臺灣博碩士論文加值系統

高爐的冷卻技術對於練鋼產業來說非常重要的，因為它可以大幅提高高爐的產量和使用壽命，而為了提高爐冷卻系統的傳熱性能，奈米流體被用於解決高爐的冷卻問題。近來研究發現複合奈米粒子比起奈米粒子擁有更高的熱傳性質，其複合方式分別有粒子混摻以及在奈米粒子上形成一層塗層，這兩種方法皆能增加奈米粒子熱傳性質。本文利用計算流體力學(CFD)探討複合奈米流體的高爐冷卻壁系統：第一個系統為單層高爐冷卻壁(cooling stave)的強制熱對流；第二個系統為多層耐火材高爐冷卻壁的強制熱對流系統，包括鐵殼層、填充材層、單層冷卻壁層、耐火襯層、礦渣層，兩個系統皆在紊流情況下，計算熱流結果，使用經濟效益值對奈米流體添加進行評估。在穩態情況下，我們考慮濃奈米流體的濃度、質量流率、二氧化鈦上的銀粒徑及奈米顆粒聚集度。我們使用計算流體力學進行數值分析，複合粒子與一般奈米粒子不同還需要考慮奈米層的厚度，故使用Maxwell的奈米粒子層修正經驗式計算複合奈米粒子的熱傳導係數，流體部分假設為單相流模式及不可壓縮流體，利用Pak經驗式和Haisheng經驗式計算奈米流體的密度和比熱容經驗式及含有粒子聚集程度的黏度及熱傳導係數關係式，得到所需要的物理條件後，實驗利用有限體積法的二階上風法離散數學方程式，其後用壓力耦合方程半隱式法(SIMPIEC)讓離散後的代數方程進行迭代。藉由以上數值方法求解獲得之速度場、溫度場以及壓力場，計算熱對流係數及摩擦因子，並經結果與討倫後，本文得到以下重要成果：
(1)單層冷卻壁系統
a.高爐冷卻壁內含有銀/二氧化鈦複合奈米粒子濃度6.43vol%的質量流率從1kg/s到4kg/s，因為強制對流作用增加流體擾動性使得熱對流係數跟摩擦因子比值(η)從0.97增加到2.15。

b.我們固定二氧化鈦濃度3 vol%及粒子聚集度2.584a，探討銀粒子徑從0nm變化為5nm對熱傳性質的影響，在固定雷諾數75700時，質量流率會隨著銀粒子徑增加從2.3kg/s變化至5.1kg/s，相對於二氧化鈦奈米流體，銀/二氧化鈦複合奈米流體的熱對流係數及Nusselt number分別提升了99%及14.8%，此為在二氧化鈦上的銀奈米粒子層增加固態奈米粒子的熱傳導係數所致。
(2)多層冷卻壁系統
a.多層高爐冷卻壁內部盤管含有濃度3.28vol%(二氧化鈦濃度1vol%;銀粒子徑5nm;粒子聚集度2.584)的複合奈米粒子，當改變質量流率從1.77kg/s變化至2.35kg/s，造成冷卻壁熱面到鐵殼層的溫度下降了10oC，此為盤管壁面的擾流強度增加，造成壁面的熱傳導也會更好。

b.當二氧化鈦濃度固定為2vol%，粒子聚集度2.584a及雷諾數61500，當改變不同銀粒子徑0nm至5nm時，會造成第二層填充材到冷卻壁熱面溫度下降了4oC，此為二氧化鈦上的銀奈米粒子層增加固態奈米粒子的熱傳導係數所致。

The technology of the furnace cooling is very important for the metallurgical industry, because it can　substantially increase throughtput and operation life of furnaces. In order to improve the heat transfer properties of blast furnace cooling system, nanofluid is used to solve the cooling problem, because of its good physical and thermal properties. Recently, it has been found that the composite nanoparticles have higher heat transfer properties than pure nanoparticles, and their composite methods are mixed with nanoparticles and formed a layer of coating silver on the nanoparticles respectively. Both methods can increase the nanoparticles heat transfer properties. In this dissertation, we use computational fluid dynamic (CFD) to study two cooling stave systems of composite nanofluids: one is the forced convective heat transfer in cooling stave,which only have stave layer, and other is the force convection heat thansfer in multi-layers stave, include furnace shell, filling material-1, stave, filling material-2, refractory lining, slag skull. The titanium dioxide nanoparticle are composed from silver nanolayer and base fluid use water in turbulent flow. In single layer cooling stave, we consider the aggregation of composite nanoparticles, mass flow rate of the fluid, and the silver particle diameter on titanium dioxide. Another one multi-layers cooling stave case, we consider mass flow rate of the fluid, and the silver particle diameter on titanium dioxide. We use the computational fluid dynamic for numerical analysis. The composite nanoparticles are different from the general nanoparticles, so the thickness of the nanolayer of silver is also considered. Therefore, Maxwell’s correction of nanoparticle layer is used to calculate the thermal conductivity of composite nanoparticles. The fluid is single-phase flow at steady state, which use Pak formula of nanofluid to calculate the density and specific heat capacity and Haisheng formula to calculate thermal conductivity coefficient with the degree of particle aggregation. After obtaining the required physical conditions, the second-order upwind method of the finite volume method is used to discrete the conservation equations. Then, the discreted algebraic equations are iterated by the semi-implicit method for pressure linked equations consistent (SIMPLEC) method. The velocity field, the temperature field and the pressure field are obtained, and the thermal convection cofficient and the friction factor are calculated. After anaylizing the result, the following important results are obtained:
(1)Single layer cooling stave
a.As composite nanofluid contained 6.43vol% of silver / titanium dioxide composite nanoparticles and flow rate was changed from 1kg/s to 4 kg/s, the ratio of convection coefficient to friction factor (η) was increased from 0.97 to 2.15 because that the forced convection was enhanced to improve the process economically.

b.The conditions which were fixed at 2.584a for the degree of aggregations and the Reynolds number was fixed by 75700 for the mass flow rate varying from 2.3 kg/s to 5.1 kg/s, inducing by different diameter of silver on titanium dioxide nanoparticles from 0nm to 5nm, compared with the TiO2 nanofluid, the heat convection coefficients and Nusselt number of as-studied composite nanofluid were increased 99% and 14.8% respectively, because that titanium dioxide coated with a layer of silver can effectivity enchance the thermal conductivity of nanoparticles.

(2)Multiple layer cooling stave
a.The cooling pipe of the multiple layer cooling stave contains composite nanofluid with a concentration of 3.28vol% (titanium dioxide concentration 1vol%; silver particle diameter 5nm; 2.584 of aggregation). When the mass flow rate change from 1.77kg/s to 2.35kg/s, it shown that the temperature of hotface of stave to furnace shell was dropped by 10oC, because the turbulence intesnsity of pipe wall will increase, which will improve heat convection coefficient.

b.The conditions which were fixed at 2.584a for the degree of aggregations, the Reynolds number was fixed by 61500 and the concentration of titanium dioxide was fixed at 2vol%, inducing by different diameter of silver on titanium dioxide nanoparticles from 0nm to 5nm, compared with the TiO2 nanofluid, the temperature as-studied composite nanofluid were decreased 4oC from filling material-2 to hotface of stave, because that titanium dioxide coated with a layer of silver can effectivity enchance the thermal conductivity of nanoparticles.

摘要 i
ABSTRACT iii
目錄 vi
圖目錄 viii
表目錄 xiii
符號說明 xv
第一章 緒論 1
1-1 前言 1
1-2 研究目的 3
1-3 研究方法 4
1-4 本文架構 5
第二章 基礎理論及文獻回顧: 6
2-1 流體動力學 6
2-1-1 流體連續介質模型 6
2-1-2 流體密度 6
2-1-3 流體壓縮性 7
2-1-4 流體膨脹性 7
2-1-5 流體黏性 8
2-1-6 流體層流與紊流 9
2-1-7 流體動力學控制方程 9
2-2 熱傳學 12
2-2-1 流體導熱性 12
2-2-2 能量守恆方程式 13
2-3 紊流模型 13
2-4 離散化概論 14
2-4-1 離散化 15
2-4-2 離散網格 15
2-4-3 有限體積法 16
2-4-4 有限體積法使用的網格 16
2-4-5 離散格式種類 17
2-4-6 二階迎風格式 18
2-5 壓力修正法 21
2-6 奈米流體介紹及相關文獻回顧 23
2-7 高爐冷卻壁介紹及相關文獻回顧 26
第三章 研究方法 40
3-1 物理模型 40
3-2 數學模式 43
3-2-1 基本假設 43
3-2-2 複合奈米顆粒參數計算 43
3-2-3 守恆方程式 45
3-2-4 奈米流體性質 48
3-2-5 冷卻壁材料性質 50
3-2-6 單層冷卻壁邊界條件 51
3-2-7 多層冷卻壁邊界條件 52
3-2-8 數值方法 52
3-2-9 變因組合 57
第四章 結果與討論 61
4-1 單層高爐冷卻壁 61
4-1-1 單層高爐冷卻壁網格敏感度測試 61
4-1-2 單層高爐冷卻壁變因討論 62
4-2 多層高爐冷卻壁 96
4-2-1 多層冷卻壁網格敏感度測試 96
4-2-2 多層冷卻壁文獻驗證 100
4-2-3 多層高爐冷卻壁變因討論 101
第五章 結論與未來方向 111
5-1 結論 111
5-2 未來方向 114
參考文獻 115

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