Solar radiation absorption of nanofluids containing metallic nanoellipsoids

Metallic nanoparticles (NP) are promising materials for solar radiation absorption due to the plasmon resonance absorption band in the visible and near IR spectrum that can be tuned modifying the NP shape. Linear optical absorption in the visible and near IR spectral region of aqueous nanofluids containing gold and silver nanoellipsoids (NEs) were studied using the Maxwell-Garnett model, and the solar weighted absorption coefficient was calculated for different concentrations, aspect ratios and NE sizes. The results show an enhance of the solar weighted absorption coefficient in almost 54% and 86% for gold and silver NEs, respectively, when compared to spherical NP of the same materials. Moreover, for a nanofluid-based direct absorption collector with 1 cm thickness, and a nanofluid of gold NEs with a low volume fraction, small NPs (2.5 nm), a high aspect ratio (AR = 4), it is possible to obtain a solar weighted absorption coefficient closer to the ideal solar radiation absorber condition.