Influence of Initial Bubble Size on the Dynamic Behavior of Fluid in a DAF Tank

To explore the impact of non-uniform initial bubble sizes on the hydrodynamics behavior of the separation zone in a dissolved air flotation (DAF) tank, a three-dimensional (3D) model of the DAF tank was established. Subsequently, computational fluid dynamics (CFD) simulations of the corresponding DAF tank were conducted based on the realizable k-ε turbulence model, the Eulerian-Eulerian multiphase flow model, and the population balance model (PBM). The reliability of the prediction results of the 3D model was evaluated by comparing the gas holdup and velocity vector data obtained from experimental results. Moreover, considering the coalescence and breakage of bubbles, the influence of different initial bubble sizes on the variation trend of the gas holdup with height in the separation zone of the DAF tank was analyzed when different flotation media, namely air, carbon dioxide, were adopted. The study reveals that as the density of the flotation medium increases, the optimal size range of the initial bubbles also gradually expands. Specifically, when air and carbon dioxide are used as the flotation media, the optimal ranges of the initial bubble sizes are 25-50 μm and 25-75 μm, respectively.