Enhanced heat transfer and thermal storage performance of molten K2CO3 by ZnO nanoparticles: A molecular dynamics study

Molten salt serves as a popular medium for thermal storage and transfer in concentrated solar power (CSP) systems. The existing experimental studies have found the capacity of enhancing the heat storage property of the molten carbonate by doping ZnO nanoparticles. However, it has been rarely reported to conduct simulations of ZnO/molten carbonate nanofluids, and the underlying mechanism of how ZnO nanoparticles enhance the heat transfer and storage capacity has less been explored. In this study, molecular dynamics (MD) simulation has been used to investigate the heat transfer and storage properties of a molten K2CO3 nanofluid containing ZnO nanoparticles. It was found that as the nanoparticle mass ratio in molten salt based nanofluids rises, their specific heat capacity initially increases but subsequently diminishes. The specific heat capacity peaks when the ZnO mass ratio is at 1 wt%, resulting in an increase of 17.83 % compared with the base salt. The thermal conductivity in nanofluids based on molten salt increases with the increasing of ZnO mass ratio. Multi-perspective analysis of the mechanism how ZnO nanoparticles enhance the thermal energy storage performance of molten salt, including the microstructural analysis, number density, vibrational density of state, and heat flow decomposition, is conducted. In addition, results of the number density illustrates that a compressed layer of K+ is formed surrounding the ZnO nanoparticles, and the change in the potential energy leads to an increasing heat capacity. Analysis of the heat flow decomposition suggests that the enhanced nonbonded interaction is the main reason for the improvement of thermal conductive performance in the nanofluids based on molten salt. The findings in the present study provide a new perspective of how ZnO nanoparticles enhance the thermophysical properties of molten salts.