Effect of nozzle design on bubbly jet entrainment and oxygen transfer efficiency

Abstract

This study investigates experimentally the effect of nozzle type, including diffusers with single- and multiple-orifices with different diameters, on the hydrodynamics and mass transfer characteristics of air-water bubbly jets discharged at the bottom of a water tank. The results revealed that for the same flow rates of air and water, the total area of the orifices independent of the number of ports controls the initial momentum of the bubbly jets and the jet-to-plume length scale of the flow. An integral model was fitted to the experimental data in order to obtain entrainment coefficients for each test and at different water depths, which confirmed that merged multiple bubbly jets can be analyzed using an equivalent single jet integral model. This resulted in an entrainment relationship described as a function of the kinematic buoyancy flux, bubble slip velocity, and distance from the source, which is similar to that available in the literature for bubble plumes, but with different constants. Finally, the model proposed here is compared to previous models and applied to practical cases including mixing and aeration of tanks and water bodies, indicating that gas transfer efficiency can be significantly enhanced by using multiple-orifice arrangements.