Multiple Impellers

⎯The hydrodynamics and the flow field in an agitated vessel were measured using 2-D time resolved particle image velocimetry (2-D TR PIV). The experiments were carried out in fully baffled cylindrical flat bottom vessels 300 and 400 mm in inner diameter. The 300 mm inner diameter tank was agitated by a Rushton turbine 100 mm in diameter, and the 400 mm inner diameter tank was agitated by a Rushton turbine 133 mm in diameter. Three liquids of different viscosities were used as the agitated liquid: (i) distilled water (ν = 9.35 × 10-7 m 2 /s), (ii) a 28 vol % aqueous solution of glycol (ν = 2 × 10-6 m 2 /s), and (iii) a 43 vol % aqueous solution of glycol (ν = 3 × 10-6 m 2 /s). The velocity fields were measured at an impeller rotation speed in the range from 300 to 850 rpm, which covers the Reynolds number range from 50000 to 189 000. This means that fullydeveloped turbulent flow was reached. The experiments were performed to investigate the applicability of the following relations: ε* = ε/(u 4 /ν) = const, /u = const, Λ/η K = const, τ Λ /τ K = const, ε* = ε/((Nd) 4 /ν) = const, Λ/d ∝ Re-1 , η K /d ∝ Re-1 , /(Nd) = const, Nτ Λ ∝ R-1 , Nτ K ∝ Re-1 , and ε/(Nq) ∝ Re. These formulas were theoretically derived in our previous work, using turbulence theory, in particular, using turbulence spectrum analysis. The correctness of the proposed relations is investigated by statistical hypothesis testing.

The purpose of this work was to investigate and compare the influence of fluid flow in a single and dual impeller batch cooling crystallizer on crystal growth kinetics of borax decahydrate. Examinations were conducted in a crystallizer of 15 dm 3 stirred by a single pitched blade turbine and straight blade turbine as well as their dual configurations. Kinetics parameters of crystal growth determined at applied mixing conditions were correlated with hydrodynamic conditions. In this paper, hydrodynamics was characterized by mixing time, which was experimentally determined, and by fluid flow patterns, which were simulated by the means of computational fluid dynamic (CFD). It was found that although the crystal growth in all systems investigated was controlled by the integration mechanism, the crystal growth rate constant changed significantly with impeller configuration. Regarding the characteristics of the final product, a dependence of the crystal size distribution on the fluid flow pattern was noticed while the number of impellers did not affect the product properties. On the other hand, mixing efficiency differed significantly with the type and number of impellers.

The influence of impeller diameter on crystal growth kinetics of borax decahydrate in a batch‐cooling crystallizer of non‐standard aspect ratio was evaluated. The dual‐impeller configuration consisted of a pitched‐blade turbine which was mounted below a straight‐blade turbine on a single shaft. Three different impeller‐to‐tank diameter ratios were investigated. In all experiments, mixing was conducted at just‐suspended impeller speed. To examine hydrodynamic conditions, mixing times were measured. The fluid flow pattern and velocity distribution were determined by computational fluid dynamics. Results showed that the smallest but also more regularly shaped crystals were produced in a system with standard diameter impellers. Product yield and power consumption were highest in this case.

The aim of this work was to determine the influence of cooling rate on the nucleation and crystal growth of borax decahydrate. All experiments were carried out in baffled stirred crystallizer with the volume of 2.14 dm3. Mother liquor saturated at 30 °C was cooled down at 3 different cooling rates in the range from the 4 to 9 °C/h. In order to analyze and compare the influence of fluid flow pattern in the crystallizer on product properties, examinations were performed using two different impeller types; radial straight blade turbine (SBT) and axial pitched blade turbine (PBT). Mixing with both of impellers was carried out at constant impeller speed of 300 rpm. Concentration of the solution was measured in line by potentiometric method, while the changes of crystal size over process time were determined by optical microscope and image analysis software. The nucleation and crystal growth behaviors for borax–water system in a batch cooling crystallizer were estimated according to Mersm...

Interaction between mixing and crystallization is often<br> ignored despite the fact that it affects almost every aspect of the<br> operation including nucleation, growth, and maintenance of the<br> crystal slurry. This is especially pronounced in multiple impeller<br> systems where flow complexity is increased. By choosing proper<br> mixing parameters, what closely depends on the knowledge of the<br> hydrodynamics in a mixing vessel, the process of batch cooling<br> crystallization may considerably be improved. The values that render<br> useful information when making this choice are mixing time and<br> power consumption. The predominant motivation for this work was<br> to investigate the extent to which radial dual impeller configuration<br> influences mixing time, power consumption and consequently the<br> values of metastable zone width and nucleation rate. In this research,<br> crystallization of bora...

Conducting crystallization in an agitated vessel requires a proper selection of mixing parameters that would result in a production of crystals of specific properties. In dual impeller systems, which are characterized by a more complex hydrodynamics due to the possible fluid flow interactions, revealing a clear link between mixing parameters and crystallization kinetics is still an open issue. The aim of this work is to establish this connection by investigating how fluid flow patterns, generated by two impellers mounted on the same shaft, reflect on metastable zone width of borax decahydrate, one of the most important parameters of the crystallization process. Investigation was carried out in a 15-dm<sup>3</sup> bench scale batch cooling crystallizer with an aspect ratio (<em>H</em>/<em>T</em>) equal to 1.3. For this reason, two radial straight blade turbines (4-SBT) were used for agitation. Experiments were conducted at different impeller spacin...

The aim of this work was to experimentally investigate the influence of impeller off-bottom clearance on crystal growth kinetics of disodium tetraborate decahydrate (borax) in a dual-impeller batch cooling crystallizer. Examinations were carried out in a crystallizer of 15 dm3 with liquid height to crystallizer diameter ratio (H/dT) of 1.3. In this research, two pitched blade turbines (PBT) with diameter D/dT=0.33, were mounted on the same shaft with a constant spacing between impellers (s/D=1.0). Mixing was performed at the impeller speed which ensured the state of complete suspension in the system (N=NJS). The impeller off-bottom clearance (C/D) was varied from 0.2 to 1.3. Crystallization was carried out by a controlled cooling of the solution saturated at 30°C. Concentration of the solution was measured in line by potentiometric method, while the changes of crystal size over time were determined by optical microscope and image analysis software. Experimental results indicate that...

Highlights • The effect of impeller off-bottom clearance and zeolite mass concentration was investigated. • Critical impeller speed increases with impeller position and zeolite mass concentration. • Rate of copper exchange is affected by impeller position and zeolite mass concentration. • Amount of copper exchanged is affected only by zeolite mass concentration.

An influence of impeller blade angle on the crystallization kinetics of borax has been investigated in detail. Its importance was studied in a batch crystallizer equipped with a four-blade turbine, whose angle was varied from 30 to 90. Heterogeneous nucleation mechanism was dominant at all examined conditions, but the rate of nucleation significantly differed. Kinetic parameters of crystal growth were determined as well. Numerical values of order of crystal growth remain almost unchanged regardless of the blade angle. Different values of crystal growth rate constants are the result of the fluid dynamics in the crystallizer, caused by the different impeller blade inclinations. In all examined systems, crystal growth is integration limited. The transition from axial to radial flow, due to different blade angles, reflects on the crystal size distribution, agglomeration ratio, and crystallization yield.

Floating solids suspension in water has been studied using up-pumping pitched blade turbines (PTU). Studies were performed to determine optimum geometry and hydrodynamic characteristics of agitated systems for floating solids suspension. The impact of floating solids concentrations and particle size on the mixing time, t m , the just completely suspended impeller speeds, N JS , and the power consumption were examined. The effects of impeller diameter and its off-bottom clearance as well as the impeller blade angle on mentioned parameters were also observed. The mixing time of suspended system was measured by a conductivity technique using the sodium chloride solution as tracer, whereas, power consumption was measured by the torque table. The efficiency of PTU impellers was compared to that of other, more conventional impellers. Obtained results point to the fact that the PTU may be a viable option if the floating slurry process requires the state of complete solids suspension and its longer time maintenance.

Product design and engineering (PDE), originally heralded as a new paradigm of chemical engineering, aims to define new and/or improved products based on customer needs and/or new technologies. A comprehensive discussion of PDE as a building block for chemical engineering education, research, and practice is still lacking, preventing a broader impact on academic and industry realities more and more concerned with the “knowledge economy”. The purpose of the present paper was to contribute to the mitigation of this gap by presenting the results of the EFCE Section Group PDE survey based on PDE academia and industry expert and practitioner feedback as well as on a literature review. Status and challenges of PDE are discussed and academic and industry perspectives are mapped.

Effect of hydrodynamics on ion exchange in a batch reactor is still not appropriately studied even though proper mixing parameters may considerably affect the process of solid suspension and its costs. In this work, hydrodynamic conditions generated by straight blade turbine (SBT) impellers on suspension in the batch reactor with and without baffles were investigated. The aim of this work was to analyze influence of impeller diameter and zeolite mass on just suspended impeller speed, (NJS) power consumption, maximum amount of copper exchanged onto zeolite NaX and copper exchange kinetics as well. All experiments were conducted at the same temperature, initial concentration of the copper solution and zeolite particle size. The obtained results showed that just suspended impeller speed decreases as impeller diameter increases in the reactor with and without baffles but this trend is considerably more pronounced in the reactor with baffles. The increase in zeolite mass causes a slight ...

Interaction between mixing and crystallization is often<br> ignored despite the fact that it affects almost every aspect of the<br> operation including nucleation, growth, and maintenance of the<br> crystal slurry. This is especially pronounced in multiple impeller<br> systems where flow complexity is increased. By choosing proper<br> mixing parameters, what closely depends on the knowledge of the<br> hydrodynamics in a mixing vessel, the process of batch cooling<br> crystallization may considerably be improved. The values that render<br> useful information when making this choice are mixing time and<br> power consumption. The predominant motivation for this work was<br> to investigate the extent to which radial dual impeller configuration<br> influences mixing time, power consumption and consequently the<br> values of metastable zone width and nucleation rate. In this research,<br> crystallization of bora...

Highlights • The effect of impeller off-bottom clearance and zeolite mass concentration was investigated. • Critical impeller speed increases with impeller position and zeolite mass concentration. • Rate of copper exchange is affected by impeller position and zeolite mass concentration. • Amount of copper exchanged is affected only by zeolite mass concentration.

Effect of hydrodynamics on ion exchange in a batch reactor is still not appropriately studied even though proper mixing parameters may considerably affect the process of solid suspension and its costs. In this work, hydrodynamic conditions generated by straight blade turbine (SBT) impellers on suspension in the batch reactor with and without baffles were investigated. The aim of this work was to analyze influence of impeller diameter and zeolite mass on just suspended impeller speed, (NJS) power consumption, maximum amount of copper exchanged onto zeolite NaX and copper exchange kinetics as well. All experiments were conducted at the same temperature, initial concentration of the copper solution and zeolite particle size. The obtained results showed that just suspended impeller speed decreases as impeller diameter increases in the reactor with and without baffles but this trend is considerably more pronounced in the reactor with baffles. The increase in zeolite mass causes a slight ...

The purpose of this work was to investigate and compare the influence of fluid flow in a single and dual impeller batch cooling crystallizer on crystal growth kinetics of borax decahydrate. Examinations were conducted in a crystallizer of 15 dm 3 stirred by a single pitched blade turbine and straight blade turbine as well as their dual configurations. Kinetics parameters of crystal growth determined at applied mixing conditions were correlated with hydrodynamic conditions. In this paper, hydrodynamics was characterized by mixing time, which was experimentally determined, and by fluid flow patterns, which were simulated by the means of computational fluid dynamic (CFD). It was found that although the crystal growth in all systems investigated was controlled by the integration mechanism, the crystal growth rate constant changed significantly with impeller configuration. Regarding the characteristics of the final product, a dependence of the crystal size distribution on the fluid flow pattern was noticed while the number of impellers did not affect the product properties. On the other hand, mixing efficiency differed significantly with the type and number of impellers.

This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the final Version of Record (VOR). This work is currently citable by using the Digital Object Identifier (DOI) given below. The final VoR will be published online in Early View as soon as possible and may be different to this Accepted Article as a result of editing. Readers should obtain the final VoR from the journal website shown below when it is published to ensure accuracy of information. The authors are responsible for the content of this Accepted Article.

An influence of impeller blade angle on the crystallization kinetics of borax has been investigated in detail. Its importance was studied in a batch crystallizer equipped with a four-blade turbine, whose angle was varied from 30 to 90. Heterogeneous nucleation mechanism was dominant at all examined conditions, but the rate of nucleation significantly differed. Kinetic parameters of crystal growth were determined as well. Numerical values of order of crystal growth remain almost unchanged regardless of the blade angle. Different values of crystal growth rate constants are the result of the fluid dynamics in the crystallizer, caused by the different impeller blade inclinations. In all examined systems, crystal growth is integration limited. The transition from axial to radial flow, due to different blade angles, reflects on the crystal size distribution, agglomeration ratio, and crystallization yield.

The effect of the impeller speed upon the metastable zone width, supersaturation level, crystal growth and the crystal size distribution of borax decahydrate have been investigated to find operating conditions of a batch cooling crystallizer. The importance of impeller speed was studied in baffled stirred crystallizer with a volume of about 2 dm 3 , equipped with four straight blade turbine (4-SBT) cooling at a constant cooling rate. The metastable zone width was determined by visual method, while concentration changes during the process were monitored in line using ion-selective electrode. The crystal size distribution was determined by optical microscope and sieve analysis respectively. The power consumption measurements were performed for all impeller speeds examined as well. On the basis of the experimental results and observations it is evident that in an agitated batch crystallizer the above mentioned parameters are significantly influenced by hydrodynamic regime in the system determined by impeller used and its revolution speed.

Gas behavior was studied in a gas-liquid reactor stirred with multiple turbines. Triple PBTs pumping either down or up and BT-6's were used. The behavior of coalescing (water) and non-coalescing (sodium sulfate solution) systems was investigated. The gas phase behavior was characterized by means of the RTD and modeled with the axial dispersion model. This model was confirmed to interpret the experimental data well for water and satisfactorily for the coalescence-inhibiting solutions. The influence of the operating conditions, turbine type and system coalescing behavior on the model parameters is discussed. Comparison is also made with similar data regarding Rushton turbines and high-solidity ratio hydrofoils, as well as gas holdup.

The aim of this work was to determine the influence of cooling rate on the nucleation and crystal growth of borax decahydrate. All experiments were carried out in baffled stirred crystallizer with the volume of 2.14 dm3. Mother liquor saturated at 30 °C was cooled down at 3 different cooling rates in the range from the 4 to 9 °C/h. In order to analyze and compare the influence of fluid flow pattern in the crystallizer on product properties, examinations were performed using two different impeller types; radial straight blade turbine (SBT) and axial pitched blade turbine (PBT). Mixing with both of impellers was carried out at constant impeller speed of 300 rpm. Concentration of the solution was measured in line by potentiometric method, while the changes of crystal size over process time were determined by optical microscope and image analysis software. The nucleation and crystal growth behaviors for borax–water system in a batch cooling crystallizer were estimated according to Mersm...

in Wiley Online Library (wileyonlinelibrary.com) Crystallization processes in a 500 mL stirred tank crystallizer with computational fluid dynamics (CFD) and population balances toward estimating how crystal size distributions (CSDs) are influenced by flow inhomogeneities was explored. The flow pattern and CSD are presented here though extensive phase Doppler particle analyzer measurements and CFD predictions for three different impeller designs (disc turbine, pitched blade turbine, and Propeller) and each rotated at three different speeds (2.5, 5, and10 r/s). As crystallization processes in practice could involve break-up and aggregation of crystals, some selected break-up and aggregation kernels are incorporated. Extensive comparison of simulations with experimental data showed consistent trends in the proper quantitative range. An attempt has also been made to develop scaling laws: (a) mean particle size with average power consumption per unit mass and (b) particle-size distribution with the turbulent energy dissipation distribution.

This review evaluates computational fluid dynamic applications to analyze solid suspension quality in stirred vessels. Most researchers typically employ either Eulerian-Eulerian or Eulerian-Lagrangian approach to investigate multiphase flow in stirred vessels. With sufficient computational resources, the E-L approach simulates flow structures with higher spatial resolution for dispersed multiphase flows. Common turbulence models such as the two-equation eddy-viscosity models (

The aim of this work was to determine the influence of cooling rate on the nucleation and crystal growth of borax decahydrate. All experiments were carried out in baffled stirred crystallizer with the volume of 2.14 dm3. Mother liquor saturated at 30 °C was cooled down at 3 different cooling rates in the range from the 4 to 9 °C/h. In order to analyze and compare the influence of fluid flow pattern in the crystallizer on product properties, examinations were performed using two different impeller types; radial straight blade turbine (SBT) and axial pitched blade turbine (PBT). Mixing with both of impellers was carried out at constant impeller speed of 300 rpm. Concentration of the solution was measured in line by potentiometric method, while the changes of crystal size over process time were determined by optical microscope and image analysis software. The nucleation and crystal growth behaviors for borax–water system in a batch cooling crystallizer were estimated according to Mersm...

The aim of this work was to experimentally investigate the influence of impeller off-bottom clearance on crystal growth kinetics of disodium tetraborate decahydrate (borax) in a dual-impeller batch cooling crystallizer. Examinations were carried out in a crystallizer of 15 dm3 with liquid height to crystallizer diameter ratio (H/dT) of 1.3. In this research, two pitched blade turbines (PBT) with diameter D/dT=0.33, were mounted on the same shaft with a constant spacing between impellers (s/D=1.0). Mixing was performed at the impeller speed which ensured the state of complete suspension in the system (N=NJS). The impeller off-bottom clearance (C/D) was varied from 0.2 to 1.3. Crystallization was carried out by a controlled cooling of the solution saturated at 30°C. Concentration of the solution was measured in line by potentiometric method, while the changes of crystal size over time were determined by optical microscope and image analysis software. Experimental results indicate that...

Main focus of this work was to investigate the influence of hydrodynamic conditions on crystallization kinetics and properties of borax crystals obtained in a 15 dm 3 dual impeller batch cooling crystallizer. The two impellers used, pitched and straight blade turbine, were mounted on the same shaft. Hydrodynamics was analyzed through the values of mixing time and specific fluid flow patterns generated. Results indicate that wider metastable zones were generally observed at impeller positions characterized by higher mixing times. In those cases, growth rate constants were lower what resulted in a formation of smaller but more regularly shaped crystals. These findings imply that dual impeller position should be taken into account in order to produce crystals of desired characteristics.