# Study on the Influence of Different Factors on Pneumatic Conveying in Horizontal Pipe
## 4 Simulation Results and Analysis
### Simulation Results and Analysis of Different Pipe Diameters  
In order to study the influence of pipe diameter on the conveying characteristics of particles, the pipe diameter of other working conditions is set to 80 mm, 90 mm, or 95 mm based on the benchmark working conditions, and the control variable method is used for simulation analysis. The simulation results are as follows. Figure 11(a) is the fluid dynamic pressure cloud diagram under different pipe diameters in the sampling section. Figure 11(b) shows the cloud diagram of particle mass concentration changes under different pipe diameters in the sampling section. It can be seen from Figure 11 that when other conditions remain unchanged and pipe diameter increases by 5 mm, the numerical variation of dynamic pressure and particle mass concentration in the pipe is small, and the solid phase mass concentration distribution is slightly different. It shows that when the diameter of the pipe is changed in a small range under the condition that conveying wind speed, mass flow rate, and pipe diameter are unchanged, the impact on the motion state of the particles is small. Figure 13 shows the relationship between the average velocity of particles in the 0.5 m pipes length in the three zones with time under different pipe diameters. It can be seen from Figure 13, the average velocity of particles in the three zones within different pipe diameters is not very different, and the time of first arriving at the sampling section is irregular. From the point of view of the average velocity after stable conveying, the change of pipe diameter in a small range has little influence on the average velocity of conveying particles in each region. On the local magnified view after the convey is stabilized, we can see that the speed changes with time in the high-speed zone are more severe than in the transition zone and the low-speed zone. Figure 12: Distribution cloud diagram of fluid dynamic pressure and solid mass concentration under different pipe diameters. (**a**) Fluid dynamic pressure cloud diagram, Pa; (**b**) particle mass concentration cloud diagram, kg/m\({}^{3}\). Figure 14a shows the average value of the final stable velocity of the particles in the three zones with the change of the pipe diameters, Figure 14b shows the pressure drop of fluid along the pipe under different pipe diameters in the sampling section 7.5 m to 8 m away from the inlet. From the specific value of Figure 14a, with the increase of pipe diameter, the average velocity in the high-speed zone decreases with a small value, and the average velocity of particles in the transition zone and the low-speed zone is the smallest when the pipe diameter is 90 mm, showing different changing trends. From Figure 14b, in the 0.5 m long pipe, when the conveying wind speed is 22 m/s and the particle mass flow rate is 0.2 kg/s, the pressure drop in the pipe gradually decreases with the increase of the pipe diameter. The pressure drop decreases linearly when the pipe diameter increases from 80 mm to 90 mm, and the pressure drop decreases becomes smaller when the pipe diameter increases from 90 mm to 95 mm. Pressure loss in gas-solid two-phase flow includes accelerated pressure loss, frictional pressure loss, gravitational compression, and local pressure loss. The analysis of the changes of pressure loss in different pipe diameters shows that when the pipe diameter increases from 80 mm to 90 mm, the average velocity of particles in the pipe gradually decreases, which means that acceleration decreases with the increase of pipe diameter, so accelerated pressure loss decreases. When the pipe diameter increases from 90 mm to 95 mm, the average velocity of particles in the low-speed zone and transition zone increases slightly, while the average velocity of particles in the high-speed zone decreases. Therefore, when the pipe diameter increases from 90 mm to 95 mm, the accelerated pressure loss is less than that in the previous working condition.