Collision rates of small solid particles with rigid spherical and spheroidal bubbles in laminar flow

Abstract

AbstractThe interaction and impact of solid particles from a dilute suspension with fixed spherical and deformed bubbles (i.e., oblate spheroids) with rigid interface was analysed numerically, a situation found for example in flotation or three-phase chemical reactors. The flow field about the bubbles was computed for laminar flow and the particles were considered as point masses incorporating all forces as there are drag, added mass, fluid inertia, transverse shear-lift, and gravity/buoyancy. Particle sizes were varied up to about 200 µm allowing for a wide range of interaction Stokes numbers. The impact efficiency was evaluated for a wide range of bubble Reynolds numbers and bubbles having different shape and size, as well as eccentricity and orientation. The volume equivalent diameter of the bubbles was between 2 and 4 mm. The bubble deformation was varied up to an eccentricity of 1.8 and the bubble orientation was modified until 45 degrees. The effect of different forces on the impact efficiency was studied in detail. Added mass, fluid inertia (part of the pressure term), and slip-shear transverse lift force cannot be neglected in liquid environments, especially for larger particles. The obtained results were also compared to the composite model of Schulze (1989), well established in the field of flotation. Finally, also the particle impact statistics (i.e., location and velocity) was evaluated.