The aimof the present experimental investigation is to study the impact of duration of various stages of nanofluid preparation on its thermal conductivity. The considered nanofluid is the Al2O3/liquid paraffin. Oleic acid is used to ensure proper stability of prepared nanofluid samples. The nanofluid is prepared using a two-step method. The influences of duration of magnetic stirring and the sonication time on the thermal conductivity of nanofluid at different nanoadditive concentrations and temperatures are evaluated. It was found that the optimal sonication time is 3 h and 15min, and a further intensification in this time breaks the bond between the nanoadditives and the surfactant, resulting in a less thermal conductivity. Moreover, the outcomes indicated that the proper duration for magnetic stirring in the first and second stages are 20 and 40min, respectively.
