Numerical calculation of particle and bubble dispersion in a fluid-phase resonance mixer

• Applicant: Professor Dr.-Ing. Martin Sommerfeld
• Subject Area: Mechanical Process Engineering ; Fluid Mechanics
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 254590687

In preliminary investigations it could be demonstrated that the fluid-phase resonance mixer (FPR-mixer) is suitable for realising effective fluid mixing. For this purpose, both numerical calculations (with OpenFOAM) as well as experiments were conducted. In the present proposal it is intended to prove the suitability of the FPR-mixer for particle and bubble dispersion. The numerical calculations shall be conducted by the Euler (LES)/Lagrange approach using again OpenFOAM.For allowing a realistic numerical calculation of particle and bubble dispersion in a liquid phase, however, the dynamics of the dispersed phase shall be analysed considering all relevant fluid forces. This implies an extension of the equation of motion accounting for drag, gravity/buoyancy, pressure term, added mass, basset-force and slip-shear lift. The coefficients for added mass and Basset term shall be taken according to Odar & Hamilton (1964) as well as those recently suggested by Michaelides & Roig (2011), which depends for the Basset term on the Strouhal number. Results obtained with both coefficients will be compared. Moreover, the importance of the different unsteady forces will be analyzed in detail and the simulation results will be compared with measurements in the FPR-mixer. These studies will be done in dependence of the Stokes-number (depending on particle- and bubble-size, density ratio and pulsation frequency) and provide corresponding recommendations regarding the importance of the unsteady forces.On the basis of these developments, numerical calculations of the dispersion of particles and bubbles are planned in order to optimise geometry (e.g. diameter of immersed pipe and bottom clearance) and operational conditions (e.g. oscillation frequency) of the FPR-mixer. The objective is achieving a homogeneous distribution of particles or bubbles as much as possible. For identifying these conditions the Stokes-number shall be varied over the relevant range. In addition the effect of the unsteady forces on the dispersion result in a technical process will be analysed in detail for the first time.For validating the numerical calculations, experiments for selected conditions will be conducted. The simultaneous measurement of the velocity fields for continuous and dispersed phase will be realised by using fluorescing tracer particles in conjunction with the application of PIV (particle image velocimetry) as well as PTV (particle tracking velocimetry). By using two CCD-cameras with appropriate optical filters both phases are reliably distinguished. In addition instantaneous dispersed phase concentration fields will be estimated.

• DFG Programme: Research Grants
• Participating Person: Professor Dr. Ralph Säuberlich