The effects of reactor internals and reactant mixing on the measured metastable zone width (MSZW) associated with the batch crystallization of l-glutamic acid from supersaturated aqueous solutions are presented. The results of cooling crystallization experiments, as carried out at three reactor scales (450 mL, 2 L, and 20 L) agitated at various stirring speeds using an industry-standard retreat curve impeller with a single beaver-tail baffle, are shown. The observed MSZWs are mostly found to decrease with increasing stirring speed, with enhanced nucleation also being observed as the reactor scale increased; albeit hindered nucleation was found at higher stirrer speeds in the 450-mL reactor experiments. The MSZW data are correlated with Reynolds number to reveal a model reflecting the combined influences of hydrodynamics and scale on the overall nucleation process.

The influence of stirrer material and agitation rate on the nucleation of batch crystallized L-glutamic acid from supersaturated aqueous solutions using temperature programmed cooling is investigated. Results obtained at the 450 mL scale size using a retreat curve impeller together with a single baffle reveal that stirrer material type and its surface morphology are important in the primary nucleation process having a significant influence on the nucleation order, as assessed via optical turbidity method, and being consistent with a surface-induced heterogeneous nucleation mechanism.

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LDA measurements and CFD predictions of the flow in a vessel stirred by a retreat curve impeller are reported. The CFD simulation was carried out using a commercial code CFX 5.5.1. The computational results have been extensively validated through the phase-resolved and phaseaveraged LDA measurements to avoid the errors associated with pseudo-turbulence. It is shown that the axial and radial velocities were well predicted quantitatively over the whole vessel by the CFD simulation but the predicted tangential and turbulent kinetic energy are less close in agreement with the experimental data.

Laser Doppler velocimetry measurements and computational fluid dynamic (CFD) simulations of turbulent flows with free-surface vortex in an unbaffled dish-bottom stirred tank reactor agitated by a Rushton turbine are presented. Measurements of the three mean and fluctuating components of the velocity vector are made in order to characterise the flow field and to provide data for CFD model validation. An Eulerian-Eulerian multiphase flow model coupled with a volume-of-fluid method for capturing the gas-liquid interface is applied to determine the vortex shape and to compute the flow field. Turbulence is modelled using the standard k−ε, shear-stress transport and the differential Reynolds-stress model with two variants of the pressure-strain correlation. The predicted mean flow field obtained using all four turbulence models are on the whole similar and generally in good agreement with measurements. However, the Reynolds-stress models provide somewhat better predictions of the mean axial velocity. The turbulent kinetic energy is well predicted in the flow below the impeller, near the bottom of the tank; whereas it is underpredicted in the region close to the impeller and near the wall by all turbulence models.