臺灣博碩士論文加值系統

本文先建立一數學模式描述直立矩形封閉容器內奈米流體自然對流熱質傳遞現象。矩形封閉容器的物理模型為一左右直立壁面分別為高低溫等溫壁面，而上下壁面假設為絕熱壁。本文並針對方形封閉容器內含氧化鋁-水奈米流體為均勻或兩元混合介質條件下進行數值模擬分析；而數值模擬主要考慮參數及其範圍分別為：萊利數(Ra=1000
~1000000)；普朗特數(Pr=6.06)；及奈米微粒體積濃度( 0.01%、1.00%、4.00%)等。由假設奈米流體為均勻混合介質之數值模擬結果顯示，封閉容器內奈米流體的熱傳係數可能較純水為低，與其熱傳導係數或動力黏滯係數之模式有密切關係。此外，由視奈米流體為非均勻混合介質的模擬結果可發現路易士數值高達60300，致使在容器邊壁形成相當細薄之濃度邊界層，而容器核心內部之流體呈現為均勻混合介質狀態。最後，本文依林建中（2004）、劉文恭(2007)實驗條件進行數值模擬，並與其實驗數據進行驗證；發現在冷熱壁溫差為2K情形下，數值預測的平均紐賽數與實驗數據頗為吻合。

In the present study, heat and mass transport phenomena associated with natural convection in a vertical rectangular enclosure filled with nanofluids is firstly modeled. The enclosure is differentially heated by two isothermal vertical walls, while the remaining walls are assumed adiabatic. Numerical simulations have then been undertaken for the mixture of Al2O3-water as the nanofluid, which may be modeled as a homogeneous or binary mixture, in a square enclosure with the pertinent dimensionless parameters in the following ranges: the Rayleigh number,Ra=1000~1000000 ; the Prandtl number, Pr=6.06 ; the volumetric fraction of nanoparticles, C = 0.01%, 1.00%, 4.00%. Numerical results from the simulations under the assumption of homogenous mixture in the enclosure clearly reveal that the ratio of heat transfer coefficient for the nanofluid to that for the base fluid (water) across the enclosure can be significantly mitigated, depending mainly on the models adopted for the thermal conductivity as well as the dynamic viscosity of the nanofluid. Moreover, the simulations for treating the nanofluid as a binary mixture, for which the Lewis number for the nanofluid is typically at a value of , show that the nanofluid in enclosure appears essentially as a homogenous mixture except for the region adjacent to the enclosing walls where considerably thin solutal boundary layer is developed. Finally, efforts were taken to validate the present simulations with the experimental results obtained by Lin (2006) and Liu (2007), respectively. Fairly good agreement was found between the predicted and measured results for the averaged Nusselt number of the nanofluid in the enclosure differentially heated with a temperature difference of 2K.

中文摘要..................................................I
英文摘要.................................................II
誌謝.....................................................IV
目錄......................................................V
表目錄.................................................VIII
圖目錄...................................................XI
符號說明...............................................XIII
第一章 　　序論.........................................1
1-1 前言.............................................1
1-2 文獻回顧.........................................2
1-3 研究目的.........................................7
1-4 本文架構.........................................7
第二章　　數值模式與數值方法..............................8
2-1　物理模型與基本假設...................................8
2-2 統御方程式...........................................9
2-3 初始與邊界條件......................................13
2-4 無因次化統御方程式及初始邊界條件....................14
2-5 數值方法與解題方式..................................21
2-5-1　網格系統........................................21
2-5-2 離散方法........................................22
2-5-3 解題流程........................................23
2-6 格點測試............................................26
第三章　　結果與討論.....................................35
3-1 奈米流體輸送現象特徵速度之估算.......................35
3-2容器內奈米流體視為均勻混合介質之數值模擬結果..........39
3-2-1 文獻比較........................................39
3-2-2 熱物性質對熱傳效率之影響........................41
3-2-3 熱傳導係數經驗公式之比較........................43
3-2-4 萊利數之影響....................................44
3-3　容器內奈米流體視為非均勻混合介質之數值模擬結果......54
3-3-1 文獻比較........................................54
3-3-2 流場、溫度場及濃度場的分析......................56
3-3-3 黏度效應的影響..................................57
3-4　數值模擬結果與實驗數據之比較........................67
3-4-1 基底流體(純水)之比較結果........................69
3-4-2 奈米流體數值模擬與實驗數據之比較結果............70
第四章　　結論與未來方向.................................78
参考文獻.................................................80
附錄A 容積性質的計算.....................................84
自述.....................................................87

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