Surface structure for ice crystal type cold storage heat exchange plate and preparation method

Abstract

The invention provides a surface structure for an ice crystal type cold storage heat exchange plate and a preparation method, and belongs to the technical field of ice making through supercooled water. The surface structure comprises a hydrophilic surface, the hydrophilic surface comprises an inflow side for inflow of water and an outflow side for outflow of water, the hydrophilic surface is provided with a sunken micro-texture, and the micro-texture is filled with a composite hydrophobic and icy coating; in the direction from the inflow side to the outflow side, the distribution density of the microtextures is gradually increased; the composite hydrophobic and icy coating comprises a bonding layer, a silicon dioxide hydrophobic layer and a PDMS wear-resistant layer from outside to inside. By changing the density of the hydrophilic characteristics, the progressive hydrophobic and oleophobic surface with the hydrophilic characteristics changing according to the set gradient is formed. Water has a large contact area with the heat exchange plate in the early stage of flowing of the heat exchange plate so as to fully absorb cold, and is in contact with more hydrophobic and icy surfaces to be separated from the heat exchange surface as soon as possible after being converted into a supercooled state in the later stage, so that the heat exchange efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of supercooled water ice making, and particularly relates to a surface structure and a preparation method of an ice crystal type cold storage heat exchange plate. Background Technique

[0002] Disclosing the information of this background technical part is only intended to increase the understanding of the overall background of the present invention, and it is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Ice crystal type cold storage, also known as supercooled water ice storage, belongs to a type of dynamic ice storage method. In its refrigeration cycle process, pure water is first pumped from an ice storage tank, transported to a heat exchanger for heat exchange. During the heat exchange process, the water is cooled to a supercooled state, and then transported to the ice storage tank. In the ice storage tank, the supercooled state of the supercooled water is eliminated, becoming a mixture of ice crystals and water, and the absorbed cold is stored therein. At this time, the ice crystals are separated from the water and suspended in the upper part of the ice storage tank, while the water in the lower part is separated and pumped out to be transported to the heat exchanger to continue the ice making cycle.

[0004] The heat exchange plate on the heat exchanger is a key component of the ice crystal type cold storage system. Its main cold storage and energy storage principle is as follows: water at 0°C flows into from the higher end of the heat exchange plate, flows on the heat exchange plate with an inclination angle of β to the lower end, and exchanges heat with the surface of the heat exchange plate during the flow process, gradually absorbing cold and transforming into a supercooled state. Then, the mixture of supercooled water and ice enters the ice storage tank. However, during this process, supercooled water is prone to adhere to the surface of the heat exchange plate to form an ice crystal layer, and the ice crystal layer adsorbed on the surface of the heat exchange plate will reduce the heat transfer efficiency. In order to improve the heat exchange efficiency, ideally, the inflowing water can fully absorb cold on the surface of the heat exchange plate and transform into a supercooled state, and after becoming supercooled water, it can quickly leave the surface of the heat exchange plate without the process of ice nucleation and adhesion.

[0005] Chinese Patent with application publication number CN 113549966A discloses a preparation method of a superhydrophobic coating for anti-icing on a metal surface. This method successively prepares a Zn-Ni alloy coating on the metal surface by electroplating, constructs a micro-nano rough porous structure with a "rose" shape on the coating surface by hydrothermal method, and modifies it by low surface energy chemical immersion in three steps to prepare a superhydrophobic anti-icing coating with excellent hydrophobicity, self-cleaning property, and chemical stability. However, the hydrophobic and ice-phobic surface prepared by this method will inhibit the adsorption and condensation of water while preventing icing, resulting in low phase change heat transfer efficiency.

[0006] A Chinese patent with application publication number CN 106752214A discloses a bionic anti-icing surface based on discontinuous wettability improvement. It coats a variety of hydrophobic coatings with different wettability from the material itself on the surface of the material to form a surface with a discontinuous wettability distribution. The principle is to form an intermittent and discontinuous freezing interface between the hydrophobic coatings to destroy the freeze-adhesion stability between the ice and the material surface, thereby reducing the adhesion strength of ice on the surface. However, the adhesion of a single hydrophobic coating to the substrate surface is weak, and there are problems such as uneven coating and poor coating durability. Long-term use of the coating will lead to changes in the surface wettability distribution, thereby affecting the anti-icing effect.

[0007] In summary, super-hydrophobic surfaces show good application prospects in terms of anti-icing performance. Their high contact angle and low rolling angle make it difficult for water droplets to stay on the surface of the material, which can effectively prevent the nucleation and adhesion of ice. Although traditional hydrophobic and ice-phobic surfaces can effectively inhibit the nucleation of ice, they will also inhibit the condensation of water into a supercooled state, reducing the overall phase change heat transfer efficiency on the surface. As a heat exchanger that directly produces and outputs cold energy, the heat exchanger plays an important role in the cold storage system. Therefore, how to inhibit ice formation without affecting the condensation of water on the surface of the heat exchanger to form supercooled water is an urgent problem that needs to be solved in the development of dynamic ice storage systems. Summary of the invention

[0008] In view of the current state of the art, the purpose of the present invention is to provide a surface structure and preparation method for ice crystal type cold storage heat exchange plate. First, a micro texture is etched on the hydrophilic surface, and then a composite hydrophobic and ice-repellent coating is filled in the micro texture, and the density of the micro texture gradually increases from the water inlet side to the outlet side, so as to obtain a flow path that matches the heat exchange supercooling process of water, so as to promote the heat exchange between water and the heat exchange plate while preventing the adhesion of the ice crystal layer.

[0009] In order to achieve the above object, the technical solution of the present invention is:

[0010] In a first aspect, a surface structure for an ice crystal cold storage heat exchange plate comprises a hydrophilic surface, the hydrophilic surface comprises an inflow side for water to flow in and an outflow side for water to flow out, a concave micro-texture is arranged on the hydrophilic surface, the micro-texture is filled with a composite hydrophobic and ice-phobic coating, and the surface of the composite hydrophobic and ice-phobic coating is flush with the hydrophilic surface; in the direction from the inflow side to the outflow side, the distribution density of the micro-texture gradually increases;

[0011] The composite hydrophobic and ice-phobic coating comprises, from outside to inside, a bonding layer, a silicon dioxide hydrophobic layer and a PDMS wear-resistant layer.

[0012] In a second aspect, the method for preparing the surface structure of the ice crystal type cold storage heat exchange plate comprises the following steps:

[0013] S1. Use a nanosecond laser to process microtextures with set dimensions and distribution positions on a hydrophilic surface;

[0014] S2. Use the electrohydrodynamic jet deposition technique to sequentially deposit an adhesive layer, a silica hydrophobic layer, and a PDMS wear-resistant layer on the hydrophilic surface;

[0015] S3. Remove the adhesive layer, silica hydrophobic layer, and PDMS wear-resistant layer outside the microtextures to obtain the surface structure for the ice crystal type cold storage heat exchange plate.

[0016] The beneficial effects of the present invention are as follows:

[0017] 1. The present invention regulates the condensation rate of water by changing the density of hydrophilic features, forming a progressive hydrophobic and ice-phobic surface where the hydrophilic features change according to a set gradient. This allows water to have a large contact area with the heat exchange plate during the initial stage of flowing through the heat exchange plate to fully absorb cold and convert to a supercooled state. Subsequently, the supercooled water after conversion can contact more hydrophobic and ice-phobic surfaces to quickly separate, reducing the residence time of supercooled water on the surface and preventing the formation of ice nuclei and phase change at the heat exchanger interface, thereby preventing the reduction of heat exchange efficiency. Therefore, this structure can inhibit ice formation without affecting water condensation, providing guarantee for the efficient operation of the heat exchange system. In particular, the composite hydrophobic and ice-phobic coating is a sandwich-structured multi-layer composite coating. The bottom epoxy resin adhesive layer helps improve the film-substrate adhesion. The middle layer of nano-SiO2 nanoparticles has excellent hydrophobicity. The top PDMS coating is beneficial for enhancing wear resistance. At the same time, the presence of microtextures can store nano-coating particles, improve the film-substrate adhesion between the coating and the substrate, and enhance the wear resistance and scratch resistance of the coating. The microtextures and the multi-layer structure act in a composite and synergistic manner to form a hydrophobic and ice-phobic coating with excellent durability.

[0018] 2. The present invention overcomes the disadvantages of the previous superhydrophobic surface preparation processes, such as cumbersome processes, expensive instruments and equipment, low applicability, and environmental unfriendliness. The electrohydrodynamic jet deposition technique used in the present invention has a simple process, strong applicability, and low cost. It can uniformly deposit hydrophobic nanoparticles into microscale textures, enabling the fragile nano-coating to be protected by the microscale structure and forming a stable superhydrophobic surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0020] Figure 1 It is a schematic diagram of the working principle of the heat exchange plate in Embodiment 1 of the present invention.

[0021] Figure 2 It is a schematic diagram of the surface features of the heat exchange plate working in Embodiment 1 of the present invention.

[0022] Figure 3 These are the test results of the hydrophobicity of Embodiment 1 and Embodiment 2 of the present invention. (a) is the contact angle of the surface, and (b) is the rolling angle of the surface.

[0023] Figure 4 This is the monitoring of the droplet condensation state of the present invention. (a) is Embodiment 1, (b) is Embodiment 2; (c) is Comparative Example 1. Detailed Description of the Invention

[0024] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0025] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0026] A surface structure for an ice crystal energy storage heat exchange plate, comprising a hydrophilic surface. The hydrophilic surface includes an inflow side where water flows in and an outflow side where water flows out. Concave microtextures are provided on the hydrophilic surface, and a composite hydrophobic and ice-phobic coating is filled in the microtextures, and the surface of the composite hydrophobic and ice-phobic coating is flush with the hydrophilic surface; in the direction from the inflow side to the outflow side, the distribution density of the microtextures gradually increases;

[0027] The composite hydrophobic and ice-phobic coating includes an adhesive layer, a silica hydrophobic layer, and a PDMS wear-resistant layer from outside to inside.

[0028] The position of the microtextures on the surface conforms to the hydrophobic and ice-phobic coating, and the periphery of the microtextures is the hydrophilic surface. Macroscopically, it is still in a superhydrophobic state, but microscopically, it is partially hydrophilic, which promotes the liquid to spread more easily and increases the contact area, thereby improving the heat transfer efficiency; as the water flows in the direction towards the outflow side, its temperature gradually decreases to the supercooled state. At this time, the hydrophobicity of the surface increases, which can effectively prevent the supercooled water from forming ice nuclei at the heat exchanger interface and undergoing a phase change, thus avoiding the problem of the ice crystal layer adsorbing on the surface of the heat exchange plate.

[0029] Optionally, the micro-textures are scattered on the hydrophilic surface. The diagonal or diameter of the micro-textures is 150 - 250 μm, and the depth is 5 - 8 μm. This size helps to form a stable air layer on the surface of the micro-textures, reducing the actual contact area between the water droplets and the surface. The presence of the air layer causes the water droplets to form a "Cassie-Baxter state" when they come into contact with the surface.

[0030] Optionally, the shape of the micro-textures includes one or more of polygons, circles, or other closed shapes.

[0031] Optionally, in the direction from the inflow side to the outflow side, the distribution density of the micro-textures increases from 15 - 25% area ratio to 45 - 55% area ratio.

[0032] Optionally, multiple micro-textures are arranged into micro-texture groups with a set length. The length direction of the micro-texture groups is perpendicular to the direction from the inflow side to the outflow side. The number of micro-textures in the width direction of the micro-texture groups at different positions is different, so that they have different widths. The distance between adjacent micro-texture groups is 200 - 300 μm.

[0033] Optionally, the material of the hydrophilic surface is 304 stainless steel or silicon nitride ceramic, and the contact angle with water is about 75°.

[0034] Optionally, the preparation raw materials of the bonding layer include epoxy resin adhesive, epoxy resin adhesive curing agent, acetone, and ethanol in a mass ratio of (4 - 5):1:(5 - 6):(5 - 6). The bonding layer is used to firmly connect the silica hydrophobic layer and the bottom surface of the micro-textures.

[0035] Optionally, the thickness of the bonding layer is 5 - 7 μm.

[0036] Optionally, the preparation raw materials of the silica hydrophobic layer include hydrophobic silica nanoparticles, ethyl cellulose, and ethanol in a mass ratio of 1:(1 - 1.5):

[0037] (2.5 - 3.5); The uneven micro-surface formed by the hydrophobic silica nanoparticles and its chemical properties achieve a hydrophobic effect.

[0038] Optionally, the preparation raw materials of the PDMS wear-resistant layer include PDMS reagent, PDMS curing agent, ethanol, and n-octane in a mass ratio of (4 - 5):1:(5 - 6):(5 - 6); PDMS itself has hydrophobic properties, which can further improve the hydrophobic properties. In addition, its wear-resistant properties are used to withstand the wear of particles in supercooled water or ice slurry.

[0039] The preparation method of the surface structure for the ice crystal type cold storage heat exchange plate described above includes the following steps:

[0040] S1. Use a nanosecond laser to process microtextures with set dimensions and distribution positions on a hydrophilic surface;

[0041] S2. Use electrohydrodynamic jet deposition technology to sequentially deposit an adhesive layer, a silica hydrophobic layer, and a PDMS wear-resistant layer on the hydrophilic surface;

[0042] S3. Remove the adhesive layer, silica hydrophobic layer, and PDMS wear-resistant layer outside the microtextures to obtain the surface structure for the ice crystal type cold storage heat exchange plate.

[0043] In the above preparation method, first use nanosecond laser technology to prepare microtextures with set dimensions and shapes, and then use electrohydrodynamic jet deposition technology to uniformly deposit a composite hydrophobic and ice-phobic coating on the hydrophilic surface; the advantage of combining nanosecond laser and electrohydrodynamic jet deposition technology is that it can achieve more precise, rapid, and environmentally friendly microtexture fabrication and coating deposition; the high-precision microfabrication and non-contact characteristics of nanosecond laser technology make it particularly suitable for microtexture processing of precision surfaces, while electrohydrodynamic jet deposition technology can provide precise and uniform coating deposition in a normal temperature environment, suitable for complex surfaces and fine coating requirements. Both processing methods have the advantages of high forming accuracy, strong controllability, wide material adaptability, and green and pollution-free, and are suitable for high-performance surface design at low cost. Finally, by removing the hydrophobic coating on the top surface of the microtexture, the hydrophilic matrix is exposed, forming a non-uniform wettability surface with alternating hydrophilic and hydrophobic characteristics.

[0044] Optionally, in S1, the hydrophilic surface is pretreated, including cleaning and preheating, to prevent excessive local temperature difference caused by the laser; the preheating temperature is 180 - 220 °C.

[0045] Optionally, in S1, the power of the nanosecond laser is 6 W, the repetition frequency is 20 KHz, and the processing speed is 15 mm / s.

[0046] Optionally, in S2, use an electrohydrodynamic jet deposition device to deposit a sandwich composite structure coating on the textured substrate surface, place the substrate on a moving platform, and uniformly deposit on the substrate surface by means of alternating linear motion in the X and Y directions.

[0047] Optionally, the electrohydrodynamic jet deposition parameters are set as follows: the height of the metal spray needle from the substrate surface is 5 - 8 mm, the movement speed of the metal spray needle is 24 mm / s, the DC voltage is 5 kV, and the slurry flow rate is 25 μL / min.

[0048] Optionally, in S3, grind off the adhesive layer, silica hydrophobic layer, and PDMS wear-resistant layer outside the microtextures to make the surface of the composite hydrophobic and ice-phobic coating in the microtextures flush with the hydrophilic surface; the grinding method can maintain the flat surface of the heat exchange plate.

[0049] Optionally, in S3, a friction and wear testing machine is used for selective removal of the coating, which can ensure uniform pressure and consistent path. The applied load is 5 - 7 N, the speed is 3 - 5 mm / s, and the reciprocating times are set according to the coating removal situation. Generally, the epoxy resin layer reciprocates 10 - 12 times, the silica layer reciprocates 5 - 7 times, and the PDMS layer reciprocates 10 - 12 times to prevent the friction tool from entering the pit and damaging the coating.

[0050] Optionally, in S2 and S3, after each layer of coating deposition or selective removal is completed, it is placed on a preheating platform at 200 - 250 °C for 5 - 7 min of drying and pyrolysis treatment. The pyrolysis process can help remove the residual solvent or moisture in the coating, ensure the curing and drying of the coating, make the structure of the coating more stable, and avoid the influence that the solvent residue may cause to the coating performance.

[0051] Optionally, it further includes step S4: uniformly heating the surface structure of the ice crystal type cold storage heat exchange plate to remove the solvent in the composite hydrophobic and ice - repellent coating, heating the coating to completely volatilize the solvent in the coating, improving the denseness and film - substrate bonding force of the coating. The heating method is to keep the temperature at 180 - 220 °C for 3 - 5 min.

[0052] Example 1

[0053] As Figure 1 shown, in the actual application process, water at 0 °C flows into from end A of the heat exchange plate, flows on the surface of the heat exchange plate with an inclination angle β (75° > β > 30°) towards end B, gradually absorbs cold and is transformed into a supercooled state. Then, the mixture of supercooled water and ice falls from end B into the ice storage tank, and the working temperature on the surface of the heat exchange plate is - 3 °C to - 5 °C. During this process, supercooled water is likely to adhere to the surface of the heat exchange plate to form an ice layer. Therefore, it is necessary to add low - heat - barrier and high - heat - conductivity hydrophilic features on the hydrophobic and ice - repellent surface contacted by the supercooled water to adjust the nucleation rate of the supercooled water.

[0054] A super - hydrophobic anti - icing surface for the surface of a heat exchange plate provided in this example, the panel substrate selects silicon nitride ceramic with a size of 15 mm × 15 mm × 5 mm, and its contact angle is 40 - 50°, which is a hydrophilic surface. The specific preparation process of processing the micro - texture on the substrate surface and then depositing the coating is as follows:

[0055] S1. Clean the surface of the substrate. Immerse the substrate in a 98% ethanol solution and perform ultrasonic cleaning for 20 min to remove impurities such as surface oil stains and dust. Heat-treat the cleaned substrate on a preheating platform to make the overall temperature of the substrate more uniform and reduce the generation of thermal stress. The heating temperature is 200 °C and the time is 2 min. Transfer the heated substrate to the laser processing area and use a nanosecond laser with a power of 6 W, a repetition frequency of 20 KHz, and a processing speed of 15 mm / s to process a square micro-texture with a side length of W = 200 μm and a depth of 5 μm. The distance between each groove is L = 200 μm. The size and shape of the micro-texture are as Figure 2 shown. After calculation, the average surface density of this micro-texture is 36.5%. The left side is the inflow side and the right side is the outflow side. In the direction from the inflow side to the outflow side, the surface density of the micro-texture surface increases from 19.6% to 47.3%. After the laser processing is completed, place the substrate in an alcohol and dilute hydrochloric acid solution for cleaning to remove the oxides and casting layers generated on the surface of the laser-processed micro-texture.

[0056] S2. Prepare a solution by mixing epoxy resin adhesive, epoxy resin adhesive curing agent, acetone, and ethanol in a ratio of 4:1:5:5, and then place it in an ultrasonic vibration instrument for 30 min to make the solution evenly mixed, obtaining an epoxy resin adhesive layer slurry. Mix hydrophobic silica particles, ethyl cellulose, and ethanol in a ratio of 1:1:2.5, and then place it on a magnetic rotor stirrer for 60 min to make the solution evenly mixed, obtaining a silica hydrophobic layer slurry. Prepare a solution by mixing PDMS reagent, PDMS curing agent, ethanol, and n-octane in a ratio of 4:1:5:5, and then place it in an ultrasonic vibration instrument for 30 min to make the solution evenly mixed, obtaining a PDMS wear-resistant layer slurry. Use an electrohydrodynamic jet deposition device to deposit a sandwich composite structure coating on the textured substrate surface. Place the substrate on a moving platform and uniformly deposit the coating on the substrate surface by means of alternating linear motion in the X and Y directions.

[0057] S3. Use the textured substrate coated with the coating as the upper specimen of a friction and wear testing machine, and place 3000-mesh sandpaper below it for counter-grinding to peel off the coating at the top of the micro-texture, exposing the hydrophilic substrate in the area other than the micro-grooves, forming a non-uniform wettability surface with alternating hydrophilic and hydrophobic characteristics. During the process, after selectively removing each layer, perform step S4. Place the substrate on a preheating platform and heat the coating to completely volatilize the solvent in the coating, improving the densification of the coating and the film-substrate bonding force. The heating temperature is set at 200 °C and the time is 5 min.

[0058] Example 2

[0059] A superhydrophobic anti-icing surface for the surface of a heat exchange plate. The panel substrate is made of silicon nitride ceramic with dimensions of 15 mm × 15 mm × 5 mm, and its contact angle is 40-50°, which is a hydrophilic surface. The specific preparation process of machining micro-textures on the substrate surface and then depositing a coating is as follows:

[0060] S1.1. Clean the surface of the substrate. Place the substrate in a 98% ethanol solution and perform ultrasonic cleaning for 20 minutes to remove impurities such as surface oil stains and dust. After cleaning, heat-treat the substrate on a preheating platform to make the overall temperature of the substrate more uniform and reduce the generation of thermal stress. The heating temperature is 200 °C and the time is 2 minutes.

[0061] S1.2. Transfer the heated substrate to the laser processing area. Use a nanosecond laser with a power of 6 W, a repetition frequency of 20 KHz, and a processing speed of 15 mm / s to machine square micro-textures with a side length of W = 200 μm and a depth of 5 μm. The distance between each groove is L = 100 μm. The size and shape of the micro-textures are as Figure 2 shown. After calculation, the average surface density of the micro-textured surface is 45.7%. The left side is the inflow side and the right side is the outflow side. In the direction from the inflow side to the outflow side, the surface density of the micro-textured surface increases from 24.6% to 53.8%. After the laser processing is completed, place the substrate in an alcohol and dilute hydrochloric acid solution for cleaning to remove the oxides and casting layers generated on the surface of the laser-machined micro-textures.

[0062] S2.1. Prepare a solution by mixing epoxy resin adhesive, epoxy resin adhesive curing agent, acetone, and ethanol in a ratio of 4:1:5:5, and then place it in an ultrasonic vibration instrument for 30 minutes to make the solution evenly mixed to obtain an epoxy resin adhesive layer slurry. Mix hydrophobic silica particles, ethyl cellulose, and ethanol in a ratio of 1:1:2.5, and then place it on a magnetic rotor stirrer for 60 minutes to make the solution evenly mixed to obtain a silica hydrophobic layer slurry. Prepare a solution by mixing PDMS reagent, PDMS curing agent, ethanol, and n-octane in a ratio of 4:1:5:5, and then place it in an ultrasonic vibration instrument for 30 minutes to make the solution evenly mixed to obtain a PDMS wear-resistant layer slurry.

[0063] S2.2. Use an electrohydrodynamic jet deposition device to deposit a sandwich composite structure coating on the textured substrate surface. Place the substrate on a moving platform and uniformly deposit the coating on the substrate surface by means of alternating linear motion in the X and Y directions.

[0064] S3. Use the textured substrate coated with the coating as the upper specimen of a friction and wear testing machine, place 3000-mesh sandpaper at the bottom for counter-grinding, strip the coating at the top of the micro-texture, so that the hydrophilic substrate is exposed in the area other than the micro-grooves, forming a non-uniform wettability surface with alternating hydrophilic and hydrophobic characteristics. During the process, after selectively removing each layer, place the substrate on a preheating platform, heat the coating to completely volatilize the solvent in the coating, improve the density of the coating and the film-substrate bonding force. The heating temperature is set at 200 °C and the time is 5 min.

[0065] Comparative Example 1

[0066] A superhydrophobic anti-icing surface for the surface of a heat exchange plate. The panel substrate is made of silicon nitride ceramic with a size of 15 mm × 15 mm × 5 mm, and its contact angle is 40-50°, which is a hydrophilic surface. The specific preparation process of processing micro-textures on the substrate surface and then depositing a coating is as follows:

[0067] S1. Clean the surface of the substrate, place the substrate in a 98% ethanol solution for ultrasonic cleaning for 20 min to remove impurities such as surface oil stains and dust. Heat-treat the cleaned substrate on a preheating platform to make the overall temperature of the substrate more uniform and reduce the generation of thermal stress. The heating temperature is 200 °C and the time is 2 min. Transfer the heated substrate to the laser processing area, and use a nanosecond laser with a power of 6 W, a repetition frequency of 20 KHz, and a processing speed of 15 mm / s to process square micro-textures with a side length of W = 200 μm and a depth of 5 μm. The distance between each groove is L = 100 μm. The size and shape of the micro-textures are as Figure 2 shown. After calculation, the average areal density of the micro-texture surface is 36.5%. The left side is the inflow side and the right side is the outflow side. In the direction from the inflow side to the outflow side, the areal density of the micro-texture surface remains unchanged, which is 36.5%. After the laser processing is completed, place the substrate in an alcohol and dilute hydrochloric acid solution for cleaning to remove the oxides and casting layers generated on the surface of the laser-processed micro-textures.

[0068] S2. Prepare a solution by mixing epoxy resin adhesive, epoxy resin adhesive curing agent, acetone, and ethanol in a ratio of 4:1:5:5, and then place it in an ultrasonic vibration instrument for 30 min to make the solution evenly mixed, obtaining an epoxy resin adhesive layer slurry; mix hydrophobic silica particles, ethyl cellulose, and ethanol in a ratio of 1:1:2.5, and then place it on a magnetic rotor stirrer for 60 min to make the solution evenly mixed, obtaining a silica hydrophobic layer slurry; prepare a solution by mixing PDMS reagent, PDMS curing agent, ethanol, and n-octane in a ratio of 4:1:5:5, and then place it in an ultrasonic vibration instrument for 30 min to make the solution evenly mixed, obtaining a PDMS wear-resistant layer slurry; use an electrohydrodynamic jet deposition device to deposit a sandwich composite structure coating on the textured substrate surface. Place the substrate on a moving platform and perform uniform coating deposition on the substrate surface by means of alternating linear motion in the X and Y directions.

[0069] S3. Place the specimen with the deposited coating on a preheating platform and heat the coating to completely volatilize the solvent in the coating, improving the densification of the coating and the film-substrate adhesion. The heating temperature is set at 200 °C and the time is 5 min.

[0070] The difference between Comparative Example 1 and Example 1 is that in S3, the coating outside the micro-texture range is not ground off, so that the silicon nitride is completely covered by the deposited coating.

[0071] Detection content

[0072] Test the hydrophobicity of the superhydrophobic anti-icing surfaces of Example 1 and Example 2. After step S2 and before step S3, detect the hydrophobic coating. The results are as Figure 3 shown. (a) is the average contact angle of this surface, and (b) is the rolling angle of this surface. The results show that the macroscopic wettability of the non-uniform wettability surfaces prepared in Example 1 and Example 2 is superhydrophobic. The rolling angle of Example 1 is 5.7°, and the rolling angle of Example 2 is 3.6°. It shows that water droplets can easily roll off on the heat exchange plate surface where 75° > β > 30°, which can effectively prevent the adhesion and formation of ice.

[0073] Test the superhydrophobic anti-icing surfaces of Example 1, Example 2, and Comparative Example 1 at room temperature of 27 °C. The test process is as Figure 1As shown, water at 0°C flows into the heat exchange plate from end A, flows towards end B on the surface of the heat exchange plate with an inclination angle of β = 45°, gradually absorbs cold energy and is transformed into a subcooled state, and then the mixture of subcooled water and ice falls from end B. The working temperature of the heat exchange plate surface is -3°C. By detecting the change of the average droplet volume V falling from end B over time, it can be seen that: compared with Comparative Example 1, the droplet volume growth rate in Example 1 and Example 2 is faster, and the droplet volume is larger within the same time. This is because the increased hydrophilic characteristics of the non-uniform wettability surface contribute to the condensation of droplets. The surface characteristics of the hydrophilic region improve the heat exchange efficiency during the condensation process, making the droplet condensation rate faster and the volume larger.

[0074] A progressive superhydrophobic anti-icing surface for the surface of a heat exchange plate provided by the present invention, on the basis of a hydrophobic and ice-phobic surface, effectively improves the condensation efficiency of water droplets on the hydrophobic and ice-phobic surface by increasing hydrophilic characteristics. By regulating the areal density of the hydrophilic characteristics on the hydrophobic surface, the regulation of the condensation rate can be achieved. After increasing the hydrophilic characteristics microscopically, the surface still shows superhydrophobicity macroscopically, but the droplet condensation volume becomes larger and the droplet condensation height increases within the same time. Compared with a smooth substrate surface, this coating can delay the icing time by up to 1 h at -30°C. Therefore, when the areal density gradient of the hydrophilic characteristics changes progressively, the purpose of sufficient cold absorption by water droplets in the early stage and rapid detachment in the later stage can be achieved.

[0075] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A surface structure for an ice crystal type cold storage heat exchange plate, characterized in that: The hydrophilic surface comprises an inflow side for water to flow in and an outflow side for water to flow out, a concave micro-texture is arranged on the hydrophilic surface, a composite hydrophobic and ice-phobic coating is filled in the micro-texture, and the surface of the composite hydrophobic and ice-phobic coating is flush with the hydrophilic surface; and the distribution density of the micro-texture gradually increases in the direction from the inflow side to the outflow side; The composite hydrophobic and ice-phobic coating comprises, from outside to inside, a bonding layer, a silicon dioxide hydrophobic layer and a PDMS wear-resistant layer.

2. The surface structure for ice crystal cold storage heat exchange plate according to claim 1, characterized in that: The micro texture is scattered on the hydrophilic surface, the diagonal or diameter of the micro texture is 150 to 250 μm, and the depth is 5 to 8 μm; Alternatively, the shape of the micro-texture includes one or more of a polygon, a circle or other closed shapes.

3. The surface structure for ice crystal cold storage heat exchange plate according to claim 1, characterized in that: In the direction from the inflow side to the outflow side, the distribution density of the micro texture increases from 15-25% area ratio to 45-55% area ratio.

4. The surface structure for ice crystal cold storage heat exchange plate according to claim 1, characterized in that: The raw materials for preparing the bonding layer include epoxy resin adhesive, epoxy resin adhesive curing agent, acetone and ethanol in a mass ratio of (4-5):1:(5-6):(5-6); Or, the raw materials for preparing the hydrophobic silica layer include hydrophobic silica nanoparticles, ethyl cellulose and ethanol in a mass ratio of 1:(1-1.5):(2.5-3.5); Alternatively, the raw materials for preparing the PDMS wear-resistant layer include a PDMS reagent, a PDMS curing agent, ethanol and n-octane in a mass ratio of (4-5):1:(5-6):(5-6).

5. The surface structure for ice crystal cold storage heat exchange plate according to claim 4, characterized in that: The material of the hydrophilic surface is 304 stainless steel or silicon nitride ceramic.

6. A method for preparing a surface structure for an ice crystal type cold storage heat exchange plate according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1, using nanosecond laser to process micro-textures of set size and distribution position on the hydrophilic surface; S2, using electrofluid jet deposition technology to deposit an adhesive layer, a silicon dioxide hydrophobic layer and a PDMS wear-resistant layer on the hydrophilic surface in sequence; S3, removing the bonding layer, the silicon dioxide hydrophobic layer and the PDMS wear-resistant layer other than the micro-texture to obtain the surface structure for the ice crystal type cold storage heat exchange plate.

7. The method for preparing the surface structure of the ice crystal type cold storage heat exchange plate according to claim 6, characterized in that: In S1, the hydrophilic surface is pre-treated, including cleaning and preheating, and the preheating temperature is 180-220°C.

8. The method for preparing the surface structure of the ice crystal type cold storage heat exchange plate according to claim 6, characterized in that: In S2, an electrofluidic jet deposition device is used to deposit a sandwich composite structure coating on the surface of a textured substrate. The substrate is placed on a moving platform and the substrate surface is uniformly deposited by alternating linear motions in the X and Y directions.

9. The method for preparing the surface structure of the ice crystal type cold storage heat exchange plate according to claim 6, characterized in that: In S3, the bonding layer, the silica hydrophobic layer and the PDMS wear-resistant layer outside the micro-texture are removed by grinding, so that the surface of the composite hydrophobic and ice-phobic coating in the micro-texture is flush with the hydrophilic surface.

10. The method for preparing the surface structure of the ice crystal type cold storage heat exchange plate according to claim 6, characterized in that: The method comprises step S4 of uniformly heating the surface structure of the ice crystal type cold storage heat exchange plate to remove the solvent in the composite hydrophobic and ice-phobic coating.

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