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Piero M Armenante - One of the best experts on this subject based on the ideXlab platform.
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Power Consumption in Stirred Tanks Provided with Multiple Pitched-Blade Turbines
Industrial & Engineering Chemistry Research, 1999Co-Authors: Piero M Armenante, Barbara Mazzarotta, Gwo-ming ChangAbstract:The power consumed by one, two, or three downward pumping, 45° six-blade pitched-blade turbines (6-PBTs) mounted on the same shaft was experimentally determined in stirred tanks under turbulent conditions. The power drawn by each individual impeller (in single- or multiple-impeller configurations), as well as the total power consumption, was measured with strain gauges mounted on the shaft and reported as individual or total power numbers. The power dissipated by single downward pumping, 45° four-blade pitched-blade turbines (4-PBTs) was also determined. Different combinations of the number of Impellers, impeller diameter-to-tank diameter ratio, off-bottom clearance of the lowest impeller, Cb1, and spacing among Impellers were tested. The overall power numbers of double 6-PBT systems were typically found to be smaller than twice the power number of a single 6-PBT. When Cb1 was low and the upper impeller distant from the lower impeller, the power number of the lower impeller and the overall power number we...
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effect of low off bottom impeller clearance on the minimum agitation speed for complete suspension of solids in stirred tanks
Chemical Engineering Science, 1998Co-Authors: Piero M Armenante, Ernesto Uehara NagamineAbstract:Abstract Considerable attention has been devoted in the past to the determination of the minimum agitation speed, N js , required to just suspend solids in mechanically stirred tanks. However, the effect of the impeller off-bottom clearance has not been well established, particularly when the impeller is positioned very close to the tank bottom. This investigation is focused on the determination of the minimum agitation speed and power dissipation required to completely suspend solid particles in tanks provided with Impellers having small clearances off the tank bottom. Four types of Impellers were used: six-blade disc turbines, six-blade flat-blade turbines, six-blade (45°) pitched-blade turbines, and Chemineer HE-3 Impellers. The effects of the impeller diameter, tank diameter, particle diameter, and physical variables were also studied. Modified correlations based on the Zwietering equation ( Zwietering, (1958) Chem. Engng Sci . 8 , 244–253) were obtained to account for the effect of impeller clearance and impeller diameter-to-tank diameter ratio on N js .
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DETERMINATION OF THE MINIMUM AGITATION SPEED TO ATTAIN THE JUST DISPERSED STATE IN SOLID·LIQUID AND LIQUID·LIQUID REACTORS PROVIDED WITH MULTIPLE Impellers
Chemical Engineering Science, 1992Co-Authors: Piero M Armenante, Yu-tsang HuangAbstract:Abstract The determination of the minimum agitation conditions to achieve the just suspended state of the solid particles or the just dispersed state of an immiscible liquid in a mechanically agitated liquid in tank reactors is a problem of considerable industrial importance. Previous investigations on this subject have been limited to single-impeller systems only. In the present work the role of multiple impeller agitation systems on the achievement of the complete suspension of dispersion state was investigated both solid-liquid and liquid-liquid systems. The effects of a number of variables such as impeller type and position, clearance of the bottom impeller off the reactor bottom, distance between the Impellers and other geometric and parameters were studied. The results indicate that, contrary to intuition, the presence of multiple Impellers may not necessarily be beneficial to the achievement of the just dispersed state. In particular, it appears that if the flow pattern of the additional Impellers contrasts with the flow pattern which would be established by a single impeller, then the just dispersed state may be achieved at agitation speed higher for the multiple impeller system than for the single impeller case. Even in the majority of cases in which the agitation speed actually decreases with the number of impeller on the shaft, it appears that the power required to achieved the just dispersed state is higher when multiple Impellers are used.
Yoshinori Kawase - One of the best experts on this subject based on the ideXlab platform.
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Change in liquid temperature behind the impeller blades with impeller speed in boiling stirred tanks
Chemical Engineering Research & Design, 2010Co-Authors: Hidemi Yoshikawa, R. Fukuda, Yoshinori KawaseAbstract:Abstract In our previous study (Fukuda, R., Tokumura, M., Znad, H.T. and Kawase, Y., 2009, Vapour generation from the Impellers in boiling stirred tank reactors. Chem Eng Res Des, 87: 452–459), it was found that in boiling stirred tanks with multiple impeller systems vapour was generated from the heater at lower impeller speeds and with an increase in impeller speed most vapour was generated from the top impeller rather than the lower Impellers and the heater. The change of nucleation sites with the impeller speed might be controlled by the local liquid temperature. Therefore we measured the liquid temperature behind the Impellers blades and found the decrease in liquid temperature with increasing impeller speed. In this paper, a simple model was developed to predict the change in liquid temperature behind the impeller blades in which nucleation takes place. In the proposed model based on the results for pressure distribution on the impeller blade in the literature, the liquid temperature behind the impeller blades is estimated from the measured power consumption. The validation of the proposed model was conducted using the experimental results in our previous study and reasonable agreement was obtained.
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Liquid-phase mixing time in boiling stirred tank reactors with large cross-section Impellers
Chemical Engineering and Processing, 2006Co-Authors: Takanori Takahashi, Atsushi Tagawa, N. Atsumi, N. Dohi, Yoshinori KawaseAbstract:Abstract Liquid-phase mixing times in boiling systems were measured in a 0.2 m i.d. stirred tank reactors with large cross-section Impellers, i.e. Maxblend and Fullzone Impellers. For reference, a triple-impeller system consisting of three six-flat blade disk turbines was also used. The impeller speed and vapor generation rate were varied from 0.83 to 7.5 s −1 and 0.011 to 0.045 m/s, respectively. Nucleation occurred at the impeller instead of the heater at higher impeller speeds, whereas vapor was mainly generated from the heater at lower impeller speeds. The mechanical power consumption decreased due to vapor generation. Although the gas hold-ups increased with increasing vapor generation rate, for the large cross-section Impellers the gas hold-ups in the boiling systems at higher gas flow rates and lower impeller speeds changed only slightly with increasing impeller speeds and were rather larger than those in the cold systems. This finding for the large cross-section Impellers was quite different from the result for the triple-impeller system. The mixing times for larger-scale Impellers decreased with increasing vapor generation rate and were almost independent on the impeller speed at low rotational speeds of impeller. At higher impeller speeds, the mixing time decreased with impeller speed. The experimental results for dimensionless mixing times were reasonably correlated with the inverse of the power number.
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power consumption and solid suspension performance of large scale Impellers in gas liquid solid three phase stirred tank reactors
Chemical Engineering Journal, 2004Co-Authors: N. Dohi, Takanori Takahashi, K Minekawa, Yoshinori KawaseAbstract:Abstract An experimental investigation into power consumption and solid suspension performance of large-scale Impellers was carried out under turbulent conditions. Two types of large-scale Impellers, i.e. Maxblend and Fullzone Impellers, were employed. For reference, a triple-impeller system, i.e. two four-pitched blade downflow disk turbines (DTs) at middle and upper positions and one Pfaudler type impeller at lower position, was also used. The power consumption and the minimum impeller speeds for off-bottom solid suspension and minimum impeller speeds for ultimately homogeneous solid suspension were measured in unaerated and aerated systems. At a given rotational speed, the power consumption of the Maxblend impeller was roughly half of that of the Fullzone impeller. The decrease in power consumption due to aeration for large-scale Impellers was smaller as compared with that for the triple-impeller system. The proposed correlation for power consumption of large-scale Impellers in three-phase systems fit the experimental data reasonably well. Interesting and unexpected solid movements caused by the large-scale Impellers in the vessels having oval bottom were observed. Since the large-scale Impellers create strong axial liquid recirculation flowing downward near the impeller shaft and upward near the wall, usually particles are expected to move outward on the tank bottom. On the contrary, however, solid particles near the bottom moved to the center of the base from the side along the oval tank bottom. The large-scale Impellers were found to be more efficient for solid suspension than the triple-impeller system. The Maxblend impeller provided the best solid suspension ability among the three Impellers used in this work. We proposed a correlation for power consumption of large-scale Impellers in gas–liquid–solid three-phase systems. Empirical correlations were also proposed for the minimum impeller speeds for off-bottom solid suspension, minimum impeller speeds for ultimately homogeneous solid suspension and power consumption at the minimum impeller speeds for ultimately homogeneous solid suspension.
J B Joshi - One of the best experts on this subject based on the ideXlab platform.
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hydrodynamic and mass transfer characteristics of single and multiple impeller hollow self inducing reactors
Industrial & Engineering Chemistry Research, 2008Co-Authors: Rupesh B Kasundra, A A Kulkarni, J B JoshiAbstract:In the present work, hydrodynamics and mass transfer characteristics of a gas-liquid stirred tank provided with hollow self-inducing Impellers were investigated. Critical impeller speed for the onset of gas induction, gas induction rate, power consumption, and mass transfer coefficient (k L a) were measured using two types of self-inducing Impellers, viz., hollow pitched-blade downflow turbine and double-disk impeller. Experiments were carried out in 100 and 800 L tanks. Mass transfer coefficient was measured with steady-state hydrazine oxidation technique with air-water as the gas-liquid system. The impeller speed was varied from 2.5 to 14 rps, and power input per unit volume was varied from 0.5 to 10 kW/m 3 . Further, the performance of a multi-impeller hollow self-inducing system has been investigated. Four different hollow Impellers in combination with three axial flow Impellers have been studied in an 800 L tank using three impeller diameters and three liquid submergences. Suitable correlations have been proposed that also take into account all the published k L a data in the literature.
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relation between flow pattern and blending in stirred tanks
Industrial & Engineering Chemistry Research, 1999Co-Authors: Ashwin W Patwardhan, J B JoshiAbstract:In the present work, the relationship between the flow pattern and blending has been investigated. The flow patterns generated by around 40 axial flow Impellers have been examined. The Impellers differed in blade angle, blade twist, blade width, impeller diameter, impeller location, and pumping direction. The mean-flow and turbulence characteristics generated by all of the Impellers have been measured using laser doppler velocimetry (LDV). On the basis of available LDV data, the flow pattern throughout the vessel was established by employing computational fluid dynamics (CFD) and subsequently used for the simulation of the blending process. The predicted mixing times were found to be in excellent agreement with the experimental measurements. It has been shown that the dimensionless mixing time (θ) varies inversely with the secondary flow number of the impeller. Comparison of the Impellers on the basis of equal power consumption per unit mass has shown that θmix ∝ NP1/3T2/3/NQS. The present CFD model has ...
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comparison of axial flow Impellers using a laser doppler anemometer
Industrial & Engineering Chemistry Research, 1992Co-Authors: Vinayak V Ranade, V P Mishra, V S Saraph, G B Deshpande, J B JoshiAbstract:Influence of shapes of eight axial flow Impellers on flow in agitated vessels was studied using a laser Doppler anemometer. The tank diameter was 500 mm with a flat bottom and provided with four standard (width = T/10) baffles. In all cases the tank to impeller diameter ratio was 3 and the Impellers were centrally located. The flow generated by different axial Impellers has been compared in terms of mean velocities, turbulent kinetic energy, pumping effectiveness, and hydraulic efficiency. The measured flow data near the impeller have been presented in the form suitable for specifying the boundary conditions to the numerical model. The two-equation (k-e) turbulence model has been shown to be adequate for predicting the bulk flow in the case of all Impellers.
Emmanuel Manlapig - One of the best experts on this subject based on the ideXlab platform.
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Studies on impeller type, impeller speed and air flow rate in an industrial scale flotation cell — Part 1: Effect on bubble size distribution
Minerals Engineering, 1995Co-Authors: B K Gorain, J-p. Franzidis, Emmanuel ManlapigAbstract:Abstract Bubble size distributions were measured at different locations in a 2.8 m3 portable industrial scale sub-aeration flotation cell, treating zinc cleaner feed in the Hellyer Concentrator in Tasmania, Australia. The cell was fitted in turn with four different impeller-stator systems, and operated over a range of air flow rates and impeller speeds. The mean bubble size was found to increase with increase in air flow rate at different locations in the cell, for all four Impellers, and to decrease with increase in impeller speed. The mean bubble size was largest close to the impeller shaft and smallest at the impeller discharge point, for all the Impellers. The shape of the bubble size distribution also changed with location in the cell. The “global mean” bubble size calculated by simple arithmetic average of the values at six locations in the cell coincided remarkably well with the mean bubble size measured halfway between the impeller shaft and the side of the cell, at the top of the pulp. In general, the Impellers produced “global mean” values of 1.0 mm or less at the manufacturer's recommended impeller speed.
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studies on impeller type impeller speed and air flow rate in an industrial scale flotation cell part 1 effect on bubble size distribution
Minerals Engineering, 1995Co-Authors: B K Gorain, J-p. Franzidis, Emmanuel ManlapigAbstract:Abstract Bubble size distributions were measured at different locations in a 2.8 m3 portable industrial scale sub-aeration flotation cell, treating zinc cleaner feed in the Hellyer Concentrator in Tasmania, Australia. The cell was fitted in turn with four different impeller-stator systems, and operated over a range of air flow rates and impeller speeds. The mean bubble size was found to increase with increase in air flow rate at different locations in the cell, for all four Impellers, and to decrease with increase in impeller speed. The mean bubble size was largest close to the impeller shaft and smallest at the impeller discharge point, for all the Impellers. The shape of the bubble size distribution also changed with location in the cell. The “global mean” bubble size calculated by simple arithmetic average of the values at six locations in the cell coincided remarkably well with the mean bubble size measured halfway between the impeller shaft and the side of the cell, at the top of the pulp. In general, the Impellers produced “global mean” values of 1.0 mm or less at the manufacturer's recommended impeller speed.
Yu-tsang Huang - One of the best experts on this subject based on the ideXlab platform.
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DETERMINATION OF THE MINIMUM AGITATION SPEED TO ATTAIN THE JUST DISPERSED STATE IN SOLID·LIQUID AND LIQUID·LIQUID REACTORS PROVIDED WITH MULTIPLE Impellers
Chemical Engineering Science, 1992Co-Authors: Piero M Armenante, Yu-tsang HuangAbstract:Abstract The determination of the minimum agitation conditions to achieve the just suspended state of the solid particles or the just dispersed state of an immiscible liquid in a mechanically agitated liquid in tank reactors is a problem of considerable industrial importance. Previous investigations on this subject have been limited to single-impeller systems only. In the present work the role of multiple impeller agitation systems on the achievement of the complete suspension of dispersion state was investigated both solid-liquid and liquid-liquid systems. The effects of a number of variables such as impeller type and position, clearance of the bottom impeller off the reactor bottom, distance between the Impellers and other geometric and parameters were studied. The results indicate that, contrary to intuition, the presence of multiple Impellers may not necessarily be beneficial to the achievement of the just dispersed state. In particular, it appears that if the flow pattern of the additional Impellers contrasts with the flow pattern which would be established by a single impeller, then the just dispersed state may be achieved at agitation speed higher for the multiple impeller system than for the single impeller case. Even in the majority of cases in which the agitation speed actually decreases with the number of impeller on the shaft, it appears that the power required to achieved the just dispersed state is higher when multiple Impellers are used.
