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研究生:黃志中
論文名稱:具多孔性隔板渠道之紊流熱傳與流場之數值研究
論文名稱(外文):Numerical Study of Turbulent Heat Transfer and Fluid Flow in a Porous-Baffled Channel
指導教授:楊玉姿楊玉姿引用關係
學位類別:碩士
校院名稱:國立成功大學
系所名稱:機械工程學系
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:1999
畢業學年度:87
語文別:中文
論文頁數:108
中文關鍵詞:多孔性隔板紊流熱傳有限差分法
外文關鍵詞:porous channelturbulent heat transferfinite-difference method
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本文主要針對流體流經矩形渠道中具有多孔性介質隔板並以週期性交錯安排的方式安置在渠道底部和頂部,其多孔性介質隔板對於紊流熱傳與流場的影響作數值預測,並與 J. J. Hwang (1997)之實驗值作比較。紊流統御方程式乃是以控制體積法(Control Volume Approach)為基礎,配合有限差分法(Finite Difference Method)及冪次法則(Power Law Scheme)來離散成差分方程式。對於紊流的行為與結構則是以 k -ε 紊流模式( k -εturbulence model)配合牆函數(Wall function)來描述。動量方程式的速度及壓力則以SIMPLE (Semi-Implicit Method for Pressure-Linked Equation )法來解出。至於格點設計方面,則採用不等間距交錯式格點系統。
本文研究的參數為入口雷諾數(Re = 1×104 ~ 5×104)、隔板之高度(h = 10、20、30 mm)及不同種類之隔板(固體與多孔性介質v0∞= 0.2、0.42、0.7),而隔板間距與渠道高度之比(S/H)固定為1.0,工作流體為空氣。流場數值計算的結果顯示固體隔板與多孔性介質隔板在隔板周圍具有不同的傳輸現象,其流場型態亦完全不同,同時也顯著地影響局部熱傳係數分佈,在相同的雷諾數及隔板高度下,多孔性介質隔板與隔板間幾乎沒有迴流,而傳統的固體隔板在隔板後都有迴流產生。相較於具有固體隔板的渠道,多孔性介質隔板之渠道由於渠道阻礙較小其摩擦損耗較低。
在熱傳效應方面相較於平滑渠道(smooth channel)不管是具有固體或多孔性介質隔板,均能增強熱傳效應,在較高的隔板高度時,多孔性介質隔板之熱傳機制層次幾乎相同,唯一不同的是受雷諾數影響,增加隔板高度,會加速流體流動其中心平均Nusselt number比值亦會增加。

This study presents the numerical calculation on turbulent heat transfer and fluid flow characteristics for rectangular channel with porous baffles which are arranged on the bottom and top channel walls in a periodically staggered way. The numerical predictions are compared with the experimental data of J. J. Hwang (1997). The turbulent governing equations are solved by a Control-Volume-based finite-difference method with power-law scheme and the well known k -εturbulence model and its associate wall function to describe the turbulent structure. The velocity and pressure terms of momentum equations are solved by SIMPLE (Semi-Implicit Method for Pressure-Linked Equation) method. In this grid design, non-uniform staggered grids are used.
The parameters studied include the entrance flow Reynolds number (Re = 1×104 ~ 5×104), the baffle height (h = 10、20、30 mm) and kind of baffles (solid and porous , v0∞= 0.2、0.42、0.7) ; whereas the baffle spacing S/H are fixed at 1.0 and the working medium is air. The flow field numerical calculations indicate that the flow patterns around the porous- and solid-type baffles are entirely different due to different transport phenomena and it significantly influences the local heat transfer coefficient distributions. The recirculation bubble that existed behind the solid-type baffle disappears in the corresponding region of the porous-type baffle. Relative to solid-type baffle channel, the porous-type baffle channel has a lower friction factor due to less channel blockage.
Concerning the heat transfer effect, both the solid-type and porous-type baffles walls enhanced the heat transfer relative to the smooth channel. It is further found that at the higher baffle height, the level of heat transfer augmentation is nearly the same for the porous-type baffle, the only difference being the Reynolds number dependence. As expected, the centerline-average Nusselt number ratio increases with increasing the baffle height because of the flow acceleration.

中文摘要………………………………………………………………Ⅰ
英文摘要………………………………………………………………Ⅱ
目錄……………………………………………………………………Ⅲ
表目錄…………………………………………………………………Ⅴ
圖目錄…………………………………………………………………Ⅵ
符號說明………………………………………………………………Ⅹ
第一章 序論……………………………………………………………1
1-1 研究動機及背景……………………………………………1
1-2 文獻回顧……………………………………………………2
1-3 本文探討之主題及方法……………………………………5
第二章 理論分析………………………………………………………7
2-1多孔性介質外流場之統御方程式…………………………7
2-1-1統御方程式……………………………………………7
2-1-2 k - 雙方程式模式及牆函數………………………10
2-2多孔性介質內流場之統御方程式………………………16
2-2-1達西定律………………………………………………16
2-2-2非達西效應……………………………………………17
2-2-3統御方程式……………………………………………22
2-3系統之統御方程式………………………………………24
2-4邊界條件與界面條件……………………………………27
2-5中線局部Nusselt number的計……………………………30
2-6摩擦係數的計算…………………………………………31
第三章 數值方法………………………………………………………33
3-1差分方程式之推導………………………………………33
3-1-1格點的配置……………………………………………33
3-1-2差分方程式……………………………………………34
3-1-3 U, V 動量方程式之差分方程式……………………41
3-1-4壓力修正方程式………………………………………42
3-1-5收斂條件………………………………………………45
3-2差分方程式的解法………………………………………46
3-2-1代數方程式之解法……………………………………47
3-2-2數值程序………………………………………………48
3-2-3電腦運算時間…………………………………………49
第四章 結果與討論……………………………………………………52
4-1 流場特性之分析…………………………………………53
4-1-1速度向量圖……………………………………………53
4-1-2雷諾數的效應…………………………………………54
4-1-3隔板高度的效應………………………………………55
4-1-4隔板種類的效應………………………………………55
4-2 熱傳特性之分析……………………………………………56
4-2-1雷諾數的效應…………………………………………57
4-2-2隔板高度的效應………………………………………57
4-2-3隔板種類的效應………………………………………57
4-3數值計算結果與實驗結果的誤差之探討…………………58
第五章 結論與建議…………………………………………………103
5-1 結論………………………………………………………103
5-2 未來研究方向之建議……………………………………104
參考文獻……………………………………108

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