DYNAMIC SIMULATION OF GAS-LIQUID 2-PHASE FLOW - EFFECT OF COLUMN ASPECT RATIO ON THE FLOW STRUCTURE

In this paper an Eulerian/Lagrangian model, describing the hydrodynami cs of a gas-liquid bubble column, is presented. The model resolves the time dependent, two-dimensional motion of small, spherical gas bubble s in a liquid using the equation of motion. The model incorporates all relevant forces acting on a bubble as it rises through the liquid, an d additionally accounts for direct bubble-bubble interactions. The liq uid-phase hydrodynamics are described using the volume-averaged Navier -Stokes equations. This model is used to study the hydrodynamic behavi our of bubble columns with aspect ratios ranging from 1.0 to 11.4. In addition to these theoretical results, experimental observations are p resented of the flow structure in a pseudo-two-dimensional bubble colu mn 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) t o the staggered vortices mode of circulation (L/D greater than or equa l to 2.0). The computational results clearly showed the presence of vo rtical structures in the liquid phase at aspect ratios exceeding 2.0. These vortical structures in the liquid phase were studied experimenta lly using neutrally buoyant tracer particles and streak photography. T he experimentally observed vortical structures are shown to resemble t he computed structures. (C) 1997 Elsevier Science Ltd.