Numerical study of heat transfer during sapphire crystal growth by heat exchanger method
Numerical study of heat transfer during sapphire crystal growth by heat exchanger method
复制标题
换热器法生长蓝宝石晶体传热过程的数值研究
DOI：
10.1016/j.ijheatmasstransfer.2014.01.033
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发表时间：
2013-09
影响因子：
5.2
通讯作者：
Liu Lijun
中科院分区：
文献类型：
--
作者：
Yang Yang;Lv Tiezheng;Wu Ming;Liu Lijun
建立了一个瞬态全局模型，研究了热交换法生长蓝宝石晶体过程中的传热过程。半透明蓝宝石的内辐射采用严格的离散坐标模型，相位变化采用固定网格法计算。预测了整个晶体生长过程中温度场、熔体流动和熔体-晶体界面形状的演变。模拟结果表明，由于内辐射的影响，蓝宝石晶体和熔体的轴向温度梯度分别沿中心线沿着呈U形分布。在坩埚壁附近，m-c界面严重弯曲，而在中心区域相对平坦，随着晶体生长，m-c界面的凸度增加。蓝宝石熔体的流动是在一个层流状态的热浮力为主。在凝固过程的最后阶段的高生长速率导致在生长的晶体的顶层处的气泡。讨论了晶界的形成机理。数值模拟结果与实验数据吻合较好。所建立的全局模型为改进HEM法生长蓝宝石晶体工艺提供了重要信息。
We developed a transient global model to study the heat transfer in sapphire crystal growth by heat exchanger method (HEM). Internal radiation in the semi-transparent sapphire was modeled with a rigorous discrete ordinate model and phase change was calculated based on a fixed-grid method in our simulations. The evolutions of thermal field, melt flow and melt-crystal (m-c) interface shape were predicted during the whole crystal growth process. Simulation results show that a U-shape distribution of axial temperature gradient appears along the centerline of the sapphire crystal and melt, respectively, due to the effect of internal radiation. The m-c interface is severely curved near the crucible wall and relatively flat at the central region with an increasing convexity when crystal grows. The sapphire melt flow is in a laminar state dominated by the thermal buoyancy force. The high growth rate at the final stage of the solidification process resulted in bubbles at the top layer of the grown crystal. The formation mechanism of the grain boundaries at the crystal periphery was discussed. The numerical simulation results show a good agreement with the experiment data. The developed global model herein provides important information to improve the growth process of sapphire crystal by the HEM technique.
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