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AAPS PharmSciTech. 2000 December; 1(4): 1–3.
Published online 2000 September 18. doi:  10.1208/pt0104_tn3
PMCID: PMC2750450

Importance of inlet air velocity in fluid bed dyring of a granulation prepared in a high shear granulator


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.

Keywords: Inlet Air Velocity, Fluid Bed Drying, Drying Uniformity, Sample Locations

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.
1. Van Scoik KG, Zoglio MA, Carstensen JT. Fluid bed drying. In: Lieberman HA, Lachman L, Schwartz JB, editors. From Pharmaceutical Dosage Forms: Tablets, Volume 2. New York: Marcel Dekker, Inc.; 1990. pp. 91–96.
2. Zoglio MA, Streng WH, Carstensen JT. Diffusion model for fluidized-bed drying. Pharm Tech. 1975;64(11):1869–1873. [PubMed]
3. Parikh DM. Airflow in batch fluid-bed processing. Pharm Tech. 1991;15(3):100–110.
4. Rowe PN, Partridge BA, Cheney AG, Henwood GA, Lyall E. The mechanisms of solids mixing in fluidized beds. Trans. Inst. Chem Eng. 1965;32:T271–T286.
5. Davies L, Richardson JF. Gas interchange between bubbles and the continuous phase in a fluidized bed. Trans Inst Chem Eng. 1966;44:T293–T305.

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