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姓名 蔡祥霖(Shiang-Lin Tsai)  查詢紙本館藏   畢業系所 機械工程學系
論文名稱 輻射傳遞對磁流體自然對流影響之研究
(Effects of radiative transfer on hydromagnetic natural convection)
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摘要(中) 現有磁流體熱輻射的研究,多以平板邊界層為主,而矩形封閉體積的磁流體自然對流已有相當多的研究文獻,故本研究將針對磁流體在矩形封閉體積中受到一高溫壁面影響的自然對流,並分析熱輻射效應對流體速度及溫度分佈的影響。流場與溫度場的計算,採用SIMPLE演算法;另外,輻射熱通量則使用離散座標法求得。文中並分析磁場強度、浮力效應及長寬比對於磁流體自然對流的影響。
計算結果顯示磁場強度越強會抑制對流流動並降低熱通量;而熱輻射效應越強,則流體速度及熱通量越大,且流體的平均溫度越高;另外,當光學厚度越大時,則會因吸收效應而增加流體溫度,進而增加對流的效果;而散射比的結果顯示,散射對於熱通量較無影響,但散射比越大則會減少對流速度,這是由於吸收效應減少的結果。壁面放射率越大,很明顯的增加了熱輻射的傳遞,對於流體的速度及熱通量都有顯著的增加,但流體的平均溫度減少。在幾何外型上,較大的長寬比,其熱傳效果較差,但流體速度及平均溫度較高;而長寬比越小時,流體速度及熱通量增加,但流體的平均溫度減少。當浮力效應越大時,會造成流體對流速度、平均溫度及熱通量的增加。
摘要(英) Magnetohydrodynamics(MHD) has long been a subject of great importance. In some cases, radiative transfer may contribute to the flow and energy transfer. However, currently available literature on the boundary layer flows. The radiation effects on MHD in a rectangular enclosure have receive very few attention. This work investigates the radiative transfer effects on the natural convection of a magnetic fluid in a rectangular enclosure. The SIMPLE is used to solve the momentum and energy equations and the discrete ordinates method is employed to solve the radiative transfer equation.
The results show that both the fluid movement and the heat flux are reduced with the application of a magnetic field. On the other hand, the radiation effects enhance the convection and heat transfer. As the optical thickness increases, the fluid temperature increases because more energy is absorbed. As a result, convection is enhanced while the scattering albedo has little effect on the heat flux, it reduces the fluid movement greatly. The boundary emissivity also affects the heat and fluid flows. As the emissivity increases, the radiative transfer increases, and hence the fluid flow and heat transfer increases.
The aspect ration(height-to-width ratio) of the enclosing rectangle has effects on the energy and momentum transfer of the system. As the aspect ratio is increased, the heat flux on the high temperature surface decreases.
關鍵字(中) ★ 自然對流
★ 磁流體
★ 熱輻射
關鍵字(英) ★ natural convection
★ radiation
★ Magnetodrodynamics
論文目次 摘要 I
誌謝 III
目錄 IV
表目錄 VI
圖目錄 VII
符號表 X
第一章、 緒論 1
1-1. 磁流體力學(MHD) 1
1-2. 磁流體力學原理 2
1-3. 文獻回顧 4
1-4. 研究目的 7
第二章、 理論分析 8
2-1. 幾何模型 8
2-2. 統御方程式 9
2-3. 邊界條件及參數定義 11
第三章、 數值方法 14
3-1. 有限體積法 14
3-1-1. 質量、動量及能量方程式 14
3-1-2. 壓力修正方程式 17
3-1-3. SIMPLE 疊代程序 18
3-1-4. 程式驗證 19
3-2. 離散座標法(Discrete Ordinate Method,DOM) 25
3-2-1. 輻射熱傳方程式 25
3-2-2. 程式驗證 27
第四章、 結果與討論 31
4-1. 磁場對磁流體對流之影響 31
4-2. 輻射傳遞對磁流體對流的影響 33
4-3. 光學厚度及散射比的影響 35
4-4. 壁面放射率的影響 37
4-5. 長寬比的影響 37
第五章、 結論與建議 39
參考文獻 80
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18. Modest, M.F., Radiative heat transfer, McGraw-Hill, New York, 1993
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指導教授 曾重仁(Chung-Jen Tseng) 審核日期 2004-7-14
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