Experimental and Simulation Study on Enhancing Thermal Energy Storage and Heat Transfer Performance of Ternary Chloride Eutectic Salt by Doping MgO Nanoparticles

Molten salt-based nanofluids exhibit more efficient heat storage and transfer performance than the same pure base molten salt (BS). In this work, nanofluids were prepared by dispersing nano-MgO in chloride BS (NaCl: CaCl₂: MgCl₂= 53: 15: 32, mole fraction) to improve its thermophysical properties, and the improvement mechanism was explored by molecular dynamics (MD) simulation. Among all the nanofluids, the nanofluid doped with 2.5% (mass fraction) 20-nm MgO has the best thermal property, with its specific heat capacity c_p increased by 38.2%. After heating at 600°C for 1000 hours, the heat storage performance of the nanocomposite samples did not deteriorate. The analysis of microstructures by MD shows that there exists a semi-solid liquid layer at the interface between nano-MgO and the molten salt due to the strong interactions between nanoparticles and molten salt. It contributes to enhancing the thermal storage capacity of nanofluids. The number density and specific heat capacity both decrease as particle size increases. Combining the experimental and simulation result analysis, the possible mechanism of enhancing the specific heat capacity of nanofluids is revealed. The nanofluid prepared in this work can serve as potential heat storage/transfer materials in concentrating solar power systems, and the heat storage/transfer mechanism proposed in this work is also helpful for understanding the thermophysical properties of other molten salt nanofluids.