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

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.