## 3 Results
### Simulation Results and Analysis
#### 3.1.3 Particle Concentration Contour Analysis  
The particle concentration contour when the inlet velocity is 0.6 m/s, is shown in Figure 8a. It can be clearly seen from the figure that the particle concentration in the inlet zone and the upper wall surface is the highest, reaching about 0.005 mg/um\({}^{3}\). As the distance from the inlet increases, the particle concentration gradually decreases. When the particle concentration is close to the middle zone of the porous media surface, the particle concentration is the lowest, about 0.001 mg/um\({}^{3}\). The distribution is relatively uniform, while the particle concentration is higher in the porous media surface near the inlet zone, due to the suction pressure, which makes it easy to produce a large amount of accumulation.  
The particle concentration contour, when the inlet velocity is 0.8 m/s, is shown in Figure 8b. It can be seen from the figure that the particle concentration in the inlet zone and the upper wall is the highest, reaching about 0.005 mg/um\({}^{3}\). With the increase in the distance from the inlet, the particle concentration gradually decreases. When approaching the middle zone of the porous media surface, the particle concentration is the lowest. Compared with the working condition of 0.6 m/s, when the flow velocity is 0.8 m/s, the particle distribution range is wider.  
The particle concentration contour, when the inlet velocity is 1 m/s, is shown in Figure 8c. It can be seen from the figure that with the increase in flow velocity, the distribution range of the particle concentration reaches the widest, and the particles gradually decrease from the pipe wall to the middle of the flow channel. Compared to the first two working conditions, the particle concentration distribution is more uniform, about 0.001 mg/um\({}^{3}\). When the flow velocity is 1 m/s, the transmembrane pressure difference is the largest, as shown in Figure 6d, which is more conducive to the improvement in membrane water productivity.  
Figure 9 shows the average particle concentration in the local zone near the wall at 0.6 m/s, 0.8 m/s, and 1 m/s, respectively. Comparing the three working conditions, it can be seen that the overall particle concentration of 0.6 m/s and 0.8 m/s varies greatly, and the difference between the lowest concentration and the highest concentration is 0.0014 mg/um\({}^{3}\). However, when the flow velocity is 1 m/s, the variation range of particle concentration is relatively uniform, and the difference between the lowest concentration and the highest concentration is only 0.0005 mg/um\({}^{3}\), due to the relatively high scour velocity near the surface of the porous media zone.  
As shown in Figure 10\(v_{\rm in}\) = 0.6 m/s, when the flow velocity is 0.6 m/s, comparing the particle concentration distribution under the two working conditions with gravity and without gravity, it can be seen that when the influence of gravity is present, most of the high\(-\)concentration particles are concentrated in the lower wall zone, and only a small amount diffuses near the surface of the porous media zone. This is due to the particle's own gravity, which can generate a radial velocity. However, when there is no gravity, most particles follow the fluid along the upper wall, which is due to a radial velocity of 0 from the particle's own gravity.  
Figure 8: Contour of particle concentration in \(X\) = 0 section.  
The water productivity of different inlet velocities is shown in Figure 11. The results show that when the inlet velocity is 0.6 m/s, the water productivity is 45.2%; when the inlet velocity is 0.8 m/s, the water productivity is 46.1%; when the inlet velocity is 1 m/s, the water productivity is 48.5%; water productivity gradually increases with an increase in inlet velocity.  
Figure 10: Particle concentration contours.  
Figure 9: Average particle concentration near the wall.