A time variant investigation on optical properties of water based Al₂O₃ nanofluid

Optical properties of nanofluids are vital for calculating performance of a Direct Absorption Solar Collector (DASC). Characteristics of nanofluids are not constant; they vary with time and growth of nanoparticles. For current investigation, nanofluidswere prepared to obtain considerable stability. Stability ratio of our nanofluidswas 100 times larger than the threshold limit. Here,we have investigated aggregation process and its effect on optical characteristics of the nanofluids using Transmission Electron Microscopy (TEM) imaging, Dynamic Light Scattering (DLS) approach and UV-visible spectroscopy. Steps of aggregation are broadly described with TEM images. Our results indicate that extinction coefficients of the nanofluids reduce rapidly with time within visible to near IR region. Quasi Crystalline (QC) and Rayleigh Approaches were used to compare the experimental behavior of optical properties of nanofluids. It was found that both of these approaches areweak to predict the optical behavior, especially atUVregion and scattering of light is found responsible for high extinctionwith the experimental results. More experimental effort is still required to get an appropriate explanation.