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研究生:黃仁傑
研究生(外文):Jen-Chieh Huang
論文名稱:空氣和水於小管徑連續U型波浪彎管內兩相流之摩擦壓降分析
論文名稱(外文):Air-Water Two-Phase Flow Friction Pressure Drop of Small Diameter U-Type Wavy Pipes
指導教授:陳英洋
學位類別:碩士
校院名稱:國立雲林科技大學
系所名稱:機械工程系碩士班
學門:工程學門
學類:機械工程學類
論文種類:學術論文
論文出版年:2003
畢業學年度:91
語文別:中文
論文頁數:160
中文關鍵詞:兩相流彎管U型波浪彎管壓降摩擦因子
外文關鍵詞:Two phase flow、Return Bend、U-Type Wavy tube、P
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在工程的應用上,例如蒸發動力系統、石化管路、冷凝及空調系統,可以發現許多流經彎曲通道的地方。但是流經過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。雖然在以往的兩相流研究報告中,對於直管部分有很詳盡的報告,但是在小管徑彎管的研究報告卻相當少見。
本文主要是量測與探討在五個彎頭之U型連續波浪彎管中,水之單相流與空氣-水之兩相流摩擦壓降分析。在本研究實驗中,測試管之內徑(D)範圍為4.95 ~ 6.55mm,而曲徑比(2R/D)範圍為4.04 ~ 7.63。單相水之實驗中,雷諾數(Re)操作範圍約為500 < Re < 15000。兩相流實驗中,水與空氣之表面速度範圍分別為UL,S = 0.02 ~ 0.7 m/s以及UG,S = 0.2 ~ 60 m/s。在U型波浪彎管所量測到的壓降損失裡,包含了在彎管下游之直管部中,因為U型彎管所引起的擾流所造成之壓降損失。如此我們可以藉此定義彎管部的摩擦因子fB以及U型彎管中兩相流之壓力梯度。
在水的單相流方面,藉由實驗數據整理出一個包含了曲徑比(2R/D)、間隔長度比(L/D)、雷諾數(Re)以及新狄恩數(Dn)等參數之彎管摩擦壓降預測公式,並得到平均誤差為12.4%的好結果。其中彎管部之摩擦係數fB在層流與紊流的轉換處並沒有發現明顯的變化,這是因為彎管造成的二次流(secondary flow)影響遠大於在直管時之流型轉換。而彎管與直管之摩擦係數比值fB/fS會隨著曲徑比(2R/D)與間隔長度比(L/D)的減小而增加。
在兩相流方面,我們可以找到兩相流之摩擦因子與總質通率(G)、曲徑比(2R/D)以及Martinelli參數(X)的相互關係。然而在總質通率G > 400 kg/m2�泅且Martinelli參數X < 0.3時,其作用影響會降低。另外可以發現當流型從間歇流(intermittent flow)轉型至波浪環狀流(wavy annular flow)時,彎管與直管的壓降斜率比值呈現不穩定的狀態,若我們能夠預料在U型波浪管之流型型態,則有助於兩相流之壓降預測。
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 hairpin is very common. As expected, the hairpin that contains many 180°return bends (U bend) 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 180°return bends.
Measured frictional pressure drops for single-phase water and two-phase air-water mixture flowing in five small diameter U-type wavy tubes were presented. The inner diameters of the wavy tubes are 4.95 – 6.55 mm, whereas the curvature ratios span from 4.04~7.63. Test range of the Reynolds number for the single-phase water tests is about 200 < Re < 18000. The two-phase superficial velocities for air and water are in the range of UL,S = 0.02 – 0.7 m/s and UG,S = 0.2 – 60 m/s. The measured pressure loss in U-type wavy tube included the loss in U bends and the loss caused by the distorted flow in the downstream straight tube. This leads to the definition of the equivalent friction factor, fB and the two-phase pressure gradient in the U-bend. An empirical friction factor equation as a function of curvature ratio and spacer length, new Dean number and Re has been correlated from the present data with a bean deviation of 5.6%. The frictional characteristics of two-phase flows in U-type wavy pipes are also found related to the Lockhart-Martinelli relationship, the total mass flux and the curvature ratio (2R/D). However, the effect of the mass flux diminishes as the mass flux increases, G > 400 kg/m2�泅 and Martinelli parameter X < 0.3.
中文摘要 i
英文摘要 ii
誌謝 iii
目錄 iv
表目錄 vi
圖目錄 vii
符號說明 x
第一章 緒論 1
1.1 研究動機與背景 1
1.2 研究目的 3
第二章 文獻回顧 4
2.1 直管部之摩擦壓降 5
2.1.1 基礎理論模式 5
2.1.2 經驗式 7
2.2 彎管部之摩擦壓降 9
2.3 流譜 14
2.3.1 流譜型態種類 14
2.3.2 彎管部分之流譜圖 16
2.3.3 流譜預測方法 17
第三章 實驗系統與分析方法 19
3.1 簡介 19
3.2 實驗系統 19
3.2.1 測試段 19
3.2.2 空氣循環系統 20
3.2.3 水循環系統 21
3.2.4 液氣混合區 21
3.3 實驗儀器設備 22
3.3.1 資料擷取系統(紀錄器) 22
3.3.2 溫度量測 22
3.3.3 壓力量測 23
3.3.4 壓力差量測 24
3.3.5 水流量量測 24
3.3.6 空氣流量量測 25
3.4 工作流體的熱力物理性質 26
3.5 實驗過程 28
3.5.1 系統測漏 28
3.5.2 實驗操作步驟 28
第四章 結果與討論 30
4.1 數據歸納 30
4.2 單相流分析結果 30
4.3 兩相流分析結果 37
第五章 結論 42
參考文獻 43
附錄一 空氣流量計校正報告 94
附錄二 不準度之計算 104
自傳 105
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【29】Dr. Ing Young Chen and Dr. Chi-Chung Wang “Air-Water Two-Phase Pressure Drop in Small Diameter U-Type Wavy Tube”, 2002
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