本研究對傳統外裝型氣罩以及四種傳統氣罩的變化形式進行實驗研究。使用雷射輔助煙霧可視化技術，探討各種形式氣罩的流動型態與氣動力特性;使用追蹤氣體(SF6)濃度偵測法，量測氣罩的洩漏程度。流場可視化的結果顯示，在環境無干擾氣流時，傳統外裝型氣罩在吸氣流量為10.5 m3/min以上，觀察不到明顯的煙霧洩漏。但是因為在實際操作時，環境中少有無干擾氣流的條件，所以經由分子擴散與紊流飄散的洩漏可能存在。另外四種傳統氣罩變化形式之流場可視化結果顯示，在傳統氣罩兩側加上具有邊界層控制器之側板時，在吸氣量10.5 m3/min時，流場結構非常的穩定，而且迴流區以及邊界層分離點存在於氣罩內側，不只無煙霧洩漏，而且對抗干擾氣流影響的能力大增。其他三種傳統氣罩的變化形式，因為只在傳統氣罩兩側加上不同尺寸的側板而入口處無邊界層控制器，因此在側板入口處即形成大範圍的迴流區，邊界層分離點存在於側板入口處，所以煙霧極容易藉著分子擴散以及紊流飄散而洩漏至環境中，更容易受到外界干擾氣流的影響而洩漏。追蹤氣體濃度測試結果顯示，在吸氣流量為10.5 m3/min時，傳統氣罩周遭的平均及最大洩漏濃度分別為0.016 ppm以及0.243 ppm;在傳統氣罩兩側加上不同尺寸的側板而入口處無邊界層控制器時，周遭的平均及最大洩漏濃度分別為1.646 ppm以及55.111 ppm;在傳統氣罩兩側加上具有邊界層控制器之側板時，周遭的平均及最大洩漏濃度分別為0.013 ppm以及0.076 ppm。在吸氣流量為15 m3/min時，傳統氣罩周遭的平均及最大洩漏濃度分別為0.037 ppm以及0.995 ppm;在傳統氣罩兩側加上不同尺寸的側板而入口處無邊界層控制器時，周遭的平均及最大洩漏濃度分別為0.012 ppm以及0.240 ppm;在傳統氣罩兩側加上具有邊界層控制器之側板時，周遭的平均及最大洩漏濃度分別為0.006 ppm以及0.026 ppm。顯然，在低吸氣量(10.5 m3/min)時，只在傳統氣罩兩側加上不同尺寸的側板而入口處無邊界層控制器時，追蹤氣體的平均與最大洩漏量反而比傳統氣罩增加非常多;在傳統氣罩兩側加上具有邊界層控制器之側板時的平均洩漏濃度與傳統氣罩的數值相當，這是因為環境幾近無擾動的原故。但是傳統氣罩的最大洩漏濃度比傳統氣罩兩側加上具有邊界層控制器之側板時的最大濃度高很多，顯示傳統氣罩的氣流不穩定度比傳統氣罩兩側加上具有邊界層控制器之側板大。在高吸氣量(15 m3/min)時，傳統氣罩兩側加上具有邊界層控制器之側板時的平均與最大洩漏濃度(分別為0.006 ppm與0.026 ppm)遠低於傳統氣罩的平均與最大洩漏濃度(分別為0.037 ppm與0.995 ppm)，這是因為在高吸氣量時，紊流引致的不穩定性使得傳統氣罩的洩漏增加。但是，傳統氣罩兩側加上具有邊界層控制器之側板的洩漏仍就非常的低。

Flow patterns and tracer-gas concentration leakage levels of a conventional and four modified suction hoods were experimentally study. Laser-light sheet assisted flow visualization technique was used to diagnose the flow patterns. The tracer-gas (Sulfur hexafluoride,SF6) concentration detection method was used to quantify the containment leakages of the hoods. Under the condition of no cross draft, no severe leakage of oil fumes was observed when the conventional suction hood was operated at a suction flow rate of 10.5 m3/min. However, previous studies indicated that the conventional hood presented severe leakage because cross draft existed in almost all the working areas. The hood installed with side flat plates presented severe leakages because boundary-layer separation occurred at the leading edge of the plates and formed large recirculation bubbles. The hood installed with side guard plates with boundary-layer separation controllers (bsc) arranged at the leading edges of the plates showed stable flow field. No oil fume leakages were observed at the inlet because the separation points of boundary layers were postponed rearward in the hood. At the low flow rate 10.5 m3/min, the average and maximum SF6 leakage concentrations of the conventional hood were 0.016 and 0.243 ppm, respectively. The corresponding leakage values of the hood installed with side plates were 1.646 and 55.111 ppm, respectively. The hood installed with bsc showed relatively smallest leakage values—0.013 and 0.076 ppm, respectively. At the medium flow rate 15 m3/min, the average and maximum SF6 leakage concentrations of the conventional hood were 0.037 and 0.995 ppm, respectively. The corresponding leakage values of the hood installed with side plates were 0.012 and 0.240 ppm, respectively. The hood installed with bsc showed negligibly small leakage values—0.006 and 0.026 ppm, respectively. Obviously, installing side plates without boundary-layer separation controllers would induce large containment leakages when compared with the conventional hood. By arranging the boundary-layer separation controllers to the side plates, the leakage levels were significantly decreased—negligibly small values were obtained. These results were corresponding to those of flow visualization.

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