# Analysis of Feed Inlet and Optimal Feeding Amount of Waste Ground Film Impurity Removal Equipment
## 2 Materials and Methods
### CFD-DEM Fluid-Solid Coupling Simulation Analysis
#### 2.2.2 Fluid-Solid Coupling Simulation
To reduce the calculation volume and improve the simulation efficiency, the effect of the thickness of the residual film on the flow field inside the separation device and the motion of the residual film were ignored. The residual film particle diameter was increased, and the residual film particle density was decreased to maintain a constant residual film mass. Particle Model Authenticity Verification Test  
The stacking angle validation test was designed to verify the accuracy of the basic physical and contact parameters of the proposed particle model, as shown in Figure 8a. For the stacking angle test, a transparent bottomless cylinder with an inner diameter of 70 mm, a thickness of 1.5 mm, and a height of 200 mm was used to fill the transparent cylinder with the material in proportion to the composition of the residual film-impurity mixture, and the cylinder was slowly lifted by clamping it with a lifting device. After all the materials flowed out from the bottom of the cylinder and formed a stable pile, vertical photographs were taken to measure the pile angle, and this test was repeated 10 times. To perform the stacking angle simulation test, EDEM 2020 software was used to model the bottomless cylinder according to its size specifications. After generating a certain amount of particles to fill the cylinder as a particle plant, a slow rise speed was set for the cylinder, and the simulated particles flowed out from the bottom of the cylinder to finally form a stable pile of particles. The pile angle of the pile of particles of the residual film-impurity mixture was measured, and the average value was taken to compare with the pile angle of the actual physical test. The stacking angle of the actual test was 39.1\({}^{\circ}\), and the stacking angle of the simulation test was 36.2\({}^{\circ}\), with a relative error of 7.4%. The simulated stacking angle matched well with the actual test stacking angle, indicating that the contact parameters of each component of the film-hybrid mixture were set reasonably and can be used for simulating working conditions. At the same time, suspension characteristics of the residual film particles using the developed contact model were investigated. The residual film particles were used as the simulation material. Suspension simulation tests were conducted to compare them with the suspension tests on the test bench. As shown in Figure 8b, the radii of the corresponding circular cross-sections from low to high were 100, 135, and 155 mm because the flow rates through the different cross-sections were the same. The flow relationship was given using Equation (4):  
\[v_{f}\pi r_{f}{}^{2}=v_{m}\pi r_{m}{}^{2} \tag{4}\]  
Figure 7: Model of residual film particles. (a) Arrangement pattern of residual film particles; (b) deformation effect after force; (c) soil particles; (d) straw pellets. where \(r_{f}\) is the material suspension position circular cross-section radius (mm); \(r_{m}\) is the thermal anemometer position circular cross-section radius (mm); \(v_{f}\) is the material suspension speed (m/s); and \(v_{m}\) is the thermal anemometer reading. The relationship between different circular cross-section radii and the corresponding position suspension speed was deduced using Equation (5):  
\[v_{f}=\frac{r_{m}{{}^{2}}v_{m}}{{r_{f}}^{2}} \tag{5}\]  
At the same test conditions, the speed of the fan was controlled using the controller. The suspension velocity of the residual film in both the simulation tests and the test bench suspension tests was in the range of 2.92-5.49 m/s. Thus, the suspension characteristics of the residual film particles in the simulation were similar to those of the residual film material used on the test bench. Therefore, the residual film particles were in agreement with the simulation results. Analysis of Simulation Results  
The mass ratio composition of the residual film-impurity mixture was 43% soil, 21% straw, and 36% residual film, and the feeding rate was set to 200 kg/h.