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論文中文名稱:考慮逆向氣流效應對橢圓管上之降膜蒸發熱質傳影響 [以論文名稱查詢館藏系統]
論文英文名稱:Study the Effect of Counter Current Airflow on Heat and Mass Transfer of Evaporating Falling Films over an Elliptic Tube [以論文名稱查詢館藏系統]
院校名稱:臺北科技大學
學院名稱:機電學院
系所名稱:能源與冷凍空調工程系
畢業學年度:106
畢業學期:第二學期
出版年度:107
中文姓名:張立旺
英文姓名:Li-Wang Chang
研究生學號:105458026
學位類別:碩士
語文別:中文
口試日期:2018/05/31
論文頁數:54
指導教授中文名:楊安石
口試委員中文名:楊安石;簡良翰;施陽正;曾豊育
中文關鍵詞:滴淋蒸發橢圓管計算流體力學(CFD)
英文關鍵詞:Falling filmEvaporationElliptic tubeCFD simulations
論文中文摘要:滴淋式熱交換器已被廣泛應用於冷凍空調、化學工程、石油煉製、海水淡化等產業,一個高效能的熱交換器,可降低能源的消耗,並節省操作成本;而如何提升熱傳效能又達到節能效果,是目前最重要的研究議題。熱交換器的設計中,橢圓管相對於圓管具有較低的摩擦壓損和增強外部氣流場中的熱傳效率等更大優勢。目前在滴淋式熱交換器研究領域中,國內外相關文獻大多侷限於二維流場模擬及熱傳性能實測,對於三維暫態的管上液膜流場模擬分析則相當地少。本文以計算流體力學軟體ANSYS/Fluent®探討滴淋式熱交換器中管上滴淋降膜的流動現象,為分析暫態下的水和空氣兩相流體流動過程,本文使用流體體積法(Volume-of-Fluid, VOF)模擬發生熱傳和質傳現象的界面運動,另連結自定義方程式(User Defined Function, UDF)模擬管上液膜表面的蒸發潛熱與顯熱熱傳模式。本研究比較理論預測與文獻實驗量測以驗證計算模型的準確性,進而探討不同入口液體質量流率與逆向氣流率之操作參分析橢圓管上表面液膜厚度、液-氣界面速度和局部熱傳係數的兩相液膜流動的熱傳特性。
論文英文摘要:Falling film heat exchangers have been broadly utilized in the industries such as refrigeration, chemical engineering, petroleum refining processing and desalinization. Considering as an alternative of circular tubes in designing heat exchangers, elliptical tubes offered major advantages over the circular ones, including lower profile drag and enhanced efficiency of heat transfer in an external airflow field. The purpose of this paper is to examine the evaporative behavior of falling films on a horizontal elliptic tube in counter-current airflows. Numerical calculations were performed using the CFD software ANSYS Fluent® to simulate the falling film flow phenomenon. As a volume tracking technique to study the transient water-air two phase flow process of falling film over horizontal elliptic tube, this study implemented the volume-of-fluid (VOF) method to characterize the interfacial movements, where the heat and mass transfer phenomena occurred. To validate the computational model, we compared the predicted heat transfer coefficients with the measured data of available literature along the circumferential angle for circular tube surfaces. We then determined the distributions of velocity, liquid film thickness of two phases in conjunction with local heat transfer coefficient at the film flow rates of 0.093, 0.149 and 0.186 kg/m-s and counter current air flow velocities of 0 and 0.25 m/s, respectively.
論文目次:摘要 i
ABSTRACT ii
誌謝 iv
目錄 v
圖目錄 vii
表目錄 ix
第一章 緒論 1
1.1研究背景及動機 1
1.2文獻回顧 2
1.2.1液膜滴淋蒸發理論 3
1.2.2滴淋流場 4
1.3研究目的 7
第二章 計算域幾何形狀及邊界條件 8
2.1幾何形狀 8
2.2邊界條件 9
第三章 理論分析 14
3.1基本假設與統御方程式 14
3.1.1統御方程式 15
3.2數值方法 19
3.2.1對流-擴散方程式的差分形式 20
3.2.2壓力-速度耦合關係的處理 22
第四章 結果與討論 26
4.1模擬值與文獻值比對分析 26
4.2網格獨立性測試 32
4.3滴淋質量流率對液膜熱質傳影響(無逆向氣流) 35
4.4逆向氣流對液膜熱質傳影響 44
第五章 結論 48
參考文獻 49
符號彙編 53
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