Bubble and Liquid Flow Behavior in a Bath Agitated by Porous Nozzle Bubbling

Air was injected through a centric wooden porous nozzle into a water bath. More than 1000 bubbles in a mean diameter of approximately 3 mm were generated during one second. The radial dispersion of the bubbles in the course of rising in the bath, mean bubble diameter, and mean bubble rising velocity were determined using a camera and a high-speed video camera. The liquid motion was driven mainly by the buoyancy force of bubbles. The mean velocity components, root mean square values of turbulence components, Reynolds shear stress and so on were measured using a two-channel laser Doppler velocimeter. These results were compared with those for a centric single-hole bottom nozzle to clarify the effects of bubble size on the above-mentioned bubble and liquid flow characteristics. In an axial region away from the nozzle where the buoyancy force of bubbles plays an important role, the radial dispersions of bubbles for the two kinds of nozzles were the same. The axial (vertical) mean velocity and turbulence production were significantly dependent on the size of bubbles. Larger bubbles promoted the turbulence production in the vertical bubbling jet.