Enhanced thermal conductivity of TiO2—water based nanofluids

Nanofluids are prepared by dispersing TiO2 nanoparticles in rod-shapes of ∅10nm×40nm (diameter by length) and in spherical shapes of ∅15 nm in deionized water. A transient hot-wire apparatus with an integrated correlation model is used to measure the thermal conductivities of these nanofluids more conveniently. The pH value and viscosity of the nanofluids are also characterized. The experimental results show that the thermal conductivity increases with an increase of particle volume fraction. The particle size and shape also have effects on this enhancement of thermal conductivity. For TiO2 particles of ∅10nm×40nm and ∅15 nm dimensions with maximum 5% volume fraction, the enhancement is observed to be nearly 33% and close to 30%, respectively over the base fluid. For 5% volumetric loading of rod-shape TiO2 nanoparticles of ∅10nm×40nm in deionized water, this enhancement is found to be 12% higher than that predicted by the Hamilton–Crosser model [I & EC Fundamentals 1 (1962) 187]. However, with the same volumetric loading, the maximum enhancement is determined to be about 16% higher than that predicted by the Bruggeman model [Y. Ding, D. Wen, R.A. Williams, in: Proceedings of 6th International Symposium on Heat Transfer, Beijing, 2004, pp. 66–76] for TiO2 nanoparticles of ∅15 nm in the same base fluid of deionized water. The measurement error is estimated to be within 2%.