(100a) Single and Multiphase Mixing in Stirred Vessels with Low Height-to-Tank Diameter Ratio Using Computational Fluid Dynamics and Particle Image Velocimetry

In many industrial applications mixing vessels have liquid height-to-tank diameter ratio H/T equal to, or larger than, 1. However, there are many instances where this ratio is lower than 1, as in all those cases in which the vessel is emptied, Even when H/T<1, sufficient agitation must still be provided in order to attain process objectives. In such cases, the fluid dynamics of even a single-phase stirred liquid can become quite complex, with different regimes possibly existing depending on the geometric characteristics of the system (such as impeller clearance, liquid height, or liquid head above the impeller). The objective of this work is to obtain a minimum liquid level, for standard impeller off-bottom distance (C/T=1/3), where adequate mixing process can still be achieved both in a single liquid phase and solid-liquid suspension. Computational Fluid Dynamic (CFD) simulation as well as Particle Image Velocimetry (PIV) was used here to study the velocity profile in the flat-bottom baffled vessels equipped with a single Ruston Turbine (RT) in different height-to-tank diameter ratios when liquid level is lover than tank diameter. A commercial pre-CFD mesh generator (Gambit 2.4.6) coupled with a CFD software package (Fluent 6.3.26) with a standard k-epsilon model was used. Results were obtained using a multiple references of frames (MRF) approach. Then transient simulation based on sliding mesh technique has been conducted. Experimental work was also conducted in solid suspension containing glass beads. All the experimental and computational studies were conducted with a single liquid phase as well as in solid-liquid suspensions with 0.5% dispersed solid. A comparison of the experimental and computation work is presented.