Numerical and Physical Modeling of Air Diffuser Plume

Abstract

A drift‐flux formulation that accounts for multiple bubble interactions is applied to describe the mean water velocity, air fraction, and plume growth for a vertical air diffuser plume that is bound on one side. A coarse‐bubble line‐diffuser source in a rectangular mixing tank is considered. Physical velocity and plume width measurements are used to calibrate the numerical model. The model is shown to be sensitive to the initial plume width and the entrainment coefficient. A dimensionless equation for the ambient water velocity at the outer edge of the plume is developed from physical measurements. The water velocity and air fraction are assumed to be uniform over the plume width. Four ordinary differential equations are developed and solved simultaneously to obtain the changes in significant plume variables with fluid depth. To reproduce the observed plume characteristics, the entrainment coefficient was 30‐60% higher than the single‐phase jet entrainment coefficient. The effect of the wall friction was minor for depths less than 1 m.