Abstract Summary (Max 250 words)
Batch rotor-stators are used in several dispersion processes that require the breakup of immiscible droplets, particle clusters or for foam generation on account of the high turbulence energy dissipation rate in the vicinity of the mixer head. The overall process performance also relies on minimal spatial variation of product properties. Blending performance of rotor-stators, on the other hand, has not been widely studied/reported. In this study, the blending performance of three different mixer head geometries of the VMI Turbotest batch rotor-stator has been determined evaluating mixing time values on the basis of power input and compared with predictions from the turbulent mixing time correlation. Turbulent power numbers were determined as 3.36, 2.47 and 2.62 for the slotted wide gap, gridded and slotted with toothed rotor mixer heads respectively. Analysis of mixing time results has shown that the dependence of mixing time on power input in the turbulent blending regime holds for all three mixer heads, as with impeller driven set-ups. A brief study with a pitched blade turbine gave results in agreement with predictions from the mixing time correlation. With the VMI Turbotester the correlation also held in its general form but with a slightly higher constant of 5.9 instead of 5.2. It could be concluded that in the turbulent regime these batch rotor-stators can achieve sufficient bulk blending, i.e. can be used for dispersion processes without the need for an additional impeller for bulk circulation.
