Direct numerical simulation of turbulent heat transfer modulation in micro-dispersed channel flow

Summary The objective 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 ran direct numerical simulations for hydrodynamically fully developed, thermally developing turbulent channel flow at shear Reynolds number Re _τ = 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. Dedicated to Professor Franz Ziegler on the occasion of his 70th birthday It is our great pleasure to take part in this Festschrift Issue dedicated to the celebration of the 70th birthday of Professor Franz Ziegler. To honour his activity and his scientific achievements, we prepared this paper, crafted with friendship and respect. We wish Franz many more productive, enjoyable and happy years and a solid and long collaboration as Editors of Acta Mechanica.