Synthesis and viscosity studies of novel ecofriendly ZnO-coconut oil nanofluid

Novel nanofluid of zinc oxide in coconut oil has been synthesized in various concentrations through ultrasonically assisted two step method. Structural and morphological studies of nanoparticles are made with the help of X-ray diffraction and Transmission Electron Microscope and it is found that the particles posses hexagonal structure with an average size of 26 nm. Viscosity of the nanofluid has been measured at various temperatures and shear rates from which the shear thinning behavior is observed in all the samples. The shear thinning is observed to be higher at low shear rates and also at high concentrations. Higher degree of shear thinning at low concentration range is attributed to the shear thinning nature of carrier liquid, but at higher concentration range there is a substantial contribution from particle - fluid interaction. The experimental viscosities of nanofluids are compared with the theoretical values obtained through Einstein, Batchelor and Wang models. A small deviation is observed which may arise due to the difference in the morphology, chemical composition and interactions. New empirical relations are proposed for predicting the viscosity of coconut oil based ZnO nanofluid at various temperatures and concentrations. (C) 2013 Elsevier Inc. All rights reserved.