Abstract In this study, we synthesized molten salt nanofluids by dispersing spherical SiO2 nanoparticles at a minute concentration (1 wt%) into a binary mixture of NaNO3-KNO3. The results showed that the heat capacity was enhanced by 15% and the viscosity was enhanced by 41–429%. Moreover, the nanofluids have shown significant non-Newtonian behavior (shear thinning). Nanofluids are known to show non-Newtonian behavior when particles have high aspect ratio (e.g., nanotube, rod-like structure) at high concentrations; however, only spherical nanoparticles were dispersed in molten salt at an extremely low concentration (1 wt%). The observed enhancement in heat capacity and the shear thinning behavior could result from the formation of dendritic salt nanostructures. Hence, we added hydroxide at an extremely low concentration (0.03 wt%) to disrupt the formation of such dendritic nanostructures to confirm their effects on the heat capacity and shear thinning behavior. The result showed that the heat capacity enhancement diminished from 15% to 3%. Moreover, the viscosity enhancement decreased from 429% to 148% at low shear rate (10/s) and from 41% to 10% at high shear rate (240/s). Furthermore, the enhanced viscosity of 10% at the highest shear rate (240/s), where the effect of the dendritic nanostructures is minimal, agreed well with a theoretical model developed for the viscosity of a simple liquid doped with nanoparticles. It supports that the dendritic salt nanostructures are primarily responsible for the enhanced heat capacity and the shear-thinning behavior of molten salt nanofluids. Material characterization using an electron microscope confirmed the presence of the dendritic salt nanostructures.

中文翻译：

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用于热能储存的熔盐纳米流体的粘度和热容特性研究

摘要 在这项研究中，我们通过将球形 SiO2 纳米粒子以微小浓度 (1 wt%) 分散到 NaNO3-KNO3 的二元混合物中来合成熔盐纳米流体。结果表明，热容提高了15%，粘度提高了41-429%。此外，纳米流体显示出显着的非牛顿行为（剪切变稀）。众所周知，当粒子在高浓度下具有高纵横比（例如，纳米管、棒状结构）时，纳米流体会表现出非牛顿行为；然而，只有球形纳米粒子以极低的浓度（1 wt%）分散在熔盐中。观察到的热容量和剪切变稀行为的增强可能是由于树枝状盐纳米结构的形成造成的。因此，我们添加了极低浓度的氢氧化物（0. 03 wt%) 以破坏这种树枝状纳米结构的形成，以确认它们对热容和剪切变薄行为的影响。结果表明，热容量增强从 15% 减少到 3%。此外，粘度增强在低剪切速率 (10/s) 下从 429% 下降到 148%，在高剪切速率 (240/s) 下从 41% 下降到 10%。此外，在最高剪切速率 (240/s) 下粘度增加 10%，其中树枝状纳米结构的影响最小，这与为掺杂纳米颗粒的简单液体的粘度开发的理论模型非常吻合。它支持树枝状盐纳米结构是熔盐纳米流体增强的热容量和剪切稀化行为的主要原因。