Evaluation of hydrodynamics in the basket dissolution apparatus using computational fluid dynamics--dissolution rate implications.

The aim of this work was to simulate the fluid flow in the basket dissolution apparatus using computational fluid dynamics (CFD) and to use the resulting velocity data (in combination with velocity data from simulated flow fields of the paddle dissolution apparatus) to relate velocities in the vicinity of a dissolving surface to dissolution rate. A further objective of the work was to compare fluid velocities between the basket and paddle dissolution apparatuses. CFD simulations of the basket apparatus were carried out using Fluent software. Flow field solutions were compared with results from flow visualisation techniques and with published ultrasound-pulse-echo velocity data. Velocity data from the flow field solution revealed velocities within the basket to be of the same order as those at the base of the paddle apparatus at the same rotation speed, supporting equivalent dissolution rate data from these locations. Dissolution rates were obtained for compacts of benzoic acid dissolved in 0.1 M HCl at 37 degrees C in the basket apparatus at 50 rpm. The relationship between maximum velocity in the vicinity of a dissolving surface and dissolution rate data from both the paddle and basket apparatuses was in good agreement with theoretical predictions. Analysis of the dissolution rates suggests a significant contribution from free convection in regions of low velocity at the base of the vessel of the basket apparatus.