Abstract:
Nanofluids, as new heat transfer fluids, are at the center of attention of researchers, while their measured thermal conductivities
are more than for conventional heat transfer fluids. Unfortunately, conventional theoretical and empirical models cannot
explain the enhancement of the thermal conductivity of nanofluids. Therefore, it is important to understand the fundamental
mechanisms as well as the important parameters that influence the heat transfer in nanofluids. Nanofluids’ thermal conductivity
enhancement consists of four major mechanisms: Brownian motion of the nanoparticle, nanolayer, clustering, and the
nature of heat transport in the nanoparticles. Important factors that affect the thermal conductivity modeling of nanofluids
are particle volume fraction, temperature, particles size, pH, and the size and property of nanolayer. In this paper, each
mechanism is explained and proposed models are critically reviewed. It is concluded that there is a lack of a reliable hybrid
model that includes all mechanisms and influenced parameters for thermal conductivity of nanofluids. Furthermore, more
work needs to be conducted on the nature of heat transfer in nanofluids. A reliable database and experimental data are also
needed on the properties of nanoparticles.
