Comparative study of the fluid dynamics of bottom spray fluid bed coaters |
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Authors: | L W Chan Elaine S K Tang Paul W S Heng |
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Institution: | (1) GEA-NUS Pharmaceutical Processing Research Laboratory, Department of Pharmacy, Faculty of Science, National University of Singapore, 18 Science Drive 4, Singapore, 117543, Singapore; |
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Abstract: | Fluid dynamics of pellets processed in bottom spray traditional Wurster coating and swirl accelerated air (precision) coating
were compared with the intent to understand and facilitate improvements in the coating processes. Fluid dynamics was described
by pellet mass flow rate (MFR) obtained using a pellet collection system and images captured using high speed photography.
Pellet flow within the partition column was found to be denser and slower in Wurster coating than in precision coating, suggesting
a higher tendency of agglomeration during the coating process. The influence of partition gap and 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, and weak suction pressure.
In precision coating, MFR was found to increase uniformly with air flow rate and atomizing pressure, whereas MFR in Wurster
coating did not correlate as well with air flow rate and 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 and dependent
on pressure differential, thus it is more responsive to changes in operational variables than Wurster coating. |
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Keywords: | fluid bed coaters coating flow pellets |
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