On the specific heat capacity of HITEC-salt nanocomposites for concentrated solar power applications

Abstract

High specific heat capacity or C_P of molten salt is crucial for concentrated solar power plants as it will enhance the energy density of thermal energy storage. It can be achieved by doping nanoparticles into molten salts. However, reported results show inconsistency in C_P enhancement (positive and negative). Since the results are based on Differential Scanning Calorimeter (DSC) measurements of small batches (<10 mg), the average C_P obtained from these results may not represent the bulk-C_P of the nanocomposite, which is an important parameter from an application viewpoint. Moreover, the methods of salt-nanoparticle composite production lack industrial scalability. In this work, we examined a potentially scalable method based on mechanical shear mixing. The molten-salt of choice was HITEC due to its lower melting point, while inexpensive alumina and silica nanoparticles were used as dopants. To compare and contrast variability in C_P enhancement, the sample selection was made by random sampling; DSC measurement was performed on small-sized batches (<10 mg), and the T-history method was applied on large-sized batches (20 g). While DSC tests indicated a mean decrease in C_P for alumina (−43%) and an increase in C_P for silica nanocomposite (+15%), T-history tests indicated a mean decrement in the bulk-C_P for both alumina (−49%) and silica nanocomposites (−3%). This anomalous behavior in C_P values was further compared using a nonparametric statistical test, the Mann–Whitney U test, which revealed that the C_P of small-sized batches is statistically different from that of large-sized batches. Given their industrial scale of usage, the C_P of the nanocomposite must be measured using both DSC and T-history methods to ascertain the effect of nanoparticles.