  Several new mechanisms have been hypothesized in the recent years to
characterize the thermal conduction behavior in nanofluids. In this paper, we
show that a large set of nanofluid thermal conductivity data is enveloped by
the well-known Hashin and Shtrikman (HS) mean-field bounds for inhomogeneous
systems. The thermal conductivity in nanofluids, therefore, is largely
dependent on whether the nanoparticles stays dispersed in the base fluid, form
linear chain-like configurations, or assume an intermediate configuration. The
experimental data, which is strikingly analogous to those in most solid
composites and liquid mixtures, provides a strong evidence for the classical
nature of thermal conduction in nanofluids.
