# Pressure Study on Pipe Transportation Associated with Cement Coal Gangue Fly-Ash Backfill Slurry
## 4 Results and Discussion
### Velocity Distribution  
The velocity distribution of the CGFB slurry flow in the pipe is shown in Figures 6 and 7 based on the different respective feeding velocities. Figure 8 shows the velocity distribution profiles under the different transportation cases of the straight pipe and 90\({}^{\circ}\) elbow pipe. The slurry velocity distribution contour on the pipe was conducted to analyze the CGFB slurry flow transportation stability characteristics. Transversal plots of the slurry flow were done in the middle section of the straight (at the position of 8500 mm away from the inlet) and the bent pipe (the position of the corner of the bending). The velocity distribution of the CGFB flow was provided on the cross-section surface based on the different inlet velocity cases of 1.4m/s, 1.6 m/s, 1.8 m/s, 2.0 m/s and 2.2 m/s, respectively. The results from the straight pipe show (Figure 6) that the slurry moves forward with the shape of a plunger in the pipe due to the different velocity magnitudes at the different positions of slurry flow. A flow core-zone area and a non-flow core-zone area at the cross-section of the slurry flow were  
Figure 5: The pressure drops under the different conveying velocities. observed and were found to be in good agreement with the conclusions related to the flow-core zone distribution [31]. The slurry concentrates at the center region within a certain radius are located in an area with a relative high velocity (shown as the red zone in Figure 6). This area was defined as the flow-core zone while the remaining area in the cross-section of the pipe was defined as the non-flow core-zone. Beyond the flow-core zone area, within the region of the non-flow core-zone, from the center area to the pipe wall, the slurry conveying velocity presents a constant decreasing trend. At the position near to the pipe wall, the slurry conveying velocity is close to zero, which is considered as due to the \"wall effects.\" With suspension, there is always a slight decrease in particle concentration near the walls of the pipe, due to the steric effects, which result in the magnetized value of zero in the simulation. The conveying velocity distribution contour is concentric in the cross-section of the slurry flow. The center is much higher while the side is lower. For the case wherein the feeding velocity is 1.4 m/s, the maximum predicted conveying velocity in the pipeline is 2.65 m/s, in which an exceeding increase of 1.25 m/s was found. For the case of 1.6 m/s, the maximum velocity in the pipeline observed is 3.04 m/s, which exceeds the corresponding feeding velocity up to 1.44 m/s. For the case of 1.8 m/s, the difference between the potential maximum conveying velocity and feeding velocity is 1.63 m/s. For the example of 2.0 m/s, the difference is 1.83 m/s and the magnitude rises to 4.22 m/s for the case of 2.2 m/s, which is more than double the feeding velocity. The increasing difference indicates that as the feeding velocity increases, the slurry tends to be more unstable and the slurry plunger shape is more obvious. The difference of the conveying velocity on the slurry flow determines the stable transportation characteristics of the CGFB. The larger the difference of the conveying velocity between the jointed points on the slurry, the more significantly unstable the transportation was. Thus, the feeding velocity of CGFB transportation in the pipe should be reasonably determined in order to maintain stable flow. Figure 6: Velocity distribution contours with 76.05% solid concentration of CGFB slurry at different feeding velocities through the straight 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. When the CGFB slurry was pumped into the pipe after configuration on the surface station, under the restriction of the pipe wall and the impacts of slurry rheological characteristic, the slurry flow deforms to the plunger shape to progress along the pipe extension.