## 3 Results and Discussion
### Particle Distributions with Different Installing Positions of the Deflector
Tables 4 and 5 show the statistical indices of the particle distributions corresponding to Figure 19. The high deflector installation seems to reduce the accumulation remarkably. This is because the deflector is installed near the observation plane, which improves the dispersal effect. Meanwhile, the high deflector installation cannot achieve a satisfying performance on reducing the accumulation of plane 1, as can be seen from Tables 2 and 3. Hence, the low deflector installation may be an optimal choice. Figure 19: The distributions of the four classes of particles at plane 2 with different installing positions of the triangular deflector: (**a**) no deflector installed, (**b**) the low deflector installation, (**c**) the middle deflector installation, and (**d**) the high deflector installation. Furthermore, combined with the central sectional contour shown in Figure 9, it is indicated that the low deflector installation is located in the high-speed area of the flow field in the vertical duct. Therefore, installing the triangular deflectors in the high-speed area of the vertical duct may be an efficient way to disperse particles with relatively large sizes and reduce particle accumulation at the entrance of the catalysts. Figure 20 illustrates the velocity distribution of plane 1 corresponding to the low deflector installation. The RSD of velocity is 8.30% and the total pressure loss is 518.91 Pa, including the two catalyst layers of 420 Pa. Compared with Figure 8, it reveals that the low deflector installation has no drastic impact on the velocity distribution and the total pressure loss. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Case** & **Small-Sized Particles** & **Medium-Sized Particles** & **Large-Sized Particles** & **Extra-Large-Sized Particles** \\ \hline No deflector installed Low deflector installation & 29.04\% & 66.36\% & 122.05\% & 162.57\% \\
20.08\% installation Middle deflector installation & 21.08\% & 52.24\% & 90.58\% & 117.44\% \\
20.08\% installation & 16.30\% & 40.84\% & 72.65\% & 97.06\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The RSDs of distributions for small-sized, medium-sized, large-sized and extra-large-sized particles at plane 2 with different installing positions of the triangular deflector. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Case** & **Small-Sized Particles** & **Medium-Sized Particles** & **Large-Sized Particles** & **Extra-Large-Sized Particles** \\ \hline No deflector installed Low deflector installation & 16.65\% & 27.41\% & 43.55\% & 55.28\% \\
20.08\% installation Middle deflector installation & 13.82\% & 21.61\% & 30.53\% & 36.78\% \\
20.08\% installation High deflector installation & 14.46\% & 22.98\% & 33.01\% & 39.46\% \\
20.08\% installation & 12.45\% & 18.53\% & 23.53\% & 27.38\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The maximum percentages of small-sized, medium-sized, large-sized and extra-large-sized particles at plane 2 with different installing positions of the triangular deflector. Figure 20: Contours of gas velocity at plane 1 with the low deflector installation (unit: m/s).