Use of computational fluid dynamics to investigate the relationship between hydrodynamics and rates of dissolution

Abstract

The hydrodynamics within the paddle (900 ml), basket (900 ml) and Levy beaker (350 ml and 550 ml) (Levy et al., 1965) dissolution apparatuses were simulated using the computational fluid dynamics (CFD) package, Fluent™. Several methods to define convergence and to validate the CFD solutions were investigated. The simulations within the paddle apparatus expanded on the work of McCarthy (2002), and included simulations of fluid flow around cylindrical compacts in difitrent locations and of different dimensions in the base of the vessel. A rotating reference frame was used to simulate fluid flow around compacts located at the centre of the vessel base of the paddle apparatus and for the Levy beaker apparatus, and a multiple rotating reference frame was used for the paddle apparatus containing off-centre compacts. Flow in the basket apparatus was simulated using a periodic model, and the geometry of one-quarter of the basket and vessel. The basket grid wire geometry was approximated by using a 2-D geometry' with perforations equal to the size of those in the wire mesh. Simulations of the hydrodynamics in each apparatus at different agitation rates revealed flow characteristics which were similar in nature but changed in magnitude at each rotation speed. At lower agitation rates secondary flow features were less evident.