Effects of Temperature and Particle Size on the Thermal Property Measurements of Al₂O₃−Water Nanofluids

An experimental investigation was conducted on the effective thermal conductivity and viscosity of Al 2 O 3 water-based nanofluids. The thermal conductivity was determined using the transient hot wire (THW) method. The results show that the thermal conductivity of Al 2 O 3 nanofluids increases with increasing nanoparticle concentrations in a distinct linear trend. Adding (1 to 5) % of Al 2 O 3 nanoparticles to water increases the effective thermal conductivity of Al 2 O 3 nanofluids by (6 to 20) % at room temperature. There is a substantial increase in the enhancement of thermal conductivity as temperature increases. At 55 °C, this value increases to around 16 %. The thermal conductivity enhancement decreases from (30 to 10) % while the particle size increases from (10 to 35) nm, but enhancement increases when the particle size is above 35 nm. The increase in thermal conductivity is 27.5 % for a particle size of 150 nm. In the viscosity measurements, the effective viscosity increases up to 60 % as the volume concentration increases from 1 % to 5 % at 25 °C. As the temperature increases, the viscosity of Al 2 O 3 nanofluids decreases exponentially. Experimental results also indicate that the viscosity of nanofluids is much higher when the nanoparticle size is smaller.