This report shows that inlet air velocity can play a critical role in maintaining proper fluidization and, ultimately, uniform drying. The mechanism by which air velocity affects fluidization has been discussed by various researchers [4–5]. An indication of good fluidization is a free downward flow of the granules at the sight glass of the drying bowl, but such limited observation could be misleading. In such cases, the exhaust air temperature can be used to detect poor fluidization. If the exhaust air temperature rises more rapidly than anticipated, as seen with process 1 (Figure 1), it is an indication that fluidization is incomplete.
In conclusion, a fundamental understanding of the mechanism of fluidization by inlet air will help in the development of a fluid bed drying process that produces uniformly dried granules and minimizes the number of process problems encountered.