A Unified Representation of Gas Dispersion in Upwardly Injected Submerged Gas Jets

Abstract

The overall dispersion of gas injected vertically upward into a liquid has been studied. A generalised model has been proposed to delineate the different forms of gas dispersion in the liquid, between gas entry at the tuyere tip and exit at the bath surface. Four dispersion zones have been identified: primarybubble, free-bubble, plume and spout. The regimes have been characterised by means of a dispersion dimensionless group, N D, based on the injection Froude number and the reduced height of the dispersion, which varies with the axial gas fraction in the different regimes. Thus it has been shown that the primary bubbles only exist for values of N D lower than about 2.0 in both the air-water and helium-water systems. The free bubbles or zone of bubble disintegration in these systems occur in the range of ND between 2.0 and 4.5 while the plume extends from about N D = 4.5 to a higher value depending on the depth of the liquid phase. The transition to spout formation beyond the plume is marked by a sudden increase in gas fraction, at a level somewhat lower than the static height of the bath.