Effect of Morphological Characteristics of Aggregates on Thermal Properties of Molten Salt Nanofluids

Abstract

Molten salt-based nanofluid is a thermal storage and heat transfer medium for concentrated solar thermal power plants formed by adding nanoparticles to molten salt, which can enhance the thermal performance of molten salt. However, the nanoparticles tend to aggregate in nanofluids, causing changes in thermal properties. In this work, molecular dynamics simulations were used to study the effect of morphological characteristics of aggregates on the thermal conductivity and specific heat capacity of molten salt-based nanofluids. The results show that the aggregated nanoparticles cause a greater increase in thermal conductivity and specific heat capacity than dispersed nanoparticles. Additionally, the increase in fractal dimension leads to thermal conductivity reduction, while there is no clear correlation between the fractal dimension and specific heat capacity. New insights into the thermal properties of aggregated nanofluids are provided by analyzing the contribution of material components, heat flux fluctuation modes, and energy compositions. It is found that the thermal conductivity of aggregated nanofluids is mainly dominated by the base liquid and collision term. However, the specific heat is not related to the variation in the contribution of different energy compositions. Moreover, compared to the dispersed nanofluid, the increased specific heat capacity of aggregated nanofluids is attributed to the thicker semi-solid layer. This study provides guidance for the design and control of the thermal properties of molten salt-based nanofluids.