本文以逆向方法及三維商業CFD套裝軟體配合實驗數據來求得具不同鰭片形狀、鰭片大小及鰭片間距之熱交換器在煙囪內於自然對流中熱傳及流體流動特性的影響。由於鰭片上的熱傳係數分布是不均勻的，因此本文中將鰭片劃分為數個子區域，並假設每一區域中的熱傳係數為常數。概先以有限差分法及最小平方法之逆向方法配合實驗量測溫度來求得鰭片上的熱傳係數。之後本文又以CFD套裝軟體配合所求知逆向結果與實驗量測溫度來求得空氣速度分布、空氣溫度分佈、鰭片表片溫度分布及鰭片上平均熱傳係數。本文結果顯示流動模式及網格點對所求結果的影響不容忽視。以CFD軟體所求的之較正確結果應在所得到之鰭片表面溫度及鰭片上熱傳係數須甚接近實驗數據及逆向結果之情況下。
結果顯示在模擬中選擇Zero-equation的紊流模式所求得結果較符合實驗量測溫度與逆向方法結果。在自然對流中隨著鰭片尺寸增加，鰭片平均熱傳係數會降低。隨著鰭片間距增加，鰭片熱傳係數增加，當間距到達某一距離時，鰭熱傳係數將維持在一定值。此外H型鰭片在鰭片與管徑比(H/d0)為5及 3時，相較於方形鰭片及環狀鰭片有較好的平均熱傳係數。

This study uses three-dimensional computational fluid dynamics (CFD) commercial package software along with inverse method and experimental data to investigate the natural convection heat transfer and fluid flow characteristics of the single-tube vertical finned tube heat exchanger. The effect of fin shape (square fin, annular fin, H-type fin), fin spacing (5, 10, 15, 20mm) and fin to tube ratio (3, 5, 10) on heat transfer coefficient are examined. Since the heat transfer coefficient on the fin is not uniform, the fin is divided into several sub-regions and the heat transfer coefficient in each sub-regions is assumed to be a constant. Later, the inverse method applies finite difference method in conjunction with the least-squares scheme and the experimental data to estimate the heat transfer coefficient on the fins. Fin temperature distribution, air temperature field and velocity distributions of air between the two fins are determined by using the CFD software with various flow model. More accurate results can be obtained, if the heat transfer coefficient obtained is close to the inverse result and experimental data. How to choose the appropriate flow model and the effect of grid points are also investigated. The results obtained using the zero-equation turbulence flow model is more suitable for this problem than laminar and RNG k-ε turbulence model. H-type fin has better heat transfer coefficient than square and annular fin when fin to tube ratio are 3 and 5.

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