Transport properties of alumina nanofluids

Recent studies have showed that nanofluids have significantly greater thermal conductivity compared to their base fluids. Large surface area to volume ratio and certain effects of Brownian motion of nanoparticles are believed to be the main factors for the significant increase in the thermal conductivity of nanofluids. In this thesis, all the three transport properties, namely, thermal conductivity, electrical conductivity and viscosity were studied for Alumina nanofluid (Aluminum oxide nanoparticles in water). Experiments were performed both as a function of volumetric concentration (3 - 8%) and temperature (2°C - 50°C). Alumina nanoparticles with a mean diameter of 36 nm were dispersed in water. Transient hot wire method as described by Nagaska and Nagashima for electrically conducting fluids was used to test the thermal conductivity. In this work, an insulated platinum wire of 0.003 inches diameter was used as the hot wire for the thermal conductivity experiments. Initial calibration was performed using de-ionized water and the resulting data was within 2.5% of standard thermal conductivity values for water. The thermal conductivity of alumina nanofluid increased with both increase in temperature and concentration. A maximum thermal conductivity of 0.7351 W/mK was recorded for an 8.47% volume concentration of alumina nanoparticles at 46.6 °C, the effective thermal conductivity at this concentration and temperature was observed to be 1.1501, which translates to an increase in thermal conductivity by 22% when compared to water at room temperature. Alumina being a good conductor of electricity, alumina nanofluid displays an increasing trend in electrical conductivity as volumetric concentration increases. A microprocessor based conductivity/TDS meter was used to perform the electrical conductivity experiments. After carefully calibrating the conductivity meters glass probe with platinum tip, using a standard potassium chloride solution, readings were taken at various volumetric concentrations. A 3457.1% increase in the electrical conductivity was measured for a meager 1.44% volumetric concentration of alumina nanoparticles in water. The highest value of electrical conductivity: 314 μS/cm was recorded for a volumetric concentration of 8.47%. For measuring the kinematic viscosity of alumina nanofluid, a standard kinematic viscometer with constant temperature bath was used. Calibrated capillary viscometers were used to measure flow under gravity at precisely controlled temperatures. The capillary viscometers were calibrated with de-ionized water at different temperatures, and the resulting kinematic viscosity values were found to be within 3% of the standard published values. An increase of 35.5% in the kinematic viscosity was observed for an 8.47% volumetric concentration of alumina nanoparticles in water. The maximum kinematic viscosity of alumina nanofluid: 2.90142 mm ²/s was obtained at 0 °C for an 8.47% volumetric concentration of alumina nanoparticles.