Abstract:
New alkali nitrate-nitrite systems were developed by using thermodynamic modeling and the eutectic points were predicted based on the change of Gibbs energy of fusion. Those systems with melting point lower than 130oC were selected for further analysis. The new compounds were synthesized and the melting point and heat capacity were determined using Differential Scanning Calorimetry (DSC). The experimentally determined melting points agree well with the predicted results of modeling. It was found that the lithium nitrate amount and heating rate have significant effects on the melting point value and the endothermic peaks. Heat capacity data as a function of temperature are fit to polynomial equation and thermodynamic properties like enthalpies, entropies and Gibbs energies of the systems as function of temperature are subsequently induced. The densities for the selected systems were experimentally determined and found in a very close range due to the similar composition. In liquid state, the density values decrease linearly as temperature increases with small slope. Moreover, addition of lithium nitrate generally decreases the density. On the basis of density, heat capacity and the melting point, thermal energy storage was calculated. Among all the new molten salt systems, LiNO3-NaNO3-KNO3-Mg(NO3)2-MgKN quinary system presents the largest thermal energy storage density as well as the gravimetric density values. Compared to the KNO3-NaNO3 binary solar salt, all the new molten salts present larger thermal energy storage as well as the gravimetric storage density values, which indicate the better thermal energy storage capacity for solar power generation systems.
