Influence of scale on the hydrodynamics of bubble columns operating in thechurn-turbulent regime: experiments vs. Eulerian simulations

The radial distribution of the liquid velocities, along with the liquid-pha se axial dispersion coefficients, have been measured for the air-water syst em in bubble columns of 0.174, 0.38 and 0.63 m diameter. The experimental r esults emphasise the significant influence of the column diameter on the hy drodynamics, especially in the churn-turbulent regime. Computational fluid dynamics (CFD) is used to model the influence of column diameter on the hyd rodynamics. The bubble column is considered to be made up of three phases: (1) liquid, (2) "small" bubbles and (3) "large" bubbles and the Eulerian de scription is used for each of these phases. Interactions between the gas ph ases and the liquid are taken into account in terms of momentum exchange, o r drag, coefficients, which differ for these two gas phases, The drag coeff icient between the small bubbles is estimated using the Harmathy correlatio n(A.I.Ch.E. Journal 6 (1960) 281-288). The drag relation for interactions b etween the large bubbles and the liquid, is developed from analysis of an e xtensive data base on large bubble swarm velocities measured in columns of 0.051, 0.1, 0.174, 0.19, 0.38 and 0.63;m diameter using a variety of liquid s (water, paraffin oil, tetradecane). The interactions between the large an d small bubble phases are ignored. The turbulence in the liquid phase is de scribed using the k-epsilon model. The three-phase description of bubble co lumns was implemented within the Eulerian framework of a commercial code CF X 4.1c of AEA Technology, Harwell, UK. Comparison of the experimental measu rements with the Eulerian simulations show good agreement and it is conclud ed that the three-phase Eulerian simulation approach developed here could b e a powerful design and scale-up tool. (C) 1999 Elsevier Science Ltd. All r ights reserved.