蒸發動力系統、石化管路、冷凝及空調系統等許多工程應用上，發現許多管路必須流經彎管的地方。但流經過90°彎頭或彎曲通道所產生的壓降損失，比僅流經直管通道之摩擦壓降要來的大。因此在設計熱交換器時，壓力損失的計算對壓縮機是否可以提供足夠的動力有很大的影響。雖然許多文獻之兩相流研究報告中，對於直管研究有很詳細的報告，但是在小管徑90°彎管的研究報告卻相當少見。
本研究是以實驗方式在室溫中以水的單相流及兩相流流過90°的彎管。本實驗共測試了2支90°玻璃彎管，內徑(D)為5.5和9.5 mm，曲徑比( 2R/D )為5.4、4.2, 其中R為彎管中心線之半徑，此實驗為不同的質通量和乾度下進行，且再分別量測對應的體積流率和壓降。水的單相測試之雷諾數的範圍約200< ReD <6000。兩相測試的混合質通量的範圍為50~500 kg/m2s。本實驗也以視覺觀察及高速相機擷取個個流動的條件的流譜圖並以D=5.5、6及9.85mm的數據分別組成三個流譜圖。
在90°水平彎管中，實驗量測之摩擦壓降會隨著質通量及蒸氣乾度的增加以及管徑的減少而增加。觀察到的流譜數據絕大部分與相同管徑的直管相似，並觀察到液體藉由離心力移至管壁外側，在外測液體隨即被移動至管壁側然後再轉回管壁內側，此現象可能是彎管的二次流所引起。然而此現象並未在較高的氣體乾度流時被發現此原因是氣相的慣性力克服二次流的旋轉力，所以在外側的液體未能被捲到管壁的外側。

All evaporator and condenser coils contain bends or other fittings to compact the heat exchanger size. The design of air-cooled heat exchangers requires the knowledge of heat transfer and frictional loss. For typical air-cooled coils, use of bend is very common. As expected, the elbows that contains many 90° bends will cause higher pressure drop than the corresponding straight tube. As a consequence, the single-phase and two-phase frictional performance of a return bend is very important for accurate estimation of the performance of an air-cooled heat exchanger. While there are a large number of investigations focusing on two-phase pressure drop in a straight tube. However, very limited data, models and correlations are currently available for two-phase flow in 90° bends.
The objective of this study is to conduct experimental investigations of two-phase flow air-water mixture and single-phase flows of water flowing in 90° horizontal bends at room temperature. A total of two 90°bends has been tested for the present study. The test tubes are made of glass tube having inner diameters (D) of 5.5 and 9.5 mm with dimensionless tube curvature ratio (2R/D) of 5.4and4.2, where R is the radius of centerline of bend. Test range of Reynolds numbers for water single-phase tests is about 200< ReD <6000. The range of mss flux for two-phase mixture is between 50 ~ 500 kg/m2s.
The resulted two-phase pressure drops were observed to algebraically increase with increasing total mass flux and vapor quality, and decreasing tube diameter. Two-phase flow patterns were taken by a combination of visual observations and high-speed camera photos to form the flow regime maps for each test tube. The data for the transition between flow patterns were recorded. Most of the observed flow pattern data in 90°bends are similar to that in straight tubes with the same tube diameter, The liquid was observed to switch to the outer tube wall by centrifugal force, the liquid at out wall was soon forced to move toward to the outside of tube wall and then switch back to the inside of the tube wall by secondary flow. However, this phenomenon is not observed at higher vapor quality due to the lack of liquid and increase of gas-phase inertia.

目錄
中文摘要..........................................i
ABSTRACT.......................................ii
誌謝...........................................iii
目錄............................................iv
表目錄.........................................vii
圖目錄..........................................xi
符號說明........................................xv
第一章 緒論....................................1
1.1 前言....................................1
1.2 研究動機與目的................................1
第二章 文獻回顧與理論分析.........................3
2.1 直管部之摩擦壓降...............................3
2.1.1 直管之基礎理論模式.......................3
2.1.2 經驗式（Empirical Correlations）........4
2.2 彎管部之摩擦壓降................................7
2.3 流譜 ........................................10
2.3.1 流譜型態種類...........................10
2.3.2 流譜預測方法...........................13
2.3.3 彎管部分之流譜圖........................15
第三章 實驗系統與方法分析..........................18
3.1 簡介 .........................................18
3.2 實驗系統.......................................18
3.2.1 空氣循環系統..................................20
3.2.2 水循環系統 ..................................22
3.2.3空氣-水流體液氣混合區 ..........................23
3.2.4 實驗測試段 ..................................24
3.2.5 拍攝段 ..................................24
3.3 實驗儀器 ..................................25
3.3.1 資料擷取系統 ..................................25
3.3.2 氣體體積流量計.................................25
3.3.3 電磁式體積流量計................................27
3.3.4 電阻式溫度檢測器................................28
3.3.5 壓力轉換器 ...................................29
3.3.6 差壓轉換器 ...................................30
3.3.7 照明設備 ...................................32
3.4 工作流體的熱力物理性質 ...........................32
3.5 實驗過程 ...................................33
3.5.1 實驗操作步驟 ...................................33
3.6 實驗觀察 ...................................34
3.6.1 流型型態分析 ...................................34
3.6.2 兩相流實驗數據換算 ...........................34
第四章 結果與討論 ...........................36
4.1單相流之直管與彎管之摩擦因子 ...................36
4.2兩相流之直管、彎管摩擦壓降分析 ...................40
4.3 兩相流譜型態特性 ...........................48
第五章 結論 ...................................93
參考文獻 ...........................................94

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