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Critical Impeller Speed for Suspending Solids in Aerated Agitation Tanks
Author(s) -
Zhu Yonggang,
Wu Jie
Publication year - 2002
Publication title -
the canadian journal of chemical engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.404
H-Index - 67
eISSN - 1939-019X
pISSN - 0008-4034
DOI - 10.1002/cjce.5450800417
Subject(s) - impeller , sparging , suspension (topology) , agitator , aeration , mixing (physics) , volatile suspended solids , suspended solids , materials science , mechanics , chromatography , chemistry , environmental science , mathematics , physics , waste management , engineering , environmental engineering , wastewater , homotopy , quantum mechanics , pure mathematics
Systematic measurements have been carried out in agitated gas‐liquid‐solids systems to determine the just off‐bottom suspension speed. A variety of solids sizes, solids concentrations, impeller sizes and tank sizes are used. The difference between the just off‐bottom suspension speeds with and without gas sparging does not show a linear relationship with the gassing rate and the relation is system‐dependent. The relative just off‐bottom suspension speed RJSS = N jsg / N js is found to be dependent only on the just suspension aeration number N a js = Q g / N js D 3 and, for DT6 impellers, the relation is RJSS = 1 + mNa n js with the values of 2.6 and 0.7 for m and n , respectively. The relation is independent of the impeller size, solids size, solids loading and tank size, and can be used to scale up laboratory data to full‐scale mixing vessels. Data from different studies support the present findings.