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 b ath. More than 1000 bubbles in a mean diameter of approximately 3 mm w ere generated during one second. The radial dispersion of the bubbles in the course of rising in the bath, mean bubble diameter, and mean bu bble rising velocity were determined using a camera and a high-speed v ideo 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 u sing a two-channel laser Doppler velocimeter. These results were compa red with those for a centric single-hole bottom nozzle to clarify the effects of bubble size on the above-mentioned bubble and liquid flow c haracteristics. In an axial region away from the nozzle where the buoy ancy force of bubbles plays an important role, the radial dispersions of bubbles for the two kinds of nozzles were the same. The axial (vert ical) mean velocity and turbulence production were significantly depen dent on the size of bubbles. Larger bubbles promoted the turbulence pr oduction in the vertical bubbling jet.