Prediction of Backmixing and Mass Transfer in Bubble Columns Using a Multifluid Model

Three-dimensional, instationary flow fields in bubble columns are numerically calculated using a Euler multifluid model. The local bubble size is calculated depending on the flow field using a transport equation for the mean bubble volume originating from a population balance equation. The resulting set of equations enables the simultaneous calculation of mass transfer and backmixing in the gas and liquid phases. Therefore, a perfect tracer is added to both the gaseous and liquid phases. From the calculations, the time-dependent concentration fields of the tracer are obtained. Assuming the one-dimensional dispersion model, the axial dispersion coefficients are calculated for comparison with experimental results. The obtained dispersion coefficients for the gas and liquid phases are in good agreement with the experimental investigations of several authors. On the basis of the reasonable prediction of the interfacial area and backmixing, the multifluid model is extended to consider mass transfer. The absorption of the gas phase reduces the overall momentum transfer; thus, the flow pattern is changed.