本文針對垂直風道中具溝槽之板鰭管式熱交換器進行混合對流熱傳研究，探討入口速度、鰭片間距與鰭片幾何形狀對熱傳性能之影響。研究中設計三種鰭片形式，分別為方形鰭片、雙溝槽H型鰭片與單溝槽U型鰭片，並以空氣作為工作流體，分析氣流通過加熱管與鰭片時之流場與熱傳特性。由於鰭片周圍流場會受到管後尾流區、邊界層發展與浮力效應影響，因此其局部熱傳係數呈現非均勻分布。
本研究結合實驗量測、逆向熱傳分析與ANSYS Fluent三維數值模擬。首先利用熱電偶量測鰭片表面溫度，並將鰭片劃分為多個子區域，透過有限差分法與最小平方法求得各區域熱傳係數，進而計算平均熱傳係數與總熱傳量。接著建立對應之Fluent三維模型，進行紊流模式、近壁面處理與網格獨立性測試，並以實驗與逆向方法結果驗證模擬設定之合理性。藉由溫度分布圖與速度流線圖，可進一步觀察不同鰭片形狀對局部流動與熱傳增強機制之影響。
結果顯示，入口速度增加會使平均熱傳係數與總熱傳量上升。在入口速度1~5 m/s 範圍內，RNG k-ε模型與逆向方法結果較為接近，因此本文選用RNG k-ε作為後續模擬之流動模型。鰭片幾何比較結果顯示，低入口速度下方形鰭片因傳熱面積較完整而具有較佳表現；當入口速度提高時，溝槽鰭片可藉由改變局部流場與削弱管後尾流區來提升熱傳效果，其中U型鰭片相較H型鰭片具有較佳之熱傳表現。此結果說明，溝槽位置與保留傳熱面積之配置，對鰭片整體熱傳性能具有重要影響。
綜合而言，本文透過實驗、逆向方法與Fluent模擬交互驗證，探討具溝槽板鰭管式熱交換器之混合對流熱傳特性，研究結果可作為後續鰭片幾何設計與數值模擬分析之參考。

This study investigates the mixed convection heat transfer characteristics of a grooved plate finned tube heat exchanger in a vertical rectangular channel. Three fin geometries are considered, including a plate fin, an H-type grooved fin, and a U-type grooved fin. The effects of inlet velocity, fin spacing, and fin geometry on the heat transfer performance are discussed Experimental measurements, inverse heat transfer analysis, and three dimensional CFD simulation using ANSYS Fluent are combined in this work. The temperatures measured on the fin surface are used as input data for the inverse method to estimate the local heat transfer coefficients, average heat transfer coefficient, and total heat transfer rate. The CFD model is then verified by comparing the numerical results with the experimental and inverse results. Different turbulence models, near-wall treatments, and grid systems are also tested to determine a suitable numerical setting for the following simulations. The results show that the average heat transfer coefficient and total heat transfer rate increase as the inlet velocity increases. In the inlet velocity range of 1–5 m/s, the RNG k-ε model shows better agreement with the experimental and inverse results and is selected for the following simulations. The grid independence test also confirms that the selected grid system can provide stable numerical results with acceptable computational cost. For the effect of fin spacing, larger fin spacing improves the airflow passage between fins and reduces the thermal accumulation near the heated tube. Therefore, the heat transfer coefficient and total heat transfer rate generally increase as the fin spacing increases. For the effect of fin geometry, the plate fin shows stable heat transfer performance because of its complete heat transfer area. However, at higher inlet velocities, the grooved fins improve the local flow field by disturbing the thermal boundary layer and reducing the wake region behind the tube. Among the grooved fins, the U-type fin provides a better balance between flow disturbance and heat transfer area, and therefore shows better overall heat transfer performance than the H-type fin under most operating conditions. Overall, this study demonstrates that the groove arrangement has an important influence on the mixed convection heat transfer behavior of plate finned tube heat exchangers. The results can provide useful reference for future fin geometry design and CFD analysis of compact heat exchangers.

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