Study on the internal two-phase flow of the inverted-umbrella aerator

Abstract

In order to reveal the gas–liquid two-phase flow pattern of inverted-umbrella aerator, the high-speed photography technology, particle image velocimetry, and Volume of Fluid model are employed to capture the free-surface dynamics and velocity distribution. The Computational Fluid Dynamics simulations are validated by experimental data and the results are in good agreement with experiment. The simulation results of flow field, streamline distribution, velocity distribution, free-surface deformation, and turbulence kinetic energy are analyzed at in time and at radial profiles sampled at several vertical positions. Back surface of each blade revealed the area of low-pressure, which can drag air into water directly from surface and thus enhance liquid aeration and oxygenation capacity. Lifting capacity of the inverted-umbrella aerator is enough to get the liquid at the bottom of the aeration tank accelerated toward liquid surface generating the hydraulic jump. As a result, liquid phase splashes capture portions of air promoting aeration of the solution. A clear circulation whirlpool is formed during the process. The circulation whirlpool starts at the bottom of the impeller moving upward along the plate until the outer edge of the impeller, which is close to the free surface. The circulation whirlpool indicates that the inverted-umbrella aerator plays a significant role in shallow aeration. The turbulence intensity created by the impeller gradually reduces with depth. The position ( z = 0.65 H) is the watershed in the tank. The oxygen mass transfer mainly occurs in the layer above watershed.