Multi-fluid model applied to calculate backmixing and mass transfer in bubble columns

For the calculation of reactive flows in bubble columns the local interfacial area is one of the key parameters. In addition backmixing causes a residence time distribution in the gas and liquid phase, thus mixing phenomena have to be considered as well. The three-dimensional, instationary flow fields in bubble columns are numerically calculated using an Euler multi-fluid model. The resulting set of equations enables the simultaneous calculation of mass transfer and backmixing in the gas and liquid phase. Therefore the local bubble size is calculated in dependence of the flow field using a transport equation for the mean bubble volume. A perfect tracer is added into both the gaseous and the liquid phase. From the calculations the timedependent concentration fields are obtained. Assuming the one-dimensional dispersion model the axial dispersion coefficients are calculated. The dispersion coefficients for the gas and liquid phase are in good agreement with experimental investigations of several authors. The multi-fluid model is then extended to consider mass transfer between gas and liquid phases.