Thermal Conductivity Affected by Temperature and Particle Size in Al2O3-Water Nanofluids

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The effective thermal conductivity of Al2O3-water nanofluids has been measured using a transient hot wire method. Experimental results demonstrate that the thermal conductivity of Al2O3 nanofluids increases linearly with increasing nanoparticle concentration. Adding 5 vol % of Al2O3 nanoparticles in water increases the effective thermal conductivity of the nanofluids by 20%. Thermal conductivity of Al2O3 nanofluids increases with an increase of temperature. The enhancement is around 1.7% at 15 °C in comparison with around 16% at 55 °C in a 1 vol % nanofluid. The particle size is another important parameter for the effective thermal conductivity. The increase of thermal conductivity reduces from 30% to 10% as the particle sizes increase from 10 nm to 35 nm. The increase of the effective thermal conductivity starts as the particle size increases above 35 nm, reaching about 27.5% in the nanofluid with the particle size at 150 nm.