Thermal efficiency of flat plate solar collector with TiO₂-based nanofluid: synergistic effect of size and facet orientation

Abstract A solar collector is an important device for collecting and converting solar energy into thermal energy. It can be synchronized to work in combination with different power sources to provide stable and continuous power. In this study, TiO 2 nanoparticles (NPs) with control on the size and the exposed facet orientation were prepared through a fluorine-free solvothermal synthesis process. The as-synthesized nanoparticles were analyzed using XRD and TEM techniques. The effect of size (about 6 and 17 nm) and facet orientation ([001] and [101]) for TiO 2 NPs as nanofluid on the performance of the solar collector was investigated experimentally. In the experimental solar collector setup, the highest absorption efficiency was 71.75% for TiO 2 NPs with the mixed effects of size and facet orientation, whereas the absorption efficiency was 71.37% for commercially available P25 NPs. Most importantly, the combination of the size and facet orientation effect led to a positive synergy effect. The obtained results represent that the performance of the solar collector was severely affected by the size and facet orientation of the NPs.