臺灣博碩士論文加值系統

隨著科技進步和工業現代化，對能源的需求越來越多，但也面臨能源短缺的問題，為節約能源，我國大力提倡節能減排，提高能源的利用率，而提高能源利用率的一個重要研究方向，即如何提高熱能動力裝置的效率。因對應的研究比較少，特別是當流體處於超臨界壓力條件下的流動與熱傳效能，更成為影響熱能動力裝置發展的瓶頸。由於業界對熱交換系統要求體積小、重量輕、熱交換效率高，因此為提供熱交換系統最佳化設計相應的理論依據，本論文以數值模擬方法探討超臨界CO2在傾斜管或螺旋管內的流動和熱傳特性，分析管內因熱物性變化造成熱浮力對熱流特性的影響，進而探究傾斜管和螺旋管內熱傳強化的方法。本研究在定壁溫(Constant Wall Temperature)和質量流率(Constant Mass Flow Rate)的條件下於傾斜管和螺旋管做數值模擬。模擬結果發現超臨界二氧化碳沿傾斜管流動方向加熱，流體因溫度差所產生劇烈的浮升力發生在：(1)靠近傾斜管入口處，(2)傾斜角度為正值，(3)入口壓力為8MPa，流體溫度接近308K；而流體熱交換最劇烈發生在：(1)浮升力強的位置，(2)二次流與主流夾角為90°時，(3)流體流速較慢時。超臨界二氧化碳在傾斜管只受到浮升力的影響，所以流體成左右對稱。而螺旋管受到浮升力和離心力的影響，流體分佈較混亂屬於非對稱流體，模擬結果發現超臨界二氧化碳於螺旋管內沿流動方向加熱，紊流強度隨著流體溫度和速度增加而增加，故改變入口雷諾數和壁面溫度時，紊流強度也會隨之改變，而改變入口雷諾數變化更顯著。

With the development of technology and the gradual modernization of the industry in Taiwan, more and more energy was demanded. But now we were confronted with the problem of energy shortage. To save energy and improve the utilization of energy, our country strongly advocated the energy conservation and emission reduction, and the most important research direction which was how to improve the efficiency of the device for thermal energy and power. Because of the corresponding research being less, especially the fluid flow and heat transfer for supercritical fluid under the conditions of the thermal power plant had become a bottleneck restricting. At present, people required their heat exchange equipment for small volume, light weight, and effective thermal efficiency. To provide the corresponding theoretical basis on optimization design of the heat exchange equipment, this thesis used numerical simulation method to mixed convection of supercritical carbon dioxide in inclined tubes and helical pipes. The effects of thermal buoyancy induced by physical property variations on the fluid flow and heat transfer were analyzed. Additionally, the heat transfer enhancement methods in inclined and helical tubes were then be explored and proposed. In the present thesis, the conditions of constant wall temperature and mass flow rate in inclined tubes and helical tubes were adopted. The predicted results show when the supercritical carbon dioxide is heated along the flow direction of the inclined tube, the strong buoyancy force generated by the temperature difference between the fluid and the fluid would occur (1) near the entrance of the inclined tube, (2) for positive inclined angle, and (3) for inlet fluid temperature close to 308K at 8 MPa. Besides, the most severe heat exchange occurred at (1) the position of strong buoyancy, (2) secondary flow and the main flow being 90 degree angle, and (3) the fluid flow rate being slow. For mixed convection inclined tubes, the supercritical carbon dioxide is influenced by the thermal buoyancy and the flow is symmetric. While for mixed convection in helical pipes, the fluid flow was affected by the floating lift and centrifugal force. Therefore, the flow distribution is more chaotic than that of the asymmetric fluid. Simulation results disclose that the supercritical carbon dioxide in the helical tube heated along the direction of flow, turbulence intensity increases with increasing temperature and velocity. So, the inlet Reynolds number and wall temperature would influence the turbulence intensity and the effects of inlet Reynolds number are relative important.

目錄

摘　要 i
ABSTRACT iii
致謝 v
目錄 vi
表目錄 viii
圖目錄 ix
第一章 緒論 1
1.1前言 1
1.2文獻回顧 2
1.2.1跨臨界流體於傾斜管內對流熱傳分析 2
1.2.2跨臨界流體於螺旋管內對流熱傳分析 6
1.3研究動機與目的 8
第二章 超臨界流體 10
2.1 CFD理論基礎 10
2.1.1 CFD軟體概述及其特點 10
2.1.2 CFD軟體應用領域 11
2.1.3 FLUENT軟體基礎知識 12
2.2超臨界流體的概念 13
2.3超臨界二氧化碳的熱物性質 15
2.4超臨界流體的熱傳性質 17
第三章 跨臨界二氧化碳於傾斜管內混合對流熱傳分析 19
3.1物理模型 19
3.2統御方程式 20
3.3網格生成及邊界條件 21
3.4計算方法及收斂條件 22
3.5計算結果分析 23
3.5.1計算模型驗證 23
3.5.2傾斜管內混合對流熱傳分析 25
第四章 跨臨界二氧化碳於螺旋管內混合對流熱傳分析 42
4.1物理模型和數學模型 42
4.2網格生成及邊界條件 45
4.3計算方法與收斂準則 46
4.4計算結果分析 47
4.4.1計算模型驗證 47
4.4.2螺旋管內流動規律分析 48
第五章 結論與建議 58
5.1結論 58
5.2建議 59
參考文獻 61
符號彙編 65、表目錄

表3.1 三種網格在不同位置X的Nuw比較 ................................................24
表3.2 三種網格在不同位置X的CfRe0比較 .......…......................................24
表3.3 傾斜管之模擬分析的參數條件 ..............…............................…........25
表4.1 不同網格系統對局部Nuw的影響...…....................................…..48
 、圖目錄

圖2.1 三種網格在不同位置X的Nuw比 ..............…...............................14
圖2.2 8MPa時二氧化碳之熱物性質 ...........…..........................................17
圖3.1 物理模型及座標系統 .......................................................................19
圖3.2 直管網格劃分 ..................................................................................22
圖3.3 不同網格系統對局部Nuw的影響 ..................................................24
圖3.4 不同網格系統對局部CfRe0的影響 ...............................................25
圖3.5 不同軸向位置之剖面溫度分佈圖(CaseⅠ, δ=30°)。(a)X = 10;(b)X =
20; (c)X = 50; (d)X = 100; (e)X = 200; (f)X = 400 ............................27
圖3.6 不同軸向位置之剖面速度分佈圖(CaseⅠ, δ=30°)。(a)X = 10; (b)
X = 20; (c)X = 50; (d)X = 100; (e)X = 200; (f)X = 400 .....................27
圖3.7 不同軸向位置之剖面溫度分佈圖(Case Ⅶ, δ=-30°)。(a)X = 10;
(b)X = 20; (c)X = 50; (d)X = 100; (e)X = 200; (f)X = 400 ..............28
圖3.8 不同軸向位置之剖面速度分佈圖(Case Ⅶ, δ=-30°)。(a)X = 10;
(b)X =20; (c)X = 50; (d)X = 100; (e)X = 200; (f)X = 400 ...............29
圖3.9 不同軸向位置之剖面無因次溫度(CaseⅠ, δ=30°) .......................30
圖3.10 不同軸向位置之剖面無因次速度(CaseⅠ, δ=30°) .......................30
圖3.11 不同軸向位置之剖面無因次溫度(CaseⅠ, δ=-30°) ....................31
圖3.12 同軸向位置之剖面無因次速度(CaseⅠ, δ=-30°) ........................31
圖3.13 不同傾斜角度在X= 20時的剖面溫度圖(To = 300K, Tw = 330K)。
(a)δ = 90°; (b)δ = 60°; (c)δ = 30°; (d)δ = 0°; (e)δ = -30°; (f)δ = -60°;
(g)δ = -90° ........................................................................................32
圖3.14 不同傾斜角度在X = 20時的剖面速度圖Re0 = 500。(a)δ = 90°;
(b)δ = 60°; (c)δ = 30°; (d)δ = 0°; (c)δ = -30°; (f)δ = -60°; (g)
δ = -90° .............................................................................................33
圖3.15 不同傾斜角度在X = 20時之無因次溫度曲線圖(To = 300K,
Tw = 30K)。(a)δ≥0; (b) δ≤0 .......................................................34
圖3.16 不同傾斜角度在X = 20時之無因次速度曲線圖(Re0 = 500)。
(a)δ≥0; (b) δ≤0 ............................................................................35
圖3.17 傾斜角度對局部摩擦係數之影響(To = 300K, Tw = 330K, Re0 = 500)。
(a)φ=90°; (b)φ=-90° ................................................................36
圖3.18 傾斜角度對局部努塞爾數之影響(To = 300K, Tw = 330K, Re0 = 500)。
(a)φ=90°; (b)φ=-90° ........................................................................38
圖3.19 擬臨界區域對局部CfRe0之影響 ……………………….…...….....39
圖3.20 擬臨界區域對局部Nuw之影響 ………………...…..……….….…….39
圖3.21 壓力為7~9MPa時，二氧化碳的熱物理性質與溫度關係 ................40
圖3.22入口壓力對CfRe0之影響(To = 300K, Tw = 330K, Re0 = 500) 。 ……41
圖3.23入口壓力對Nuw之影響(To = 300K, Tw = 330K, Re0 = 500)。 ……….41
圖4.1 物理模型及座標系統 …………………………………………….…….42
圖4.2 螺旋管網格劃分 …………………………………………………..……46
圖4.3 不同網格系統對局部Nuw的影響 ……..…………………………..…48
圖4.4 不同軸向角ω/360° = 1、2、3截面溫度分佈圖(T0 = 293.15K,
Re0 = 50000)。(a)Tw = 303.15K; (b)Tw = 323.15K; (c)Tw = 343.15K
……………………………………………………………………...……50
圖4.5 不同軸向角ω/360° = 4、5、6截面溫度分佈圖(T0 = 293.15K,
Re0 = 50000)。(a)Tw = 303.15K; (b)Tw = 323.15K; (c)Tw = 343.15K
…………………………………………………………………………...50
圖4.6 不同軸向角ω/360° = 1、2、3截面速度分佈圖(T0 = 293.15K,
Re0 = 50000)。(a)Tw = 303.15K; (b)Tw = 323.15K; (c)Tw = 343.15K
………………………………………...…………………………………51
圖4.7 不同軸向角ω/360° = 4、5、6截面速度分佈圖(T0 = 293.15K,
Re0 = 50000)。(a)Tw = 303.15K; (b)Tw = 323.15K; (c)Tw = 343.15K
………………………………………...…………………………………51
圖4.8 不同軸向角ω/360° = 1、2、3截面紊流動能分佈圖(T0 = 293.15K,
Re0 = 50000)。(a)Tw = 303.15K; (b)Tw = 323.15K; (c)Tw = 343.15K
………………………………………...…………………………………52
圖4.9 同軸向角ω/360° = 4、5、6截面紊流動能分佈圖(T0 = 293.15K,
Re0 = 50000)。(a)Tw = 303.15K; (b)Tw = 323.15K; (c)Tw = 343.15K
………………………………………...…………………………………53
圖4.10不同軸向角ω/360° = 1、2、3截面溫度分佈圖(T0 = 293.15K,
Tw = 323.15K)。(a) Re0 = 10000; (b) Re0 = 50000; (c) Re0 = 100000
………………………………………...…………………………………54
圖4.11不同軸向角ω/360° = 4、5、6截面溫度分佈圖(T0 = 293.15K,
Tw = 323.15K)。(a) Re0 = 10000; (b) Re0 = 50000; (c) Re0 = 100000
………………………………………...…………………………………54
圖4.12不同軸向角ω/360° = 1、2、3截面速度分佈圖(T0 = 293.15K,
Tw = 323.15K)。(a) Re0 = 10000; (b) Re0 = 50000; (c) Re0 = 100000
………………………………………...…………………………………55
圖4.13不同軸向角ω/360° = 4、5、6截面速度分佈圖(T0 = 293.15K,
Tw = 323.15K)。(a) Re0 = 10000; (b) Re0 = 50000; (c) Re0 = 100000
………………………………………...…………………………………55
圖4.14不同軸向角ω/360° = 1、2、3截面紊流強度分佈圖(T0 = 293.15K,
Tw = 323.15K)。(a) Re0 = 10000; (b) Re0 = 50000; (c) Re0 = 100000
…………………….…………………...………...………………………56
圖4.15不同軸向角ω/360° = 4、5、6截面紊流強度分佈圖(T0 = 293.15K,
Tw = 323.15K)。(a) Re0 = 10000; (b) Re0 = 50000; (c) Re0 = 100000
…………………….…………………...………...………………………57

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