Physical Reasoning of Double- to Single-Loop Transition in Industrial Reactors using Computational Fluid Dynamics

Document Type : Regular Article

Authors

1 National Institute of Technology Warangal 1, Warangal, Telangana, 506004, India

2 National Institute of Technology Warangal 2, Warangal, Telangana, 506004, India

Abstract

Double- to single-loop pattern transition and a significant reduction in the power number with a decrease in the clearance of the Rushton turbine impeller in a baffled reactor was elucidated in earlier research works. The present work investigates the physical reasons behind these phenomena using the computational fluid dynamics approach. The Reynolds Averaged Navier–Stokes equations with standard  turbulence model closure were used to model the turbulent flow conditions in the reactor vessels. The Multiple Reference Frame (MRF) approach was adopted to model the impeller baffle interactions in the reactor vessels. The implicit Volume of Fluid (VOF) method was employed to simulate the aeration process in the reactor configurations considered. The development of a low pressure region below the impeller of a low clearance vessel deflects the discharge streams downward, leading to the formation of a single-loop pattern. The downward movement of the discharge streams reduces the vortex activity behind the impeller blades, leading to weaker form drag and a decrease in the power number of the impeller. Similarly, a high clearance vessel provides a low pressure region above the impeller which deflects the discharge streams above the impeller, resulting in a single-loop pattern and a considerable increase in the air entrainment due to superior vortex and turbulence activity present near the free liquid surface. The standard reactor vessel was found to provide superior bulk mixing of fluid as the overall turbulent dissipation rate is 35% more than that associated with low and high clearance vessels.

Keywords

References

Alonzo-Garcia, A., V. X. Mendoza-Escamilla, S. A. Martinez-Delgadillo, I. Gonzalez-Neria, C. C. Gutiérrez-Torres and J. A. Jiménez-Bernal (2019). On the Performance of Different RANS Based Models to Describe the Turbulent Flow in an Agitated Vessel using Non-Structured Grids and PIV Validation. Brazilian Journal of Chemical Engineering 36(1), 361-382.##
ANSYS (2013). ANSYS Fluent Theory Guide. ANSYS, Inc., Canonsburg, USA.##
Armenante, P. M., E. U. Nagamine and J. Susanto (1998). Determination of Correlations to Predict the Minimum Agitation Speed for Complete Solid Suspension in Agitated Vessels. Canadian Journal of Chemical Engineering 76(3), 413–419.##
Armenante, P. M. and E. U. Nagamine (1998). Effect of low off-bottom impeller clearance on the minimum agitation speed for complete suspension of solids in stirred tanks. Chemical Engineering Science 53(9), 1757–1775.##
Bates, R. L., P. L. Fondy and R. R. Corpstein (1963). An Examination of Some Geometric Parameters of Impeller Power. I & EC Process Design & Development 2(4), 310–314.##
Conti, R., S. Sicardi and V. Specchia (1981). Effect of the stirrer clearance on particle suspension in agitated vessels. Chemical Engineering Journal 22(3), 247–249.##
Coroneo, M., G. Montante, A. Paglianti and F. Magelli (2011). CFD prediction of fluid flow and mixing in stirred tanks: Numerical issues about the RANS simulations. Computers & Chemical Engineering 35, 1959-1968.##
Debab, A., N. Chergui, K. Bekrentchir and J. Bertrand (2011). An Investigation of Heat Transfer in a Mechanically Agitated Vessel. Journal of Applied Fluid Mechanics 4(2), 43-50.##
Deglon, D. A. and C. J. Meyer (2006). CFD modelling of stirred tanks: Numerical considerations. Minerals Engineering 19, 1059-1068.##
Delafosse, A., A. Line, J. Morchain and P. Guiraud (2008). LES and URANS simulations of hydrodynamics in mixing tank: Comparison to PIV experiments. Chemical Engineering Research & Design 86, 1322-1330.##
Deshmukh, N. A. and J. B. Joshi (2006). SURFACE AERATORS: Power Number, Mass Transfer Coefficient, Gas Hold up Profiles and Flow Patterns. Chemical Engineering Research and Design 84(A11), 977-992.##
Escudie, R., D. Bouyer and A. Line (2004). Characterization of Trailing Vortices Generated by a Rushton Turbine. AIChE Journal 50(1), 75-86.##
Escudie, R. and A. Line (2003). Experimental Analysis of Hydrodynamics in a Radially Agitated Tank. AIChE Journal 49(3), 585-603.##
Galletti, C. and E. Brunazzi (2011). Flow Instabilities in Mechanically Agitated Stirred Vessels. In Tech, Rijeka, Croatia.##
Galletti, C., E. Brunazzi, M. Yianneskis and A. Paglianti (2003). Spectral and wavelet analysis of the flow pattern transition with impeller clearance variations in a stirred vessel. Chemical Engineering Science 58(17), 3859–3875.##
Hirt, C. W. and B. D. Nicholas (1981). Volume of fluid method for the dynamics of free surface boundaries. Journal of Computational Physics 39, 201-225.##
Huang, Y. and M. A. Green (2015). Detection and tracking of vortex phenomena using Lagrangian coherent structures. Experiments in Fluids 56(147), 1-12.##
Ibrahim, S. and A. W. Nienow (1995). Power curves and flow patterns for a range of impellers in Newtonian fluids: 40<Re<5×105. Trans IChemE 73 Part A(5), 485–491.##
Joshi, J. B., N. K. Nere, C. V. Rane, B. N. Murthy, C. S. Mathpati, A. W. Patwardhan and V. V. Ranade (2011). CFD simulation of stirred tanks: Comparison of turbulence models. Part I: Radial flow impellers. Canadian Journal of Chemical Engineering 89, 23–82.##
Karpinska, A. M. and J. Bridgeman (2016). CFD-aided modelling of activated sludge systems- A critical review. Water Research 88, 861-879.##
Kulkarni, A. L. and A. W. Patwardhan (2014). CFD modeling of gas entrainment in stirred tank systems. Chemical Engineering Research & Design 92, 1227-1248.##
Launder, B. E. and D. B. Spalding (1974). The Numerical Computation of Turbulent Flows. Computer Methods in Applied Mechanics & Engineering 3, 269–289.##
Lee, K. C. and M. Yianneskis (1998). Turbulence properties of the impeller stream of a rushton turbine. AIChE Journal 44(1), 13-24.##
Li, L. C., N. Chen, K. F. Xiang and B. P. Xiang (2020). A Comparative CFD Study on Laminar and Turbulent Flow Fields in Dual-Rushton Turbine Stirred Vessels. JAFM 13(2), 413-427.##
Li, Z., Y. Bao and Z. Gao (2011). PIV experiments and large eddy simulations of single-loop flow fields in Rushton turbine stirred tanks. Chemical Engineering Science 66(6), 1219–1231.##
Mollaabbasi, R. and J. M. Najmabad (2016). Experimental Investigation and Optimization of Solid Suspension in Non-Newtonian Liquids at High Solid Concentration. JAFM 9(4), 1907-1914.##
Montante, G., K. C. Lee, A. Brucato and M. Yianneskis (2001a). Experiments and predictions of the transition of the flow pattern with impeller clearance in stirred tanks. Computers & Chemical Engineering 25(4), 729–735.##
Montante, G., K. C. Lee, A. Brucato and M. Yianneskis (2001b). Numerical simulations of the dependency of flow pattern on impeller clearance in stirred vessels. Chemical Engineering Science 56(12), 3751–3770.##
Montante, G., K. C. Lee, A. Brucato and M. Yianneskis (1999). An Experimental Study of Double-to Single-Loop Transition in Stirred Vessels. Canadian Journal of Chemical Engineering 77(4), 649–659.##
Motamedvaziri, S. and P. M. Armenante (2012). Flow regimes and surface air entrainment in partially filled stirred vessels for different fill rations. Chemical Engineering Science 81, 231-250.##
Nienow, A. W. (1968). Suspension of solid particles in turbine agitated baffled vessels. Chemical Engineering Science 23(12), 1453–1459.##
Ochieng, A., M. S. Onyango, A. Kumar, K. Kiriamiti and P. Musonge (2008). Mixing in a tank stirred by a Rushton turbine at a low clearance. Chemical Engineering Processing 47(5), 842–851.##
Patil, H., A. K. Patel, K. Devarajan and A. Venu Vinod (2019, December). Comparison of Different off Bottom Impeller Clearances to Investigate the Effect on Hydrodynamics in Rushton Turbine Stirred Tank. In Proceedings of the International Conference on New Frontiers in Chemical, Energy and Environmental Engineering (INCEEE-2019), NIT Warangal, Telangana, India.##
Patil, S. S., N. A. Deshmukh and J. B. Joshi (2004). Mass-Transfer Characteristics of Surface Aerators and Gas-Inducing Impellers. Industrial & Engineering Chemistry Research 43, 2765-2774.##
Roache, P. J. (1994). Perspective: A Method for Uniform Reporting of Grid Refinement Studies. Journal of  Fluids Engineering 116, 405-413.##
Ryma, A., H. Dhaouadi, H. Mhiri and P. Bournot (2013). CFD Study of Turbine Submergence Effects on Aeration of a Stirred Tank. International Journal of Chemical & Molecular Engineering 7(4), 173-178.##
Wu, H. and G. K. Patterson (1989). Laser-Doppler Measurements of Turbulent Flow Parameters in a Stirred Mixer. Chemical Engineering Science 44(10), 2207-2221.##
Yapici, K., B. Karasozen, M. Schafer and Y. Uludag (2008). Numerical investigation of the effect of the Rushton type turbine design factors on agitated tank flow characteristics. Chemical Engineering Proceedings 47, 1340-1349.##
Yianneskis, M., Z. Popiolek and J. H. Whitelaw (1987). An experimental study of the steady and unsteady flow characteristics of stirred reactors. Journal of Fluid Mechanics 175, 537-555.##
Zamiri, A. and J. T. Chung (2018). Numerical evaluation of turbulent flow structures in a stirred tank with a Rushton turbine based on scale-adaptive simulation. Computers and Fluids 170, 236-248.##
Zhang, Y., Z. Gao and Z. Li (2017). Transitional Flow in a Rushton Turbine Stirred Tank. AIChE Journal 63(8), 3610-3623.##
Zhu, Q., H. Xiao, A. Chen, S. Geng and Q. Huang (2019). CFD study on double- to single-loop flow pattern transition and its influence on macro mixing efficiency in fully baffled tank stirred by a Rushton turbine. Chinese Journal of Chemical Engineering 27, 993-1000.##
Journal of Applied Fluid Mechanics
Volume 15, Issue 5 - Serial Number 67
September and October 2022
Pages 1621-1634

Files

Cited by

History

  • Received: 17 March 2022
  • Revised: 25 May 2022
  • Accepted: 05 June 2022
  • Available online: 06 July 2022

Share

How to cite

Statistics