熔盐在凝固过程中的微米尺度实验及模拟研究

Micron-scale experimental and numerical study of molten salt solidification process

本文采用可视化实验和相场法数值模拟相结合的方法在微米尺度下研究了太阳盐凝固过程中固液相转变机理.实验研究发现,太阳盐颗粒凝固过程可划分为三个典型阶段,各阶段的相转变规律及固-液相边界形貌结构不同.此外,太阳盐凝固结晶过程是典型的枝状晶形貌,其初始结晶的位置较为随机,并显著影响了各个方向枝状晶的演变过程.当晶核位置靠近中心时,各个方向的主枝晶的增长较为一致,使得总体形貌呈现很好的对称性.在相场法模拟中,基于控制变量法探讨了各项异性模数j、无量纲潜热系数K和各项异性强度δ三个关键相场参数对枝状晶的影响.基于实验结果进行对比分析,进一步优化了模型参数,结果表明当K=2.4,j=9,δ=0.01时,数值模型可准确模拟实际太阳盐颗粒的晶体演变过程.

The solid-liquid phase transformation mechanism during solar salt solidification was investigated at the micron-scale via a combination of visualization experiment and numerical simulation with the phase-field method.The solidification process of solar salt particles was divided into three typical stages,with different phase transition patterns and solid-liquid phase boundary morphologies.In addition,the crystallized solar salt featured a typical dendritic morphology,and the initial crystallization site was random and significantly affected dendrite evolution in all directions.When the nucleation site was close to the center,the growths of the main dendrites in the different directions were more consistent,and consequently,the overall morphology featured good symmetry.Through phase-field simulation,the effects of three key phase-field parameters,namely the mode number of anisotropy j,the dimensionless latent heat K,and the strength of anisotropyδ,on the dendrites were explored via the controlled variable method.The model’s vital input parameters were further optimized according to the experimental results.The results showed that the numerical model could accurately simulate the crystal evolution of the actual solar salt particles at K=2.4,j=9,andδ=0.01.