Convective heat transfer of high temperature molten salt in a vertical annular duct with cooled wall

• Convective heat transfer of molten salt in a vertical annular duct was measured.
• Nusselt number of molten salt in annular duct was higher than that of circular tube.
• Heat transfer correlations for transition and turbulent convection were proposed.
• The correlation included the effects of duct structure and temperature difference.
• The proposed correlations fit with experimental data and classical correlations.

Convective heat transfer performances of high temperature molten salt in a vertical annular duct with cooled wall were experimentally investigated within the range of Reynolds number 3000–16,000, Prandtl number 4.8–7.6, and fluid temperature 300–400 °C, respectively. The results showed that Nusselt number of molten salt flow in annular duct was remarkably higher than that of circular tube, and it increased with Reynolds number and Prandtl number. Because of variable thermal properties and annular configuration, the heat transfer correlation for fully developed turbulent flow was proposed based on Wiegand correlation and Sieder–Tate correlation, while the heat transfer correlation for transition flow was established by Gnielinski equation and Wiegand equation. Based on the experimental data, the modified heat transfer correlations for molten salt flow in annular duct were developed by least-squares method, and the modified correlations for transition and turbulent flow had good agreement with experimental data.