## 4 Experimental Procedure and Results  
Initially, the average velocities of air at the inlet of the flooded-bed scrubber at different fractions of the scrubber fan's maximum rotational speed were measured, keeping the face air quantity constant. The purpose of this step was to establish a relationship between the quantity of air through the flooded-bed scrubber (scrubber capacity) and the percentage of maximum fan speed. Continuous traversing at the inlet of the flooded-bed scrubber was performed using a vane anemometer. The result of the velocity measurement is presented in Table 1.  
The air quantity survey was performed at four different cross-sections along the length of the test gallery face. The locations of the cross-section from the inlet were 12.0 (39.3 ft), 14.7 (48.37 ft), 17.2 (56.5 ft), and 22.6 m (74.3 ft), respectively (Figure 5). Each cross-section was divided into a 0.61 m \(\times\) 0.61 m (2.0 ft \(\times\) 2.0 ft) square grid, and air velocity measurements were taken at points shown as blue dots in Figure 6 using a hot wire anemometer.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**\% Fan RPM** & **Velocity, m/s (fpm)** & **Quantity, m3/s (cfm)** \\ \hline
40 & 6.84 (1347) & 2.51 (5336) \\
50 & 8.13 (1600) & 2.99 (6336) \\
75 & 11.79 (2320) & 4.33 (9187) \\
80 & 13.65 (2687) & 5.02 (10,642) \\
90 & 16.23 (3195) & 5.97 (12,652) \\
100 & 17.58 (3460) & 6.46 (13,701) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Air quantity through scrubber at different fan speeds.  
Figure 5: Three-dimensional CAD drawing of the PRL longwall test gallery.  
For the first stage comparison, the quantity of air passing through each cross-section was calculated as the product of the area-weighted average velocity and the total area of the cross-section. The experiment was repeated for all four cross-sections with three different percentages of maximum fan speeds: 0% (scrubber fan turned off), 50%, and 100%. The face-air quantity was always kept constant at 23.23 m\({}^{3}\)/s (49,200 cfm). See Table 2 for the results of the air quantity through different cross-sections at different scrubber capacities. For the second stage comparison, six points from each cross-section were picked. The points were located inside the blue, dashed-line rectangle at the center of each cross-section, as shown in Figure 6. Table 3 presents the velocities at six points for each of the four cross-sections at 0%, 50%, and 100% scrubber fan capacities. The data inside the red, dashed-line rectangle in Table 3 are examples of velocities at six points for cross-section number 2 at 50% scrubber fan capacity.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Cross-Section No.**} & \multicolumn{3}{c}{**Quantity (m\({}^{3}\)/s)**} \\ \cline{2-4}  & **0\% Fan Max RPM** & **50\% Fan Max RPM** & **100\% Fan Max RPM** \\ \hline
1 & 21.14 & 22.09 & 22.10 \\
2 & 24.39 & 23.70 & 24.05 \\
3 & 22.68 & 23.05 & 24.26 \\
4 & 21.30 & 19.45 & 17.31 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Results of air quantity survey showing quantity through different cross-sections for different scrubber fan capacities.  
Figure 6: Cross-section of the longwall panel (not to scale) with 0.61 m x 0.61 m grid and measurement points.