百葉窗型鰭片兼具面積擴展、增加擾動及斷續建立邊界層等增強熱傳效果之優點，廣泛應用在實際氣冷式熱交換器，本文是利用數值方法和紊流模式，探討三維百葉窗型熱交換器之流場與熱傳現象，並延伸百葉窗型鰭片幾何形狀影響三維流場的觀念，模擬汽車內水箱護罩及保險桿至水箱之間的引擎室流場，分析其對水箱冷卻性能之影響，進而研究影響百葉窗型鰭管式熱交換器熱液動性能之各種幾何參數，且利用田口方法尋求百葉窗鰭管式熱交換器之最佳化設計。
首先探討三維連續變化百葉窗角度熱交換器之熱流現象，在文中設計五種個案，四種連續變化百葉窗角度：case A、case B、case C、case D及固定角度： case E，(case A (+ 2°) 的前4片百葉窗角度為20° 、22°、 24°、26°遞增2°連續變化，經過轉向區後4片則與前4片對稱向下，百葉窗角度為26°、24°、22°、20°遞減2°連續變化，case B (+ 4°) 前4片百葉窗角度則為20°、 24°、 28°、 32°遞增4°連續變化，後4片對稱向下遞減4°為32°、 28°、 24°、20°，case C (-2°)則為26°、24°、22°、20°、20°、22°、24°、26°，case D(-4°)則為32°、28°、24°、20°、20°、24°、28°、32°，case E固定百葉窗角度均為20°)，分析在各種雷諾數下，比較其對熱交換器之熱液動性能的影響，結果發現4種個案之熱傳性能因子j均比固定角度case E熱傳性能因子jo為高，不同個案與固定角度case E之熱傳性能因子比值j/jo和摩擦因子f/fo的變化。其中case B (+4°)在Re=500時有最高值，j/jo提高到118%， case D (-4°)，case A (+2°)， case C (-2°)也分別提高115%，109%和107%，摩擦因子f/f0以Re=200時最大，分別提高到119%,118%, 110%, 及109%。若與平板型鰭片比較其面積縮減率(1-A/Aref)，則case B (+4 °)最高可達25.5%，case D(-4 °)，case A (+2 °)， case C (-2 °)也分別達23.4%，20.2%和17.5%，而固定角度case E則小於14%，可以證明連續變化百葉窗角度可以改善百葉窗鰭片型熱交換器熱性能。
其次是探討汽車內水箱護罩及保險桿至水箱之間的引擎室流場，並分析其對水箱冷卻性能之影響。汽車之水箱護罩及保險桿空氣流入口也是百葉窗幾何形狀，文中以紊流之流動模式來模擬引擎室的空氣流動情形，建立接近實際汽車形體的真實模型及網格點，並有系統地變更空氣流經水箱護罩及保險桿之入口角度(α = -15° ~ 15°， β= -5°~15°)、位置及大小(通風開口率=25%~33%)等各種參數進行數值模擬。分析結果發現：(1)當水箱護罩空氣入口角度α向下變化至-15°時，空氣流量相對於α=0°時增加5.1%，熱傳量也增加4.4%。(2)保險桿空氣入口角度β向上增加時，熱傳量隨β持續增加，在β=15°時，相對於β=0° 時增加4.8%，空氣流量變化率也隨β增加而變大，但在β=10°時有最大值。 (3)同時變更保險桿、水箱護罩之空氣入口角度及開口位置，可以大幅改善水箱熱傳性能，在α= -15°及β= +15°時，熱傳量改變率提高至12.6 %。(4)增加保險桿及水箱護罩之開口面積，當通風開口率增加至33.0 %時，空氣流量改變率則增加48.1 %，熱傳量改變率也增加34.1%。
於百葉窗鰭管式熱交換器熱液動分析與最佳化設計部分是探討三維百葉窗鰭管式熱交換器之流場與熱傳現象，進而分析影響其性能之參數，並尋求最佳化設計，本文計算模式與前人實驗比較，發現兩者很吻合，熱傳因子j值平均誤差在3.13%以內，證實可以成功的模擬實際熱交換器的熱液動情形，大部分熱傳因子j值和壓降因子f值都隨雷諾數增加而變小，但在雷諾數小於1700時，j值卻隨雷諾數減少而變小，且鰭片節距(Fp)越小越明顯；由參數分析可以發現，在所有參數中以橫向管節距(Pt)影響熱交換器之性能幅度最大，高達40.85%，其次是鰭片節距(Fp)為20.95%，管外徑(dc) 為11.29%再居次，至於鰭片厚度(δ) 和百葉窗節距(Lp) 兩者都在10%以下，其餘百葉窗角(θ) 、縱向管節距 (Pl)及縱向管排數(N)影響幅度均不大；經過田口方法所得之參數最佳水準組合之面積縮減率1-A/Aplain在低雷諾數時隨雷諾數增加而變大，在雷諾數 Re=1000 時，1-A/Aplain可以達到最高值44%，在高雷諾數時則隨雷諾數增加而變小，再與其他組合比較都是最高者，即在本研究所設計範圍內，可以找到熱交換器之最佳性能曲線之參數組合。

In the present study, the 3-D thermal-hydraulic analysis for louver fin heat exchangers and engine room (between the grille and radiator) are investigated with numerical method and turbulence model. Moreover, a three-dimensional numerical geometric optimization study to maximize the total heat transfer rate for louver-fin with round tubes of heat exchangers.
Firstly, successively increased or decreased louver angle patterns are proposed and 3-D numerical analysis on heat and fluid flow are carried out. Five different cases of successively increased or decreased louver angles (+2°,+4°,-2°,-4°, and uniform angle 20°) are investigated: case A (20°,22°,24°,26°,26°,24°,22°,20°), case B (20°,24°,28°,32°,32°,28°,24°,20°), case C (26°,24°,22°,20°,20°,22°,24°,26°), case D (32°,28°,24°,20°,20°,24°, 28°,32°), case E (uniform angle 20°) . For case A (+2°), case B (+4°), case C (-2°) and D (-4°), the maximum heat transfer improvement interpreted by j/j0 are 109%, 118%, 107% and 115%, and the corresponding friction factor ratio f/f0 are 110%, 119%, 108% and 116%, respectively, where j/j0 and f/f0 are the Colburn factor ratio and friction factor ratio between successively variable louver angles and uniform angle, respectively. It is also shown that the maximum area reduction for case B can reach up to25.5% compared to a plain fin surface. The present results indicated the successively variable louver angle patterns applied in heat exchangers could effectively enhance the heat transfer performance.
Secondly, a numerical analysis of the three-dimensional heat transfer and fluid flow for vehicle cooling system was developed. The flow field of the engine room between the grille and radiator was analyzed. The results show that, as the airflow inlet grille angle α is varied from 15° to -15°, the air flow rate compared with α = 0°(horizontal) is changed from -11.9 % to +5.1 %; while the heat flux from radiator is changed from -9.2 % to +4.4 %. When the airflow inlet bumper angles β is varied from -5° to +15°, the heat flux from radiator compared with β = 0° (horizontal) is increased up to +4.4%. When the airflow inlet grille angle α = -15° and bumper grill angles β = +15°, its air flow rates and heat flux compared with (α = 0°, β = 0° ) can be increased to +9.5% and + 7.5%, respectively. The results indicated that the optimal angles for cooling efficiency are existed.
Thirdly, a comparative study of effects of fin pitch, fin collar outside diameter, transverse tube pitch, longitudinal tube pitch, number of longitudinal tube rows, louver height, louver angle, fin thickness, and louver pitch on fin performance of louver fin-and-tube heat exchanger is conducted by numerical method. The parameters of louver fin-and-tube heat exchangers are optimized by the Taguchi method. Eighteen kinds of models are made by compounding levels on each factor, and the heat transfer and flow characteristics of each model are analyzed. The results show that fin collar outside diameter, transverse tube pitch and fin pitch, are the main factors that influence significantly the thermal hydraulic performance of the heat exchanger. Therefore, these three factors are considered as the main factors for an optimum design of a heat exchanger. The optimal conditions are acquired, and the reproducibility of the results is verified by analytical results.

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