Minimum agitation speed for solid suspension and mixing time in a torispherical -bottomed pharmaceutical stirred tank under different baffling conditions
Otto H. York Department of Chemical, Biological and Pharmaceutical Engineering
Master of Science
Armenante, Piero M.
Perna, Angelo J.
Solid particle suspension
The minimum agitation speed, NS, required to just suspend solid particles dispersed in water was experimentally determined in this work for a glass-lined type of mixing tank provided with a torispherical bottom and agitated with a retreat-blade impeller under different baffling configurations. Ns for the same tank but equipped with a different agitation system, namely an axial impeller, was also experimentally determined for the purpose of comparing of performances of the two systems. The effect of impeller off- bottom clearance and the vessel's liquid level on the minimum agitation speed were also experimentally studied. Njs, was experimentally determined using Zwietering's method, requiring that the solids do not rest on the tank bottom for more than 1-2 seconds. The value of Nis was found to depend strongly on the type of baffling, and was highest in the unbaffled tank and with solid particles 1501.1m in size and lowest in the partially baffled system.
The mixing time, θ95, required to disperse a tracer in the liquid to achieve a 95% homogeneity level was also experimentally determined in the same system for the partially baffled and fully baffled configurations. A colorimetric method coupled with image processing was used to determine the mixing time.
njit-etd2010-073 (58 pages ~ 2,441 KB pdf)
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Created April 15, 2011