# Research on the Influence of Rectifying Orifice Plate on the Airflow Uniformity of Exhaust Hood
## 3 Results
### Influence of Double-Layer Rectifying Orifice Plate on the Airflow Uniformity of Exhaust Hood  
For an exhaust hood with a double-layer rectifying orifice plate, the wind velocity non-uniformity is at least 25.02%. However, according to engineering practices, it is generally required to reduce the wind velocity non-uniformity to below 20% to significantly enhance the capture efficiency of dust and toxic pollutants by the exhaust hood. Therefore, to further improve the airflow uniformity of the exhaust hood, we propose using a double-layer rectifying orifice plate. Considering the previously mentioned results, the lower rectifying  
Figure 2: The influence of the single-layer rectifying orifice plate on the airflow uniformity. (**a**) Wind velocity contour of the monitoring surface under different \(d\); (**b**) center axis wind velocity distribution of the monitoring line under different \(d\); (**c**) histogram compares the average wind velocity and wind velocity non-uniformity of the monitoring surface under different \(d\); (**d**) wind velocity contour of the monitoring surface under different \(a\); (**e**) center axis wind velocity distribution of the monitoring line under different \(a\); (**f**) average wind velocity and wind velocity non-uniformity of the monitoring surface under different \(a\). - orifice plate was modeled with \(d\) = 2 mm and \(\alpha\) = 35.43%. Initially, we examined an upper rectifying orifice plate with a fixed porosity of 35.43% and apertures of \(d\) = 2, 3, 4, 5, and 6 mm. The simulation results for the wind velocity contour and center axis wind velocity distribution for a double-layer rectifying orifice plate, considering various porosities and apertures, are shown in Figure 3.  
Figure 3a displays the wind velocity contour of the monitoring surface under different apertures. It can be observed that when \(d\) = 2 mm, the central region of the monitoring  
Figure 3: The influence of a double-layer rectifying orifice plate on the airflow uniformity. (**a**) Wind velocity contour of the monitoring surface under different \(d\); (**b**) center axis wind velocity distribution of the monitoring line under different \(d\); (**c**) histogram compares the average wind velocity and wind velocity non-uniformity of the monitoring surface under different \(d\); (**d**) wind velocity contour of the monitoring surface under different \(a\); (**e**) center axis wind velocity distribution of the monitoring line under different \(\alpha\); (**f**) average wind velocity and wind velocity non-uniformity of the monitoring surface under different \(\alpha\). surface has a slightly lower wind velocity compared to the edge areas; as the aperture increases, there is a slight increase in the wind velocity in the central region of the exhaust hood. Figure 3b shows the center axis wind velocity distribution along the monitoring line under different apertures. It is apparent that the center axis wind velocities are relatively consistent across different apertures, but the curve for \(d\) = 2 mm is the flattest, indicating more stable wind velocities under this condition. Further analysis of the average wind velocity and wind velocity non-uniformity of the monitoring surface is shown in Figure 3c. Through our calculation, we found that as the aperture increases, the average wind velocity slightly increases, from the lowest at \(d\) = 2 mm with 0.5771 m/s to 0.5863 m/s at \(d\) = 6 mm. Surprisingly, the wind velocity non-uniformity decreases with the increasing aperture, which contradicts our previous results. At \(d\) = 2 mm, the wind velocity non-uniformity is the highest, at 18.19%; at \(d\) = 6 mm, it is the lowest, at 17.92%. Consequently, we further analyzed the effect of the porosities \(\alpha\) = 4.91%, 17.91%, 35.43%, 47.79%, and 62.98% under the optimal aperture \(d\) = 6 mm. Figure 3d shows the wind velocity contour of the monitoring surface under different porosities. As the porosity increases, the low wind velocity area in the center of the exhaust hood continuously decreases.