Numerical and experimental study on heat transfer and flow features of representative molten salts for energy applications in turbulent tube flow

This article investigated the heat transfer performance and flow friction of molten salts in turbulent tube flow, where four salts including Hitec, Solar Salt, NaF-NaBF4, and FLiNaK were studied. A computational model was developed to analyze the flow and heat transfer features of the salts in the tube, and experiments were conducted to test the heat transfer performance of a representative salt Hitec in the tubes of a salt-oil heat exchanger. Comparison of simulation results with the experimental data shows that the average errors are smaller than +/- 4%, which validates the simulation model. Based on the model, firstly the influences of heat flux uniformity at the tube outer wall were examined. The results show that the non-uniform wall flux can lead to local high-temperature region but influences little on the flow friction coefficient and the heat transfer performance. Then, the model was utilized to investigate the friction and heat transfer features of the salts under broad ranges of the temperature and the velocity. Comparisons of the simulated heat transfer results with Hansen's, Sider-Tate's and Gnielinski's correlations show that the largest errors can reach +25%, +13% and -15%, respectively. Furthermore, the errors between the simulated friction coefficients and the Filonenko's correlation are smaller than +/- 2%, which indicates that this correlation is suitable for predicting the friction of the salts. Finally, to predict the heat transfer performance more accurately for these representative salts, a new correlation was developed. It was found that the errors between all simulation results and the proposed correlation are smaller than +/- 5%, while the corresponding values for 80% experiment data of three salts are also lower than +/- 5%. The current study can offer beneficial results and correlation for the applications of molten salts in energy systems. (C) 2019 Elsevier Ltd. All rights reserved.