Hydrodynamics in a vessel stirred by simple and double helical ribbon impellers

2013 ◽  
Vol 3 (1) ◽  
Author(s):  
Houari Ameur ◽  
Mohamed Bouzit ◽  
Abdellah Ghenaim
Keyword(s):  
Power Consumption ◽  
Finite Volume Method ◽  
Satisfactory Agreement ◽  
Rotational Speed ◽  
Flat Bottom ◽  
Helical Ribbon ◽  
Shear Thinning Fluids ◽  
Tank Bottom ◽  
Volume Method ◽  
Fluid Rheology

AbstractThe present paper treats the agitation of shear thinning fluids in a cylindrical unbaffled vessel with a flat-bottom. Two kinds of impellers have been used: simple and double helical ribbons. This work is achieved with the help of CFD package (CFX-12.0), which is based on the finite volume method to solve the continuity and momentum equations. The effect of impeller rotational speed, fluid rheology, impeller size, impeller clearance from the tank bottom on the flow fields and power consumption have been investigated. Finally, a comparison between the two impellers is made. It was found that the best performance is obtained with double helical ribbon impeller placed at the middle of the tank, with moderate blade size and operating at Re g > 20. Our results have been compared with those of other literatures and a satisfactory agreement is observed.

scholarly journals CFD Investigation Of Mixing Of Yield-Pseudoplastic Fluid With Anchor Impeller

2021 ◽  
Author(s):  
Poonam Prajapati
Keyword(s):  
Power Consumption ◽  
Mixing Time ◽  
Diameter Ratio ◽  
Cfd Modeling ◽  
Cylindrical Tank ◽  
Flat Bottom ◽  
Pseudoplastic Fluid ◽  
Impeller Blade ◽  
Blade Width ◽  
Fluid Rheology

The Anchor impeller, which is a close clearance impeller, produces high shear near the vessel wall and is recommended for mixing of highly viscous fluids. A thorough search of the literature suggests that few publications have beeen devoted to the computational fluid dynamics (CFD) modeling of mixing of non-Newtonian fluids with the anchor impeller. Thus the objectives of this study are (i)to generate a 3-D flow field for mixing of yield-pseudoplastic fluid in a flat bottom cylindrical tank equipped with two-and four-blade anchor impellers using CFD modeling technique, (ii) to evaluate the effects of fluid rheology agitator speed, number of blades, vessel clearance and impeller blade width on power consumption, mixing time and flow patterns, and (iii) to determine the optimum value of clearance to diameter ratio and impeller blade width to diameter ratio on the basis of minimum mixing time. The study was carried out for a yield-stress pseudoplastic fluid, using a CFD package (Fluent), to simulate the 3-D flow domain generated in a cylindrical tank equipped with two-and four-blade anchor impellers. The multiple reference frame (MRF) technique was employed to model the rotation of impellers. The rheology of the fluid was approximated using the Herschel-Bulkley model. To validate the model, CFD results for the power were compared to experimental data. After the flow fields were calculated, the simulations for tracer homogenization was performed to simulate the mixing time. The effect of impeller speed, fluid rheology, and number of impellers on power consumption, mixing time, and flow pattern were explored. The optimum values of c/D (clearance to diameter) and w/D (impeller blade width to diameter) ratios were determined on the basis of minimum mixing time.

Granular Flow of Corn Stover Particles in a Helical Ribbon Stirred Tank

2017 ◽  
Vol 15 (3) ◽  
Author(s):  
Juan Huang ◽  
Gance Dai
Keyword(s):  
Power Consumption ◽  
Corn Stover ◽  
Rotational Speed ◽  
Solid Phase ◽  
Flow Characteristics ◽  
Stirred Tank ◽  
Core Material ◽  
Granular Bed ◽  
Helical Ribbon ◽  
High Solids Loading

Abstract The flow characteristics and power consumption of corn stover particles in a helical ribbon stirred tank was investigated in the context of simultaneous saccharification and fermentation of corn stover at high solids loading. It was found that the particles in the tank can be divided into conveyed material and core material according to their flow characteristics. The flow of the former materials was frictional regime and the latter was intermediate flow; the conveyed material avalanched into the core at the top of granular bed. The granular bed dilated when the impeller was rotating, which was beneficial for the entrance of liquid enzyme into the solid phase and for the successful proceeding of the saccharification of the corn stover. The power of granular mixing was linearly proportional to the impeller rotational speed due to the discrete characteristic of the particles and flow dynamics of the conveyed material. The ratio of power consumption to the impeller rotational speed (P/N) was linear proportional to loading ratio and the dimensionless torque (M/mgR) was 0.48. The power consumption increased first and then decreased as the corn stover particles evolved from granular/wet granular to paste/slurry. The maximum power consumption was at 83 % (w/w) moisture content.

scholarly journals CFD Investigation Of Mixing Of Yield-Pseudoplastic Fluid With Anchor Impeller

2021 ◽  
Author(s):  
Poonam Prajapati
Keyword(s):  
Power Consumption ◽  
Mixing Time ◽  
Diameter Ratio ◽  
Cfd Modeling ◽  
Cylindrical Tank ◽  
Flat Bottom ◽  
Pseudoplastic Fluid ◽  
Impeller Blade ◽  
Blade Width ◽  
Fluid Rheology

The Anchor impeller, which is a close clearance impeller, produces high shear near the vessel wall and is recommended for mixing of highly viscous fluids. A thorough search of the literature suggests that few publications have beeen devoted to the computational fluid dynamics (CFD) modeling of mixing of non-Newtonian fluids with the anchor impeller. Thus the objectives of this study are (i)to generate a 3-D flow field for mixing of yield-pseudoplastic fluid in a flat bottom cylindrical tank equipped with two-and four-blade anchor impellers using CFD modeling technique, (ii) to evaluate the effects of fluid rheology agitator speed, number of blades, vessel clearance and impeller blade width on power consumption, mixing time and flow patterns, and (iii) to determine the optimum value of clearance to diameter ratio and impeller blade width to diameter ratio on the basis of minimum mixing time. The study was carried out for a yield-stress pseudoplastic fluid, using a CFD package (Fluent), to simulate the 3-D flow domain generated in a cylindrical tank equipped with two-and four-blade anchor impellers. The multiple reference frame (MRF) technique was employed to model the rotation of impellers. The rheology of the fluid was approximated using the Herschel-Bulkley model. To validate the model, CFD results for the power were compared to experimental data. After the flow fields were calculated, the simulations for tracer homogenization was performed to simulate the mixing time. The effect of impeller speed, fluid rheology, and number of impellers on power consumption, mixing time, and flow pattern were explored. The optimum values of c/D (clearance to diameter) and w/D (impeller blade width to diameter) ratios were determined on the basis of minimum mixing time.

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