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研究生:白凱莉
研究生(外文):Kai-Li Pai
論文名稱:一個蛇行熱交換器之熱效率與第二定律效率之分析
論文名稱(外文):Effectiveness and Second-Law Efficiency of a Serpentine Heat Exchanger
指導教授:沈君洋
學位類別:碩士
校院名稱:國立中興大學
系所名稱:機械工程學系所
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:2008
畢業學年度:96
語文別:中文
論文頁數:44
中文關鍵詞:蛇行熱交換器熱效率第二定律效率
外文關鍵詞:serpentine heat exchangereffectivenesssecond-law efficiency
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本研究採用一維之熱傳模式對一種蛇行熱交換器進行模擬分析,於分析模式中,管道外側之流體考慮為不混合之狀態,而於兩個相鄰之平行管道間流動,管道內側之流體則考慮為混合之狀態,而於矩形管道內持續地由入口回繞至出口。此熱交換器之熱效率可表示為整體熱容率比值(Ct*)、整體熱傳單位數(Ntuo)與管排數之函數,針對熱效率進行分析時發現,對一個固定之Ct*值而言,熱交換器之熱效率會隨著Ntuo值之上升而呈現先上升後微降之狀態。本研究亦針對此熱交換器進行熱力學第二定律之分析,以尋求最佳之操作條件,研究之結果顯示,當管內流體流經熱交換器後之出口溫度愈高,且管外流體流出熱交換器後之出口溫度愈低,此時熱交換器之第二定律效率會較大,且在一個固定之Ntuo値下,最佳之Ct*值約位於1.0之處。研究中亦分析兩個熱交換器經逆向串聯成ㄧ個新的熱交換器組之性能,分析之結果並與單個交換器之性能比較,結果顯示,此熱交換器組之熱效率與第二定律效率兩者均會明顯地上升。
This work adopted a one-dimensional model to analyze the performance of a serpentine heat exchanger which is composed of rectangular tubes. The fluid outside the tube is considered to be unmixed and it flows between two neighboring parallel tubes. The fluid inside the tube is considered to be mixed and it flows in a serpentine manner from the inlet to the exit. The effectiveness of the heat exchanger (ε) is presented as a function of ratio of heat capacitance rates (Ct*), overall number of transfer units (Ntuo) and number of tubes. For a fixed Ct* value, the initially increases with the Ntuo value. As the Ntuo value is large, it would slightly decrease with an increase of the Ntuo value. The second-law efficiency was also evaluated to search for optimum operating conditions. As the exit temperature of the tube-side fluid is higher and the exit temperature of the shell-side fluid is lower, the heat exchanger has a higher second-law efficiency value. For a fixed Ntuo value, the optimum Ct* value was found to be around 1.0. This work also analyzed the overall performance of two serpentine heat exchangers connected in series and in counterflow arrangement. As compared with a single serpentine heat exchanger, both the ε and the second-law efficiency can be largely upgraded.
摘要 Ⅰ
ABSTRACT Ⅱ
誌謝 Ⅲ
目錄 Ⅳ
圖目錄 Ⅵ
符號說明 Ⅷ
第一章 緒論 1
1-1 前言 1
1-2 相關研究 3
1-3 研究目的 8
第二章 熱效率之理論分析模式 10
2-1 管道外側流體之能量平衡 10
2-2 管道外側流體於X方向之平均溫度 13
2-3 管道內側流體之能量平衡 14
2-4 無因次化之主宰方程式 (GOVERNING EQUATIONS) 17
2-5 熱效率 19
第三章 第二定律效率之理論分析模式 21
3-1 管道外側流體之壓降 21
3-2 管道外側流體之有效可逆功 ( EXERGY ) 21
3-3 管道內側流體之有效可逆功 ( EXERGY ) 23
3-4 無因次化 24
3-5 第二定律效率 ( SECOND-LAW EFFICIENCY ) 25
3-6 兩個相同之熱交換器逆向串聯後之第二定律效率 26
第四章 熱效率與第二定律效率分析之結果 31
4-1 熱效率分析之結果 31
4-2 第二定律效率分析之結果 35
4-3 兩個熱交換器逆向串聯後之第二定律效率分析之結果 37
第五章 結論 39
參考文獻 41
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