 0°<β≤25°, and the width P2 of the V-shaped groove structure (3) is 30μm~60μm.

5. The composite microstructure based on multi-directional Laplace pressure gradient enhanced bead condensation according to claim 4, characterized in that: When the half-opening angle β of the V-shaped groove structure (3) is ≤7°, the condensed liquid droplet (6) undergoes a self-bouncing behavior in the V-shaped groove structure (3); when the half-opening angle β of the V-shaped groove structure (3) is greater than 7°, the condensed liquid droplet (6) undergoes a self-propulsion behavior in the V-shaped groove structure (3).

6. The composite microstructure based on multi-directional Laplace pressure gradient enhanced bead condensation according to claim 1, characterized in that: The surface contact angles of the super-hydrophobic substrate (1) and each wedge-shaped column structure (2) are both θ, and θ>160°.

7. The composite microstructure based on multi-directional Laplace pressure gradient enhanced bead condensation according to claim 6, characterized in that: The surface contact angle θ values ​​of the super-hydrophobic substrate (1) and each wedge-shaped column structure (2) are both 165.8°.

8. The method for preparing a composite microstructure based on multi-directional Laplace pressure gradient enhanced bead condensation according to any one of claims 1 to 6, characterized in that: The steps include: A plurality of wedge-shaped column structures (2) are processed on a copper substrate by a laser direct writing method, and the plurality of wedge-shaped column structures (2) are distributed in multiple rows on the top surface of the copper substrate, wherein the wedge-shaped column structures (2) have a wide end and a narrow end, and the plurality of wedge-shaped column structures (2) in each row are arranged alternately with the wide end and the narrow end, and each wedge-shaped column structure (2) in two adjacent rows is symmetrical along the axis direction of the super-hydrophobic substrate (1), and a gap is provided between the two symmetrically arranged wedge-shaped column structures (2) in the two adjacent rows, and a V-shaped groove structure (3) with a V-shaped longitudinal section is formed between the two adjacent wedge-shaped column structures (2) in each row; Cleaning the surfaces of the copper substrate and the plurality of wedge-shaped column structures (2); A nano-blade-shaped oxide substrate is processed on the surface of a copper substrate and a plurality of wedge-shaped column structures (2) by chemical etching, and then a layer of coating is covered on the surface of the nano-blade-shaped oxide substrate by molecular self-assembly method to form a super-hydrophobic substrate (1) and a super-hydrophobic three-dimensional composite microstructure.

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