Multi-stage spontaneous liquid discharge enhanced condensation heat transfer patterned surface and preparation method thereof

Abstract

The invention discloses a circumferential multi-stage spontaneous liquid discharge enhanced condensation heat transfer patterned surface and a preparation method thereof, and the surface is circular and consists of a plurality of wedge-shaped hydrophilic regions and hydrophobic regions. Condensate drops generated in the hydrophobic area can spontaneously migrate to the hydrophilic area under the action of the wettability boundary, and then are conveyed from the wedge-shaped tip end to the tail end under the driving of Laplace differential pressure force. Condensate can be efficiently collected to the main road along the wedge-shaped branches and conveyed outwards in the radial direction along the circumference. The patterned surface further comprises a plurality of layers of concentric circular ring areas, a circular ring where each stage of crotch is located represents a primary structure, and the structures effectively transport condensate to an annular liquid drainage groove under the capillary action of an annular porous medium arranged on the periphery, so that spontaneous liquid drainage under microgravity is achieved. A plurality of drainage areas are designed on the surface, and the width of the main drainage channel is gradually increased outwards in the radial direction of the circumference. According to the invention, the condensation heat transfer efficiency is obviously improved, and the long-term effect of drop-shaped condensation heat transfer is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of condensation and heat and mass transfer, and relates to a surface, and in particular to a patterned surface for enhancing condensation heat transfer through multi-stage spontaneous drainage and a preparation method thereof. Background Art

[0002] With the rapid development of aerospace manufacturing technology, its onboard equipment is increasingly moving towards high power and miniaturization. This trend has brought unprecedented challenges to thermal control systems, especially in terms of efficient heat exchange, temperature uniformity and reliability. Compared with traditional single-phase flow loop heat exchange systems, gas-liquid two-phase flow systems exhibit excellent isothermal performance. Under microgravity conditions, condensation heat transfer, as a crucial physical process in two-phase phase change heat transfer equipment in space, is widely involved in many application scenarios such as space fluid management, life support systems, spacecraft cooling, and spacecraft fluid recycling.

[0003] At present, the research on microgravity condensation heat transfer mainly focuses on film condensation, but because the thermal resistance of film condensation is often more than one order of magnitude larger than that of droplet condensation, it is not an ideal condensation heat transfer method. Realizing droplet condensation in a microgravity environment can greatly improve the condensation heat transfer efficiency, which has important practical significance. At present, domestic and foreign researchers have achieved droplet condensation and increased the drainage speed through a variety of surfaces, including super-liquid-repellent surfaces, wedge-shaped patterned surfaces, and non-uniform wettability surfaces. For example, Grooten found that adding a striped titanium coating to the surface of polyvinylidene fluoride is more conducive to the discharge of condensed droplets. The droplet film coexistence condensation heat transfer coefficient of the non-uniform wetting surface prepared by Ma is about 23% higher than that of complete droplet condensation. Alwazzan conducted condensation experiments outside the horizontal tube with a wettability gradient and found that the heat transfer coefficient of the surface can reach up to 1.8 times that of a pure hydrophobic surface. Ghosh et al. prepared a non-uniform wetting structure similar to the texture of a banana leaf, and the droplets can spontaneously migrate from the wedge tips on both sides to the central hydrophilic zone, which increases the drainage rate by 19%. Huang used a manufacturing process combining screen printing and chemical modification to prepare a non-uniformly wettable wedge-shaped pattern surface, which enabled the spontaneous migration of droplets from the tip of the wedge to the bottom. Mahapatra used a horizontally arranged wedge structure with alternating hydrophilic and hydrophobic layers to gather and drain condensate. The heat transfer coefficient of this wedge-shaped hydrophilic / hydrophobic surface was increased by more than 30% compared to a pure hydrophobic surface.

[0004] In summary, how to construct a non-uniform wettability wedge-shaped patterned surface with high condensation efficiency and good drainage effect to achieve steady-state droplet condensation and promote rapid drainage of droplet condensation is the key to restricting droplet condensation heat transfer on functionalized surfaces. Summary of the invention

[0005] The present invention provides a circumferential multi-stage spontaneous drainage patterned surface for enhancing condensation heat transfer and a preparation method thereof, so as to overcome the dependence of drainage on gravity and solve the problem of retention of condensate in the hydrophilic area under large supercooling.

[0006] To achieve the above object, the present invention provides a circumferential multi-stage spontaneous drainage patterned surface for enhancing condensation heat transfer, comprising a circular substrate, a super lyophilic region is provided on the surface of the substrate, and a super lyophobic region is provided outside the super lyophilic region on the surface of the substrate;

[0007] The super-lyophilic area is composed of a plurality of tree-like wedge-shaped areas evenly distributed around the circumference; each tree-like wedge-shaped area is divided into a wedge-shaped main road and a plurality of wedge-shaped branch roads, and the wedge-shaped branch roads are symmetrically distributed on both sides of the wedge-shaped main road.

[0008] Preferably, the substrate is brass, the super lyophilic region is processed from the substrate surface and has a super hydrophilic micro-nano structure, and the super lyophobic region is processed from the substrate surface and has a super lyophobic micro-nano structure.

[0009] Preferably, each of the tree-like wedge-shaped areas is composed of six wedge-shaped branch roads.

[0010] Preferably, in each of the tree-like wedge-shaped areas, the sizes of the multiple wedge-shaped branch roads increase proportionally from the center of the base toward the outside.

[0011] Preferably, the wedge-shaped main road and the plurality of wedge-shaped branch roads have a wedge angle at the tip of 8-12°.

[0012] Preferably, the present invention also provides a method for processing a circumferential multi-stage spontaneous drainage patterned surface for enhancing condensation heat transfer for promoting rapid drainage of droplet condensation, characterized in that it comprises the following steps:

[0013] Step 1: Processing a copper foil mask on an ultra-thin copper plate by laser processing;

[0014] Step 2: Use 240#, 600#, 800#, and 1000# sandpaper to polish the surface of the copper plate, and use anhydrous ethanol, hydrochloric acid, and deionized water to ultrasonically clean for 5 minutes to remove the surface oxide layer and residual impurities and oil stains. After drying with nitrogen, a clean initial copper plate can be obtained;

[0015] Step 3: The initial copper plate obtained in step 2 is immersed in a mixed solution of 2 mol / L NaOH and 5% K2S2O8 and etched in a water bath at 60°C for 1 hour, and the surface of the copper plate exhibits super lyophilicity;

[0016] Step 4: Paste the copper foil mask obtained in step 1 onto the super-lyophilic substrate obtained in step 3, and spray the exposed part with hydrophobic material (fluorosilane-modified silica solution). After the surface is naturally dried, spray again. Repeat this process 2 to 3 times. Each spraying lasts 10-15 seconds, with the nozzle 20-30 cm away from the surface.

[0017] Step 5: After the copper foil mask is torn off, a super-hydrophilic wedge-shaped patterned surface with a super-hydrophobic background is obtained.

[0018] Alternatively, a series of surfaces can be produced by changing the number of wedge patterns, vertex angles and other parameter sizes in step 1 while keeping other steps unchanged.

[0019] The beneficial effects of the present invention are as follows: the present invention provides a circumferential multi-stage spontaneous drainage enhanced condensation heat transfer patterned surface and a preparation method thereof, wherein the surface has a super-lyophilic pattern area and a super-lyophobic area, and integrates the steady-state droplet condensation characteristics of the super-lyophobic surface and the capillary ability of the super-lyophilic pattern, specifically:

[0020] 1. The circumferential multi-stage spontaneous drainage patterned surface for enhancing condensation heat transfer of the present invention increases the surface roughness by forming a micro / nano structure on the surface, thereby increasing the contact area between the liquid and the surface. This helps to improve the heat transfer efficiency and make the condensation heat transfer more rapid and efficient.

[0021] Second, the super-liquid-repellent micro-nanostructure and super-liquid-philic pattern in the patterned surface of the circumferential multi-stage spontaneous drainage and enhanced condensation heat transfer of the present invention can automatically guide the liquid to flow to a specific area, thereby achieving spontaneous drainage. After spontaneously migrating to the hydrophilic area using the wettability gradient at the wettability boundary, it is transported from the tip of the wedge to the end under the action of the Laplace pressure difference. After the condensate transported by the wedge branch is collected in the main road, it is transported radially outward along the circumference under the action of the Laplace pressure difference, and then transported to the annular drainage groove under the capillary force of the annular porous medium arranged at the periphery. This design reduces the possibility of liquid residue and keeps the surface dry and clean.

[0022] 3. The present invention provides a circumferential multi-stage spontaneous drainage patterned surface for enhanced condensation heat transfer and a preparation method thereof, which provides a simple preparation method, and can realize the preparation of the patterned surface by etching technology and masking technology. This method is relatively simple and low in cost, which is conducive to large-scale production and application promotion.

[0023] The present invention can realize rapid renewal of surface condensation and enhance droplet condensation heat transfer, provide a theoretical basis for the design and manufacture of enhancements for condensation heat transfer in space, and promote the development of spacecraft thermal control technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1It is a schematic diagram of a patterned surface for circumferential multi-stage spontaneous drainage to enhance condensation heat transfer;

[0025] Figure 2 It is a schematic diagram of a wedge-shaped mask pattern design for circumferential multi-stage spontaneous drainage to enhance condensation heat transfer;

[0026] Figure 3 It is a schematic diagram of two types of channel drainage on a patterned surface for circumferential multi-stage spontaneous drainage to enhance condensation heat transfer;

[0027] Figure 4 A circumferential multi-stage spontaneous drainage patterned surface for enhanced condensation heat transfer and a preparation method thereof;

[0028] Figure 5 It is a patterned surface contact angle and drainage image of circular multi-stage spontaneous drainage to enhance condensation heat transfer.

[0029] In the figure: substrate 1, super lyophilic area 2, super lyophobic area 3, wedge-shaped main road 21, wedge-shaped branch road 22. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with specific embodiments.

[0031] Embodiment 1: This embodiment provides a circular multi-stage spontaneous drainage patterned surface for enhanced condensation heat transfer.

[0032] The surface of the substrate 1 combines a super-lyophobic area 3 and a super-lyophilic area 2, wherein the super-lyophilic area 2 adopts a dendritic structure design. In order to effectively manage the flow of liquid, the drainage channel is divided into two levels: the wedge-shaped main channel 21 (level 1) is driven by the Laplace pressure difference force to transport from the wedge tip to the end. This channel usually has a larger diameter and a wider space, which can accommodate more liquid flow. The wedge-shaped branch channel 22 (levels 2, 3, and 4) effectively transfers the collected liquid to the main channel, which is a multi-level drainage channel oriented from the inside to the outside of the circumference. These channels form a complex structure on a microscopic scale, which can effectively guide the liquid flow in a specific direction, thereby achieving efficient liquid separation or transportation. The super-lyophilic area 2 is designed as a symmetrical wedge-shaped dendritic structure with a taper between 8-12°, while the secondary channel is designed with equal width, and its width does not exceed the maximum width of the main channel.

[0033] In the process of condensation and liquid collection, the two channels undertake the important task of collecting liquid on the surface and draining it efficiently. Due to the dense layout of the channels, almost all the liquid on the surface can be effectively captured, thus achieving comprehensive recovery of the entire surface liquid. The coordinated transportation of the two channels ensures that the collected liquid can be continuously transported outward, reducing the accumulation of surface liquid and enhancing condensation heat transfer.

[0034] Embodiment 2: This embodiment provides a circular multi-stage spontaneous drainage patterned surface for enhanced condensation heat transfer and a preparation method thereof.

[0035] In the present embodiment, the super-lyophobic area 3 is a nanostructure processed on the substrate surface and having super-lyophobic properties. In the present embodiment, the nanostructure is a nano copper oxide structure. The super-lyophilic area 2 is an area that is not hydrophobically treated under the protection of the mask, and its shape is consistent with the mask pattern shape. The pattern in the super-lyophilic area 2 is distributed in a circular array.

[0036] This embodiment includes the following steps: Figure 2 , 4 shown.

[0037] Step 1: Use laser processing to process a copper foil mask on an ultra-thin copper plate. Figure 2 shown.

[0038] Step 2: Use 240#, 600#, 800#, and 1000# sandpaper to polish the surface of the copper plate, and use anhydrous ethanol, hydrochloric acid, and deionized water for ultrasonic cleaning for 5 minutes to remove the surface oxide layer and residual impurities and oil stains. After drying with nitrogen, a clean initial copper plate can be obtained.

[0039] Step 3: Immerse the initial copper plate obtained in step 2 in a mixed solution of 2 mol / L NaOH and 5% K2S2O8 and etch it in a water bath at 60°C for 1 hour, and the surface of the copper plate becomes super-lyophilic.

[0040] Step 4: Paste the copper foil mask obtained in step 1 onto the super-lyophilic substrate obtained in step 3, and spray the exposed part with a hydrophobic material (fluorosilane-modified silica solution), wait for the surface to dry naturally, and then spray again, repeating this process 2 to 3 times. Each spraying lasts 10-15 seconds, with the nozzle 20-30 cm away from the surface.

[0041] Step 5: After the copper foil mask is torn off, a super-hydrophobic background with a surface contact angle of nearly 160° and a super-hydrophilic wedge-shaped patterned surface with a surface contact angle of nearly 0° are obtained.

[0042] Alternatively, a series of surfaces can be prepared by changing the number of wedge-shaped patterns, vertex angles and other parameters in step 1, while keeping other steps unchanged. The condensate is steadily condensed in drops on the surface of the lyophobic area, and the patterning can absorb and transfer the condensate through Laplace pressure difference force and capillary force.

[0043] Experimental verification shows that the above process can obtain a stable copper-based new type of non-uniform wettability wedge-shaped patterned surface, and a 10μL droplet can be self-driven on the wedge-shaped pattern, promoting the rapid transmission of the droplet condensate out of the condensation area.

Claims

1. A patterned surface for multi-stage spontaneous drainage to enhance condensation heat transfer, characterized in that: The invention comprises a circular substrate (1), wherein a super lyophilic region (2) is provided on the surface of the substrate (1), and a super lyophobic region (3) is provided outside the super lyophilic region (2) on the surface of the substrate (1); the super lyophilic region (2) comprises a plurality of tree-like wedge-shaped regions uniformly distributed around the circumference; each tree-like wedge-shaped region is divided into a wedge-shaped main road (21) and a plurality of wedge-shaped branch roads (22), and the wedge-shaped branch roads (22) are symmetrically distributed on both sides of the wedge-shaped main road (21).

2. A patterned surface for multi-stage spontaneous drainage to enhance condensation heat transfer, characterized in that: The substrate (1) is brass, the super lyophilic region (2) is processed on the surface of the substrate (1) and has a super hydrophilic micro-nano structure, and the super lyophobic region (3) is processed on the surface of the substrate (1) and has a super lyophobic micro-nano structure.

3. A patterned surface for multi-stage spontaneous drainage to enhance condensation heat transfer, characterized in that: Each of the tree-like wedge-shaped areas is composed of six wedge-shaped branch roads (22).

4. A patterned surface for multi-stage spontaneous drainage to enhance condensation heat transfer, characterized in that: In each of the tree-like wedge-shaped areas, the sizes of the multiple wedge-shaped branch roads (22) increase proportionally from the center of the base (1) toward the outside.

5. A patterned surface for multi-stage spontaneous drainage to enhance condensation heat transfer, characterized in that: In the wedge-shaped main road (21) and the plurality of wedge-shaped branch roads (22), the wedge angle at the tip is 8-12°.

6. The method for preparing a patterned surface for multi-stage spontaneous drainage and enhanced condensation heat transfer according to claim 1, characterized in that: The steps include: Step 1: Processing a copper foil mask on an ultra-thin copper plate by laser processing; Step 2: Use 240#, 600#, 800#, and 1000# sandpaper to polish the surface of the copper plate, and use anhydrous ethanol, hydrochloric acid, and deionized water to ultrasonically clean for 5 minutes to remove the surface oxide layer and residual impurities and oil stains. After drying with nitrogen, a clean initial copper plate can be obtained; Step 3: The initial copper plate obtained in step 2 is immersed in a mixed solution of 2 mol / L NaOH and 5% K2S2O8 and etched in a water bath at 60°C for 1 hour, and the surface of the copper plate exhibits super lyophilicity; Step 4: Paste the copper foil mask obtained in step 1 onto the super-lyophilic substrate obtained in step 3, and spray the exposed part with hydrophobic material (fluorosilane-modified silica solution). After the surface is naturally dried, spray again. Repeat this process 2 to 3 times. Each spraying lasts 10-15 seconds, with the nozzle 20-30 cm away from the surface. Step 5: After the copper foil mask is torn off, a patterned surface with multi-stage spontaneous drainage and enhanced condensation heat transfer and a preparation method thereof are obtained.

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