Tian Yushi, Shi Pengzhao, Xu Lijun, Qiu Shengtao, Zhu Rong
School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China.
National Engineering Research Center of Continuous Casting Technology, Central Iron and Steel Research Institute, Beijing 100081, China.
Materials (Basel). 2022 Apr 12;15(8):2810. doi: 10.3390/ma15082810.
The multiphase flow and spatial distribution of bubbles inside a continuous casting (CC) mold is a popular research issue due to its direct impact on the quality of the CC slab. The behavior of bubbles in the mold, and how they coalesce and break apart, have an important influence on the flow pattern and entrapment of bubbles. However, due to the limitations of experiments and measurement methods, it is impossible to directly observe the multiphase flow and bubble distribution during the CC process. Thus, a three-dimensional mathematical model which combined the large eddy simulation (LES) turbulent model, VOF multiphase model, and discrete phase model (DPM) was developed to study the transient two-phase flow and spatial distribution of bubbles in a continuous casting mold. The interaction between the liquid and bubbles and the coalescence, bounce, and breakup of bubbles were considered. The measured meniscus speed and bubble diameter were in good agreement with the measured results. The meniscus speed increased first and then decreased from the nozzle to the narrow face, with a maximum value of 0.07 m/s, and appeared at 1/4 the width of the mold. The current mathematical model successfully predicted the transient asymmetric two-phase flow and completely reproduced the coalescence, bounce, and breakup of bubbles in the mold. The breakup mainly occurred near the bottom of the submerged entry nozzle (SEN) due to the strong turbulent motion of the molten steel after hitting the bottom of the SEN. The average bubble diameter was about 0.6 mm near the nozzle and gradually decreased to 0.05 mm from the nozzle to the narrow face. The larger bubbles floated up near the SEN due to the effect of their greater buoyancy, while the small bubbles were distributed discretely in the entire mold with the action of the molten steel jet. Overall, the bubbles were distributed in a fan shape. The largest concentration of bubbles was in the lower part of the SEN and the upper edge of the SEN outlet.
连铸结晶器内的多相流及气泡的空间分布是一个热门研究课题，因为它直接影响连铸板坯的质量。结晶器内气泡的行为及其合并与破裂方式，对流动模式和气泡截留有着重要影响。然而，由于实验和测量方法的限制，无法直接观察连铸过程中的多相流和气泡分布。因此，开发了一种三维数学模型，该模型结合了大涡模拟（LES）湍流模型、VOF多相模型和离散相模型（DPM），以研究连铸结晶器内的瞬态两相流和气泡的空间分布。考虑了液体与气泡之间的相互作用以及气泡的合并、反弹和破裂。测量得到的弯月面速度和气泡直径与测量结果吻合良好。弯月面速度从水口到窄面先增大后减小，最大值为0.07 m/s，出现在结晶器宽度的1/4处。当前的数学模型成功预测了瞬态非对称两相流，并完全再现了结晶器内气泡的合并、反弹和破裂。破裂主要发生在浸入式水口（SEN）底部附近，这是由于钢水撞击SEN底部后产生强烈的湍流运动。水口附近的平均气泡直径约为0.6 mm，从水口到窄面逐渐减小至0.05 mm。较大的气泡由于浮力较大在SEN附近上浮，而小气泡在钢水射流的作用下离散分布在整个结晶器内。总体而言，气泡呈扇形分布。气泡浓度最大的区域在SEN的下部和SEN出口的上边缘。
