Free Convection Flow and Heat Transfer of Nanofluids of Different Shapes of Nano-Sized Particles over a Vertical Plate at Low and High Prandtl Numbers

In this paper, free convection flow and heat transfer of nanofluids of differently-shaped nano-sized particles over a vertical plate at very low and high Prandtl numbers are analyzed.  The governing systems of nonlinear partial differential equations of the flow and heat transfer processes are converted to systems of nonlinear ordinary differential equation through similarity transformations. The resulting systems of fully-coupled nonlinear ordinary differential equations are solved using a differential transformation method - Padé approximant technique. The accuracy of the developed approximate analytical methods is verified by comparing the results of the differential transformation method - Padé approximant technique with those of previous works as presented in the literature. Thereafter, the analytical solutions are used to investigate the effects of the Prandtl number, the nanoparticles volume-fraction, the shape and the type on the flow and heat transfer behaviour of various nanofluids over the flat plate. It is observed that as the Prandtl number and volume-fraction of the nanoparticles in the basefluid increase, the velocity of the nanofluid decreases while the temperature increases.  Also, the maximum decrease in velocity and the maximum increase in temperature are recorded in lamina-shaped nanoparticles, followed by platelets, cylinders, bricks, and sphere-shaped nanoparticles, respectively. Using a common basefluid for all nanoparticle types, it is established that the maximum decrease in velocity and the maximum increase in temperature are recorded in TiO2 followed by CuO, Al2O3 and SWCNTs nanoparticles, respectively. It is hoped that the present study will enhance the understanding of free convection boundary-layer problems as applied in various industrial, biological and engineering processes.

Keywords:

Free convection , Boundary layer , Prandtl number , Nanofluid , differential transformation method , Padé-approximant technique