# Numerical Simulation of Liquid Film Characteristics during Atomization of Aluminum Alloy Powder
## 3 Simulation Results and Discussion  
### Comparative Analysis of Velocity and Pressure Distribution on Different Disk Surfaces  
In the early stage, the research group conducted experimental studies to compare the influences of the structure size and rotation speed of the three types of disk shapes, spherical, conical, and biconical, on the particle size distribution of the atomized powder under the same process conditions. It is known that the atomized disk shape has an important influence on the particle size distribution of atomized powder. Compared with other disk shapes, the spherical disk offers a higher yield and median diameter of atomized powder than the small-particle-size atomized powder. The yield of atomized powder with a narrow particle size distribution is higher [8]. However, the mechanism and effect of the disk structure on the atomized molten metal is not clear, so it is necessary to carry out an atomization simulation of different disk structures to reveal the internal influence mechanism. The VOF method was first used to simulate the velocity distribution of the disk surface, with the results shown in Figure 5. The atomized molten metal of the flat disk and spherical disk was spread and moved on the disk surfaces with a rotational speed of 10,000 rpm. It can be seen from Figure 5 that, under the same atomization conditions, the molten metal speed at the edge of the spherical disk was approximately 15 m/s, and the molten metal speed at the edge of the flat disk was approximately 11 m/s. The molten metal speed of the boundary layer on the surface of the spherical disk was higher and the distribution was relatively more uniform. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Material** & **Density kg/m3** & **Dynamic Viscosity** & **Thermal Conductivity** & **Specific Heat J/(kg.\({}^{\circ}\)C)** \\  & & **Pa-s** & **W/(m\({}^{\circ}\)C)** & \\ \hline Nitrogen & 1.145 & 1.788 \(\times\) 10\({}^{-5}\) & 0.026 & 1040.76 \\ Aluminum alloy & 2719 & 0.0016 & 125 & 871 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Material parameters. Figure 4: Meshing diagram. (**a**) Three-dimensional grid model; (**b**) cross-section grid model; (**c**) flat disk local grid model; (**d**) spherical disk local grid model. In the process of atomization with different disk shapes, a cloud diagram of the pressure distribution on the surface of the disk was obtained, shown in Figure 6, when the molten metal spread and moved on the surface of the disk. According to the color distribution of the cloud diagram, it can be seen that the pressure distribution on the surface of the spherical disk is more uniform than that on the flat disk. This is because the liquid film of the flat disk is continuous in the middle part, and in other areas it is in an independent ribbon state. The pressure distribution on the surface of the atomizing disk is related to the force exerted on the liquid metal film on the disk surface; in other words, the pressure distribution is related to the distribution state of the liquid film on the surface and the stress state of the liquid film. The pressure in the red area in the center of the rotating disk is higher, which is caused by the height of the liquid column where the molten metal is poured through the nozzle to the atomizing disk. There is a ring-shaped low-pressure area, where the liquid film thickness suddenly decreases; it appears in the outer ring of the high-pressure area in the center of the rotating disk. a bright and higher-pressure area appears in the outer ring of the low-pressure area, which then changes steadily. The above changes are mainly attributed to the fact that, when the molten metal flows to the rotating disk, the liquid flow momentum changes from axial to radial, the liquid impacts the disk surface, and the liquid film in the low-pressure area will suddenly become thinner.