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研究生:馬震烜
研究生(外文):Chen Hsuan MA
論文名稱:吹吸式工業通風氣罩之紊流擴散數值模擬
論文名稱(外文):Numerical Simulations of Turbulent Diffusion in Push-pull Ventilation System
指導教授:陳明志陳明志引用關係
指導教授(外文):Ming-Jyh CHERN
學位類別:碩士
校院名稱:國立臺灣科技大學
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:2005
畢業學年度:93
語文別:英文
論文頁數:105
中文關鍵詞:吹吸式氣罩工業通風計算流體力學紊流擴散
外文關鍵詞:push-pull hoodventilationcomputational-fluid dynamicsturbulence diffusion
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本論文主要探討吹吸式通風氣罩在不同的吹氣與吸氣速度下之流場現象與特徵變化情形。吹氣端裝置於污染槽的一側,並將吸氣端裝置於相對於污染槽的另一端。因此,污染物會受到吹氣氣流的帶動,吹送至吸氣端後帶出至流場外。在數值模擬部份,本文採用標準 k-e紊流模式模擬流動情形,並配合適當的演算法則,進而求解質量方程式,動量方程式與紊流方程式。為分析流場中濃度大小分佈情形,本研究也採用質傳方程式加以分析流場中濃度變化。本研究中模擬 1.0 m 與 1.5 m 的污染槽,配合污染源蒸散速度0.03,0.05 與0.07 m/s,並以速度場、濃度場等方式呈現流場形態,除定性的分析外,並以定量的濃度量測表示流場特性。吹吸式氣罩在不同的吹吸速度配比下,流場模態基本上可以分為四種:散逸模態、過渡模態、包圍模態與強吸模態。其中包圍模態與強吸模態皆可以安全捕捉蒸氣污染物。因此,只要吹吸氣流與蒸氣的速度之配比能維持在這兩個模態內操作,氣罩的功能都是安全的,但是基於能量節約的考量,強吸模態可能就不見得需要。本研究著重於濃度的分析與量測,並由全場濃度圖判定各模態之污染物散逸情況,進而討論各模態之最佳操作範圍。研究結果顯示,即使在強吸模態下,仍有少部份污染物會散逸至氣罩捕集區域外。另一方面,本文也將吹吸式氣罩之幾何尺寸影響納入討論中,這些幾何參數包括吹氣與吸氣端擋板,吹氣與吸氣口的高度,以及吹吸氣口距液面的距離。這些幾何尺寸的影響並不顯著,但是不良的幾何尺寸設計仍會降低氣罩的效率。因此,最佳的吹吸速度配比,加上適當的幾何參數才是設計氣罩的目標。最後,對於氣罩的設計步驟做一簡單的敘述。
This study presents the numerical simulation on the push-pull ventilation system. The push-pull system is a device which is commonly used in capturing pollutants from large area tanks of industrial chemical processes. An air jet is blown (or pushed)
from one side of a tank and collected (or pulled) by an exhaust hood on the opposite side. The function of the push flow is to cover the pollutants and bring them to the pull channel. In this study, the standard k-e turbulence model is employed to describe the flow structures and characteristics. Moreover, the turbulence mass transfer equation is adopted to show the concentration distribution above the open surface tank. We simulate the flow in tank of area by 1.0 m*1.0 m and 1.5 m*1.0 m, with the pollutant evaporation velocities varies at 0.03, 0.05, and 0.07 m/s. All the flow fields can be concluded in four dominant modes: dispersion, transition, encapsulation, and strong suction. The push and pull flow velocities should be adjusted into encapsulation and strong suction modes to ensure all the vapor can be captured by the exhaust hood. However, if the energy usage and costs are considered, the encapsulation mode is the suitable region to operate. According to the observations, the pollutants may still disperse to the surroundings under the strong suction mode. The other geometric parameters such as the flange size, push and pull channel size, offset distance, and etc.,
would also have effects upon the flow characteristics. In conclusion, for a variety of lengths of tanks and pollutant evaporation velocities, the push and pull flow velocity must be matched so that the optimal operation would be generated. Furthermore, the flange size and other parameters are determined to enhance the capture efficiency of the push-pull system. The recommendations for design guidelines are introduced in this study.
CONTENTS
CHINESE ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . i
ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . v
CONTENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi
NOMENCLATURES . . . . . . . . . . . . . . . . . . . . . . . . . x
LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . xiii
LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . xiv

1 INTRODUCTION
1.1 Motivations . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Literature Review . . . . . . . . . . . . . . . . . . . . . 3
1.4 Synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2 MATHEMATICAL FORMULAE AND NUMERICALMODEL
2.1 Governing Equations . . . . . . . . . . . . . . . . . . . . 8
2.2 Turbulence Model (Standard k − ε Model). . . . . . . . . . . 9
2.3 Turbulent Mass Transfer Equation . . . . . . . . . . . . . . 12
2.4 Boundary Conditions . . . . . . . . . . . . . . . . . . . . 14
2.5 NumericalMethods . . . . . . . . . . . . . . . . . . . . . . 17
2.5.1 Grid Generation. . . . . . . . . . . . . . . . . . . . . . 17
2.5.2 Finite VolumeMethod . . . . . . . . . . . . . . . . . . . 18
2.6 SOLA method and parameters . . . . . . . . . . . . . . . . . 19
2.7 Validation of Proposed NumericalModel . . . . . . . . . . . 20
2.7.1 Flow Patterns of wall jet. . . . . . . . . . . . . . . . . 20
2.7.2 Turbulent Channel Flow Passes a Square Cylinder . . . . . 20
2.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3 ANALYSIS OF PUSH-PULL VENTILATION SYSTEM
3.1 Simulations of push-pull system . . . . . . . . . . . . . . 23
3.1.1 Length of tank L = 1.0 m/s . . . . . . . . . . . . . . . 24
3.1.2 Length of tank L = 1.5 m/s . . . . . . . . . . . . . . . 25
3.2 Variations of Hc . . . . . . . . . . . . . . . . . . . . . . 25
3.3 Flow Patterns and Concentration Fields . . . . . . . . . . . 27
3.3.1 Dispersion Mode. . . . . . . . . . . . . . . . . . . . . . 27
3.3.2 Transition Mode. . . . . . . . . . . . . . . . . . . . . . 28
3.3.3 Encapsulation and Strong SuctionMode . . . . . . . . . . . 29
3.4 Diagrams of CharacteristicModes . . . . . . . . . . . . . . 30
3.5 Comparisons . . . . . . . . . . . . . . . . . . . . . . . . 31
3.5.1 Suggestions of ACGIH . . . . . . . . . . . . . . . . . . . 31
3.5.2 Comparison with rules of ACGIH . . . . . . . . . . . . . . 32
3.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . 33

4 EFFECTS OF TANK GEOMETRY AND DESIGN GUIDELINES
4.1 Influences of Various Geometric Parameters . . . . . . . . . 36
4.1.1 Effect of Flange Size . . . . . . . . . . . . . . . . . . 36
4.1.2 Effect of Offset Distance . . . . . . . . . . . . . . . . 38
4.1.3 Effect of Channel Height . . . . . . . . . . . . . . . . . 39
4.2 Design Guidelines for Parameters . . . . . . . . . . . . . . 41
4.3 Design Procedure . . . . . . . . . . . . . . . . . . . . . . 42
4.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . 43

5 CONCLUSIONS AND SUGGESTIONS
5.1 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . 45
5.2 Suggestions. . . . . . . . . . . . . . . . . . . . . . . . . 47
BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . 49
CURRICULUMVITAE. . . . . . . . . . . . . . . . . . . . . . . . 105
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