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研究生:葉長泰
論文名稱:矩形容器內冰熔解熱流現象影響之研究-高萊利數之結果
論文名稱(外文):A study on thermal-fluid phenomenon during melting of ice in a vertical rectangular enclosure:results of high rayleigh numbers
指導教授:何清政
學位類別:碩士
校院名稱:國立成功大學
系所名稱:機械工程學研究所
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:1997
畢業學年度:85
語文別:中文
論文頁數:128
中文關鍵詞:熔解熱流高萊利數
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本文分別以數值模擬方法與實驗方法探討──左、右壁分別為高、低溫,上、下壁為絕熱邊界,高寬比為2矩形容器內冰熔過程之熱流現象。數值模擬方面,針對Ste=0.101,Sc=0.1和0.5時不同萊利數(106×107, 6×107)對冰熔過程熱流現象之影響。實驗方面則針對Ra=6×107,Ste=0.101,Sc=0.1和0.5進行探討。數值結果顯示:萊利數愈高時,其熔解體積比例與平均熱傳量愈高,並有促使液態區對流更為不穩定之效應。在Sc=0.5,萊利數Ra≧4×106時,其熱壁平均熱傳量於冰熔解初期達到最小值,而後上升至一定值進而趨於穩態;而Sc=0.1時,當Ra≧5×106其熱壁平均熱傳量則在達最小值後上升至最大值,再略降至一定值後趨於穩態。當Ra=6×107時在液態區出現振盪自然對流之現象;Sc=0.1時,在Fo≧0.15,液態區流場左、右環流出現互相消長之不穩定現象。Sc=0.5時,在Fo=0.117∼0.158期間,液態區流場強度呈現高頻且大振幅不規則跳動的振盪自然對流現象。實驗方面,結果發現冰熔解開始一段時間後(Sc=0.1時,Fo=0.06875∼0.1125;Sc=0.5時,Fo=0.1125∼0.2),液態區水之最大密度線開始擺動並維持一段時間,此時流場呈現一左、右環流內含封閉小迴流存在於最大密度線之波峰/谷旁之多迴流結構。水最大密度線擺動時之行為如一上行之行進坡;當擺動停止後,其形狀呈一波浪狀。
The present study aims to investigate both numerically and experimentally thermalfluid phenomenon during melting of ice in a vertical rectangular enclosure of AR=2. Transient numerical simulations have been undertaken to understand the effect of Rayleigh numbers in the range of 106∼6×107 with Ste=0.101 and Sc=0.1, 0.5. Experimental visualization of temperature and velocity fields has been conducted for Ra=6×107, Ste=0.101, Sc=0.1 and 0.5. Numerical Results indicate that the increase of Rayleigh number enlarges the melting ratio and average heat flux of vertical wall and tends to make convective flow in liquid zone more unstable. In the case of Sc=0.5, the average heat flux of the hot wall reaches a minimum value first and then asymptotically approaches to steady state when Ra≧4×106. With Sc=0.1 and Ra≧5×106, the average heat flux of the hot wall features a local minimum and then maximum value before reaching a steady state. At Ra=6×107, an oscillatory natural convection was detected in liquid zone. For Sc=0.1, there exists the unsteadiness between the left and right re-circulating flows in the liquid zone after Fo≧0.15. During the time interval from Fo=0.117 to 0.158 under Sc=0.5, an oscillatory convective flows with a warily moving maximum density contour has been predicted. Similar as oscillatory convection but at higher frequency and larger amplitude was experimentally observed during early stage of the melting process for Sc=0.1 and 0.5.
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