Experimental investigation of heat transfer performance of molten HITEC salt flow with alumina nanoparticles

This study explores the effect of nanoparticle concentration on the laminar convective heat transfer performance of a molten nano-HITEC fluid in a mini circular tube. An innovative piston molten salt apparatus and a preparation process of molten HITEC nanofluid were developed to prevent the precipitation of nanoparticles during the measuring process. The results in this study demonstrate that the measurement of the mean Nusselt number of the pure HITEC fluid is in good agreement (within ±10%) with that published in the literature available. A concentration of nanoparticles of 0.25 wt.% in the nano-HITEC fluid, which maintains uniform dispersion for approximately 30 min, results in the maximum enhancement of the mean Nusselt number, i.e., 11.6%. A concentration of 0.063 wt.%, which is the concentration resulting in the maximum enhancement of the specific heat in our previous study (Ho and Pan, 2014), results in a 9.2% increase in the mean Nusselt number of HITEC nanofluid, and the precipitation phenomenon was not observed within an hour. In addition, a new correlation considering particle concentration for the laminar convective heat transfer performance of the nano-HITEC fluid is developed in this study, by which more than 93.9% of the experimental data can be predicted within ±10% of deviation. In conclusion, the HITEC fluid with concentration of alumina nanoparticles of up to 0.25 wt.% have all shown an increase in the heat transfer performance, and based on the previous investigation (Ho and Pan, 2014), also revealed positive effect on the specific heat capacity. Therefore, it may be an excellent working fluid for applications of thermal storage system in a concentrating solar thermal power system.