热毛细效应下熔融硅水平流动及凝固特性分析

发布时间：2018-03-14 12:50

本文选题：熔融硅　切入点：热毛细　出处：《江苏大学》2017年硕士论文　论文类型：学位论文

【摘要】：近几十年来,随着世界经济和人口数量的迅速增长,能源短缺和环境污染问题日益严重,大力开发清洁能源成为各国保护生态环境、保持经济可持续发展的重要举措。太阳能电池以其清洁、安全、高效率等优点得到了国家大力扶持。硅带技术(水平拉膜制备技术)凭借其制备流程简单、提拉速率高、原材料损耗少等优点引发了人们的广泛关注。水平拉膜制备过程其实就是熔融硅水平固化和水平流动的综合过程。为了使横向拉膜技术获得更稳定的生长环境,能够制备质量高、厚度准确可控的硅带,本论文使用数值模拟方法对热毛细效应下硅熔体水平固化以及水平流动过程进行系统研究。首先,介绍了数值模拟基本方法、凝固过程传热计算理论、凝固过程流场计算理论、热毛细对流数值模拟理论,为数值模拟提供理论基础。然后,在Fluent模拟软件里建立了热毛细作用下熔融硅水平流动物理模型和数学模型。考虑了熔融硅在水平温度梯度Ma、液池底部垂直热流密度Q和两种情况耦合效应下水平流动模拟分析。得到了液层内流场和温度场的分布云图。深入分析了水平温差Ma、底部热流密度Q、及两种情况耦合作用下各种流型的变化规律。研究结果表明,当液池底部热流密度Q为零时,且两侧温差Ma较小时,熔体流动为稳态流动,随着两侧温度差Ma的不断增大,矩形液池内流动逐渐由稳态转变为波动再次转变为由两个旋转方向相反的且大小不同非对称双胞流动,最后流动转型为紊乱流动状态;当两侧温度差Ma较小时,底部热流密度Q对熔融硅水平流动作用明显,随着底部热流密度Q的不断增大流体由稳态转变为由多个旋转方向交替相反的漩涡流胞,并且流动构型随着热流密度Q的增加没有发生明显变化;当水平温差Ma和垂直热流密度Q耦合作用时,流动构型和仅仅施加垂直热流密度Q接近,较小的热流密度对热毛细对流有抑制作用。最后在COMSOL数值分析软件中建立了水平管道状凝固模型,采用自适应网格划分法划分网格,并且使用显热容法求解高度非线性方程。对熔融硅在温度场和流场耦合作用下水平固化过程进行数值模拟,模拟结果显示:熔融硅在水平凝固过程中产生了相变。并且通过等效热容的数学分析方法计算了在相变过程中型速度场分布、等温线分布。结果还发现:在靠坩埚口附近形成了流线型涡旋流。并且在凝固区和结晶区出现了很明显的热流密度变大现象,结晶结束后热流密度慢慢消失。
[Abstract]:In recent decades, with the rapid growth of world economy and population, the problem of energy shortage and environmental pollution is becoming more and more serious. Solar cells have been greatly supported by the state because of their advantages of cleanness, safety and high efficiency. Silicon tape technology (horizontal film drawing technology) is characterized by its simple preparation process and high drawing rate. The advantages of low loss of raw materials have aroused widespread concern. The preparation process of horizontal film drawing is in fact a comprehensive process of horizontal solidification and horizontal flow of molten silicon. In order to obtain a more stable growth environment for transverse film drawing technology, The silicon tape with high quality and controllable thickness can be prepared. In this paper, the horizontal solidification and horizontal flow process of silicon melt under the effect of thermal capillary are studied systematically by numerical simulation method. Firstly, the basic method of numerical simulation is introduced. The theory of heat transfer calculation in solidification process, the theory of flow field calculation in solidification process, and the numerical simulation theory of thermal capillary convection provide the theoretical basis for numerical simulation. A physical model and a mathematical model for the horizontal flow of molten silicon under the action of thermal capillary are established in Fluent software. The horizontal effect of the melt silicon is considered under the horizontal temperature gradient, the vertical heat flux Q at the bottom of the liquid tank and the coupling effect between the two conditions. Flow simulation analysis. The distribution of flow field and temperature field in liquid layer is obtained. The horizontal temperature difference Ma, the bottom heat flux Q, and the variation law of various flow patterns under the coupling of the two conditions are analyzed in depth. When the heat flux Q at the bottom of the tank is 00:00, and the temperature difference between the two sides is small, the melt flow is steady flow, and with the increase of the temperature difference Ma on both sides, The flow in the rectangular liquid cell gradually changed from steady state to fluctuation and then changed from two asymmetric double cell flows with opposite rotating directions and different sizes, finally the flow changed into a turbulent flow state, when the temperature difference between two sides was small, The effect of bottom heat flux Q on the horizontal flow of molten silicon is obvious. With the increasing of bottom heat flux Q, the fluid changes from steady state to swirl cell, which is alternately opposite from several rotating directions. When the horizontal temperature difference Ma is coupled with the vertical heat flux Q, the flow configuration is close to that of only applying the vertical heat flux Q, and the flow configuration does not change obviously with the increase of the heat flux Q, and when the horizontal temperature difference Ma is coupled with the vertical heat flux Q, the flow configuration is close to the vertical heat flux. The small heat flux can restrain the convection of the heat capillary. Finally, the horizontal pipe solidification model is established in the COMSOL numerical analysis software, and the adaptive meshing method is used to mesh the convection. The highly nonlinear equation is solved by the sensible heat capacity method. The horizontal solidification process of molten silicon under the coupling of temperature field and flow field is numerically simulated. The simulation results show that the phase transition occurs during the horizontal solidification of molten silicon, and the distribution of medium velocity field in the process of phase transformation is calculated by the mathematical analysis method of equivalent heat capacity. It is also found that a streamline vortex flow is formed near the crucible entrance, and the heat flux increases obviously in the solidification and crystallization regions, and the heat flux slowly disappears after crystallization.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN304.12;TM914.4

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