Hydrodynamic studies on glycol based Al2O3 nanofluid flowing through straight tubes and coils

Laminar flow hydrodynamic characteristics of alumina based nanofluids (0-2.5 vol.%) flowing through straight tubes and helical coils with different combinations of curvature and pitch ratio have been studied. Two types of glycol-water based mixtures, ethylene glycol/water (EG/W) and propylene glycol/water (PG/W) in 60:40 wt ratio, were used as the base fluids. The friction factor of nanofluids was found to be higher than that of the base fluids for both the straight tube as well as helical coil geometry, which further increased with increase in nanoparticle volume concentration. At the same Reynolds number, friction factor increased with nanoparticle concentration in the base fluid, which could be due to the presence of Brownian motion and increased collision rate of nanoparticles. Two new correlations to predict the friction factor for the laminar flow of alumina nanofluids through straight tubes and helical coils have been proposed.