## 4 Simulation of Pneumatic Conveying
### Influence of Different Wind Speeds on Conveying Characteristics
#### 4.3.1 Effect of Conveying Wind Speed on Distribution State of Solid Feed in Tube  
After stable transportation, the motion state and distribution of solid feed are observed, as well as the distribution state of solid feed in the pipe within the sampling section (4.5-5.5 m from the entrance of the pipeline) under different transportation wind speeds, as shown in Figure 2. Different colors represent different particle size ranges of solid feed. Solid feed according to particle size from small to large is colored in black, red, green and blue. The simulation results show that, under the same conditions, with the increase in the conveying wind speed, the speed difference between the upper and lower end of the particles at the bottom of the pipeline increases, and the particles will be subjected to upward force according to the Bernoulli principle. At the same time, the particle rotation causes the Magnus effect lift caused by the superposition of the circulation around the particles and the air flow, and the amount of accumulated feed at the bottom of the pipeline  
\begin{table}
\begin{tabular}{l l} \hline Density (kg/m\({}^{3}\)) & 1190 \\ Poisson ratio & 0.32 \\ Shear modulus (Pa) & \(1.07\times 10^{9}\) \\ \hline \end{tabular}
\end{table}
Table 1: Conveying pipeline parameters.  
decreases, the suspension amount increases and the flow pattern of the particle group transitions from sedimentation to suspension flow.  
When the conveying wind speed is 1.5 times the suspension speed of solid feed (V = 15.5 m/s), the solid feed accumulates at the bottom of the pipeline, resulting in a dense deposit flow. Under this condition, most of the solid feed is transported in the front of the pipeline, there is more friction and collision between the wall and the bottom of the pipeline and the wear is greater. In the actual conveying process, with the increase in the conveying wind speed, the accumulation of solid feed at the bottom of the pipe gradually decreased, the suspension amount in the pipe increased and the particles suspended in the upper part of the pipe were still small. When the conveying wind speed is 2 times the suspension velocity (V = 20.6 m/s) or higher, the quantity of particles deposited at the bottom of the pipeline is markedly decreased, the interspace of particle groups is increased, the friction collision between particles and the pipe wall is reduced, the wear of the pipe wall is reduced, the transport time was shortened from 8.25 s to 6.83 s and the conveying efficiency is greatly improved.  
The analysis of the simulation results shows that the sediment flow of solid feed is formed because it is not only affected by the drag force provided by the wind but also affected by its own gravity during transportation. When the conveying wind speed is low, the gravity of the solid feed itself dominates and, consequently, particles accumulate at the bottom of the pipe and are transported along the pipe, forming a sedimentary flow at the bottom of the pipe. With the increase in conveying wind speed, according to the Bernoulli principle and Magnus effect, the lift force on solid feed gradually increases, and the influence on the lift force of small particle size solid feed gradually becomes greater than the influence of gravity. Accordingly, the suspended solid feed increases with the increase in conveying wind speed. In the conveying process, in order to achieve suspension transportation of solid feed, the actual conveying wind speed should be greater than 2 times the suspension speed.