High-pressure water atomization device design method based on analogue simulation

Abstract

The invention relates to the field of high-pressure water atomization, in particular to a high-pressure water atomization device design method based on analogue simulation. The design method comprises the steps that multiple possible factors possibly influencing high-pressure water atomization are obtained; constructing a double-nozzle high-pressure water atomization geometric model; setting boundary conditions, and determining a calculation model; for a plurality of possible factors, a single variable method is adopted, simulation is conducted on the geometric model for multiple times, a plurality of simulation results are obtained, and each simulation result comprises a liquid drop particle size distribution effect picture and a liquid drop particle size distribution condition; and according to the simulation result, selecting actual factors influencing high-pressure water atomization from a plurality of possible factors, and determining the influence condition of each actual factor on high-pressure water atomization so as to guide the design of the high-pressure water atomization device. Through a numerical simulation method, the change condition of the molten metal under high-pressure water impact is explained, the design of the water atomization high-pressure water spraying frame device is guided through the simulation result, the design period is short, the design cost is low, and powder is finer.

Description

Technical Field

[0001] The invention relates to the field of high-pressure water atomization, and in particular to a design method of a high-pressure water atomization device based on simulation. Background Art

[0002] Powder metallurgy (PM) refers to a set of processes for producing net-shape (or near-net-shape) metal parts from metal powders, which offers flexibility in part design, energy efficiency, and density / porosity control. Due to these characteristics, PM is considered an inherently sustainable technology. With the improvement of various powder metallurgy processes and the emergence of metal AM, the powder metallurgy industry has entered a new era with greater capabilities but stricter requirements for raw powders. As a result, the demand for high-quality and consistent metal powders is increasing.

[0003] Water atomized powders are usually irregular in shape, with a rough surface, poor fluidity, and contain a large number of voids, which is not conducive to products with morphology requirements, such as magnetic powders with low magnetic loss and spraying and welding powders that require high fluidity. In addition, the particle size distribution range of water atomized powders is large, which will reduce the number of end users who need a tighter particle size distribution. Water atomization technology needs to be improved to produce higher quality powders with tighter PSD to expand the application and market of water atomized powders.

[0004] The process of preparing metal powder by water atomization is very complicated. Its complexity comes not only from the kinetic reaction between high-temperature metal melt and water phase, but also includes the comprehensive application of phase change theory and thermodynamic principles, as well as a deep understanding of the powder forming mechanism. However, the detailed atomization mechanism and specific flow field characteristics involved are not yet completely clear, and it is costly and time-consuming to optimize and design the nozzle structure through experiments to improve the performance of atomized powder.

[0005] Therefore, there is an urgent need to design a model that can simulate the process of preparing metal powder by water atomization, so as to guide the design of high-pressure water atomization equipment through simulation. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a design method for a high-pressure water atomization device based on simulation. It uses a numerical simulation method to explain the changes of molten metal under the impact of high-pressure water, and uses the simulation results to guide the design of a water atomization high-pressure water spray rack device. The design cycle is short, the design cost is low, and the powder is finer.

[0007] In order to solve the above technical problems, the technical solution of the present invention is: a design method of a high-pressure water atomization device based on simulation, the method comprising:

[0008] Get multiple possible factors that may affect high pressure water atomization;

[0009] Construct a dual-nozzle high-pressure water atomization geometric model: construct the flow field part and the two nozzle parts. The two nozzle parts are extracted based on the internal shape of the nozzle to simulate the flow of the fluid inside the nozzle and spray relative to each other. The flow field part is a cylinder, which simulates the external flow field formed by the interaction between the water flow ejected from the nozzle and the surrounding static air. The guide part of the metal melt is added to the flow field part.

[0010] The geometric model is meshed, the area near the nozzle outlet is locally encrypted, the boundary conditions of the geometric model are set, and the computational model of the geometric model water atomization numerical simulation is determined. The computational model includes a turbulence model for simulating the turbulent flow process of the fluid and a discrete phase model for simulating the nozzle spraying process.

[0011] For multiple possible factors, a single variable method is used to perform multiple simulations through the constructed model to obtain multiple simulation results, each of which includes a droplet size distribution effect diagram and droplet size distribution situation;

[0012] According to the simulation results, the actual factors affecting the high-pressure water atomization are selected from multiple possible factors, and the influence of each actual factor on the high-pressure water atomization is determined to guide the design of the high-pressure water atomization device.

[0013] Furthermore, the method further comprises:

[0014] Based on multiple actual factors, orthogonal experiments are used to design multiple actual factor parameter combinations, and the constructed model is used to simulate multiple actual factor parameter combinations. According to the simulation results, the best actual factor parameter combination is selected;

[0015] The parameters in the best actual factor parameter combination are used as the design parameters of the high-pressure water atomization device to design the high-pressure water atomization device.

[0016] Furthermore, the method further comprises:

[0017] According to the simulation results of various actual factor parameter combinations, at least one key factor is selected from the actual factors, and the structure related to the key factor in the high-pressure water atomization device is set to an adjustable or controllable structure.

[0018] Further, the steps to set the boundary conditions of the geometric model are:

[0019] The inlet boundary condition of the nozzle part is set as the pressure inlet, the lower boundary of the flow field part is set as the pressure outlet, and the pressure outlet parameters are set as the ambient atmospheric conditions. The other surfaces of the flow field part except the lower boundary are set as adiabatic no-slip walls, and the contact angle between the wall and water is defined as a neutral contact angle of 90 degrees. The inlet boundary of the guide part is set as the velocity inlet.

[0020] Furthermore, the turbulence model is the RNG k-ε model, which includes two transport equations, namely the transport equation for the turbulent kinetic energy k and the transport equation for the turbulent dissipation rate ε;

[0021] The transport equation of turbulent kinetic energy k is:

[0022]

[0023] The transport equation for the turbulent dissipation rate ε is:

[0024]

[0025] In the formula, μ represents the effective viscosity; μ t represents the turbulent dynamic viscosity; t is time; C 1ε , C 2ε and C 3ε is a constant coefficient; G k Turbulent kinetic energy generation caused by mean velocity gradient; G b Turbulent kinetic energy generation caused by buoyancy; Y M represents the effect of compressible turbulent pulsation expansion on the total dissipation rate; k, ε represent turbulent kinetic energy and turbulent dissipation rate respectively; σ k , σ ε is the Prandtl number corresponding to the turbulent kinetic energy and turbulent dissipation rate; u i and u j represents the velocity components in the i and j directions; x i and x j They represent the axial coordinates in the i and j directions respectively; ρ represents the fluid density; S k and S ε Represents a user-defined source item.

[0026] Furthermore, in the multiphase flow composed of discrete phase and fluid, the Lagrangian method is used to describe the discrete phase, and the fluid is described as the continuous phase. The equation of motion of the discrete phase particles is:

[0027]

[0028] f y represents the additional acceleration term; f D (u-up) represents the resistance per unit particle mass; u p represents the continuous phase velocity; ρ represents the continuous phase density; ρ p Indicates the particle density.

[0029] Furthermore, each simulation result also includes a velocity cloud distribution diagram and a velocity cloud distribution curve along an axis.

[0030] Furthermore, multiple practical factors that affect high-pressure water atomization include atomization water pressure, spray top angle and smelting temperature.

[0031] After adopting the above technical scheme, the present invention constructs a model for simulating high-pressure water atomization, observes the changes of molten metal under high-pressure water impact through numerical simulation, and explains its influence on the formation stage of water mist and the multiphase flow law of molten metal atomization and fragmentation stage by changing the corresponding parameters, and uses the simulation results to guide the actual water atomization powder making process to achieve the purpose of reducing costs and saving time. Moreover, the present invention can also obtain the best combination of actual factor parameters based on simulation, so as to fundamentally promote high-pressure water atomization of ultrafine metal powder. The water atomization high-pressure water spray rack device obtained by this method has a short design cycle, low design cost and finer powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A flow chart of a method for designing a high-pressure water atomization device based on simulation of the present invention;

[0033] Figure 2 Schematic diagram of the double-nozzle high-pressure water atomization geometric model of the present invention;

[0034] Figure 3 This is the droplet size distribution effect diagram under different atomization water pressures;

[0035] Figure 4 This is a chart showing the droplet size distribution on the cross section at a height of 35 mm under different atomization water pressures;

[0036] Figure 5 Velocity distribution cloud diagrams of the xy section (left), yz section (middle) and xz section at 40 mm (right) under different atomization water pressures;

[0037] Figure 6 The average velocity distribution of droplets along the y-axis under different atomization water pressure conditions;

[0038] Figure 7 The droplet size distribution effect diagram under different spray vertex angles;

[0039] Figure 8 The droplet size distribution diagram of the xz section at 35mm under different spray vertex angles;

[0040] Fig. 9 Velocity distribution cloud diagrams of the xy section (left), yz section (middle) and xz section at 40 mm (right) at different injection top angles;

[0041] Fig.10 The average velocity distribution of the droplet along the y-axis at different spray vertex angles;

[0042] Fig.11 Take a panoramic view of the platform for the water atomization powder making experiment;

[0043] Fig.12 This is a diagram of an open water atomization powder making equipment;

[0044] Fig.13 The fragmentation of molten tin under different atomization water pressures and the partial enlarged picture;

[0045] Fig.14 The fragmentation of molten tin at different injection top angles and the local enlarged image. DETAILED DESCRIPTION

[0046] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments in conjunction with the accompanying drawings.

[0047] like Figure 1 As shown, a design method of a high-pressure water atomization device based on simulation, the method includes:

[0048] Step S1, obtaining multiple possible factors that may affect high-pressure water atomization, namely, atomization water pressure, spray vertex angle, smelting temperature and guide tube elongation. These possible factors can be obtained through experience, literature, etc.;

[0049] Step S2, constructing a dual-nozzle high-pressure water atomization geometric model: constructing a flow field part and two nozzle parts. The two nozzle parts are extracted based on the internal shape of the nozzle (this embodiment uses the German LECHLER nozzle, model 602.701.A3.00.00.2, belonging to the plane fan atomizer series) to simulate the flow of fluid inside the nozzle and relative injection; the flow field part is a cylinder, simulating the external flow field formed by the interaction of water flow from the nozzle with the surrounding still air. Since the research involves the situation of crushing metal, a guide part for the metal melt is added to the flow field part. The initial diameter of the guide part is 4mm, and the initial extension is 3mm. The specific geometric model is as follows Figure 2 shown.

[0050] In this step, in order to reduce errors and ensure the accuracy of the results, the internal structure of the nozzle is three-dimensionally modeled according to the actual size and proportion, so as to more accurately simulate the performance of the nozzle in actual work. Due to the large scale of the actual atomization chamber, building a three-dimensional model completely in accordance with the 1:1 ratio will require a huge amount of calculation and calculation time, and at the same time, the performance requirements of the computer are high and the calculation process is prone to divergence. Therefore, in this embodiment, in addition to drawing the inside of the nozzle in a 1:1 ratio, the flow field part is simplified and set to a cylinder with a diameter of 45mm and a height of 48mm.

[0051] Step S3, meshing the geometric model, locally encrypting the area near the nozzle outlet, setting the boundary conditions of the geometric model, and determining the computational model for numerical simulation of water atomization of the geometric model, wherein the computational model includes a turbulence model for simulating the turbulent flow process of the fluid and a discrete phase model for simulating the nozzle spraying process;

[0052] In this step, ANSYS Meshing is used to mesh the geometric model. In the area near the nozzle outlet, due to the complex two-phase flow state and high-speed flow, the area is locally encrypted and the target mesh size is set to 0.04mm to improve accuracy. For the surface mesh, the minimum size is set to 0.04mm, the maximum size is set to 0.4mm, and the growth rate is 1.1. For the volume mesh, a polyhedral mesh is used, and the maximum length of the cell is set to 0.4mm, and the growth rate is 1.1. After balancing the computational cost and the accuracy of the results, the number of meshes for the geometric model is finally determined to be 4.5 million.

[0053] Preferably, the inlet boundary condition of the nozzle part is set to a pressure inlet. In the flow field part, the lower boundary is set to a pressure outlet, and the outlet parameters are set to ambient atmospheric conditions, while other surfaces are set to adiabatic no-slip walls, and the contact angle between the wall and water is defined as a neutral contact angle of 90 degrees. Before the calculation, the entire fluid domain is initialized, and the mass fraction of the water phase is initialized to 0, that is, the entire fluid domain is filled with gas to simulate the process of water being sprayed in. The flow of the molten metal needs to be considered, so the inlet boundary of the diversion part is set to a velocity inlet.

[0054] The water atomization process usually involves complex multiphase flow, in which the atomized droplets interact with the gas and break up and aggregate in the process. This embodiment uses a turbulence model and a discrete phase model to describe the interaction between the molten metal and the atomized droplets. Preferably:

[0055] Turbulence Models:

[0056] The water atomization process usually involves complex multiphase flow, in which the atomized droplets interact with the gas and break up, aggregate and other phenomena occur in this process. Therefore, choosing a suitable turbulence model is crucial to accurately simulate this process. This embodiment uses the RNG k-ε model for calculation. The model introduces the calculation of turbulent vortices and can more accurately simulate turbulent phenomena, including turbulent vortices formed near the nozzle part outlet, which is particularly important for simulating complex flow fields around the nozzle. Secondly, the internal structure of a flat fan nozzle is usually complex and has an irregular geometry. The RNGk-ε model has high accuracy and reliability when dealing with complex geometries. In addition, the RNG k-ε model also has high computational efficiency. Compared with other turbulence models, the equations it uses are relatively simple and the required computing resources are relatively small. This greatly shortens the simulation time and improves efficiency. The RNG k-ε model includes two transport equations: one is the transport equation for turbulent kinetic energy k, and the other is the transport equation for turbulent dissipation rate ε. Its expression is as follows:

[0057] The transport equation of turbulent kinetic energy k is:

[0058]

[0059] The transport equation for the turbulent dissipation rate ε is:

[0060]

[0061] In the formula, μ represents the effective viscosity; μ t represents the turbulent dynamic viscosity; t is time; C 1ε , C 2ε and C 3ε is a constant coefficient; G k Turbulent kinetic energy generation caused by mean velocity gradient; G b Turbulent kinetic energy generation caused by buoyancy; Y M represents the effect of compressible turbulent pulsation expansion on the total dissipation rate; k, ε represent turbulent kinetic energy and turbulent dissipation rate respectively; σ k , σ ε is the Prandtl number corresponding to the turbulent kinetic energy and turbulent dissipation rate; u i and u j represents the velocity components in the i and j directions; x i and x j They represent the axial coordinates in the i and j directions respectively; ρ represents the fluid density; S k and S ε Represents a user-defined source item.

[0062] Discrete Phase Model:

[0063] Since the flat fan nozzle used in the current study is a device that sprays liquid in a specific way. When liquid is sprayed through a flat fan nozzle, a fan-shaped spray or droplet distribution is usually formed. Therefore, in the process of water atomization powder making, when two nozzles spray at a certain angle, the droplets may contact and collide with each other. Therefore, this paper uses the flat-fan-atomizer function in the discrete phase model (Discrete Phase Model, DPM) in ANSYS Fluent software to define a flat, fan-shaped spray by setting some key parameters, thereby replacing the nozzle used in the two-nozzle injection simulation. The particles generated by the flat-fan atomizer sprayer can calculate the trajectory, velocity, and interaction with the continuous phase (such as gas). In addition, the transmission, collision, fragmentation, adhesion and other behaviors of the particles can also be predicted. Use the discrete phase model to simulate the nozzle spray process.

[0064] In multiphase flow composed of discrete phase and fluid, the Lagrangian method is used to describe the discrete phase, and the fluid is described as the continuous phase. The equation of motion of the discrete phase particles is:

[0065]

[0066] Here, f y represents the additional acceleration term; f D (uu p ) represents the resistance per unit particle mass; u p represents the continuous phase velocity; ρ represents the continuous phase density; ρ p Indicates the particle density.

[0067] The solution parameters are shown in Table 1.

[0068] Table 1: Calculation parameters

[0069]

[0070] Step S4, for multiple possible factors, a single variable method is used to perform multiple simulations through the constructed model to obtain multiple simulation results, each simulation result includes a droplet size distribution effect diagram, a droplet size distribution situation, a velocity cloud distribution diagram and a velocity cloud distribution curve along the axis, etc.;

[0071] Step S5, selecting actual factors affecting high-pressure water atomization from multiple possible factors according to the simulation results, and determining the influence of each actual factor on high-pressure water atomization to guide the design of the high-pressure water atomization device.

[0072] In this step, the actual factors affecting high-pressure water atomization selected include atomization water pressure, spray top angle and smelting temperature.

[0073] The following is a detailed explanation of the impact of some practical factors on high-pressure water atomization, combined with some simulation data.

[0074] 1. The influence of atomizing water pressure (injection pressure) on atomization characteristics:

[0075] Keeping other possible factors except the atomizing water pressure unchanged, changing the atomizing water pressure, and performing multiple simulations (wherein the spray top angle is 35°, and the atomizing water pressure range is set at 2.5 MPa to 5 MPa).

[0076] Figure 3 The figure shows the effect of droplet size distribution under different atomizing water pressures. It can be seen that with the increase of atomizing water pressure, the distribution range of droplets with larger particle size gradually decreases, and the droplet distribution becomes more delicate and uniform. When the atomizing water pressure = 2.5MPa, droplets with larger particle size and smaller droplets are distributed alternately in the entire atomizing area, without obvious distinction. When the atomizing water pressure increases to 5MPa, droplets with larger particle size gradually gather near the intersection of the two fan-shaped sprays, while small droplets gather at the edge and bottom area of ​​the flow field. This is because as the atomizing water pressure increases, the jet airflow velocity increases, resulting in more intense collisions between the high-speed airflow and the ejected droplets. This will make it easier for larger droplets to be split into smaller droplets in the flow field, while causing smaller droplets to diffuse to the edge and bottom areas of the flow field.

[0077] Figure 4 The droplet size distribution on the cross section at a height of 35 mm under different atomization water pressures (3MPa, 4MPa, 5MPa). As can be seen from the figure, under different pressures, most droplet sizes are mainly distributed in the range of 100-300μm, while a small number of droplets are distributed in the range of 0-100μm and 300-600μm.

[0078] By comparing the data under different water pressures, it is found that with the increase of pressure, the proportion of droplets above 400μm decreases, while the proportion of droplets in the range of 0-400μm shows irregular changes. Among them, the proportion of droplets of 0-100μm first decreases and then increases; the proportion of droplets of 100-200μm first increases and then decreases; the proportion of droplets of 200-300μm continues to decrease; and the proportion of droplets of 300-400μm first decreases, then increases, and then increases. This phenomenon shows that increasing pressure tends to produce more small and medium-sized droplets, the distribution of droplets becomes more concentrated, the droplet size range is reduced, the proportion of larger droplets gradually decreases, and the main distribution tends to 100-300μm. This is because with the increase of atomization water pressure, larger droplets are more likely to be broken into small droplets. At the same time, in the dynamic process of spray motion, droplets may collide and merge, or change their motion trajectory due to the influence of air resistance, thereby increasing the complexity and uncertainty of the droplet motion process. These factors work together to make the distribution of droplet size more complex and variable.

[0079] Figure 5The velocity distribution cloud diagrams of the xy section (left), yz section (middle) and xz section at 40 mm (right) under different atomizing water pressures show that the basic characteristics of the flow field under different atomizing water pressures are similar to those described in Section 3.2.1, but due to the change in water pressure, the flow field distribution has changed. By observing the velocity cloud diagrams of the xy section under different pressures, we can find that as the water pressure increases, the velocity in the near-axis area below the intersection (i.e., the velocity area formed by the intersection of the two sprays in the yz section) gradually increases. Moreover, when the atomizing water pressure = 2.5 MPa, the velocity below the intersection hardly expands outward, and is mainly concentrated in the central axis area; as the water pressure increases, the range of the velocity extending downward and on both sides becomes larger and farther. This is because at a lower water pressure of 2.5 MPa, the atomization effect is weak, the atomization effect is insufficient, the generated droplets are larger, and the kinetic energy is lower, so the droplets are mainly concentrated in the area close to the nozzle, and the droplets diffuse weakly to the sides and below, that is, there are more droplets on the central axis near the intersection. As the water pressure increases to 5MPa, the atomization effect is enhanced, and more small droplets are produced. These droplets have a higher surface area to volume ratio and are more easily affected by the momentum transfer effect, so that the velocity not only increases significantly on the central axis, but also the droplet cloud begins to extend to the areas farther away on both sides and below. Looking at the xz section at 40mm from the origin, we can see that when the atomization water pressure = 2.5MPa, the velocity distribution on both sides and the center is relatively uniform, with no significant difference. As the water pressure increases, the flow rate from the middle to the two sides becomes uneven. Although the speed becomes denser than before, the increase rate of the flow rate on both sides is significantly faster than that in the middle. This is because increasing the water pressure will cause the liquid flow rate in the nozzle to increase, which usually increases the velocity of the droplets ejected. As the water pressure increases, the ejected droplets will have higher initial kinetic energy, and the momentum conversion generated by the interaction of these droplets and the interaction between the droplets and the air become more significant, especially near the intersection. Higher water pressure causes the droplets sprayed on both sides to increase their velocity faster due to more momentum. In contrast, the droplets in the middle may not increase as much as on the two sides due to fewer droplet collisions on a straight path and air resistance. Therefore, as the water pressure increases, the velocity on both sides increases faster than in the middle, causing the velocity distribution observed at 40 mm to change from uniform to uneven, resulting in dense velocity on both sides and relatively sparse velocity in the middle.

[0080] Figure 6The average velocity distribution of droplets along the y-axis under different atomization water pressure conditions. It can be seen that under different water pressures, the change trend of the axis velocity is similar. Due to the flow field effect, the velocity begins to form above the spray intersection area; when approaching the spray intersection area, the velocity will increase slightly. This is because a vortex structure is formed at this time, which will cause the velocity to increase in the local area; until reaching the intersection area, the velocity suddenly changes and increases sharply, causing the fluid to enter the high-speed range. Under different atomization water pressure conditions, the velocity reaches the maximum value within a short distance, and with the increase of atomization water pressure, the maximum velocity also increases accordingly. When the atomization water pressure = 5MPa, the maximum speed reaches 87.5m / s. It should be noted that the maximum speed is not always maintained, but changes continuously in the high-speed range; when away from the intersection, the speed suddenly decreases, and the speed decreases more slowly as the atomization water pressure increases. This phenomenon reveals the direct influence of water pressure on the dynamic behavior of droplets, and also reflects the instability and complexity of fluid dynamics problems in flow field environments.

[0081] Overall conclusion: With the increase of atomization water pressure, the distribution range of droplets with larger particle size gradually decreases, and the droplet distribution becomes more delicate and uniform.

[0082] 2. The influence of the spray vertex angle α on the atomization characteristics:

[0083] Keeping other possible factors except the spray vertex angle unchanged, changing the spray vertex angle, multiple simulations were performed, in which the atomizing water pressure was 5 MPa, and the spray vertex angles (the angle between the spray direction and the vertical direction) of the two fan-shaped nozzles were 35°, 40°, and 45°, respectively.

[0084] Figure 7The figure shows the droplet size distribution effect at different spray vertex angles. According to the results shown in the figure, we can first observe that as the angle increases, the coverage of the two sprays after the intersection is correspondingly expanded. When α = 45°, the spray touches the wall during movement, thereby changing its motion state. This is because as the spray vertex angle increases, the spray jet of each nozzle diffuses in a narrower fan shape in space. This means that the spray range of each droplet becomes narrower, that is, the distribution of droplets in space is more concentrated. In this case, when the droplets intersect with each other, the collision and interaction between them will be more intensive, resulting in more droplets affecting each other in a larger area, resulting in a wider coverage. Secondly, we can also find that in the process of α increasing from 35° to 40°, the droplet size of the two sprays below the intersection decreases; while in the range from 40° to 45°, the change in the size of the droplet size is not significant. This is because when the angle increases from 35° to 40°, compared to the original wider fan-shaped distribution, the droplets at the intersection of the two sprays have a narrower distribution, which increases the chances of collision and interaction, causing the droplets to be subjected to more mechanical shear forces, thereby promoting the breakup of the droplets and reducing the droplet size. At the same time, increasing the angle will increase the velocity of the fluid and the interference it receives, thereby enhancing the turbulent effect. This turbulent effect will cause more liquid mixing and shearing, promote the breakup and refinement of droplets, and produce smaller droplets within a larger angle range. When increasing from 40° to 45°, the change in droplet size is not obvious. This may be because the droplets have reached a dynamic equilibrium, and the interaction and collision between them have reached a state of equilibrium, making the change in droplet size no longer so sensitive.

[0085] Figure 8 The droplet size distribution of the xz section at 35mm at different spray vertex angles. As shown in the figure, when the nozzle angle increases from 35° to 45°, the droplet size distribution changes significantly. At the initial angle (35°), the droplets are mainly concentrated in the particle size range of 100-300μm, and a small part is distributed in the range of 0-100μm and 300-600μm. However, as the angle rises to 45°, the proportion of droplets in the range of 100-400μm begins to decrease, and small droplets of 0-100μm become more common. This phenomenon shows that higher spray angles help to produce smaller droplets. It is worth noting that when the angle increases from 40° to 45°, the change in droplet size is not significant. This phenomenon shows that when the nozzle vertex angle changes within a certain range, there may be a certain balance point, the droplet size tends to be stable within this range, and further increasing the angle will not have a significant refinement effect.

[0086] Fig. 9The velocity distribution cloud diagrams of the xy section (left), yz section (middle) and xz section at 40mm (right) at different injection top angles. By comprehensively observing the changes in the velocity cloud diagrams of the three sections at different angles, we can draw the following observations. First, on the xy section and the xz section, as α increases from 35° to 45°, the velocity in the area formed by the intersection of the sprays increases significantly. This shows that increasing the spray angle can promote the interaction and collision between droplets, thereby increasing the velocity. Secondly, it is observed on the xy section and the yz section that with the increase of α, the velocity distribution in the horizontal direction after the two sprays cross becomes wider, which is consistent with the changing trend of the droplet size distribution. Finally, it is observed on the yz section that with the increase of α, the width of the intersection area of ​​the two sprays becomes smaller. From a geometric point of view, this is because as α increases, the contact width of the two sprays at the intersection decreases, resulting in a decrease in the width of the area where they intersect.

[0087] Fig.10 The average velocity distribution of the droplet along the y-axis at different injection apex angles. It can be found that the change trend of the velocity along the y-axis at different angles is similar. But the difference is that with the increase of the injection apex angle, the vortex structure is formed earlier, and the speed inside the vortex increases significantly. This shows that increasing the injection angle can accelerate the formation of the vortex structure and enhance its strength. Then, the droplet enters the high-speed range, and with the increase of the injection apex angle, the speed in this area also increases accordingly, especially when α is 45°, the maximum speed reaches 97m / s.

[0088] Overall conclusion: As the spray angle increases, the coverage of the two sprays after the intersection is correspondingly expanded. The spray range of each droplet becomes narrower, that is, the distribution of droplets in space is more concentrated. The droplet size tends to be stable, and further increasing the angle will not have a significant refinement effect.

[0089] The above simulation results are verified through some specific experiments below.

[0090] 1. Experimental equipment

[0091] In order to study the powder crushing mechanism in the process of preparing metal powder by water atomization and the influence of atomization water pressure and jet vertex angle on the metal crushing process, we built a simple water atomization powder making experimental shooting platform. Fig.11 The platform consists of three main parts, including high-pressure water pump, open water atomization powder making equipment and high-speed shooting system.

[0092] The high-pressure water pump drives the atomization process by providing high-pressure water flow. The high-pressure water pump can generate enough pressure to form a high-speed jet of water at the nozzle outlet.

[0093] The open water atomization powder making equipment is used to complete the water atomization powder making experiment. Fig.12 As shown, it includes a metal inflow area, an atomization area and a powder collection area. The metal inflow area includes an insulation crucible and a guide tube to ensure the smooth progress of the metal inflow process. The capacity of the crucible is 5kg and the rated temperature is 1700℃, which can meet the temperature requirements for the atomization of the metal melt. Its main function is to pour the molten metal into the crucible after the metal is melted, and then prevent the metal from cooling and solidifying rapidly through the heat retention characteristics of the insulation crucible, thereby blocking the flow of the guide tube. The guide tube is made of corundum ceramic material, with a diameter of 4mm and a temperature resistance of 1600℃. The function of the guide tube is to guide the liquid metal to the atomization area to ensure that the metal flows smoothly and enters the next stage smoothly. The atomization area is mainly composed of two fan-shaped nozzles, and the nozzles are arranged in a V-shaped nozzle structure, that is, the two nozzles are symmetrically arranged at a certain angle on both sides of the central axis of the atomization device. Each nozzle is connected to a short hard pipe made of 316 stainless steel (SS) and connected by threads, which makes the nozzle easy to replace. The brackets that hold the nozzles are made of adjustable aluminum profiles, each of which provides three degrees of freedom: rotation around a pivot point to change the angle of the nozzle top angle, horizontal translation to change the distance between the nozzle and the molten metal stream, and vertical translation to change the height of the nozzle. The base of each nozzle bracket is fixed to a steel frame that holds the entire nozzle assembly. We set a pressure gauge on each of the two pipes connecting the nozzles, and the water pressure at the nozzle can be easily controlled to the required level by adjusting the pressure regulating valve of the water pump. The powder collection area is a rectangular box filled with filtered tap water. When the atomized powder falls into it, the powder is wetted by the water and settles to the bottom of the box. In this way, the powder can be collected. The water is separated from the powder by using a filter or screen, so that the water flows out of the pores of the screen or filter. Next, the wet powder is dried using an electric heater to evaporate the water and finally obtain dry powder.

[0094] The high-speed shooting system uses a PHANTOM T3610 high-speed camera to shoot the atomization process and record the morphological changes of water mist and metal liquid flow during the atomization process.

[0095] 2. Experimental test methods

[0096] Water atomization powder making process experiment: This experiment will use high-speed camera technology to observe the flow state and crushing process of molten metal under the action of high-pressure water mist, and explore the physical mechanism behind it. Secondly, by adjusting the atomization water pressure (Pwater = 3, 4, 5MPa) and the spray vertex angle (α = 35°, 40°, 45°), record and analyze the effects of these parameter changes on the crushing process and the final powder shape and particle size, in order to find the law and verify the results of numerical simulation. In the specific operation, first melt the low-melting-point metal tin bar in a homemade heating device, use a furnace to keep it and the heat-insulating crucible at a high temperature for a period of time, and then quickly place the molten metal in the crucible fixture of the water atomization powder making equipment and fix the position. Subsequently, start the water pump, wait for the water mist to stabilize, then pour the molten metal tin into the atomization powder making, and record it at high speed. The metal used in the experiment is Sn63A.

[0097] 3. Water atomization experiment and result analysis

[0098] 3.1. Keep other possible factors except the atomizing water pressure unchanged, and change the atomizing water pressure to conduct experiments (the spray top angle remains unchanged at 35°, and the atomizing water pressures are 3MPa, 4MPa and 5MPa respectively).

[0099] Fig.13 The figure shows the crushing of molten tin under different atomizing water pressures and the local magnified picture. From the experimental results, it can be seen that when the atomizing water pressure is 3MPa, the crushing process of the metal melt is not thorough. Most of the melt fails to be effectively crushed after passing through the spray intersection area, forming a large melt block flowing out. Only a small amount of the melt is broken into particles, and these broken particles tend to aggregate into small particle clusters; as the atomizing water pressure increases to 4MPa, we observe significant improvements. At this stage, larger melt blocks are effectively crushed, increasing the number of small particle melts. However, despite the improvement in crushing efficiency, most of the small particles still tend to aggregate together to form connected particle clusters, which indicates that the dispersion of the powder is still insufficient; when the pressure is 5MPa, the experimental results show a more ideal melt crushing effect. Under this condition, only a few particles aggregate, while most particles can exist independently. The above phenomena show that higher atomizing water pressure can significantly improve the crushing and dispersion of particles, thereby producing finer and more evenly distributed metal powders. In addition, a gradual decrease in particle size was observed with the continuous increase in atomization water pressure, which further confirmed that atomization water pressure is a key parameter in controlling the powder particle size distribution.

[0100] 3.2. Keep other possible factors except the spray vertex angle unchanged, and change the spray vertex angle to conduct experiments (the atomization water pressure is 5MPa, and the spray vertex angles are 35°, 40° and 45° respectively).

[0101] Fig.14The figure shows the fragmentation of molten tin at different injection vertex angles and a partial enlarged view. It can be seen that as the injection vertex angle increases, the melt is more thoroughly broken after passing through the intersection area. First, the small metal particles after fragmentation appear more independent in structure, and the adhesion phenomenon almost disappears. Second, the average particle size of the powder particles gradually decreases. These experimental results show that the adjustment of the injection vertex angle not only improves the fragmentation efficiency of the melt, but also has a significant impact on the physical properties of the metal powder after fragmentation.

[0102] By comparing the simulation and experimental results, it can be seen that under the same conditions, the melt fragmentation effect presented by the simulation is better. This is because the alloy tin selected in the experiment has a lower melting point, and the process from melting the metal tin to pouring it into the crucible is affected by the distance and ambient temperature, which accelerates the cooling of the molten tin, which leads to some differences with the results in the simulation. However, with the adjustment of the atomization water pressure and the spray top angle, the effect consistent with the simulation results can still be achieved, further proving that the design of the high-pressure water atomization device can be guided by the simulation results.

[0103] In some embodiments, Figure 1 As shown, the method also includes:

[0104] Step S6, based on multiple actual factors, using orthogonal experiments to design multiple actual factor parameter combinations, using the constructed model to simulate the multiple actual factor parameter combinations, and selecting the best actual factor parameter combination according to the simulation results;

[0105] Step S7, using the parameters in the best actual factor parameter combination as the design parameters of the high-pressure water atomization device to design the high-pressure water atomization device.

[0106] In a specific example, through simulation, multiple actual factors are selected including atomizing water pressure, spraying top angle and melting temperature, and the best actual factor parameter combination is determined as: atomizing water pressure 5 MPa, spraying top angle 45°, melting temperature 500°C.

[0107] The following is a verification of the best actual factor parameter combination selected in the simulation of the above example in conjunction with specific experiments.

[0108] An orthogonal water atomization experiment was designed to statistically analyze the quality of water atomized powder under different atomization water pressure, spray angle and melting temperature parameters, as shown in Table 2.

[0109] Table 2: Statistical results of water atomized powder quality under different atomization water pressure, spray angle and melting temperature parameters

[0110]

[0111] As can be seen from Table 2, in Experiment 9, the weight of 50-200 mesh powder, 200-325 mesh powder and powder weight greater than 325 mesh are all the heaviest, and the water atomized powder has the best quality, which is consistent with the best actual factor parameter combination selected by simulation. This proves that it is desirable to select the best actual factor parameters through simulation, and also proves that the simulation model in this embodiment has a good simulation effect.

[0112] Table 3: Average signal-to-noise ratio of each practical factor

[0113]

[0114] As can be seen from Table 3, the signal-to-noise ratio of atomizing water pressure is the largest, so the influence of atomizing water pressure on particle size is the most significant, followed by nozzle angle, and the influence of melting temperature on powder mesh size is relatively small. However, a process level may have a large signal-to-noise ratio for one factor and a small signal-to-noise ratio for another factor, so the single use of Taguchi method may have certain limitations, so the gray correlation analysis is carried out next.

[0115] Grey correlation method analysis: First, the signal-to-noise ratio is dimensionless, and then the grey correlation degree is calculated. Since each experimental design is orthogonal, the grey correlation degree of each level of each process factor can be calculated.

[0116] Table 4: Dimensionless signal-to-noise ratio

[0117]

[0118] Table 5: Correlation coefficient and grey correlation degree of signal-to-noise ratio

[0119]

[0120] By calculating the grey correlation degree of each experiment, we can find that the grey correlation degree of Experiment 9 is the largest, so the effect of Experiment 9 is the best.

[0121] In some embodiments, Figure 1 As shown, the method also includes:

[0122] Step S8, selecting at least one key factor from the actual factors according to the simulation results of the various actual factor parameter combinations, and setting the structure related to the key factor in the high-pressure water atomization device to an adjustable or controllable structure.

[0123] From the analysis of the simulation results and the results of the water atomization orthogonal experiment, it can be seen that the atomization water pressure has the greatest impact on the particle size, followed by the nozzle angle. Therefore, the atomization water pressure and the nozzle angle can be set to be controllable or adjustable, and more attention should be paid to the atomization water pressure during design and subsequent use.

[0124] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for designing a high-pressure water atomization device based on simulation, characterized in that: Methods include: Construct a dual-nozzle high-pressure water atomization geometric model: construct the flow field part and the two nozzle parts. The two nozzle parts are extracted based on the internal shape of the nozzle to simulate the flow of the fluid inside the nozzle and spray relative to each other. The flow field part is a cylinder, which simulates the external flow field formed by the interaction between the water flow ejected from the nozzle and the surrounding static air. The guide part of the metal melt is added to the flow field part. The geometric model is meshed, the area near the nozzle outlet is locally encrypted, the boundary conditions of the geometric model are set, and the computational model of the geometric model water atomization numerical simulation is determined. The computational model includes a turbulence model for simulating the turbulent flow process of the fluid and a discrete phase model for simulating the nozzle spraying process. For multiple possible factors that may affect high-pressure water atomization, a single variable method is used to perform multiple simulations through the constructed model to obtain multiple simulation results, each of which includes a droplet size distribution effect diagram and droplet size distribution situation; According to the simulation results, the actual factors affecting the high-pressure water atomization are selected from multiple possible factors, and the influence of each actual factor on the high-pressure water atomization is determined to guide the design of the high-pressure water atomization device.

2. The method for designing a high-pressure water atomization device based on simulation according to claim 1, characterized in that: The method also includes: Based on multiple actual factors, orthogonal experiments are used to design multiple actual factor parameter combinations, and the constructed model is used to simulate multiple actual factor parameter combinations. According to the simulation results, the best actual factor parameter combination is selected; The parameters in the best actual factor parameter combination are used as the design parameters of the high-pressure water atomization device to design the high-pressure water atomization device.

3. The method for designing a high-pressure water atomization device based on simulation according to claim 2, characterized in that: The method also includes: According to the simulation results of various actual factor parameter combinations, at least one key factor is selected from the actual factors, and the structure related to the key factor in the high-pressure water atomization device is set to an adjustable or controllable structure.

4. The method for designing a high-pressure water atomization device based on simulation according to claim 1, characterized in that: The steps to set the boundary conditions of the geometric model are: The inlet boundary condition of the nozzle part is set as the pressure inlet, the lower boundary of the flow field part is set as the pressure outlet, and the pressure outlet parameters are set as the ambient atmospheric conditions. The other surfaces of the flow field part except the lower boundary are set as adiabatic no-slip walls, and the contact angle between the wall and water is defined as a neutral contact angle of 90 degrees. The inlet boundary of the guide part is set as the velocity inlet.

5. The method for designing a high-pressure water atomization device based on simulation according to claim 1, characterized in that: The turbulence model is the RNGk-ε model, which includes two transport equations, namely the transport equation for turbulent kinetic energy k and the transport equation for turbulent dissipation rate ε. The transport equation of turbulent kinetic energy k is: The transport equation for the turbulent dissipation rate ε is: In the formula, μ represents the effective viscosity; μ t represents the turbulent dynamic viscosity; t is time; C 1ε , C 2ε and C 3ε is a constant coefficient; G k Turbulent kinetic energy generation caused by mean velocity gradient; G b Turbulent kinetic energy generation caused by buoyancy; Y M represents the effect of compressible turbulent pulsation expansion on the total dissipation rate; k, ε represent turbulent kinetic energy and turbulent dissipation rate respectively; σ k , σ ε is the Prandtl number corresponding to the turbulent kinetic energy and turbulent dissipation rate; u i and u j represents the velocity components in the i and j directions; x i and x j They represent the axial coordinates in the i and j directions respectively; ρ represents the fluid density; S k and S ε Represents a user-defined source item.

6. The method for designing a high-pressure water atomization device based on simulation according to claim 1, characterized in that: In multiphase flow composed of discrete phase and fluid, the Lagrangian method is used to describe the discrete phase, and the fluid is described as the continuous phase. The equation of motion of the discrete phase particles is: f y represents the additional acceleration term; f D (u-up) represents the resistance per unit particle mass; u p represents the continuous phase velocity; ρ represents the continuous phase density; ρ p Indicates the particle density.

7. The method for designing a high-pressure water atomization device based on simulation according to claim 1, characterized in that: Several possible factors include atomizing water pressure, spray tip angle, smelting temperature and guide tube extension.

8. The method for designing a high-pressure water atomization device based on simulation according to claim 1, characterized in that: Each simulation result also includes a velocity cloud distribution diagram and a velocity cloud distribution curve along the axis.

9. The method for designing a high-pressure water atomization device based on simulation according to claim 1, characterized in that: Several practical factors that affect high-pressure water atomization include atomization water pressure, spray tip angle and smelting temperature.

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