CFD modelling of turbulent drop breakage in a kenics static mixer and comparison with experimental data

This study has investigated drop breakage in liquid–liquid systems by means of advanced numerical modelling tools based on computational fluid dynamics (CFD). A static mixer with 24 standard Kenics inserts was analysed with the volume fraction of dispersed phase equal to 0.1%. Four superficial velocities were used resulting in Reynolds numbers of 12 000, 15 000, 18 000 and 21 000, respectively. To simulate the evolution of the drop size distribution (DSD), the population balance equation (PBE) was coupled with the multi-phase description and added to the standard equations in the CFD code with proper kinetic expressions for the breakage rate. Instead of solving the original PBE, transport equations for the moments of the DSD were solved and the closure problem was overcome by using the quadrature method of moments (QMOM). As expected, the predicted drop size decreased along the mixer and pressure drop, final size distribution and Sauter mean drop diameters, d32, all agreed well with data reported in a previous experimental study, the best agreement for d32 being from −10% to +9%, obtained with the finest mesh, 927 k.