Impeller Pumping Capacity Research Articles

Effect of emulsification parameters on the rheology, texture, and physical stability of cosmetic emulsions: A multiscale approach

This study presents a multiscale approach for the production of cosmetic emulsions to evaluate the influence of emulsification on the macroscopic and microscopic properties of the product. This study evaluates the effects of the impeller pumping capacity and tip velocity on the rheological and textural properties of the cosmetic emulsions at the macroscopic scale as well as the effect of these parameters on the average drop size and the drop size distribution at the microscopic scale. This study also considers the influence of the pumping capacity and tip velocity on the physical stability of cosmetic emulsions. Two dispersed phase concentrations were used in this study (i.e., 30 % and 80 % w/w) to evaluate the effect of the product formulation on the performance of the cosmetic emulsions. The results showed that the impeller pumping capacity and the tip velocity are key parameters to control the energy demand and drop formation during the emulsification process (mean drop size and drop size distribution). These parameters also govern the microscopic structure of the emulsions, which has a strong influence on the macroscopic performance of the product. Thus, the tip velocity and pumping capacity are proposed as appropriate scale-up factors for the emulsification process.

The Effect of the Spargers Design on the Wastewater Treatment of Gas-Liquid Dispersion Process in a Stirred Tank.

The hydrodynamic and power characteristics of curved Rushton impeller in an air-wastewater system were investigated using the CFD-PBM method. Studies were conducted primarily in a mixing vessel of diameter 0.39 m. The inference of operating conditions, sparger distribution, and numbers on bulk flow patterns, gas-filled cavity formation, and power consumption have been investigated in detail. It found that the gassed power consumption is closely related to cavity shape and flow patterns. In particular, the development of large cavities causes a significant reduction in power drawn, impeller pumping capacity, and gas dispersion capability. The sparger distribution and location have a strong influence on relative power drawn, power required to disperse gas, and stability of operation. Of the sparger configurations studied, the use of three sparger distributions is suggested, since relative power drawn, gas dispersion capability, and flow patterns in dispersing gas are all enhanced.

Application of Theoretical and Experimental Findings for Optimization of Mixing Processes and Equipment

The homogenization of the agitated batch and ensuring the suspension of particles are the most frequently encountered requirements in terms of mixing applications. These operations are affected by the flow of the agitated batch. The geometrical parameters of the mixing system, especially the shape of the agitator blade, affect flow and circulation in the agitated batch. The present work provides a general description of the most common processes in the agitated batch (blending and particle suspension), hydrodynamic parameters (flow in agitated batches, pumping and circulation capacity of impellers) and the geometrical configurations of the mixing equipment (shape of vessel, baffle and impeller, and their mutual arrangement) that influence the process. The dimensionless process characteristics of the agitator were derived by theoretical analysis. These characteristics were applied to evaluate an extensive set of experimental data with various geometric configurations of the mixing equipment. This study shows how the flow in the agitated batch, caused by the pumping and circulating effects of the agitators, affects the parameters and energy efficiency of these processes, depending on the geometric configuration of the mixing equipment. Moreover, the benefits of the hydrofoil impellers used for these mixing processes are presented.

Investigation of the detrimental effect of the rotational speed on gas holdup in non-Newtonian fluids with Scaba-anchor coaxial mixer: A paradigm shift in gas-liquid mixing

Our research findings challenge the paradigm that a high rotational speed of impellers can intensify the gas dispersion. Interestingly, we observed the deterioration in the gas holdup at the higher rotational speeds. Electrical resistance tomography (ERT) and computational fluid dynamics (CFD) were extensively utilized to shed light on the hydrodynamics of Scaba-anchor coaxial mixer and its impact on the aeration efficiency in non-Newtonian fluids, for the first time. The working fluid was 1 wt% carboxymethyl cellulose solution, which is a non-Newtonian fluid and obeys the power law model. At a fixed central impeller speed of 290 rpm, as the anchor impeller speed was increased from 15 to 50 rpm, the decrease in the local gas holdup was attributed to the decline in the Scaba impeller pumping capacity and its aerated power consumption. On the other hand, at a constant anchor impeller speed of 10 rpm, when the Scaba rotational speed was increased from 290 to 430 rpm, the gas holdup decreased surprisingly even with an increasing Scaba’s pumping capacity at higher rotational speed. The sharp drop in the local gas holdup was the consequence of a poor axial gas dispersion. With a minimal fluid shear stress at low agitation speed, our research findings hold promise to optimize energy savings while enhancing the aeration efficiency in non-Newtonian fluids at low Reynolds numbers.

Ice growth on the cooling surface in a jacketed and stirred eutectic freeze crystallizer of aqueous Na 2 SO 4 solutions

Abstract Eutectic freeze crystallization (EFC) has been pronounced a promising separation technique to recover ice and salt simultaneously in an energy-efficient manner. Alike other freeze concentration methods, the accumulation of an ice layer, commonly known as ice-scaling, on the heat exchanger surface during operation thwarts the commercial application of EFC as the advantage of low energy requirement is outstripped by high investment cost, scaling up and operational complexities associated with the use of a scraper blade to remove the ice-scaling. Therefore, the aim of this research work is to investigate the ice-scaling phenomenon on a subcooled heat exchanger surface in the absence of mechanical scrapping. For a continuous EFC system, the influence of temperature driving force (ΔT) and the degree of agitation on the onset/induction time (tind) of ice-scaling are considered while keeping the other parameters, e.g., solution concentration (4 wt% Na2SO4 (aq) solution), the level of initial undercooling (0.28 °C) and the residence time (30 min) constant. The experimental results show that at a certain level of agitation, tind is inverse proportional to ΔT. At a low level of ΔT (i.e., 6.0 °C), the effect of the degree of agitation on tind becomes substantial. At the eutectic condition, the heat transfer coefficient of the solution (hsol) in the crystallizer prevails over that of mass transfer (kl). In the experimental setup, the overall heat transfer coefficient for a jacketed vessel type crystallizer is restricted by the heat transfer coefficient of the jacket side coolant (hj). The power number (Np) and pumping number (Nq) for a two-blade paddle type impeller and a crystallizer of specific dimensions and orientation are estimated by means of computational fluid dynamics (CFD) modeling and are used to calculate the specific power input (e) and impeller pumping capacity (Q) at different levels of agitation. Furthermore, CFD simulations of heat transfer from the coolant to the bulk solution are performed to investigate the effect of the agitation level on solution cooling in the non-crystallizing condition.

The effect of internal impellers on mixing in an electrochemical reactor with rotating rings electrodes

An electrochemical reactor with rotating electrodes has been used to to remove pollutants from aqueous media. Poor mixing and passivation of electrodes surface have been identified as the major drawbacks for the operation of this type of reactors because they adversely affect the critical reactions that take place in the liquid bulk. In this work, three different reactor configurations are proposed and their performance on reactor mixing time and process costs is evaluated. CFD simulations, based on previously validated models, were used to observe mixing inside the electrochemical reactors. Three different arrays were used for the rotating rings electrodes: (a) without impellers, (b) with four internal vertical fins and (c) with a pitched blade central impeller. Power consumption, torque, and parameters such as turbulent intensity, mixing time, among others, were evaluated for all configurations. The reactor with no impellers showed two separated zones of recirculation, reducing the reactor mixing and performance. The reactor with pitched blade impeller, showed no significant improvement due to its low central impeller pumping capacity at low rotational speeds (150rpm). The array with 4 vertical fins operated at 130rpm presented the highest flow/power ratio, and the lowest mixing time.

Evaluation and accuracy of the local velocity data measurements in an agitated vessel

Velocity measurements of the flow field in an agitated vessel are necessary for the improvement and better understanding of the mixing processes. The obtained results are used for the calculations of the impeller pumping capacity, comparison of the power consumption etc. We performed various measurements of the local velocities in an agitated vessel final results of which should be processed for several purposes so it was necessary to make an analysis of the obtained data suitability and their quality. Analysed velocity data were obtained from the LDA (Laser Doppler Anemometry) and PIV (Particle Image Velocimetry) measurements performed on a standard equipment where the flat bottomed vessel with four baffles was agitated by the six-blade Rushton turbine. The results from both used methods were compared. The frequency analyses were examined as well as the dependency of the data rates, time series lengths etc. The demands for the data processed in the form of the ensemble-averaged results were also established.

Advanced impeller design: Anti-ragging impeller, ARI2

The waste water treatment plant anoxic denitrification process employs agitated vessels which contain process fluids contaminated with fibrous, rag-like materials that have a tendency to collect on impeller blades and adversely affect mixing performance. The existing Philadelphia Mixing Solutions Ltd. anti-ragging impeller made from fiberglass reinforced plastic is not cost effective for this low torque application. The challenge was to design an impeller that replicated the performance of the original impeller but utilized common industrial manufacturing processes to reduce cost. The flexible construction technology chosen was sheet metal fabrication. The design effort produced a highly skewed, forward raked, hydrofoil impeller with applications that extend beyond the waste water treatment industry. The performance of the new impeller was evaluated by comparing it to the fiberglass impeller as well as three other common impeller types used in stirred tanks. Impeller pumping capacity was measured using 2-D Particle Image Velocimetry and impeller power draw was measured using a load cell and tachometer. The characteristic dimensionless impeller power and flow number, Np and Nq, were computed to be 0.17 and 0.42, respectively.

A Study of CFD Simulations of the Flow Pattern in an Agitated System with a Pitched Blade Worn Turbine

Abstract This paper presents a numerical analysis of an agitated fully baffled cylindrical vessel with a down pumping four blade worn or unworn pitched blade impeller (α = 45° and 30°) under a turbulent flow regime. CFD simulations predict the pumping capacity of the system equipped by worn and unworn pitched blade impeller. Experimental data were taken from the authors’ previous work and compared with results of numerical computations. A good agreement with experimental data was obtained. The ensemble-average mean velocity field with worn and unworn impellers was computed. It follows from the simulation results that the wear rate of the impeller blade has a significantly negative effect on the velocity distribution in an agitated liquid. The greater the destruction of the worn blade, the higher is the deformation of the velocity field around the rotating impeller, with a simultaneous decrease in impeller pumping capacity.

An experimental method to evaluate global pumping in a mixing system: Application to the Maxblend™ for Newtonian and non-Newtonian fluids

This work introduces an experimental method to determine the global pumping capacity of an impeller in a transparent vessel using a decolorization method. Contrary to commonly used experimental methods such as Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV), this new inexpensive and easy-to-use method can be employed to quickly fill the lack of data in the literature about the impact of impeller geometry on the pumping efficiency. The new method was first applied to three well-known mixing systems and a Newtonian fluid to assess its reliability and accuracy: a six-blade Rushton turbine (RT), a pitched blade turbine (PBT) with four 45° blades, and a three-blade hydrofoil propeller (HP). It was then applied to evaluate the global pumping capacity of the Maxblend™ impeller in the case of Newtonian and non-Newtonian fluids. The results obtained show that, for the Newtonian fluid, the Maxblend™ impeller performs better than the other three impellers in the transitional regime, and it has a similar pumping capacity than that of the PBT and the RT in the complete turbulent regime. In this case, it was also noticed that the HP is outperformed by the other tested impellers over the entire range of Reynolds numbers. Moreover, it was observed that the extreme shear-thinning behavior of the non-Newtonian fluid used does not significantly affect the pumping generated by the Maxblend™ impeller in the transitional regime, that is for Reynolds number larger than 80. A global flow number, normalized by the power draw, is also introduced. Based on this criterion, the HP is shown to perform the best in the fully turbulent regime. Mixing times evaluated by means of the decolorization method also reveal that the Maxblend™ impeller is the most efficient for all regimes.

Gas-liquid-solid Operation of a High Aspect Ratio Self-ingesting Reactor

Gas-liquid stirred vessels are widely employed to carry out chemical reactions involving a gas reagent and a liquid phase. The usual way for introducing the gas stream into the liquid phase is through suitable distributors placed below the impeller. An interesting alternative is that of using “self ingesting” vessels where the headspace gas phase is injected and dispersed into the vessel through suitable surface vortices. In this work the performance of a Long Draft Tube Self-ingesting Reactor (LDTSR) dealing with three-phase (gas-liquid-solid) systems, is investigated. Preliminary experimental results on the effectiveness of this contactor for particle suspension and gas-liquid mass transfer performance in the three-phase system, are presented. Mass-transfer parameter kLa was measured by the recently introduced Simplified Dynamic Pressure Method (SDPM). It is found that the presence of low particle fractions causes a significant increase of the minimum speed required for vortex ingestion of the gas. Impeller pumping capacity and gas-liquid mass transfer coefficient are found to be affected by the presence of solid particles.

Bioprocess Improvement by Design-Modified Bioreactor Flow Properties

ABSTRACTThe aim of this study was to achieve bioprocess intensification by bioreactor flow field improvement. Two component properties of the flow field, namely, flow and shear are represented by two macroscopic mixing characteristics—impeller pumping capacity, Fl, and rate of kinetic energy dissipation, ϵ. Mixing rates are affected by impeller design and may be the result of a design-imposed flow modification of characteristics, e.g. higher or lower bioreactor circulation and/or turbulence properties can be achieved. The results illustrated that two basic impeller types—a modifiedflat-blade and modified inclined blade, could tailor a stirred bioreactor flow field in a pre-selected style. The design modification was aimed at higher oxygen transfer via increased ϵ or improved ϵ-distribution in the bioreactor bulk. Zones of different ϵ were revealed, implying different oxygen tension and bioreaction intensity. For the sake of prognostic evaluation, the mass transfer coefficient kL was determined. The designs of slotted flat and inclined blades were found to be prospective in terms of energy efficiency and can be recommended for design retrofitting of existing bioreactors.

On hydraulic efficiency of pitched blade impellers

This study provides a description of a pitched blade impeller as an axial pump. For the turbulent flow regime of an agitated liquid in a fully baffled cylindrical vessel under a few simplifying assumptions, we formulate the relation among the impeller dimensionless total head, the impeller power number, and the dimensionless impeller pumping capacity (the flow number). The hydraulic efficiency of pitched blade impeller is determined from experimental data found in literature (the flow numbers and the power numbers). It follows from the results of the calculations that the hydraulic efficiency of pitched blade impellers increases significantly with decreasing pitch angle, and also with decreasing impeller vessel diameter ratio.

Comments on "Suspension Mixing Tank - Design Heuristic"

The study deals with analysis of the process characteristics of agitated system with a pitched blade impeller and radial baffles (impeller power input and impeller pumping capacity) under turbulent regime of flow of agitated batch. Original experimental data are compared with results of CFD simulation in a pilot plant mixing system published in literature.

Using electrical resistance tomography and computational fluid dynamics modeling to study the formation of cavern in the mixing of pseudoplastic fluids possessing yield stress

Electrical resistance tomography (ERT) provides a non-intrusive technique to examine, in three dimensions, the homogeneity and flow pattern inside the mixing tank. In this study, a 4-plane 16-sensor ring ERT system was employed to study the shape and the size of cavern generated around a radial-flow Scaba 6SRGT impeller in the mixing of xanthan gum solution, which is a pseudoplastic fluid possessing yield stress. The size of cavern measured using ERT was in good agreement with that calculated using Elson's model (cylindrical model). The 3D flow field generated by the impeller in the agitation of xanthan gum was also simulated using the commercial computational fluid dynamics (CFD) package (Fluent). The CFD model provided useful information regarding the impeller pumping capacity, flow pattern, and the formation of cavern around the impeller. CFD results showed good agreement with the experimental data and theory.

Pumping Capacity of Pitched Blade Impellers in a Tall Vessel with a Draught Tube

A study was made of the pumping capacity of pitched blade impellers (two, three, four, five and six blade pitched blade impellers with pitch angles α = 35° and 45°) coaxially located in a cylindrical pilot plant vessel with cylindrical draught tube provided with a standard dished bottom. The draught tube was equipped with four equally spaced radial baffles above the impeller pumping liquid upwards towards the liquid surface. In all investigated cases the liquid aspect ratio H/T = 1.2 - 1.5, the draught tube / vessel diameter ratios DT /T = 0.2 and 0.4 and the impeller / draught tube diameter ratio D/DT = 0.875. The pumping capacity of the impeller was calculated from the radial profile of the axial component of the mean velocity in the draught tube below the impeller at such an axial distance from the impeller that the rotor does not affect the vorticity of the flow. The mean velocity was measured using a laser Doppler anemometer with forward scatter mode in a transparent draught tube and a transparent vessel of diameter T = 400 mm. Two series of experiments were performed, both of them under a turbulent regime of flow of the agitated liquid. First, the optimum height of the dished bottom was sought, and then the dependences of the dimensionless flow rate criterion and the impeller power number on the number of impeller blades were determined for both pitch angles tested under conditions of optimum ratio HT /DT. It follows from the results of the experiments that the optimum ratio HT /DT = 0.25 when the cross sectional areas of the horizontal flow around the bottom and the vertical inflow to the draught tube are the same. For all the tested pitched blade impellers the impeller power number when α = 45° exceeds the value of this quantity when pitch angle α = 35°, while the flow rate number when α = 35° exceeds this quantity when α = 45°. On the other hand, the absolute values of the impeller power number when the draught tube was introduced correspond fairly well to the dimensionless impeller power input measured in a system without a draught tube. However, the absolute values of the flow rate number found in the former system are significantly lower than the dimensionless impeller pumping capacity determined in the latter system. The hydraulic efficiency of pitched blade impellers N3Qp/Po for the investigated geometry of the agitated systems does not depend on the number of impeller blades, but it is significantly lower than the quantity determined in an agitated system with a dished bottom but without the draught tube.

Study of Pumping Capacity of Pitched Blade Impellers

A study was made of the pumping capacity of pitched blade impellers in a cylindrical pilot plant vessel with four standard radial baffles at the wall under a turbulent regime of flow. The pumping capacity was calculated from the radial profile of the axial flow, under the assumption of axial symmetry of the discharge flow. The mean velocity was measured using laser Doppler anemometry in a transparent vessel of diameter T = 400 mm, provided with a standard dished bottom. Three and six blade pitched blade impellers (the pitch angle varied within the interval a Îá24°; 45°ń) of impeller/vessel diameter ratio D/T = 0.36, as well as a three blade pitched blade impeller with folded blades of the same diameter, were tested. The calculated results were compared with the results of experiments mentioned in the literature, above all in cylindrical vessels with a flat bottom. Both arrangements of the agitated system were described by the impeller energetic efficiency, i.e, a criterion including in dimensionless form both the impeller energy consumption (impeller power input) and the impeller pumping effect (impeller pumping capacity). It follows from the results obtained with various geometrical configurations that the energetic efficiency of pitched blade impellers is significantly lower for configurations suitable for mixing solid-liquid suspensions (low impeller off bottom clearances) than for blending miscible liquids in mixing (higher impeller off bottom clearances).

Impeller Geometry Effect on Velocity and Solids Suspension

The effect of varying impeller geometrical parameters, including impeller type, number of impeller blades, blade pitch angle and blade thickness, on the turbulent velocity fields in mixing tanks has been studied through LDV measurements. Pitch bladed turbines and disc turbines were used in the experiments. It was found that universal time-mean velocity profiles exist for both pitch bladed turbines and disc turbines. Flow number correlations based on power number for both pitch bladed turbines and disc turbines are presented. It was found that there is a link between impeller pumping capacity and the S parameter in the Zwietering correlation, and this can be expressed as NQ × S = K, where NQ is the impeller flow number and K is a non-dimensional constant independent of the solid/liquid material property and impeller geometry.

The effect of impeller pumping and fluid rheology on solids suspension in a stirred vessel

AbstractPumping velocities of different impellers were measured using laser Doppler velocimetry. It was found that there is a link between impeller pumping capacity and the 5 parameter in the Zwietering correlation. Measurements showed that Njs increases with impeller spacing for dual impeller configurations. A dual‐impeller configuration shows less sensitivity to solids loading change than a single‐impeller configuration, and the change in Njs is larger for small impeller spacing than for large impeller spacing. An increase in slurry cloud height and a reduction in Njs resulted at a small increase of non‐Newtonian viscosity.

Solids suspension with axial‐flow impellers

The objective of this work is to investigate the pumping performance of axial-flow impellers and its influence on solids suspension. This will provide a basis for relating impeller pumping capacity to the S value in the Zwietering's correlation.