Internal annular wall jets: Radial flow in a stirred tank

Kresta, Suzanne M.; Bittorf, Kevin J.; Wilson, David J.

doi:10.1002/aic.690471103

Cited by 16 publications

(4 citation statements)

References 25 publications

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“…Attention will be focused on the prediction of the values at the wall since, for those locations, experimental data are available for comparison. As suggested by Kresta et al and Kemoun et al, the impeller discharge stream can be described as a submerged jet. Kemoun et al divided the jet in three regions: (a) a potential core, (b) a self-preserving zone, and (c) a zone with strong lateral expansion.…”

Section: Resultsmentioning

confidence: 98%

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Effect of Macroinstabilities in Single- and Multiple-Impeller Stirred Tanks

Paglianti

Liu

Montante

et al. 2008

Ind. Eng. Chem. Res.

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In this work, a simplified analysis of the features of macroinstabilities in stirred tanks is proposed. The experimental part of the study is based on the collection of time series acquired by pressure transducers placed on the tank wall. The measurements are not invasive, because of the probe position, and they can be easily performed in laboratory and in industrial equipment, due to the instrumentation characteristics. With respect to previous investigations, the experimental analysis is extended from Rushton and pitched-blade turbines to Chemineer BT-6 and the effect of multiple impellers (MIs) is considered. The MI presence, frequency, velocity, and strength are obtained from the analysis of the collected pressure time traces; simplified correlations for their prediction are proposed. Finally, the dynamic pressure components associated to the MIs are presented, and a simplified model to assess their importance with respect to those produced by the blade passage frequency is suggested.

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Section: Resultsmentioning

confidence: 98%

“…Because in our approach the centerline liquid velocity has to be evaluated at the vessel wall, its distance from the impeller along the jet, d , has to be known. This distance has been evaluated as suggested by Kresta et al, and the angle β, shown in Figure , has been derived from interpolation of experimental data: …”

Section: Resultsmentioning

confidence: 99%

Effect of Macroinstabilities in Single- and Multiple-Impeller Stirred Tanks

Paglianti

Liu

Montante

et al. 2008

Ind. Eng. Chem. Res.

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“…There are many characterization studies regarding the flow pattern of radial and axial flow impellers (for example (Kresta and Wood 1993;Armenante and Chou 1996;Kumaresan and Joshi 2006)). The radial flow generated with radial flow impeller first hits the wall and change direction, making motion upward and downward (Kresta et al 2001;Kumaresan and Joshi 2006). Downward jet hits the bottom of the vessel and is redirected to the center.…”

Section: Resultsmentioning

confidence: 99%

Experimental Investigation and Optimization of Solid Suspension in Non-Newtonian Liquids at High Solid Concentration

Mollaabbasi¹,

Najmabad²

2016

JAFM

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This research deals with experimental work on solid suspension and dispersion in stirred tank reactors that operate with complex fluids. Only suspended speed (Njs) throughout the vessel was characterized using Gamma-Ray Densitometry. The outcomes of this study help to understand solid suspension mechanisms involving changes the rheology of the fluid and provide engineering data for designing stirred tanks. All experiments were based on classic radial and axial flow impellers, i.e., Rushton Turbine (RT) and Pitched Blade Turbine in down pumping mode (PBT-D). Three different liquids (water, water+CMC, and water+PAA) were employed in several concentrations. The CMC solution introduced as a pseudo plastic fluid and PAA solution was applied as a Herschel Bulkley fluid. The rheological properties of these fluids were characterized separately. According to the findings, the critical impeller speeds for solid suspension for non-Newtonian fluids were more eminent than those for water. Experiments were performed to characterize the effects of solid loading, impeller clearance and viscosity on Njs. Also the PSO method is employed to find suitable parameters of Zwietering's correlation for prediction of Njs in Non Newtonian fluids.

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“…By modifying the boundary conditions, Kresta et al (2001) extended the Goertler solution to include the effect of the recirculating flow outside the jet region:…”

Section: Department Of Chemical and Materials Engineering Universitymentioning

confidence: 99%

CFD Simulations of Three‐dimensional Wall Jets in a Stirred Tank

Bhattacharya

Kresta

2002

Can J Chem Eng

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1C omputational fluid dynamics (CFD) is increasingly being used for the simulation of stirred tanks due to recent advances in computer speed and efficiency of numerical schemes. While simulations involving both steady state (Kresta and Wood, 1991;Fokema et al., 1994;Harvey et al., 1995; Ranade and Dommetti, 1996 and others) and time varying (Perng and Murthy, 1992; Derksen and Van den Akker, 1999) methods have been reported in the literature, emphasis has mainly been on the quantitative validation of flow close to the impeller. The main objective of this study is to extend the existing protocols for simulating time-averaged velocity fields to flow near the tank wall and in the bulk of the tank.Studies with axial impellers show that wall jets form in the region between the baffles and the tank wall and drive the bulk flow, imposing a single characteristic velocity scale on both the upflow at the wall and the recirculation in the center of the tank. Accuracy in prediction of the mean flow characteristics of the wall jets and the simulation of the bulk flow in the tank are therefore intimately linked. Moreover, Bittorf (2000) has shown that the velocities in the three-dimensional wall jets, in balance with the settling velocities of the solids, determine the cloud height of suspended solids at high solids concentration. The cloud height of the suspended solids along with the just suspended speed (N js ) of the impeller determines the uniformity of solids distribution in a stirred tank. While explicit relations between N js and the fluid/particle properties and the impeller type are available, the cloud height model proposed by Bittorf (2000) requires an accurate description of the effect of size, off-bottom clearance and speed of the impeller on the core velocity or source velocity of the jet. This study aims to address these issues by developing a low-cost CFD protocol which can be used to obtain geometry dependent parameters to the degree of accuracy required, without having to resort to scale model experiments.While a detailed description of the wall jets is available in Bittorf and Kresta (2001), the key results are restated here to facilitate comparison with CFD simulations in later sections. Figure 1a shows one of the wall jets formed between the baffle and the tank wall. The expansion of the jet and the decay of axial velocity in a vertical plane close to the baffle are shown for different axial positions in the tank. At any axial location, the axial velocity (U ) increases rapidly from the no slip condition at the wall to its maximum value (U m ), and then decreases with a smaller gradient. At y~ 1.7b, the axial velocity reverses direction due to recirculation and asymptotically approaches the recirculating velocity (U R ). The The flow near the tank wall in a stirred tank driven by a 45°pitched-blade turbine is simulated with Multiple Reference Frames, the k-e turbulence model and standard wall functions. The results are compared to the three-dimensional wall jet identified in a previous paper. The self-...

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Internal annular wall jets: Radial flow in a stirred tank

Cited by 16 publications

References 25 publications

Effect of Macroinstabilities in Single- and Multiple-Impeller Stirred Tanks

Effect of Macroinstabilities in Single- and Multiple-Impeller Stirred Tanks

Experimental Investigation and Optimization of Solid Suspension in Non-Newtonian Liquids at High Solid Concentration

CFD Simulations of Three‐dimensional Wall Jets in a Stirred Tank

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