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Hsiu-po Kuo - One of the best experts on this subject based on the ideXlab platform.
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Transition from binder to matrix-forming: The effect of hydroxypropylmethylcellulose concentration on the properties of starch/hydroxypropylmethylcellulose granules prepared in a high shear granulator
Journal of the Taiwan Institute of Chemical Engineers, 2020Co-Authors: An-ni Huang, H.h. Cheng, Wen-chuin Hsu, Chiung-yin Huang, Hsiu-po KuoAbstract:Abstract The effects of the hydroxypropylmethylcellulose (HPMC) concentration and the operation parameters on the starch/HPMC granule properties prepared in a high shear granulator are investigated. At a lower concentration of 3.8% or 4.9%, HPMC acts as an intergranule binder. At a higher concentration of 7.2%, HPMC acts as an intragranule matrix-forming polymer. At the intermediate HPMC concentration of 6.1%, HPMC shows dual roles as a binder and as matrices. At the intermediate HPMC concentration, a new granule oscillating growth profile is observed. The Impeller Rotational Speed has a more pronounced effect on the granule size distribution at the intermediate HPMC concentrations. The prepared granules are rounder and have narrow size distributions. The granules also show the highest compaction loading of 140 N and the highest tablet crushing force of 39.95 N.
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stage wise characterization of the high shear granulation process by Impeller torque changing rate
Advanced Powder Technology, 2019Co-Authors: Chiayi Lin, An-ni Huang, Hsiu-po Kuo, Hsuchen Wang, Wanyi HsuAbstract:Abstract Fine cornstarch powders are wet granulated in a lab-scale high shear granulator. The torque required for maintaining the Impeller passing through the bed with a constant rotating Speed is monitored during the continuous binder addition granulation process. A new method is proposed to identify 6 stages during the granulation process based on the fraction of the positive Impeller torque changing rate in a characteristic period of time. The morphologies and the behavior of the bed are found intrinsically different in the identified 6 stages. The influence of the Impeller blade inclined angle on the Impeller torque in each stage is initially reported. The Impeller with planner 45° blades requires higher torques in Stages I and II due to the overall powder bed mass loading. The Impeller with steeper 60° blades requires higher torques in Stages III and IV due to the higher collision frequencies between the blade and granules. The suitable granulation liquid binder to solid powder mass ratio can be readily identified in Stages II and III, and its range is found to increase with the increasing of the Impeller Rotational Speed and is independent to the blade inclined angle.
J C Leuliet - One of the best experts on this subject based on the ideXlab platform.
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laminar mixing performances of a stirred tank equipped with helical ribbon agitator subjected to steady and unsteady Rotational Speed
Chemical Engineering Research & Design, 2002Co-Authors: Jeanyves Dieulot, Guillaume Delaplace, Romuald Guerin, J P Brienne, J C LeulietAbstract:This paper investigates the way of improving the mixing of highly viscous Newtonian fluids in a tank using suitable operating conditions (unsteady stirring approaches). The agitator used is a non standard helical ribbon Impeller fitted with an anchor at the bottom. The degree of homogeneity in the tank is followed using a conductivity method after a tracer injection. It is shown that the use of time-dependent Rotational Speed during the mixing process allows energy savings. For the unsteady stirring approaches tested, energy savings can reach up to 60% compared to the energy required to obtain the same mixing time with constant Impeller Rotational Speed. Finally, a model is provided which allows the prediction of the mixing process of the agitated system with Newtonian fluids for both steady and unsteady stirring approaches.
Stephen Grano - One of the best experts on this subject based on the ideXlab platform.
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Model and experimental study of the effect of Impeller Rotational Speed on the flotation rate from a small-scale flotation cell — implications for the effect of bubble velocity
Mining Metallurgy & Exploration, 2007Co-Authors: R. Newell, Stephen GranoAbstract:A series of flotation experiments were carried out in a 2.25-dm^3 laboratory-scale Rushton turbine cell using hydrophobic quartz particles. Flotation was performed at a constant mean bubble diameter over a range of superficial gas velocities and Impeller Rotational Speeds. The overall flotation rate constant increased linearly with increasing superficial gas velocity (and hence bubble surface area flux). The rate constant also increased linearly with increasing energy dissipation, until a maximum value was reached. A further increase in energy dissipation had little effect on the rate constant. The dependency of the rate constant on energy dissipation is a reflection of the size range and hydrophobicity of the particles used in this study. The flotation rate constant increased with increasing particle size, except at the highest energy dissipation value examined, for which the flotation rate of the larger particles reached a plateau and, in some cases, decreased. Good agreement was obtained between the experimental results and those predicted by a fundamental flotation model using experimentally measured values for mean energy dissipation and the Sauter mean bubble diameter. The bubble velocity was adjusted to obtain the best fit to the experimental data. The inferred bubble velocity, based on the flotation model, was found to increase with increasing superficial gas velocity (and bubble surface area flux) and was found to decrease with increasing Impeller Rotational Speed. While the inferred bubble velocities were significantly lower than experimentally measured bubble velocities, and, except at low superficial gas velocity values, significantly higher than the bubble swarm velocity calculated from gas holdup measurements, similar trends with Impeller Rotational Speed and superficial gas velocity were observed in all cases.
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hydrodynamics and scale up in rushton turbine flotation cells part 1 cell hydrodynamics
International Journal of Mineral Processing, 2007Co-Authors: Ray Newell, Stephen GranoAbstract:Abstract The effect of operating parameters on the hydrodynamics of three geometrically similar Rushton turbine flotation cells with volumes of 2.25, 10 and 50 dm 3 was determined. The operating parameters investigated were superficial gas velocity ( J g ), Impeller Rotational Speed ( N ), and frother (methyl isobutyl carbinol, MIBC) concentration. Mean energy dissipation values measured using Laser Doppler Velocimetry (LDV) and a torque turntable method were in good agreement. As the cell volume was increased, the mean energy dissipation was proportional to N 3 D , rather than N 3 D 2 as may be expected based on dimensional analysis. Possible reasons for this difference are discussed. Aeration resulted in a slight increase in mean energy dissipation. Bubble diameters were measured using a University of Cape Town bubble size analyzer to determine the frother concentration at which a constant bubble diameter was achieved for all operating conditions and cell volumes. The critical frother concentration was 20 ppm MIBC. The mean bubble velocity was estimated by determining the time required to achieve steady state gas holdup in the top part of the cell after commencing gas sparging. For a constant mean bubble diameter, the bubble velocity increased with increasing superficial gas velocity. As the energy dissipation was increased for a given superficial gas velocity, the bubble velocity decreased linearly until a critical energy dissipation was reached. Above this value, bubble velocity decreased only slightly. As the cell volume increased, the bubble velocity, at the same superficial gas velocity and energy dissipation, also increased.
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Effect of Impeller Rotational Speed on the size dependent flotation rate of galena in full scale plant cells
Minerals Engineering, 2006Co-Authors: Stephen GranoAbstract:Abstract The first three rougher cells in the lead circuit of the Elura concentrator (formerly Pasminco Australia Limited) were selected as the plant cells for investigation. Metallurgical surveys were performed and various hydrodynamic measurements taken, allowing the galena flotation rate constant and the bubble surface area flux ( S b ) in these cells to be calculated over a wide range of gas flow rates, and at two Impeller Rotational Speeds. It was determined that altering the Impeller Rotational Speed did not significantly change the rate constant dependency on S b when flotation was considered on an unsized basis. The analysis was further extended to examine the same cells parameters on a size-by-size basis. The results obtained have been used to identify differences in the flotation behaviour of the various particle size fractions, independently of surface hydrophobicity. It is shown that the physical conditions for effective flotation of fine ( 53 μm) particle size fractions differ substantially, suggesting that a specific hydrodynamic environment will favour a high flotation rate for fine galena, which may be detrimental to the recovery of coarse galena, and vice versa. These observations are in accord with metallurgical practice that suggest that it is difficult to improve fine particle flotation without also compromising coarse particle stability efficiency simply by modifying the cell hydrodynamics alone. A fundamental flotation model was applied to quantify differences in the flotation rate of the various particle size fractions with Impeller Rotational Speed.
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hydrodynamics and scale up in rushton turbine flotation cells part 2 flotation scale up for laboratory and pilot cells
International Journal of Mineral Processing, 2006Co-Authors: Ray Newell, Stephen GranoAbstract:Abstract A series of flotation experiments was carried out in three Rushton turbine cells of volumes 2.25, 10 and 50 dm 3 using hydrophobic quartz particles to determine a set of scale-up criteria that would produce the same size-by-size flotation rate constants. Flotation was performed at a constant Sauter mean bubble diameter over a range of superficial gas velocities and Impeller Rotational Speeds. The overall flotation rate constant increased linearly with increasing superficial gas velocity (and hence bubble surface area flux). The rate constant also increased linearly with increasing energy dissipation, until a maximum value was reached. A further increase in energy dissipation had little effect on the rate constant. The dependency of the rate constant on energy dissipation is a reflection of the size range and hydrophobicity of the particles used in this study. Good agreement was obtained between the experimental results and those predicted by a fundamental flotation model using experimentally measured values for mean energy dissipation and the Sauter mean bubble diameter. The bubble velocity was adjusted to obtain the best fit of the experimental data. This inferred bubble velocity was found to increase with increasing superficial gas velocity and decrease with increasing Impeller Rotational Speed. To achieve scale-up of the flotation rate constants, maintaining a constant bubble surface area flux was used as one criterion. The other operating variable was the Impeller Rotational Speed, which, for successful scale-up was adjusted so that N 3 D was constant over the cell volume range. This enabled the measured mean energy dissipation for the three cells to be held constant as the cell volume increased.
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Hydrodynamics and scale up in Rushton turbine flotation cells: Part 1 — Cell hydrodynamics
International Journal of Mineral Processing, 2006Co-Authors: Ray Newell, Stephen GranoAbstract:Abstract The effect of operating parameters on the hydrodynamics of three geometrically similar Rushton turbine flotation cells with volumes of 2.25, 10 and 50 dm 3 was determined. The operating parameters investigated were superficial gas velocity ( J g ), Impeller Rotational Speed ( N ), and frother (methyl isobutyl carbinol, MIBC) concentration. Mean energy dissipation values measured using Laser Doppler Velocimetry (LDV) and a torque turntable method were in good agreement. As the cell volume was increased, the mean energy dissipation was proportional to N 3 D , rather than N 3 D 2 as may be expected based on dimensional analysis. Possible reasons for this difference are discussed. Aeration resulted in a slight increase in mean energy dissipation. Bubble diameters were measured using a University of Cape Town bubble size analyzer to determine the frother concentration at which a constant bubble diameter was achieved for all operating conditions and cell volumes. The critical frother concentration was 20 ppm MIBC. The mean bubble velocity was estimated by determining the time required to achieve steady state gas holdup in the top part of the cell after commencing gas sparging. For a constant mean bubble diameter, the bubble velocity increased with increasing superficial gas velocity. As the energy dissipation was increased for a given superficial gas velocity, the bubble velocity decreased linearly until a critical energy dissipation was reached. Above this value, bubble velocity decreased only slightly. As the cell volume increased, the bubble velocity, at the same superficial gas velocity and energy dissipation, also increased.
Guillaume Delaplace - One of the best experts on this subject based on the ideXlab platform.
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the influence of stirring Speed temperature and solid concentration on the rehydration time of micellar casein powder
Dairy Science & Technology, 2010Co-Authors: Romain Jeantet, Pierre Schuck, Christophe Andre, Guillaume DelaplaceAbstract:Rehydration is an essential quality attribute of dairy powders. Before industrial use, most powders are generally dissolved in mechanically stirred tanks in order to obtain a homogeneous solution as quickly as possible. The purpose of the present study was to investigate the effect of stirring conditions on the rehydration properties of a micellar casein powder. The powder particle size distribution was initially monitored during rehydration process under various conditions: hydrodynamic (400-1000 rpm), temperature (26-30 °C) and solid concentration (4.8-12% [w/w]) conditions. Then, the time required to achieve a predetermined rehydration value was determined. Finally, rehydration times were correlated to hydrodynamic conditions using a process relationship obtained from experimental data and dimensional analysis. The results showed that increasing temperature and/or agitation resulted in decreasing the rehydration time and analysis of the data enabled their respective influences to be compared. For example, increasing the temperature by only 4 °C has the same influence on rehydration time as doubling the stirring Speed. Therefore, it could be concluded that temperature has a major effect on rehydration behaviour. The process relationship suggested that for the mixing system investigated, under isothermal conditions and for the range of flow conditions and suspensions studied, the number of revolutions required to achieve a desired degree of rehydration is independent of the Impeller Rotational Speed. However, increasing the solid concentration from 4.8% to 12% significantly increased the number of revolutions required. These results are consistent with the hydrodynamic theory that higher stirring Speeds are required at higher solid concentrations in freshly suspended powders. L'aptitude a la rehydratation est une propriete essentielle des poudres laitieres car la plupart d'entre elles sont rehydratees avant usage. Cette operation est generalement effectuee en cuve agitee afin d'obtenir une solution homogene aussi vite que possible. L'objectif de cette etude etait de determiner l'influence de la vitesse d'agitation sur le temps de rehydratation d'une poudre de caseine micellaire. L'evolution de la distribution de taille des particules a ete mesuree en fonction du temps au cours d'essais de rehydratation sous differentes conditions d'agitation (400 a 1000 tour*min−1), de temperature (26 a 30 °C) et de concentration solide/liquide (4,8 a 12 % (p/p)). A partir des evolutions obtenues pour chacune des conditions experimentales, un temps de rehydratation necessaire pour atteindre un degre donne de rehydratation a ensuite ete determine. Enfin, les temps de rehydratation mesures ont ete correles aux conditions hydrodynamiques par une relation de procede decoulant des donnees experimentales et d'une analyse dimensionnelle. Les resultats obtenus permettent de comparer les effets respectifs d'une augmentation de la temperature et/ou de l'agitation sur le temps de rehydratation: une augmentation de seulement 4 °C (26 a 30 °C) se traduit par la meme diminution du temps de rehydratation qu'un doublement de la vitesse d'agitation (400 a 800 tour*min−1). On peut ainsi conclure a un effet preponderant de la temperature sur le processus de rehydratation. La relation de procede obtenue montre que, pour le melangeur utilise, en conditions isothermes et sur les gammes de vitesse d'agitation et de concentration testees, le nombre de revolutions necessaire pour atteindre un degre de rehydratation donne est independant de la vitesse d'agitation. Cependant, ce nombre augmente significativement avec la concentration de la solution lorsque la concentration augmente de 4,8 a 12 %. Ces resultats sont en accord avec la theorie hydrodynamique, la vitesse minimale de mise en suspension des particules croissant avec la concentration.
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The influence of stirring Speed, temperature and solid concentration on the rehydration time of micellar casein powder
Dairy Science & Technology, 2010Co-Authors: Romain Jeantet, Pierre Schuck, Thierry Six, Christophe Andre, Guillaume DelaplaceAbstract:(400 ∼ 1000 rpm) (26 ∼ 30 °C) (4.8 ∼ 12% w/w) 4 °C 4.8% 12%, L’aptitude à la réhydratation est une propriété essentielle des poudres laitières car la plupart d’entre elles sont réhydratées avant usage. Cette opération est généralement effectuée en cuve agitée afin d’obtenir une solution homogène aussi vite que possible. L’objectif de cette étude était de déterminer l’influence de la vitesse d’agitation sur le temps de réhydratation d’une poudre de caséine micellaire. L’évolution de la distribution de taille des particules a été mesurée en fonction du temps au cours d’essais de réhydratation sous différentes conditions d’agitation (400 à 1000 tour·min^−1), de température (26 à 30 °C) et de concentration solide/liquide (4,8 à 12 % (p/p)). À partir des évolutions obtenues pour chacune des conditions expérimentales, un temps de réhydratation nécessaire pour atteindre un degré donné de réhydratation a ensuite été déterminé. Enfin, les temps de réhydratation mesurés ont été corrélés aux conditions hydrodynamiques par une relation de procédé découlant des données expérimentales et d’une analyse dimensionnelle. Les résultats obtenus permettent de comparer les effets respectifs d’une augmentation de la température et/ou de l’agitation sur le temps de réhydratation: une augmentation de seulement 4 °C (26 à 30 °C) se traduit par la même diminution du temps de réhydratation qu’un doublement de la vitesse d’agitation (400 à 800 tour·min^−1). On peut ainsi conclure à un effet prépondérant de la température sur le processus de réhydratation. La relation de procédé obtenue montre que, pour le mélangeur utilisé, en conditions isothermes et sur les gammes de vitesse d’agitation et de concentration testées, le nombre de révolutions nécessaire pour atteindre un degré de réhydratation donné est indépendant de la vitesse d’agitation. Cependant, ce nombre augmente significativement avec la concentration de la solution lorsque la concentration augmente de 4,8 à 12 %. Ces résultats sont en accord avec la théorie hydrodynamique, la vitesse minimale de mise en suspension des particules croissant avec la concentration. Rehydration is an essential quality attribute of dairy powders. Before industrial use, most powders are generally dissolved in mechanically stirred tanks in order to obtain a homogeneous solution as quickly as possible. The purpose of the present study was to investigate the effect of stirring conditions on the rehydration properties of a micellar casein powder. The powder particle size distribution was initially monitored during rehydration process under various conditions: hydrodynamic (400–1000 rpm), temperature (26–30 °C) and solid concentration (4.8–12% [w/w]) conditions. Then, the time required to achieve a predetermined rehydration value was determined. Finally, rehydration times were correlated to hydrodynamic conditions using a process relationship obtained from experimental data and dimensional analysis. The results showed that increasing temperature and/or agitation resulted in decreasing the rehydration time and analysis of the data enabled their respective influences to be compared. For example, increasing the temperature by only 4 °C has the same influence on rehydration time as doubling the stirring Speed. Therefore, it could be concluded that temperature has a major effect on rehydration behaviour. The process relationship suggested that for the mixing system investigated, under isothermal conditions and for the range of flow conditions and suspensions studied, the number of revolutions required to achieve a desired degree of rehydration is independent of the Impeller Rotational Speed. However, increasing the solid concentration from 4.8% to 12% significantly increased the number of revolutions required. These results are consistent with the hydrodynamic theory that higher stirring Speeds are required at higher solid concentrations in freshly suspended powders.
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The influence of stirring Speed, temperature and solid concentration on the rehydration time of micellar casein powder
Dairy Science & Technology, 2010Co-Authors: Romain Jeantet, Pierre Schuck, Thierry Six, Christophe Andre, Guillaume DelaplaceAbstract:Rehydration is an essential quality attribute of dairy powders. Before industrial use, most powders are generally dissolved in mechanically stirred tanks in order to obtain a homogeneous solution as quickly as possible. The purpose of the present study was to investigate the effect of stirring conditions on the rehydration properties of a micellar casein powder. The powder particle size distribution was initially monitored during rehydration process under various conditions: hydrodynamic (400-1000 rpm), temperature (26-30 °C) and solid concentration (4.8-12% [w/w]) conditions. Then, the time required to achieve a predetermined rehydration value was determined. Finally, rehydration times were correlated to hydrodynamic conditions using a process relationship obtained from experimental data and dimensional analysis. The results showed that increasing temperature and/or agitation resulted in decreasing the rehydration time and analysis of the data enabled their respective influences to be compared. For example, increasing the temperature by only 4 °C has the same influence on rehydration time as doubling the stirring Speed. Therefore, it could be concluded that temperature has a major effect on rehydration behaviour. The process relationship suggested that for the mixing system investigated, under isothermal conditions and for the range of flow conditions and suspensions studied, the number of revolutions required to achieve a desired degree of rehydration is independent of the Impeller Rotational Speed. However, increasing the solid concentration from 4.8% to 12% significantly increased the number of revolutions required. These results are consistent with the hydrodynamic theory that higher stirring Speeds are required at higher solid concentrations in freshly suspended powders.
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Stirring Speed, temperature and solid concentration influence on micellar casein powder rehydration time
Dairy Science & Technology, 2010Co-Authors: Romain Jeantet, Pierre Schuck, Thierry Six, Christophe Andre, Guillaume DelaplaceAbstract:Rehydration is an essential quality attribute of dairy powders. Before industrial use, most powders are generally dissolved in mechanically stirred tanks in order to obtain a homogeneous solution as quickly as possible. The purpose of the present study was to investigate the effect of stirring conditions on the rehydration properties of a micellar casein powder. The powder particle size distribution was initially monitored during rehydration process under various conditions: hydrodynamic (400-1000 rpm), temperature (26-30 °C) and solid concentration (4.8-12% [w/w]) conditions. Then, the time required to achieve a predetermined rehydration value was determined. Finally, rehydration times were correlated to hydrodynamic conditions using a process relationship obtained from experimental data and dimensional analysis. The results showed that increasing temperature and/or agitation resulted in decreasing the rehydration time and analysis of the data enabled their respective influences to be compared. For example, increasing the temperature by only 4 °C has the same influence on rehydration time as doubling the stirring Speed. Therefore, it could be concluded that temperature has a major effect on rehydration behaviour. The process relationship suggested that for the mixing system investigated, under isothermal conditions and for the range of flow conditions and suspensions studied, the number of revolutions required to achieve a desired degree of rehydration is independent of the Impeller Rotational Speed. However, increasing the solid concentration from 4.8% to 12% significantly increased the number of revolutions required. These results are consistent with the hydrodynamic theory that higher stirring Speeds are required at higher solid concentrations in freshly suspended powders. L'aptitude à la réhydratation est une propriété essentielle des poudres laitières car la plupart d'entre elles sont réhydratées avant usage. Cette opération est généralement effectuée en cuve agitée afin d'obtenir une solution homogène aussi vite que possible. L'objectif de cette étude était de déterminer l'influence de la vitesse d'agitation sur le temps de réhydratation d'une poudre de caséine micellaire. L'évolution de la distribution de taille des particules a été mesurée en fonction du temps au cours d'essais de réhydratation sous différentes conditions d'agitation (400 à 1000 tour*min−1), de température (26 à 30 °C) et de concentration solide/liquide (4,8 à 12 % (p/p)). À partir des évolutions obtenues pour chacune des conditions expérimentales, un temps de réhydratation nécessaire pour atteindre un degré donné de réhydratation a ensuite été déterminé. Enfin, les temps de réhydratation mesurés ont été corrélés aux conditions hydrodynamiques par une relation de procédé découlant des données expérimentales et d'une analyse dimensionnelle. Les résultats obtenus permettent de comparer les effets respectifs d'une augmentation de la température et/ou de l'agitation sur le temps de réhydratation: une augmentation de seulement 4 °C (26 à 30 °C) se traduit par la même diminution du temps de réhydratation qu'un doublement de la vitesse d'agitation (400 à 800 tour*min−1). On peut ainsi conclure à un effet prépondérant de la température sur le processus de réhydratation. La relation de procédé obtenue montre que, pour le mélangeur utilisé, en conditions isothermes et sur les gammes de vitesse d'agitation et de concentration testées, le nombre de révolutions nécessaire pour atteindre un degré de réhydratation donné est indépendant de la vitesse d'agitation. Cependant, ce nombre augmente significativement avec la concentration de la solution lorsque la concentration augmente de 4,8 à 12 %. Ces résultats sont en accord avec la théorie hydrodynamique, la vitesse minimale de mise en suspension des particules croissant avec la concentration.
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laminar mixing performances of a stirred tank equipped with helical ribbon agitator subjected to steady and unsteady Rotational Speed
Chemical Engineering Research & Design, 2002Co-Authors: Jeanyves Dieulot, Guillaume Delaplace, Romuald Guerin, J P Brienne, J C LeulietAbstract:This paper investigates the way of improving the mixing of highly viscous Newtonian fluids in a tank using suitable operating conditions (unsteady stirring approaches). The agitator used is a non standard helical ribbon Impeller fitted with an anchor at the bottom. The degree of homogeneity in the tank is followed using a conductivity method after a tracer injection. It is shown that the use of time-dependent Rotational Speed during the mixing process allows energy savings. For the unsteady stirring approaches tested, energy savings can reach up to 60% compared to the energy required to obtain the same mixing time with constant Impeller Rotational Speed. Finally, a model is provided which allows the prediction of the mixing process of the agitated system with Newtonian fluids for both steady and unsteady stirring approaches.
Alessandro Paglianti - One of the best experts on this subject based on the ideXlab platform.
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Measurement of Gas Hold-up Distribution in Stirred Vessels Equipped with Pitched Blade Turbines by Means of Electrical Resistance Tomography
Chemical engineering transactions, 2017Co-Authors: Antonio Busciglio, M. Opletal, Tomáš Moucha, Giuseppina Montante, Alessandro PagliantiAbstract:Gas dispersion is a widespread operation in the process industry. The effectiveness of the dispersion affects fluid mixing, heat and mass transfer rates and, as a consequence, the chemical or biochemical reactions involved. In this work, the gas-liquid dispersion in stirred tanks equipped with pitched blade turbines (PBT) is investigated by means of Electrical Resistance Tomography (ERT). The main goal of this study is the assessment of gas-distribution in the vessel. Measurements are taken in case of different fluid dynamic regimes, which occurrence depends on the operating conditions. The effect of Impeller Rotational Speed on gas-liquid dispersion is investigated in vessels having different sizes. The adoption of ERT allows the assessment of gas distribution through the vessel volume without any particular limitation about the maximum gas volume fraction, so that experimental conditions close to that adopted in industrial operation can be effectively managed. The transition between flooding and loading regime is investigated, in which the Impeller starts to effectively distribute the gas throughout the liquid phase. The vessel size is found to play a role in determining the condition at which loading regime occurs. The data could be either used to set up simplified correlations for the transition between flooding/loading regimes or as a valuable benchmark for CFD simulation, given the detailed information available about the spatial distribution the dispersed gas.
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spectral and wavelet analysis of the flow pattern transition with Impeller clearance variations in a stirred vessel
Chemical Engineering Science, 2003Co-Authors: Chiara Galletti, Michael Yianneskis, Elisabetta Brunazzi, Alessandro PagliantiAbstract:Abstract The double- to single-loop pattern transition in stirred vessels stemming from a change in the off-bottom clearance of a Rushton turbine has been investigated by laser doppler anemometry. Time-resolved data showed the transition occurring within a range of clearance values and allowed the distinction of three types of flow: the double-loop regime, the single-loop regime and an unstable one termed “transitional state”. Experiments of up to 3– 4 h duration showed that both the onset and the lifetimes of these types of flow were random; however, in the transitional state, the flow varied between the two circulation patterns in a periodic manner, with a frequency linearly related to the Impeller Rotational Speed. The results have important implications for mixing process and vessel design as well as CFD predictions of the flows which are discussed.
