Convective heat transfer of high temperature molten salt in transversely grooved tube

• Transversely grooved tube can evidently enhance heat transfer of molten salt.
• Nusselt number increased with grooved height and Reynolds number.
• Experimental correlation for molten salt heat convection was developed.
• Heat convection of molten salt will be worsening at very high temperature.
• Heat transfer worsening phenomena occurs with low heat transfer coefficient.

Convective heat transfer of high temperature molten salt in transversely grooved tube was experimentally investigated using electric power through the testing tube, and average (length-mean) Nusselt numbers were reported and correlated. Various experiments were respectively carried out within the range of inlet temperature 250–500 °C, and relative groove height 0, 0.038, 0.046 and 0.092. Experimental results showed that the transversely grooved tube can remarkably enhance molten salt heat transfer, and Nusselt number increased with the groove height and Reynolds number. Based on the experimental data and Sieder–Tate correlation, experimental correlation with groove height effect was developed by least-squares method, and it had a good agreement with experimental data. Because of high temperature instability of molten salt, heat transfer worsening phenomena of molten salt at very high temperature were found. As the temperature of molten salt adjacent to the wall was higher than the operating temperature, Nusselt number of molten salt in transversely grooved tube was remarkably less than the experimental correlation.