Do temperature and nanoparticle size affect the thermal conductivity of alumina nanofluids?

This study investigates the effects of nanoparticle size and temperature on the thermal conductivity enhancement of water-based alumina (Al2O3) nanofluids, using the centrifuging method and relative centrifugal forces of differing magnitude to produce nanofluids of three different particles without dispersants and surfactants. We determined the coupling dependency in heat conduction enhancement relative to nanoparticle size and temperature of the alumina nanofluids and also experimentally showed that the effect of temperature on thermal conductivity is strongly dependent on nanoparticle size. Also, our experimental data presented that the effective medium theory models such as the Hashin and Shtrikman bounds are not sufficient to explain the thermal conductivity of nanofluids because they cannot account for the temperature-and size-dependent nature of water-based alumina nanofluids. (C) 2014 AIP Publishing LLC.