Experimental Investigation Of Molten Salt (LiNO₃) Forced Convection Heat Transfer In Horizontal Tubes

Solar thermal power generation technologies are the most possible to compete with fossil fuels in economy as wind power and hydrodynamic power,and is considered to be one of the most promising candidates for providing a major share of the clean and renewable energy needed in the future. The appropriate heat transfer fluid and storage medium is a key technological issue for the future success of solar thermal technologies. Molten salt is one of the best heat transfer and thermal storage fluid for both parabolic trough and tower solar thermal power system. It is very important that molten salt heat transfer mechanisms are understood and can be predicted with accuracy. But the study on molten salts heat transfer is rarely.To better understand the heat transfer mechanisms of molten salts, we built a high temperature molten salt circular system. Many difficult engineer aspects such as preheating, heat preservation, freeze/thaw, thermal cycling and shock, and molten-salt pump cooling were considered in the design and construction of the experimental system. We first choose molten salt LiNO3 in the system, because the heat transfer mechanisms of LiNO3 is similar to mixed molten salt, and some of basic thermo physical properties of LiNO3 is known. The experimental results of molten salt LiNO3 turbulent flow in a horizontal tube was introduced and analysis in this paper. The average forced convective heat transfer coefficients of molten salt(LiNO3) in turbulent flows was measured and calculated through the method of adjusting the molten salt flow rate and keeping the oil flow rate constant. Then the overall heat transfer coefficients of our molten salt-oil exchanger under difference flow rate conditions were obtained, and we analyzed these experimental data in three methods, Wilson plot, the least square method and the optimized method. Finally, the Nusselt number equation under our experimental conditions was given.Molten salt is the important representative to the middle Prandtl number fluid. Our study will lay a foundation for grasping the heat transfer mechanisms of middle Prandtl number fluid. It also gave some reference for designing the heat transfer and storage system of solar thermal power generation.