## 3 Application
### Separation  
Using the differences in physical and chemical properties of each component in the mixture, the process of distributing each component to different spatial regions is called separation. Typical applications include the cyclone separator [50; 51; 52; 53], hydrocyclone [54; 55], classifier [56; 57; 58], filter [59; 60; 61; 62] and dust collector [63; 64]. In the separation process, CFD-DPM is used to obtain the fluid and particle behavior in the internal space, so as to further study the separation performance [65; 66; 67]. In the conventional study of particle separation using the fluid phase, CFD-DPM is used for gas-solid or solid-liquid two-phase flow in dilute conditions. In some more complex flow systems, such as dense conditions and multiphase flow [51; 68], considering the problems of particle collision and liquid phase simulation, DPM needs to be further combined with other numerical methods. [PERSON] et al. used DDPM to simulate the high load particle flow in a multistage shelter, and heat transfer was considered [65]. [PERSON] et al. combined large eddy simulation (LES), VOF and Lagrange discrete phase model to simulate the multiphase flow in the hydrocyclone, and they input the fluid data into MATLAB to obtain the pressure distribution and particle path in the transition period of the hydrocyclone [54] (Figure 5). Using an electromagnetic field to control the movement of particles can also effectively separate particles in two-phase flow [63; 69; 70; 71]. Due to the influence of an electromagnetic field on experimental measurement, experimental analysis has considerable difficulty, which needs to be further combined with numerical simulation. In the process of numerical simulation, particles are affected by fluid force or electrostatic force. Multi-field coupling needs to be considered when using CFD-DPM. [PERSON] et al. used a modified DPM to predict the capture of magnetic particles in microfluidic systems. The model considers two-way particle-fluid coupling and can provide strict magnetic prediction without cumbersome numerical magnetic field analysis, which has been applied to the magnetic bead separation process in microfluidic systems [72; 73]. [PERSON] et al. developed a simulation procedure to predict the motion of gas, ions and particles inside a simple parallel-plate channel containing a single corona wire [69]. The electric field effect is obtained by UDF programming in the DPM to solve the coupling system of electric fi  
Figure 5: Snapshots showing the development of particles with LES turbulence VOF-DPM model during the transitional period [54]. equation. The technology of controlling particles using an electric field has been widely used in dust collectors [74; 75]. A reasonable turbulence model has a decisive impact on accurate simulation. The simple flow can be effectively described by the general Reynolds-averaged Navier-Stokes equation (RANS). Because the Reynolds stress model (RSM) more strictly considers the rapid changes of streamline bending, vortex and rotation, especially when there are heavy vortices and anisotropic turbulence in the air flow system, the RSM model is used more for the separation machinery containing a vortex [76; 77; 78]. The corresponding alternative model is the renormalization group (RNG) k-\(\epsilon\) model [79]. For some unsteady and non-equilibrium processes, LES will also be used [66]. In order to test and verify the reliability of these numerical models and results, laser doppler velocimetry (LDV) and particle image velocimetry (PIV) are applied to particle tracking in two-phase flow. For multiphase flow detection in a non-transparent environment, [PERSON] et al. measured the internal flow dynamics by using a dual-planar high-speed electrical resistance tomograph (ERT),which realized the cross-validation of multiphase flow numerical prediction [68]. In general, the application of CFD-DPM in the separation process is well established, and the editable DPM expands the further development of the model in multiple physical fields.