開放液面槽吹吸式氣罩的流場與逸散關係探討

Flow Field Patterns and Contaminant Dispersion of Push-Pull Hoods on Open Surface Tanks

開放液面槽的大面積的化學蒸氣發生源通常需要使用吹吸式氣罩方能達到有效的有害物控制。但是影響吹吸式氣罩性能的因素甚多，造成其設計的困難。本研究於一設置吹吸式氣罩的模擬開放液面槽，以氣流可視化技術，配合 SF6 追蹤氣體濃度量側探討吹吸式氣罩的性能。氣流可視化技術係以雷射光頁照明，觀察於吹氣口及模擬液面釋放的煙霧，將流場模態依控制效果由低而高歸納為散佈、過渡、包覆與強吸四種形式，發現在其他條件固定的狀況下，存在一最適操作點，可以最低的吸氣風量達到控制效果較佳的流場模態。SF6 追蹤氣體濃度量測則用於測試局部逸散與吸氣口捕集效率。經整理各種測試結果，發現流場達到強吸模態時，大多可有效抑制局部逸散，且達到接近 100% 的吸氣口捕集效率。此外，亦發現開放槽若設置側板可降低局部逸散。

Chemical vapor from an open surface tank can be controlled effectively only by a push-pull hood because of the large contamination release area. However, the performance of a push-pull hood is subject to many factors, which makes its design a difficult task. In this study, an open surface tank installed with a push-pull hood was simulated to investigate the performance of push-pull hoods. The experiments were performed by employing the air-flow visualization technique and SF6 trace gas measurement. The air-flow visualization technique used an illuminating laser light sheet to observe the smoke released from the push nozzle and simulated liquid surface. Four types of flow field--dispersion, transition, encapsulation, and strong suction--were observed. The dispersion pattern showed the weakest control effect, and the strong suction pattern showed the most significant control effect. The observation also revealed an optimum operation point where the most effective pattern can be achieved with the smallest pull flow rate. The SF6 concentration was measured to obtain the local dispersion and capture efficiency of the pull hood. It was found that when the flow field was under a strong suction pattern the local dispersion could be restrained, and the capture efficiencies were nearly 100% in most cases. The experimental data also showed that guide plates installed on open surface tanks can further restrain local dispersion.