Melting and solidification of a metal surface subjected to a rapid high heat load

热核聚变反应堆的第一壁暴露在高热负荷下，以防等离子体破坏；然后对第一壁面的熔化、蒸发和再凝固进行了预测。这将对第一壁寿命的估计造成严重的问题。本研究旨在通过实验和数值方法研究金属表面在高速高热负荷作用下的熔化行为。特别地，开发了一种数值方法来模拟熔化和由此产生的热毛细流动。在模拟实验中，将低熔点金属薄膜暴露在红外块的单侧加热下。观察了熔融和热毛细流动，熔体层的运动形成了波浪形的再凝固表面。在日本原子研究所，一位在场的研究者利用氢离子束进行了密集的加热实验。再凝固后的金属表面有两个明显的特征。一种是光滑的表面，周围有环形树篱，另一种是粗糙的表面，分布着波浪状的凸起。在数值分析中，考虑了熔体表面的变形，计算了熔体层的热毛细流动。采用边界拟合坐标法进行计算。在不同的头部输入和深宽比下，成功地计算了自由表面的挠度。结果表明：当深宽比越小、热输入越大时，地表变形越突出；研究了表面张力温度系数的符号对表面变形的影响，发现对表面变形有相当大的影响。为了进行高效的数值计算，尝试了利用转发器阵列进行并行计算。对并行化的效率进行了检验，并通过优化通信顺序获得了较高的效率。

A first wall of a thermonuclear fusion reactor is exposed to a high heat load in case of a plasma disruption ; then melting, evaporation and resolidification of the first wall surface are anticipated. This would cause a serious problem for estimation of the first wall life. The present study aims to investigate experimentally and numerically the melting behavior of a metal surface subjected to a rapid high heat load. Especially, a numerical method was developed to simulate the melting and the resultant thermocapillary flow. In a simulation experiment, a thin film of a low-melting-point metal was exposed to one-sided heating of an infrared lump. The melting and thermocapillary flow were observed, and the movement of the melt layer resulted in a wavy resolidified surface.Intensive heating experiments were performed by one of the present investigators using the hydrogen ion beam at Japan Atomic Research Institute. Two distinguished features were observed on the metal surface after the resolidification. One was the smooth surface with a surrounding ring hedge and the other was a rough surface with distributed wavy bumps.In the numerical analysis, thermocapillary flow of the melt layer was calculated with the surface deformation taken into consideration. The calculation was made using the boundary fit coordinate method. The deflection of the free surface was calculated successfully for various head inputs and depth-width ratios.The results indicated that the surface deformation was more prominent for the smaller depth-width ratio and the larger heat input. The effect of the sign of the surface tension temperature coefficient was investigated and found to have a considerable influence on the surface deformation.To perform an efficient numerical calculation, the parallel computation using a transputer array was attempted. The efficiency of the parallelism was examined and an high efficiency was attained by optimizing the communication order.