Thermal convection enhancement of laminar particle-laden flow in a square duct: Fully resolved numerical investigation

Due to the complex lateral and rotational motions of loaded particles in a base fluid, the effects accordingly on the heat transfer characteristics of the internal channel flow, especially with non-spherical particles, has not yet been described in detail in the literature. Many numerical approaches are simplified with macroscopic estimations or empirical coefficients for hydraulic forces and heat fluxes on particle surfaces. These approaches are not sufficient for a comprehensive understanding of the heat transport including the heat conduction inside the particles. Thus, a fully resolved scheme is needed. The method in this study is built on coupling Lattice-Boltzmann Method (LBM) for heat and mass transfer in fluid; Discrete Element Method (DEM) for particle motion updates; and Finite Element Method (FEM) for thermal conduction inside the particles. The results show that particles have a weak tendency toward the equilibrium position that lies about 0.3 times the duct width away from the center line. Meanwhile, the orientation of a single oblate spheroid particle in a simple shear flow has higher chances to stay parallel to shear gradient direction (log-rolling), but particles in internal duct flows are slightly likely to be perpendicular to the radial directions than parallel. The overall thermal convection enhancement of the particle-laden duct flow compared to the base fluid duct flow with respect to Nusselt number at Ref = 16 is almost twice as high as the effective thermal conductivity enhancement at stagnant state.