Bubble and liquid flow characteristics in a vertical bubbling jet

Abstract

A vertical bubbling jet was formed in a cylindrical water bath by injecting air from a centric single-hole nozzle. Bubble characteristics, such as gas holdup (void fraction), bubble frequency, mean bubble rising velocity, mean chord length, were measured using a two-needle electro-resistivity probe. In addition, liquid flow characteristics, represented by the axial mean velocity, rms values of axial and radial turbulence components, Reynolds shear stress, effective kinematic viscosity, skewness and flatness factors for axial and radial turbulence components, were measured with a two-dimensional laser Doppler velocimeter. The flow field in the bubbling jet was essentially classified into two regions with respect to the axial distance from the nozzle exit. One is located near the nozzle where the inertia force of injected gas plays an important role. The other is located far from the nozzle in which the buoyancy force of bubbles governs the flow. In this study the experimental results of liquid flow characteristics in the latter region were compared with those for a single-phase round jet. Turbulence production in the bubbling jet was found to mainly occur in the wake of bubbles and to be approximately two times as large as the turbulence production in the single-phase round jet. The turbulence structures for the two jets also were different from each other.