Numerical investigation on the impact of geometric complexity on radiative properties of nanofluid in photothermal conversion

Radiative properties of medium are crucial for direct solar energy-driven photothermal applications, which necessitates development of high-performance nanofluids (NFs) by adding nanoparticles (NPs) to enhance energy efficiency. Sicne the shape and size of NPs have major impacts on the scattering and absorption behaviors of the NFs medium, the objective of this study is to perform numerical investigation on the impact of geometric complexity of TiN NPs on radiative properties of NFs with localized surface plasmon resonance effects and photothermal conversion efficiency. The results showed that the cubic NPs had broader absorption bands and higher resonance peaks compared with other shapes, leading to improved solar absorption and photothermal conversion, indicated by solar-weighted absorption coefficient (SWAC) of 41.3%. The response of macroscopic medium to thermal radiation extinction was revealed by analyzing the scattering behavior of microscopic NPs at specific wavelengths. For NPs with the same feature size and shape factor, differences in shape led to variation of SWAC by up to 37.4%, while for NPs with the same shape factor and effective radius, the SWAC was changed by only 2.9%. This study offers new insights into normalizing evaluation of photothermal performance based on shape factors and effective radii of NPs, which has important implications for improving photothermal conversion efficiency by optimizing geometric parameters of NPs and NFs medium in practical applications.