Abstract
The effects of mesoporous size and structure on the solidification characteristics of solar salt are simulated by molecular dynamics (MD). The mixed nitrate model with different scales and two structures is established by using Material Studio software, and the model is applied to the Lammps software package for simulation calculation. The changes of freezing point, supercooling, and phase transformation latent heat are summarized. The micro mechanism of solidification characteristics of nano solar salt is analyzed by radial distribution function, potential energy temperature curve and Gibbs free energy theory. The results show that the freezing point of solar salt first increases and then decreases with the increase of nanopore scale. The nanowire structure will also increase the phase transition temperature on the same scale, and the phase transition points of the two eventually tend to be stable with the increase of scale. The supercooling of solar salt decreases with the increase of mesoporous scale, but there is an abnormal increase. Under the two different structures, the solidification enthalpy gradually decreases with the increase of scale, and the phase transition latent heat of nanowire solar salt is 30%–37% higher than that of nanoparticle structure on the same scale.
Highlights
The results show that the freezing point of solar salt first increases and then decreases with the increase of nanopore scale
式中, Tc (rnp)为纳米晶体的凝固温度, rnp 为纳米粒 子半径, Tc (∞)为块体的凝固温度, Vs 为大块晶体 的摩尔体积, γsl 为固-液相的界面能, Hc (T )为摩尔 凝固焓, δ 为表面处液层的厚度
Summary
关键词:太阳盐, 尺度, 过冷度, 凝固特性 PACS:05.70.–a, 31.15.at, 61.30.Cz, 61.66.Fn 近年来利用熔盐进行太阳能光热发电取得较 大进展, solar salt(60%NaNO3+40%KNO3, 质量含 量) 即太阳盐, 是当前太阳能电站中最普及的两种 熔盐介质之一. 使用 Material Studio 软件分别建立不同尺度、两种结构的混合硝 酸盐模型, 模型通过 Lammps 进行模拟计算, 总结 凝固点、过冷度、相变潜热随尺度和结构的变化规 律, 利用径向分布函数 (radical distribution function, RDF)、势能-温度曲线、吉布斯自由能等表征 参数对太阳盐凝固特性的微观机理进行分析. 在 Materials Studio(MS) 软件中构建硝酸盐 分子模型, 如图 1 所示, 并将 NaNO3 和 KNO3 以 质量比为 6∶4 进行混合, 构建太阳盐 (solar salt) 模型. 表 1 太阳盐 (w (NaNO3)∶w (KNO3) = 6∶4) 中 NaNO3和 KNO3 的离子数 [22] Table 1.
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