Stability, thermophysical properties and performance assessment of alumina–water nanofluid with emphasis on ultrasonication and storage period

Owing to the improvements in thermophysical properties, nanofluids are considered advantageous over pure fluids in heat transfer applications. However, these improvements may be regarded as meaningful for applications provided that optimum dispersion of nanoparticles is ensured throughout the process, which mostly depend on preparation technique. In this study, alumina (Al ₂ O ₃ )–water nanofluids of 0.5 vol% were prepared using ultrasonication (up to 5 h) and stored at stationary condition until 30 days. We have evaluated stability as temporal volume fraction by measuring density. Further, thermal conductivity and viscosity were measured, and heat transfer performance was analyzed for the case of fully developed laminar flow inside a tube. All the measurements were conducted at 25 °C temperature. Results revealed that longer ultrasonication reduces sedimentation of nanoparticles and hence, increases stability of nanofluids. Thermal conductivity increased, while viscosity decreased with increasing sonication time. Moreover, these thermophysical properties decreased with storage periods. It was observed, until 30 days of storage that ultrasonication process for different durations induced significant changes in viscosity, although those in thermal conductivity was not as pronounced. All the prepared samples were determined beneficial as heat transfer fluids over water, even after 30 days from preparation.