Dynamic simulations of multiphase flow in bubble columns.

Abstract

The aim of this paper is to introduce tracker particles to capture the hydrodynamics of support beads used in gas-liquid-solid biological reactors through the use of computational fluid dynamics. The gas-liquid interactions were modelled using an algebraic slip mixture model, where the gas and liquid phases are treated as a pseudo-continuous mixture. The interactions between the gas and liquid phases are calculated as force terms in the momentum conservation equation. With this model and the standard k-? turbulence model, the turbulent motion of gas-liquid flow is captured for a representative case of bubble column with an aspect ratio of 5:1[1, 2, 3]. A superficial gas velocity of 0.02 m s-1 returned vertical velocities of 0.15 ± 0.02 m s-1 at a height of 2.5 column diameters, this is a reasonable value for a column of less than 0.2 m diameter. In the two-dimensional case the two large eddies developed, showing the overall flow structure, though the flow was stable. For the three-dimensional case a dominant mode with a frequency of 4 min-1, which took 20 seconds to develop after the initialisation of the flow field. Particles were injected into the flow regime and generally followed the motion of the vortical structures present, this was due to the low density of the particles with respect to the liquid phase, leading to lows levels of particle slip. The motion of the particles was analysed by assessing the direction in which the particles were travelling within the column, leading to a measure of the mixing properties in different parts of the column.