臺灣博碩士論文加值系統

本研究為使用數值模擬方法，分析傳統式氣櫃與吹吸式氣櫃，內部及其拉門開口附近之流場結構及污染物質之擴散現象。傳統式氣櫃為於氣櫃頂部進行抽氣，固定流量Q為0.5 m3s-1，改變拉門開度，觀察流場現象。吹吸式氣櫃在改變抽氣位置於氣櫃底部前方，形成前下吸之型式，並於拉門底部提供補給吹氣氣流，觀察在吹吸比不同下之流場型態。本文採有限體積法配合k-ε紊流模式求解質量方程式、動量方程式與紊流方程式來模擬流動情形。
由傳統式氣櫃模擬結果得知，當氣櫃於操作中，氣櫃內會產生四主要迴流區，包括拉門後方渦漩、門檻附近渦漩、兩邊柱後方渦漩及實驗人員與拉門間之渦漩。四主要渦漩有其關連性，且隨拉門開度之大小有所變化，污染物亦隨流場結構而傳遞、擴散，並於實驗人員呼吸處做污染物濃度值檢測，比照美國ASHRAE[19]標準，得知傳統式氣櫃並不符合標準。另吹吸式氣櫃之模擬結果，當吹吸速度不同時亦會產生四種流場型態，根據Huang[7]定義，此四種模態為內凹模態(concave curtain)、筆直模態(straight curtain)、弱吸模態(under-suction)以及過吹模態(over-blow)。其中內凹模態為最佳之操作模態，實驗人員若在此流場模態下進行氣櫃操作，為最安全之狀態，而過吹模態為最劣之模態，不被推薦使用。本研究發現吹吸式氣櫃吹吸速度間之相互關係，且吸氣速度之臨界值與拉門開度之關係可列成經驗式，以供設計或操作人員參考。

A fume hood is a device which prevents pollutants leaking at a laboratory.
The function of a fume hood is to use a fluid flow to bring out pollutants from the exhaust.In this study, we simulate a three-dimension air flow captured by conventional and push-pull fume hoods using the commercial
software STAR-CD TM. The finite volume method and standard k-ε turbulence model are employed to describe structures and characteristics of lows.Moreover, the turbulent mass transfer equation is adopted to predict the distribution of concentration. Therefore we can obtain the flow patterns and pollutant distribution inside the hood.
There are different flow patterns, when various sash openings of the conventional fume hood are considered. Four characteristic vortices are found in flows, i.e. vortices behind the sash, vortices in the vicinity of the doorsill and the gatepost, and a vortex pair between the manikin and sash. Those vortices transport pollutants and, as a result, they connot be removed out the hood. According to numerical results, the concentration of pollutant at the measuring point is higher than the standard of ASHRAE[19] The predicted results of a push-pull fume hood reveal that all the flow fields can be concluded in four dominant modes: concave curtain, straight curtain, under-suction, and over-blow. The ratio of push and pull flow speeds should be adjusted into a concave curtain mode to ensure that all pollutants do not leak out. Furthermore, we find the relationship between the critical values of pull flow speed and sash opening. It can be fitted to empirical formulae which are useful for design and operation of a push-pull fume hood.

中文摘要
英文摘要
目錄
符號索引
表目錄
圖目錄
1 導論
1.1研究動機
1.2文獻回顧
1.3美國標準
1.4論文架構
2 物理模型與數值分析
2.1數值方法
2.1.1控制方程式
2.1.2紊流模式
2.1.3紊流傳輸方程式
2.1.4邊界設定
2.1.5有限體積法與STAR-CD
2.2數值模式驗證
2.3小結
3 傳統式氣櫃
3.1傳統式氣櫃基本分析
3.1.1流場分析
3.1.2污染物質擴散分析
3.2實驗人員對傳統式氣櫃之影響
3.2.1流場分析
3.2.2污染物質擴散分析
3.3傳統式氣櫃前有無實驗人員站立之比較
3.3.1流場分析之比較
3.3.2物質擴散分析之比較
3.4小結
4 吹吸式氣櫃
4.1吹吸式氣櫃基本分析
4.1.1流場分析
4.1.2物質擴散分析
4.2實驗人員對吹吸式氣櫃之影響
4.2.1流場分析
4.2.2物質擴散分析
4.3吹吸式氣櫃與傳統式氣櫃流場與物質擴散之比較
4.4小結
5 結論與建議
5.1結論
5.2建議
參考文獻

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