Characterisation of Flow Pattern in a Rotor-Stator High Shear Mixer
Multi-scale and/or multi-disciplinary approach to process-product innovation
CFD & Multiscale Modelling in Chemical Engineering (T3-4P)
Keywords: High shear mixer, flow field, CFD, LDA,
The flows in a rotor-stator high shear mixer (Silverson) at various rotor speeds (2000, 4000, 6000 and 8000 RPM) operating in water have been simulated using Fluent 6.2 and the theoretical results verified by LDA measurements of the velocity field. The mixing head consisted of a four blade rotor of 28.2 mm diameter and a standard 6 holes stator with a rotor-stator gap of 0.175 mm, and was placed off centre in a cylindrical vessel of 10 cm diameter to improve macromixing. The transient simulations were carried out using the sliding mesh method with approximately 600 thousand hybrid cells, of which 300 thousand cells were used in the rotor-stator region. The Reynolds stresses model (RSM) was employed to account for highly anisotropic turbulent flow due to the interaction between the rotor and stator and the eccentric configuration of the mixing head.
The rotor produces a high tangential velocity flow which impinges the stator holes creating jets in radial-tangential direction which eventually hit the tank wall. Behind the jets, the fluid flows in the opposite direction toward the holes which then merges with the jets. Strong circulation flow has been observed in region below the mixing head whilst the flow above the mixing head is relatively slow. This can be explained by the design of mixing head with the inlet at the bottom and the outlet through the holes in the stator. The high rotational speed of the rotor also creates a vortex below the rotor-stator head. The vortex centre is slightly shifted from the rotor-stator axis. The prediction of the fluid velocity profile across the stator holes is in a good agreement with LDA measurements. The mixing time (t95) and flow number obtained from this simulation was 14.3 seconds and 0.173 respectively and the detailed discussion of average velocity field and local energy dissipation rates will be presented in the paper.
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Presented Tuesday 18, 13:30 to 15:00, in session CFD & Mutliscale Modelling in Chemical Engineering (T3-4P).
