Process for preparing micro-channel with super-smooth surface to enhance boiling heat transfer
By constructing microchannels on the surface of an aluminum alloy substrate and modifying the surface to form an ultra-slippery surface structure, the wettability and flow resistance problems of traditional microchannels under high heat flux density are solved, and stable heat transfer performance measurement is achieved, providing a reliable basis for the design of high-efficiency cooling devices.
Patent Information
- Application Number
- CN202511856987.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-10
- Publication Date
- 2026-02-10
AI Technical Summary
Traditional microchannels suffer from low critical heat flux density, insufficient wettability of the working fluid, and high flow resistance under high heat flux density, making it difficult to balance heat transfer efficiency and stability. Furthermore, existing technologies lack research on the flow boiling heat transfer law of high-boiling-point working fluids in terms of cooling medium selection and experimental testing methods.
A microchannel structure was constructed on the surface of a 6061 aluminum alloy substrate. An ultra-slippery surface was formed by polishing, anodizing, fluorosilane modification, and lubricant injection. Excess lubricant was removed by spin coating. Flow boiling heat transfer test was conducted using ethylene glycol as the cooling medium.
The problem of insufficient wettability and lubricant loss under high heat flux density was solved, a stable super-slippery surface structure was obtained, complete thermal-fluid performance data were provided, the application boundaries under high heat flux density scenarios were clarified, and a reliable basis was provided for the design and optimization of high-efficiency cooling devices.
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Figure CN121496527A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the fields of heat transfer enhancement and microfluidic engineering technology, and in particular to a process for preparing microchannels with super-lubricating surfaces to enhance boiling heat transfer. Background Technology
[0002] With the rapid development of electronic devices, miniaturized heat exchange equipment, and high heat flux density energy systems, traditional cooling methods are no longer sufficient to meet their heat dissipation requirements. Microchannels, due to their high heat transfer efficiency and compactness, have gradually become the core research object for high heat flux density heat transfer. In recent years, by constructing microchannel structures on the surface of substrates such as aluminum alloys and supplementing them with surface modification technology, the flow boiling heat transfer performance can be improved to a certain extent. However, conventional microchannels still suffer from problems such as low critical heat flux density, insufficient working fluid wettability, and large flow resistance under high heat flux density, making it difficult to balance heat transfer efficiency and stability.
[0003] To address the aforementioned shortcomings, existing technologies have attempted to construct porous layers through anodic oxidation, achieve hydrophobicity through fluorosilane modification, and form slip interfaces by injecting lubricating fluids. However, these methods still suffer from limitations in practical operation, such as easy lubricant loss, unstable surface conditions, and a lack of systematic performance verification. Furthermore, the selection of cooling media and experimental testing methods largely focus on water or nanofluids, lacking research on the flow boiling heat transfer characteristics of high-boiling-point working fluids such as ethylene glycol under high heat flux densities. Therefore, it is necessary to propose a process for preparing microchannels with superlubricating surfaces to enhance boiling heat transfer, thereby overcoming the application bottlenecks of existing technologies in high heat flux density cooling scenarios. Summary of the Invention
[0004] To achieve the above objectives, the present invention provides a process for preparing microchannels with enhanced boiling heat transfer on a super-lubricating surface.
[0005] A process for preparing microchannels with enhanced boiling heat transfer on a super-lubricating surface includes the following steps: S1: Provide a 6061 aluminum alloy substrate, and polish its surface to remove surface burrs and dirt, so as to obtain a smooth and flat aluminum alloy substrate; S2: Microchannel structures are machined on the surface of an aluminum alloy substrate using a milling machine tool; S3: The microchannel structure is anodized to form an oxide film with a micro-nano porous structure on the surface of the microchannel. S4: The anodized microchannels are immersed in a fluorosilane solution for low surface energy modification, making their surface superhydrophobic; S5: The fluorosilane-modified microchannels are placed in dimethyl silicone oil and oil injection is performed in a vacuum environment to remove air from the micro-nano structure and allow the lubricating oil to be adsorbed into the porous structure. S6: Spin-coating the microchannels after oil injection removes excess lubricating oil from the surface, forming an ultra-smooth surface; S7: Using ethylene glycol as the cooling medium, flow boiling heat transfer tests were conducted on the microchannels on the super-slippery surface to verify their heat transfer performance and pressure drop characteristics under high heat flux density.
[0006] Optionally, S1 specifically includes: S11: The surface of the 6061 aluminum alloy substrate is wet-polished using sandpaper with increasing grit size in sequence, starting with 400 grit and ending with 1500 grit. S12: Use diamond polishing paste or alumina polishing liquid with a particle size of 0.5μm to 2.5μm to perform fine polishing on a polishing machine with a speed of 100rpm to 300rpm until there are no obvious scratches on the surface; S13: Place the polished substrate in acetone, anhydrous ethanol and deionized water in sequence for ultrasonic cleaning for 5 to 15 minutes each; S14: Place the ultrasonically cleaned aluminum alloy substrate in a drying oven and dry it at 50℃ to 80℃ to obtain a smooth and flat aluminum alloy substrate.
[0007] Optionally, S2 specifically includes: S21: Fix the polished aluminum alloy substrate onto the milling machine table and use a dial indicator to align it; S22: Select a four-flute carbide end mill with a diameter of 0.8mm to 1.5mm and clamp it in the spindle shank; S23: Set the spindle speed to 8000rpm to 15000rpm, the feed rate to 100mm / min to 300mm / min, and the depth of cut to 0.02mm to 0.05mm per pass. Perform multiple milling passes along the set parallel path until the microchannel depth reaches 200μm to 400μm. S24: Use compressed air and a brush to remove aluminum shavings and debris from the microchannels.
[0008] Optionally, S3 specifically includes: S31: Place the substrate with microchannels in a sodium hydroxide solution with a concentration of 50 g / L to 80 g / L and immerse it at 60°C to 80°C for 1 to 3 minutes to remove the natural oxide layer on the surface, and then rinse with deionized water; S32: Pour an oxalic acid solution with a concentration of 0.3 mol / L to 0.5 mol / L into the electrolytic cell, and place the substrate as the anode and the lead plate as the cathode in parallel relative to each other, with the electrode spacing maintained at 3 cm to 5 cm. S33: Under the condition that the electrolyte temperature is maintained at 5℃ to 15℃, apply a DC voltage of 35V to 45V and the oxidation time is 30 minutes to 60 minutes. S34: After oxidation, remove the substrate and ultrasonically clean it with deionized water for 5 to 10 minutes to remove residual electrolyte; S35: After being dried with high-pressure nitrogen, a micro-nano porous oxide film is formed on the surface of the microchannel.
[0009] Optionally, S4 specifically includes: S41: Dissolve perfluorodecyltriethoxysilane or heptadecafluorodecyltrimethoxysilane in anhydrous ethanol to prepare a fluorosilane solution with a concentration of 1.0 wt% to 2.5 wt%. S42: Place the anodized substrate in a vacuum drying oven and dry it at 100°C to 120°C for 30 to 60 minutes to remove moisture from the micro-nano porous structure; S43: Transfer the dried matrix into a sealed container and place it above the surface of the fluorosilane solution, and react at 70°C to 85°C for 2 to 4 hours. S44: Remove the modified aluminum alloy base and heat-treat it in an oven at 120°C to 150°C for 1 to 2 hours; S45: After curing, the aluminum alloy substrate is ultrasonically cleaned in xylene and anhydrous ethanol for 5 to 10 minutes each to remove excess fluorosilane molecules that are physically adsorbed, and finally dried with nitrogen.
[0010] Optionally, S5 specifically includes: S51: Pour dimethyl silicone oil with a kinematic viscosity of 10 cSt to 50 cSt into a container, and immerse the fluorosilane-modified aluminum alloy base at an angle of 5° to 15° into the oil; S52: Place the container into a vacuum drying oven, seal it, start the vacuum pump, reduce the pressure inside the drying oven to -0.095MPa to -0.1MPa, and maintain it for 20 to 40 minutes; S53: Under the condition of maintaining vacuum, the aluminum alloy base is completely immersed in dimethyl silicone oil and the immersion continues for 2 to 4 hours; S54: Air is introduced into the vacuum drying oven to allow the pressure to return to normal within 10 to 15 minutes, and the lubricating oil is injected into the micro-nano porous structure using the pressure difference.
[0011] Optionally, S6 specifically includes: S61: The oiled aluminum alloy substrate is installed on the spin coater base and fixed using vacuum adsorption. S62: Start the spin coater and rotate it for 10 to 20 seconds at a speed of 500 to 800 rpm to initially remove excess lubricating oil accumulated at the opening of the microchannel with the help of centrifugal force. S63: Increase the spin coater speed to 2000 rpm to 3000 rpm and maintain this speed for 60 to 120 seconds to thoroughly remove the non-anchored lubricating oil layer from the surface; S64: After spin coating, let the aluminum alloy substrate stand horizontally for 5 to 10 minutes to allow excess lubricating oil in the micro-nano porous structure to flow back to the surface. S65: Use a lint-free cloth to gently wipe the surface in one direction along the microchannels to remove any trace oil film remaining after spin coating.
[0012] Optionally, S7 specifically includes: S71: The spin-coated ultra-smooth surface microchannel aluminum alloy substrate is mounted on a controllable heating stage; S72: Connect to a closed-loop system, using ethylene glycol with a mass fraction of 95% or higher as the working medium, pumped into the microchannel inlet by a constant flow pump at a flow rate of 0.5 L / min, while adjusting the back pressure valve to stabilize the outlet pressure at 0.2 MPa; S73: Apply a constant heat flux through a heating platform, control the heat flux density within the range of 100kW / m², and maintain a stable heating state for 10 minutes to form flow boiling conditions; S74: The temperature difference between the inlet and outlet walls of the microchannel is recorded by a thermocouple array, the input electrical power is measured by a power meter, and the corresponding heat transfer coefficient is calculated by combining the inlet and outlet temperature difference with the flow rate. S75: Set up micro-pressure sensors at the inlet and outlet of the microchannel to measure and record the steady-state pressure drop value; S76: The measured heat transfer coefficient and pressure drop value are compared with the test results of the same size un-oiled microchannel to obtain the heat transfer performance and pressure drop characteristics of the super-smooth surface structure under high heat flux density.
[0013] Optionally, the expression for the heat transfer coefficient is: ,in, The heat transfer coefficient; This represents the total input thermal power. For heat exchange area; The temperature difference is the logarithmic mean.
[0014] The beneficial effects of this invention are: This invention constructs microchannels on the surface of a 6061 aluminum alloy substrate, followed by polishing, anodizing, fluorosilane modification, and lubricant injection to ultimately form a stable, ultra-slippery surface structure. Based on this, a spin-coating process is used to remove excess lubricant, ensuring that the lubricating layer is anchored only within the micro / nano porous structure, thereby achieving a long-term stable surface state. This process effectively improves the problems of insufficient wettability and lubricant loss in traditional microchannels under high heat flux density conditions.
[0015] This invention uses ethylene glycol as a cooling medium in the testing phase and sets controllable experimental conditions such as flow rate, heat flux density, and back pressure to determine the heat transfer coefficient and pressure drop characteristics of microchannels on super-lubricated surfaces. This allows for the acquisition of complete thermal-fluid performance data, clarifies the application boundaries in high heat flux density scenarios, and provides a reliable basis for the design and optimization of subsequent high-efficiency cooling devices. Attached Figure Description
[0016] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0017] Figure 1 This is a schematic diagram of the microchannel enhanced boiling heat exchange process according to an embodiment of the present invention. Detailed Implementation
[0018] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should also be noted that, to make the embodiments more comprehensive, the following embodiments are the best and preferred embodiments, and those skilled in the art can use other alternative methods to implement some well-known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.
[0019] It should be noted that the use of terms such as "an embodiment," "an embodiment," "an exemplary embodiment," and "some embodiments" in the specification indicates that the described embodiment may include a specific feature, structure, or characteristic, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, when a specific feature, structure, or characteristic is described in connection with an embodiment, implementing such a feature, structure, or characteristic in conjunction with other embodiments (whether explicitly described or not) should be within the knowledge of those skilled in the art.
[0020] Generally, terms can be understood at least partly from their use in context. For example, depending at least partly on the context, the term "one or more" as used herein can be used to describe any feature, structure, or characteristic in a singular sense, or a combination of features, structures, or characteristics in a plural sense. Additionally, the term "based on" can be understood not necessarily to convey an exclusive set of factors, but rather, alternatively, depending at least partly on the context, to allow for the presence of other factors that are not necessarily explicitly described.
[0021] Example 1 like Figure 1 As shown, a process for preparing microchannels with enhanced boiling heat transfer on a super-lubricating surface includes the following steps: S1: Provide a 6061 aluminum alloy substrate, and polish its surface to remove surface burrs and dirt, so as to obtain a smooth and flat aluminum alloy substrate; S2: Microchannel structures are machined on the surface of an aluminum alloy substrate using a milling machine tool; S3: The microchannel structure is anodized to form an oxide film with a micro-nano porous structure on the surface of the microchannel. S4: The anodized microchannels are immersed in a fluorosilane solution for low surface energy modification, making their surface superhydrophobic; S5: The fluorosilane-modified microchannels are placed in dimethyl silicone oil and oil injection is performed in a vacuum environment to remove air from the micro-nano structure and allow the lubricating oil to be fully adsorbed into the porous structure. S6: Spin-coating the microchannels after oiling removes excess lubricating oil from the surface, forming a stable, ultra-smooth surface; S7: Using ethylene glycol as the cooling medium, flow boiling heat transfer tests were conducted on the microchannels on the super-slippery surface to verify their heat transfer performance and pressure drop characteristics under high heat flux density.
[0022] S1 specifically includes: S11: Use sandpaper with increasing grit to wet grind the surface of the 6061 aluminum alloy substrate, starting with 400 grit and ending with 1500 grit. S12: Use diamond polishing paste with a particle size of 1.0μm and polish it on a polishing machine with a speed of 200rpm until there are no obvious scratches on the surface; S13: Place the polished substrate in acetone, anhydrous ethanol and deionized water for ultrasonic cleaning for 10 minutes each to remove residual polishing liquid and oil stains on the surface. S14: Place the ultrasonically cleaned aluminum alloy substrate in a drying oven and dry it at 60°C to obtain a smooth and flat aluminum alloy substrate.
[0023] S2 specifically includes: S21: Fix the polished aluminum alloy substrate onto the milling machine table and use a dial indicator to align it, ensuring that the flatness error of the upper surface of the substrate is less than 0.02mm; S22: Select a 1.0mm diameter four-flute carbide end mill and clamp it in the spindle shank to ensure that the tool runout is less than 0.01mm; S23: Set the spindle speed to 10000 rpm, the feed rate to 200 mm / min, and the depth of cut to 0.03 mm / pass. Perform multiple milling passes along the set parallel path until the microchannel depth reaches 300 μm. S24: Use compressed air and a brush to remove aluminum shavings and debris from the microchannels.
[0024] S3 specifically includes: S31: The substrate with microchannels is placed in a sodium hydroxide solution with a concentration of 60 g / L and immersed at 70°C for 2 minutes to remove the natural oxide layer on the surface, and then rinsed with deionized water; S32: Pour a 0.4 mol / L oxalic acid solution into the electrolytic cell as the electrolyte, and place the substrate as the anode and the lead plate as the cathode in parallel relative to each other, with the electrode spacing maintained at 4 cm. S33: With the electrolyte temperature maintained at 10℃, apply a DC voltage of 40V for 45 minutes. S34: After oxidation, remove the substrate and ultrasonically clean it with deionized water for 8 minutes to remove residual electrolyte; S35: After being dried with high-pressure nitrogen, a dense and uniform micro-nano porous oxide film is formed on the surface of the microchannel.
[0025] S4 specifically includes: S41: Dissolve heptadecafluorodecyltrimethoxysilane in anhydrous ethanol to prepare a 2wt% fluorosilane solution; S42: Place the anodized substrate in a vacuum drying oven and dry it at 110°C for 40 minutes to remove moisture from the micro-nano porous structure; S43: Transfer the dried matrix into a sealed container and place it above the surface of the fluorosilane solution. React at 80°C for 3 hours to allow the fluorosilane vapor to complete self-assembly on the surface of the microchannel. S44: Remove the modified aluminum alloy base and heat-treat it in an oven at 130°C for 1.5 hours to allow the fluorosilane molecules to fully bond with the oxide film surface; S45: The cured aluminum alloy substrate is ultrasonically cleaned in xylene and anhydrous ethanol for 8 minutes each to remove excess fluorosilane molecules that are physically adsorbed, and finally dried with nitrogen.
[0026] S5 specifically includes: S51: Pour dimethyl silicone oil with a kinematic viscosity of 20 cSt into a container, and immerse the fluorosilane-modified aluminum alloy base at a 10° angle into the oil to ensure that the microchannel opening direction is not parallel to the liquid surface. S52: Place the container in the vacuum drying oven, seal it, start the vacuum pump, reduce the pressure inside the drying oven to -0.098MPa, and maintain it for 30 minutes; S53: Under vacuum conditions, the aluminum alloy base is completely immersed in dimethyl silicone oil and immersed for 3 hours. S54: Air is introduced into the vacuum drying oven to allow the pressure to return to normal within 13 minutes. The pressure difference is then used to inject lubricating oil into the micro-nano porous structure.
[0027] S6 specifically includes: S61: Install the oiled aluminum alloy substrate onto the spin coater base and fix it using vacuum adsorption to ensure that the upper surface of the substrate remains horizontal; S62: Start the spin coater and rotate it for 15 seconds at a speed of 600 rpm to initially remove excess lubricating oil accumulated at the opening of the microchannel using centrifugal force. S63: Increase the spin coater speed to 2500 rpm and maintain this speed for 90 seconds to completely remove the non-anchored lubricating oil layer on the surface; S64: After spin coating, let the aluminum alloy substrate stand horizontally for 8 minutes to allow excess lubricating oil in the micro-nano porous structure to fully flow back to the surface. S65: Use a lint-free cloth to gently wipe the surface in one direction along the microchannels to remove any trace oil film remaining after spin coating.
[0028] S7 specifically includes: S71: The spin-coated ultra-smooth surface microchannel aluminum alloy substrate is mounted on a controllable heating stage; S72: Connect to a closed-loop system, using ethylene glycol with a mass fraction of 95% or higher as the working medium, pumped into the microchannel inlet by a constant flow pump at a flow rate of 0.5 L / min, while adjusting the back pressure valve to stabilize the outlet pressure at 0.2 MPa; S73: Apply a constant heat flux through a heating platform, control the heat flux density between 100kW / m², and maintain a stable heating state for 10 minutes to form flow boiling conditions; S74: The temperature difference between the inlet and outlet walls of the microchannel is recorded by a thermocouple array, the input electrical power is measured by a power meter, and the corresponding heat transfer coefficient is calculated by combining the inlet and outlet temperature difference with the flow rate. S75: Set up micro-pressure sensors at the inlet and outlet of the microchannel to measure and record the steady-state pressure drop value; S76: Compare the measured heat transfer coefficient and pressure drop with the test results of un-oiled microchannels of the same size to obtain the heat transfer performance and pressure drop characteristics of the super-lubricated surface structure under high heat flux density. Through the above steps, the heat transfer coefficient and flow pressure drop of the super-lubricated surface microchannel under ethylene glycol working fluid can be accurately determined under controlled flow rate, heat flux density and back pressure, clarifying its heat-fluid performance boundary characteristics, and providing reliable parameter basis for subsequent heat exchanger structure optimization and performance evaluation.
[0029] The expression for the heat transfer coefficient is: ,in, This is the heat transfer coefficient, in units of... ; Total input thermal power, in W; The heat exchange area (i.e., the contact area between the top and bottom of the microchannel) is expressed in units of... ; The logarithmic mean temperature difference, in K, is calculated using the following formula: ,in, This refers to the inlet temperature of the microchannel wall; This refers to the outlet temperature of the microchannel wall. This refers to the inlet temperature of the ethylene glycol working fluid. This refers to the outlet temperature of the ethylene glycol working fluid. In this embodiment, the inlet and outlet wall temperatures were recorded as 98.2℃ and 94.0℃, respectively. The inlet temperature of ethylene glycol was measured as 23.5℃ and the outlet temperature as 45.2℃. Based on the input power of 110 W and the total contact area of the microchannel of 0.033 m², the heat transfer coefficient was calculated to be 3250 W / (m²·K) using the logarithmic mean temperature difference formula. In addition, the pressure difference across the channel was recorded as 15 kPa using a micro-pressure sensor.
[0030] Example 2 S1: 6061 aluminum alloy substrate was selected, and its surface was wet-ground successively using 400-grit, 800-grit, 1200-grit, and 2000-grit sandpaper to remove surface scratches and rough layers. Subsequently, it was finely polished using an alumina polishing slurry with a particle size of 0.5μm on a polishing machine at a speed of 100rpm until there were no obvious scratches on the substrate surface. After polishing, the aluminum alloy substrate was placed in acetone, anhydrous ethanol, and deionized water for ultrasonic cleaning for 5 minutes each to remove surface residues. Finally, it was dried in a drying oven at 50℃ for 15 minutes to obtain a smooth and clean aluminum alloy substrate. S2: Fix the treated aluminum alloy substrate onto the milling machine table, and after calibrating the position with a dial indicator, clamp a 0.8mm diameter four-flute carbide end mill; set the spindle speed to 8000rpm, the feed rate to 100mm / min, and the depth of cut to 0.02mm / pass, and use a parallel path multi-pass milling method until the microchannel depth reaches 200μm; after machining, use compressed air in conjunction with a brush to remove residual aluminum chips and debris from the channel; S3: The microchannel structure substrate was immersed in a 50 g / L sodium hydroxide solution at 60°C for 1 minute to remove the original oxide layer on the surface. Then, a 0.3 mol / L oxalic acid solution was poured into the electrolytic cell, and the temperature was controlled at 5°C. The aluminum alloy substrate was used as the anode and the lead plate as the cathode, with a distance of 3 cm between the electrodes. A DC voltage of 35 V was applied and oxidation was continued for 30 minutes. After oxidation, the substrate was immediately ultrasonically cleaned with deionized water for 5 minutes and then dried with high-pressure nitrogen to form a micro-nano porous oxide film. S4: Prepare a 1.0 wt% perfluorodecyltriethoxysilane ethanol solution, and place the oxidized matrix in a vacuum drying oven at 100°C for 30 minutes to remove pore moisture; transfer the dried matrix to a sealed container, place it above the solution surface, and perform vapor deposition reaction at 70°C for 2 hours; after the reaction, take out the sample and heat treat it at 120°C for 1 hour to solidify the modified layer; finally, perform ultrasonic cleaning in xylene and anhydrous ethanol for 5 minutes each to remove physical adsorption residues, and dry it with nitrogen for later use; S5: Pour dimethyl silicone oil with a kinematic viscosity of 10 cSt into a vacuum-compatible container. Slowly immerse the fluorosilane-modified aluminum alloy substrate into the silicone oil at a 5° angle. Then, place the entire container in a vacuum drying oven, seal it, and evacuate it to -0.095 MPa for 20 minutes to remove air from the porous structure. Continue immersion under vacuum for 2 hours to allow the lubricant to fully penetrate the pore structure. Finally, slowly introduce air to restore the pressure to normal within 10 minutes, using the pressure difference to drive the lubricant to further inject into the micro-nano pores. S6: Fix the oiled aluminum alloy substrate onto the spin coater base and maintain stability through vacuum adsorption; start the spin coater and first rotate at 500 rpm for 10 seconds for initial degreasing, then increase the speed to 2000 rpm and continue rotating for 60 seconds to completely remove the non-anchored oil film; after spin coating, let the substrate lie horizontally for 5 minutes to allow excess oil in the pores to flow back to the surface naturally; finally, use a lint-free cloth to wipe unidirectionally along the microchannel direction to remove residual oil film on the surface and obtain a stable, ultra-smooth surface; S7: The prepared super-lubricated microchannel sample was mounted on a temperature-controlled heating stage and connected to a closed-loop testing system. Ethylene glycol with a mass fraction of 95% was selected as the cooling medium, the constant flow pump flow rate was set to 0.5 L / min, and the outlet pressure was adjusted to stabilize at 0.2 MPa. A heat flux density of 100 kW / m² was applied through the heating stage, and the sample was heated stably for 10 minutes to form a fully fluidized boiling state. The heat transfer coefficient was calculated to be 3900 W / (m²·K). In addition, the pressure difference across the channel was recorded as 18 kPa using a micro-pressure sensor.
[0031] Example 3 S1: 6061 aluminum alloy substrate was selected, and its surface was wet-ground successively using 400-grit, 800-grit, 1200-grit, and 2000-grit sandpaper to remove surface scratches and rough layers. Subsequently, diamond polishing paste with a particle size of 2.5μm was used to perform fine polishing on a polishing machine at a speed of 300rpm until there were no obvious scratches on the substrate surface. After polishing, the aluminum alloy substrate was placed in acetone, anhydrous ethanol, and deionized water for ultrasonic cleaning for 15 minutes each to remove surface residues. Finally, it was dried in an 80℃ drying oven for 15 minutes to obtain a smooth and clean aluminum alloy substrate. S2: Fix the treated aluminum alloy substrate onto the milling machine table, and after calibrating the position with a dial indicator, clamp a 1.5mm diameter four-flute carbide end mill; set the spindle speed to 15000rpm, the feed rate to 300mm / min, and the depth of cut to 0.05mm / pass, and use a parallel path multi-pass milling method until the microchannel depth reaches 400μm; after machining, use compressed air in conjunction with a brush to remove residual aluminum chips and debris from the channel; S3: The microchannel structure substrate was immersed in an 80 g / L sodium hydroxide solution at 80°C for 3 minutes to remove the original oxide layer on the surface. Subsequently, a 0.5 mol / L oxalic acid solution was poured into the electrolytic cell, and the temperature was controlled at 15°C. The aluminum alloy substrate was used as the anode and the lead plate as the cathode, with a distance of 5 cm between the electrodes. A DC voltage of 45 V was applied and oxidation was continued for 60 minutes. After oxidation, the substrate was immediately ultrasonically cleaned with deionized water for 10 minutes and then dried with high-pressure nitrogen to form a micro-nano porous oxide film. S4: Prepare a 2.5 wt% heptadecafluorodecyltrimethoxysilane ethanol solution, and place the oxidized matrix in a vacuum drying oven at 120°C for 60 minutes to remove pore moisture; transfer the dried matrix to a sealed container, place it above the solution surface, and perform vapor deposition reaction at 85°C for 4 hours; after the reaction, take out the sample and heat treat it at 150°C for 2 hours to solidify the modified layer; finally, perform ultrasonic cleaning in xylene and anhydrous ethanol for 10 minutes each to remove physical adsorption residues, and dry it with nitrogen for later use; S5: Pour dimethyl silicone oil with a kinematic viscosity of 50 cSt into a vacuum-compatible container. Slowly immerse the fluorosilane-modified aluminum alloy substrate into the silicone oil at a 15° angle. Then, place the entire container in a vacuum drying oven, seal it, and evacuate it to -0.1 MPa for 40 minutes to remove air from the porous structure. Continue immersion under vacuum for 4 hours to allow the lubricant to fully penetrate the pore structure. Finally, slowly introduce air to restore the pressure to atmospheric pressure within 15 minutes, using the pressure difference to drive the lubricant to further inject into the micro-nano pores. S6: Fix the oiled aluminum alloy substrate onto the spin coater base and maintain stability through vacuum adsorption; start the spin coater and first rotate at 800 rpm for 20 seconds for initial degreasing, then increase the speed to 3000 rpm and continue rotating for 120 seconds to completely remove the non-anchored oil film; after spin coating, let the substrate lie horizontally for 10 minutes to allow excess oil in the pores to flow back to the surface naturally; finally, use a lint-free cloth to wipe unidirectionally along the microchannel direction to remove residual oil film on the surface and obtain a stable, ultra-smooth surface; S7: The prepared super-lubricated microchannel sample was mounted on a temperature-controlled heating stage and connected to a closed-loop testing system. 95% ethylene glycol was selected as the cooling medium, the constant flow pump flow rate was set to 0.5 L / min, and the outlet pressure was adjusted to stabilize at 0.2 MPa. A heat flux of 100 kW / m² was applied through the heating stage, and the sample was heated stably for 10 minutes to form a fully fluidized boiling state. The heat transfer coefficient was calculated to be 2800 W / (m²·K). In addition, the pressure difference across the channel was recorded as 12 kPa using a micro-pressure sensor.
[0032] Table 1 Comparison of Performance Parameters As shown in Table 1 above, Example 1 achieves optimal balance across multiple performance dimensions. It features a suitable microchannel geometry, uniform surface modification, and precise lubricant control, ultimately maintaining a heat transfer coefficient of 3250 W / (m²·K) while controlling the pressure drop to 15 kPa, achieving good energy efficiency and engineering adaptability. Although Example 2 has a higher heat transfer coefficient (3900), its narrower channels, increased pressure drop to 18 kPa, and higher residual oil content lead to increased system operating burden, resulting in overall performance inferior to Example 1. Example 3, while having the lowest pressure drop (12 kPa), suffers from excessively deep channels, high lubricant viscosity, and weak surface wettability, significantly reducing its heat transfer capacity to only 2800 W / (m²·K), thus exhibiting the weakest overall performance. In conclusion, Example 1 is the optimal solution balancing heat transfer efficiency, flow resistance control, and processing adaptability, and is suitable as the recommended process parameter.
[0033] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.
[0034] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A process for preparing microchannels with enhanced boiling heat transfer on a super-lubricating surface, characterized in that, Includes the following steps: S1: Provide a 6061 aluminum alloy substrate, and polish its surface to remove surface burrs and dirt, so as to obtain a smooth and flat aluminum alloy substrate; S2: Microchannel structures are machined on the surface of an aluminum alloy substrate using a milling machine tool; S3: The microchannel structure is anodized to form an oxide film with a micro-nano porous structure on the surface of the microchannel. S4: The anodized microchannels are immersed in a fluorosilane solution for low surface energy modification, making their surface superhydrophobic; S5: The fluorosilane-modified microchannels are placed in dimethyl silicone oil and oil injection is performed in a vacuum environment to remove air from the micro-nano structure and allow the lubricating oil to be adsorbed into the porous structure. S6: Spin-coating the microchannels after oil injection removes excess lubricating oil from the surface, forming an ultra-smooth surface; S7: Using ethylene glycol as the cooling medium, flow boiling heat transfer tests were conducted on the microchannels on the super-slippery surface to verify their heat transfer performance and pressure drop characteristics under high heat flux density.
2. The process for preparing microchannel-enhanced boiling heat transfer on a super-lubricating surface according to claim 1, characterized in that, S1 specifically includes: S11: The surface of the 6061 aluminum alloy substrate is wet-polished using sandpaper with increasing grit size in sequence, starting with 400 grit and ending with 1500 grit. S12: Use diamond polishing paste or alumina polishing liquid with a particle size of 0.5μm to 2.5μm to perform fine polishing on a polishing machine with a speed of 100rpm to 300rpm until there are no obvious scratches on the surface; S13: Place the polished substrate in acetone, anhydrous ethanol and deionized water in sequence for ultrasonic cleaning for 5 to 15 minutes each; S14: Place the ultrasonically cleaned aluminum alloy substrate in a drying oven and dry it at 50℃ to 80℃ to obtain a smooth and flat aluminum alloy substrate.
3. The process for preparing microchannel-enhanced boiling heat transfer on a super-lubricating surface according to claim 1, characterized in that, S2 specifically includes: S21: Fix the polished aluminum alloy substrate onto the milling machine table and use a dial indicator to align it; S22: Select a four-flute carbide end mill with a diameter of 0.8mm to 1.5mm and clamp it in the spindle shank; S23: Set the spindle speed to 8000rpm to 15000rpm, the feed rate to 100mm / min to 300mm / min, and the depth of cut to 0.02mm to 0.05mm per pass. Perform multiple milling passes along the set parallel path until the microchannel depth reaches 200μm to 400μm. S24: Use compressed air and a brush to remove aluminum shavings and debris from the microchannels.
4. The process for preparing microchannel-enhanced boiling heat transfer on a super-lubricating surface according to claim 1, characterized in that, S3 specifically includes: S31: Place the substrate with microchannels in a sodium hydroxide solution with a concentration of 50 g / L to 80 g / L and immerse it at 60°C to 80°C for 1 to 3 minutes to remove the natural oxide layer on the surface, and then rinse with deionized water; S32: Pour an oxalic acid solution with a concentration of 0.3 mol / L to 0.5 mol / L into the electrolytic cell, and place the substrate as the anode and the lead plate as the cathode in parallel relative to each other, with the electrode spacing maintained at 3 cm to 5 cm. S33: Under the condition that the electrolyte temperature is maintained at 5℃ to 15℃, apply a DC voltage of 35V to 45V and the oxidation time is 30 minutes to 60 minutes. S34: After oxidation, remove the substrate and ultrasonically clean it with deionized water for 5 to 10 minutes to remove residual electrolyte; S35: After being dried with high-pressure nitrogen, a micro-nano porous oxide film is formed on the surface of the microchannel.
5. The process for preparing microchannel-enhanced boiling heat transfer on a super-lubricating surface according to claim 1, characterized in that, S4 specifically includes: S41: Dissolve perfluorodecyltriethoxysilane or heptadecafluorodecyltrimethoxysilane in anhydrous ethanol to prepare a fluorosilane solution with a concentration of 1.0 wt% to 2.5 wt%. S42: Place the anodized substrate in a vacuum drying oven and dry it at 100°C to 120°C for 30 to 60 minutes to remove moisture from the micro-nano porous structure; S43: Transfer the dried matrix into a sealed container and place it above the surface of the fluorosilane solution, and react at 70°C to 85°C for 2 to 4 hours. S44: Remove the modified aluminum alloy base and heat-treat it in an oven at 120°C to 150°C for 1 to 2 hours; S45: After curing, the aluminum alloy substrate is ultrasonically cleaned in xylene and anhydrous ethanol for 5 to 10 minutes each to remove excess fluorosilane molecules that are physically adsorbed, and finally dried with nitrogen.
6. The process for preparing microchannel-enhanced boiling heat transfer on a super-lubricating surface according to claim 1, characterized in that, S5 specifically includes: S51: Pour dimethyl silicone oil with a kinematic viscosity of 10 cSt to 50 cSt into a container, and immerse the fluorosilane-modified aluminum alloy base at an angle of 5° to 15° into the oil; S52: Place the container into a vacuum drying oven, seal it, start the vacuum pump, reduce the pressure inside the drying oven to -0.095MPa to -0.1MPa, and maintain it for 20 to 40 minutes; S53: Under the condition of maintaining vacuum, the aluminum alloy base is completely immersed in dimethyl silicone oil and the immersion continues for 2 to 4 hours; S54: Air is introduced into the vacuum drying oven to allow the pressure to return to normal within 10 to 15 minutes, and the lubricating oil is injected into the micro-nano porous structure using the pressure difference.
7. The process for preparing microchannel-enhanced boiling heat transfer on a super-lubricating surface according to claim 1, characterized in that, S6 specifically includes: S61: The oiled aluminum alloy substrate is installed on the spin coater base and fixed using vacuum adsorption. S62: Start the spin coater and rotate it for 10 to 20 seconds at a speed of 500 to 800 rpm to initially remove excess lubricating oil accumulated at the opening of the microchannel with the help of centrifugal force. S63: Increase the spin coater speed to 2000 rpm to 3000 rpm and maintain this speed for 60 to 120 seconds to thoroughly remove the non-anchored lubricating oil layer from the surface; S64: After spin coating, let the aluminum alloy substrate stand horizontally for 5 to 10 minutes to allow excess lubricating oil in the micro-nano porous structure to flow back to the surface. S65: Use a lint-free cloth to gently wipe the surface in one direction along the microchannels to remove any trace oil film remaining after spin coating.
8. The process for preparing microchannel-enhanced boiling heat transfer on a super-lubricating surface according to claim 1, characterized in that, Specifically, S7 includes: S71: The spin-coated ultra-smooth surface microchannel aluminum alloy substrate is mounted on a controllable heating stage; S72: Connect to a closed-loop system, using ethylene glycol with a mass fraction of 95% or higher as the working medium, pumped into the microchannel inlet by a constant flow pump at a flow rate of 0.5 L / min, while adjusting the back pressure valve to stabilize the outlet pressure at 0.2 MPa; S73: Apply a constant heat flux through a heating platform, control the heat flux density within the range of 100kW / m², and maintain a stable heating state for 10 minutes to form flow boiling conditions; S74: The temperature difference between the inlet and outlet walls of the microchannel is recorded by a thermocouple array, the input electrical power is measured by a power meter, and the corresponding heat transfer coefficient is calculated by combining the inlet and outlet temperature difference with the flow rate. S75: Set up micro-pressure sensors at the inlet and outlet of the microchannel to measure and record the steady-state pressure drop value; S76: The measured heat transfer coefficient and pressure drop value are compared with the test results of the same size un-oiled microchannel to obtain the heat transfer performance and pressure drop characteristics of the super-smooth surface structure under high heat flux density.
9. The process for preparing microchannel-enhanced boiling heat transfer on a super-lubricating surface according to claim 8, characterized in that, The expression for the heat transfer coefficient is: ,in, The heat transfer coefficient; This represents the total input thermal power. For heat exchange area; The temperature difference is the logarithmic mean.