No abstract

This study aims to investigate the specific heat capacity of a carbonate salt eutecticbased multiwalled carbon nanomaterial (or high temperature nanofluids). The specific heat capacity of the nanomaterials was measured both in solid and liquid phase using a differential scanning calorimetry (DSC). The effect of the carbon nanotube (CNT) concentrations on the specific heat capacity was examined in this study. The carbonate molten salt eutectic with a high melting point around 490 C, which consists of lithium carbonate of 62% and potassium carbonate of 38% by the molar ratio, was used as a base material. Multiwalled CNTs were dispersed in the carbonate salt eutectic. A surfactant, sodium dodecyl sulfate (SDS) was utilized to obtain homogeneous dispersion of CNT into the eutectic. Four different concentrations (0.1, 0.5, 1, and 5 wt.%) of CNT were employed to explore the specific heat capacity enhancement of the nanomaterials as the concentrations of the nanotubes varies. In result, it was observed that the specific heat capacity was enhanced by doping with the nanotubes in both solid and liquid phase. Additionally, the enhancements in the specific heat capacity were increased with increase of the CNT concentration. In order to check the uniformity of dispersion of the nanotubes in the salt, scanning electron microscopy (SEM) images were obtained for pre-DSC and post-DSC samples. Finally, the specific heat capacity results measured in present study were compared with the theoretical prediction.

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.