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研究生:劉恩廷
研究生(外文):En-Ting Liu
論文名稱:以水霧做為海龍替代物滅火劑性能評估之數值模擬
論文名稱(外文):Water Mist over Tsuji Burner: Numerical Simulation for Performance Evaluation of Halon Replace Agents
指導教授:陳俊勳陳俊勳引用關係
指導教授(外文):Chiun-Hsun Chen
學位類別:碩士
校院名稱:國立交通大學
系所名稱:機械工程系
學門:工程學門
學類:機械工程學類
論文種類:學術論文
論文出版年:1999
畢業學年度:87
語文別:英文
論文頁數:79
中文關鍵詞:海龍替代品二相流多孔燃燒器擴散對沖火焰火焰延展率臨界液滴濃度滅火效率PSI-Cell 模式
外文關鍵詞:Halon replacement agentstwo-phase flowTsuji burnercounterflow diffusion flameflame stretch ratedroplet concentrationfire suppression efficiencyPSI-Cell model
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一理論模式用來解析一水霧流過由Tsuji Burner所造成擴散對沖火焰之火焰
與液滴交互作用。其統御方程式由兩個部份構成。其中,氣相燃燒模式採用由
陳俊勳和翁芳柏[10]所發展的理論模式。在液相方面,液滴的運動由牛頓第二
運動定律來描述,並同時考慮液滴在流場中的熱傳及質傳;一些實驗關係式也
被用來描述液滴的行為。最後,再用PSI-Cell模式來處理二相之間的藕合。
當液滴沿其軌跡運動時,會從火焰中吸收熱量,並在流場中產生水蒸氣。
由液滴蒸發所產生的水蒸氣會稀釋氧和燃料的濃度而由相變化所吸收的熱量也
會降低火焰的溫度,兩者都會使火焰強度減弱。若採用50微米的液滴,當水霧
的流量增加到空氣流量的7%時,在停滯區的包封火焰前端會被熄滅而後退到尾
流區形成尾流火焰。當水霧的流量大於15%,火焰就完全熄滅。至於80微米的
液滴,在流量4.5%時會產生尾流火焰,在10%以上的流量則沒有火焰存在。從
研究中也發現,在相同的水霧流量下,較小液滴情況下的火焰強度較強。此外
,也對液滴大小的效應做一研究,藉由同時改變液滴大小及相對應的水霧流量
以固定液滴的數量流率。液滴大小為55微米時會產生尾流火焰,在70微米以上
則沒有火焰存在。本論文亦討論了該模式在未來可以繼續研發的方向。
The interaction between the water mist and counterflow diffusion flame over Tsuji burner is studied numerically. The governing system comprises two parts. The gas phase combustion model adopted one developed by Chen and Weng [10]. In the liquid phase, the motion of droplet is described by the Newton''s second law, and its heat and mass transfer is considered by including some empirical correlations. Finally, the PSI-Cell model is used to handle the two-phase coupling.
The evaporation of droplets absorbs heat from flame and subsequently generates vapors in the flow field. The generated vapors dilute both the oxidizer and fuel concentrations and the heat absorption by phase change lowers the flame temperature. For 50 mm droplets, the flame front of envelope flame is extinguished from the forward stagnation area and retreats to downstream to become a wake flame as the mist flow rate increases to 7%. The wake flame no longer exists when mist flow rate is greater than 15%. The critical values of the envelope flame transforming into wake one and flame extinction for 80 mm droplets are 4.5% and 10% separately. It is found that the flame is stronger for the smaller droplet sizes under the same mist flow rate. Besides, the effect of varying droplet size are studied by changing the size of droplet and corresponding mist flow to keep the number flow rate constant. The critical sizes of the envelope flame transforming into wake one and flame extinction are 55 mm and 75 mm separately. Finally, the possible future extensive works are discussed as well.
Page
Abstract in Chinese i
Abstract in English ii
Contents v
List of Figures vii
List of Tables ix
Nomenclature x
Chapter I Introduction 1
1.1 Motivation 1
1.2 Literature Review 3
1.3 Scope of Present Study 6
Chapter II Mathematical Analysis 8
2.1 Introduction 8
2.2 Gas Phase Model 8
2.2.1 Conservation Equations in Dimensional Form 9
2.2.2 Chemical Kinetics 11
2.2.3 Boundary Conditions in Dimensional Form 12
2.2.4 Dimensionless Governing Equations and Boundary Conditions 13
2.3 Droplet Model 18
Chapter III Numerical Algorithms 25
3.1 The Grid Generation Technique 25
3.2 Transformation of Gas Phase Governing Equations and Boundary Conditions 27
3.3 Numerical Algorithm and Solution Procedure for Gas Phase 28
3.3.1 Finite Difference Equations 28
3.3.2 Pressure Correction Equation 29
3.3.3 Computational Sequence for Gas Phase Equations 30
3.4 Numerical Solution for the Droplet Equations 31
3.5 Complete Gas-Droplet Computation 32
Chapter IV Results and Discussion 33
4.1 The Effect of Varying Vapor Mass Fraction in Air 34
4.2 The Effect of Varying Mist Flow Rate on Envelope Flame 35
4.2.1 50 mm Droplets 36
4.2.2 80 mm Droplets 39
4.3 The Effect of Varying Droplet Size 41
Chapter V Conclusion 43
References 46
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