Stirrer Type Research Articles

Influence of Spacing of Multiple Impellers on Power Input in an Industrial‐Scale Aerated Stirred Tank Reactor

AbstractDespite the fact that aerated stirred tank reactors are widely used in industry and often studied, their design and scale‐up still remains challenging. Especially the specific power input is a crucial and geometry‐dependent scale‐up parameter, usually calculated with the dimensionless power number Po. Within the scope of this study, the power number is measured for different stirrer types and configurations in a laboratory and an industrial‐scale aerated stirred tank reactor. Good agreements to literature are found for the unaerated case for the two‐stage stirrer configurations at different stirrer spacing for both scales. By literature only the aerated case in the laboratory scale can be predicted. Scale‐up of an aerated industrial‐scale reactor is challenging because of a specific influence of the aeration. In case of a three‐stage Rushton configuration, an asymmetrical distribution of the stirrers should be preferred to ensure a high power number as well as good power performance under aerated conditions.

Multiphase Stirred Tank Bioreactors – New Geometrical Concepts and Scale‐up Approaches

AbstractMainly with respect to biotechnological cases, current developments in the field of impeller geometries and findings for multistage configurations with a specific view on aerated stirred tanks are reviewed. Although often the first choice, in the given case the 6‐straight blade disc turbine is usually not the best option. Furthermore, quantities usable for scale‐up, specifically applicable in this field are discussed. Only quantities taking local conditions into account appear to be able to actually compare different stirrer types and scales.

Catalytic hydrogenation and dehydrogenation performance of 9-ethylcarbazole as a liquid organic hydrogen carrier

The hydrogenation characteristics of 9-ethylcarbazole (9-ECZ) over Raney-Ni catalyst within the pressure range 0.2–0.8 MPa was investigated in this work. Initially, hydrogenation experiments were performed over various catalysts which revealed that 5 wt.% Ru/Al2O3 was the most active catalyst, whereas, Raney-Ni being least expensive was chosen for this study. Ten grams of 9-ECZ and 1 g of Raney-Ni were added to the stirrer type reactor, the effect of various parameters such as temperature, pressure, catalyst dosage, and stirring speed were examined. The results indicated that the optimal reaction temperature was 160 °C at a maximal pressure (0.8 MPa), stirring speed (800 rpm). Furthermore, 2 g of 9-ECZ was used with Raney-Ni dosages of 0.2 and 1.0 g and the corresponding hydrogen uptake was 5.16 wt.% and 5.81 wt.%, respectively. Lastly, three cyclic experiments were conducted to investigate the reversibility of the hydrogenation and dehydrogenation of 9-ECZ at 180 °C.

Experimental investigation of a two-zone model for semi-batch precipitation in stirred-tank reactors

A zone model for the semi-batch precipitation process of sparingly soluble salts in stirred-tank reactors is presented. The low product solubility of these substances leads to high levels of supersaturation during the process. Consequently, nucleation and growth rates are fast and solids formation only takes place in a part of the reactor close to the feed pipe. The presented local mixing environment (LME) model extends an existing model for semi-batch processes, which consists of two zones. In the mixing zone, a steady-state plug-flow reactor (PFR) is used to imitate the local flow environment of the feed. The tank is approximated as a well-mixed storage tank outside the mixing zone. Exchange streams between the two zones are estimated by dimensional analysis considering stirrer type, size and rotational speed. The correctness of the two-zone hypothesis and the accuracy of the LME model is validated by barium sulfate precipitation in an experimental comparison setup using different stirrer types, rotational speeds and feed rates. The PFR is represented in the experiments as a pipe-in-pipe reactor in jet-in-cross-flow (JICF) or coaxial-flow (COAX) arrangement. The experimental results show that the semi-batch precipitation of sparingly soluble salts in stirred-tanks can be successfully simplified by the assumption of a PFR mixing zone. The LME model is simple to implement, scalable and reaches acceptable results in the experimental validation. It is therefore a promising model for future application in process simulation of industrial precipitation processes.

Parametric Testing of Metasurface Stirrers for Metasurfaced Reverberation Chambers

In this paper, the correlation coefficients and the total scattering cross sections (TSCSs) for different types of metasurfaced stirrers and the traditional metallic stirrer, and the effects on field uniformity when such stirrers are used in reverberation chambers, are analyzed. Three metasurfaced stirrers are considered: A stirrer with two unit cells arranged alternatively (#1), a stirrer with two unit cells arranged in a chessboard-like manner (#2), and a stirrer with two unit cells in random arrangement (#3). From the correlation coefficient and TSCS results obtained in simulations, it follows that metasurfaced stirrer #1 is the best option. Field uniformity analysis of the resulting metasurface reverberation chambers (MRC) equipped with the different stirrers also supports this conclusion.

An experimental and numerical analysis of the fluid flow in a mechanically agitated vessel

The mixing process is a widespread phenomenon, which plays an essential role among a large number of industrial processes. The effectiveness of mixing depends on the state of mixed phases, temperature, viscosity and density of liquids, mutual solubility of mixed fluids, type of stirrer, a what is the most critical - the shape of the impeller. In the present research, the objective is to analyse the process of the fluid flow in the mechanically agitated vessel with new impeller type. Velocity field values were determined using computer simulation and experimental particle image velocimetry method. The basis for the assessment of the intensity degree and efficiency of mixing was the analysis of velocity vectors distribution and power number. An experimental and numerical study was carried out for various stirred process parameters to determine optimal conditions for the mixing process.

A modified microemulsion method for fabrication of hydrogel Tragacanth nanofibers

Tragacanth is a nontoxic, biodegradable and biocompatible polymer applied as a nanostructure form in various fields such as biomedicine and food industry. Here, hydrogel Tragacanth nanofibers were fabricated using a modified microemulsion method. The effective parameters on the fabrication of nanofibers such as emulsifier type, stirrer type, processing time and concentrations of emulsifier, Tragacanth and aluminum chloride were studied and the conditions were optimized for high quality nanofibers. SEM images indicated Tragacanth nanofiberswere successfully synthesized with average diameter of 50 nm and uniformdistribution. Appear a peak at 1110 cm-1 related to Al-C bonds and reduce intensity ofthe peaks at 1742 and 1629 cm-1 and in FT-IR spectrum of nanofibersprove the successfully synthesis. Further, the hydrogel properties of the synthesized nanofibers can be proved by the swelling of 142% and drying time of 3 h.

Hydrodynamics and Bubble Size Distribution in a Stirred Reactor

A study of the hydrodynamics of two-phase stirred tanks is presented. The hydrodynamics in large-scale reactors is shown to be mainly a function of the superficial gas velocity and the stirring in the system. Six configurations for the stirrer have been tested: two single-stage and four two-stage configurations. The three hydrodynamic regimes (short circuit, load and flood) were observed for these configurations. The results show that the gas holdup, measured using the difference in level between aerated and non-aerated states, achieves a maximum value for the mixed two-stage combination. For this configuration, a study of the residence time distribution was carried out by employing the tracer (pulse injection) method, thus allowing the determination of the dead volume and the modeling of the flow in the reactor, corresponding to a perfectly mixed reactor. In stirred tank reactors, the study of the bubble size distribution has a great importance on the flow dynamics, the dimensions of bubbles are measured photographically; this investigation shows the presence of fine bubbles (d < 10 mm) with the experimental bubble size distribution curves exhibiting classical log-normal function traits within ± 3%. The characterization of the hydrodynamics and the flow regimes in the stirred reactor permits to optimize the operating parameters (stirrer type and configuration, stirring speed, gas velocity) within the reactor in order to treat the water contaminated by persistent pollutants.

Capacity building of rural women through training on detergent making in Mansa district

The present study was conducted in Mansa district. A total 40 rural women was selected who had taken training from Krishi Vigyan Kendra, Mansa on detergent making during 2015. It was observed that the respondents had no knowledge regarding type of stirrer, type of container for mixing ingredients, precautions while mixing raw material, shelf life of detergent, raw ingredients and quality of raw ingredients before getting training. There was a need to give more emphasizes on above said aspects. The respondents take training and gain the knowledge in every aspect of detergent making process like raw ingredients of detergent is 95%, quality of raw material and precaution while mixing of raw material is 92.5% gain in knowledge. 85% respondents learned about awareness about shelf life of detergent followed by 82.5% gain in knowledge regarding type of stirrer to be used for mixing ingredients, knowledge gain in regarding use of mixing material is 77.5% and bare handed awareness while mixing ingredients is 75 per cent. Impact of the training is 45% respondents save their money by preparing detergent at home which they earlier purchased from the market. Making detergent at home gave them satisfaction and self confidence as well. 22% of the respondents prepare and sold in their own village and relatives. 17.5% respondents prepare detergent and sold to shopkeepers while 15% sold in other villages.

Implementation of quality by design principles in the development of microsponges as drug delivery carriers: Identification and optimization of critical factors using multivariate statistical analyses and design of experiments studies

Microsponges drug delivery system (MDDC) was prepared by double emulsion-solvent-diffusion technique using rotor–stator homogenization. Quality by design (QbD) concept was implemented for the development of MDDC with potential to be incorporated into semisolid dosage form (gel). Quality target product profile (QTPP) and critical quality attributes (CQA) were defined and identified, accordingly. Critical material attributes (CMA) and Critical process parameters (CPP) were identified using quality risk management (QRM) tool, failure mode, effects and criticality analysis (FMECA). CMA and CPP were identified based on results obtained from principal component analysis (PCA-X&Y) and partial least squares (PLS) statistical analysis along with literature data, product and process knowledge and understanding. FMECA identified amount of ethylcellulose, chitosan, acetone, dichloromethane, span 80, tween 80 and water ratio in primary/multiple emulsions as CMA and rotation speed and stirrer type used for organic solvent removal as CPP.The relationship between identified CPP and particle size as CQA was described in the design space using design of experiments – one-factor response surface method. Obtained results from statistically designed experiments enabled establishment of mathematical models and equations that were used for detailed characterization of influence of identified CPP upon MDDC particle size and particle size distribution and their subsequent optimization.

Characterization of Newly Developed Semisolid Stir Joining Method for Cast Cu Base Alloy (Cu-Al-Si-Fe) and Effect of Stirrer Type on Uniformity of Microstructure

In this research, the semisolid stir joining method was used to overcome the problem of hot cracking in welding aluminum and silicon bronzes. Moreover, the effects of grooved and cylindrical tools on the microstructure and mechanical properties of samples were examined. After welding specimens, mechanical tests were carried out to find differences between the cast and welded samples. Optical microscopy and scanning electron microscopy were used to study microstructure. X-ray diffraction was used to investigate compounds formed during casting and welding. The solidus and liquidus temperatures of the alloy were measured by differential scanning calorimetry. In this study, the temperature of the work pieces was raised to 1203 K (930 °C) that is in the semisolid region, and the weld seams were stirred by two different types of tools at the speed of 1600 rpm. Macro and micro-structural analyses show uniformity in the phase distribution for specimens welded by cylindrical tool. Desirable and uniform mechanical properties obtained when the cylindrical tool was used.

Characterization of stirrers for screening studies of enzymatic biomass hydrolyses on a milliliter scale

The evaluation of mixing quality is an important factor for improving the geometry of stirred-tank reactors and impellers used in bioprocess engineering applications, such as the enzymatic hydrolysis of plant materials. Homogeneity depends on different factors, including the stirrer type and the reactor type (e.g., ratio of diameter/height, ratio of impeller tip diameter/reactor diameter) with or without baffles. This study compares two impellers for enzymatic hydrolysis of suspensions of biomass particles on a milliliter scale. Both impellers were derived from industrially relevant geometries, such as blade and grid stirrers, although the geometry of the second stirrer was slightly modified to an asymmetric shape. The stirrers were investigated with different stirrer-reactor configurations. This was done experimentally and with the aid of computational fluid dynamics. The flow field, mixing numbers, power characteristics and initial conversion rates of sugars were considered to compare the two stirrers. The simulated mixing numbers and power characteristics in baffled and unbaffled milliliter-scale reactors were found to be in good agreement with the measured mixing times and power consumption. The mixing numbers required to reach homogeneity were much higher for the symmetric impeller and remained at least twice as high as the mixing numbers required when using the asymmetric impeller. The highest initial sugar releases from milled corn stover suspensions were achieved with the asymmetric impeller shape. Regardless of the differences in the flow fields or mixing times, diverging enzymatic sugar releases could be confirmed for Newtonian media only.

Discrete Particle Simulation of Particle Flow in a Stirred Mill: Effect of Mill Properties and Geometry

Particle flow in a stirred mill was modeled using discrete element method, focusing on the effect of mill properties and stirrer configurations, such as particle-wall friction, the size of disc holes, distance between stirrers, and stirrer shape, on the flow properties of grinding media. The flow properties were analyzed in terms of velocity field, porosity distribution, collision frequency, collision energy, impact energy, and power draw. The results indicate that although particle-wall sliding friction coefficient affects the energy transfer from discs to particles, too high a sliding friction may lead to a decrease in energy efficiency. The distance between discs significantly affects the circulation of grinding media between discs. Among the different stirrer types considered, energy transfer is more effective when disc holes are present. Pin stirrer shows increased grinding rates which also results in relatively high power consumption. Although different collision environments exist with different stirrer types, it is shown that the grinding rate can be determined by the first-order kinetics where the rate constant is dependent on the impact energy, for a given material. Grinding efficiency has been compared for different grinding materials under different operating conditions. The results suggest that selection of stirrer geometry also depends on the feed size and the type of material to be ground. Discussion has also been made of the usefulness of particle scale information in the design and control of stirred mills of different types.

Flow Field Analysis of Stirred Liquid‐Liquid Systems in Slim Reactors

AbstractPrevious studies have shown the great potential, but also the great challenges, in handling slim reactors often used for polymerization reactions. Experiments and simulations were carried out in reactors with aspect‐to‐diameter ratios of up to 5, to test and to evaluate the mixing and dispersion efficiency for liquid‐liquid systems of single‐ and multiple‐stage impellers. Therefore, power consumption, mixing time and minimum dispersion speed were determined for five different stirrer types under turbulent conditions. It was found that the dimensionless mixing time is highly sensitive to the configuration of the impellers, with almost no dependency on the turbulent power number. Another focus was the analysis of the effect of the baffles. The influence of the baffle length in slim reactors on the mixing time and the macroscopic flow field was determined.

Glucose Oxidation in Slurry Reactors and Rotating Foam Reactors

Glucose oxidation using platinum promoted by bismuth was studied as a three-phase model reaction. Using catalyst nanoparticles and measuring the oxygen concentration in the bulk liquid, the kinetic parameters and mass transfer characteristics were determined at a temperature of 333 K. The overall reaction rate was studied experimentally using three different support types: slurry catalysts, pellets, and a solid foam stirrer. The glucose conversion rate and the deactivation rate of the catalyst depend strongly on the ratio between mass transfer and reaction rate. At low catalyst concentrations, the glucose oxidation process is liquid–solid mass-transfer-limited. The block stirrer shows a superior performance over the slurry catalysts due to the high liquid–solid volumetric mass transfer coefficient. The bimodal pore size distribution of the catalyst layer further increases the conversion rate. Using slurry catalysts, a loading of 1 wt % in combination with pure oxygen feed is required to achieve acceptable conversion rates. Under these conditions, the gas–liquid mass transfer and partially the liquid–solid mass transfer are the rate-limiting steps. The foam block stirrer shows good gas–liquid mass transfer rates and high liquid–solid mass transfer rates, which still increase at high power input. Working under external mass transfer control and using this stirrer type, the catalyst loading can be strongly reduced to loadings less than 0.4 wt %, while the conversion rate remains comparable to slurry particles with loadings of 1 wt %. As the catalyst is fixed, attrition and agglomeration in high viscosity liquids are circumvented. There is further no need for filtration, and the catalyst can simply be reused.

J023031 血栓溶解用マイクロ撹祥器の動作解析と制御に関する研究([J02303]医療福祉のメカトロニクス)

A cerebral thrombus or blood clot might cause cerebral stroke and even decease if the clot could not be dissolved within several hours after it was formed. This paper presents a fundamental study on development of a new type of mechanical micro stirrer for assisting the dissolution of the thrombus with a few amount of thrombolytic agent. The micro stirrer is made of a simple structure with a piezoelectric. An efficient excitation method for stirring up the thrombus to get a quick dissolution is investigated. Furthermore, to evaluate the dissolution state in vivo, the method using the stirrer as both the stimulator to beat the clot and the probe to evaluate its solubility is proposed.

Scaleup of Lipase-Catalyzed Polyester Synthesis

One of the critical steps for the commercialization of new enzyme-based products is the successful scaleup of the catalyzed reaction. In the study presented here, we achieved a scaleup for the enzymatic production of glycerol adipate on a 500 g scale in a heated, solvent-free system. The influence of various reaction conditions (i.e., temperature, pressure, enzyme concentration, reactants ratio, stirrer type, stirring rate, and reaction time) on the substrate conversion and molecular weight of the product was investigated. Conversions were higher than 0.9, and molecular weights were in the desired range of 2000−3000 Da. Space time yields of 370 g d−1 L−1 could be achieved. Maximal polymer yield was achieved at 60 °C, < 20 mbar, 3 wt % Novozym 435, glycerol:adipic acid ratio 1.1:1, <48 h while stirring at 100 rpm.

Effect of hydrodynamic conditions of the kinetics of Bentonite Suspension Flocculation by Cationic Polyelectrolytes and the strength of formed flocs

The influence of Zetag and SNF FO cationic polyelectrolytes on the aggregation kinetics of bentonite particles in a flow system is studied in detail as a function of the dose of added polymer, charge density of its macromolecules, the regime and intensity of system stirring, and the type of stirrer (magnetic and mechanical stirrers). It is shown that there is an optimal regime, namely, the alternation of slow and rather rapid stirring, that provides the formation of the largest and strongest flocs. The rate of aggregation and the size of formed flocs increase with the amount of added reagent irrespective of the intensity of system stirring, as well as with an increase in the charge density of polyelectrolyte, which is responsible for the affinity of macromolecules for the surface. The effect of polymer charge on the flocculation kinetics is exhibited first of all upon the slow stirring of suspension. The difference in the sizes of aggregates resulted from the flocculation of macromolecules with different charges is leveled with an increase in stirring intensity. An empirical method for comparing the efficiency of the flocculating action of polymers in suspensions prepared using different types of stirrers is proposed.

Struvite precipitation from urine – Influencing factors on particle size

Struvite crystallisation is a fast and reliable phosphorus removal and recovery process for concentrated waste streams – such as hydrolysed human urine. In order to optimise P-elimination efficiency, it is beneficial to obtain larger particle sizes: they are easier to separate and less prone to wash-out than smaller particles. This paper presents the results of a study on the effect of process parameters on particle size in a single step struvite precipitation. Crystals formed in batch experiments with real hydrolysed urine were shown to have an average size of >90 μm at pH 9 and 20 °C. This is reduced to 45 μm when changing stirrer type. Particle size increases with lower supersaturation. The results showed that under otherwise constant conditions, particle size decreases with lower temperature and has a minimum between pH 9 and 10. Deviating trends are observed at pH <8. Struvite formation in a CSTR (continuously stirred tank reactor) process was shown to be a reliable stable process that does not require any pH control. A method based on conductivity measurement is presented to estimate ionic strength, which is needed for equilibrium calculations.

Prevention of Stirring-Induced Microparticle Formation in Monoclonal Antibody Solutions

Monoclonal antibodies are being widely used for the treatment of various diseases. Microparticle formation in high-concentration protein solutions is a major problem during the manufacture of therapeutic monoclonal antibodies, because aggregation leads to fouling of aseptic filters and may lead to an immunogenic reaction in patients. We found that stirring using a traditional bottom-magnetic type stirrer results in extensive and sustained formation of 500-nm diameter protein microparticles arising from shear stress on protein molecules. The antibody solution stirred for only 5 min using this type of stirrer exhibited significant fouling of aseptic filter membranes. In contrast, a top-entering type stirrer did not lead to the formation of microparticles, and the solution did not exhibit membrane fouling even after 30 min of stirring. We conclude that a top-entering type stirrer is more suited for the manufacture of concentrated therapeutic monoclonal antibody solutions.