本研究以實驗方法探討具交錯排列肋條的矩形管道之流場與熱傳特性。流場研究的設備為一臥式水洞，其測試段管道的寬高比為4，肋條排列在管道上、下表面。測試段為透明壓克力所製成，以利流場可視化與質點影像速度儀(PIV)量測。採用質點軌跡流場觀察法(PTFV)以及質點影像速度儀，針對不同的肋條高度與節距進行實驗研究，雷諾數範圍在3500~14000之間。質點軌跡流場觀察法以比重1.03的塑膠顆粒作為媒介，配合雷射光頁與高速攝影機得到流場可視化的照片。以質點影像速度儀對流場作定量分析，得到流場穩態與瞬時的資訊。為了消弭流場瞬時速度變化的差異性，採用時間平均方式取得平均速度。量化分析的結果顯示，管道內流場具有剪流層、主要渦漩與角落渦漩的特徵。紊流統計分析顯示，在頻譜圖上無明顯的特徵頻率存在，而各位置的概率密度函數皆呈現高斯分佈。由於剪流層渦漩的成長與配對現象，造成剪流層具有大的速度梯度、高紊流強度、高剪應力之特性。依據流場軌跡的型式與迴流區長度的分佈情形，可將流場分為Thru-flow、Oscillating-flow，以及Cell-flow三種特徵模態。Thru-flow之再接觸點的位置小於0.5p，管道中心區域主流幾乎不受肋條影響，流體經過肋條後的加速效果較不明顯。Oscillating-flow之再接觸點的位置大於0.5p或與管道壁面無再接觸的發生，管道中心區域主流因為肋條的高度增加而呈現上下震盪的軌跡。Cell-flow受到上下交錯肋條的抑制，管道中心區域的主流以接近90o向下偏折，部份流體捲入肋條後方的低壓區，另一部份的流體向下游流動受到上方肋條後方迴流的影響，緊貼著壁面流動。Cell-flow的渦度約為Oscillating-flow與Thru-flow的2.5倍。紊流強度方面，Cell-flow的軸向紊流強度約為Oscillating-flow與Thru-flow的2.2倍與3.5倍，Cell-flow的橫向紊流強度約為Oscillating-flow與Thru-flow的2.4倍與4.2倍。針對流場特性所區分的模態，另外使用一套加熱氣流的設備以進行熱傳性能實驗。雷諾數範圍在400~20000之間，測試段以6061 T6鋁合金製造。利用熱電偶量測測試環境溫度、測試段的入口溫度、測試段上多點溫度及測試段出口的溫度。結果顯示，因為具Cell-flow特徵之流場具有高渦度、高紊流強度與高壁面剪應力，使得其熱傳率遠高於Thru-flow與Oscillating-flow。但Cell-flow造成極大的壓力損失，使得Thru-flow的熱傳性能係數(紐塞數與摩擦係數的比值)高於Oscillating-flow與Cell-flow。若不計較其壓力損失，則建議h/B與p/h操作於Cell-flow區域，可得到較高的熱傳率。

The flow structure, turbulence characteristics, heat transfer performance, and the correlations between the flow and heat transfer properties in the rectangular channels installed with staggered ribs are studied. The flow experiments are performed in a water tunnel by using the particle tracking flow visualization method (PTFV) and the particle image velocimetry (PIV). The test section is a rectangular channel which is made of transparent acrylic so that the flow visualization and the PIV measurements are possible. The time-evolving instantaneous and time-averaged flow and streamline patterns are obtained. The statistical properties of the turbulence, e.g., the probability density function, autocorrelation coefficient, power spectrum density function, time and length scales of the turbulence, turbulence intensity, shear stress, vorticity, and apparent viscosity are extracted from the measured raw data of the PIV experiments. Three characteristic flow patterns: thru-flow, oscillating-flow, and cell-flow, are identified. The vorticity as well as the axial and transverse turbulence intensities of the cell-flow are drastically larger than those of the oscillating-flow and the thru-flow by about 2 to 5 percents. The heat transfer experiments are conducted in a heated wind tunnel with a rectangular test section which the geometry is similar to that used in the flow experiment. The temperature measurements are done by attaching 40 T-type fine-wire thermocouples of 127 µm bead diameter to test section. It is found that the heat transfer coefficient of the cell-flow is the highest among the three characteristic flow patterns because the turbulence intensity and the wall shear stress of the cell-flow is much higher than those of the oscillating-flow and thru-flow. The flow properties and the heat transfer characteristics are apparently closely related.

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