Numerical Studies on Thermally Induced Flow of Nanofluid in a Vertical Annulus

A numerical investigation of the thermally induced flow of nanofluid (Al2O3 + water) inside a vertical annulus has presently been carried out. The simulations are carried for various nanoparticle concentrations at a constant heat flux of 3 kW/m2 using computational fluid dynamics (CFD) solver ANSYS Fluent. Two viscosity models namely Brinkman and Buongiorno and thermal conductivity model of Maxwell’s are adopted to estimate heat transfer rates. Uncertainty in the results of heat transfer due to the adoption of two different formulae of viscosity is discussed in detail. The average heat transfer coefficient estimated on the basis of both viscosity models increases with nanoparticle concentration. Nanoparticle concentration has a much more pronounced effect on heat transfer coefficient when estimated on the basis of the Brinkman model. The heat transfer coefficient is found to enhance by 10.86% when estimated using the Brinkman viscosity model while it is only just 3.91% in the case of Buongiorno viscosity model-based nanofluids.