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Thermoelectric magnetohydrodynamic flows during various crystal growth processes with an externally applied magnetic field.

机译:在各种晶体生长过程中,热电磁流体动力学在外部施加磁场的作用下流动。

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The thermoelectric magnetohydrodynamic (TEMHD) effects occur when the applied magnetic field interacts with electric currents and when there is a temperature gradient along the liquid-solid interface with different absolute thermoelectric powers for the solid and liquid. This thesis presents the first models to investigate the TEMHD effects during various crystal growth processes, with an assumed temperature profile along the crystal-melt interface and an externally-applied uniform axial magnetic field.; The TEMHD flow exhibits different behavior under various magnetic field strengths. For strong magnetic fields, the flow becomes inertialess. For arbitrary strength magnetic fields, the inertial, viscous and electromagnetic damping effects are important. For weak magnetic fields, there is no electromagnetic damping in the melt motion, and the result is an ordinary hydrodynamic flow with a prescribed thermoelectric body force concentrated near the bottom of the melt domain.; All the models involve a radially outward flow near the crystal-melt interface which helps produce uniform and homogeneous crystals. Numerical results are presented for Bridgman and float zone processes with strong fields. The azimuthal motion dominates the melt motion. As the magnetic field strength is increased from zero to large values, the azimuthal and meridional motions first increase from zero to maxima and then decay back toward zero for very strong magnetic fields. Numerical results for traveling heater method are presented for arbitrary strength magnetic fields. The flow is inertialess at the beginning and the convective effects emerge as the Reynolds number Re is increased for a particular case. For relatively weak magnetic field strength, the convective effects dominate the EM damping effects for very large Re. For weak magnetic field case, the convective effects emerge as thermoelectric body force is increased, and they dominate the melt motion for strong body force. A similarity problem is considered to understand the insights for weak magnetic field case. The solutions reflect the numerical results for weak field cases. While strong magnetic field results are useful for terrestrial crystal growth processes, the arbitrary strength field and weak field results will be useful for future crystal growth experiments in space.
机译:当所施加的磁场与电流相互作用时,以及当沿着液-固界面存在温度梯度且固体和液体的绝对热功率不同时,就会发生热电磁流体动力学(TEMHD)效应。本文提出了第一个模型,研究了在各种晶体生长过程中的TEMHD效应,并假设了沿晶体-熔体界面的温度分布以及外部施加的均匀轴向磁场。 TEMHD流在各种磁场强度下表现出不同的行为。对于强磁场,流动变得无惯性。对于任意强度的磁场,惯性,粘性和电磁阻尼效应都很重要。对于弱磁场,在熔体运动中没有电磁阻尼,结果是普通的流体动力流,其中规定的热电体力集中在熔体域的底部附近。所有模型均在晶体-熔体界面附近发生径向向外流动,这有助于产生均匀且均质的晶体。给出了具有强磁场的Bridgman和浮区过程的数值结果。方位角运动主导着融化运动。当磁场强度从零增加到较大值时,方位角和子午线运动首先从零增加到最大值,然后针对非常强的磁场衰减回零。给出了任意强度磁场行进加热器方法的数值结果。在开始时,流动是无惯性的,并且对流效应随着特定情况下雷诺数Re的增加而出现。对于相对弱的磁场强度,对于非常大的Re,对流效应主导EM阻尼效应。对于弱磁场情况,对流效应随着热电体力的增加而出现,并且它们在熔体运动中占主导地位,从而产生强体力。考虑相似性问题以了解弱磁场情况的见解。解反映了弱场情况下的数值结果。虽然强磁场结果对于地面晶体生长过程很有用,但任意强度场和弱场结果对于将来在太空中进行晶体生长实验都是有用的。

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