Computational fluid dynamics (CFD) and experimental analyses of some of the basic characteristics of air sparging in a tall stirred vessel equipped with a three-stage impeller are presented. The impeller was assembled from a radial ABT impeller as the lower

a turbine 6PBT45 as the middle and an axial Scaba-type 3SHP1 impeller as the upper. All the impellers were of the same diameter

i.e

.

225 mm

while the vessel diameter was 450 mm. The impeller's rotational speed was 178 r·min

-1

. The aeration regime was established with an air volumetric flow rate of 28.3 m

3

·h

-1

. To the best of our knowledge

this study is the first to consider the very high gassing rate by means of CFD in a tank stirred by three-stage axial/radial impellers. The numerical simulation was performed using the ANSYS Fluent (R17.2

2016) code for solving the governing equations of fluid dynamics in single- and multi-phase systems. While discussing the bubble size distribution

a discrete population balance model (PBM) was used. Adopting CFD

the stirring power and the total void fraction (the total gas holdup) were calculated. The results were in good agreement with the m

easured values using a laboratory experimental device.