Application of extended quadrature method of moments for simulation of bubbly flow and mass transfer in gas-liquid stirred tanks

In the present paper, two gas-liquid stirred tanks, one agitated by a radial impeller and another by an axial impeller, are modelled using the open-source computational fluid dynamic (CFD) package OpenFOAM (open source field operation and manipulation). The combined effect of the bubble break-up and coalescence in the tank is considered by a population balance model (PBM) called extended quadrature method of moments (EQMOM). The three-dimensional simulation is made using a multiple reference frame (MRF), a well-established method for the modelling of mixers. Dispersed gas and bubble dynamics in the turbulent flow are modelled using the Eulerian-Eulerian approach (E-E) with mixture k-epsilon turbulent model and the modified Tomiyama drag coefficient for the momentum exchange. The model is developed to predict the spatial distribution of gas phase fraction, Sauter mean bubble diameter (d32), number density function (NDF), dissolved oxygen (DO) evolution, and flow structure. The numerical results are compared with experimental data and a fair agreement is achieved. The results of the axial impeller are discussed based on four impeller rotational speeds with different volumetric mass transfer coefficients.