CFD Simulation of Particle Distribution in Stirred Vessels

In this work the particle concentration distribution in two-phase stirred tanks is simulated on the basis of information on the three-dimensional flow field, as obtained by numerical solution of the flow equations (CFD) using the well known k – ɛ « turbulence model. Two modelling approaches are attempted. In the simpler method the flow field is first simulated neglecting the influence of the solid phase; on the basis of the resulting flow field a very simple sedimentation model is employed for solving the solids mass balance equations in order to compute the particle concentration field. In this case no inertial effects on the solid particles are considered, so that the convective and diffusional exchanges for the solid phase are assumed to coincide with those for the liquid phase. In the more advanced approach the momentum balance equations for both the solid and liquid phases are simultaneously solved. Experimental data on the axial profiles of particle concentration have been obtained in a laboratory scale agitated tank. The experimental technique utilized is non intrusive being based on light attenuation measurements and is also able to provide information at high particle concentrations. The comparison of experimental data with simulation results is satisfactory with both simulation approaches. Differences between the two approaches concerning their accuracy and computational effort are discussed. The need to make a suitable estimate of the particle drag coefficients in turbulent fluid media is emphasized.