# Research on the Influence of Rectifying Orifice Plate on the Airflow Uniformity of Exhaust Hood
## 5 Conclusions  
Through analyzing the simulation and experimental results obtained from varying the apertures and porosities of the rectifying orifice plates, we evaluated their influence on the airflow uniformity and drew the following conclusions:  
1. The average wind velocity of the exhaust hood generally increases with the increase in aperture and porosity of the rectifying orifice plate. The impact of the aperture on the airflow uniformity of the exhaust hood depends on the position of the plate. Near the exhaust hood outlet, the airflow uniformity is negatively correlated with the aperture; near the exhaust hood inlet, the airflow uniformity is positively correlated with the aperture. A rectifying orifice plate with a porosity of 35.43% can effectively improve the airflow uniformity of the exhaust hood. 2. Exhaust hoods with a double-layer rectifying orifice plate structure can improve airflow uniformity by approximately 40% compared to those with a single-layer structure. When designing exhaust hoods with more stringent requirements for airflow uniformity, a multi-layer rectifying orifice plate structure can be used to further enhance airflow uniformity. The results of this study can guide the optimization of exhaust hood design and improve the airflow uniformity by setting appropriate rectifying orifice plates, thereby effectively enhancing the capture efficiency of the entire parallel-flow push-pull ventilation system for dust and toxic pollutants. Figure 5: Measured velocity and average velocity at measuring points 1 to 5. **Author Contributions:** Conceptualization: L.L. and C.D. ; Data curation: L.L. and B.Y. ; Formal analysis: L.L. ; Funding acquisition: C.D. ; Investigation: L.L. ; Project administration: Y.W. ; Resources: C.D. ; Supervision: C.D. ; Validation: L.L. and Y.W. ; Writing--original draft: L.L. ; Writing--review and editing: C.D., B.Y. and Y.W. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by the National Key Research and Development Program of China (2022 YFC2905003) and the fundamental research found for China Academy of Safety Science and Technology (2023 JBKY21). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The data presented in this study are available on request from the corresponding author. **Conflicts of Interest:** The authors declare no conflicts of interest. **Nomenclature**  
**Symbol**: **Property**: **Units**: \(\begin{array}{ll}\text{L}_{1}&\text{Length of the upper rectifying orifice plate}&\text{mm}\\ \text{W}_{1}&\text{Width of the upper rectifying orifice plate}&\text{mm}\\ \text{L}_{2}&\text{Length of the lower rectifying orifice plate}&\text{mm}\\ \text{W}_{2}&\text{Width of the lower rectifying orifice plate}&\text{mm}\\ d&\text{Aperture of the rectifying orifice plate}&\text{mm}\\ \alpha&\text{Opening ratio of the rectifying orifice plate}&\text{%}\\ L&\text{Length of the rectifying orifice plate}&\text{mm}\\ W&\text{Width of the rectifying orifice plate}&\text{mm}\\ m&\text{Number of holes on the rectifying orifice plate}&/\\ h&\text{Height from the upper rectifying orifice plate to}&\text{mm}\\ n&\text{Number of measuring points}&/\\ \beta&\text{Wind velocity non-uniformity}&\text{%}\\ \text{v}_{i}&\text{Measured wind velocity at the measuring point}&\text{m/s}\\ \text{\text{\  
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