本研究採用逆向三維計算流體力學方法，結合實驗溫度量測資料與最小平方法，探討具有相變化材料之建築物內三維暫態自然對流熱傳特性。研究中建立具有水平鰭片之封閉空腔模型，於側壁及頂壁配置加熱源，並於熱壁內設置石蠟作為相變化材料，以分析不同時間下空腔內之溫度場、速度場、熱傳特性及石蠟吸熱行為。藉由鰭片改變空腔內流場結構，進一步探討其對自然對流與熱能傳遞之影響。
首先比較層流模型、零方程式模型、標準 k-ε 模型及 RNG k-ε 模型之預測結果，並以均方根誤差（RMSE）、平均熱傳係數及最大速度作為評估指標。結果顯示，不同流動模型適用於不同加熱階段，其中層流模型較適合加熱初期（200-300 s），零方程式模型較適合過渡階段（1000 s），而RNG k-ε模型則較適用於2000 s之後的流動階段。
溫度場與速度場分析結果顯示，隨加熱時間增加，高溫區域逐漸由熱壁向空腔內部擴散，空腔內自然對流循環逐漸建立。由於水平鰭片的存在，流場受到導引與阻擋作用，於鰭片前端及空腔中央形成局部迴流區與封閉渦流結構，並隨時間逐漸發展至穩定狀態。最大速度由初期約0.02 m/s增加至後期約0.06 m/s，且與修正後經驗公式具有良好一致性。平均熱傳係數則呈現先快速增加後逐漸趨於穩定之趨勢，反映流場與溫度場逐漸接近穩態之現象。
石蠟吸熱分析結果顯示，上側石蠟之吸熱量於各時間點皆高於側邊石蠟，主要係因高溫空氣受浮力作用聚集於空腔上方，使上側熱壁長時間維持較高溫度。此外，石蠟吸熱量隨時間呈現雙峰變化趨勢，其變化與石蠟熱材料性質測試結果具有良好對應關係。於4000-6000 s及12000-14000 s期間，石蠟吸熱量明顯增加，分別對應石蠟熱材料性質曲線之第一吸熱峰與主要吸熱峰區域，顯示數值模擬能合理反映石蠟於不同溫度區間之吸熱與相變化行為。
綜合上述結果可知，逆向CFD方法可有效結合實驗與數值模擬，獲得實驗中不易直接量測之熱傳資訊；同時，相變化材料可有效吸收熱壁所提供之熱能，延緩建築物內部溫度上升，顯示其於建築節能與熱能調節應用上具有發展潛力。

A three-dimensional transient inverse computational fluid dynamics method was developed in this study by integrating experimental temperature measurements with the least-squares method to investigate natural convection and heat transfer in a closed cavity containing phase change materials. The physical model consisted of a closed cavity heated from the side and top walls and equipped with a horizontal fin. Paraffin was embedded in both heated walls to examine the transient temperature field, velocity field, heat transfer characteristics, and paraffin heat absorption behavior. In the inverse procedure, the input heat source was iteratively corrected using the measured temperatures, allowing the numerical results to reasonably represent the actual thermal conditions.
To determine suitable flow models for different heating stages, the laminar, zero-equation, standard k"-" ε, and RNG k"-" ε models were evaluated. Model selection was based on the root-mean-square error of the measured temperatures, the maximum velocity in the cavity, and the predicted flow structures. The results indicated that the laminar model was more suitable at 200–300 s, whereas the zero-equation model provided a more appropriate description of the flow characteristics at 1000s. From 2000s onward, the RNG k"-" ε model exhibited better overall predictive performance. As the heating time increased, natural-convection circulation gradually developed within the cavity. The horizontal fin redirected the flow paths and induced local recirculation regions near the leading edge of the fin and in the central region of the cavity. The maximum cavity velocity increased from approximately 0.02 m⁄s during the initial heating stage to approximately 0.06 m⁄s at later times and agreed well with the modified empirical correlation. The average heat transfer coefficient on the side heated wall initially increased rapidly and subsequently approached a nearly stable value.
The paraffin heat absorption results showed that the heat absorption rate of the upper paraffin was generally higher than that of the side paraffin. This behavior was primarily attributed to the buoyancy-driven accumulation of hot air in the upper region of the cavity, which maintained a relatively high temperature near the top heated wall. Significant increases in paraffin heat absorption were observed during 4000-6000s and 12000-14000s, corresponding respectively to the first and primary endothermic peak regions of the paraffin thermal-property curve. These results demonstrate that the proposed inverse CFD method can effectively integrate experimental measurements and numerical simulations to obtain flow and heat transfer information that is difficult to measure directly. The phase change material can also absorb heat transferred from the heated walls and delay the temperature rise inside the cavity, indicating its potential for building energy efficiency and thermal regulation applications.

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