In this paper a detailed hydrodynamic model for gas liquid two-phase flow will be presented. The model is based on a mixed Eulerian Lagrangian approach and describes the time-dependent two-dimensional motion of small, spherical gas bubbles in a bubble column operating in the homogeneous regime. The motion of these bubbles is calculated from a force balance tbr each individual bubble, accounting for all relevant forces acting on them. Contributions from liquid-phase pressure gradient, drag, virtual mass, liquid-phase vorticity and gravity are considered, whereas direct bubble-bubble interactions are accounted for via an interaction model resembling the collision model developed by Hoomans et a/. (1996) to model gasfluidized beds. The liquid-phase hydrodynamics are described using the volume-averaged, unsteady, Navier-Stokes equations. A preliminary model validation has been performed by comparing the computational results with experimental observations published previously in literature by various authors. The model is shown to predict correctly the motion of a bubble plume in a pseudo-two-dimensional bubble column operated at different superficial gas velocities, provided that a detailed description of the bubble dynamics is incorporated in thc model. The effect of bubble column aspect ratio on the hydrodynamic behaviour of the column has also been investigated. Our model predicts the effect of aspect ratio on the flow structure in the bubble column. The importance of the various forces acting on the bubbles will also be discussed and it will be shown that the added mass lbrce and the lift force cannot be neglected in bubble column simulation. Finally, the model has been used to study the start-up behaviour of a two-dimensional bubble column. It will be shown that the history of the gas-liquid two-phase flow significantly affects the flow structure ultimately obtained in a bubble column. This finding has, to our knowledge, not been reported before in literature..~, 1997 Elsevier Science Ltd. All rights reserved

Abstract--ln this paper an Eulerian/Lagrangian model, describing the hydrodynamics of a gas-liquid bubble column, is presented. The model resolves the time dependent, twodimensional motion of small, spherical gas bubbles in a liquid using the equation of motion. The model incorporates all relevant forces acting on a bubble as it rises through the liquid, and additionally accounts for direct bubble-bubble interactions. The liquid-phase hydrodynamics are described using the volume-averaged Navier-Stokes equations. This model is used to study the hydrodynamic behaviour of bubble columns with aspect ratios ranging from 1.0 to 11.4. In addition to these theoretical results, experimental observations are presented of the flow structure in a pseudo-two-dimensional bubble column with different aspect ratios. A clear transition in the gas-liquid flow pattern could be observed, both experimentally and theoretically, from the well-known 'cooling tower' mode of circulation (L/D = 1.0) to the staggered vortices mode of circulation (L/D >1 2.0). The computational results clearly showed the presence of vortical structures in the liquid phase at aspect ratios exceeding 2.0. These vortical structures in the liquid phase were studied experimentally using neutrally buoyant tracer particles and streak photography. The experimentally observed vortical structures are shown to resemble the computed structures. ~(:.: 1997 Elsevier Science Ltd

Abstract-In this paper a "hierarchy of models' is discussed to study the fluid dynamic behaviour of gas-liquid bubble columns. This 'hierarchy of models' consists of a Eulerian Eulerian two fluid model, a Eulerian-Lagrangian discrete bubble model and a Volume Tracking or Marker Particle model. These models will be briefly reviewed and their advantages and disadvantages will be highlighted. In addition, a mixed Eulerian Lagrangian model and a volume tracking model, both developed at Twente University, will be discussed. Some selected results obtained with these models will be presented with emphasis on the results obtained with the volume tracking model. Finally, a brief discussion on advanced experimental techniques, which reflect the recent progress in experimental fluid dynamics, will be presented. ~ 1997

No abstract

No abstract