Heat transfer in water based nanofluids (TiO₂-H₂O, Al₂O₃-H₂O and Cu-H₂O) over a stretching cylinder

Two-dimensional steady natural convection heat transfer to water based nanofluids (TiO₂-water, Al₂Ol₂-water, and Cu-water) flowing over a stretching cylinder has been investigated numerically. Using the similarity transformations, the continuity, momentum, and energy equations are reduced to a set of nonlinear, ordinary differential equations. These equations are solved numerically using MATLAB. Because of the algebraic decay of the similarity functions, numerical integration is performed using a compressed coordinate. The axial velocity is the result of forced convection due to stretching, and natural convection induced by the heated cylinder. The results show that the flow velocity with a nanofluid is smaller compared with the velocity of the base fluid for the same stretching and heating conditions, which is basically caused by the increase of viscosity and density. The presence of nanoparticles reduces the thickness of the hydrodynamic boundary layer and enhances the heat transfer rate. The location of the zero shear stress on the surface of the cylinder occurs at shorter and shorter distances (along the cylinder) as the solid volume fraction of nanoparticles increases.