Eulerian simulations for determination of the axial dispersion of liquid and gas phase in bubble columns operating on the churn-turbulent regime

摘要

Fully three-dimensional (3D) transient simulations using computational fluid dynamics (CFD) have been carried out for bubblc columns operating in the churn-turbulent flow regime. The bubble column is considered to be made up of three phases: (I) liquid, (2 "small" bubbles and (3) "large" bubbles and the Eulerian description is used for each of these phases. Interactions between bot! bubble populations and the liquid are taken into account in terms of momentum exchange, or drag, coefficients, which differ for thl "small" and "large" bubbles. Water and Tellus oil, with a viscosity 75 times that of water, were used as liqui'd phase and air as gaseou phase. The transient tracer responses in the gas and liquid phases were monitored at three different stations in the column and th results analysed in terms of a one-dimensional axial dispersion model. The 3D simulation results for radial distribution of liqui, velocity (V L(r)), centre-Iine liquid velocity (V JO), axial dispersion coefficients of the liquid (Dax.J and gas (D.x.G) phases, for column of 0.174, 0.38 and 0.63 m in diameter were compared with experimental data generated in our laboratories and also 1iteratur correlations. There is good agreement between the values of V L(r), V L(O) and Dax.L from 3D simulations with measured experimentl data. The axial dispersion coefficient of the small bubble population was almost the same as that of Dax.L' whereas the dispersion ofth large bubbles is significantly lower in magnitude. It is concluded that 3D transient Eulerian simulations are potent tools f( investigating the gas and liquid residence time distributions and have potential use as scale-up tools.