Mass transfer from bubble swarms
ABSTRACT: A technique that quantifies the mass transfer from a bubble swarm, without looking at individual bubble transfer, is described. The technique is applied to bubble plumes that are not affected by ambient boundary conditions. The bubble and surface volumetric mass transfer coefficients for oxygen are separately determined for 179 aeration tests, with sparger depths ranging from 2.25 m to 32 m, using a multiple component mass transfer model. Two empirical characterization equations are developed for surface and bubble mass transfer coefficient, correlating the coefficients to air flow, sparger depth, cross-sectional area and volume. The characterization equations indicate that the bubble transfer coefficient increases with increasing gas flow rate and depth, and decreases with increasing water volume. The mass transfer coefficient for fine bubble spargers is approximately six times greater than for coarse bubble spargers. The surface transfer coefficient increases with increasing gas flow rate and sparger depth. The characterization equations make it possible to predict the gas transfer that will occur across bubble interfaces and across the free surface with a bubble plume at depths up to 32 m and with variable air discharge in deep tanks and reservoirs.