Direct Numerical Simulation Of The Particles Sedimentation With Thermal Convection

Owing to the wide existence of the multiphase flows in natural and industrial processes, the research on the phenomenon, mechanism and process of the multiphase flows is of important significance. The Arbitrary Lagrangian-Eulerian (ALE) technique was used in the direct numerical simulation of the particles sedimentation with thermal convection in the parallel walls. The fluid motion is computed from the Navier-Stokes using the finite-element method. The particle was tracked according to the equations of motion of a rigid body under the action of gravity and hydrodynamic forces arising from the motion of the fluid, avoiding lots of experience and supposition of force enforced on particles. Three situations that are particle sedimentation without thermal convection, sedimentation with thermal convection in hot or cold fluid are studied using the direct numerical simulation method. The numerical results show that the thermal convection and wall effect which control the particles motion and interaction. A single isothermal particle experiences different regimes of motion with the sedimentation Reynolds number increasing: steady motion with and without overshoot; weak, strong and irregular oscillations. Compared with isothermal particle, the thermal convection varies the particle sedimentation velocity and its oscillation amplitude, and the particle migrates off the centerline at low Re. During the sedimentation of cold particle in the hot fluid, there are vortex shedding arising induced by the thermal convection, the sedimentation velocity and the oscillation amplitude of particle are increased, the periodic drafting, kissing and tumbling (DKT) scenario was found in these two cold particles sedimentation, and the cold particles tend to disperse. During the sedimentation of hot particle in the cold fluid, the warm wake forms a strong upward thermal plume, the sedimentation velocity and the oscillation amplitude of particle are decreased, the drafting, kissing and tumbling scenario was not found in the sedimentation of two hot particles, and hot particles tend to aggregate. Under the same heat transfer condition, the influence of thermal convection on particle motion will be decreased with the particle- fluid density ratio increasing. The suppression of the sedimentation velocity and the oscillation amplitude of particle by wall effect were increased with the channel width decreasing.