Comparative study of the fluid dynamics of bottom spray fluid bed coaters
Fluid dynamics of pellets processed in bottom spray traditional Wurster coating; swirl accelerated air (precision) coating were compared with the intent to understand; facilitate improvements in the coating processes. Fluid dynamics was described by pellet mass flow rate (MFR) obtained using a pellet collection system; images captured using high speed photography. Pellet flow within the partition column was found to be denser; slower in Wurster coating than in precision coating, suggesting a higher tendency of agglomeration during the coating process. The influence of partition gap; load on the MFR indicated that the mechanism of transport of pellets into the coating zone in precision coating depended on a strong suction, whereas in Wurster coating, pellets were transported by a combination of peripheral fluidization, gravity,; weak suction pressure. In precision coating, MFR was found to increase uniformly with air flow rate; atomizing pressure, whereas MFR in Wurster coating did not correlate as well with air flow rate; atomizing pressure. This demonstration showed that transport in precision coating was air dominated. In conclusion, fluid dynamics in precision coating was found to be air dominated; dependent on pressure differential, thus it is more responsive to changes in operational variables than Wurster coating.
L. W. Chan1?Elaine S. K. Tang1?Paul W. S. Heng1Email:phapaulh@nus.edu.sg
[1] Department of Pharmacy, National University of Singapore, 18 Science Drive 4, 117543 Singapore
