# Study on Airflow Field Distribution and Dust Distribution Characteristics at Blast Piles
## 3 Results and Discussion  
### Analysis of Dust Generation Characteristics and Particle Size Distribution from Blast Piles  
Through extensive field investigations of excavation procedures in open-pit mines, it becomes evident that the dust emanating from blast piles stems predominantly from three \begin{table}
\begin{tabular}{c c} \hline \hline
**Model** & **Define** \\ \hline Slower & Pressure-based \\ Time & Transient \\ Gravity & Y = -9.8 m/s\({}^{2}\) \\ Viscous mode & k-epsilon realizable \\ Energy & Off \\ Discrete phase model & On \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Parameter settings of the calculation model. \begin{table}
\begin{tabular}{c c} \hline \hline
**Injection** & **Unit** & **Define** \\ \hline Material & Coal-hv \\ Total flow rate & kg/s & 0.2 \\ Min. diameter & m & PM2.5 2.5 \(\times\) 10\({}^{-6}\) \\ Max. diameter & m & PM100 1 \(\times\) 10\({}^{-4}\) \\ Mean. diameter & m & PM10 1 \(\times\) 10\({}^{-5}\) \\ Inlet velocity magnitude & m/s & 0, 1, 3 \\ DPM boundary type & & Trap \\ DPM boundary type & & Escape \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Dust injection source parameters and boundary conditions. distinct sources: (1) Dust arising from the drilling process: Given the substantial quantity of explosives necessitated in open-pit mining and the utilization of large-diameter blast holes, the drilling phase generates considerable dust, as illustrated in Figure 5. This dust is typically replenished into the blast holes prior to detonation and subsequently dispersed into the atmosphere post-explosion. Characterized by uniformly small particle sizes, this dust plays a pivotal role in the overall dust emission. (2) Dust generated during blasting: Under the intense force of explosives, rocks undergo fragmentation, liberating a substantial quantity of minute dust particles within the resultant fractures. A portion of these particles ascend to the surface of the blast pile or adhere to the rock surface via fracture pathways. The particle size distribution of this dust exhibits considerable variability, largely influenced by the inherent properties of the rock material. (3) Dust produced during shoveling: While the quantity of dust generated during this stage is comparatively modest, it primarily arises from the mutual collisions among rocks and between the shovel bucket and the rocks [30; 31]. Notably, the continuous application of external energy during this process leads to the lifting of a substantial amount of dust by external forces, thereby imparting initial kinetic energy that facilitates dust dispersal. This step is crucial in the release and dissemination of dust into the environment. Figure 6 illustrates the S3500 laser particle size analyzer and the dust samples. To ensure accurate measurements and minimize experimental errors, duplicate experiments were performed. The particle size distribution is shown in Tables 4 and 5, showing the cumulative and frequency distributions of particle sizes, as well as the sphericity and particle size distribution. Figure 5: The dust generation during the drilling process. Figure 6: Experimental objects: (**a**) S3500 laser particle size analyzer (**b**) coal dust sample. As the two experimental data sets were very close, we selected one set to create particle size and sphericity distribution graphs, as shown in Figures 7 and 8. From the graphs, it is evident that the particle size distribution does not follow a complete normal distribution. There is a normal distribution for particles smaller than 7 \(\upmu\)m, but not for those larger than 7 \(\upmu\)m. This indicates that the dust sample has an uneven particle size distribution and poor consistency. For dust in the blast pile after blasting, the composition is complex, including rock powder, explosive powder, coal powder, fine sand particles, etc., and thus it is reasonable that it does not follow a normal distribution.