A multi-stage injection micro-mixer structure suitable for scCO2 and paint miscibility

Abstract

This invention relates to a multi-stage injection micro-mixer structure suitable for the miscibility of scCO2 and coatings. This structure effectively solves the problems of unsatisfactory miscibility in the mixing process of scCO2 and oil-soluble coatings in existing technologies, improving the coating spraying effect and quality. The structure includes coating channels, multiple scCO2 channels, and connecting holes. By utilizing the multi-stage injection of scCO2 with gradually increasing diameter connecting holes, scCO2 is injected into the coating channels in a small-scale, multi-stage manner, achieving miscibility with the coating. Simultaneously, multiple inclined baffles are arranged on the inner wall of the coating channels to introduce flow disturbances, increase the Reynolds number and flow rate of the coating fluid, and promote effective mixing of the coating and scCO2. This invention not only achieves highly efficient miscibility between scCO2 and coatings but also avoids clogging problems caused by high fluid resistance, improving coating spraying efficiency and quality, reducing coating consumption and cost, reducing environmental pollution, and increasing operational flexibility and applicability.

Description

Technical Field

[0001] This invention belongs to the field of micro mixers and relates to a mixer, particularly a multi-stage injection micro mixer structure suitable for the miscibility of scCO2 and coatings, which can achieve efficient, uniform and stable mixing of scCO2 and coatings, thereby improving the effect and environmental performance of coating spraying processes. Background Technology

[0002] Coatings are materials that form a protective or decorative film on the surface of objects, and are widely used in construction, furniture, automobiles, aviation, shipbuilding, and other fields. The main components of coatings are pigments, resins, solvents, and additives. The role of the solvent is to give the coating appropriate viscosity and flowability, facilitating spraying or brushing. Traditional oil-based coatings primarily use volatile organic compounds (VOCs) as solvents, such as toluene, ethyl acetate, and acetone. These solvents are directly released into the atmosphere after spraying, damaging the environment and affecting human health. VOC emissions not only lead to environmental problems such as air pollution, the greenhouse effect, and ozone layer depletion, but also cause health problems such as irritation, allergies, and poisoning of the respiratory tract, eyes, and skin.

[0003] In light of this, industry and research have begun exploring new alternative technologies to reduce or eliminate VOC emissions. Supercritical CO2 (scCO2) technology, due to its environmentally friendly characteristics, is considered a promising new spraying process to replace organic solvents. scCO2 refers to CO2 in a state between gas and liquid under certain temperature and pressure conditions, possessing characteristics such as high density, low viscosity, high diffusivity, and high solubility. scCO2 can react with resins and pigments in oil-soluble coatings to form a homogeneous coating solution, which is then sprayed onto the surface of an object using a spray gun. When the coating solution comes into contact with air, the CO2 rapidly desolvates, causing the coating to solidify into a thin film, while the CO2 can be recycled and reused, achieving zero emissions. scCO2 spraying technology offers advantages such as energy saving, reduced consumption, emission reduction, and improved coating quality, making it a green coating technology with broad development prospects.

[0004] Currently, most scCO2 spraying systems employ a mixing chamber or agitator where two fluids collide directly to mix scCO2 and paint. A mixing chamber is a small mixing room located at the spray gun exit, where scCO2 and paint are delivered separately through different pipes, and mixing is achieved through high-speed collision of the two fluids. Agitator, on the other hand, is a container equipped with a stirring device located upstream of the spray gun. scCO2 and paint are delivered separately through different pipes to the container, where mixing is achieved through the rotation of the stirring device, and then the mixed paint solution is delivered to the spray gun.

[0005] Both of the above methods have some defects and shortcomings in practical work. The disadvantage of the mixing chamber is that if the mixing time is too short, the mixing is insufficient, which can easily cause phenomena such as coating layering, sedimentation, and solidification, affecting the quality and uniformity of the coating film. The disadvantage of the mixing tank is that if the mixing time is too long, the mixing is over-mixed, which can easily cause phenomena such as coating decomposition, oxidation, and polymerization, affecting the performance and stability of the coating film. These defects result in the miscibility effect of the two mixing methods in actual operation being less than ideal, becoming an uncontrollable factor, making it impossible to obtain the best spraying effect by controlling the temperature, pressure, and mixing ratio of the coating and supercritical CO2. The complete mixing of coating and scCO2 is a key factor affecting the spraying quality. If the mixing is insufficient, it may lead to problems such as color difference, uneven gloss, or insufficient adhesion on the coating surface. Based on the above reasons, how to design a mixing device that can achieve efficient, uniform, and stable mixing of scCO2 and coating to ensure the effect and environmental performance of the coating spraying process is an urgent technical problem to be solved. Summary of the Invention

[0006] (I) Purpose of the Invention

[0007] To address the aforementioned defects and shortcomings of existing technologies in the mixing process of supercritical carbon dioxide (scCO2) and oil-soluble coatings, particularly the unsatisfactory miscibility of scCO2 and oil-soluble coatings due to the mixing chamber and stirring tank, this invention proposes a multi-stage injection micromixer structure suitable for the miscibility of scCO2 and coatings, taking into full account the flow characteristics of scCO2 and the high viscosity of coatings. This structure includes coating channels, multiple scCO2 channels, and connecting holes. By utilizing the multi-stage injection of scCO2 with gradually increasing diameter connecting holes, scCO2 is injected into the coating channels in a small-scale, multi-stage manner, achieving better miscibility and avoiding clogging problems caused by excessive flow resistance while maintaining a small fluid scale. Furthermore, the baffle design in the micromixer ensures that the coating achieves a relatively high Reynolds number in the pipeline, thereby improving fluid mixing efficiency. This allows for a relatively small micromixer size, facilitating the selection of appropriate pipeline numbers and diameters in actual production, and adjustment based on the flow rate range of the coating and scCO2. With this design, the micro mixer can not only meet the challenges of high flow rates, but also be modularly applied in parallel or series, greatly improving operational flexibility and applicability.

[0008] (II) Technical Solution

[0009] To achieve the objective of this invention, the present invention adopts the following technical solution:

[0010] A multi-stage injection micromixer structure suitable for the miscibility of scCO2 and coatings includes at least one columnar structure extending along its length, wherein the columnar structure is located at two end faces along its length, the first end face forming an inlet face and the second end face forming an outlet face, characterized in that...

[0011] The columnar structure has a paint channel extending along its length and open at both ends at its center. The inlet end of the paint channel is formed on a first end face of the columnar structure and is in fluid communication with an external paint storage container via at least one pipe. The outlet end of the paint channel is formed on a second end face of the columnar structure and is in fluid communication with an external spraying device via at least one pipe.

[0012] The inner wall of the coating channel is provided with multiple baffles that extend radially and are inclined toward the outlet in a discrete and staggered manner along its length to introduce flow disturbance, and at least each of the baffles has a generally smooth streamlined shape on its frontal surface to reduce fluid resistance and promote effective mixing of coating and scCO2.

[0013] The columnar structure also includes several scCO2 channels extending along its length, open at one end and closed at the other. Each scCO2 channel is evenly distributed circumferentially around the coating channels. The inlet end of each scCO2 channel is formed on the first end face of the columnar structure and is fluidly connected to an external scCO2 supply source via a pipeline. The other end of each scCO2 channel is closed and extends along its length to near the outlet face of the columnar structure, ensuring that the scCO2 can pass through approximately the entire columnar structure and fully mix with the coating.

[0014] Each scCO2 channel and the coating channel are provided with a plurality of radially extending connecting holes distributed along the length direction. The inlet end of each connecting hole communicates with the inner cavity of the scCO2 channel, and the outlet end of each connecting hole communicates with the inner cavity of the coating channel. Each connecting hole is perpendicular to the main flow direction of the fluid in the coating channel at least in its outlet direction to promote uniform distribution and effective injection of scCO2. The diameter of each connecting hole gradually increases from the inlet end to the closed end of the scCO2 channel. The diameter of the connecting hole near the inlet face of the columnar structure is smaller, and the diameter of the connecting hole near the outlet face of the columnar structure is larger to optimize the injection pressure and flow distribution of scCO2.

[0015] Preferably, the micro-mixer structure has a sensor device for detecting the uniformity of mixing near the outlet surface of the columnar structure. This sensor device can monitor the uniformity of the coating and scCO2 mixture in real time to ensure the quality of the final product.

[0016] Preferably, the number of scCO2 channels is determined according to the following formula:

[0017]

[0018] Where N is the number of scCO2 channels, Where is the flow rate of scCO2, Dc is the diameter of each scCO2 channel, and v is the design velocity of scCO2 in the channel to ensure uniform distribution of scCO2.

[0019] Preferably, each of the baffles includes a micro / nanostructured surface, the micro / nanostructured surface being designed to generate a micro-turbulence effect during coating flow to improve mixing efficiency and reduce the required mixing distance.

[0020] Preferably, a layer of superhydrophobic or superhydrophilic nanomaterial is coated on the surface of the baffle, and the wettability of the fluid is adjusted according to the properties of the coating to affect the fluid's adhesion and separation, thereby reducing flow resistance and scaling. The superhydrophobic or superhydrophilic surface shape is optimized to conform to the following mathematical expression:

[0021] y = Asin(kx + φ)

[0022] Where A is the amplitude of the surface, k is the wave number of the surface, and φ is the phase of the surface.

[0023] Preferably, the frontal surface of each of the baffles is designed based on fluid dynamics principles, and its surface shape is optimized to conform to the following mathematical expression:

[0024]

[0025] Where dP / dx represents the pressure gradient, μ is the dynamic viscosity of the coating, L is the baffle length, Q is the fluid flow rate, and D is the coating channel diameter, in order to achieve optimal hydrodynamic performance.

[0026] Preferably, the plurality of baffles are interconnected along the length of the inner wall of the coating channel and are spiral in shape to increase the rotation and turbulence of the fluid. The surface shape of the spiral baffles is optimized to conform to the following mathematical expression:

[0027] x = rcosθ, y = rsinθ, z = hθ

[0028] Where x, y, and z represent the three-dimensional coordinates of the surface of the helical baffle, r is the helical radius, θ is the helical angle, and h is the helical height.

[0029] Preferably, the diameter of the connecting hole gradually increases from the inlet end to the closed end of the scCO2 channel, and the rate of change is optimized and determined based on the specific physical properties of the coating and scCO2 using the following formula:

[0030]

[0031] Where ΔD represents the increment of the diameter of adjacent connecting holes, and Let ρ represent the density and viscosity of scCO2, respectively. paint and μ paint These represent the density and viscosity of the coating, respectively. This design ensures that the injection of scCO2 is not only uniform along the entire length of the coating channel, but also adapts to the specific mixing requirements of different coatings combined with scCO2, thereby improving mixing efficiency and reducing the potential risk of clogging.

[0032] Preferably, the design of the connecting holes adopts a hydrodynamically optimized stepwise diffusion mode to achieve effective penetration and mixing of scCO2 in the coating pipeline. The diameter and spacing of the connecting holes at each stage are precisely calculated using the following formula:

[0033] D n =D0·a n-1 S n =S0·b n-1

[0034] Among them, D n and S n Let D0 and S0 represent the diameter of the nth-level connecting hole and the spacing between two adjacent connecting holes, respectively. D0 and S0 represent the initial diameter of the connecting hole and the spacing between the connecting holes, respectively. a and b are increment coefficients, and n is the number of connecting hole levels. This progressive design takes into account the pressure loss and diffusion efficiency of scCO2 when entering the coating channel, aiming to maximize the contact surface area while reducing the risk of channel blockage that may occur as the pressure increases.

[0035] Preferably, the outlet end of each of the connecting holes is designed to be tapered, thereby increasing the jetting effect of the fluid, improving the mixing efficiency of the fluid and the coating, and optimizing the coating spraying effect. The shape of the outlet end of the tapered connecting hole conforms to the following mathematical expression:

[0036] r = αx

[0037] Where r is the radius of the outlet end of the connection hole, x is the length of the outlet end of the connection hole, and α is the cone angle of the outlet end of the connection hole.

[0038] (III) Technical Effects

[0039] Compared with the prior art, the multi-stage injection micromixer structure of the present invention, which is suitable for the miscibility of scCO2 and coatings, has the following beneficial and significant technical effects:

[0040] (1) This invention proposes a multi-stage injection micro-mixer structure for mixing supercritical carbon dioxide (scCO2) with oil-soluble coatings, solving the problem of unsatisfactory miscibility caused by the mismatch between the high viscosity of the coating and the flow characteristics of scCO2 in existing technologies. Compared with traditional mixing chambers or stirred tanks, this invention achieves better miscibility and higher operating efficiency through its structural design. Its significant technical effects include efficient mixing of coatings and scCO2 at the microscale, and prevention of clogging in high-flow-rate operation, ensuring the reliability of continuous production.

[0041] (2) This invention utilizes a multi-stage vertical injection method with gradually increasing diameter connecting holes to inject scCO2 into the coating channel in a small-scale, multi-stage manner, achieving better miscibility with the coating. This method maintains a small fluid scale while avoiding potential clogging issues caused by excessive flow resistance, thus improving coating efficiency and quality. Simultaneously, the progressively enlarging connecting holes effectively balance the injection pressure and flow distribution at each stage, preventing "fluid short-circuiting." This avoids the situation where, due to pressure drop, most scCO2 near the inflow point is injected through the connecting hole at that point, affecting the miscibility at subsequent points and compromising uniformity.

[0042] (3) The baffle design in the micro mixer of the present invention ensures that the coating obtains a relatively high Reynolds number and flow rate in the pipeline, thereby improving the fluid mixing efficiency. This allows the micro mixer to be relatively small in size, making it easier to select the appropriate number and diameter of pipelines as needed in actual production, and to adjust according to the flow range of the coating and scCO2, thus improving the flexibility and applicability of operation.

[0043] (4) The micro mixer of the present invention can not only meet the challenge of large flow rate, but also be modularly applied in parallel or series connection, which greatly improves the scale and standardization of production and reduces production costs and risks. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the overall appearance of the multi-stage injection micro-mixer structure of the present invention, which is suitable for the miscibility of scCO2 and coatings.

[0045] Figure 2 This is a schematic diagram of the inlet surface of a multi-stage injection micromixer;

[0046] Figure 3 yes Figure 2 AA section view;

[0047] Figure 4 yes Figure 2 BB cross-sectional view;

[0048] Figure 5 yes Figure 3 CC section view.

[0049] Explanation of reference numerals in the attached figures:

[0050] Columnar structure 10, columnar structure inlet face 11, columnar structure outlet face 12, paint channel 20, baffle plate 21, scCO2 channel 30, connecting hole 40. Detailed Implementation

[0051] To better understand the present invention, the following embodiments further illustrate its content. Throughout the accompanying drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions. The described embodiments are some, but not all, of the embodiments of the present invention. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The structure and technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings, providing one embodiment of the present invention.

[0052] Example 1

[0053] like Figures 1-5 As shown, the multi-stage injection micro-mixer structure of the present invention, which is suitable for the miscibility of supercritical carbon dioxide (scCO2) and coatings, includes at least a columnar structure 10 extending along the length direction. Of the two end faces of the columnar structure 10 located along the length direction, the first end face is formed as an inlet face 11 and the second end face is formed as an outlet face 12.

[0054] A coating channel 20 extending along its length and open at both ends is provided at the center of the columnar structure 10. The inlet end of the coating channel 20 is formed on the first end face of the columnar structure 10 and is in fluid communication with an external coating storage container through at least one pipe. The outlet end of the coating channel 20 is formed on the second end face of the columnar structure 10 and is in fluid communication with an external spraying device through at least one pipe. Furthermore, a plurality of baffles 21, which extend radially and are inclined toward the outlet direction, are provided on the inner wall of the coating channel 20 along its length in a discrete and staggered manner to introduce flow disturbance. At least each baffle 21 has a generally smooth streamlined shape on its frontal surface to reduce fluid resistance and promote effective mixing of coating and scCO2.

[0055] The columnar structure 10 is also provided with several scCO2 channels 30 extending along its length direction, with one end open and the other end closed. Each scCO2 channel 30 is evenly distributed around the coating channel 20 in the circumferential direction. The inlet end of each scCO2 channel 30 is formed on the first end face of the columnar structure 10 and is fluidly connected to an external scCO2 supply source through a pipeline. The other end of each scCO2 channel 30 is closed and extends in the length direction to a position close to the outlet face of the columnar structure 10, so as to ensure that scCO2 can pass through the entire columnar structure 10 and be fully mixed with the coating.

[0056] Each scCO2 channel 30 and the coating channel 20 are provided with a plurality of radially extending connecting holes 40 distributed along the length direction. The inlet end of each connecting hole 40 is connected to the inner cavity of the scCO2 channel, and the outlet end of each connecting hole 40 is connected to the inner cavity of the coating channel 20. Each connecting hole 40 is perpendicular to the main flow direction of the fluid in the coating channel 20 at least in its outlet direction to promote uniform distribution and effective injection of scCO2. The diameter of each connecting hole 40 gradually increases from the inlet end to the closed end of the scCO2 channel 30. The diameter of the connecting hole near the inlet face of the columnar structure 10 is smaller, and the diameter of the connecting hole near the outlet face of the columnar structure 10 is larger to optimize the injection pressure and flow distribution of scCO2.

[0057] This invention relates to a multi-stage injection micro-mixer structure suitable for the miscibility of supercritical carbon dioxide (scCO2) and coatings. Its working principle is as follows: When coatings enter the inlet of the coating channel from an external coating storage container via pipeline, scCO2 from an external scCO2 supply source enters the inlet of each scCO2 channel via pipeline. Then, it is injected into the coating channel in a small-scale, multi-stage manner through connecting holes, where it miscibly mixes with the coating to form an scCO2 / coating solution. This solution flows out through the outlet of the coating channel and enters the external spraying equipment for spraying. During this process, the diameter of the connecting holes gradually increases from the inlet to the closed end of the scCO2 channel, causing the injection velocity of scCO2 to gradually decrease, thus improving the miscibility of scCO2 and coatings. Simultaneously, the presence of baffles makes the flow of coatings in the coating channel more turbulent, thereby improving fluid mixing efficiency. This allows the micro-mixer to be relatively small in size, facilitating the selection of appropriate pipeline numbers and diameters as needed in actual production, and allowing adjustments based on the flow range of coatings and scCO2. With this design, the micro mixer can not only meet the challenges of high flow rates, but also be modularly applied in parallel or series, greatly improving operational flexibility and applicability.

[0058] Example 2

[0059] Based on Example 1, as a preferred embodiment of the present invention, the micro mixer structure has a sensor device for detecting the uniformity of mixing near the outlet surface of the columnar structure 10. This sensor device can monitor the uniformity of the coating and scCO2 mixture in real time to ensure the quality of the final product.

[0060] In a preferred embodiment of the present invention, the number of scCO2 channels 30 can be determined according to the following relationship:

[0061]

[0062] Where N is the number of scCO2 channels, Where is the flow rate of scCO2, Dc is the diameter of each scCO2 channel, and v is the design velocity of scCO2 in the channel to ensure uniform distribution of scCO2.

[0063] In a preferred embodiment of the present invention, each baffle 21 may include a micro-nano structure surface, the structure of which is designed to generate a micro-turbulence effect during the flow of the coating, thereby improving mixing efficiency and reducing the required mixing distance.

[0064] In a preferred embodiment of the present invention, a layer of superhydrophobic or superhydrophilic nanomaterial can be coated on the surface of the baffle 21, and the wettability of the fluid can be adjusted according to the properties of the coating to affect the fluid's adhesion and separation, thereby reducing flow resistance and scaling. The superhydrophobic or superhydrophilic surface shape conforms to the following mathematical expression:

[0065] y = Asin(kx + φ)

[0066] Where A is the amplitude of the surface, k is the wave number of the surface, and φ is the phase of the surface.

[0067] In a preferred embodiment of the present invention, the design of the frontal surface of each baffle 21 can be based on the principles of fluid dynamics, and its surface shape is optimized to conform to the following mathematical expression:

[0068]

[0069] Where dP / dx represents the pressure gradient, μ is the dynamic viscosity of the coating, L is the baffle length, Q is the fluid flow rate, and D is the coating channel diameter, in order to achieve optimal hydrodynamic performance.

[0070] In a preferred embodiment of the present invention, multiple baffles 21 can be interconnected along the length of the inner wall of the coating channel 20 and form a spiral shape to increase the rotation and turbulence of the fluid. The surface shape of the spiral baffles is optimized to conform to the following mathematical expression:

[0071] x = rcosθ, y = rsinθ, z = hθ

[0072] Where x, y, and z represent the three-dimensional coordinates of the surface of the helical baffle, r is the helical radius, θ is the helical angle, and h is the helical height.

[0073] In a preferred embodiment of the present invention, the diameter of the connecting hole 40 gradually increases along the direction from the inlet end to the closed end of the scCO2 channel 30, and its rate of change can be optimized and determined according to the specific physical properties of the coating and scCO2 through the following relationship:

[0074]

[0075] Where ΔD represents the increment of the diameter of adjacent connecting holes, and Let ρ represent the density and viscosity of scCO2, respectively. paint and μ paint These represent the density and viscosity of the coating, respectively. This design ensures that the injection of scCO2 is not only uniform along the entire length of the coating channel 20, but also adapts to the specific mixing requirements of different coatings combined with scCO2, thereby improving mixing efficiency and reducing the potential risk of clogging.

[0076] In a preferred embodiment of the present invention, the design of the connecting hole 40 can adopt a hydrodynamically optimized stepwise diffusion mode to achieve effective penetration and mixing of scCO2 in the coating pipeline. The diameter and spacing of the connecting holes at each stage are precisely calculated using the following formula:

[0077] D n =D0·a n-1 S n =S0·b n-1

[0078] Among them, D n and S n Let D0 and S0 represent the diameter of the nth-level connecting hole and the spacing between two adjacent connecting holes, respectively. D0 and S0 represent the initial diameter of the connecting hole and the spacing between the connecting holes, respectively. a and b are increment coefficients, and n is the number of connecting hole levels. This progressive design takes into account the pressure loss and diffusion efficiency of scCO2 when entering the coating channel 20, aiming to maximize the contact surface area while reducing the risk of channel blockage that may occur as the pressure increases.

[0079] In a preferred embodiment of the present invention, the outlet end of each connecting hole 40 can be designed to be tapered, thereby increasing the jetting effect of the fluid, improving the mixing efficiency of the fluid and the coating, and optimizing the coating spraying effect. The shape of the outlet end of the tapered connecting hole conforms to the following mathematical expression:

[0080] r = αx

[0081] Where r is the radius of the outlet end of the connection hole, x is the length of the outlet end of the connection hole, and α is the cone angle of the outlet end of the connection hole.

[0082] The objectives of this invention have been fully and effectively achieved through the above embodiments. Those skilled in the art will understand that this invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments described above. Although the invention has been described with reference to what is currently considered the most practical and preferred embodiments, it should be understood that the invention is not limited to the disclosed embodiments, and any modifications that do not depart from the functional and structural principles of the invention will be included within the scope of the claims.

Claims

1. A multi-stage injection micromixer structure suitable for the miscibility of scCO2 and coatings, comprising at least one columnar structure extending along its length, wherein the columnar structure is located at two end faces along its length, the first end face forming an inlet face and the second end face forming an outlet face, characterized in that, The columnar structure has a paint channel extending along its length and open at both ends at its center. The inlet end of the paint channel is formed on a first end face of the columnar structure and is in fluid communication with an external paint storage container via at least one pipe. The outlet end of the paint channel is formed on a second end face of the columnar structure and is in fluid communication with an external spraying device via at least one pipe. The inner wall of the coating channel is provided with multiple baffles that extend radially and are inclined toward the outlet in a discrete and staggered manner along its length to introduce flow disturbance, and at least each of the baffles has a generally smooth streamlined shape on its frontal surface to reduce fluid resistance and promote effective mixing of coating and scCO2. The columnar structure also includes several scCO2 channels extending along its length, open at one end and closed at the other. Each scCO2 channel is evenly distributed circumferentially around the coating channels. The inlet end of each scCO2 channel is formed on the first end face of the columnar structure and is fluidly connected to an external scCO2 supply source via a pipeline. The other end of each scCO2 channel is closed and extends along its length to near the outlet face of the columnar structure, ensuring that the scCO2 can pass through approximately the entire columnar structure and fully mix with the coating. Each scCO2 channel and the coating channel are provided with a plurality of radially extending connecting holes distributed along the length direction. The inlet end of each connecting hole communicates with the inner cavity of the scCO2 channel, and the outlet end of each connecting hole communicates with the inner cavity of the coating channel. Each connecting hole is perpendicular to the main flow direction of the fluid in the coating channel at least in its outlet direction to promote uniform distribution and effective injection of scCO2. The diameter of each connecting hole gradually increases from the inlet end to the closed end of the scCO2 channel. The diameter of the connecting hole near the inlet face of the columnar structure is smaller, and the diameter of the connecting hole near the outlet face of the columnar structure is larger to optimize the injection pressure and flow distribution of scCO2.

2. The multi-stage injection micromixer structure suitable for the miscibility of scCO2 and coatings according to claim 1, characterized in that, The micro-mixer structure has a sensor device near the outlet surface of the columnar structure to detect the uniformity of mixing. This sensor device can monitor the uniformity of the coating and scCO2 mixture in real time to ensure the quality of the final product.

3. The multi-stage impinging micro-mixer structure suitable for scCO2 and paint miscibility according to claim 1, characterized in that, The number of scCO2 channels is determined according to the following formula: where N is the number of scCO2 channels, is the flow rate of scCO2, Dc is the diameter of each scCO2 channel, and v is the design velocity of scCO2 in the channel to ensure uniform distribution of scCO2.

4. The multi-stage injection micromixer structure suitable for the miscibility of scCO2 and coatings according to claim 1, characterized in that, Each of the baffles includes a micro / nanostructured surface designed to generate micro-turbulence during coating flow, thereby improving mixing efficiency and reducing the required mixing distance.

5. The multi-stage injection micromixer structure suitable for the miscibility of scCO2 and coatings according to claim 1, characterized in that, A layer of superhydrophobic or superhydrophilic nanomaterial is coated on the surface of the baffle plate, and the wettability of the fluid is adjusted according to the properties of the coating to affect the fluid's adhesion and separation, thereby reducing flow resistance and scaling. The superhydrophobic or superhydrophilic surface shape is optimized to conform to the following mathematical expression: y = Asin(kx + φ) Where A is the amplitude of the surface, k is the wave number of the surface, and φ is the phase of the surface.

6. The multi-stage impinging micro-mixer structure suitable for scCO2 and paint miscibility according to claim 1, wherein, The design of the frontal surface of each baffle is based on fluid dynamics principles, and its surface shape is optimized to conform to the following mathematical expression: Where dP / dx represents the pressure gradient, μ is the dynamic viscosity of the coating, L is the baffle length, Q is the fluid flow rate, and D is the coating channel diameter, in order to achieve optimal hydrodynamic performance.

7. The multi-stage impinging micro-mixer structure suitable for scCO2 and paint miscibility according to claim 1, characterized in that, The plurality of baffles are interconnected along the length of the inner wall of the coating channel and are spiral in shape to increase the rotation and turbulence of the fluid. The surface shape of the spiral baffles is optimized to conform to the following mathematical expression: x = rcosθ, y = rsinθ, z = hθ Where x, y, and z represent the three-dimensional coordinates of the surface of the helical baffle, r is the helical radius, θ is the helical angle, and h is the helical height.

8. The multi-stage impinging micro-mixer structure suitable for scCO2 and paint miscibility according to claim 1, characterized in that, The diameter of the connecting hole gradually increases from the inlet end to the closed end of the scCO2 channel, and its rate of change is optimized and determined based on the specific physical properties of the coating and scCO2 using the following formula: where ΔD represents the increment of the diameter of the adjacent connecting holes, and respectively represent the density and viscosity of scCO2, ρ paint and μ paint respectively represent the density and viscosity of the paint.

9. The multi-stage impinging micro-mixer structure suitable for scCO2 and paint miscibility according to claim 1, wherein, The design of the connecting holes adopts a hydrodynamically optimized stepwise diffusion mode to achieve effective penetration and mixing of scCO2 in the coating pipeline. The diameter and spacing of the connecting holes at each stage are precisely calculated using the following formula: D n =D0·a n-1 S n =S0·b n-1 Among them, D n and S n Let D0 and S0 represent the diameter of the nth level connecting hole and the spacing between two adjacent connecting holes, respectively. D0 and S0 represent the initial diameter of the connecting hole and the spacing between the connecting holes, respectively. a and b are incrementing coefficients, and n is the number of connecting hole levels.

10. The multi-stage impinging micro-mixer structure suitable for scCO2 and paint miscibility according to claim 1, wherein, The outlet end of each of the aforementioned connecting holes is designed to be tapered, thereby increasing the jetting effect of the fluid, improving the mixing efficiency between the fluid and the coating, and optimizing the coating spraying effect. The shape of the outlet end of the tapered connecting hole conforms to the following mathematical expression: r＝αx Where r is the radius of the outlet end of the connection hole, x is the length of the outlet end of the connection hole, and α is the cone angle of the outlet end of the connection hole.

Images