Bubble columns are widely used for carrying out gas−liquid and gas−liquid−solid reactions in a variety of industrial applications. The dispersion and interfacial heat- and mass-transfer fluxes, which often limit the overall chemical reaction rates, are closely related to the fluid dynamics of the system through the liquid−gas contact area and the turbulence properties of the flow. There is thus considerable interest, within both academia and industry, to improve the limited understanding of the complex multiphase flow phenomena involved, which is preventing optimal scale-up and design of these reactors. In this paper, the progress reported in the literature during the past decade regarding the use of averaged Eulerian multifluid models and computational fluid dynamics (CFD) to model vertical bubble-driven flows is reviewed. The limiting steps in the model derivation are the formulation of proper boundary conditions, closure laws determining turbulent effects, interfacial transfer fluxes, and the bubble coalescence and breakage processes. Examples of both classical and more recent modeling approaches are described, evaluated, and discussed. Physical mechanisms and numerical modes creating bubble movement in the radial direction are outlined. Special emphasis is placed on the population balance modeling of the bubble coalescence and breakage processes in two-phase bubble column reactors. The constitutive relations used to describe the bubble−bubble and bubble−turbulence interactions, the bubble coalescence and breakage criteria, and the daughter size distribution models are discussed with a focus on model limitations. The demand for amplified modeling, more accurate and stable numerical algorithms, and experimental analysis providing data for proper model validation is stressed.

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Fluid particle coalescence and breakage phenomena are important for optimal operation of many industrial process units. In particular, in bubble column reactors, the bubble size distribution determines the interfacial momentum, heat, and mass transfer fluxes through the contact area and may thus limit the overall process performance. To elucidate the mechanisms of the coalescence and breakage phenomena, extensive wellplanned model-based experimental investigations are required. In addition, a suitable modeling framework considering the microscopic phenomena is needed to interpret the data achieving extended understanding of the important mechanisms, enabling the formulation of more sophisticated mechanistic kernel functions. This article presents a combined multifluid-population balance model for describing the behavior of vertical bubbledriven flows in bubble columns. In the present modeling approach, the Maxwellian average transport equations for the disperse phase are formulated in terms of a density function. The main advantage of this novel modeling concept is that we obtain a set of transport equations expressed in terms of the set of internal coordinates. All the important moments like the void fraction, contact area, Sauter mean diameter, average disperse phase velocity, mean mass, and momentum fluxes, etc., can then be computed from the predicted density function in a post processing procedure. For model validation, the model predictions are compared to experimental data gathered from the literature. The agreement between the available data and the model predictions ais considered very good. It is concluded that the model is a viable tool for parameter fitting of novel coalescence and breakage kernels provided that sufficient experimental data are made available.

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