熱交換器節能廣泛使用嵌入式熱傳強化裝置來提升管流之熱傳強化效果，進而提高熱性能係數。為強化嵌入物的結構強度，本研究發明肋化十字與X型縱向嵌入物，其中嵌入物的表面帶有90°或45°五種節距的肋條以及在邊緣處設計成開槽和沒開槽的形式。量測之紐賽數、摩擦係數和熱性能係數的雷諾數範圍定在5000-2,5000。流體模擬結果顯示了管道內置肋狀條可以改善熱性能。與具有複雜幾何形狀的扭旋片、線圈和百葉窗嵌入物相比，肋狀條導引出的多渦流結構可以提升紊流強度和增進流體混合，以至於協同角減少，進而提高熱傳效果。十字或X型肋狀條之紐賽數(摩擦係數)分別提高到Dittus-Boelter (Blasius)公式值的1.38-3.17 (4.22-21.75)倍或1.43-3.39 (8.53-43.41)倍。邊緣開槽減少壓降，進一步提升熱性能係數。節距比為10的+45-N肋狀條具有最高的熱性能係數，其範圍在1.47-1.11間，並隨雷諾數的增加而降低。考慮工業應用需求，利用本研究產生之數據庫回歸經驗公式，可供設計人員計算管道內置十字或X型肋狀條之平均紐賽數和凡寧摩擦係數。

Currently, inserts are widely used to improve the heat transfer efficiency of the ducted flow in heat exchangers. Integration of Nusselt number and friction coefficient into aerothermal performance index (API) for comparison of thermal performance of different inserts is commonly adopted in this technical community. Since common inserts such as coiled, twisted, vortex/swirl generator and louvered stripe have complex geometries, we have designed cross and X-shaped ribbed inserts to simplify the shape and increase the structural rigidity of the duct. The surface of the insert with and without edge notches is roughened by the 90° or 45° ribs with five rib-pitches. The Nusselt numbers, friction factors, and APIs of the enhanced ducts with the various types of cross and X-shaped ribbed inserts are measured at Reynolds numbers in the range of 5000-2,5000. Flow simulations show that the ribbed stripe insert trips multi-cellar vortices, which increase turbulence kinetic energy and improve the fluid mixings, leading to heat transfer enhancement. The experimental results show that the Nusselt numbers (friction factor) with the cross or X-ribbed stripes are increased to 1.38-3.17 (4.22-21.75) and 1.43-3.39 (8.53-43.41) times the values of the Dittus-Boelter (Blasius) formula levels, respectively. The presence of edge notches reduces pressure drops across the enchanted ducts. This further improves the aerothermal performance with the cross and X ribbed stripes. Among all the inserts, the +45-N stripe with a rib pitch-to-height ratio of 10 shows the highest API in the range of 1.47-1.11. To assist industrial applications, the empirical correlations calculating the average Nusselt number and the Fanning friction coefficient for ducts with the cross or X-ribbed stripes are devised.

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