【作者】 耿旭；

【导师】 过增元； 李志信；

【作者基本信息】 清华大学 ， 工程热物理， 1997， 博士

【摘要】 本文针对渗金属锯条的双层辉光离子渗金属工艺过程和提拉法晶体生长过程中提出的质量控制问题,研究了复杂结构辐射换热数值计算及其在上述两个工艺过程中产品质量控制与提高方面的应用。 复杂结构的辐射换热计算所遇到的主要问题是:结构复杂导致计算量巨大;辐射角系数的计算因遮挡或数值计算误差而难以满足对称性和完整性,从而导致辐射换热计算不准确。本文从基本的辐射换热关系式出发,用误差传递的思想研究了角系数的计算误差对辐射换热计算的影响,表明对角系数施加完整性约束可以大大提高辐射换热计算的准确性。在对前人的角系数修正方法进行分析的基础上,对于遮挡是产生角系数计算误差的主要原因的渗金属炉内料筐温度场的工程计算,提出了一种更加简单的角系数修正方法,即将偏离完整性的角系数的计算误差分配给自身表面,该方法与文献中报道的将上述误差均匀分配给各非零角系数的方法相比,使得辐射换热计算的准确性大大提高,辐射能量的计算偏差可保证在10%以内,可以满足工程计算的需要。 在对渗金属炉内的换热进行分析之后,建立了表面间以辐射换热方式耦合在一起的具有内热源的多个平板的导热的物理模型,进行了二维和三维数值分析,研究了辅助阴极、辐射屏、料筐几何结构、材料发射率和辅助辐射板等因素对渗金属炉内料筐温度分布的影响。指出:辅助阴极具有重新分配炉内的热源分布和隔热保温的双重作用,合理添加辅助阴极对改善料筐内温度场的均匀性具有重要的作用;在渗金属炉的顶部减少辐射屏层数,可以在保证竖直方向满足工艺要求的同时改善水平方向的温度场的均匀性;料筐的几何结构对温度场有重要影响,锯条背之间的距离以60毫米为好;减少料筐材料的发射率有利于局部控制料筐温度。本文还提出了应用辅助辐射板局部控制料筐温度分布的方法。用热点偶测量了炉内的温度,为数值计算提供了参考。 本文完善了提拉法晶体生长的整体模型,在模型中加入了辐射换热的计算,研究了晶体生长过程中产生混合对流的各种因素以及辐射换热对相变面形状的影响。指出,混合对流对相变面变凸(有利于提高晶体质量)有重要的作用,本文提出了在利用混合对流改变相变面形状的基础上应用局部控制辐射换热(即在三相交界附近添加辐射环)来进一步控制相变面形状的方法。更多还原

【Abstract】 This dissertation is concerned with thermal radiation heat transfer in plasma surface alloying process and Czochralski crystal growth. The numerical method of the diffusive-gray enclosure radiation heat transfer in complex geometry was studied, and its application was introduced into these two processes to improve the quality of handsaw and single crystal.The complex geometry always makes the thermal radiation calculation extremely expensive and difficult to satisfy the important physical constraints of reciprocity and closure in computation of the view factor. Uncertainty analysis method was applied to diffuse-gray enclosure radiation problems in this paper. Analyses of the effect of uncertainties in view factors on the radiation heat transfer show that strict enforcement of view factor closure constraint can greatly reduce the sensitivity of the results to the errors in view factors. Based on the review of several view factors rectification algorithms, a simple rectification scheme was adopted to rectify the uncertainties of view factors resulting from obstructions in an enclosure. It was found that this rectification scheme is superior to the others for the reduction of heat flux sensitive to uncertainties in view factors, and the energy conservation can be matched very well.Two and three dimensional mathematical models were developed to simulate the radiation heat transfer in the plasma surface alloying process. The effects of the supplementary cathode, shield, configuration of the frame, emissivities and auxiliary plates on the temperature distribution were numerically studied. It points out: a rational arrangement of supplementary cathode can greatly uniformize the handsaw temperature duo to its double actions of redistributing heat source and reducing thermal radiation;less shield layers at the top of the furnace leads to more uniform horizontal temperature distribution. The horizontal plate between two rows of handsaws can enhance the radiative heat transfer at the center place, and therefore can reduce the temperature difference along both horizontal and vertical directions. The temperature in the frame was measured by thermal couples. The results show that the three-dimensional simulation are reasonable.The global model of CZ crystal growth considering the diffusive-gray enclosure radiation heat transfer was developed in this paper. The effects of the combined convection of the melt and radiative heat transfer on the shape of melt-crystal interface were numerically analyzed. A new method of controlling the melt-crystal interface by changing the local radiative heat transfer is presented.更多还原