Viscosity of magnetite–toluene nanofluids: Dependence on temperature and nanoparticle concentration

•Viscosity of magnetite in toluene nanofluid increases monotonically with particle concentration.•Clusters formed at higher particle concentration are monodisperse.•With increasing temperature, viscosity decreases due less fraction of immobile fluid molecules.

We examine the dependence of the viscosity of nanofluids, comprised of magnetite nanoparticles dispersed in toluene, on particle concentration and temperature. The nanofluid viscosity increases monotonically with particle concentration. We show that although the nanoparticles aggregate to form clusters with increasing concentration, the cluster size is fairly monodisperse and hence the viscosity can be expressed as a function of only the particle concentration. The viscosity of the nanofluid is found to decrease with temperature, similarly to the characteristics of the carrier liquid. We describe these dependencies through an empirical correlation, since the observations are useful to employ such nanofluids in engineering applications.