Numerical and experimental investigation of single phase flow characteristics in stirred tanks using Rushton turbine and flotation impeller Manjunath Basavarajappa a,⇑ , Teri Draper b , Pal Toth b , Terry A. Ring b , Sanja Miskovic a,1 a Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT 84112, USA b Department of Chemical Engineering, University of Utah, Salt Lake City, UT 84112, USA article info Article history: Received 12 March 2015 Revised 21 July 2015 Accepted 24 August 2015 Keywords: CFD Turbulence Flotation impeller PIV Flow transition abstract In this study, computational fluid dynamics (CFD) simulations are used to investigate turbulent single phase flow characteristics in lab-scale stirred tanks with different geometric variations. Water at standard conditions is used as operating fluid. Rushton turbine (RT) and flotation impeller (FI) are used to agitate the fluid leading to turbulent flows in the tank. For FI, impeller diameter, d, is varied and three sizes corresponding to d values of 75, 100, and 150 mm are considered. Additionally, for 75 and 100 mm FI, off-bottom clearance, C, is varied from 100 (D=3) to 60 mm (D=5). The impeller based Reynolds number, Re, ranged from 29,000 to 120,000. CFD results are compared with LDA data from the literature for RT and in-house PIV data for FI. CFD predictions for FI are found to match experimental measurements satisfactorily with accurate prediction of flow transition at lower C. The normalized flow properties are observed to be invariant with Re for both impellers in fully turbulent regime. Mean flow characteristics for FI suggests that the flow is characterized by strong radial and tangential velocities close to impeller with peak values along disc level. Turbulence kinetic energy profiles close to impeller are characterized by two peaks suggesting development of trailing vortex which is further verified using swirling strength visualization. For FI with diameter equal to 100 mm, flow transition in which mean flow changes from radial flow (double loop) to axial-type (single loop) flow is observed when C is reduced. Both PIV mea- surements and CFD simulation are able to predict this transition accurately. Using both torque on rotating parts and volume averaged dissipation rate of turbulence kinetic energy, power numbers are calculated for both impellers. The axial-type flow at smaller clearance is marked by significant drop in power number value. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Stirred tanks are extensively used in chemical, pharmaceutical, oil and gas, and minerals and metallurgical industries or blending, suspending, contacting, and dispersing applications. The flows generated in the stirred tanks are predominantly turbulent due to high impeller rotation speeds used to achieve necessary process conditions. Radial impellers are mainly used for dispersion and mixing applications and for processes that require high values of turbulence kinetic energy, k, and turbulence energy dissipation rate,  (Joshi et al., 2011a). Various factors like tank size, impeller shape, impeller size, number of impeller blades, number of blades, and off-bottom clearance affect the flow in stirred tanks. Recently, Joshi et al. (2011a,b) reviewed CFD results reported in the litera- ture for single and multiphase flows in stirred tanks using radial and axial impellers. Furthermore, Joshi et al. (2011a,b) compared results predicted by different turbulence models with experimen- tal laser Doppler anemometry (LDA) measurements. Joshi et al. (2011b) have reviewed all the widely used modeling approaches in the literature and summarized the shortcomings associated with each of them. Based on their comparison of CFD predictions and experimental measurements, they recommend using large eddy simulation (LES) to obtain accurate predictions of turbulent quan- tities in the impeller region. However, LES is still very expensive for industrial size tanks at high Reynolds numbers and requires modeling of filtered scales that are not completely resolved. For the radial impellers, the off-bottom clearance plays an important role in determining the type of flow pattern that is http://dx.doi.org/10.1016/j.mineng.2015.08.018 0892-6875/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail addresses: manjunath.basavarajappa@utah.edu (M. Basavarajappa), sanja.miskovic@utah.edu (S. Miskovic). 1 Principal corresponding author. Minerals Engineering 83 (2015) 156–167 Contents lists available at ScienceDirect Minerals Engineering journal homepage: www.elsevier.com/locate/mineng