Direct numerical simulation of the sedimentation of solid particles with thermal convection

Abstract

Dispersed two-phase flows often involve interfacial activities such as chemical reaction and phase change, which couple the fluid dynamics with heat and mass transfer. As a step toward understanding such problems, we numerically simulate the sedimentation of solid bodies in a Newtonian fluid with convection heat transfer. The two-dimensional Navier-Stokes and energy equations are solved at moderate Reynolds numbers by a finite-element method, and the motion of solid particles is tracked using an arbitrary Lagrangian-Eulerian scheme. Results show that thermal convection may fundamentally change the way that particles move and interact. For a single particle settling in a channel, various Grashof-number regimes are identified, where the particle may settle straight down or migrate toward a wall or oscillate laterally. A pair of particles tend to separate if they are colder than the fluid and aggregate if they are hotter. These effects are analysed in terms of the competition between the thermal convection and the external flow relative to the particle. The mechanisms thus revealed have interesting implications for the formation of microstructures in interfacially active two-phase flows. Dispersed two-phase flows often involve interfacial activities such as chemical reaction and phase change, which couple the fluid dynamics with heat and mass transfer. As a step toward understanding such problems, we numerically simulate the sedimentation of solid bodies in a Newtonian fluid with convection heat transfer. The twodimensional Navier-Stokes and energy equations are solved at moderate Reynolds numbers by a finite-element method, and the motion of solid particles is tracked using an arbitrary Lagrangian-Eulerian scheme. Results show that thermal convection may fundamentally change the way that particles move and interact. For a single particle settling in a channel, various Grashof-number regimes are identified, where the particle may settle straight down or migrate toward a wall or oscillate laterally. A pair of particles tend to separate if they are colder than the fluid and aggregate if they are hotter. These effects are analysed in terms of the competition between the thermal convection and the external flow relative to the particle. The mechanisms thus revealed have interesting implications for the formation of microstructures in interfacially active two-phase flows. Disciplines Engineering | Mechanical Engineering

Heat Transfer Enhancement in a Stagnant Dielectric Liquid by the Up and Down Motion of Conductive Particles Induced by Coulomb Forces

“…An exact numerical solution of the current problem requires a direct numerical solution (DNS) technique such as arbitrary Lagrangian-Eulerian method (ALE) (Gan et al, 2003) or Distributed Lagrange Multiplier/Fictitious Domain method (DLM/FD) (Dan and Wachs, 2010). Such simulations for the current problem are very complicated particularly due to the electric field effects.…”

Direct numerical simulations of particle sedimentation with heat transfer using the Lattice Boltzmann method

“…Gan et al [4] 2 investigated the effects of heat transfer on the sedimentation of double cold and hot particles. It was found that cold particles would tend to repel each other while hot particles would attract each other.…”

Size and thermal effects on sedimentation behaviors of two spheres

“…They demonstrated that interaction mechanism for particulate flow was associated with lubrication, long bodies, and wakes. Gan et al [3] investigated the effects of heat transfer on the behaviors of double circular particles during sedimentation. They found that cold particles would tend to repel each other while hot particles attract.…”