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

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.