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 Al2O3 water-based nanofluids. The thermal conductivity was determined using the transient hot wire (THW) method. The results show that the thermal conductivity of Al2O3 nanofluids increases with increasing nanoparticle concentrations in a distinct linear trend. Adding (1 to 5) % of Al2O3 nanoparticles to water increases the effective thermal conductivity of Al2O3 nanofluids by (6 to 20) % at room temperature. There is a substantial increase in the enhancement of thermal conductivity as temperature increases. At 55 degrees 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 degrees C. As the temperature increases, the viscosity of Al2O3 nanofluids decreases exponentially. Experimental results also indicate that the viscosity of nanofluids is much higher when the nanoparticle size is smaller.