Coherent flow structures in bubble column reactors

This paper reviews the flow patterns in bubble columns with a focus on transient flow structures. The subject of mean flow pattern has not been covered in view of the earlier publication (Joshi, J.B. Computational flow modelling and design of bubble column reactors. Chemical Engineering Science 56 (2001) 5893-5933), which also deals with the subject of the formulation of governing equations and the description of interface force terms for gas-liquid dispersions. The published literature in the last ten years has been analyzed on a coherent basis and the present status has been brought out for (i) Euler-Euler versus Euler-Lagrange approach, (ii) closure formulation for eddy diffusivity in gas-liquid dispersions, (iii) numerical issues such as grid size, discretization scheme and the solution algorithms and (iv) two-dimensional versus three-dimensional formulation. The following geometries of bubble columns have been investigated in the past: (i) two-dimensional column with off-center sparging, (ii) two-dimensional column with central sparging, (iii) two-dimensional column with uniform sparging and (iv) cylindrical columns with uniform sparging. All these cases have been covered in the present paper. A critical account of the predictive capability of all the models for transient flow structures has been presented. This paper also includes the application of multiresolution analysis of velocity-time series for the identification of coherent flow structures. (C) 2002 Elsevier Science Ltd. All rights reserved.