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系統識別號 U0026-0107202011043000
論文名稱(中文) 濕空氣經鰭片熱交換器凝濕冷卻之計算流體力學分析
論文名稱(英文) Computational Fluid Dynamics Analysis of Moist Air Flowing Through the Finned-Tube Heat Exchanger with Condensation
校院名稱 成功大學
系所名稱(中) 機械工程學系
系所名稱(英) Department of Mechanical Engineering
學年度 108
學期 2
出版年 109
研究生(中文) 鄧宇喆
研究生(英文) Yu-Che Teng
學號 N16074051
學位類別 碩士
語文別 中文
論文頁數 94頁
口試委員 指導教授-張錦裕
口試委員-呂金生
口試委員-林建南
中文關鍵字 熱交換器  冷凝  鰭片效率  數值模擬 
英文關鍵字 Heat Exchanger  Condensation  Fin Efficiency  Numerical Simulation 
學科別分類
中文摘要 濕空氣流經熱交換器表面時,倘若其表面溫度低於濕空氣露點,濕空氣內的水蒸氣將冷凝成水滴,附著於鰭片上形成水膜。此時熱交換器同時具有溫差造成的顯熱熱傳及濃度差產生的潛熱熱傳。
本文主要目的即是分別以理論分析與數值模擬討論熱交換器於除濕過程中熱、質傳效益。數值模擬方面則是使用商業套裝軟體ANSYS CFX搭配Wall Condensation Model進行計算,分別對矩形管、矩形鰭片與板鰭管式熱交換器三種模型進行三維數值模擬,再將模擬結果與理論得出之一維近似解進行比對。
從矩形管模擬結果可以發現,當加快進口流速時,熱、質傳係數及總熱傳係數皆有顯著提升。將模擬結果與一維近似解進行比對後,發現近似解會以0.6 ~ 16.2(%)之誤差稍微高估顯熱熱傳係數,並以2.1~ 18.1(%)之誤差低估質傳係數,且質傳係數之誤差會隨進口流速增加而增加,最終近似解會以7.2 ~ 19.1(%)之誤差低估總熱傳係數。
從矩形鰭片模擬結果可以發現,鰭片狀況可以依濕空氣凝結水產生多寡分為全乾、半乾濕及全濕狀態。當鰭片處於全乾或全濕狀態時,增加空氣相對濕度僅令鰭片效率略微下降,但於半乾濕狀態時則隨空氣相對濕度增加迅速下降,而全乾狀態之鰭片效率均較全濕狀態高出15 ~ 20(%)左右。比較一維近似解與模擬結果,發現進口流速越高,近似解會越低估鰭片效率。而乾、濕鰭片效率最大誤差皆出現在進口流速5 (m/s)之情況,誤差分別為14.56(%) 與38.45(%)。
從板鰭管熱交換器模擬結果可發現,濕空氣自進口流入熱交換器後,受到管群干擾導致其背風側出現渦流,而管群亦會阻礙空氣通行,使流道縮減區的流速加快,進而提升該處顯熱熱傳係數與質傳係數。鰭片效率表現則與矩形鰭片模擬結果趨勢相同。比較一維近似解與模擬結果,熱交換器處於乾盤管狀態時,近似解會稍微高估顯熱熱傳係數及低估鰭片效率,兩者平均誤差皆在10(%)左右;而熱交換器若處於濕盤管狀態,近似解則會大幅高估顯熱熱傳係數與質傳係數,並大幅低估鰭片效率。
英文摘要 The purpose of the study was to investigate the heat and mass transfer performance of the fin-tube heat exchanger by using theoretical and CFD analysis. The study used Threlkeld method to calculate 1-D approximate solution for wet coil heat exchanger. In order to verify the accuracy of the approximate solution, the study also used ANSYS CFX with Wall Condensation Model to compute the 3-D flow fluid analysis with rectangular tube, rectangular fin, plate fin-tube heat exchanger models and to calculate their heat, mass transfer coefficient and overall heat transfer coefficient. Finally, compare the results of numerical simulation with those of 1-D approximate solution.
According to the results of the rectangular tube model, it can be found that the heat, mass transfer coefficient and overall heat transfer coefficient were significantly improved when increasing the inlet flow rate. After comparing the simulation results with the 1-D approximate solution, approximate solution overestimated heat transfer coefficient with the errors of 0.6~16.2% and underestimated mass transfer coefficient with the errors of 2.1~18.1%. Finally, approximate solution overestimated overall heat transfer coefficient with the errors of 7.2~19.1% .
Based on the results of the rectangular fin model, it can be found that fin efficiency will change along with inlet relative humidity. The situation of the fin was divided into three parts: dry-coil, half-dry-half-wet, wet-coil. Dry fin efficiency was 15~20% higher than wet fin efficiency. After comparing the simulation results with the 1-D approximate solution, the errors of the fin efficiency were increased when increasing the inlet flow rate. The max errors of dry and wet fin efficiency were 14.56% and 38.45% respectively.
At last, according to the results of the plate fin-tube heat exchanger model, when moist air went through the heat exchanger, the vortex appeared on the leeward side because of disturbance from the tube bank. Simultaneously, obstruction from the tube bank also led to enhancement of air flow rate. Therefore, its heat and mass transfer coefficient were improved. Furthermore, Fin efficiency performance was the same as the trend of rectangular fin model results. After comparing the simulation results with the 1-D approximate solution, approximate solution overestimated heat transfer coefficient and underestimated fin efficiency at dry coil condition, both errors were around 10%. In contrast, approximate solution overestimated heat, mass transfer coefficient and underestimated fin efficiency at wet coil condition substantially.
論文目次 摘要 I
Abstract III
誌謝 IV
目錄 V
表目錄 VII
圖目錄 VIII
符號說明 XII
一、 緒論 1
1-1 前言 1
1-2 文獻回顧 2
1-3 研究動機與目的 6
二、濕盤管熱質傳一維之近似解理論 7
2-1 濕空氣熱質傳推導 7
2-2 鰭片效率近似解推導 11
2-3 熱傳量、總熱傳係數與出口參數計算 16
2-4 顯熱熱傳係數之近似關係式 23
2-4.1 矩形管模型 23
2-4.2 板鰭管熱交換器模型 25
三、濕盤管之三維計算流體力學分析 28
3-1 物理模型 28
3-2 統御方程式推導 32
3-2.1 基本假設 32
3-2.2 流體區統御方程式 32
3-2.3 擴散統御方程式 34
3-2.4 紊流模型 35
3-3 邊界條件及結果參數計算 39
3-3.1 邊界條件 39
3-3.2 壁面冷凝模型 (Wall Condensation Model) 45
3-3.3 結果參數計算 47
3-4 數值方法 48
3-5 解題流程 48
3-6 格點測試 49
四、結果與討論 54
4-1 矩形管模擬 54
4-2 矩形鰭片模擬 71
4-3 板鰭管熱交換器模擬 78
五、結論 89
參考文獻 91

表目錄
表4- 1、 下不同速度之熱、質傳係數表 57
表4- 2、不同進口流速下碳鋼鰭片之鰭片效率與近似解比較表 73
表4- 3、不同進口流速下不銹鋼鰭片之鰭片效率與近似解比較表 73
表4- 4、 ,乾、濕鰭片效率與近似解之誤差(以碳鋼為例) 74
表4- 5、 、 下乾、濕鰭片效率與近似解比對表 80


圖目錄
圖2- 1、濕盤管熱交換示意圖 10
圖2- 2、圓鰭管之鰭片熱傳示意圖 14
圖2- 3、不同尺寸下圓鰭管鰭片效率分佈圖 15
圖2- 4、板鰭管熱交換器之 、 尺寸示意圖 15
圖2- 5、無鰭片之近壁面熱傳途徑示意圖 20
圖2- 6、有鰭片之近壁面熱傳途徑示意圖 20
圖2- 7、濕盤管焓值變化示意圖 21
圖2- 8、不同溫度下飽和焓值對照圖 22
圖2- 9、不同溫度下b值對照圖 22
圖2- 10、矩形管模型示意圖 24
圖2- 11、板鰭管式熱交換器模型示意圖(交錯式排列) 27
圖3- 1、矩形管模型示意圖 29
圖3- 2、矩形鰭片模擬之模型示意圖 30
圖3- 3、板鰭管熱交換器模型示意圖 31
圖3- 4、矩形管邊界條件示意圖 42
圖3- 5、矩形鰭片之邊界條件示意圖 43
圖3- 6、板鰭管式熱交換器邊界條件示意圖 44
圖3- 7、壁面冷凝模型水膜簡化示意圖 46
圖3- 8、數值模擬流程圖 51
圖3- 9、矩形管局部網格示意圖 52
圖3- 10、矩形鰭片局部網格示意圖 52
圖3- 11、板鰭管熱交換器網格示意圖 53
圖4- 1、 下 分佈 58
圖4- 2、 下熱傳率比較圖 59
圖4- 3、 下 分佈 60
圖4- 4、 下熱傳率比較圖 61
圖4- 5、 下 分佈 62
圖4- 6、 下熱傳率比較圖 63
圖4- 7、 下不同速度之平均溫度比較圖 64
圖4- 8、 下不同速度之平均壁溫比較圖 64
圖4- 9、 下不同速度之平均比濕比較圖 65
圖4- 10、 下不同速度之平均相對濕度比較圖 65
圖4- 11、 下不同速度之總熱傳率比較圖 66
圖4- 12、 下不同速度之顯熱熱傳係數 比較圖 67
圖4- 13、 下不同速度之質傳係數 比較圖 67
圖4- 14、 下不同速度之顯熱熱傳係數 比較圖 68
圖4- 15、 下不同速度之質傳係數 比較圖 68
圖4- 16、 下不同速度之總熱傳係數 比較圖 69
圖4- 17、 下不同速度之熱、質傳係數比對圖 69
圖4- 18、 空氣濕度線與近似解比較圖 70
圖4- 19、 空氣濕度線與近似解比較圖 70
圖4- 20、 、碳鋼鰭片於不同進口相對濕度下鰭片溫度分佈 75
圖4- 21、 、不銹鋼鰭片於不同進口相對濕度下鰭片溫度分佈 76
圖4- 22、 、碳鋼鰭片於不同進口流速下鰭片效率分佈 77
圖4- 23、 、不銹鋼鰭片於不同進口流速下鰭片效率分佈 77
圖4- 24、 下板鰭管式熱交換器 分佈 81
圖4- 25、 下板鰭管式熱交換器 分佈 82
圖4- 26、 下板鰭管式熱交換器 分佈 83
圖4- 27、 ,不同進口流速下板鰭管式交換器鰭片溫度分佈 84
圖4- 28、 下熱傳、質傳係數分佈圖 85
圖4- 29、 不同進口相對濕度下鰭片效率變化圖 85
圖4- 30、 、不同速度下乾盤管顯熱熱傳係數比較圖 86
圖4- 31、 、不同速度下乾盤管鰭片效率比較圖 86
圖4- 32、 、不同速度下濕盤管顯熱熱傳係數比較圖 87
圖4- 33、 、不同速度下濕盤管質傳係數比較圖 87
圖4- 34、 、不同速度下濕盤管鰭片效率比較圖 88
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