Rewetting effects and droplet motion on partially wetted powder surfaces

In high shear mixer granulation, the powder is agitated in a vessel while liquid is sprayed onto the powder. Formation of "nuclei" can be predicted using a nucleation regime map. However, this approach assumes that only dry powder enters the spray zone. Industrial granulation processes com...

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Bibliographic Details
Published in:AIChE journal 2009-06, Vol.55 (6), p.1402-1415
Main Authors: Hapgood, Karen P, Nguyen, Thanh H, Hauw, Sunarko, Iveson, Simon M, Shen, Wei
Format: Article
Language:English
Subjects:
Applied sciences
Chemical engineering
Correlation analysis
drop penetration
Exact sciences and technology
granulation
Laplace transforms
nucleation
powder
Sintering, pelletization, granulation
Solid-solid systems
spreading
wetting
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Summary:In high shear mixer granulation, the powder is agitated in a vessel while liquid is sprayed onto the powder. Formation of "nuclei" can be predicted using a nucleation regime map. However, this approach assumes that only dry powder enters the spray zone. Industrial granulation processes commonly add 20-50 wt % fluid, and the partially wetted powder recirculates many times through the spray zone. The effect of partially wetted powder re-entering the spray zone is not currently known. To investigate, droplets were added to a powder bed at controlled separation distances and time intervals. A strong correlation between drop penetration time and droplet motion on the powder bed surface was observed. For fast penetrating systems, nucleation was only slightly affected by the presence of the previous droplet. However, systems with long penetration times showed lateral droplet motion due to Laplace pressure differences. Implications for the nucleation regime map are discussed. © 2009 American Institute of Chemical Engineers AIChE J, 2009
ISSN:0001-1541
1547-5905
DOI:10.1002/aic.11772