Motion of a spherical particle in a microbubble plume and the behavior of microbubbles around the particle

This study aims to investigate the motion of a solid spherical particle in a microbubble plume and the behavior of bubbles around the particle. Microbubbles (mean diameter 0.037 mm) released into a rectangular conduit by the electrolysis of water rise via buoyancy and form a bubble plume in the conduit. A solid spherical particle with a diameter of 10 mm and density of 1022 kg/m3 is placed on a mesh stretched across the cross-section near the bottom of the conduit, and microbubbles are then released from the cathode. Experiments are conducted with the bubble volumetric flux in the conduit j G at 0.05 and 0.09 mm/s. The particle repeatedly rises and falls when j G = 0.05 mm/s, and it rises almost vertically when j G = 0.09 mm/s. The absolute value of the vertical velocity of the particle is lower than that of the bubble. There is a belt-like region where the bubble velocity is extremely lower behind the particle. Such wake behind the particle clearly appears when the particle is falling, because the bubble velocity relative to the particle is higher.