An experimental system has been built to research the heat transfer characteristics of gas cooled molten salt heat exchangers. Based on the system, a prototype tube-and-shell gas cooled molten salt heat exchanger was experimentally investigated. A nitrate salt mixture (NaNO₃-KNO₃-NaNO₂) was chosen as the hot fluid in the tube side. Helium and air were chosen as the gas fluids in the shell side, respectively. A modified Wilson plot method was used to separate the heat coefficients in both sides. Convective heat transfer data of molten salt in tube bundles are obtained within the range of Re from 4138 to 11191 and Pr from 9.8 to 18.9. It is compared with two empirical correlations: Gnielinski’s Equation and Hausen’s Equation. Comparison of the heat transfer characteristics between air and helium in the shell side is also discussed. A detailed thermal resistance analysis inside the heat exchanger is made and the way to improve its thermal performance is clarified.

Conclusions

In the tube-and-shell gas cooled molten salt heat exchanger, convective heat transfer data of molten salt in the tube side has a max deviation of 15% compared with Hansen’s equation and 18% compared with Gnielinski’s Equation. It can be indicated that forced convection heat transfer characteristics of molten salt in tube bundles with a gas cooled condition can also be represented by the two empirical equations. Helium has the same heat transfer behavior as air, but it has better heat transfer performance when used as the coolant in the shell side. A detailed thermal resistance analysis inside the heat exchanger indicates that the shell-side thermal resistance is dominant. Reducing the shell-side thermal resistance is more efficient to improve the performance of a gas cooled molten salt heat exchanger.

The results have been published on Applied Thermal Engineering 108 (2016) 1429–1435.