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研究生: 李國楨
Guo-jen Li
論文名稱: 板式熱交換器之熱流模擬與熵增分析
The numerical simulation of thermofluids and entropy generation in plate heat exchangers
指導教授: 吳俊諆
Jiunn-chi Wu
口試委員:
學位類別: 碩士
Master
系所名稱: 工學院 - 機械工程學系
Department of Mechanical Engineering
畢業學年度: 98
語文別: 中文
論文頁數: 94
中文關鍵詞: 數值模擬板式熱交換器山形紋板片壓降熱傳紊流熵增加
外文關鍵詞: Heat transfer, Pressure drop, Chevron plate, Plate heat exchangers, Numerical simulation, Turbulent flow, Entropy generation
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  • 本研究建立三維全尺寸的K070山型紋板式熱交換器模型,以數值模擬分析板式熱交換器的流場、壓降及熱傳特性,並以熱力學第二定律的熵增定理分析板式熱交換器的系統,找出最佳操作雷諾數。本研究的模型共有三個流道,工作流體為水,考慮的流道雷諾數介於300-12000之間,以ANSYS FLUENT套裝軟體進行層流和紊流分析,並與經驗關係式及解析解作驗證。
    本研究預測的摩擦因子與其他研究學者提出的關係式接近,紊流部份誤差小於5%,層流部份平均誤差約11%。熱傳方面,由模擬結果得到冷水側及熱水側的熱傳關係式,預測值落於其他研究提出的關係式範圍之內,最大誤差小於36%。熵增加的分析結果顯示,K070型板式熱交換器的流道雷諾數為3900時,總熵增加最低,系統效率可達到理論的最大值。
    本研究成功建立出多流道考慮共軛熱傳的板式熱交換器模型,且預測結果具有一定準確度,能在板式熱交換器的研發初期快速驗證設計理念,提供研究人員設計與改良的依據。


    In this study, a three dimensional calculation with real-size geometry of K070 chevron plate heat exchanger which consisted of thee flow channels have been conducted. The characteristics of flow, pressure drop and heat transfer in plate heat exchangers are investigated numerically. Also, the analyses of second law of thermodynamics (i.e. entropy generation) are presented. The numerical simulations are carried out using ANSYS FLUENT with water as working fluid in the Reynolds number (Re) range from 300-12000, which cover laminar and turbulent regime, and numerical results were validated with empirical and analytical correlations.
    The numerical friction factors are found in good agreement within 5% for turbulent flow and average error of 11% for laminar flow with empirical correlations. Nusselt number (Nu) correlations of cold and hot water side which obtained by numerical results have been proposed. Values of numerical Nu correlations agree within empirical and analytical correlations. Deviations of computed Nu with empirical and analytical correlations are up to 36%. The analyses of entropy generation indicate that the optimal Re of K070 plate heat exchangers is 3900.
    A model of three channels chevron plate heat exchanger considered conjugate heat transfer has been established. It can be useful to verify the design concepts in the early research and development.

    摘要......................................................i Abstract.................................................ii 致謝....................................................iii 目錄.....................................................iv 圖目錄..................................................vii 表目錄....................................................x 符號說明.................................................xi 第一章 緒論...............................................1 1.1 前言..................................................1 1.2 文獻回顧..............................................2 1.2.1 實驗研究............................................3 1.2.2 模擬研究............................................5 1.2.3 熵增加的研究........................................6 1.3 研究動機與目的........................................7 1.4 論文架構..............................................8 第二章 數值模擬計算方法..................................15 2.1 計算流體力學.........................................15 2.1.1 計算流體力學軟體簡介...............................16 2.2 幾何外型及基本假設...................................18 2.3 統御方程式...........................................19 2.4 紊流方法.............................................20 2.4.1 標準k-ε紊流模式....................................21 2.4.2 RNG k-ε紊流模式....................................22 2.4.3 Realizable k-ε紊流模式.............................23 2.5 壁面函數.............................................25 2.6 數值模擬.............................................26 2.6.1 網格生成...........................................26 2.6.2 邊界條件...........................................27 2.6.3 收斂標準...........................................27 2.7 物理量及熵增加之計算.................................28 2.7.1 壓降...............................................28 2.7.2 熱傳...............................................29 2.7.3 熵增加.............................................31 第三章 模擬驗證..........................................39 3.1 網格獨立性測試.......................................39 3.2 模擬驗證.............................................39 第四章 結果與討論........................................49 4.1 流場特性與壓降分析...................................49 4.2 熱傳性能分析.........................................51 4.3 熵增加分析...........................................53 第五章 結論..............................................71 5.1 結論.................................................71 5.2 未來改進方向.........................................72 參考文獻.................................................73 附錄A....................................................77

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