Convective heat transfer in the laminar-turbulent transition region of molten salt in annular passage

Convective heat transfer in the laminar-turbulent transition region of molten salt in annular passage was experimentally investigated within the range of Reynolds number 4000-10,000 and fluid temperature 250-400 °C. The results showed that Nusselt number of molten salt flow in annular passage was remarkably larger than that of circular tube, and it increased with Reynolds number and Prandtl number. The modified Gnielinski correlation with annular configuration effect was proposed, and it fit with the experimental data with nonuniform probability deviations less than 14.3%. By considering the cooling process with large heat transfer temperature difference, a developed heat transfer correlation was established by optimizing the exponents of Prandtl number ratio and Reynolds number, and it had very good agreements with experimental data with uniform probability deviations less than 10.2%. In the developed heat transfer correlation, the exponent of Reynolds number was very close to that in Gnielinski correlation, while the exponent of Prandtl number ratio was remarkably larger than that for the heating process.