Magnetic convection

磁场已被用于各种制造工艺，例如半导体材料的直拉晶体生长和/或连续铸钢工艺，从而通过使熔融材料的对流平静，可以期望更高质量的固化产品。这是因为液态金属的普朗特数低至0.01。振荡对流对于液态金属是常见的，并且导致凝固产品中的不均匀结构。为了避免这些现象，有时强磁场已被用于试错基础上没有详细了解的相关机制的传输现象，如热，质量和动量传递。本文对磁场对晶体生长的影响进行了精确的模拟和数值分析。第一个系统是直拉法晶体生长过程中的熔体对流。所考虑的系统是在高度为H的圆柱形坩埚中的InSb熔融金属， ...更多信息 直径为1.25H，晶体棒直径为0.625H。晶体棒被冷却，自由表面被辐射冷却。然后，在没有磁场的情况下，即使在轴对称坩埚中，也计算了单个单侧对流辊。在水平横向磁场作用下，计算了垂直磁场平面内上升流和平行磁场平面内下降流的自由表面稳定对流。这导致在自由表面上的椭圆形温度轮廓期望提供椭圆形横截面单晶棒。通过文献调查，我们发现Kajigaya等人的报告已经在水平磁场中制造了GaAs的椭圆横截面单晶棒。这表明现有的理论分析得到了实验报告的有力支持，并对单晶棒的生长给出了理论解释。作为第二个研究课题，研究了磁化力引起的对流。其中之一是关于氧气从位于12特斯拉超导磁体孔中的垂直管的顶部和底部开口流出的对流和扩散过程。垂直管直径为50 mm，长度为600 mm，充满纯氧气体。在时间零点，管道的顶部和底部开口打开，导致氧气的自然通风。氧气的平均分子量略大于环境空气的平均分子量，导致在无磁场的情况下氧气快速流出。随着磁场强度的增加，垂直管中部高度处的平均氧浓度逐渐降低。在12特斯拉下，氧气浓度在2000秒后下降到初始浓度的30%。目前的现象是模拟的质量和动量的平衡方程和数值求解。然后，所得的瞬态浓度的氧气在一个中间的高度同意相当不错，与以前的实验，以确保模型方程。详细的图形可视化阐明了上述特征。当管道中的下半部分氧气从底部开口流出时，管道的上半部分充满空气，然后磁化力作用将氧气拉回管道的中心高度，并且高浓度的氧气长时间保持在中间高度。在管道的中间高度处，氧气的浓度随着扩散而逐渐降低，除此之外还有广泛的研究成果。它们是直拉法晶体生长中的尖形磁场、旋转磁场、Seebeck对流和超导磁体内腔中磁化力引起的准非重力场。少

The magnetic field has been employed for various manufacturing processes such as Czochralski crystal growth of semi-conducting material and/or continuous steel casting processes so that higher quality of solidified products can be expected by calming the convection of molten materials. This is because the Prandtl number of liquid metal is as low as 0.01. The oscillatory convection is common for liquid metal and causes nonuniform structure in the solidified product. To avoid these phenomena sometimes strong magnetic field has been employed in trial and error bases without detailed understanding on the related mechanism of transport phenomena such as heat, mass and momentum transfer. In the present research program, an exact modeling on the effect of magnetic field and acurate numerical analyzes were carried out.The first system considered is melt convection in a Czochralski crystal growth process. The system considered is molten metal of InSb in a cylindrical crucible with H in height, … More 1.25H in diameter with a crystal rod of 0.625H in diameter. The crystal rod is cooled and the free surface is radiatively cooled. Then, without a magnetic field, a single one-sided convection roll was computed even in an axi-symmetric crucible. With a horizontal lateral magnetic field, a stable convection over a free surface was computed with rising flow in a perpendicular plane of a magnetic field and downward flow in a parallel plane. This caused elliptic temperature contours over a free surface to expect to provide an elliptic cross-sectional single crystal rod. By making a literature survey, we found a report by Kajigaya et al. to have manufactured an elliptic cross sectional single crystal rod of GaAs in a horizontal magnetic field. This means present theoretical analyzes are strongly supported by their experimental report and to give theoretical explanation for their growing of a single crystal rod.As a second research subject, the convection due to magnetizing force was studied. One of them is about the convection and diffusion process of oxygen gas flowing out from top and bottom openings of a vertical pipe located1 in a bore of a super-conducting magnet as strong as 12 Tesla. The vertical pipe is 50 mm in diameter and 600 mm in length and is filled with pure oxygen gas. At time zero, top and bottom openings of the pipe are opened and natural ventilation of oxygen gas is resulted. The average molecular weight of oxygen gas is slightly larger than that of ambient air to result in quick flowing out of oxygen gas in the case of no magnetic field. As the magnetic strength was increased, the average concentration of oxygen at a mid height of the vertical pipe was found to decrease more and more gradually. At 12 Tesla, the concentration of oxygen decreased to 30 % of the initial one after 2000 seconds. Present phenomena was modeled by balance equations for mass and momentum and numerically solved. Then the resulted transient concentration of oxygen gas at a mid height agreed quite well with previous experiments to assure the model equations. Detailed graphic visualization clarified above characteristics. When bottom half of oxygen gas in the pipe flows out from a bottom opening with the top half of the pipe filled with air, then magnetizing force works to pull back the oxygen gas into the central height of the pipe and high concentration of oxygen gas was kept at the mid-height for a long time. The concentration of oxygen gas at a mid-height of the pipe decreased gradually with diffusion.There are extensive research results other than this. They are the cusp-shaped magnetic field in a Czochralski crystal growth, the rotational magnetic field, Seebeck convection and quasi non-gravitational field due to magnetizing force in a bore of a super-conducting-magnet. Less