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

Abstract

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