# Pressure Study on Pipe Transportation Associated with Cement Coal Gangue Fly-Ash Backfill Slurry
## 4 Results and Discussion
### Velocity Distribution
When the slurry goes through the bending section, due to the difference of the conveying velocity impacts on the slurry flow points, a new flow shape was formed to satisfy the pipe deformation. Thus, the flow-core zone (the higher-velocity distribution area) moves outside the pipe latter well while the non-flow core-zone (the lower velocity distribution area) concentrates at the pipe inner wall (shown in Figure 7). The conveying velocity distribution of the CGFB slurry in the bending section is diffused without the concentric circles. As the inlet velocity increases, the pressure loss increases but the area of the flow-core zone decreases, which indicates that a more significant unstable flow characteristic reaching. The offset of the points of the slurry center and the pipe well in the conveying velocity is gradually decreased compared with the straight pipe. When the feeding velocity is 1.4 m/s, the potential maximum conveying velocity at the corner of the pipe is 2.57 m/s, while the velocity in the straight  
Figure 8: The velocity distribution profiles on the same cross-section of the CGFB slurry along the horizontal pipe at different axial positions: (**a**) velocity profile on the straight pipe; (**b**) velocity profile on the 90\({}^{\circ}\) elbow pipe. Figure 7: Velocity distribution contours with 76.05% solid concentration of CGFB slurry at different feeding velocities through the elbow pipe: (**a**) 1.4 m/s; (**b**) 1.6 m/s; (**c**) 1.8 m/s; (**d**) 2.0 m/s; (**e**) 2.2 m/s. pipe is 2.65 m/s; when the feeding velocity is 1.8 m/s, the maximum conveying velocity in the bend is 3.24 m/s, while the maximum velocity in the straight pipe is 3.43 m/s; when the feeding velocity is 2.0 m/s, the maximum velocity in the bend is 3.56 m/s, while the maximum velocity in the straight pipe is 3.83 m/s; when the conveying velocity is 2.2 m/s, the monitored velocity in the bend is 3.87 m/s, while the responding velocity in the straight pipe is 4.22 m/s. The maximum conveying velocity of the straight pipe slurry is higher than the bending pipe conveying velocity, which shows that the restriction impacts of the bent pipe are more obvious than of the straight pipe. Figure 8 provides the conveying velocity distribution profiles of the different conditions for the slurry through the straight pipe and 90\({}^{\circ}\) elbow pipe, respectively. The velocity profile of high-concentration slurry in a flow cannot be observed in the laboratory [32; 33]. However, computational fluid dynamics (CFD) generate a vertical velocity profile which agrees well with the theoretical prediction. The measured points were set in a perpendicular direction with the slurry's advancing direction. In Figure 8, the velocity distribution was plotted on the Y-axis, whereas the location in the pipe's middle section from one side to another side was plotted on the X-axis. It was observed that a lower conveying velocity magnitude appears near to the region of the wall and the higher magnitude is distributed around the center. The value also indicates the stress contributed by particles would be constant in the velocity gradient and would be zeroed instantly once the flow is stopped. From Figure 8, the higher the inlet velocity of the slurry, the more dramatic the offset on the slurry conveying velocity at different positions in the pipe transportation, which causes worse stability for the CGFB slurry flow. From the Figure 8, it was observed that asymmetric nature of particles about longitudinal axis in the straight pipe. It was also noticed that the higher conveying velocity concentration zone shifts away from the central location to the pipe wall with the deformation of the pipe. But the concentration zone maintains the same position because of the CGFB slurry well homogeneous characteristic as the Bingham flow.