Effect of Baffle Design on the Off-bottom Suspension Characteristics of Axial-flow Impellersina Pilot-scale Mixing Vessel

M. Špidla, V. Sinevič and V. Machoň

Abstract
The work aimed to determine the optimum system parameters for complete particle suspension. The experiments performed in a pilot-scale vessel (D = 1 m) were focussed on a study of the effects of geometrical vessel arrangements and, above all, on the effect of alterations to the shape of the baffles. The experiments sought above all to determine the critical impeller speed, ncr, and impeller power consumption, P, in a vessel equipped with non-standard, arrow-headed baffles, and also to compare these experimental data with results arising from measurements undertaken in the same vessel, but equipped with four standard straight baffles. Three types of axial-flow impellers were investigated, each of them in two sizes. The suspension volume fraction, φ, varied up to 10 %, with particle diameter from 0.1 to 3 mm. The results aid the selection of the most favourable types of baffles and impeller giving the minimum power consumption and/or the minimum speed for just-suspended particles. It is shown that the installation of arrow-headed baffles appears to be energetically more advantageous compared with the standard baffling.

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Keywords
Mixing, solids suspension, non-standard baffles, critical impeller speed, power consumption, pilot-scale mixing vessel