Abstract
Molecular dynamics method is used to simulate the influence of the mesopore size and structure on the heat transport characteristics of the mixed nitrate. The Material Studio software is used to establish the mixed nitrate models of different scales and two structures, and the NaNO<sub>3</sub>-KNO<sub>3</sub> models of different proportions that reach the eutectic state. By calculating the models and sorting out the calculation results, the phase transition of mixed nitrates on a nanometer scale is calculated and the micro-mechanism of heat transport characteristics is analyzed. The results show that the phase transition temperature of the solar salt first increases and then decreases with the increase of the nanopore size, and finally is consistent with the melting point on a macro scale. The proportion of cations has a great influence on the phase transition temperature of mixed nitrate, and the nanowire structures also change the phase transition temperature of nitrate. The bulk thermal expansion coefficient of nitrate decreases with the increase of mesoporous size, increases with the increase of NaNO<sub>3</sub> content, and changes with the mesoporous structure. The enhancement of the interaction between ions will increase the thermal conductivity, but it will not have much effect on the specific heat capacity at a constant pressure.
Highlights
The results show that the phase transition temperature of the solar salt first increases and then decreases with the increase of the nanopore size, and finally is consistent with the melting point on a macro scale
而定压比热容并没 有随着尺度的增大而有较大的变化, 仅随体系内 NaNO3 和 KNO3 的比例变化而变化
Summary
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以及达到共晶状态的不同比例的 NaNO3-KNO3 模型, 通过 对模型进行运算并整理计算结果, 对纳米尺度下混合硝酸盐热输运特性的微观机理进行分析. 借鉴 纳米金属粒子和有机聚合物模型 [11] 的模拟过程, 使 用 Material Studio 软件建立离子数不同和结构不 同的太阳盐模型以及达到共晶状态 [26] 的不同比例 的 NaNO3-KNO3 模型, 通过模拟数据的整理分析, 总结径向分布函数、相互作用能、相变温度、体热膨 胀系数、导热率和定压比热容等参数的变化, 对纳 米尺度下混合硝酸盐相变特性的微观机理进行分析. 在 Material Studio 软件中去对称 后运用 Amorphous Cell 模块的 Calculation 来建 立模型, 加入 NaNO3 和 KNO3 构建混合硝酸盐模 不同比例的硝酸盐模型的离子总数保持 在 460 个离子左右, 不同尺度的太阳盐模型的离子 总数为 460, 920, 1380, 1840, 2300, 2760, 两种孔 结构的太阳盐模型的离子总数为 460 和 920, 各类 混合硝酸盐中 NaNO3 和 KNO3 的具体数量以及 模型的尺度如表 1 和表 2 所列, 结构如图 2 所示. Ion numbers of NaNO3 and KNO3 in solar salts ( w(NaNO3) : w(KNO3) = 6 : 4 ).
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