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Three-dimensional Numerical Simulation of Thermocapillary Convection in Detached Solidification Under Axial Magnetic Field

Author: MengHaiYong
Tutor: PengZuo
School: Chongqing University
Course: Power Engineering and Engineering Thermophysics
Keywords: Detached solidification Axial magnetic field Thermocapillary convection Numerical Simulation Microgravity
CLC: TK124
Type: Master's thesis
Year: 2011
Downloads: 43
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Abstract


Detached Bridgman technique is a new method of melt growth, combining the advantages of both classical Bridgman and Czochralski methods, and better quality crystals can be obtained. So, the method is good at growing CdZnTe crystal growth which is more sensitive to heat stress. This new method of crystal growth has some success in microgravity conditions,but the results are not satisfactory. The reason lies that the free surface tension drives the thermocapillary convection in the melt. In order to weaken the strength of the flow in the melt, the axial magnetic field is applied. The results can provide a theoretical basis of detached Bridgman technique successfully growth of CdZnTe crystals.In this paper, the three-dimensional physical model and governing equations for CdZnTe in detached solidification are established under axial magnetic field and microgravity. Numerical simulations of flow in the melt with different values of Ha and Ma are conducted using the finite-difference method. The distributions of streamline and isotherm of the melt and free surface are obtained. Meanwhile, the effect of axial magnetic field on the melt flow is analyzed.The results showed: (1) The axial magnetic field significantly suppresses the thermocapillary convection in the melt. (2)When the top surface of the melt is solid wall, a toroidal roll is caused in the melt by the surface tension gradient on the free surface. The axial magnetic field significantly weaken the strength of the toroidal roll and make the center of it approach to the free surface, as well as the flow cell area become smaller. When the value of Ma is fixed, the inhibition effect of magnetic field is enhanced gradually with Ha increasing, and the non-linear temperature distribution gets decreased on the free surface. When Ha is kept at a certain value, with Ma increasing, both the velocity and the non-linear temperature distribution on the free surface get increased. The critical Ma gets increased as the intensity of magnetic field increasing. (3) When the top surface of the melt is free surface, two roll cells with opposite direction are observed in the melt driven by both the surface tension gradient on the two free surfaces. When axial magnetic field is applied, both toroidal roll cells in the melt will be inhibited by the Lorentz force. And their intensities are gradually reduced with the increase of magnetic field. At the same time, the structures of upper roll cell are significantly simplified with the increase of Ha. When the value of Ma is fixed, with Ha increasing, the velocity on the free surface is gradually reduced. The critical Ma gets increased as the intensity of magnetic field increasing.

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CLC: > Industrial Technology > Energy and Power Engineering > Thermal engineering, heat > Thermal Engineering Theory > Heat Transfer
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