Impeller Type Research Articles

Studying particle attrition in a solid-liquid agitated vessel using focused beam reflectance measurement (FBRM)

Over-processing particles during mixing in the mineral and chemical processing industries can lead to particle damage and diminished product quality. Therefore, the mixing tank design needs to be optimized to keep particles suspended while minimizing energy consumption and particle attrition. This study investigates particle attrition in a mechanically agitated vessel using focused beam reflectance measurement (FBRM). The effects of three different impeller types were studied under baffled and unbaffled conditions using solids concentrations from 5 to 30 wt%. Increasing solids concentration increased the particle count up to three times due to increased levels of particle attrition. The increase in particle counts due to attrition was lower under unbaffled conditions for 25 and 30 wt% solids for all impellers, indicating process intensification possibilities with lower particle attrition for these solids concentrations. Compared to a pitched blade or Ruston turbine, an A310 impeller minimized particle attrition close to zero under unbaffled conditions.

Investigation on pH influence for the effective transportation of coal water slurry using experimental design

ABSTRACT The present study aims to identify the pH values in preparation of coal water slurry (CWS) that were evaluated. Rheological characteristics and stability of coal water slurry (CWS) were observed with two types of impellers at pH varying from 6.99 to 7.24. The results showed that the concentration of coal water slurry, rheological characteristics and stability of CWS for propeller and rushton impellers. The parameters that are most effected on the objectives are impeller speed (N) and ratio of clearance height with diameter of tank (C/T). The third parameter, ratio of slurry height with tank diameter (Z/T), is not effecting on output. The pH values of concentrated coal water slurry are favorable to transport to coal gasifier. For propeller impeller, the pH values vary from 6.99 to 7.15; for Rushton impeller pH values vary from 7.12 to 7.24 comparatively Rushton impeller having more base which is most favorable and obtain good CWS concentration. The influence of coal particle size is also investigated on pH values for optimal parameters of equipment.

Power draw characteristics and comparison of scaling criteria for sawtooth impellers used in high shear mixing of shear thinning paint slurry

Power draw characteristics and scale-up procedures for high-speed sawtooth impellers were introduced by investigating various production sizes, fluids, impellers, and scale-up criteria to obtain the same product properties between different scales. The relationship between dimensionless Power number, Reynolds number, and Froude numbers were found for each impeller type at transitional flow regimes. The effect of Froude number was found to be very little, even though there was a deep vortex formation and no baffles in the mixing tank. Metzner – Otto constant which gives the relationship between rotational speed and shear rate was found as 20.7 and 12.4 for sawtooth impeller with big and small teeth, respectively. Productions were made by equalizing tip speed, shear rate, and power per volume between the commercial production and laboratory scales. In the result of rheological behavior measurement, stability test, and optical color evaluation, it was observed that the equal tip speed method gives a more intense dispersion in smaller batch sizes while the power per volume and shear rate method results in an insufficient particle size reduction performance.

Solid-liquid suspension in a stirred tank driven by an eccentric-shaft: Electrical resistance tomography measurement

Aiming at improving particle suspension performance in the stirred tank, the eccentric-shaft agitation and two-half-pitched-blade (THPB) impeller were proposed. The power consumption and suspension characteristics of THPB impellers under the eccentric-shaft, concentric and eccentric agitation schemes were experimentally studied. Effects of solid loadings and impeller rotation speeds were discussed. Results were compared with their counterparts of the two-flat-blade (TFB) impeller. It was found that, when running at the same rotation speed, although power consumption of eccentric-shaft agitation is large, its suspension performance is the best. When operated under the equal-power condition, for the eccentric-shaft agitation scheme, TFB has the best suspension performance. For the concentric and eccentric agitation schemes, THPB impellers behave better than TFB. Under the lower-than- N js condition, increasing rotation speed can improve the suspension performance. Given the simple design and good suspension performance of eccentric-shaft agitation, it is promising to be applied in the industries. • Development of the eccentric-shaft agitation scheme. • Electrical resistance tomography (ERT) measurements of solid-liquid suspension performance. • Comparison of performances among the concentric, eccentric and eccentric-shaft agitation schemes. • Discussion on the effect of impeller type, rotation speed and solid loading.

Power number and hydrodynamic characterization of a stirred vessel equipped with a Retreat-Blade Impeller and different types of pharmaceutical single baffles

• Vessels with single baffles are commonly found in pharmaceutical facilities. • The experimental Power Numbers (Po) for an RBI in single-baffle vessels were determined. • Results for beavertail, D-type, H-type, finger-type, fin-type baffles were obtained. • CFD predictions for Power Numbers were in good agreement with experiments. • A power-law correlation for Po vs. the area of the baffles in the liquid was derived. Many operations conducted in the pharmaceutical industry take place in glass-lined vessels provided with a Retreat-Blade Impeller (RBI) and one of different types of single baffles. Little information is available on the power dissipated by the RBI and on the hydrodynamic of such systems. Here, the turbulent Power Numbers, Po’s, for an RBI in a scaled-down vessel equipped with one of the different types of single baffles used in the pharmaceutical industry (beavertail, D-type, H-type, finger-type, fin-type baffles) were experimentally determined for different positions of the baffles and computationally obtained, together with the velocity distribution. Vortex formation, occurring with the beavertail baffle, was also quantified experimentally and computationally. The experimental Po values were in close agreement with the computational predictions. Additionally, a simple power-law correlation was established between Po and the dimensionless vertical cross-sectional area of the baffles, resulting in an equation with a good fit with the experimental data.

Analyzing the effect of using axial impellers in large-scale bioreactors.

In high-performance industrial fermentation processes, stirring and aeration may account for significant production costs. Compared to the widely applied Rushton impellers, axial-pumping impellers are known to yield a lower power draw and at the same time improve mixing. However, their lower gas dispersion capability requires stronger agitation, compromising these benefits. Diverse advanced impeller forms have been developed to cope with this challenge. We apply alternating radial and axial impellers and demonstrate strong gas dispersion and energy-efficient mixing for the first time in a large-scale (160 m3 ) bioreactor, based on experimental and computational fluid dynamics simulation data. For equal operating conditions (stirrer speed, aeration rate), this setup yielded similar gas hold-ups and better mixing times (35%) compared to a classical Rushton-only configuration. Hence, applying a radial impeller on an upper level for improving gas dispersion maintains the benefits of axial impellers in terms of reducing energy demand (up to 50%). We conclude that this effect is significant only at large-scale, when bubbles substantially expand due to the release of the hydrostatic pressure and have time to coalesce. The work thus extends current knowledge on mixing and aeration of large-scale reactors using classical impeller types.

Characterization of a small-scale crystallizer using CFD simulations and X-ray CT measurements

• Single and multiphase CFD of a small-scale crystallizer with two stirrer types. • Indications when each stirrer is preferably used based on hydrodynamics. • X-ray CT applied in mixing studies used for the validation of the CFD simulations. Although small-scale crystallizers have gained increasing importance in recent years, their hydrodynamic properties have not yet been thoroughly studied. The purpose of this work is to characterize an intensively stirred small-scale crystallizer and to analyze whether its fluid mechanics behavior deviates from being homogeneously well-mixed. To this aim, single and multiphase computational fluid dynamics (CFD) simulations have been conducted. Two types of stirrers, including one overhead stirrer (OS) and one magnetic stirrer (MS), were compared. The single-phase CFD simulations showed that the mixing characteristics of the two stirrers differ significantly, thereby leading to variations in the distribution of solids. The MS is an axial flow type impeller, which is better at handling solid suspensions than the OS. The simulations were complemented by X-ray computed tomography measurements, which confirmed that spatial variations in solid distribution occur and that assuming a homogeneous suspension might lead to errors when modeling crystallization processes.

Method and Critical Aspect of Semisolid Mixing

Semisolid preparations are widely used to deliver drugs through the skin, cornea, rectal tissue, nasal mucosa, vagina, buccal tissue, urethral membrane, and outer ear lining. They can prevent the first-pass metabolism, reduce side effects, provide immediate local effects, and increase patient compliance. However, an improper manufacturing process will produce a system with bad characteristics, one of which is the mixing process. Several conditions that need to be considered, such as vacuum, temperature, humidity, pressure, stirring speed, stirring time, shear stress, the volume of the mixture, and type of impeller, can affect the consistency, size, and dispersion of particle size, homogeneity, porosity, reactivity, and other characteristics that affect the quality of the semisolid system. Therefore, this article discusses the critical aspects of semisolid mixing, the types, principles, and specifications of several mixer tools and impellers, and how they affect the characteristics of semisolid systems. This review concludes that each type of semisolid preparation requires an impeller and mixer with the specifications and mixing conditions that suit the needs in maintaining the stability and quality of the semisolid system.

Large blade impeller application for turbulent liquid–liquid and solid–liquid mixing

AbstractApplication of large blade impellers to turbulent single‐phase and two‐phase mixing is investigated in this work in order to provide a quantitative basis for estimating the possible advantages in industrial mixing operations with respect to fast impeller types. The analysis is based on the discussion of three‐dimensional velocity fields collected in a single‐phase vessel stirred by a Maxblend impeller by stereoscopic particle image velocimetry and of dispersed phase distribution and liquid mixing time obtained in solid–liquid and liquid–liquid systems by electrical resistance tomography. The results highlight that turbulent two‐phase mixing can be efficiently performed in baffled vessels stirred by large blade impellers both in shear‐rate controlled and bulk‐motion controlled processes.

Scale-up study of aerated coaxial mixing reactors containing non-newtonian power-law fluids: Analysis of gas holdup, cavity size, and power consumption

The use of coaxial mixers has significantly improved gas dispersion in non-Newtonian fluids. However, to the best of our knowledge, no scale-up investigation of an aerated coaxial mixer has been reported in the literature. This study aims to explore the gas hold-up, energy dissipation rate, power consumption and cavity size in order to provide the guideline for scaling-up of the coaxial mixers. Through the use of computational fluid dynamics and electrical resistance tomography, the effects of the aeration rate, central impeller type, rotating mode, impeller speed, and pumping direction on the gas dispersion efficacy in both small-scale and large-scale coaxial mixers containing non-Newtonian fluids were investigated. For the coaxial mixer in the co-rotating mode, the same flow regime was achieved when the central impeller tip speed and the anchor impeller rotational speed were kept constant in both small-scale and large-scale systems. It was observed that maintaining the aeration rate per volume of the non-Newtonian fluid constant was beneficial to preserve the performance of the large-scale coaxial mixer the same as its small-scale counterpart. The use of specific power consumption as a scale up criterion effectively improved the energy dissipation rate uniformity, which is critical for shear sensitive applications.

Investigation of power consumption, torque fluctuation, and local gas hold-up in coaxial mixers containing a shear-thinning fluid: Experimental and numerical approaches

The performance of a coaxial bioreactor in the intensification of gas dispersion in shear-thinning fluids in terms of the power consumption of the central and anchor impellers, torque fluctuation for the anchor impeller, global and local gas hold-up, and cavity size was assessed. Electrical resistance tomography and computational fluid dynamics methods were used to evaluate the effects of the central impeller type, impeller speed, pumping direction, and rotating mode on the efficacy of the aerated coaxial mixers. Unlike the coaxial mixer equipped with a radial-flow impeller, for the coaxial mixer furnished with an axial-flow impeller, the rotating mode had a pronounced effect on the relative power demand. Surprisingly, it was observed that increasing the central impeller speed increased the contribution of the anchor impeller to the total power consumption of the co-rotating coaxial mixer furnished with a down-pumping impeller. Furthermore, by increasing the central impeller speed the torque fluctuation of the coaxial mixer was diminished due to the uniform distribution of the energy dissipation rate. Unexpectedly, for a coaxial mixer furnished with a down-pumping impeller in both rotating modes and an up-pumping impeller in the counter-rotating mode, the gas hold-up decreased by a further increase in the central impeller speed.

Impact of crystallization conditions and filtration cake washing on the clustering of metformin hydrochloride crystals

Crystallization is one of the basic methods employed in the pharmaceutical and chemical industry to produce powder products with controlled purity. Crystallization is commonly associated with the filtration and drying of solid material, where these unit operations can significantly affect the properties of the final material. This study focuses on the interplay of crystallization, filtration, cake washing, and drying to prevent the formation of crystal clusters. In this work, metformin hydrochloride crystalizing in rod-like crystals is used as a model drug. First, the crystallization parameters, such as stirring speed, cooling rate, impeller type, and solvent type, were varied. It was found that in all cases, metformin hydrochloride crystalizes in single rod-like crystals with various crystal size distribution, where the cooling rate and solvent type lead to non-uniform crystal growth demonstrated by very polydisperse crystal size distribution. Experimental results and Computational Fluid Dynamics simulation confirmed that stresses during crystallization were not sufficient to cause significant crystal breakup. In the next step, filtration connected with filter cake washing and subsequent drying was used to study the formation of crystal clusters. It was found that crystal cake was significantly stronger for the non-washed samples than for washed cake. Both the measured apparent elasticity modulus and the apparent hardness confirmed a strong impact of the washing solvent, allowing quality control when developing a crystal production process.

Process parameter optimization for the preparation of soap granules by Comil

A conical screen mill is commonly used to reduce particle size and produce granules of the required particle size. In the present work, an experimental study was designed to explore the use of a comil for the milling of soft solids. As a helpful example for research on soft solids, soap noodles were selected for optimizing the milling parameters such as impeller speed and type, screen type and size, and design of the milling cycle. A preferable combination of the comil parameters was the one generating a minuscule percentage of fines as also the one causing no damage or softening of the structure whatsoever due to agitation or temperature. The study involves comparing the particle sizes statistically and computing different parameters for designing the process. The particle size distribution of the soap granules obtained from the comil affects the soap bar's hardness and friability when punched. Hence, it was deduced that, for soft solids like soap noodles, comil can be helpful in particle size reduction, provided the parameters are optimized according to the mechanical properties of the material. Finally, this work presents a novel application to the comil equipment and gives a new processing technique for soap noodles.

Difference of clogging performance between radial and swept back impeller of axial pump

Abstract An axial pump which is used to pump water out of a river often sucks in solid bodies such as leaves and branches. These foreign substances may clog the passage and lead to dangerous conditions such as a decline in the performance of the pump. In this investigation, we conducted the clogging experiments by putting polyester strings in an axial drain pump which has two types of impellers, a radial blade impeller and a swept back blade impeller. By visualizing behavior of the strings in the pump using a high-speed video camera, we compared the anti-clogging performance between the two impellers and investigated the mechanism of clogging. The results of these experiments showed that the pass rate of the strings that flowed into the swept back blade impeller was higher than that in the radial blade impeller. It is because strings that are caught in the leading edge of the swept back blade tend to move to the tip side and be pulled towards the suction surface. In addition to the experiments, we carried out the simulations of these experiments using a CFD-DEM (Discrete Element Method) coupling analysis. The results were in good agreement with the experiments qualitatively.

Effects of impeller designs and configurations on the flow field in multiple impeller system using Computational Fluid Dynamics (CFD)

The work presents the computational study of the flow field in multiple impellers stirred vessel with various impeller types and configurations at 300rpm, 450rpm and 600rpm. Three types of impellers are investigated, namely the pitched blade impeller (PB), flat blade impeller (FB) and sawtooth impeller (ST). In this study, the flow patterns, turbulent kinetic energy dissipation, and power consumption in dual impellers system have been studied using computational fluid dynamics (CFD) by employing the multiple reference frame (MRF) and realizable k-ɛ turbulence model. The results from PBFB and reversed FBPB indicate efficient and powerful mixing with the merging of flows from both impellers that circulates the entire vessel. Besides, the FB and ST configuration exhibits the mixing characteristics that enhance both dispersion and mixing homogeneity. It is proven in this study that the combination of axial and radial impellers improves the weak mixing zones in the stirred vessel by the complex flow patterns produced. On top of that, utilizing two different impellers could achieve two mixing objectives in a system with the exceptional features of each impeller. The results establish promising effects of the reverse rotation in axial impellers and the arrangement of two different impellers in a multiple impeller system. With the rapid growth of industrialization, understanding the fluid dynamics in a multiple impeller stirred vessel is fundamental to optimize and scale up industrial mixing operations. Hence, the empirical findings in this study will be beneficial in selecting the suitable combination of impellers and the orientations that will enhance industrial mixing operations. Apart from that, the present work also illustrates that the computational technique used can be extremely valuable in determining the fluid dynamics in complex multiple impeller system which is challenging to analyse experimentally.

Experimental Study on Operational Stability of Centrifugal Pumps of Varying Impeller Types Based on External Characteristic, Pressure Pulsation and Vibration Characteristic Tests

This study performed external characteristics, dynamic pressure, and vibration tests on the closed impeller model, semi-open type impeller model, and open impeller model in order to study the influence of the impeller structure on the operational stability of the pump. According to the research findings, the external characteristics of the three impellers enjoyed favorable stability with flat curves under low flow rates. As the flow increases, the stability of the external characteristics weakens, and the poorest stability can be observed in the open impeller, while the enclosed impeller has the best stability under a large flow rate. In addition, intense pressure fluctuations arise near the casing tongue due to the dynamic and static interference between the blade and the casing tongue, causing a large amplitude of pressure pulsation near the casing tongue and the pump outlet. It can be seen that the stability of pressure pulsation of the closed impeller in the casing tongue area was the best, whereas the stability of pressure pulsation of the open impeller was the poorest. The minimum casing vibration can be found in the closed impeller, followed by the semi-open impeller, and the open impeller, with the maximum vibration. In addition, the optimum stability of rotor vibration can be observed in the closed impeller, semi-open impeller, and open impeller with similar stability of rotor vibration.

Predicting the diameters of droplets produced in turbulent liquid–liquid dispersion

AbstractThe droplet size distribution in liquid–liquid dispersions is a complex convolution of impeller speed, impeller type, fluid properties, and flow conditions. In this work, we present threea priorimodeling approaches for predicting the droplet diameter distributions as a function of system operating conditions. In the first approach, called the two‐fluid approach, we use high‐resolution solutions to the Navier–Stokes equations to directly model the flow of each phase and the corresponding droplet breakup/coalescence events. In the second approach, based on an Eulerian–Lagrangian model, we describe the dispersed fluid as individual spheres undergoing ongoing breakup and coalescence events per user‐defined interaction kernels. In the third approach, called the Eulerian–Parcel model, we model a sub‐set of the droplets in the Eulerian–Lagrangian model to estimate the overall behavior of the entire droplet population. We discuss output from each model within the context of predictions from first principles turbulence theory and measured data.

New Insights into the Gas Dispersion and Mass Transfer in Shear-Thinning Fluids Inside an Aerated Coaxial Mixer via Analysis of Flow Hydrodynamics and Shear Environment

The performance of an agitated bioreactor is hampered by an intense shear environment and low mass-transfer coefficient (kLa). The gas hold-up, kLa, and shear environment achieved by a coaxial mixer comprising a central impeller and an anchor impeller for various central impeller types, impeller speeds, pumping directions, and rotating modes were explored using tomography, dynamic pressure, and computational fluid dynamics methods. A novel method was introduced to explore the performance of aerated coaxial mixers in enhancing the mass transfer through analyzing the gas and liquid flow patterns. The results showed that the gas flow pattern created by the down-pumping pitched blade-anchor (PBD-anchor) mixer led to higher gas hold-up compared to that for the up-pumping pitched blade-anchor (PBU-anchor) mixer. However, the liquid flow pattern generated by the PBD-anchor mixer demonstrated poor mixing, resulting in a lower kLa compared to that for the PBU-anchor mixer. For all configurations, the mass-transfer efficiency attained in the co-rotating mode was higher than that in the counter-rotating mode. The shear environment generated by a coaxial mixer was comprehensively analyzed for the first time. Due to a lower shear environment, a bioreactor furnished by the co-rotating PBD-anchor is more suitable for shear-sensitive applications.

An overview of the effect of stirrer design on the mechanical properties of Aluminium Alloy Matrix Composites fabricated by stir casting

An overview of the effect of stirrer design on the mechanical properties of Aluminium Alloy Matrix Composites fabricated by stir casting

An energy consumption improvement method for centrifugal pump based on bionic optimization of blade trailing edge

The centrifugal pump is one of the most widely used types of power machinery in the water resource utilization and chemical industries. Its energy consumption cost accounts for a large proportion of its total economic cost. In this paper, an energy consumption improvement method for centrifugal pump is proposed by referring to the bionic structure to reduce the energy loss of the centrifugal pump. Four types of impellers with different types of sinusoidal tubercle trailing edges (STTE) are designed. Experiment and numerical simulation are combined to explore the beneficial effects of STTEs. Experimental research shows that this structural change will not affect the performance of the pump. On this basis, the entropy generation rate analysis method was introduced, and the numerical calculation results were analyzed to explore the internal influence of the STTE on the energy loss characteristics of the centrifugal pump. Results show that the use of STTEs can adjust the proportion of energy loss of each component in a centrifugal pump and effectively reduce the overall energy loss. Quantitative research indicated that the STTE3 has the optimal effect of reducing energy consumption. The use of STTE3 can reduce the total energy consumption by more than 5% at all flow rate conditions and reach a peak of 16.95% under 1.2 times nominal flow rate conditions. Thus, the bionic structure optimization method to improve the internal energy loss characteristics of centrifugal pumps will be beneficial and can provide a certain degree of reference for the hydraulic design of centrifugal pumps.