Computational Fluid Dynamics Simulation of Hydrodynamics in USP Apparatus 3-the Influence of Dip Rate

Purpose: This study investigated the influence of dip rate on USP Apparatus 3 hydrodynamics in the presence of a solid dosage form (e.g. tablet) using Computational Fluid Dynamics (CFD) simulations. The primary variables of interest were the liquid phase velocity in the computational domain and wall shear stresses on the tablet surfaces.

Methods: Geometry building and model setup were based on a number of simplifying assumptions. Computational grid-independent solutions were achieved for dip rates ranging from 5 to 10 dips per minute (dpm).

Results: For all cases studied, the hydrodynamics exhibited a periodicity dictated by the dip rate. Cycle-to-cycle variations were found to be negligible. Higher velocities were predicted in the wake of the tablet and they peaked at midway positions both during the up- and downstrokes of the cylinder. Three sub-regions of velocity were identified inside the reciprocating cylinder. Results also showed localized vortices/recirculations specific to the up- and downstroke, in addition to local stagnation zones. The wall shear stresses and velocity magnitudes scaled proportionately with increasing dip rates while exhibiting qualitatively similar behavior in their spatial and temporal distributions.

Conclusions: Based on the predictions of the 2D axisymmetric CFD model, the hydrodynamics in USP Apparatus 3 is characterized by complex and periodic flow structures.