Two-level synergistic scatterings from porosity and particle aggregation in Cu nanofluids for the enhancement of solar thermal conversion

Abstract Nanofluids are considered as an important substance for solar heat collection due to the excellent photothermal conversion properties. The porosity and aggregation of nanoparticles are significant factors to photothermal conversion property, but the aggregation of porous nanoparticles and aggregates configuration have not been carefully studied. In this paper, the comprehensive influence of porosity and aggregation configurations to nanoparticles photothermal conversion ability is studied by finite-different time-domain method. It is found that the pores and aggregation can significantly improve the light absorption capacity of copper nanoparticles. Specifically, the absorption cross section of nanoparticle with 55% porosity increases by 25%, and absorption cross section of straight chain configuration is about 6.9 × 103 nm2 which is 8.78 times than non-aggregated particles. Furthermore, a synergistic effect of porosity and aggregation is found, i.e. porous aggregated nanoparticles have higher absorption cross section. For example, the increasement of porous straight chain configuration becomes 10 times. The calculated electric field distribution indicates that the enhancement of absorption efficiency comes from the multiple scattering at the particle and pore surfaces. This research is expected to give a new design direction of high photothermal efficiency of nanofluids.