波浪型鰭片(Wavy fin)主要利用平板型鰭片(Plain fin)折成波浪型鰭片增加流場擾動，提高熱傳效率。百葉窗型鰭片(Louver fin)則在鰭片上挖出百葉窗形狀之洞口，利用邊界層破壞原理使邊界層所產生的熱阻下降增加熱傳效果。凸型百葉窗型鰭片(Convex Louver fin)利用波浪型鰭片加工出百葉窗形狀，有增加熱傳面積和邊界層破壞之優點，其有絕佳熱傳能力。本文利用數值方法針對不同參數探討三維凸型百葉窗型熱交換器之熱流現象，研究參數包含百葉窗起始角度(θ_"initial" = 20°、24°)、百葉窗連續變角度(Δθ = 0°, 1° , 2°及3°)及百葉窗之定角度("θ" _"uniform" = 20°~ 28°)，並在不同正向風速為1 ~ 12 m/s (以鰭片間距為特徵長度，〖"Re" 〗_"in" "=173~2076" )下進行數值運算，進而探討空氣進口速度(Vin)、百葉窗定角度(θ)與百葉窗連續變角度(Δθ)對熱傳性能之影響。此外，編寫Fortran程式將計算流體力學商用軟體與簡易共軛梯度法(Simplified Conjugate Gradient Method ,SCGM)結合，在固定進口風速(Vin)下，以熱交換器面積縮減率為目標函數，對凸型百葉型鰭片做最佳化分析。
運用數值計算方法得知，在固定速度下百葉窗型鰭片與凸型百葉窗型鰭片皆有邊界層效應，但在凸型百葉窗鰭片下緣，有渦流產生，此渦流同時增加氣體熱傳率與摩擦。故發現發現熱傳因子j、壓降因子f，凸型百葉窗型鰭片皆大於百葉窗型鰭片。
根據分析結果，發現熱傳因子j、壓降因子f與面積縮減率皆隨百葉窗角度增加而增大。當角度為20°上升至24°時，熱傳因子j、壓降因子f與面積縮減率(相較於板鰭片)上升16.8%、27.1%、11.8%，且角度為20°上升至28°時，熱傳因子j、壓降因子f與面積縮減率(相較於板鰭片)上升25.7%、61.1%、13%。但在角度為28°時，其熱傳因子j和面積縮減率上升逐漸趨緩，主要因為角度越大在下緣處產生渦流越劇，其壓降上升加劇。
另外亦發現，增加百葉窗連續變角度(Δθ)可提升熱傳因子j及面積縮減率，但也同時提高壓降因子f；以起始角度為20°之鰭片為例，其連續變角度(範圍Δθ =1°~3°)之凸型百葉窗型鰭片可使熱傳因子j增加7%、14%、19.6%，而壓降因子f則提升9.5%、20%、32.8%及面積縮減率增加6.3%、11.6%、14%。
本文同時以最佳化方法搜尋最佳百葉窗起始角度(θ_initial)與百葉窗連續變角度(∆θ)組合 (百葉窗起始角度約落在18° ~ 23°間，百葉窗連續變角度約介於2.5°~ 3°) ， 依照最佳化結果，在"V" _"in" =2、4、6、8、10及12 m/s下，面積縮減率分別達50.9%、63.4%、55.5%、47.9%、40.6% 及33.3%。

關鍵詞：凸型百葉窗型鰭片、熱交換器、最佳化分析

SUMMARY
The results showed that both the f and j factors are increased with the increase of the uniform louver angle; for a given louver pitch, increasing the uniform louver angle(θ_uniform), from 20° to 28°, the f and j factors are increased by 25.7% and 61.1%, respectively. Besides, the numerical results showed that both the f and j factors are also increased with the increase of the successive variable angle; with the same initial louver angle(θ_initial =20°), increasing the successive variable angle(Δθ), from 0° to 3°, the f and j factors are increased by 19.6% and 32.8%.Finally, the results of optimization analysis revealed that, with inlet frontal velocity ranging from 1 to 12 m/s, the optimal values of initial louver angle and successive variable angle are in the range of (18° to 23° ) and (2.5° to 3°), respectively. It is also found that, under the optimum conditions, the area reduction ratio could reach up to 33.3 % to 63.4%.
Key words:Numerical simulation, Thermoelectric generator, Pin fin.

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