Dense Solid-Liquid Suspensions in Top-Covered Unbaffled Stirred Vessels

摘要

In the present work solids suspension is investigated in an unbaffled tank stirred by arnRushton turbine and provided with a top-cover in order to avoid the formation of thernwell known central vortex. The data obtained are compared with those pertainingrnbaffled stirred tanks via comparison with the well known Zwietering's correlation. Therndependence of Njs on particle concentration is found to be similar to that wellrnestablished for baffled vessels, while, as a difference from the latter, Njs is found torndecrease when liquid viscosity increases. Results also show that Njs is substantiallyrnindependent of particle size, a feature that may advice the adoption of unbaffled tanksrnwhen large heavy particles are to be dealt with. On the other hand, a smaller exponentrnfor the scale-up rule is found with respect to baffled tanks, which implies the need forrnlarger specific power consumptions the larger the vessel size and may limit usefulrnapplications to small to medium plant sizes. Finally, a correlation akin to Zwietering'srncorrelation is proposed for top-covered unbaffled stirred tanks.