臺灣博碩士論文加值系統

局部排氣裝置能否發揮有效性能，氣罩設計是否正確是關鍵因素之一。外裝型氣罩構造簡單、操作容易，在一般作業場所使用最為普遍。但此型氣罩的捕集性能常受外在環境影響，此攸關於氣罩捕集性能與局部排氣裝置的經濟效益。有鑑於此，本研究根據風速量測，探討外裝型氣罩排氣風量與張角變化，對於氣罩開口面風速與氣罩中軸延伸風速的影響。實驗以側吸式局部排氣裝置配合三種排氣量、五組不同張角的氣罩進行量測，評估各種參數組合下外裝型氣罩捕集性能的變化。
結果顯示，氣罩開口面風速與開口面積成反比，當氣罩張角大於50°後，吸氣氣流會過於集中，開口面風速呈現不均勻分布，即使排氣量提升，氣流也只侷限於中軸部分，無法有效改善氣罩捕集性能；張角50°以下之氣罩開口風速分布均勻、吸氣風速較優良。顯示氣罩張角變化對於其捕集性能存在一個臨界值，當張角大於此臨界值時，其捕集性能則不再隨排氣量比例的增加而改變，故經濟效益比較不佳。最後建議外裝型氣罩張角設計於50°以下的範圍，再依作業需求擇一適宜張角之氣罩，以達最佳的捕集效果。

The effect of a local exhaust device significantly depends on the design of its exhaust hood. The exterior-type hood is the most frequently used hood in the local exhaust devices because of its simple construction and easy operation. However, this type of hoods is easily affected by a variety of environmental factors. which have negative impacts on the capture performance and economical benefit.
This study concerned the effects of hood taper angle and exhaust flow-rate to the opening and axial velocity of the exterior-type hoods based on the measurements on air speed. The experimental device was a side-exhausted device, which was operated under three exhaust flow rates, and five configurations of exterior hoods with different taper angles. The capture performance was evaluated at different combinations of parameters.
The results showed that the average air velocity on the opening is reversely proportional to the opening area. While the taper angle, measured outward from the central axis, is larger than 50°, the air velocity at the opening becomes less uniform. The exhaust flow concentrates at the middle of the opening even with an increase of the exhaust flow rate. Therefore, the capture performance cannot be effectively improved by a strong exhaust flow. While the taper angle is less than 50°, the air flow distributes uniformly on the opening which results in a better capture performance. This study recommends that the taper angle of an exterior-type hood should not exceed 50°, and the angle should also be selected based on the required capture range of an operation.

誌謝 i
摘要 ii
Abstract iii
目錄 iv
圖目錄 vi
表目錄 viii
符號索引 ix
第 一 章 緒論 1
1-1 研究動機 1
1-2 研究目的 2
1-3 論文大綱 3
第 二 章 文獻探討 5
2-1 外裝型氣罩的種類與運用 5
2-2 外裝型氣罩理論回顧 9
2-2-1 氣罩中軸風速計算 9
2-2-2 側風、坦坡與凸緣對氣罩捕集性能之影響 11
第 三 章 研究設備與方法 13
3-1 研究設備 13
3-1-1 局部排氣裝置 13
3-1-2 排氣機 15
3-1-3 文氏管流量計 15
3-1-4 氣罩 17
3-1-5 壓力轉換器 23
3-1-6 熱線式風速計 24
3-2 研究方法 25
3-2-1 氣罩中軸延伸風速 26
3-2-2 氣罩開口面吸氣風速 27
3-2-3 評估氣罩開口面有效位置 30
第 四 章 結果與討論 31
4-1 氣罩中軸延伸風速 31
4-2 氣罩開口面吸氣風速 33
4-2-1 氣罩開口面平均吸氣風速 33
4-2-2 氣罩開口面風速均勻度 34
4-2-3 氣罩開口面吸氣風速分布 35
4-2-4 排氣量比與氣罩吸氣風速比 41
4-3 評估氣罩開口面有效位置 42
4-3-1 氣罩外開口中軸風速計算 42
4-3-2 氣罩內開口中軸風速計算 43
第 五 章 結論與建議 49
5-1 結論 49
5-2 後續研究建議 50
參考文獻 51
附錄 局部排氣風機校正 53

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