Wurster particle positions

In Fig. 7.50, snapshots of the particle positions and their velocities after the same process time are displayed. The granulator is cut vertically in the middle, and the central plane and the parts behind that plane are shown. The color indicates the particle velocity blue particles move slowly (v < 0.5 m s ) and red particles are fast (v > 1.5 m s ). It can be seen from Fig. 7.50 that for all spout velocities the particles are concentrated at the center in the lower part of the Wurster tube. For high spout... 

Fig. 7.50 Instantaneous particle positions and velocity distributions inside the Wurster tube at t= 1.4s colors indicate the velocity magnitude.

Typical snapshots of particle positions and velocities are shown in Fig. 4.19 for the three investigated apparatuses. The top-spray fluidized bed and the Wurster equipment were cut along the central vertical plane in order to show the particles at... 

Fig. 4.19 I nstantaneous particle positions and particle velocity distributions at identical process conditions, (a) Conventional fluidized bed with top spray (b) Wurster equipment (c) ProCell spouted bed (Fries, 2012). Colors indicate the particle velocities.

Draft Tube Designs and Spouted Beds A draft tube is often employed to regnlate particle circnlation patterns. The most common design is the Wurster draft tnbe flnidbea employed extensivelvin the pharmacentical industry, nsnally for coating and layered growtJi applications. The Wurster coater nses a bottom positioned spray, bnt other variations are available (Table 20-47). 

In a top-spray fluidised bed, air is introduced through a uniform air distribution plate. Compared to the particle motion in the bottom-spray fluidised bed, the fluidisation pattern is less controlled. Particular to the top-spray method, the nozzle is positioned above the particle bed, and coating liquid is sprayed coimtercurrently, or down, into the fluidising core particles. Compared to a Wurster fluid bed, it is more... 

Fluid bed coating One version of this coating is known as Wurster coating and was developed in the 1950s and 1960s. The Wurster coater relies upon a bottom-positioned nozzle spraying the wall material up into a fluidized bed of core particles. Another version sprays the wall material down into the core particles. 

Fig. 7.56 Instantaneous position and velocity distribution of the particles in the Wurster zone for different gap distances at time t= 1.4s.

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