TO EVALUATE THE PERFORMANCE OF MOLTEN SALT COOLANTS IN PARABOLIC TROUGH COLLECTORS (PTCs)

Renewable energy sources such as solar, wind, hydro, and geothermal are potential energy sources with the capacity to mitigate environmental impacts. Parabolic trough collectors (PTCs) are the widely used application of solar energy. Molten salts are promising high-temperature, low-pressure coolants for thermal energy storage of concentrated solar power plants. The present novel work is aimed to develop a computational fluid dynamics (CFD) methodology for candidate molten salt coolants (FLiBe, Nafzirf, FliNaK, and NaNO<sub>3</sub>-NaNO<sub>2</sub>-KNO<sub>3</sub>) to compare their thermal hydraulic characteristics in terms of friction factor and Nusselt number distribution for a simple circular tube under turbulent flow conditions. This study is necessary for the thermal-hydraulic design of PTCs. The axial distributions of friction factor and Nusselt number of FliNaK, FLiBe, Nafzirf, and NaNO<sub>3</sub>-NaNO<sub>2</sub>-KNO<sub>3</sub> salts in a simple circular tube under Reynolds number range of 20,000-100,000 have been compared. The predicted friction factor f<sub>∞</sub>), Nusselt number (Nu<sub>∞</sub>), and hydrodynamic entrance length (L<sub>H</sub>) have been compared with available correlations for fully developed conditions. Blasius and Petukhov correlations adequately guessed the predicted f<sub>∞</sub> of salts, whereas the Gneilinski correlation is found to be in close agreement with the predicted Nu<sub>∞</sub> of salts, hence validating the proposed numerical scheme for investigating thermal-hydraulic characteristics of molten salts. NaNO<sub>3</sub>-NaNO<sub>2</sub>-KNO<sub>3</sub> seems to be the potential candidate with high values of thermal efficiency for solar applications.