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論文中文名稱:圓管奈米流體強制對流之熱傳增益與熵增分析 [以論文名稱查詢館藏系統]
論文英文名稱:Investigation of forced convection heat transfer and entropy generation of nanofluid in a circular 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:製造科技研究所
畢業學年度:101
出版年度:102
中文姓名:陳宜鋒
英文姓名:Yi-Feng Chen
研究生學號:100568047
學位類別:碩士
語文別:中文
口試日期:2013-06-29
論文頁數:132
指導教授中文名:洪祖全
指導教授英文名:Tzu-Chen Hung
口試委員中文名:侯順雄;林大惠
口試委員英文名:Shuhn-Shyurng Hung;Ta-Hui Lin
中文關鍵詞:奈米流體熵產生CFD層流紊流定熱通量定壁溫
英文關鍵詞:NanofluidEntropy generationForce convectionLaminar flowTurbulent flowConstant heat fluxConstant wall temperature
論文中文摘要:本文首先使用計算流體力學方法模擬奈米流體層流及紊流圓管強制對流熱傳增益分析,接著使用熱力學第二定律進行熵增(entropy generation)分析。圓管邊界為固定熱通量(constant heat flux)或固定壁溫條件(constant wall temperature),流動現象假設為單相流(single phase)。本文探討TiO2奈米流體於層流及紊流對流場中,藉由增加奈米顆粒濃度(volume fraction of nanoparticle)與Re數,分析熱對流係數(heat transfer coefficient)增益現象。結果得到,奈米流體之熱對流係數隨著奈米顆粒濃度與Re數增加而提高,且熱對流係數高於一般水溶液基礎流體(base fluid)。數值分析結果與實驗文獻相當一致,平均誤差在10 %以內。
第二部分則分析Al2O3奈米流體於管流的熵增現象,邊界條件亦使用固定熱通量或固定壁溫條件進行參數分析。造成熵增加有諸多原因,而層流管流熱流場中熵產生主要來自於有限溫差熱傳所引起的熱力學不可逆(Ns)T;但是當雷諾數逐漸提升時,紊流管流熱流場中熵產生則變成黏滯摩擦引起的熱力學不可逆(Ns)P所主導。此部分參數分析包含無因次溫度、無因次長度、Re數、Nu數及奈米顆粒濃度等。整體而言,有限溫差熱傳之熵增現象(Ns)T隨顆粒濃度以及Re數增加而減小;黏滯摩擦之熵增現象(Ns)P隨顆粒濃度以及Re數增加而提升。為了便於觀察熵增趨勢,最後則引入無因次Be數比較有限溫差熱傳(Ns)T或黏滯摩擦(Ns)P兩者的貢獻何項較為顯著。
論文英文摘要:In this study, we aimed at investigating nanofluid laminar and turbulent forced convection heat transfer in a circular tube using computational fluid dynamics, and analyzing entropy generation due to flow and heat transfer in nanofluids employing the second law of thermodynamics. In the first part, boundary condition in a circular tube was subjected to a constant wall heat flux or a constant wall temperature condition. And the flow was assumed to be single-phase. The TiO2 nanofluids in laminar and turbulent flow field were numerically studied. The results showed that forced convection heat transfer coefficient of nanofluids increased with nanoparticles concentration and Re number, and that the forced convection heat transfer coefficient of nanofluid is higher than that of base fluid. It was also found that the numerical results were in good agreement with the experimental data obtained from the literature. The average error was around 10 %.
In the second part, analyses of entropy generation of Al2O3 nanofluids flowing through a circular tube with constant wall temperature or constant heat flux were conducted. There are many factors causing entropy increase. At laminar flow entropy generated mainly from the finite temperature difference heat transfer caused by the irreversible thermodynamics (Ns)T; however, when the Reynolds number is gradually increased, at turbulent flow the dominant factor on entropy generation becomes viscous friction caused by irreversible thermodynamics (Ns)P. Parametric study includes the dimensionless temperature, dimensionless length, Re number, Nu number and nanoparticle concentration. It was seen that entropy generation due to the finite temperature difference heat transfer (Ns)T decreased with the increase of particle concentration and Re number; and that entropy generation caused by the viscous friction (Ns)P increased with particle concentration and Re number. Finally Bejan number was used to compare the contribution of finite temperature difference heat transfer (Ns)T and viscous friction (Ns)P.
論文目次:摘要.......................................................i
ABSTRACT..................................................ii
誌謝......................................................iv
目 錄......................................................v
表目錄...................................................vii
圖目錄..................................................viii
第一章 緒論...............................................1
1.1 前言...................................................1
1.2 文獻回顧...............................................3
1.3 研究動機與目的.........................................9
1.4 研究分析流程圖........................................11
1.4.1 熱傳數值分析流程....................................11
1.4.2 熵增理論分析流程....................................12
第二章 奈米流體性質及熱流機制............................13
2.1 奈米流體的物理性質....................................13
2.1.1 熱傳導係數..........................................13
2.1.2 密度................................................15
2.1.3 黏滯係數............................................16
2.1.4 熱容量..............................................17
2.1.5 熱擴散係數..........................................18
2.2 奈米流體的熱傳機制....................................20
2.2.1 布朗運動............................................20
2.2.2 固液介面效應........................................21
2.2.3 團聚效應............................................22
2.2.4 聲子彈道傳輸........................................23
2.3 奈米流體於管流的流動機制..............................26
2.3.1 摩擦因子............................................26
2.3.2 局部熱對流係數h(x)及紐塞爾數Nu(x)...................28
2.3.3 平均熱對流係數have及紐塞爾數Nuave...................29
第三章 研究方法..........................................32
3.1 熱傳數值分析..........................................32
3.1.1 數值模擬分析流程....................................35
3.1.2 SIMPLE法求解流程....................................36
3.1.3 結構網格與非結構網格................................37
3.1.4 鬆弛因子及收斂條件..................................39
3.1.5 邊界條件............................................40
3.2 熵增理論分析..........................................43
3.2.1 定熱通量熵增方程式..................................43
3.2.2 定壁溫熵增方程式....................................46
第四章 結果與討論........................................50
4.1 TiO2奈米流體於層流圓管定熱通量下之熱傳增益探討........50
4.2 TiO2奈米流體於紊流圓管定熱通量下之熱傳增益探討........57
4.3 Al2O3奈米流體於層流圓管定熱通量下之熵增分析...........64
4.4 Al2O3奈米流體於紊流圓管定熱通量下之熵增分析...........83
4.5 Al2O3奈米流體於層流圓管定壁溫下之熵增分析............101
第五章 結論.............................................118
參考文獻.................................................122
符號彙編.................................................129
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