An experimental investigation on the solar-thermal energy conversion performance of Fe2O3 nanofluid with the focus on nanoparticles shape and concentration

Today, the application of nanoparticles with controlled morphologies in solar energy conversion and storage systems is highlighted. This study focused on the assessment of Fe2O3 water-based nanofluids in volumetric solar absorbers and compared the performance of three shapes (blade, spherical, and octahedral), and three concentrations of nanoparticles (0.005, 0.01, and 0.02 vol%). First, a set of homogeneous nanofluids were prepared using a probe ultrasonic apparatus and by adding an anionic surfactant. In addition to long-time stability and narrow particles size distribution, obtained nanofluids presented a considerable light absorption capability in the visible region. It was seen that the light absorption spectrum was broadened with increasing the nanofluid concentration. Moreover, for each concentration, the blade nanoparticles improved the extinction coefficient and the solar-weighted absorption fraction relatively higher than the other shapes. For example, at a concentration of 0.02 vol% and penetration distance of 1 cm, the blade-nanofluid absorbed 96.2% of incident solar energy, which was higher than the spherical nanofluid with 93.5% and octahedral nanofluid with 87.2%. The results of thermal tests conducted in a set of bath direct solar collectors showed that the highest solar-thermal conversion efficiency after 1 hour of light exposure was related to 0.02% blade-nanofluid (82%). In these conditions, the growth of bulk temperature was observed 2.31 times higher than pure water.