Wurster coater apparatus

The real coating process in the studied Wurster coater apparatus with the bed mass of 3 kg contains about 21.8x10 particles with the size of 550 im. Unfortunately, the numerical effort for the calculation of the DPM model increases with increasing the number of simulated particles. The DPM model is unable to represent this number of particles, at least with the actually available computing power. However, the number of particles can be reduced by conservation of the particle and fluid dynamics in the simulated apparatus and its real geometry. In this work a scaling approach proposed by Link et al. (2009) and extended by Sutkar et al. (2013) has been used, in which the scahng of the particle size was carried out. Due to the size increase, the adequate properties of sohd and gas phase have been adapted to keep the dimensionless numbers Archimedes At) and Reynolds Re) and the velocities of minimal fluidization and elutriation constant. 

Figure 15 Cross-cut view of the studied Wurster coater apparatus.

Figure 18 Simulated steady-state flow field in the empty Wurster coater apparatus.

The radial distribution of the particle velocities depends significandy on the height, as it can be seen in Fig. 27. Here, the time-averaged total velocities and their vertical components are presented for different gap distances. The time-averaged total velocity of particles v, which are moved on a radial distance r from the central axis of the Wurster-coater apparatus, is given as ... 

Processes based on fluidized bed coating have been developed (49). In this process, the bioactive agent is dissolved in an organic solvent along with the polymer. This solution is then processed through a Wurster air suspension coater apparatus to form the final microcapsule product. A solvent partition technique based on continuous injection of a polymer-drug solution into flowing mineral oil has been reported (50). 

Fig. 6.2-83 Principle of the Wurster coater (right) and outline of an apparatus (left) (courtesy Glatt, Binzen, Germany)...

Fig. 6.2-86 SEM photographs of particles that were coated with fluidized bed coaters a) coated with ethylcellulose in a top-spray fluid-bed processor, b) coated with ethylcellulose in a Wurster apparatus, c) vacuum top-spray coated (retard) pellet, cut open,...

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