Thermal properties measurement of binary carbonate salt mixtures for concentrating solar power plants

Abstract

Specific heat capacity of an alkali molten salt mixture which is composed of lithium carbonate and potassium carbonate was measured using a differential scanning calorimeter (DSC). The specific heat capacity measurement was performed for 14 different composition ratios of the molten salt mixture to examine the effect of composition ratios on the specific heat capacity. The measured specific heat capacity values were compared with theoretically predicted values by the thermal equilibrium model. Additionally, changes in both melting point and latent heat of fusion were also investigated with change in the composition of two salts. In results, according to the heat flow curves in liquid phase obtained from DSC, the carbonate molten salt mixture could be categorized to three distinct groups: (1) gradually increased specific heat capacity, (2) dramatic decrease in the specific heat capacity, and (3) uniform specific heat capacity. Moreover, the specific heat capacity of the carbonate salt mixtures was strongly dependent upon the mole fraction of lithium carbonate. The specific heat capacity of the salt mixtures was drastically increased up to that of pure lithium carbonate in liquid phase, and decreased down to that of pure potassium carbonate in solid phase. In comparison with theoretical prediction, while the predictions were linearly increased with mole fraction of lithium carbonate, however, the measured data showed no linearity in the change of the specific heat capacity. The effect of the composition was also shown in the melting temperature and latent heat of fusion.