Enhanced Specific Heat Capacity of Molten Salt-Metal Oxide Nanofluid as Heat Transfer Fluid for Solar Thermal Applications

In this study, a molten salt-based high temperature nanofluid is explored for solar thermal energy conversion applications. The efficacy of the nanofluid as a heat transfer fluid (HTF) in concentrating solar power systems is explored in this study. The molten salt can enable higher operating temperature resulting in enhancement of the overall system efficiency for power generation (using, for example, a Rankine cycle or Stirling cycle). However, the usage of the molten salt as the HTF is limited due to their low specific heat capacity values (compared with, for example, water or silicone oils). The low specific heat of molten salt can be enhanced by doping small amount of nanoparticles. Solvents doped with minute concentration of nanoparticles are termed as "Nanofluids." Nanofluids are considered as attractive coolants for thermal management applications due to their anomalously enhanced thermal properties (compared with the neat solvent). In this study, a minute concentration of titanium dioxide nanoparticles (1% by mass) are dispersed in eutectic of chloride salts (KCl-CaCl₂-LiCl). The synthesis process involves dissolving the individual components in water followed by mixing, ultrasonication and evaporation of the water from the mixture. The specific heat capacity of the nanofluid is measured by a differential scanning calorimeter (DSC) and compared with traditional thermodynamic models for mixtures of fluids (equilibrium model). The specific heat of the nanofluid is enhanced by 5% compared with the pure eutectic. In addition, Transmission Electron Microscopy (TEM) is performed to verify the size of the nanoparticles and to estimate the amount of agglomeration of the titanium dioxide nanoparticles.