(3.239.33.139) 您好!臺灣時間:2021/03/05 18:26
字體大小: 字級放大   字級縮小   預設字形  
回查詢結果

詳目顯示:::

我願授權國圖
: 
twitterline
研究生:曹心宇
研究生(外文):Hsin-Yu Tsao
論文名稱:外界風對空冷器之散熱效能的數值模擬分析
論文名稱(外文):Numerical Investigation of Crosswind Effect on the Performance of Air-Cooled Heat Exchangers
指導教授:林顯群林顯群引用關係
指導教授(外文):Sheam-Chyun Lin
口試委員:陳呈芳楊旭光周永泰
口試委員(外文):Cheng-Fang ChenShiuh-Kuang YangYung-Tai Chou
口試日期:2020-01-17
學位類別:碩士
校院名稱:國立臺灣科技大學
系所名稱:機械工程系
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:2020
畢業學年度:108
語文別:中文
論文頁數:160
中文關鍵詞:空冷器散熱性能側風效應流場可視化廢熱回吸
外文關鍵詞:Air-Cooled Heat ExchangerHeat-dissipating PerformanceCrosswind EffectFlow Field VisualizationThermal Recirculation
相關次數:
  • 被引用被引用:0
  • 點閱點閱:54
  • 評分評分:系統版面圖檔系統版面圖檔系統版面圖檔系統版面圖檔系統版面圖檔
  • 下載下載:0
  • 收藏至我的研究室書目清單書目收藏:0
現今製造業在產能極大化的目標下,促使機台、鍋爐等都朝此規劃,故導致能量密度日益擴大,同時製程中的廢熱也隨之增多,加上環境保育意識抬頭;而空冷器的排熱設計不僅效能高且具經濟性,所以在廠房頂端設置空冷器設備,以主動之氣體流動來協助廠房熱能排出是當今主要之散熱方案。不過在廠房啟用後,空冷器會在特定時刻或季節其運作散熱效能低於預期,尤其是季節風或海陸晝夜溫差形成對流旺盛時,而不穩定的廢熱排除效率是製程中重要的負面因素,有必要針對此物理現象做進一步了解;因此本研究針對空冷器在廠域受外界環境風向吹入下,進行流場、溫度與空冷器之散熱量做系統化之模擬分析。首先選定壹廠域規劃並參考風向玫瑰圖,設定合理的環境風速與風向進行流場分析,發現此廠域規劃之空冷器間存有熱回流現象;而熱回流是左右空冷器散熱效能最主要因素,為確保系統整體之散熱量在全年皆不致降低,在流場模擬中對外界環境風向與風速兩參數,深入探討二者相互影響程度並研擬有效改善方案。模擬結果顯示當外界北風吹入廠域時,其對迎風面第一組空冷器之出風造成壓力,出風因此倒灌並被南向空冷器再次吸入,此短循環現象使廢熱不斷向南累積,故是對於原始廠域規劃之空冷器效率最嚴苛的狀態,隨著外界北風速度的提升,空冷器彼此間流場相互影響的程度也加劇,進而降低散熱性能高達5.2%;然而此現象並非隨著風速增加而持續擴大,當超過7m/s北風後,對空冷器的出風流場之負面影響不增反降;若北風速達15m/s,其散熱性能約僅比無風降低3.16%;風速超過15m/s後散熱效能回升趨緩且逐漸穩定。為減緩7m/s北風下空冷器短循環之現象,改善對策透過建立不同擋風板後的新模型,以阻斷北風對空冷器熱回流之現象並以數值模擬判定不同上和下擋風板位置設置下之改善成效,在最佳改善方案中,在第三與第四組空冷器間設立下擋風板能使7m/s北風下之散熱性能比原始提升4.8%。另外,並進一步建立不同風向和風速與空冷器出風速對散熱能力變化的無因次分析,得知北風速與空冷器出風速在比值為1.6時為總散熱量最低之臨界點;而外界風與空冷器呈45 ͦ夾角時帶來最佳之總體散熱量。
Nowadays, the dissipation heat generated during the manufacture process increases rapidly and forms a critical task for constructing an industry factory. Without the environmental concerns induced by waste-water treatment in the traditional water-cooled system, the air-cooled heat exchanger has become the primary choice due to its high efficiency and low operation cost. However, it is reported that the downgrade on heat-dissipating ability of heat exchanger is observed under a crosswind at specific day or season. Clearly, the stability of waste-heat removal efficiency is a vital requirement in the manufacturing process; therefore, this research intends to analyze the flow field associated with the air-cooled heat exchanger under various environmental wind speeds and directions. At first, a comprehensive CFD simulation for the original plant setup with a roof-installed cooling system is executed to identify the adverse flow pattern for affecting the heat removal capability. In the succeeding flow visualization, the interaction among heat exchangers can be examined carefully under different ambient winds. As a result, under a crosswind parallel to the main building, the exhausted air from heat exchanger is partially inhaled back into a neighboring heat exchanger to form an undesirable thermal recirculation, which significantly influences the temperature distribution and degrades the overall cooling performance of heat exchanger system. In addition, this unfavorable effect on heat exchanger is accumulated along the wind path from upstream toward downstream locations. It is revealed that this performance decline continues up to the largest reduction -5.2% at 7m/s North wind. Beyond this wind velocity, a stable temperature distribution is developed to initiate a gradual recovery to approach the limiting 3.16% decrease on cooling capability at the 15m/s crosswind.
Thereafter, the installation of blocking plate is proposed to terminate the thermal-recirculation phenomenon happened between adjacent air-cooled heat exchangers. The upper and lower blocking plates are placed near the inlet and outlet of heat exchanger to prevent the inhaling of discharge air with dissipated heat. With the aids of numerical verification, it is illustrated that the lower blocking plate leads to a superior enhancement on cooling performance compared to that of the upper blocking plate. Also, under the severest condition of 7m/s North wind, the highest 4.8% improvement on heat-removing capacity is obtained with the implement of lower blocking plate located between the 3rd and the 4th heat exchangers. Moreover, based on CFD results, the change of cooling capacity for the air-cooled system can be expressed as function of wind direction and velocity ratio of the exhausting air speed to the crosswind speed. Additionally, the largest reduction on cooling performance occurs at 1.6 velocity ratio. Also, the maximum thermal-dissipation capability is obtained under a crosswind with a 45˚with respect to the arrangement of heat exchangers. In conclusions, this work establishes a reliable CFD analysis scheme to successfully demonstrate the influences on the cooling capability of air-cooled heat exchangers causing by the environmental wind speed and direction.
第一章 緒論
1.1前言
1.2文獻回顧
1.3研究動機與目的
1.4 研究方法與流程
第二章 空冷器系統介紹
2.1空冷器基本結構與工作原理
2.2空冷器分類
第三章 物理模型
3.1散熱廠房模型介紹
3.2空冷器性能與阻抗狀態定義
3.3 模型之網格建構
3.4邊界條件設定
第四章 數值方法
4.1統御方程式與紊流模型
4.1.1統御方程式
4.1.2紊流模式
4.2數值計算方法
4.2.1 數值求解流程
4.2.2 離散化方程式
4.2.3 上風差分法
4.2.4 速度與壓力耦合
第五章 原始廠域規劃之模擬分析
5.1環境條件設定與模擬定義
5.2北風0~20 m/s時之模擬分析
5.2.1空冷器之流場分析
5.2.2空冷器之散熱量分析
5.2.3空冷器之溫度場分析
5.3模擬廠域之最佳化
5.4外界0~7m/s於不同風向之模擬分析
5.4.1空冷器之流場分析
5.4.2空冷器之散熱量分析
5.4.3空冷器之溫度場分析
5.5不同外界風向和風速之無因次分析
第六章 改善方案之廠域模擬分析
6.1改善措施之方向探討
6.2建立上擋風板之數值分析
6.2.1散熱量分析
6.2.2流場分析
6.2.3溫度場分析
6.3建立下擋風板之狀態分析
6.3.1散熱量分析
6.3.2流場分析
6.3.3溫度場分析
第七章 結論與建議
7.1結論
7.1.1原始廠域規劃之分析結果
7.1.2改善方案廠域模型之分析結果
7.2建議
參考文獻
[1] 李紹騰,陳明源,陳若華,“工業廠房建築物自然通風手法之研究”,營建產業永續發展研討會,2011年。
[2] Jonas Allegrini, Viktor Dorera, and Jan Carmelieta, “Coupled CFD, radiation and building energy model for studying heat fluxes in an urban environment with generic building configurations,” Sustainable Cities and Society, Volume 19, pp. 385-394, 2015.
[3] 王順志,“廠房通風散熱問題訪查研究”,勞動部勞動及職業安全衛生研究所,2016年。
[4] A.F. Perez and D.G. Kroger, “The effect of the heat exchanger arrangement and wind-break wallson the performance of natural draft dry-cooling towers subjected to cross-winds, ” Journal of Wind Engineering and Industrial Aerodynamics, Volume 58, 293-303, 1995.
[5] A.F. du Preez and D.G. Kriiger, “Experimental investigation into the influence of cross-winds in the performance of dry-cooling towers,” N&O JOERNAAL, Volume 9, NR. 2, 1993.

[6] D.D. Derksen, T.J. Bender, and D.J. Bergstrom, “A study on the effects of wind on the air intake flow rate of a cooling tower: part 1. wind tunnel study,” Journal of Wind Engineering and Industrial Aerodynamics, Volume 64, No. 1, pp. 47-59, 1996.

[7] R. Al-Waked and M. Behnia, “The performance of natural draft dry cooling towers under crosswind: CFD study,” International Journal
of Energy Research, Volume 28, No. 2, pp. 147-161, 2004.
[8] J. Madad-Nia, H. Koosha and M. Mirzaei, “Effect of wind break walls on performance of a cooling tower model,” Mechanical & Aerospace Engineering, Volume 3, No. 4, pp. 61-67, 2008.
[9] M. Goodarzi and R. Keimanesh, “Heat rejection enhancement in natural draft cooling tower using radiator—type windbreakers,” Energy Conversion and Management, Volume 71, pp. 120-125, 2013.
[10] K. Duwenhage and D.G. Kroger, “The influence of wind on the performance of forced draught air-cooled heat exchangers,” Journal of Wind Engineering and Industrial Aerodynamics, Volume 62, No. 2-3, pp. 259-277, 1996.
[11] Gunnar Tamm and Yogesh Jaluria, “Flow of hot gases in vertical shafts with natural and forced ventilation,” International Journal of Heat and Mass Transfer, Volume 114, pp. 337-353, 2017.
[12] 趙之東,楊豐利,”直接空冷凝汽器的發展和現狀” ,北京科學出版社,1990年。
[13] 馬義偉,”空冷器設計與應用”,哈爾濱工業大學出版社,1998年。
[14] B. E. Launder and D. B. Spalding, “Lectures in mathematical models of turbulence,” Academic Press, London, England, 1972.
[15] S. V. Patankar and D. B. Spalding, “A calculation procedure for heat, mass and momentum transfer in three-dimensional parabolic flows,” International Journal of Heat Mass Transfer, Vol. 15, No. 10, pp. 1787-1806, 1972.
電子全文 電子全文(網際網路公開日期:20220226)
連結至畢業學校之論文網頁點我開啟連結
註: 此連結為研究生畢業學校所提供,不一定有電子全文可供下載,若連結有誤,請點選上方之〝勘誤回報〞功能,我們會盡快修正,謝謝!
QRCODE
 
 
 
 
 
                                                                                                                                                                                                                                                                                                                                                                                                               
第一頁 上一頁 下一頁 最後一頁 top
無相關論文
 
無相關期刊
 
無相關點閱論文
 
系統版面圖檔 系統版面圖檔