Stirring Efficiency Research Articles

Design of experiments optimization of N,N,N-trimethyl chitosan synthesis using N,N-diisopropylethylamine base

This study presents a novel synthesis method of N,N,N-trimethyl chitosan (TMC) by using a non-nucleophilic base and optimizing the solvent system for enhanced scalability, while addressing critical factors such as viscosity management and stirring efficiency. The study objectives also included achieving high N,N,N-trimethylation without O-methylation while minimizing reagent use. Eight bases, three solvent systems, and varying levels of dilution were explored to mitigate viscosity challenges and gas evolution. 1H NMR spectroscopy was used to characterize the TMC products. The integral values of the peaks at 3.3, 3.0, and 2.8 ppm, corresponding to trimethyl, dimethyl, and monomethyl groups, were used to quantify the methylation degrees. The most promising initial results were obtained with N,N-diisopropylethylamine (DIPEA) base, and DMF as solvent. Using 6 eq methyl iodide (MeI) relative to chitosan and DIPEA as base, up to 68 % DTM was achieved. Applying Design of Experiments (DoE), the method was further optimized under diluted conditions, crucial for industrial scalability and viscosity control. Results from a full factorial design (32) revealed that diluted medium effectively prevented viscosity concerns, achieving a notably low viscosity of 5.9 cP in the reaction mixture, a 16-fold decrease in viscosity, compared to initial experiments. It was also established that both the MeI reagent and the base addition are significant factors for the DTM response, with both factors showing quadratic effects. The DoE model demonstrated high significance (R = 0.97), high precision for future prediction (Q2 = 0.87), good model validity (0.84) and excellent reproducibility (0.96). The results mark a notable advancement in TMC synthesis, offering an efficient and practical method with significant implications for industrial applications.

Influence of operating parameters on the flow of the molten bath during the swirl-type oxygen lance blowing process

ABSTRACT In top-blowing steelmaking, the flow behaviour of molten steel during supersonic jet impact into the molten bath is crucial for the refining process. In this study, the effects of lance height and operation pressure on velocity distribution and the flow characteristics of the molten bath during the swirl-type oxygen lance blowing process in a 260t converter were explored. The results demonstrate that compared to the traditional oxygen lance, the stirring efficiency of a molten bath with the swirl-type oxygen lance is improved due to the tangential momentum of the jet and the increase in cavity diameter. As the lance height increases, the flow is improved at the bottom and surroundings of the molten bath, and the dead zone volume of the molten bath decreases first and then increases. The best stirring efficiency is achieved at H = 40de. As the operation pressure increases, the impact strength of the jet increases, the flow at the upper zone of the bath is significantly improved, and the dead zone volume decreases.

Development of Lab-Scale Continuous Stirred-Tank Reactor as Flow Process Tool for Oxidation Reactions Using Molecular Oxygen.

The use of sustainable oxidants is of great interest to the chemical industry, considering the importance of oxidation reactions for the manufacturing of chemicals and society's growing awareness of its environmental impact. Molecular oxygen (O2), with an almost optimal atom efficiency in oxidation reactions, presents one of the most attractive alternatives to common reagents that are not only toxic in most cases but produce stoichiometric amounts of waste that must be treated. However, fire and explosion safety concerns, especially when used in combination with organic solvents, restrict its easy use. Here, we use state-of-the-art 3D printing and experimental feedback to develop a miniature continuous stirred-tank reactor (mini-CSTR) that enables efficient use of O2 as an oxidant in organic chemistry. Outstanding heat dissipation properties, achieved through integrated jacket cooling and a high surface-to-volume ratio, allow for a safe operation of the exothermic oxidation of 2-ethylhexanal, surpassing previously reported product selectivity. Moving well beyond the proof-of-concept stage, we characterize and illustrate the reactor's potential in the gas-liquid-solid triphasic synthesis of an endoperoxide precursor of antileishmanial agents. The custom-designed magnetic overhead stirring unit provides improved stirring efficiency, facilitating the handling of suspensions and, in combination with the borosilicate gas dispersion plate, leading to an optimized gas-liquid interface. These results underscore the immense potential that lies within the use of mini-CSTR in sustainable chemistry.

Optimization of mixing behaviors in a multistage vanadium shale leaching tank by a double-layer impeller at different speeds

BackgroundMultistage vanadium-containing shale leaching tanks often suffer from uneven solid phase distribution and mineral deposition at the bottom of the tank, leading to low leaching efficiency. MethodsIn this study, the solid‒liquid flow, tracer diffusion and power consumption in a multistage vanadium shale leaching tank with an inlet and outlet were numerically investigated and compared, the samples were stirred by a double-layer impeller with the same and different speeds, and the numerical model was validated by water model experiments. Significant FindingsThe results showed that the maximum velocity near the liquid surface increased from 1.24 m/s to 1.47 m/s and the average velocity increased from 1.15 m/s to 1.24 m/s when the lower impeller speed increased from 34 r/min to 44 r/min. The volume of the low-speed region decreased from 1.15 m3 to 0.63 m3, and the stirring power was reduced by 14.7%. In addition, increasing the lower impeller speed could effectively shorten the response time and increase the peak molar concentration of the tracer. A stirring speed of 34 rpm for the upper impeller and 44 rpm for the lower impeller could achieve good stirring efficiency with proper stirring power.

Effect of Prestirring Time on Carbon Removal from Coal Fly Ash in the Flotation Technology.

Coal fly ash (CFA) is one of the industrial byproducts of burning coal for energy production and has unburned carbon, which negatively affects its full potential use. The flotation technology can be effective in separating unburned carbon from CFA, and the prestirring time is crucial for the ideal initial conditions during the flotation process. To find the suitable prestirring time, eight prestirring times, including 0, 1, 2, 3, 4, 5, 6, and 7 min, were selected in this paper, followed by flotation of CFA after prestirring. Parameters such as loss on ignition (LOI), the removal rate of unburned carbon (RUC), contact angle, and particle size volume fraction were used to assess the effect of prestirring time on flotation results. The results showed that the prestirring time significantly affects the CFA flotation performance. As the prestirring time increased, the LOI of CFA first decreased and then increased, and the contact angle showed the opposite trend. Besides, the prestirring time of over 2 min positively affected the fineness of the tailings. Overall, the prestirring time of 3 min had the most significant carbon removal effect, obtaining an LOI of tailings of 0.96%, a yield of 74.56%, an RUC of 72.70%, and a volume fraction less than 45 μm of 36.65%. This study provides theoretical support for improving stirring efficiency and saving flotation costs in industrial applications and is conducive to the recycling of CFA resources.

CFD Predictions for Mixing Times in an Elliptical Ladle Using Single- and Dual-Plug Configurations

Argon bottom stirring is commonly practiced in secondary steelmaking processes due to its positive effects on achieving uniform temperatures and chemical compositions throughout a steel melt. It can also be used to facilitate slag metal refining reactions. The inter-mixing phenomena associated with argon gas injection through porous plugs set in the bottom and its stirring efficiency can be summarized by evaluations of 95% mixing times. This study focuses on investigating the impact of different plug positions and ratios of argon flow rates from two plugs on mixing behavior within a 110-tonne, elliptical-shaped industrial ladle. A quasi-single-phase modeling technique was employed for this purpose. The CFD findings revealed that the optimal position of the second plug is to be placed diametrically opposite the existing one at an equal mid-radius distance (R/2). An equal distribution of argon flow rates yielded the best results in terms of refractory erosion. A comparative study was conducted between single- and dual-plug-configured ladles based on flow behavior and wall shear stresses using this method. Furthermore, a transient multiphase model was developed to examine the formation of slag open eyes (SOE) for both single- and dual-plug configurations using a volume of fluid (VOF) model. The results indicated that the dual-plug configuration outperformed the current single-plug configuration.

Chaotic mixing properties under rotation plus revolution revealed by purification experiments and numerical simulations

BackgroundThe purification process of Zn-containing solid waste causes severe pollution, and energy and material consumption because of its low mechanical stirring efficiency. Thus, a new effective stirring method called rotation plus revolution (RPR) has been proposed. MethodsThe enhanced mixing performance of eccentric rotation (ER), orbital rotation (OR), and RPR were investigated through purification experiments and numerical simulations. Combined with chaotic mixing theory, the influence of momentum transfer on the reaction rate controlled by diffusion is analyzed. Significant findingsCompared with ER and OR, RPR induces a specific chaotic attractor state in the fluid, which destabilizes the flow field, thereby realizing chaotic mixing and destroying the isolated mixing region. RPR promotes sufficient momentum diffusion, and the trajectory of folding and stretching increases the effective collision probability per unit time, greatly improving the reaction rate. At 60 min, the purification rate of RPR reached 96.9%, which was 37.8 and 35.1% higher than those of ER and OR, respectively. RPR also had a higher energy utilization rate, and its unit ion purification energy decreased by 2.3% and 20.4% compared with ER and OR, respectively. Overall, RPR improved the purification efficiency with low energy consumption, thereby saving energy and reducing emissions.

3D uniformity measurement of stirring system based on dual-camera positioning

This investigation proposes a dual-camera positioning method and the average distance in the cube (AD-Cube) method to explore the effect of three-dimensional (3D) spatial multiphase stirring. The 3D trajectories of the tracer ball were reconstructed in the stirring system using a dual-camera positioning method. The AD-Cube method for calculating the mixing uniformity within the cube region was proposed and verified by rigorous and valid numerical validation (the standard reference value was approximately 0.6617). The negative correlation coefficient between conductometry and the AD-Cube method for the evaluation of the mixing effect was −0.9118. The stirring region was equally divided into several 3D blocks, and the relationship between the whole and local was elaborated to provide more accurate information for the 3D uniformity metric. Moreover, the volume of the stirring dead zone was estimated by discrete blocking, and the influence of the stirring paddle height from the bottom and agitating motor speed on the stirring effect was studied. This study provides a theoretical basis for optimizing the parameters of a 3D stirring system, designing chemical reactors, and measuring and evaluating the 3D uniformity of stirring systems. • The proposed method is based on dual-camera positioning and computational geometry. • The 3D uniformity of stirring system is characterized by the novel method. • Effectiveness of the novel method is verified on both numerical and experimental. • Evaluation indicator is established to evaluate the 3D stirring efficiency. • The method can be used in engineering fields of evaluation of 3D uniformity.

Improving the Reverberation Chamber Performance Using a Reconfigurable Source Stirring Antenna Array

An antenna array composed of 16 asymmetric distributed monopoles on a circular dielectric substrate is proposed to use as a reconfigurable source stirrer in a reverberation chamber (RC). The distance between antennas is above λ2 to ensure the isolation between antennas below −15 dB. In order to ensure the mutual independence of the stirring modes of the antenna array, the 16 monopoles are asymmetrically distributed on both sides with X and Y as axes. The stirring efficiency of a stirrer is related to its size, and usually a higher stirring efficiency means a larger stirrer. The source stirring technique can achieve high efficiency, but the rotation of a source stirring antenna is limited to the radius of the turntable in an RC. To solve this problem, we propose to use an antenna array as a reconfigurable source stirrer, which can achieve a high efficiency of source stirring. As the antenna array can achieve source stirring and mechanical stirring at the same time, the source stirring section is not limited to the radius of the turntable; the switch between the selected antennas of the antenna array can increase the actual stirring samples of the stirring. Thus, the efficiency can be improved significantly and has been verified by the measurement results. The volume occupied by the conventional mechanical stirrer is reduced, which improves the working volume. The figures of merit, such as the field uniformity (FU), the independent sample numbers, the average K-factor, and the total scattering cross-section (TSCS), are measured and compared to the conventional mechanical stirring, mechanical stirring, and source stirring of the antenna array. Measurement results of the reconfigurable stir are illustrated below. FU has the best convergence and the lowest value, below 0.5 dB. The independent sample number is the largest. K-factor is the lowest, and most ranges are below −15 dB. Additionally, the proposed method has the largest TSCS, above 2 m2. These confirm that the proposed reconfigurable source stirring technique outperforms other three stirring techniques significantly. The antenna array can be easy to disassemble and install in different RC. With a wide range of working band, the proposed method can be applied to 5G OTA testing.

Numerical analysis of effect of Reynolds number on interaction of density-stratified fluid with a vortex ring

In this study, the effect of Reynolds number (Re) on the mixing process of a two-layer density-stratified fluid, caused by the interaction between a vortex ring and the density interface, was numerically investigated using an improved vortex-in-cell method. The density-stratified fluid consisted of water (upper layer) and an aqueous sodium chloride solution (lower layer). Re of the simulated vortex ring was varied from 644 to 1932. We numerically investigated the behavior of the vortex ring and density-stratified fluid, and compared the same with that from a previously conducted experimental study from the literature. The vortex structure generated during the interaction was visualized in three dimensions. Furthermore, the mixing process was evaluated in terms of the stirring index, gradient of concentration, and stirring efficiency. The mixing behavior of the vortex ring was a function of the interaction pattern. For example, for a large Re, with the penetrative pattern, the stirring efficiency reached a constant value that was smaller than that from the partially penetrative pattern. The results showed that a strong stirring caused by an increase in Re of the vortex ring would not always lead to effective mixing.

Reductive Recyclization of sp3-Enriched Functionalized Isoxazolines into α-Hydroxy Lactams.

An efficient synthesis (up to a 200 g scale) of 3-hydroxypyrrolidin-2-ones bearing alkyl substituents or functional groups at the C-5 position is described. The reaction sequence started from 1,3-dipolar cycloaddition of in situ generated nitrile oxides with (meth-)acrylates into 3-substituted isoxazoline-5-carboxylates. The catalytic hydrogenolysis of the isoxazoline N-O bond was optimal upon using H2 (1 atm) at rt, with the following order of the catalyst activity: Pd-C > Pd(OH)2-C > Pt-C. The reactions with Pt-C were more selective for the synthesis of pyrrolidones, while Pd-C provided the fastest conversion rates. The stirring efficiency had a positive impact on conversion rather than elevated temperatures (up to 40 °C) or pressure (up to 50 atm). The diastereoselectivity was governed mainly by steric factors, with a dr of 1:1 to 3:1 (cis- and trans-isomers could be separated). Higher homologues (isoxazolinylacetates and -propanoates) were suitable for the synthesis of 6- or 7-substituted 4-hydroxypiperidones and 5-hydroxyazepanones, respectively. The proposed methods are tolerant to functional groups, including CF3 (but not CHF2 or CH2Cl), ester, and most N-Boc-protected amines. The utility of hydroxyl groups in lactams was shown by functional group transformations. Hydrogenolysis of C(5)-functionalized isoxazolines, bearing trimethylsilyl, phosphonate, or sulfone groups, was also studied to demonstrate limitations.

Influence of different stirring speed on fracture properties of wedge splitting specimens

Because the stirring efficiency and the quality of finished products are impacted by the mixing speed of the concrete mixer, the influence of the mixing speed at the same process condition on the mechanical properties of concrete properties should be studied. The test adopts the wedge splitting process, and it indicates that the compressive strength of the concrete reaches its maximum at the stirring speed of 1.4 m/s, and the peak value exists around 1.4 m/s. Furthermore, there is a continuous reduction of the concrete strength at the speed extending. In accordance with the fracture test data, the ratio of crack load/limit load decreases continuously with the increase of mixing speed. The concrete is not liable to crack at a relatively low mixing speed and is unstable while with a significantly high mixing speed. The stirring model is established and the numerical simulation is carried out. Three pressure fields at different rotating speeds are simulated, which directly reflect the pressure distribution and value at different rotating speeds.

Formation mechanism and chaotic reinforcement elimination of the mechanical stirring isolated mixed region

Abstract The isolated mixed region (IMR) is gradually formed during stirring and reduces the mixing efficiency. The unsteady-state formation process of the IMR was modeled and its formation mechanism was analyzed. The rotating frequency of the impeller was optimized using the chaos mathematical theory to improve the stirring efficiency without increasing the power consumption. The calculated results demonstrate that the IMR is a coherent structure, and its formation process is based on the free shear effect of the mixed layer. The chaotic stirring method can accelerate the momentum dissipation process by 37% by eliminating the IMR, and increase the speed by up to 31%. Therefore, chaotic mixing can eliminate the IMR in a shorter time and lower the power consumption.

Horizontal flow reactor optimization for biogas recovery during high solid organics fermentation: Rheological characteristic analyses

Continuous improvements in human living standards, water supply quality, and poor solid waste collection systems in China has led to increased production of municipal sewage sludge and organic solid waste (MOSW), which incurs a potential risk for human health and the environment. Solid anaerobic fermentation, which has exhibited advantageous energy recovery and biosolid stabilization, has been considered for urban organic solid waste treatment. The primary objective of this study was to optimize horizontal flow reactor operations for the efficient fermentation of high solid organics and subsequent biogas production via rheological characteristic analyses. The effects of operational parameters, such as paddle type, paddle diameter, pitch diameter ratio, stirring efficiency, torque, and power consumption, on the reactor performance were simulated using computational fluid dynamics (CFD). The solid content greatly influenced the rheological characteristics of the MOSW; increasing the solid content (5 %–30 %) of the MOSW led to a significant decline in the rheological index (0.532 to 0.224). The optimized parameters simulated by CFD included a screw-type stirring paddle with a pitch of 0.6 D, pitch of the screw with the value of 0.75 D, stirring shaft (set vertically and eccentrically downward) with the value of 0.15 D, and stirring speed less than 10 rpm. Moreover, the higher the consistency coefficient, the lower the rheological index and required power consumption. The reactor energy consumption analysis indicated that the average energy consumption can reach 48.20 kJ/m3 with an efficient operation.

Vibration‐Based Monitoring of Gas‐Stirring Intensity in Vacuum Tank Degassing

Liquid steel is typically stirred in a vacuum tank using argon gas injection to achieve a homogeneous composition and high‐purity steel. The aim of this work is to study the effect of vessel vibration on the operational state monitoring of the gas stirring in a vacuum tank degasser. Following an extensive analysis of vibration features, the root mean square (RMS) of vertical velocity is found to be the best feature for the measurement of the stirring intensity caused by the volumetric gas injection rate into the ladle. Smoothing is conducted using a centered median filter with a window length of 21 s. In this work, the operational state monitoring of gas stirring is described using a ladle responsiveness value (LRV). This describes the ability of a ladle to generate the maximum amount of vibration with the minimum amount of argon gas. The LRV summarized for each ladle reveals significant differences between them. Correspondingly, a rolling ladle responsiveness value (rLRV) is used for online monitoring of possible gas leakages. The rLRV can also be used for the online monitoring of the stirring efficiency and as its comparison with the overall efficiency of a specific ladle or all ladles.

Physical and Mathematical Modeling of Swirling Gas Jets Impinging onto a Liquid Bath Using a Novel Nozzles‐Twisted Lance

Physical and mathematical modeling is performed in a 10:1 scaled‐down basic oxygen furnace (BOF) steelmaking vessel to study impingement onto a bath of swirling gas jets from a novel nozzles‐twisted lance. The particular aspects with respect to the swirling jets‐induced cavity characteristic, jets’ stirring efficiency, and bath flow field are focused upon, and their discrepancies with those created by conventional oxygen lance jets are assessed. Results show that compared with the conventional jets, the swirling jets strike a greater impact area with a shallower but wider cavity and facilitate bath surface flow. Due to a more intensive bath horizontal flow, which shows an increase in intensity by 0.34–1.66 times than that of conventional jets, the swirling jets shorten bath mixing time by 11–60%, depending on the nozzle twist angle of the lance. These results suggest that the lance height of the nozzles‐twisted lance is operated more flexibly than that of the conventional one. This not only enables sufficient bath stirring efficiency and improves slagging but also contributes to postponing lance tip erosion and prolonging its life span in plant operations, whereas the enhanced flows in the regions near the sidewall accelerate refractory erosion there.

Influence of vessel dimensions on particles homogenization and heat removing in TMF stirrer

Purpose The purpose of this paper is to determine how the shape of the container affects the efficiency of a traveling magnetic field (TMF) stirring. Design/methodology/approach The modeling approach is based on finite element software Comsol which includes harmonic electromagnetic (EM), transient CFD and particle tracing modules. For evaluating efficiency of stirring the particle, homogenization parameter is used. Findings It has been determined that the use of an elliptical cylinder-shaped vessel allows better heat removal from the side surface and, at the same time, the stirring efficiency does not drop significantly. Practical implications The results of the work can be used in the design of EM stirring installations in which exothermic reactions occur. Originality/value The transient simulation of particle transport in a TMF-driven melt flow gives the opportunity to estimate the efficiency of stirring process in different vessel shapes.

A Source Stirred Reverberation Chamber Using a Robotic Arm

In a reverberation chamber, the stirring efficiency of the source stir technique is very high. However, to apply the source stir, the configuration (position, orientation, or polarization) of the transmitting (Tx) antenna has to be changed every time in the stirring process. To solve this problem, we use a three-dimensional printed robotic arm to control the position and orientation of the Tx antenna; thus, the source stirring process can be performed automatically. The measurement results are validated and compared with that from mechanical stirrers. Figures of merit such as autocorrelation, average K -factor, and total scattering cross-section are presented. The statistical distribution is also verified by using Kolmogorov–Smirnov test. Results show that the source stir technique outperforms the mechanical stirring technique significantly.

Development perspectives of metal gas-dynamic stirring in a ladle with a side lance application

Blow-off of a liquid metal bath through a lance, located in the bottom part of a ladle wall, is usually considered as one of well-known long time ago variant of steel refining in ladle. However, despite a wide repute and availability of a series of advantages, the technology was not widely spread. An estimation of stirring efficiency and splashes formation at different variants of compressed air supply made. The studies were done at a transparent water model with a color indicator application. It was determined, that upper and bottom lances shifting relating to ladle symmetry axle promotes the stirring intensification and simultaneous decrease of splashes height. The best results were obtained at the simultaneous utilization of asymmetrically located submerged lance and a side lance, oriented in gas-liquid flow direction in the bottom part of the vessel. The side lance is more preferable in maintenance, since for them a ladle fringe is not required as in the case with bottom lances, it is not subjected to falling metal stream action as well as to metal and slag residuals action after tapping finishing. It is possible to provide an improvement of stirring conditions and metal tapping by shifting and inclination of a side lance. Industrial tests showed, that a facility for metal blow off through porous insertions, installed in ladle wall, have a high throughput ability, provide a reliable operation within a course of ladle lining campaign without intermediate repair. It does not require capital outlays and can be recommended for industrial application.

Full-Thickness Intraoral Mucosa Barrier Models for In Vitro Drug-Permeation Studies Using Microneedles

The use of permeation enhancers such as microneedles (MNs) to increase drug penetration across intraoral mucosa has increased in recent years. Permeation studies, commonly performed using vertical diffusion cells, are a well-established way to preview formulations and enhance their performance during the development stage. However, to our knowledge, the existing intraoral mucosa barrier models do not permit permeation using MN-pretreated mucosa due to their insufficient thickness. Therefore, the objective of this study was to develop a barrier model using thick palate tissues to perform in vitro permeation studies, with physical enhancement of the permeability of intraoral mucosa by pretreatment with MNs. The adapted Franz-type cells used in the permeation experiments were validated (cell dimensions and volume, sealing effectiveness, stirring and dissolution efficiency, temperature control, and establishment of uniaxial flux). Commercially available MNs were used in the palatal mucosa. Optical images of the mucosa were acquired to analyze the microperforations created. In vitro permeation studies were conducted with the MN-pretreated mucosa. This work presents a new in vitro method for the evaluation of MNs as permeation enhancers, with the aim of improving the absorption of drug formulations topically applied within the oral cavity.