臺灣博碩士論文加值系統

近年來高功率電子設備需要發展有效的排熱技術，此技術使用有相變或無相變的流體流過具有細長的長方形流道密集熱交換器以將廢熱移除，在密集熱交換器有限的空間內前後對應的流道通常用突擴和突縮段來連接，流體流過此接頭在它對應的上下游會產生分離流和渦旋流，如此壓力能量會減少而產生額外的摩擦壓降。在此突擴和突縮段的兩相流摩擦壓降和流動特性的知識是非常需要的，然而目前有關小長方形流道突擴段壓降的資料卻是有限，因此本研究的目的就是要探討在此小長方形流道兩相流的突擴段摩擦壓降和流型的變化，此長方形測試流道的乾度、流量、長寬比對壓降和流型的影響在此研究將會列入考量。此實驗將用透明的壓克力板做成7支有突擴段的長方形流道以方便觀察兩相流型的變化，這些測試段將具有類似的幾何形狀和結構，其流道的窄度(mm)和寬度(mm)是6x2、6x4、4x2、4x4，這4個長方形測試段都直接連接在一支2 mm的小圓管，寬度(mm)是9x3、6x3，這2個長方形測試段都直接連接在一支3 mm的小圓管，由於小圓管的截面積都小於這7支長方形管的截面積，所以從圓管流入長方形管的接合處就有突擴的面積。測試的空氣和水之質通率從500到2000 kg/m2.s和乾度則從0.01到0.7，所獲得的空泡比、流型和摩擦壓降的數據將用來比對現有模式預測的正確度，另外在突擴段所量得的兩相流摩擦壓降數據將用來整理成實用的數學經驗式用來預測小長方形流道突擴段的兩相流壓降，並且將會細加檢視流過這突擴段的兩相流流型和結構的變化用來解釋在這突擴段內壓力急遽的變化。

Recently, the advances of the high performance electronic devices have been resulted a great demand in developing efficient heat removal techniques for dissipating increasingly large heat flux from compact heat exchangers in small rectangular channels. In the limited space of compact heat exchangers, the adjacent channels can be connected by abrupt flow area changes. Due to the nature of the geometries involved, the flow would induce a region of flow separation and cause significant pressure loss at the abrupt flow area change. The knowledge of frictional pressure drop and flow characteristics at the abrupt flow area change is very needed for the design of such compact heat exchangers. However, very few data are available for the two-phase flow pressure drop at the sudden expansion and contraction in smaller rectangular channels. Therefore, this research is proposed to visualize the flow structure and measure the two-phase pressure drop at the sudden expansion in small rectangular channels. The effects of the aspect ratio of the rectangular test section, area ratio, flow rate and gas quality for flow across the abrupt flow area change will be considered in this study. The test sections will also be arranged in horizontal longitudinal and transverse orientations to see the influence of gravity force on the flow pattern and pressure drop. Seven test sections are made of transparent acrylic resin, so that the flow pattern and flow structure could be visualized. The test sections have the same overall structures with 6x2, 6x4, 4x2, 4x4. The four rectangular channels are connected with a 2 mm diameter tube, 9x3, 6x3, 3x6 are connected with a 3 mm diameter tube. The area of the tube is smaller than the area of the rectangular channels. As fluid flows into the tube and then enters the rectangular channel, it will observe a sudden expansion at the interconnection between the round tube and the rectangular channel. The total mass flux of the air-water mixture is ranged from 500 to 2000 kg/m2.s and quality is changed from 0.01 to 0.7. Based on the obtained data of void fraction, generated flow regime and frictional loss, the adequacy of the existing predictive methods will be examined and their differences will be discussed. In addition, the two-phase frictional pressure drop data at the sudden expansion will be correlated to propose correlations for the prediction of two-phase pressure drops at the sudden expansion. The flow separation and flow pattern change at the sudden expansion and contraction will be visualized for the interpretation of the large pressure change in the sudden expansion areas.

中文摘要
英文摘要
致謝
目錄
表目錄
圖目錄
符號說明
第一章 緒論
1.1 研究背景與動機
1.2 研究目的
第二章 文獻回顧
2.1 單相流壓降
2.1.1 單相流突擴壓降
2.2 兩相流壓降
2.2.1 基礎理論模式
2.2.2 經驗式
2.3 兩相流面積驟變壓降
2.3.1 兩相流突擴壓降
2.4 流型
2.4.1 流型型態種類
2.4.2 流譜預測方法
第三章 實驗系統與分析方法
3.1 簡介
3.2 實驗系統
3.2.1 空氣循環系統
3.2.2 水循環系統
3.2.3 液氣混合區
3.2.4 測試段
3.2.5 流出段
3.2.6 拍攝段
3.3 實驗儀器
3.3.1 資料擷取系統
3.3.2 空氣流量量測
3.3.3 水流量量測
3.3.4 溫度量測
3.3.5 壓力量測
3.3.6 壓力差量測
3.3.7 照明設備
3.4 工作流體的熱力物理性質
3.5 實驗過程
3.5.1 實驗操作步驟
3.6 實驗觀察
3.6.1 流型型態分析
3.6.2 兩相流實驗數據換算
3.7 輔助軟體
3.7.1 LabView
3.7.2 Visual Basic
第四章 結果與討論
4.1 兩相流突擴段壓降
第五章 結論
參考文獻

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