Enhanced heat transfer by inertial particles in turbulent channel flow

We present results of direct numerical simulation of heat transfer in turbulent particle-laden channel flow. We show an enhancement of the heat transfer when heavy inertial particles with a high specific heat are added to the flow. The simulations employ a coupled Eulerian-Lagrangian computational model in which the momentum and energy transfer between the discrete particle - and the continuous fluid phase are fully taken into account. The effect of turbophoresis, resulting in an increased particle concentration near a solid wall due to the heterogeneity of the wall-normal velocity fluctuations, is held responsible for the increased heat transfer. As a result, the transport properties in the region near the walls differ from that in the bulk of the flow. To support the turbophoresis interpretation of the enhanced heat transfer, results of simulations employing no particle-fluid coupling and simulations with two-way coupling at considerably lower specific heat, or considerably lower particle concentration are also included. The combination of these simulations allows distinguishing contributions to the Nusselt number due to mean flow, turbulent fluctuations and explicit particle effects.