## 4 The Effect of Air Leakage on the Evaporation of Water from Goaf
### Effect of Time and Air Leakage Variation on Coal Body Moisture  
Figure 5a-c corresponds to the variation in moisture evaporation at air leakage volumes of 0.02, 0.03 and 0.04 m\({}^{3}\)/s, respectively. At time 0 day, the moisture of the coal body at measurement points M1-M15 is around 30%. The main reason for the inconsistency in the coal moisture at measurement points M1-M15 is that the distribution and size of the coal particles around each measurement point are not exactly the same and there is a certain error. In addition, it can be seen from the figure that the coal moisture at all measurement points gradually decreases with the increase in evaporation time. The moisture of the coal body decreases from about 30% to about 7%. Under different air leakage volumes, the coal moisture of all three groups of experiments decreased rapidly in the initial 4 days' time. After 4 days, the rate of coal moisture reduction gradually decreased and then stabilized. The time from the beginning to the stabilization of the coal moisture was 15, 11 and 7 days for the air leakage volumes of 0.02, 0.03 and 0.04 m\({}^{3}\)/s, respectively. Thus, it can be concluded that the larger the air leakage amount at the air inlet, the more moisture the air flow takes away from the model of the goat, the faster the coal moisture evaporates and the shorter the time for the coal moisture to stabilize.  
From the process of moisture reduction to stabilization, Figure 6a,b mainly depicts the moisture evaporation volume and moisture evaporation rate at different coal body moisture measurement points when the inlet air leakage volume is 0.02, 0.03 and 0.04 m\({}^{3}\)/s, respectively. From the figure, it can be seen that the moisture evaporation amount and moisture evaporation rate at measurement point 12 are the greatest when the air inlet leakage is certain. Additionally, the water evaporation amount and water evaporation rate at measurement point 14 are the smallest. For the air inlet leakage of 0.02, 0.03 and 0.04 m\({}^{3}\)/s, the moisture evaporation rates at measurement point 12 were 27.04, 29.3 and 29.41%, and the moisture evaporation rates at measurement point 14 were 18.29, 16.69 and 21.03%, respectively. Similarly, the moisture evaporation rates at measurement point 12 were 1.94,  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Serial Number**} & \multicolumn{2}{c}{**Air InletStatic**} & \multirow{2}{*}{**Wind Speed Valuem/s**} & \multirow{2}{*}{**Air Leakage Volume3/s**} \\  & & Pressure Value/Pa & & \\ \hline
1 & 6 & 2.1 & 0.02 \\
2 & 10 & 3.2 & 0.03 \\
3 & 15 & 4.2 & 0.04 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Airflow parameters at the inlet.  
Figure 5: Variation in water evaporation with different air leakage volumes: (**a**) Change in water evaporation when the air leakage is 0.02 m\({}^{3}\)/s; (**b**) Change in water evaporation when the air leakage is 0.03 m\({}^{3}\)/s; (**c**) Change in water evaporate on when the air leakage is 0.04 m\({}^{3}\)/s.  
2.67 and 3.90%/day, and those at measurement point 14 were 1.3, 1.52 and 3.00%/day. In addition, taking the air inlet leakage volume of 0.04 m\({}^{3}\)/s as an example, the moisture evaporation rates at different measurement points were ranked; then, the moisture evaporation rate at measurement point 12 was the largest, reaching 3.90%/day. The rate of water evaporation was 3.59%/d at measurement point 3, followed by measurement points 5, 6, 9, 11, 13 and 15, wherein the evaporation rate was around 3.5%/day. The rate of water evaporation was at the same level. Among these measurement points, the relatively large moisture evaporation rates were found at measurement points 6, 9, 11 and 15. The very small moisture evaporation rates were found at measurement points 4, 10 and 14, with 2.88, 2.95 and 2.99%/day, respectively.