Numerical Simulation of Gas-Liquid Flow in a Stirred Tank with a Rushton Impeller

The gas-liquid flow field in a stirred tank with a Rushton diskturbine, including the impeller region, was numerically simulatedusing the improved inner-outer iterative procedure. Thecharacteristic features of the stirred tank, such as gas cavity andaccumulation of gas at the two sides of wall baffles, can be capturedby the simulation. The simulated results agree well with availableexperimental data. Since the improved inner-outer iterative algorithmdemands on empirical formula and experimental data for the impellerregion, and the approach seems generally applicable for simulatinggas-liquid stirred tanks.

Effect of Butternut Squash (Cucurbita moschata) Seed Powder on the Chemical and Rheological Properties of Stirred Cultured Camel Milk and Yoghurt

Research shows that producing fermented camel milk is hard because of the milk’s inability to form a firm coagulum, attributed to low levels of κ-casein and ꞵ-lactoglobulin and the large casein micelle size, leading to a weak network of casein formation. In an effort to address this issue, researchers turned to corn starch as a thickening agent, discovering that a concentration of 2.0% effectively improved the viscosity and significantly reduced syneresis in stirred camel milk yoghurt and cultured camel milk. This study explores alternatives to corn starch, focusing on butternut squash seeds as a promising substitute due to their hydrocolloid composition. By incorporating butternut squash (Cucurbita moschata) seed powder (BSSP) as a thickening agent, this study aimed at enhancing the chemical and rheological properties of stirred camel milk yoghurt and cultured camel milk. Fermented camel milk was prepared using 4 litres of camel milk, 2% starter cultures (thermophilic culture for yoghurt and mesophilic aromatic culture for stirred cultured camel milk) and BSSP 0.0% (negative control), 0.4%, 0.8%, 1.2%, 1.6%, 2.0% mixed with 0.4% gelatin. 2.0% corn starch mixed with 0.4% gelatin was used as a standard for comparison. Results showed that increasing the BSSP level significantly (p < 0.05) decreased the moisture content while increasing the total solid content of stirred fermented camel milk products. There was an increase in ash content with an increase in BSSP levels. There was a significant (p < 0.05) reduction in the pH, with an increase in BSSP levels in stirred fermented camel milk samples. Increasing the concentration of BSSP from 0.4% to 2.0% resulted in a significant (p < 0.05) increase in viscosity and a reduction in syneresis of stirred camel milk yoghurt and stirred cultured camel milk samples. This study demonstrated that BSSP effectively enhances the viscosity, reduces syneresis and increases acidity in stirred fermented camel milk products during storage.

Effect of aspect ratio of elliptical stirred vessel on mixing time and flow field characteristics in the absence of baffles

Elliptical tanks were used as an alternative to circular tanks in order to improve mixing efficiency and reduce mixing time in unbaffled stirred tanks(USTs). Five different aspect ratios of elliptical vessels were designed to compare their mixing time and flow field. Computational fluid dynamics(CFD) simulations were performed using the k–ε model to calculate the mixing time and simulate turbulent flow field features, such as streamline shape, velocity distribution, vortex core region distribution, and turbulent kinetic energy(TKE) transfer. Visualization was also carried out to track the tinctorial evolution of the liquid phase. Results reveal that elliptical stirred tanks can significantly improve mixing performance in USTs. Specifically, the mixing time at an aspect ratio of 2.00 is only 45.3% of the one of a circular stirred tank. Furthermore, the secondary flow is strengthened and the vortex core region increases with the increase of aspect ratio. The axial velocity is more sensitive to the aspect ratio than the circumferential and radial velocity. Additionally, the TKE transfer in elliptical vessels is altered. These findings suggest that elliptical vessels offer a promising alternative to circular vessels for enhancing mixing performance in USTs.

Application of the CatBoost Model for Stirred Reactor State Monitoring Based on Vibration Signals

Stirred reactors are key equipment in production,and unpredictable failures will result in significant economic losses and safety issues.Therefore,it is necessary to monitor its health state.To achieve this goal,in this study,five states of the stirred reactor were firstly preset:normal,shaft bending,blade eccentricity,bearing wear,and bolt looseness.Vibration signals along x,y and z axes were collected and analyzed in both the time domain and frequency domain.Secondly,93 statistical features were extracted and evaluated by ReliefF,Maximal Information Coefficient(MIC)and XGBoost.The above evaluation results were then fused by D-S evidence theory to extract the final 16 features that are most relevant to the state of the stirred reactor.Finally,the CatBoost algorithm was introduced to establish the stirred reactor health monitoring model.The validation results showed that the model achieves 100%accuracy in detecting the fault/normal state of the stirred reactor and 98%accuracy in diagnosing the type of fault.

Micromixing characteristics in a gas-liquid-solid stirred tank with settling particles

The parallel-competing iodide-iodate reaction scheme was used to study the micromixing performance in a multi-phase stirred tank of 0.3 m diameter.The impeller combination consisted of a half elliptical blade disk turbine below two down-pimping wide-blade hydrofoils,identified as HEDT + 2WH_D.Nitrogen and glass beads of100 μm diameter and density 2500 kg-m^(-3) were used as the dispersed phases.The micromixing could be improved by sparging gas because of its additional potential energy.Also,micromixing could be improved by the solid particles with high kinetic energy near the impeller tip.In a gas-solid-liquid system,the gas-liquid film vibration with damping,due to the frequent collisions between the bubbles and particles,led to the decrease of the turbulence level in the liquid and caused eventually the deterioration of the micromixing.A Damping Film Dissipation model is formulated to shed light on the above micromixing performances.At last,the micromixing time t_m according to the incorporation model varied from 1.9 ms to 6.7 ms in our experiments.

Numerical Simulation of Gas-LiquId Flow in a Horizontal Elbow

Gas-liquid flow(GLF),especially slug and annular flows in oil and gas gathering and transportation pipelines,become particularly complex inside elbows and can easily exacerbate pipeline corrosion and damage.In thisstudy,FLUENT was used to conduct 3D simulations of slug and annular flow in elbows for different velocitiesto assess the ensuing changes in terms of pressure.In particular,the multifluid VOF(Volume of Fraction)modelwas chosen.The results indicate that under both slug and annular flow conditions,the pressure inside the elbow islower than the outside.As the superficial velocity of liquid and gas increase,the pressure and liquid flow velocityat different positions of the elbow also increase,while the secondary flow weakens.Under annular flow conditions,the liquid film on the outer side of the elbow is thicker than that on the inner side,and the liquid velocityin the main liquid film zone is the lowest.

Experimental and CFD studies of solid-liquid slurry tank stirred with an improved Intermig impeller

The improved Intermig impeller has been used in the seed precipitation tank in China, which could enhance the mixing and suspension of Al(OH)3 particles and the power consumption declined largely. The flow field, solids hold-up, cloud height, just off-bottom speed and power consumptions were investigated in solid-liquid mixing system with this new type of impeller by CFD and water experiment methods. Compared with the standard Intermig impeller, the improved one coupled with specially sloped baffles could promote the fluid circulation, create better solids suspension and consume less power. Besides lower impeller off-bottom clearance is good for solid suspension and distribution. The just-off-bottom speed was also determined by a power number criterion. Meanwhile, the predicted results were in good agreement with the experimental data.

3D MERGE与3D SPACE STIR序列在腰椎间盘突出症检查中的应用比较

目的:对比三维多回波恢复梯度回波(3D MERGE)、三维可变反转角快速自旋回波(3D SPACE STIR)序列在腰椎间盘突出症(LDH)检查中的应用效果。方法:选择2020年1月~2022年11月收治的135例LDH患者,回顾性分析患者临床和磁共振成像(MRI)资料,所有患者均接受常规MRI扫描及3D MERGE、3D SPACE STIR序列扫描,对比3D MERGE、3D SPACE STIR序列测量神经根直径的一致性,评价两种序列的图像质量参数[信噪比(SNR)、对比噪声比(CNR)]、图像清晰度评分。结果:3D MERGE和3D SPACE STIR序列测量的L3~S1神经根直径比较差异无统计学意义(P>0.05),且两组序列测量的L3、L4、L5和S1直径均显示出较高相关性(r=0.957,0.986,0.975,0.972,P<0.05);3D MERGE序列的SNR及CNR均高于3D SPACE STIR序列,神经根显示分级、图像清晰度评分优于3D SPACE STIR序列,差异有统计学意义(P<0.05)。结论:3D MERGE、3D SPACE STIR序列在LDH神经根直径测量中具有极高一致性,3D MERGE序列较3D SPACE STIR序列能够更清晰显示神经跟的解剖形态,图像质量更好。

Study on Honey Stirred Yoghurt

[Objective] In this study, the aim was to study the optimal formula and technique of honey stirred yoghurt. [Method] The optimum formula and production technique of the honey stirred yoghurt were confirmed by studying the effects of the additive amount of honey, the adding time of honey, thermal death point, the ho- mogenization pressure and stability test on the sensory quality of stirred yoghurt. [Result] The experiment showed that the fermentation temperature of the honey stirred yoghurt should not be too high, and it should be close to that of common yoghurt. In addition, the fermentation time should not be too long, because along with the extension of fermentation time, there would be abnormal smell in the yo- gurt. The optimum formula and production technique were as follows： the additive amount of honey, sugarcane and fermentation agent was respectively 3%; two-sec- tion homogeneous pressures of the fresh milk were I ： 70 MPa, I1：30 MPa; the thermal death point was 85 ℃ and the time was 10 min; the fermentation occurred at 42℃, and the fermentation of the products was stopped when the ultimate acidity was among 0.70%-0.75%. [Conclusion] The study could provide some refer- ences for the production and processing of honey stirred yoghurt.

Drawdown mechanism of light particles in baffled stirred tank for the KR desulphurization process

To improve the efficiency of the desulfurization process, the drawdown mechanism of light particles in stirred tank is studied in this paper. For both up and down pumping modes, the just drawdown speeds(Njd) of floating particles in transformative Kanbara Reactor(KR) are measured in one and four baffled stirred tanks experimentally. Then numerical simulations with standard k-ε model coupled with volume of fluid model(VOF) and discrete phase model(DPM) are conducted to analyze the flow field at the just drawdown speed Njd. The torques on the impeller obtained from experiments and simulations agree well with each other, which indicates the validity of our numerical simulations. Based on the simulations, three main drawdown mechanisms for floating particles, the axial circulation, turbulent fluctuation and largescale eddies, are analyzed. It's found that the axial circulation dominates the drawdown process at small submergence(S = 1/4 T and 1/3 T) and the large-scale eddies play a major role at large submergence(S = 2/3 T and 3/4 T). Besides, the turbulent fluctuation affects the drawdown process significantly for up pumping mode at small submergence(S = 1/4 T and 1/3 T) and for down pumping mode at large submergence(S = 2/3 T and 3/4 T). This paper helps to provide a more comprehensive understanding of the KR desulphurizer drawdown process in the baffled stirred tank.

Experimental study of power consumption, local characteristics distributions and homogenization energy in gas–liquid stirred tank reactors

In this paper, the power consumption, the vertical local void fraction and the local gas–liquid interfacial area are investigated in the aerated stirred tank reactors(STRs) equipped with a rigid-flexible impeller. Meanwhile, the regressive correlation based on power consumption and interfacial area is proposed. Then a novel homogenization energy(HE = RSDPtm) expression based on power consumption and local interfacial area is redefined and used to indicate the mixing efficiency. The optimal operating mode is selected based on the change of the HE value. This paper can provide research ideas for structural optimization of stirred reactors.

Study on macro-instability in stirred tank

Macro-instability(MI)is an important natural phenomenon affecting the mixing performance in stirred tank significantly,which results from movement and evolution of large eddies.Factors associated with MI frequency in mixing operation and energy dissipation related to MI were reviewed.Flow pattern in turbulent regime contains many coherent structures,which have much energy vortices and may result in flow field MI.Adjustment of coherent structure and controlling MI may contribute to energy saving and good mixing performance.Controlling methods for MI was prospected.

An innovative flake graphite upgrading process based on HPGR,stirred grinding mill, and nanobubble column flotation

Physical upgrading of graphite is typically achieved with many stages of grinding and flotation to produce a concentrate with approximately 95% carbon grade.An innovative grinding and column flotation process has been developed for efficient graphite upgrading to substantially simplify the process flowsheet and reduce operating costs.In this process,a high-pressure grinding roller(HPGR) and a stirred mill were employed as primary comminution techniques and a nanobubble flotation column as a key separation process.The results obtained with a crystalline flake graphite sample with a carbon grade of 11.15% show that the novel process can produce a concentrate with 94.82% carbon grade and 97.89% recovery from an open circuit of one rougher and two cleaner flotation stages.Scanning electron microscope(SEM)microphotographs indicate that HPGR offers the advantage of more effective protection of graphite flakes during crushing.Grinding test results show that stirred mill could not only protect graphite flakes but also promote the efficient liberation of graphite.Compared with the traditional flotation process,nanobubble flotation can effectively recover ultrafine graphite.The new process possesses a number of important advantages over the traditional method,including substantially higher graphite recovery,greatly simplified process flowsheet,better protection of flake size,reduced reagent consumption and process costs,etc.

THEORETICAL AND EXPERIMENTAL STUDIES ON BUBBLE DIAMETER AND GAS HOLDUP IN AERATED STIRRED TANKS

Experiments were carried out in geometrically similar vessels with diameters of 0.287, 0.495 and 1.1m respectively. Bubble diameter distribution was measured with a dual electric conductivity probe placed in the tanks. Gas holdup was measured by spillover method. Considering the coalescence of bubbles in the upper circulation region of the aeration stirred tank, introducing the concepts of turbulence decay and effective viscosity of gas-liquid system into this work, and taking into account the equilibrium between the surface energy of the bubbles and the energy supplied by agitation, mathematical models for bubble diameter and mean gas holdup were derived. The mathematical models were confirmed by experimental data.

Effect of the Inclination of Baffles on the Power Consumption and Fluid Flows in a Vessel Stirred by a Rushton Turbine

The role of baffles in mechanically stirred tanks is to promote the stability of power drawn by the impeller and to avoid the fluid swirling, thus enhancing mixing. The present paper numerically investigates the baffles effects in a vessel stirred by a Rushton turbine. The geometric factor of interest is the baffle inclination which is varying between 25°, 32.5°, 45°, 70° and 90° at different impeller rotational speeds. The impeller rotational direction has also been varied. The vortex size and power consumption were evaluated for each geometrical configuration. It was found that the best configuration is the baffle inclination by = 70° at a negative angular velocity.

Experimental study and simulation of a three-phase flow stirred bioreactor

In order to obtain the reasonable operating conditions and minimize the power consumption in the stirred bioreactor, the hydrodynamic experiments in the stirred bioreactor have been taken to obtain the basic data. Subsequently, an Eulerian model for the gas–liquid–solid three phase flow in the stirred bioreactor has been proposed and the CFD simulation has been conducted. By comparing the results of experiment and simulation, it can be concluded that the simulation results were consistent with the experimental data. The inner relationship between operating variables and indicators could be obtained by comparing the results of just suspension speed, gas holdup, power consumption and operational maps, further the reasonable operating conditions could be also determined under the minimum power consumption. The operational maps could provide the theoretical foundation for industrial application of the gas–liquid–solid stirred bioreactors under the low solid concentration(no more than 20 wt%).

Effects of casting speed on microstructure and segregation of electromagnetically stirred Aluminum alloy in continuous casting process

Recently, a semi-solid metal processing has been acknowledged as a cost-effective technique to be able to manufacture high quality product for the transportation industry. In this study a hypo-eutectic Al alloy was fabricated by means of an electromagnetic stirrer in continuous casting process and the microstructural change during solidification due to a fluid flow by electromagnetic stirring was examined. Due to the forced fluid flow during solidification a dendritic phase of primary α phase of Al alloy was turned into a globular phase, which can make the Al alloy get a thixotropic behavior in the semi-solid region. In order to establish the quantitative relationship between microstructure and the process parameters, the morphology shape, a silicon distribution and a size of primary α phase were observed according to casting speed in continuous casting machine. The primary α phase was turned into the degenerate dendrites approaching a spherical configuration with increasing casting speed. The fine-grained and equiaxed microstructure appeared at higher casting speed. A segregation behavior of Si element was declined with increasing casting speed and a very uniform distribution of Si element was observed on the billet at a casting speed of 600 mm·min-1. A thickness of the solidifying shell of the billet was shortened with increasing the casting speed.

Study on gas–liquid flow characteristics in stirred tank with dual-impeller based on CFD-PBM coupled model

Study on gas–liquid flow in stirred tank with two combinations of dual-impeller(six-bent-bladed turbine(6BT)+six-inclined-blade down-pumping turbine(6 ITD),the six-bent-bladed turbine(6BT)+six-inclinedblade up-pumping turbine(6ITU))was conducted using computational fluid dynamics(CFD)and population balance model(PBM)(CFD-PBM)coupled model.The local bubble size was captured by particle image velocimetry(PIV)measurement.The gas holdup,bubble size distribution and gas–liquid interfacial area were explored at different conditions through numerical simulation.The results showed that the 4 mm bubbles accounted for the largest proportion of 33%at the gas flow rates Q=0.76 m^(3)·h^(-1) and 22%at Q=1.52 m^(3)·h^(-1) for combined impeller of 6BT+6ITU,while the bubbles of 4.7 mm and 5.5 mm were the largest proportion for 6BT+6ITD combination,i.e.25%at Q=0.76 m^(3)·h^(-1) and 22%at Q=1.52 m^(3)·h^(-1),respectively,which indicated that 6BT+6ITU could reduce bubble size effectively and promote gas dispersion.In addition,the gas holdup around impellers was increased obviously with the speed compared with gas flow rate.So it was concluded that 6ITU impeller could be more conductive to the bubble dispersion with more uniform bubble size,which embodied the advantages of 6BT+6ITU combination in gas–liquid mixing.

Numerical Study of Solid-Liquid Two-Phase Flow in StirredTanks with Rushton Impeller(Ⅱ) Prediction of Critical Impeller Speed

Three-dimensional solid-liquid flow is mathematically formulated by means of the 'two-fluid' approach and the two-phase k-ε-AP turbulence model. The turbulent fluctuation correlations appearing in the Reynolds time averaged governing equations are fully incorporated. The solid-liquid flow field and solid concentration distribution in baffled stirred tanks with a standard Rushton impeller are numerically simulated using an improved 'inner-outer'iterative procedure. The flow pattern is identified via the velocity vector plots and a recirculation loop with higher solid concentration is observed in the central vicinity beneath the impeller. Comparison of the simulation with experimental data on the mean velocities and the turbulence quantities of the solid phase is made and quite reasonable agreement is obtained except for the impeller swept volume. The counterpart of liquid phase is presented as well.The predicted solid concentration distribution for three experimental cases with the average solid concentration up to 20% is also found to agree reasonably with the experimental results published in the literature.

Computational Fluid Dynamics Approach to the Effect of Mixing and Draft Tube on the Precipitation of Barium Sulfate in a Continuous Stirred Tank

The effect of mixing on the precipitation of barium sulfate in a continuous stirred tank is simulated numerically with different feeding location, feed concentration, impeller speed and residence time through solving the standard momentum and mass transport equations in combination with the moment equations for crystal population balance. The numerical method was validated with the literature data. The simulation results including the distribution of the local supersaturation ratio distribution in the precipitator, mean crystal size and coefficient of variation under different operating conditions compared well with experimental data in the literature. The effect of the presence of a draft tube on precipitation were also investigated, and it is suggested that the installation of a draft tube increased the mean crystal size, in general agreement with experimental work in the literature.