Experimental studies on entrainment characteristics of alumina-water nanofluids

Abstract

This thesis presents experimental investigation on the preparation and thermo-physical properties of Al2O3-water nanofluid. In addition, the entrainment characteristics of Al2O3-water nanofluids in a vertical tube have been studied experimentally. Applications of Al2O3-water nanofluid along with its advantages and disadvantages are also discussed. Entrainment in two-phase passive heat transfer devices is also discussed along with their application using nanofluid as working fluid. Nanofluids are solid-liquid composite materials consisting of solid nanoparticles with sizes typically of 1 to 100 nm suspended in a liquid (base fluid). In this work, alumina nanoparticles of 40-50 nm diameters were suspended in distilled water by two step method to prepare a stable Al2O3-water nanofluid. The volume concentration of Al2O3 nanoparticles has been varied between 0.01%, 0.05% and 0.1% vol. to study its thermo-physical properties. The prepared Al2O3-water nanofluids were stable over a period of three weeks without using any surfactant. Results showed that the density and viscosity of nanofluids decrease on increasing the temperature and increase on increasing the particle concentration. The thermal conductivity of nanofluids was found to increase with increasing the particle concentration as well as temperature. Entrainment of nanoparticles into the vapour phase has been experimentally studied in a vertical pipe using Al2O3-water nanofluids of different concentrations at different temperatures. In comparison with pure water, nanofluid resulted in severe entrainment due to the foaming action of the nanoparticles. The degree of entrainment increased with increasing the particle concentration as well as temperature.