## 4 Results and Discussion
### Fluid Flow Fields  
As analyzed below, the complex two-phase gas-solid flow field, characterized by the formation of different vortices within the real-sized industrial-scale micron air classifier, was successfully described using the TWC-CFD-DPM in ANSYS 2022 R2 with the assistance of the HPC. Using this method, the effects of the fluid flow on the particles and the particles on the fluid were considered. The guide cone's effects on the complex two-phase gas-solid flow field within the micron air classifier and its classification performance could be fully understood by analyzing the vortices formed in the classification regions. This was not fully reflected in previous steady simulations with downscaled models using one-way coupling. Figures 3 and 4 show the 2D vector graphs and path lines of the flow field within the classifier under the four different guide cones. A large vortex was generated in the lower half of the rotor cage in all the simulated cases (Figure 3a). This vortex prevented the airflow from entering the rotor cage, consequently diminishing the effective classification height of the rotor cage. The vortex occupied different positions in the classification chamber under the different guide cone structures. The position of the vortex was the lowest when \(d\) = 808 mm, enabling the airflow to carry material particles into the rotor cage more effectively. In this case, the material particles easily entered the rotor cage for more effective classification. Furthermore, alterations in \(d\) corresponded to changes in the size of the material recirculation gap, which caused changes in terms of the sizes, shapes, positions, and rotational directions of the vortices formed in the guide cone and the coarse material cone (as shown in Figure 3b). These vortices helped to retain the particles for a longer period of time, providing the opportunity for secondary classification in the coarse material cone and the guide cone before they escape through the coarse material outlet. The fine particles have the opportunity to undergo re-rinsing backward into the guide cone and the classification chamber. For example, when the guide cone had a bottom diameter of 808 mm, the vortex formed directly under the material recirculation gap. This vortex may have facilitated or hindered the flow of fine particles traveling upward again into the guide cone and the classification chamber later. From Figure 3b, it can be clearly seen that this vortex had different positions, sizes, shapes, and rotational directions with different guide cone structures, resulting in differences in the classifier's capacity for secondary classification. The different vortices formed in the coarse material cone and the guide cone directly affected the secondary classification ability in these regions, impacting the classification performance of the classifier. This problem is further analyzed in the following sections.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Input Parameter** & **Value** & **Input Parameter** & **Value** \\ \hline Outlet mass airflow rate (kg/s) & 6.125 & Rotor speed (rpm) & 280 \\ Particle–wall restitution coefficient & 0.5 & Feed flow rate (kg/s) & 1.574 \\ Viscosity (kg/m/s) & 1.789 \(\times\)\(10^{-5}\) & Particle density (kg/m\({}^{3}\)) & 2650 \\ Gas density (kg/m\({}^{3}\)) & 1.225 & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Simulation conditions.