Effect of submerged entry nozzle wall surface morphologies on boundary layer structure and alumina inclusions transport
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摘要: 鋁鎮靜鋼液澆注過程中，浸入式水口耐材內壁特征受到鋼液侵蝕和夾雜物聚集影響，從近光滑壁面逐漸向多孔耐火材料壁面和含結瘤物的粗糙結瘤壁面轉變，壁面形貌的變化影響邊界層流場結構和氧化鋁夾雜物的輸運。采用物理模擬的方法在浸入式水口模型內壁鑲嵌多孔耐火材料結構和含結瘤物耐材壁面結構，結合粒子圖像測速技術研究不同特征壁面附近流場邊界層。使用MATLAB耦合流場測速結果和氧化鋁夾雜物運動數學模型，研究了不同特征壁面的流場邊界層中氧化鋁夾雜物的運動軌跡。使用象限分析法確定了浸入式水口邊界層流場存在上拋和下掃事件。氧化鋁夾雜物位于下掃事件區域時，朝向壁面運動，粒徑為1 μm的氧化鋁夾雜物在下掃事件中運動軌跡更接近壁面，增加了沉積的可能性；氧化鋁夾雜物位于上拋事件區域時，遠離壁面運動。多孔耐火材料壁面和結瘤壁面邊界層內氧化鋁夾雜物運動幅度大于光滑壁面邊界層流場內氧化鋁夾雜物運動幅度。壁面狀態由近光滑壁面轉變為多孔耐火材料和結瘤壁面時，流場邊界層中下掃事件平面占比由10.17%增加到39.77%，上拋事件平面占比由32.96%減小到9.24%；同時，流場邊界層中下掃事件發生的概率由25.83%增加到28.24%，這將加速氧化鋁夾雜物在多孔耐火材料和結瘤壁面的沉積進程。Abstract: During the Al-killed steel continuous casting process, the molten steel corrosion and the accumulation of alumina inclusion deposits affect the submerged entry nozzle (SEN) wall surface, including the surface morphologies of the smooth wall, porous refractory wall, and clogged wall. The SEN wall surface morphology affects the boundary layer structure and alumina inclusions transport. In this study, a physical modeling method was adopted, and the surface morphologies simulation was realized by filling up the natural porous refractory material and inserting the real clog material in the polymethyl methacrylate SEN model. The velocity in the boundary layer was measured using the particle image velocimetry (PIV) technology, and the alumina inclusions transport path in the boundary layer was calculated by MATLAB software. The MATLAB codes combined the velocity data from the PIV measurement results and the inclusion transport equation. The four-quadrant analysis showed that sweep and ejection events existed in the boundary layer. The fluctuations of the velocity and the turbulent kinetic energy in the normal direction were increased in the porous refractory and the clogged wall boundary layer when the sweep and ejection events existed. The transport of the alumina inclusions with a diameter of 1–15 μm was affected by the ejection and the sweep events. The alumina inclusions moved toward the boundary in the sweep event. During the sweep event, the transport path of alumina inclusions with 1 μm diameter was close to the boundary; the alumina inclusions were more easily attached to the boundary. The alumina inclusions escaped from the boundary in the ejection event. In the porous refractory and the clogged walls, the alumina inclusion transport path in the normal direction was increased. When the SEN wall’s morphologies changed from smooth wall to porous refractory wall and clogged wall, the sweep event area proportion increased from 10.17% to 39.77%, and the ejection event area proportion decreased from 32.96% to 9.24%. Moreover, the sweep event’s probability increased from 25.83% to 28.24% when the morphologies of the SEN wall changed from smooth wall to porous refractory wall and clogged wall, which will increase the alumina inclusion deposition rate in the porous refractory wall and the clogged wall boundary.
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圖 1 鋼液澆注過程浸入式水口壁面特征變化示意圖。（a）近光滑壁面；（b）多孔耐火材料壁面；（c）結瘤壁面
Figure 1. Schematic of SEN wall surface changing morphologies during casting: (a) smooth wall；(b) porous refractory wall；(c) clogged wall
圖 3 邊界層流場內上拋、下掃事件示意圖
Figure 3. Schematic of the ejection and sweep events in boundary layer
圖 4 邊界層流場速度特征。（a）近光滑壁面；（b）多孔耐火材料壁面；（c）粗糙結瘤物壁面；（d）速度分布
Figure 4. Boundary layer velocity: (a) smooth wall；(b) porous refractory wall；(c) clogged wall; (d) velocity distribution
圖 5 法向湍流動能云圖。（a）近光滑壁面；（b）多孔耐火材料壁面；（c）結瘤壁面；（d）三種壁面條件下平均法向湍流動能大小
Figure 5. Rxx contour: (a) smooth wall; (b) porous refractory wall; (c) clogged wall; (d) average Rxx distribution
圖 6 不同壁面狀態下，在距離壁面0.5 mm處，1 s時間內的邊界層流場法向和流向脈動速度象限統計。（a）光滑壁面；（b）多孔材料壁面；（c）結瘤壁面；（d）下掃事件與上拋事件概率統計
Figure 6. u' and v' distribution at a distance of 0.5 mm to the boundary during one second in the different wall morphologies: (a) the smooth wall; (b) the porous wall; (c) the refractory wall; (d) the probability statistic of the sweep and ejection events
圖 7 壁面附近上拋、下掃事件的平面分布。（a）近光滑壁面；（b）多孔壁面；（c）結瘤壁面；（d）三種壁面條件流場邊界層內上拋、下掃事件平面占比
Figure 7. Sweep and ejection events distribution near the wall boundary: (a) smooth wall；(b) porous refractory wall；(c) clogged wall; (d) area proportion of the sweep and the ejection events in the boundary layer
圖 8 氧化鋁夾雜物在多孔耐火材料壁面邊界層流場不同事件中的運動軌跡。（a）下掃事件；（b）上拋事件
Figure 8. Alumina inclusions transport path in the porous refractory wall boundary layer: (a) the sweep event; (b) the ejection event
圖 9 粒徑1 μm的夾雜物在邊界層流場不同事件中的運動軌跡。（a）下掃事件；（b）上拋事件
Figure 9. Transport path of alumina inclusions with 1 μm diameter in the boundary layer under different events: (a) the sweep event; (b) the ejection event
圖 10 邊界層內氧化鋁夾雜物運動機理示意圖。（a）近光滑壁面；（b）多孔耐火材料壁面和結瘤壁面
Figure 10. Schematic of the alumina inclusion transport in the boundary layer: (a) smooth wall；(b) porous refractory and clogged wall
表 1 原型與模型流體物理性質和浸入式水口幾何參數
Table 1. Physical properties of the fluids in prototype and physical model and the SEN geometric parameters
Parameter Value Molten steel density, ρP/(kg·m?3) 7020 Molten steel viscosity, μP/(Pa?s) 0.0067 Water density (25°C), ρm/(kg·m?3) 997.074 Water viscosity (25°C), μm/(Pa?s) 8.937×10?4 Diameter of inner nozzle/mm 40 Flow rate/(L·min?1) 45 
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