本文利用三維計算流體力學逆向方法 (three-dimensional CFD inverse method)，探討封閉空腔內上下交錯垂直鰭片之自然對流熱傳特性。研究中改變下方鰭片高度 (𝐻𝑓1)、上方鰭片高度 (𝐻𝑓2) 及兩鰭片間距 (𝑑)，共建立 27 組幾何配置，並分析其對溫度分布、速度流線及平均熱傳係數之影響。
數值模擬採用 ANSYS Fluent 18.0 進行三維自然對流分析，並結合實驗量測溫度與最小平方法 (least squares method) 反算熱傳率。本文亦進行網格獨立性測試與流動模型比較，並以均方根誤差 (root mean square error, RMSE) 評估模型準確度。結果顯示，零方程式紊流模型 (zero-equation turbulence model) 與實驗結果較為吻合，因此作為後續分析之主要流動模型。
研究結果顯示，增加上方鰭片高度會限制熱羽流 (thermal plume) 向上發展，使平均熱傳係數下降；增加下方鰭片高度雖可增加換熱面積，但若自然對流循環未同步增強，仍會降低單位面積熱傳能力。此外，鰭片間距對中、長鰭片配置影響較明顯，適當增加間距可改善可流通空間並提升熱傳表現。綜合而言，封閉空腔內鰭片設計需同時考量換熱面積與流場通暢性，並非單純增加鰭片高度即可提升散熱效果。

This study employs a three-dimensional computational fluid dynamics inverse method to investigate the natural convective heat transfer characteristics of vertically staggered fins in an enclosed cavity. The lower fin height (𝐻𝑓1), upper fin height (𝐻𝑓2), and fin spacing (𝑑) are varied to establish 27 geometric configurations. The effects of these parameters on temperature distribution, velocity streamlines, and average heat transfer coefficient are analyzed.
The numerical simulations are performed using ANSYS Fluent 18.0. Experimental temperature data are combined with the least squares method to inversely estimate the heat transfer rate. A grid independence test and a comparison of different flow models are also conducted, and the root mean square error (RMSE) is used to evaluate the accuracy of the numerical results. The results show that the zero-equation turbulence model provides better agreement with the experimental data and is therefore selected as the main flow model for subsequent analysis.
The results indicate that increasing the upper fin height restricts the upward development of the thermal plume and reduces the average heat transfer coefficient. Increasing the lower fin height increases the heat transfer area; however, if the natural convection circulation is not enhanced accordingly, the heat transfer performance per unit area decreases. In addition, fin spacing has a more significant effect for medium and long fin configurations. Increasing the spacing properly can enlarge the available flow passage and improve heat transfer performance. Overall, fin design in an enclosed cavity should consider both heat transfer area and flow passage, rather than simply increasing fin height.

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