高溫鋼鐵冶煉製程中常利用氣體底吹來提升冶煉效率，但製程中底吹氣體所伴隨的氣泡回擊現象會嚴重的侵蝕底吹管口及其周圍之耐火材料，導致製程中斷及冶煉成本提高。由於常溫的底吹氣體在吹入高溫鐵水的過程中會不斷吸熱，因此在適當的製程條件下有機會在底吹管口附近形成一鐵相固凝物，藉由此固凝物可避免氣泡直接回擊爐底，此為減緩爐底侵蝕的方法之一。如何經由製程操作條件來預估固凝物之型態、尺寸及生長情形，對於高溫冶煉製程極為重要，因此本研究藉由物理模型、相似性換算及數值模擬解析等實驗方法，來探討爐內固凝物之生成。

物理模型包含水模及蠟模，分別以水及蠟來模擬鐵水，吹入低溫空氣來模擬氣體及鐵水間的溫差，實驗將觀察不同操作條件下固凝物之生成及型態。實驗可觀察到水模及蠟模之固凝物皆為圓錐狀，內部皆有一與管徑相同之中空圓柱供氣體流通。水模及蠟模實驗皆顯示固凝物達穩態後的尺寸皆會隨著液相過熱度下降、氣體流量上升或氣體溫度下降而增加。由於蠟之固凝物生成後不易斷裂且邊界較易分辨，因此較易針對固凝物成長速率與達穩態所需時間(成長時間)做觀察，結果顯示固凝物成長速率與成長時間亦會隨著液相溫度下降及氣體流量上升而增加。因此在探討蠟模固凝物之達穩態尺寸、成長時間與平均成長速率之關連後，可得固凝物之成長速率與其成長時間成正比，達穩態時的高度則與其成長時間的平方成正比。

相似性換算法ASCM (Accretion Similarity Conversion Method)是用來關聯物理模型與高溫冶煉爐間的物理變數，目的是將水模或蠟模固凝物之生成情形，合理的關連至其他相似的系統中。相似性換算法ASCM是利用帕金漢π理論找出關連兩相似系統間之重要的無因次群，再加上考量同系統間之物理變數所推導之圓柱狀固凝物熱傳解析方程式發展而成。為了使無因次化方程式對固凝物熱傳凝固系統之描述更精確，研究將圓柱狀固凝物之假設改良為較合理的圓錐狀固凝物，此時推衍出來之相似性換算法為Modified ASCM。相似性換算法主要包含熱狀態相似性換算、流量相似性換算及固凝物尺寸相似性換算三步驟，利用這三步驟即可求出兩系統間對應之液相過熱度、氣體流量及固凝物尺寸。本研究並藉由水模及蠟模之實驗結果驗證Modified ASCM之準確性及可靠度，結果顯示其誤差在合理範圍內。

本研究也針對水模進行固凝物生成之熱傳解析，採用熱擴散區域的技巧來決定氣液邊界吸熱區域的大小，並利用高斯分佈來分配熱傳遞量。數值模擬解析之固凝物尺寸與水模實驗量測到之固凝物尺寸相當符合，因此可與水模實驗結果得到相互的驗證。

In pyrometallurgical processes, gas bottom-blown technique has been widely applied to agitate the liquid bath inside the vessel to enhance metallurgical efficiency via high mixing intensity. In general, the erosion of refractory lining near gas bottom-blown tuyere is severer than other area inside the vessel due to back attack of blown gas bubbles. One of the countermeasures to alleviate the erosion is to generate an iron accretion sitting on the refractory lining via appropriate bottom-blown conditions. The covering of the accretion can protect the refractory lining from being eroded by the back attack of gas bubbles. Therefore, how to generate accretion with proper size and shape is one important issue for high performance gas bottom- blown process.

Due to high temperature operation, it is extremely difficult to visualize what is happening inside the pyrometallurgical vessels. Therefore, water and wax models were adopted to investigate the effects of gas bottom-blown condition on growth, shape and dimensions of the accretion formed. In the experimental results of physical models, the accretions were all in cone shape with a hollow channel for gas flowing through. Final sizes of the accretions at steady state were proportional to gas flow rate and were inversely proportional to the liquid temperature. In addition, the accretion formation time and growth rate increased with gas flow rate and decreased with liquid temperature. Therefore, it can be concluded that accretion growth rate and time are both proportional to the final accretion sizes. The results showed that the final heights of accretions were directly proportional to growth rate and squared of growth time.

The most important point that whether experimental data of the cold model are accurately applied to the hot model is how to connect the systematic parameters between the two units. In the study, Buckingham Pi theorem was adopted to derive the important dimensionless parameters for correlating conditions of accretion formation in the similar systems. Then, by combining dimensionless parameters with heat transfer equations that describe the heat transfer across the accretion, quantitative relations based on the similarity conversion between different conditions of the similar systems was established. Hereafter, the method mentioned above is called Accretion Similarity Conversion Method (ASCM). Based on the experimental data in the water model, the accuracy of the estimated dimensions of the wax accretion by ASCM is acceptable.

Moreover a numerical analysis was conducted to estimate accretion sizes on the water model. Thermal diffusion zone and Gaussian distribution methods were adopted to express the heat flux distribution between the gas and liquid interface. The results indicated that sizes of solid accretions inside the water model could be relatively precisely estimated by the numerical analysis.

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