Effect of Nano-Silica on The Thermo-Physical Properties of the Thermal Eutectic (Na0.6K0.4)NO3 System

Abstract

Here, we investigate the effect of adding nano-silica particles on the thermo-physical properties of the (Na_0.6K_0.4)NO₃ based thermal energy storage systems. Five different systems tagged as M₀₀, M₀₁, M₀₂, M₀₃ and M₀₄, with different nano-silica percentage of 0, 1, 2, 3, and 4 wt%, respectively, were prepared. Various experimental techniques were employed to study the thermo-physical properties of the systems during (solid-solid) phase P₁, (solid-liquid) phase P₂ and (liquid-solid) phase P₃, and to clarify the effect of nano-silica on the thermal energy storage efficiency during both charging and discharging processes. According to the Differential Scanning Calorimeter (DSC) thermal analysis, it was found that the system M₀₂ whose nano-silica addition rate of 2 wt%, has the most favorable thermal characteristics (i.e., highest specific heat and lowest enthalpy change). Moreover, the addition of 2 wt% represents the optimum distribution of nano-silica inside the principal base system M₀₀. This leads to an improvement in the porosity of the system due to the degree of homogeneity caused by the thermophoresis effect distribution, the high surface area of the nano-silica with the activity of the M₀₀ matrix alongside the degree of the alkalinity of nano-silica. Besides, the electric conductivity measurements showed that the 2wt% percentage is the optimum one for thermal energy storage systems.