# Pressure Study on Pipe Transportation Associated with Cement Coal Gangue Fly-Ash Backfill Slurry
## 4 Results and Discussion
### Pressure Drop  
The pressure loss contour of the straight pipe and 90\({}^{\circ}\) elbow pipe was analyzed. It was observed that as the feeding velocity increases, the highest pressure loss was found for all transportation case. On the straight pipe transportation example, the maximum predicted pressure loss up to 92,600 Pa that occurred at the case of feeding velocity of 2.2 m/s for the total length of 17,000 mm. At the same inlet velocity in the bending pipe, the maximum pressure loss was 31,700 Pa, in which the delivery length of the slurry was near 4142 mm. Table 2 provides the predicted maximum pressure loss from the CFD simulation calculation.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Transportation Pipe Feeding Velocity (m/s)** & **1.4** & **1.6** & **1.8** & **2.0** & **2.2** \\ \hline
**Predicted pressure loss on straight case (Pa)** & 65,600 & 72,200 & 78,900 & 85,700 & 92,600 \\
**Predicted pressure loss on elbow case (Pa)** & 19,800 & 22,600 & 25,500 & 28,500 & 31,700 \\ \hline \hline \end{tabular}
**Note:** the total delivery length for predicted pressure loss on straight case is 17,000 mm; the total delivery length for predicted pressure loss on elbow case is 4142 mm.  
\end{table}
Table 2: Predicted pipe transportation pressure loss based on the CFD simulation.  
A pressure drop (\(\Delta\)_p_/_l_) is introduced to describe the pressure loss of the CGFB slurry in this paper, which was calculated in terms of the pressure loss per unit length through the pipeline [30]. Figure 5 shows the predicted pressure drop profile on the CGFB slurry suspension flow for the straight pipe and 90\({}^{\circ}\) elbow pipe at velocities of 1.4 m/s, 1.6 m/s, 1.8 m/s, 2.0 m/s and 2.2 m/s, respectively.  
The profile clearly shows the increasing inlet velocity of the slurry, resistance and local resistance loss both increased but the local resistance increase is very significant. These results support the notion that the local resistance is significantly higher than the resistance at the same transportation conditions associated with high-concentration slurry pipeline transportation. But regarding the CGFB slurry, the difference on the transportation resistance between the straight case and elbow cases is not large because of the slurry adequate fluidity and the lower conveying velocity in pipe. It was realized that for the slurry transportation case with the feeding velocity of 1.4 m/s, the value of the pressure drop is noticed at 3860 Pa/m in the straight pipe and 4780 Pa/m in the 90\({}^{\circ}\) elbow pipe. The factor of the local resistance over the total resistance is 1.24. Similarly, for the velocity of 2.2 m/s, the magnitude of pressure drop was observed at 5450 Pa/m for the straight example, while it was 7650 Pa/m with the elbow pipe. In this situation, the factor extends to 1.40. Under this level of the magnitude of the pressure drop, the CGFB slurry can be delivery for a longer distance compared with the traditional pastes slurry.  
This result agrees well with the pilot plant test results and it supports the conclusions that the CGFB slurry can satisfy the coal mine backfilling requirements with a large scale, large flow and high safety [11]. The CGFB backfilling technology is one of the potential methods to deliver the backfilling materials to 3000 m in the coal mine currently.