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The motion of the solid particles in the enclosed cavity is important, to investigate the interaction between the motion of the solid particles and the fluid flow, the motion of a neutrally buoyant elliptical particle in a lid-driven square cavity is studied with the lattice Boltzmann method. To understand, predict and control the motion of the elliptical particle, the effects of the aspect ratio, initial orientation, initial position, particle size and Reynolds number are studied. The obvious characteristic of the motion of the elliptical particle in the square cavity is the existence of the limit cycle, which is created by the inertia of the elliptical particle, confinement of the boundaries of the square cavity and vortex behavior. Compared with the circular particle, with the increase of the aspect ratio, the roundness of the limit cycle decreases, namely, the limit cycle becomes flatter. Especially, the limit cycle is insensitive to the initial orientation and position, namely, the limit cycle is the same no matter where the elliptical particle is placed initially. With the increase of the particle size, the confinement of the boundaries becomes stronger, and the limit cycle is squeezed toward the center of the square cavity. Finally, with the increase of the Reynolds number, the vortex at the top left corner develops, and the limit cycle is pushed toward the bottom right corner of the square cavity. • A global limit cycle for the motion of the elliptic particle is observed. • The limit cycle is insensitive to the initial position of the elliptic particle. • The limit cycle shrinks toward the center of the square cavity with the increase of the particle size. • The limit cycle migrates toward the bottom right corner of the square cavity with the increase of Re. [ABSTRACT FROM AUTHOR]

A two-dimensional study of mass transfer from a circular composite particle settling in a vertical channel is conducted with the lattice Boltzmann method. The particle is composed of two materials, one insoluble while the other soluble in the ambient fluid. In the problem, mass transfer, particle motion and fluid flow are closely coupled, where the concentration at the particle surface and particle properties vary with mass transfer. It is observed that mass transfer follows a Schmidt number independent scaling law of [ t / ( t ν Sc ) ] - 1.5 ( t is the physical time, t ν is the momentum diffusion time scale and Sc is the Schmidt number), which is quite different from the pure diffusion of a stationary particle, ∼ ( t / t α ) - 0.5 ( t α is the mass diffusion time scale). An analysis of the concentration and flow pattern around the particle suggests that the scaling law for a settling particle is related to both diffusion distance and convection distance, while it is only relevant to the diffusion distance in the case of a stationary particle. For a settling particle, mass transfer is enhanced by two mechanisms due to convection, i.e., the concentration around the particle surface transported to the downstream of the particle by the fluid flow and the interface of mass transfer stretched with the particle motion, which are absent in the case of a stationary particle. Thus, the rate of mass transfer in the case of a settling particle is much higher than that for a stationary particle. [ABSTRACT FROM AUTHOR]