Bubble-size distributions and flow fields in bubble columns are calculated numerically. The population balance is simplified and reduced to a balance equation for the average bubble volume. Models developed predict the rate of bubble breakup and coalescence based on physical principles. The flow fields are numerically calculated for bubble columns with cylindrical cross sections using the Euler-Euler method. The newly derived balance equations for the average bubble volumes are implemented into a commercial CFD code. The solutions of the balance equation for high superficial gas velocities result mainly in two fractions: one for the fraction with small and the other for the fraction with large bubble diameters. Both are considered pseudocontinuous phases, in addition to the liquid phase. The calculated flow fields are characterized by several large-scale vortices. The local volume fractions of gas and liquid are locally inhomogeneous and highly time-dependent. The time-averaged flow field is axisymmetric and stationary. The calculated volume fractions, velocities, and bubble-size distributions agree well with existing and previously published experimental results for bubble columns up to 0.3 m in diameter.

Bubble‐Size distributions and flow fields in bubble columns

Design of a prototype miniature bioreactor for high throughput automated bioprocessing

Heat and mass transfer in three-phase fluidized-bed reactors—an overview

Abstract The mechanisms and modeling concepts proposed in the literature for the fluid particle (i.e., bubble and drops) breakage phenomena in laminar and turbulent dispersions are examined. Four categories are considered for the breakage mechanisms: (i) turbulent motions and inertial stresses, (ii) viscous shear stresses, (iii) shearing-off processes, and (iv) interfacial instability. In the first category, six breakage criteria have been proposed. The constitutive equations for the breakage frequency and daughter size probability density functions for these mechanisms are examined. A brief survey of experimental analyses performed to understand the behavior of these functions is provided. It is concluded that extensive, well-planned, model-based experiments are required to elucidate the underlying mechanisms for fluid particle breakage. In particular, single particle experiments in known flow regimes are needed to determine the functionality of the breakage frequency, number of daughters, and the daughter size distribution functions and for parameter fitting. Size distribution measurements in the same flow regimes are useful for model validation studies.

Josette P.M. Spronken

Papers

The influence of gas density and liquid properties on bubble breakup