Flow and mixed convection heat transfer of Hitec salt in multi-sided heating pipes

Abstract Molten salt is one of the most commonly used heat storage working fluids in solar thermal power. However, its heat transfer coefficient is low. Optimizing the heat transfer condition could improve the heat transfer performance of molten salts, thereby facilitating convection that enhances heat transfer. In trough and tower solar thermal power generation systems, the heating surface of the molten salt collector tube differs with the different angles of sunlight heating. Numerical simulations on the characteristics of the flow and mixed convection heat transfer of Hitec salt in one-, two-, and three-sided heating conditions in pipes were carried out in this study. The results of mixed convection and heat transfer of molten salt on different multisided heating surfaces showed that the heat accumulated at the heating surfaces and then transferred to the mainstream core region. Under nonuniform heating conditions, the buoyancy effect generated a vortex, which changed the shape of the core area of the mainstream and resulted in the enhancement of the heat transfer ability. Double side heating showed the strongest buoyancy effect. The degree of heat accumulation under three-sided heating was the lowest, and the nonuniformity of the heat transfer process in one-sided heating was the highest.