Effective thermal conductivity and thermal diffusivity of nanofluids containing spherical and cylindrical nanoparticles

The effective thermal conductivity and thermal diffusivity of Au/toluene, Al2O3/water, TiO2/water, CuO/water and CNT/water nanofluids have been measured by using the transient short-hot-wire technique. The average diameters of An, Al2O3, TiO2 and CuO spherical particles are 1.65, 20, 40 and 33 urn, respectively. The average length and diameter of CNFs are 10 mu m and 150 nm, respectively. The uncertainty of the present measurements is estimated to be within 1% for the thermal conductivity and 5% for the thermal diffusivity. The measured results demonstrate that the effective thermal conductivities of the nanofluids show no anomalous enhancements and can be predicted accurately by the model equation of Hamilton and Crosser for the spherical nanoparticles, and by the unit-cell model equation of Yamada and Ota for carbon nanofibers. (c) 2006 Elsevier Inc. All rights reserved.