STRUCTURE OF TURBULENT ROUND BUBBLING JET GENERATED BY PREMIXED GAS AND LIQUID INJECTION

An air-water mixture was injected into a cylindrical water bath throug h a single-hole bottom nozzle to generate a vertical turbulent bubblin g jet. A parameter called jet Volume fraction, defined as the ratio of the air flow rate to the total flow rate of air and water, was introd uced to specify the bubbling jet. The jet volume fraction was raised f rom zero to approximately 0.5 in order to study the effects of bubble concentration on the mean flow and turbulence characteristics in the w ater phase. Bubble diameters were roughly 2 mm and almost independent of the jet volume fraction. Water velocity measurements were made usin g a two-channel laser Doppler velocimeter. The effect of the jet volum e fraction on the axial mean velocity of water was relatively weak, wh ereas the turbulence characteristics were significantly modulated. Tur bulence production was enhanced with an increase in the jet volume fra ction. The skewness and flatness factors, however, were not influenced by bubbles and agreed well with their respective values for single-ph ase free jets. Simplified methods of correlating the axial mean veloci ty, the root-mean-square values of the axial and radial turbulence com ponents and Reynolds shear stress were proposed. (C) 1997 Elsevier Sci ence Ltd.