本實驗的目的是為了減少透過扭旋片增強熱傳效率伴隨的壓降損失，將扭旋片設計成擁有成對的傾斜肋條及抽氣槽，通過沿扭旋片上傾斜肋條與抽氣槽產生之模擬流場和壓力場與實驗量測的紐賽數及凡寧摩擦係數進行相關性檢驗。上述的傾斜橫向肋條將傳統垂直肋條後方的循環渦流轉化為螺線式渦流並形成分離流，而傾斜的抽氣槽則使質量，動量和能量能夠在沿扭旋片分隔的兩個軸向渦旋之間進行交換。由扭旋片和傾斜的肋條、抽氣槽相互作用引起的流場機制改善傳熱性能與減少肋條造成的形狀阻力。在雷諾數10,000~50,000範圍內，紐賽數成長至Dittus-Boelter的4.2-3.8倍，此熱傳提升的代價則是凡寧摩擦係數增加至Blasius的32.5-40.2倍。與先前鋸齒狀(肋條)扭旋片的管流相比，在方形管中由沿著扭旋片上傾斜肋條、抽氣槽所引起的熱傳強化幾乎保持相同，但凡寧摩擦係數有顯著的減少。傾斜的肋槽達到空氣熱性能改進的結果預期能在熱交換器上加入並應用。為了幫助這些應用，因而設計經驗公式用於計算由方形管內插入傾斜肋槽扭旋片增強之平均紐賽數及凡寧摩擦係數。

In the literature, the heat transfer enhancements (HTE) and pressure drop augmentations are simultaneously incurred by using the modified twist-tapes with ribs. By using the regularly spaced or perforated twist-tapes, the pressure drop penalties are moderated with the HTE effectiveness weakened. As an attempt to moderate the considerable pressure-drop augmentations caused by a ribbed twist-tape, the present study proposed the twist-tape with the inclined ribs and slots as a new type of twisted tape insert with the associated heat-transfer and pressure-drop performances investigated. With a conventional twisted tape in a tube to separate the flow stream along two spiral pathways, the newly slot-rib twisted tape permits the mass, momentum and energy exchanges through the tape and provides the perforation effect to reduce the flow resistances owing to large pressure gradients. The aerothermal performances of the rib-slot twist tape at the Reynolds number of 10000, 20000, 30000, 40000, 50000 with air as the coolant are numerically and experimentally studied. The results show that, with the Reynolds numbers in the range of 10000 to 50000, the Nusselt numbers are elevated to 3.8 to 4.2 times of the Dittus-Boelter correlation (plain tube) values with the friction factors raised to 32.5 to 40.2 times of the Blasius equation (plain tube) levels. With the inclined ribs and slots, the friction factor augmented by the present rib-slot twist-tape is reduced from that caused by the ribbed twist-tape whereas the heat transfer enhancements generated by the ribbed and the present rib-slot twist-tapes are similar. With the reduced pressure-drop penalties and the raised HTE effectiveness, the aerothermal performance factors attributed to the present rib-slot twist-tape are improved from many types of twisted tapes. Based on the experimental data generated, the empirical correlations for calculating the Nusselt number, Fanning friction factor and heat transfer power ratio for the square duct fitted with the present rib-slot twist-tape are proposed for relevant applications.

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