渦流產生器(vortex generator)係利用結合於熱交換器鰭片上之凸出物，使空氣流經時產生縱向渦漩(longitudinal vortices)以增進熱傳的裝置。本研究分別於板鰭片與矩形鰭片之鰭管式熱交換器上加裝塊狀型(block type)渦流產生器，並探討兩種不同排列方式-對齊式(in-lined)與交錯式(staggered)。在理論方面，假設三維穩態流場，探討固體表面(鰭片、管壁與渦流產生器)為定溫時，在不同正向風速下(1~4m/s)，三維熱流場通道內溫度和壓力之變化。同時為求瞭解渦流產生器熱傳增強效果，將與不具渦流產生器之熱交換器相互比較。更進一步以數值方法探討渦流產生器展開角度(30°~60°)與擺放位置(渦流產生器前緣至管中心之橫向距離)(2~20mm)對熱交換器之熱傳因子(Colburn factor, j)與摩擦因子(Friction factor, f)的影響。另外，透過撰寫Fortran程式將計算流體力學(Computational Fluid Dynamics, CFD)商用軟體與最佳化方法-簡易共軛梯度法(Simplified Conjugate Gradient Method, SCGM)結合。以相同熱傳量與風扇功率下，熱交換器所能縮減之最大熱傳面積為目標函數，進行最佳化搜尋。
理論分析結果發現，裝設渦流產生器於板鰭片與矩形鰭片上，(1)渦流產生器展開角度的影響為：當渦流產生器展開角度變大，熱傳因子j 與摩擦因子f 皆隨之增加。而(2)擺放位置的影響為：隨渦流產生器前緣至管中心之橫向距離的增大，熱傳因子j 與摩擦因子f 亦隨之增加。此外，增設渦流產生器於板鰭管式熱交換器上，影響對齊式排列之熱傳效果較交錯式排列大，但壓降亦相對地增加。
而後經過最佳化搜尋找到最佳組合(展開角度介於34.9°~53.8°，擺放位置於5.5~19.0mm)。最佳化結果如下，對齊式板鰭片之熱傳因子j 相對於無渦流產生器之板鰭片約提升16.8~30.9%，然而，摩擦因子f 僅提升12.7~24.6%；面積縮減率可縮減15~26%之鰭片面積。而在交錯式板鰭片裡，熱傳因子j 增加8.0~12.8%，摩擦因子f僅增加6.0~10.1%；面積縮減率可縮減8~14 %。另一方面，對齊式矩形鰭片之熱傳因子j 相對於無渦流產生器之板鰭片約提高9.8%，而摩擦因子f 僅約提高3.9%，其面積縮減率則可縮減約15%之鰭片面積。

A series of 3-D computational fluid dynamics analyses were carried out to study the thermal-hydraulic characteristics for the in-lined and staggered fin-tube heat exchangers with block type vortex generators mounted behind the tubes. Two types of heat exchangers were investigated in the study: (1) plate fin and tube heat exchangers and (2) rectangular fin and tube heat exchangers.
Firstly, the effects of vortex generator span angles (θ) and transverse locations (Ly) on the heat transfer performance and pressure loss (in terms of j and f factors) at various frontal velocities, ranging from 1 to 4 m/s, were evaluated in detail. Furthermore, optimization was investigated respect to the span angle and transverse location of vortex generators by use of a simplified conjugate-gradient method (SCGM). A search for the optimum span angle (θ) and transverse distance (Ly), ranging from 30°< θ < 60° and 2 mm < Ly < 20 mm, respectively, is performed. The area reduction ratio of mounting vortex generators relative to the plate fin without vortex generators is the objective function to be maximized.
The numerical results showed that the values of j and f factors were increased with increase of vortex generators’ span angle and transverse location. The influences on the plate-fin heat exchanger were more significant for the in-lined arrangement than the staggered arrangement. Optimization analyses provided the following conclusions: (1) For the in-lined plate-fin heat exchanger, the optimal θ and Ly are in the range of 48.8°~53.8° and 7.5~8.5 mm. The increases of j and f factors are 16.8~30.9% and 12.7~24.6%, respectively. The area reduction ratio could reach up to 15~26%. (2) For the staggered plate-fin heat exchanger, the optimal θ and Ly are in the range of 41.9°~52.6° and 5.5~7.5 mm. The increases of j and f factors are 8.0~12.8% and 6.0~10.1%, respectively. The optimum values of area reduction ratio are achieved at 8~14%. (3) For the in-lined rectangular-fin heat exchanger, the optimal θ and Ly are in the range of 34.9°~42.2° and 15.9~19.0 mm. The increases of j and f factors are about 9.8% and 3.9%, respectively. The area reduction ratio is about 15% at the optimum condition.

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