THERMAL AND HYDRODYNAMIC ANALYSIS OF NANOFLUID FLOW IN A CIRCULAR PIPE USING EULER-GRANULAR MIXTURE MODEL

Abstract

The current research work involves the study of thermo-hydrodynamic behavior of nanofluids in a circular pipe under constant heat flux conditions. The numerical work was carried out with water as the base fluid and Al<sub>2</sub>O<sub>3</sub>, CuO, and graphene as the nanoparticles using the Eulerian-granular multiphase model. By varying the nanoparticle volume fraction from 0 to 5%, pipe diameter from 5 to 20 mm, and inlet velocity from 10 to 25 m/s, it was observed that at higher nanoparticle volume fractions, thicker boundary layers with quick development of fully developed flow were achieved. The increment in nanoparticle volume fraction enhanced the Nusselt number, and with the use of graphene nanoparticles, the Nusselt number increased by about five times as compared to pure water. The particle motion within the fluid was dominated by the thermophoresis effect indicated by a lower wall temperature and was enhanced by a higher turbulent kinetic energy. Apart from the choice of base fluid, the choice of nanoparticles plays a significant role in determining the heat transfer performance. Graphene, with its superior thermophysical properties when dispersed in water, led to the lowest wall shear stress and highest effective thermal conductivity as a result of lowest effective viscosity as well as low pressure drop requirement and highest flow strain rate, followed by Al<sub>2</sub>O<sub>3</sub> and CuO, respectively, in that order.