## 3 Experimental Results and Analysis
### Droplet Size Analysis with Orthogonal Experiment  
The orthogonal test results of the droplet size are shown in Table 3. In accordance with the orthogonal experiment theory, it was necessary to average the three factors in this paper at the same level to find the overall average of each factor at the same level. The MAX of each horizontal average of these three factors was subtracted from the minimum value, and the value range of each influencing factor was obtained. The large range indicates that the difference in the influencing factors was large. This factor was an important factor in the three factors; the small range showed that the difference of the influencing factors was small, and through the analysis of the range method, the primary and secondary influence of the various factors on the droplet size could be obtained. D\({}_{[3,2]}\) was the Sauter mean diameter (SMD), which could better reflect the droplet size. The droplet size analyzed in this section was D\({}_{[3,2]}\).  
Figure 4: Droplet size distribution under different water supply pressures and outlet diameters at a 70 cm axial distance of the circular-hole rotating core micro-fog nozzle.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Serial Number** & **S/cm** & **D/mm** & **P/MPa** & **D\({}_{\mathbf{50}}\)** & **D\({}_{[3,2]}\)** & **D\({}_{[4,3]}\)** \\ \hline \(1\) & 30 & 0.5 & 1 & 681.3 & 516.1 & 677.2 \\ \(2\) & 30 & 0.7 & 3 & 658.2 & 160.5 & 482.8 \\ \(3\) & 30 & 1.1 & 2 & 668.1 & 238.6 & 533.3 \\ \(4\) & 50 & 0.5 & 3 & 296.0 & 111.3 & 349.8 \\ \(5\) & 50 & 0.7 & 2 & 80.3 & 58.3 & 152.2 \\ \(6\) & 50 & 1.1 & 1 & 98.0 & 64.4 & 153 \\ \(7\) & 70 & 0.5 & 2 & 105.9 & 86.2 & 238.1 \\ \(8\) & 70 & 0.7 & 1 & 62.0 & 47.0 & 160.6 \\ \(9\) & 70 & 1.1 & 3 & 71.9 & 53.5 & 101.4 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Orthogonal experiment results.  
Figure 5 shows the combined mean and range of the three factors. Through the range size comparison, it can be seen that of the three influencing factors, the axial distance had the greatest influence on the SMD, followed by the outlet diameter, and, finally, the water supply pressure. It can be seen from Figure 5a that when the S was 30 cm, the range of the SMD was 305.1 \(\upmu\)m; when the S was 50 cm, the range of the SMD was 78.0 \(\upmu\)m; when the S was 70 cm, the range of the SMD was 62.2 \(\upmu\)m. Due to the increase of the S, the SMD gradually became smaller. The main reason was that the droplets with a smaller particle size could move farther because of the small air obstruction caused by their small size. It can be seen from Figure 5b that the range of the SMD decreased first and then increased with the increase of the D. As shown in Figure 5c, the SMD continued to decrease due to the increase of the P, but the increase continued to decrease. When the P increased from 1.0 MPa to 3.0 MPa, the SMD decreased from 209.2 \(\upmu\)m to 127.7 \(\upmu\)m and then to 108.4 \(\upmu\)m. This was because when the pressure difference increased, the diameter of the gas core in the center of the nozzle would increase, resulting in the thinning of the liquid film. Therefore, under the influence of higher power and larger disturbance wave expansion on the surface, the liquid film was broken, resulting in the smaller droplet size.  
It can be seen from Figure 5 that the range was the smallest when the S was 70 cm, the range was the smallest when the S was 0.7 mm, and the range was the smallest when the P was 2 MPa. Therefore, an S of 70 cm, a D of 0.7 mm, and a P of 2 MPa was the best solution to improve the dust removal efficiency.