[bageshwar]

AGGLOMERATING FLUIDIZED BED
(http://xps-simulation.com/case-studi...-fluidized-bed)
Our computational models can run on a standard workstation computer geared up with a state-of the art Graphical Processing Unit (GPU), and assists in design and development of processes helping to bring down costs



The GOAL
Coating has progressed through systematic research with its application in pharmaceutical industry. Different powders are used for making tablets and granules which are coated depending upon their application. Most of the powders are cohesive by nature, where few powders exhibit cohesive nature after getting wet when sprayed with liquid (coating). Experiments become complex in the handling and fluidization of these powders. Such powders tend to form agglomerates of random massive size and shape due to interparticle forces. This effects the powder flow and flow properties, creating difficulties in understanding the fluidization process. In the case of cohesive powders, the interparticle forces are considerable and they control the behavior of a bed composed of fine particles. Thus, during fluidization, the bed of powder cracks into large portions and the gas tends to flow into the gap between the fissures. Then, channeling occurs in the bed and, eventually, the gas-solid contact is very low and any heat and mass transfer operation is weakened. When particles are fluidized with air and where the distance between the particles are very small, there arises a particle-particle interaction forces. The magnitude of these forces increases with the size reduction of the particles and becomes dominating compared to the weight of the particles. Owing to this cohesive behavior of powders agglomerates can be formed thereby making it difficult to understand the flow behavior and coating process.



Our SOLUTION
Fully coupled CFD-DEM simulations were conducted to investigate the applicability of the van der Waals cohesive force model to a spray fluid bed. For the present simulation DEM was executed on the Graphic Unit Processing Unit (GPU) and the CFD on the Central Processing Unit (CPU). For this, DEM code XPS® was coupled with CFD code AVL FIRE™. Based on this approach a bottom spray fluid bed coater was simulated for a process of 30 sec. The growth and breakage of agglomerates was numerically confirmed. Number of particles sprayed over the simulation time and mean velocity were monitored in both cohesive and non-cohesive systems to understand the behavior of fluidization.



Source: M. Adepu, “A comparative numerical study of cohesive and non-cohesive particles in a fluidized bed”, Master Thesis; Rutgers University, USA; Research Center Pharmaceutical Engineering GmbH, Austria. (https://rucore.libraries.rutgers.edu...b/47244/PDF/1/)