Characteristics of the mixed convection heat transfer of molten salts in horizontal square tubes

• Published in: Solar energy 2017-05, Vol.147, p.248-256
• Main Authors: Chen, Xia, Wang, Chao, Wu, Yuting, Liu, Bin, Ma, Chongfang
• Format: Article
• Language: English
• Subjects: Accuracy; Buoyancy; Computational fluid dynamics; Computer simulation; Convection; Convection heating; Correlation analysis; Flow velocity; Fluid flow; Forced convection; Heat transfer; Magnetism; Mass flow rate; Mixed convection; Molten salt; Molten salts; Nusselt number; Reynolds number; Salts; Side heating; Solar energy; Square tube; Tubes
• ISSN: 0038-092X; 1471-1257
• DOI: 10.1016/j.solener.2017.03.031

•Mixed convection heat transfer of molten salt is experimentally studied.•A good agreement has been reached between experiment and previous numerical results.•Numerical simulation of two sides heating for molten salt have been carried out.•Vortexes caused by buoyancy effect changes the shape of mainstream core area.•Vortexes generated in mixed convection process intensifies the heat transfer effect. Molten salt is an important working fluid in the field of solar energy. However, the mixed convection heat transfer of molten salts has not been investigated. In this study, the performance of the mixed convection heat transfer of molten salt in horizontal square tubes under different side heating conditions is experimentally and numerically examined. The bottom side heating is experimentally studied, and a correlation is fitted on the basis of the experimental data. A good agreement between the correlations and the experimental data is achieved. The experimental results show that the mass flow rate of molten salt and the Reynolds number (Re) increase with the increase in the pump frequency. Moreover, the Nusselt number (Nu) increases with the increase in Re. The maximum enhancement of Nu in the mixed convection heat transfer compared with the forced convection heat transfer is approximately 50%. The experimental results and previous simulation results of the mixed convection heat transfer of molten salt with bottom surface heating are also compared. The comparison results also show a good agreement. The two-side heating condition (bottom and lateral side) is numerically examined. The simulation results of the two-side heating show that the vortexes caused by the buoyancy effect change the shape of the mainstream core area and strengthen the performance of heat transfer.