Nanofluids based on molten carbonate salts for high-temperature thermal energy storage: thermophysical properties, stability, compatibility and life cycle analysis

Molten salts-based nanofluids have been widely considered for Thermal Energy Storage (TES) applications due to their enhanced thermophysical properties. However, the application of such fluids faces many challenges, among which are the correct determination of their properties, stability, compatibility with construction materials and the overall environmental impact. In this work, we attempt to provide a comprehensive analysis of nanofluids based on nano-alumina and molten carbonate salt for the benefit of next-generation high-temperature TES applications. In particular, considerable statistics, cross-verification, novel preparation and characterization methods were applied to record ~12% increase of thermal conductivity, ~7% increase of heat capacity and ~35% increase of viscosity. It was demonstrated that such nanofluids have poor dispersion stability under static conditions; however, the enhanced thermophysical properties can be maintained by mechanical stimuli, e.g. mixing or redistribution. We show that some nanoparticles interact with typical construction materials such as stainless steel 310 by forming mixed oxides and considerably reducing the corrosion rates. An erosion study has been performed demonstrating negligible effect of nanoparticles even in the case of their strong agglomeration. Finally, life cycle analysis revealed that viscosity and preparation method of such nanofluids must be targeted to minimize the environmental impact.