Numerical Simulation of Mixing and Drying of Pharmaceutical Particles in a Bubbling Fluidized Bed Reactor

The bubbling fluidized bed flow regime is characterized by high heat and mass transfer rate and relatively short drying times. In this project, the gas-solid mixing and drying of pharmaceutical particles in a bubbling fluidized bed reactor was simulated using the commercially available FLUENT 6.3 Computational Fluid Dynamics (CFD) code. The simulations are based on the two phase model and on the Eulerian-Eulerian approach. The mathematical model used is composed of the continuity, momentum and energy equations. Additionally, the classic drying curve model is used which includes pre-warming period, constant-rate period, and falling rate period. An effective thermal conductivity is used in the energy balance. The expressions of thermal conductivity, particle density, and drying rate were added in a form of an executable code by means of a user defined function (UDF). Moisture transfer in each phase was simulated using a user defined scalar transport equation (UDS). In order to determine the optimum particle mixing, numerical simulations were performed at different particle diameters, bed heights, inlet velocities and inlet velocity distributions, respectively. Moreover, to better understand the effect and impact of gas distribution on gas-solid flow patterns, 3-dimensional simulations were carried out using a perforated gas distributor. Simulation results are compared with experimental data to validate the potential of our model and to refine it for scale up purposes.