Experimental Investigation of Coupling Effects between Particle Size and Temperature on the Thermal Conductivity of Alumina Nanofluids

This study investigates the effects of nanoparticle size and temperature on the thermal conductivity enhancement ofwater-based alumina (Al 2 O 3 ) nanofluids, using the centrifuging method and relative centrifugal forces of differing magni-tude to produce nanofluids of three different particles without involving any dispersants or surfactants. We determined thecoupling dependency in thermal conductivity enhancement relative to nanoparticle size and temperature of the aluminananofluids and also experimentally showed that the effect of temperature on thermal conductivity is strongly dependenton nanoparticle size. Also, our experimental data presented that the effective medium theory models such as the Maxwellmodel and Hasselman and Johnson model are not sufficient to explain the thermal conductivity of nanofluids since theycannot account for the temperature- and size-dependent nature of water-based alumina nanofluids. Nomenclature a K : Kapitza radius [m]a p : Radius of particle [m]d : Mean particle diameter [m]d