L. Moldavsky

Fluidized bed in a confined volume

Coarse solid elastic enough particles form a packed bed in a vertical cylinder confined from below and from above by permeable elastic plates. A gas is forced through the lower plate with a velocity exceeding the terminal (transport) velocity. Adjacent to the lower plate the particles are entrained and impact on the upper plate. As a result, fluidization regimes of still unreported types take place in the confined cylinder. These regimes are analyzed qualitatively by a theoretical model proposed here. This model describes the mean motions of the gas and particles. It includes the mass and momentum equations for the gas and particle phases and the equation of the kinetic energy of particle fluctuations. The system of equations is supplemented by constitutive equations for the averaged drag force, granular pressure, kinetic energy dissipation due to inelastic particle collisions, and energy generation. It is assumed that generation of the kinetic energy is caused by the lateral Magnus force due to particle rotation. Steady state solutions of the equations are obtained, which describe the fluidization regimes in a confined cylinder, namely disperse for a fluidized bed with increasing or decreasing volume fraction and for an inverted packed bed. Experiments are performed to show the existence of the disperse regime of fluidization. Stability of the disperse bed with respect to small perturbations is considered. It is shown that a disperse fluidized bed is unstable for sufficiently concentrated dispersions where the bulk modulus of elasticity of the granular phase is negative. The effect of vibrations of the upper plate upon fluidization regimes is also studied. Resonant frequencies are detected in the concentration region where the bulk modulus of elasticity is positive.

Particle motion in simple shear flow with gravity

The motion of aerosol particles in simple shear flow, subject to gravity, is analyzed. The combination of gravity and shear-induced lift is shown to give rise to particle drift. It is shown that in shear flow near a wall, when gravity points in the direction of flow, particles drift towards the wall, while for gravity pointing against the flow the drift is away from the wall. These results are also demonstrated experimentally, with fair qualitative agreement between analysis and experiments.

ELECTROSTATIC POROUS FILTER WITH A BLOCKING ELECTRODE

Abstract This work proposes to add to an electrostatic filter an auxiliary blocking electrode, charged by the same charge as the particles. The effect of the blocking electrode is to increase the collection efficiency of the electrostatic filter. Experiments performed on an electrostatic filter equipped with a permeable blocking electrode indicate that such an electrode roughly doubles the collection efficiency of the filter. A mathematical model was developed to account for the effect of the blocking electrode. The model facilitates calculations of the major parameters of the electrode, as part of a design of a more efficient electrostatic filter.

Enhancing the efficiency of the electrostatic filter

This work considers the increase of the collection efficiency of the electrostatic filter by the installation of a blocking permeable electrode. This electrode is placed at the outlet of the collection zone and is charged by the same charge as the particles. The electrostatic force, which is generated by the blocking electrode, acts on the particles in a direction generally opposite to that of the gas flow, resulting in stronger curvatures of the particle trajectories, leading to higher capture efficiencies.