## 4 Experimental Results and Discussion  
### Droplet Size and Velocity Distribution on Axis Direction  
The impact of surface tension and viscosity on axis droplets can be assessed by analyzing the droplet velocity and size at nine different points along the axis of the fog field, ranging from Z = 3 cm to Z = 19 cm. The relationship between surface tension, viscosity, and droplet size is presented in Figure 6.  
The results shown in Figure 6 reveal that the droplet size of the tested dust suppression solution increases steadily and continuously from Z = 3 cm to Z = 13 cm, and the increasing rates of droplet size for all three types of droplets exceed 100%. Specifically, the 2% dodecyl alcohol solution has the smallest droplet size, while the droplet size difference between 5% dodecyl alcohol and pure water solution is not significant. Decreasing the surface tension (approximately every decrease of 20 mN\(\cdot\)m\({}^{-1}\)) tends to make the droplet size smaller while increasing the viscosity (approximately every increase of 0.25 \(\times\) 10\({}^{-3}\) Pa\(\cdot\)s) tends to make the droplet size larger. In the axial direction, although the surface tension of the 5% dodecyl solution relative to water decreased by 25.4% and the viscosity increased by 64%, the droplet size did not change significantly. Therefore, to optimize the atomization effect, a small reduction in surface tension can effectively decrease the droplet size, while a large adjustment in viscosity is required to increase the droplet size. Moreover, in the axial direction, adjusting surface tension appears to be more effective than adjusting viscosity. The droplet sizes of the three solutions fluctuated between Z = 13 cm and Z = 19 cm, where the surface tension increased from 33.6 mN\(\cdot\)m\({}^{-1}\) to 71.97 mN\(\cdot\)m\({}^{-1}\) and the viscosity increased from 0.89 \(\times\) 10\({}^{-3}\) Pa\(\cdot\)s to 1.46 \(\times\) 10\({}^{-3}\) Pa\(\cdot\)s. However, no significant difference in droplet size was observed within this range. This interval is located at the edge of the fog zone, and the changes in droplet size are less affected by surface tension and viscosity. The velocity changes of droplets with different dust suppression solutions are presented in Figure 7. It is observed that the droplet velocity gradually decreases from Z = 3 cm to Z = 13 cm along the axial direction. At Z = 3 cm, the droplet velocity of the 2% dodecyl alcohol solution with the smallest surface tension reaches 12.8 m/s, which is twice that of water. As compared to the 2% dodecyl alcohol solution, the droplet velocity of the 5% dodecyl alcohol solution decreases by 34.0%, with an increase of 30.4% in viscosity. This is due to the fact that the kinetic energy generated by the atomized droplets at the nozzle outlet is higher than the surface tension energy, which causes the droplets to continue breaking up and forming droplets with higher velocity. However, with the increase of viscosity, the viscous interaction between the broken droplets increases, resulting in velocity attenuation and increased particle size, which is consistent with the trend observed in Figure 6.  
Figure 6: Droplet size distribution on axis direction. Figure 7: Droplet velocity distribution on the axis direction. Between Z = 13 cm and Z = 19 cm, the droplet velocity of dodecyl alcohol solution and pure water did not show a significant difference; instead, it remained in a fluctuating state. This is mainly due to the location of this interval, which is at the edge of the fog field, where droplets are more susceptible to environmental factors, resulting in the weakening of the influence of surface tension and viscosity on the atomized droplets.