Direct Numerical Simulation of Turbulent Heat Transfer Modulation in Micro-Dispersed Channel Flow

The object of this paper is to study the influence of dispersed micrometer size particles on turbulent heat transfer mechanisms in wall-bounded flows. The strategic target of the current research is to set up a methodology to size and design new-concept heat transfer fluids with properties given by those of the base fluid modulated by the presence of dynamically-interacting, suitably-chosen, discrete micro- and nano- particles. We run Direct Numerical Simulation (DNS) for hydrodynamically fully-developed, thermally-developing turbulent channel flow at shear Reynolds number Re=150 and Prandtl number Pr=3, and we tracked two large swarms of particles, characterized by different inertia and thermal inertia. Preliminary results on velocity and temperature statistics for both phases show that, with respect to single-phase flow, heat transfer fluxes at the walls increase by roughly 2% when the flow is laden with the smaller particles, which exhibit a rather persistent stability against non-homogeneous distribution and near-wall concentration. An opposite trend (slight heat transfer flux decrease) is observed when the larger particles are dispersed into the flow. These results are consistent with previous experimental findings and are discussed in the frame of the current research activities in the field. Future developments are also outlined.Comment: Pages: 305-32

MHD non-orthogonal stagnation point flow of a nanofluid towards a stretching surface in the presence of thermal radiation

This article investigates the theoretical study of steady stagnation point flow with heat transfer of a nanofluid towards a stretching surface. It is assumed that the fluid impinges on the wall obliquely. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. The basic partial differential equations are reduced to ordinary differential equations which are solved numerically using the fourth-order Runge–Kutta method. Numerical results are obtained for distributions of velocity, temperature and concentration, as well as, for the local Nusselt number and local Sherwood number for several values of governing parameters. The results indicate that the local Nusselt number decreases with an increase in both Brownian motion parameter Nb and thermophoresis parameter Nt. However, the local Sherwood number increases with an increase in both thermophoresis parameter Nb and radiation effect R, but it decreases as the values of Nt increase. Keywords: Nanofluid, MHD stagnation flow, Stretching sheet, Thermal radiation effects, Heat and mass transfe