Al2O3 nanoparticles for enhanced thermal performance in NaCl–KCl–Na2CO3 system: From thermodynamic prediction to system level assessment

With the introduction of the Brayton cycle technology, molten salts have become one of the most promising thermal storage materials in thermal energy storage (TES) systems. In this study, a novel eutectic salt (ES) NaCl–KCl–Na2CO3 was used as the base salt and Al2O3 nanoparticles (NPs) as additives to prepare Nano-ES. Both thermal analysis and molecular dynamics results showed that the doping of Al2O3 NPs improved the thermophysical properties of the ES. In particular, the TES density and liquid-state thermal conductivity of the ES increased by 11.60 % and 28.62 %, respectively, when the content of NPs was 2.0 wt%. The improvement in thermophysical properties was attributed to the NPs-induced change in the microstructure of the ES. However, the doping of NPs led to inevitable increase in the viscosity of the ES, which directly affected the strength of natural convection. This study further analyzed the melting process of ES and Nano-ES in shell-tube TES system, and the results showed that the melting rate of TES materials was affected by natural convection and thermal conductivity. The ES with lower viscosity and thermal conductivity exhibited a melting rate close to that of Nano-ES at 420–540 s stage. The viscosity of the TES materials should not be neglected during the application of TES systems. This study provides an important guiding significance for the selection of molten salts and additives for high-temperature TES systems.