# Research on the Influence of Rectifying Orifice Plate on the Airflow Uniformity of Exhaust Hood
## 3 Results  
### Influence of Single-Layer Rectifying Office Plate on the Airflow Uniformity of Exhaust Hood  
In this part, we study the influence of the aperture and porosity of a single-layer rectifying orifice plate on the airflow uniformity of the exhaust hood. Figure 2 displays the wind velocity contours of the monitoring surface and the center axis wind velocity distribution along the monitoring line at the rectifying orifice plate with varying apertures and porosities. We initially analyze the lower rectifying orifice plates with the different apertures of \(d\) = 2, 3, 4, 5, and 6 mm under a condition of fixed porosity.  
Figure 2a shows the wind velocity contour of the monitoring surface under varying apertures. It can be observed that as the aperture increases, the area of low wind velocity in the diagram significantly increases. Figure 2b presents the center axis wind velocity distribution along the monitoring line under different apertures. As the aperture increases, the maximum wind velocity appears around 400 mm of the exhaust hood and then begins to decrease. Notably, the curve for \(d\) = 2 mm exhibits a smaller difference between the maximum and minimum wind velocities, while the curve for \(d\) = 6 mm shows a larger disparity. Yet, the center axis wind velocity can only quantitatively analyze the airflow uniformity at the center of the exhaust hood. Therefore, we analyzed the average wind velocity and wind velocity non-uniformity of the monitoring surface as shown in Figure 2c. At \(d\) = 2 mm, the average wind velocity is 0.6418 m/s, and at \(d\) = 6 mm, it is 0.6496 m/s. Clearly, as the aperture increases, the average wind velocity slightly increases, but the aperture has almost no influence on the average wind velocity. However, the impact of the aperture on the wind velocity non-uniformity is very substantial. At \(d\) = 2 mm, the wind velocity non-uniformity is 26.01%, compared to 31.79% at \(d\) = 6 mm, indicating a decrease of 5.78%. We then further explored the influence of porosity \(\alpha\) = 4.91%, 17.91%, 35.43%, 47.79%, and 62.98% under the optimal aperture \(d\) = 2 mm.  
Figure 2d shows the wind velocity contour of the monitoring surface under different porosities. As the porosity increases, the area of low wind velocity initially decreases and then increases. Figure 2e presents the center axis wind velocity distribution along the monitoring line under different porosities. It is observed that as the porosity increases, the maximum wind velocity shifts from about 1000 mm to 400 mm of the exhaust hood. At \(\alpha\) = 17.91%, the center axis wind velocity shows a relatively flat trend, indicating a more uniform distribution of the wind velocity at this condition. Interestingly, when calculating the average wind velocity and wind velocity non-uniformity of the monitoring surface, as shown in Figure 2f, it is found that, at \(\alpha\) = 17.91%, the wind velocity non-uniformity is 25.81%, compared to 25.02% at \(\alpha\) = 35.43%. This inconsistency with the conclusions drawn from the center axis wind velocity suggests that the center axis wind velocity does not fully represent the distribution of the airflow of the exhaust hood. Additionally, as the porosity increases, the average wind velocity initially decreases and then increases. When \(\alpha\) = 17.91%, the minimum average wind velocity is 0.6377 m/s. Based on these findings, a rectifying orifice plate with \(d\) = 2 mm and \(\alpha\) = 35.43% was chosen to achieve optimal airflow uniformity. This setup resulted in an average wind velocity of 0.6400 m/s and a wind velocity non-uniformity of 25.02%.  
\begin{table}
\begin{tabular}{c c} \hline
**Parameters** & **Settings** \\ \hline Convergence Standard & \(10^{-6}\) \\ Exhaust Hood Outlet Boundary Type & Velocity-Inlet \\ Inlet Velocity Magnitude (m/s) & 13 \\ Hydraulic Diameter (m) & 0.2 \\ Turbulence Intensity (\%) & 3.53 \\ Boundary Type of the Computational Domain & Outflow (Surrounding) \\ Wall (Top and Bottom) \\ \hline \end{tabular}
\end{table}
Table 1: _Cont._