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Theoretical analysis of fluid mixing time in liquid-continuous impinging streams reactor

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Journal of Central South University 2015年第8期22卷 3217-3222页

作者：罗燕周剑秋郭钊余蓓熊卉 School of Mechanical and Power Engineering Nanjing Tech University School of Mechanical and Electrical Engineering Wuhan Institute of Technology

The mixing time of impact zone in liquid-continuous impinging streams reactor(LISR) is theoretically calculated by empirical model and modern micromixing model of the fluid mixing process, and the variation laws of macromixing time and micromixing time are quantitatively discussed. The results show that under a continuous and stable operating condition, as the paddle speed increases, the macromixing time and micromixing time calculated by the two models both decrease, even in a linkage equilibrium state. Simultaneously, as the paddle speed increases, the results figured by the two models tend to be consistent. It indicates that two models both are more suitable for calculation of mixing time in high paddle speed. Compared with the existing experimental results of this type of reactor, the mixing time computed in the speed of 1500 r/min is closer to it. These conclusions can provide an important reference for systematically studying the strengthening mechanism of LISR under continuous mixing conditions.

关键词： impinging stream reactor empirical model theoretical model mixing time comparative analysis

Optimization of mixing time in a ladle with dual plugs

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International Journal of Minerals,Metallurgy and Materials 2010年第6期17卷 709-714页

作者： Dian-qiao Geng Hong Lei Ji-cheng He Key Laboratory of Electromagnetic Processing of Materials （Ministry of Education of China） Northeastern University Shenyang 110819 China

Based on the two-phase fluid （Eulerian-Eulerian） model, a mathematical model about the gas-liquid flow and mixing behavior was developed to investigate the effect of the offset of dual plugs, the included angle of dual plugs with a center point, and gas flow rate on the mixing time in a ladle with dual plugs. Numerical results indicate that two types of recirculation zones exist in the ladle. One is the middle recirculation between gas and liquid plumes, and the other is the sidewall recirculation between plumes and the ladle sidewall. The correction shows that the mixing time is in proportion to -0.2676 power of gas flow rate. There is a unique optimum offset of dual plugs with a particular included angle, in turn, a unique optimum included angle of dual plugs exits with a particular offset.

关键词： ladles refining mixing time optimization numerical simulation

CFD Simulation of Local and Global mixing time in an Agitated Tank

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Chinese Journal of Mechanical Engineering 2017年第1期30卷 118-126页

作者： LI Liangchao XU Bin Key Laboratory of Testing Technology for Manufacturing Process of Ministry of Education Southwest University of Science and TechnologyMianyang 621010China

The Issue of mixing efficiency in agitated tanks has drawn serious concern in many industrial processes. The turbulence model is very critical to predicting mixing process in agitated tanks. On the basis of computational fluid dynamics（CFD） software package Fluent 6.2, the mixing characteristics in a tank agitated by dual six-blade-Rushton-turbines（6-DT） are predicted using the detached eddy simulation（DES） method. A sliding mesh（SM） approach is adopted to solve the rotation of the impeller. The simulated flow patterns and liquid velocities in the agitated tank are verified by experimental data in the literature. The simulation results indicate that the DES method can obtain more flow details than Reynolds-averaged Navier-Stokes（RANS） model. Local and global mixing time in the agitated tank is predicted by solving a tracer concentration scalar transport equation. The simulated results show that feeding points have great influence on mixing process and mixing time. mixing efficiency is the highest for the feeding point at location of midway of the two impellers. Two methods are used to determine global mixing time and get close result. Dimensionless global mixing time remains unchanged with increasing of impeller speed. Parallel, merging and diverging flow pattern form in the agitated tank, respectively, by changing the impeller spacing and clearance of lower impeller from the bottom of the tank. The global mixing time is the shortest for the merging flow, followed by diverging flow, and the longest for parallel flow. The research presents helpful references for design, optimization and scale-up of agitated tanks with multi-impeller.

关键词： agitated tank mixing time computational fluid dynamics(CFD) detached eddy simulation(DES) numerical simulation

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

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Chinese Journal of Chemical Engineering 2024年第1期65卷 63-74页

作者： Yuan Yao Peiqiao Liu Qian Zhang Zequan Li Benjun Xi Changyuan Tao Yundong Wang Zuohua Liu School of Chemistry and Chemical Engineering Chongqing UniversityChongqing 400044China Hubei Three Gorges Laboratory Yichang 443007China Department of Chemical Engineering Tsinghua UniversityBeijing 100084China

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.

关键词： mixing time CFD Stirred tank Secondary flow mixing performance

Large Eddy Simulations of mixing time in a Stirred Tank

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Chinese Journal of Chemical Engineering 2006年第1期14卷 1-7页

作者：闵健高正明 College of Chemical Engineering Beijing University of Chemical Technology Beijing 100029 China

Large eddy simulations (LES) of mixing process in a stirred tank of 0.476m diameter with a 3-narrow blade hydrofoil CBY impeller were reported. The turbulent flow field and mixing time were calculated using LES with Sma-gorinsky-Lilly subgrid scale model. The impeller rotation was modeled using the sliding mesh technique. Better agree-ment of power demand and mixing time was obtained between the experimental and the LES prediction than that by the traditional Reynolds-averaged Navier-Stokes (RANS) approach. The curve of tracer response predicted by LES was in good agreement with the experimental. The results show that LES is a reliable tool to investigate the unsteady and quasi-periodic behavior of the turbulent flow in stirred tanks.

关键词： large eddy simulations subgrid scale model mixing time hydrofoil impeller

3D numerical investigation of effects of density and surface tension on mixing time in bottom-blown gas-stirred ladles

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Transactions of Nonferrous Metals Society of China 2021年第10期31卷 3177-3191页

作者： Matin GHADIMI REZAEI Pooyan HASHEMI TARI Mohammad EMAMZADEH Leili TAFAGHODI KHAJAVI Mechanical Engineering Department Shahid Beheshti UniversityTehran16589-53571Iran Material Science and Engineering Department McMaster UniversityHamilton L8S 4L7Canada

In molten phase metallurgical processes,mixing via gas injection has a vital role in obtaining a homogeneous *** efficiency of mixing depends on operational variables such as gas flow rate and slag height as well as physical properties of the molten phases.A numerical simulation is conducted to study the above parameters in the flow behavior of a bottom-blown *** molten metal and the slag are modeled by water and oil,*** numerical results,particularly the mixing time,are validated against experimental *** results show that mixing time increases as the slag height increases and decreases as the density of the slag material *** mixing time decreases with an increase in the density of the primary phase;however,it increases as the surface tension between air and water increases.A case with properties close to a real molten metal is also *** performance of the system is influenced by the momentum rather than the dissipative ***,the effect of the density of the molten phase on the mixing process is more pronounced compared to the effect of the surface tension between the air and the molten phase.

关键词： gas-stirred ladle mixing time density surface tension tracer concentration numerical simulation

Numerical simulation of flow characteristics of side-bottom combined blowing in iron bath reactor

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Journal of Iron and Steel Research International 2023年第2期30卷 236-248页

作者： Yi-bo He Wen-ke Guo Yi-hong Li Guang-ming Liu Xin Cui School of Materials Science and Engineering Taiyuan University of Science and TechnologyTaiyuan030024ShanxiChina

A numerical model of an iron bath smelting reduction furnace with side-bottom combined blowing was established to study the influence of blowing arrangements on the stirring effect of the molten pool,and the accuracy of numerical simulation was verified by water model *** comparing the flow field of molten pool with single nozzle,double nozzles(symmetrical and asymmetrical),and four nozzles(symmetrical and asymmetrical),the proportion of dead zone,average turbulent kinetic energy,and mixing time,the results show that asymmetrical bottom blowing is better than symmetrical bottom blowing,and the effect of double nozzles bottom blowing was better than that of four nozzles bottom *** mixing effect is the worst under the condition of single *** the bottom blowing is asymmetrical with double nozzles,the mixing time is the *** the condition of double nozzles asymmetrical bottom blowing,when the insertion angle and depth of side lance are larger and deeper,the velocity streamline of molten slag layer is denser and the value is larger;meanwhile,the reflux of molten iron layer is larger,the proportion of dead zone is smaller,and the whole molten pool is fully *** the insertion depth of the side lance is deeper,the gas holdup in the molten pool is greater and the stirring of the molten pool is more intense,while the insertion angle has little effect on the gas *** comparing the influence of different side blowing conditions on the slag layer,it is found that the slag layer is divided into two layers by double-layer side lance,with the critical surface of the slag layer at about 200-260 mm from the bottom,and the insertion depth of the lower side lance has a greater influence on the layering of the slag.

关键词： Iron bath smelting reduction Side-bottom combined blowing Numerical simulation mixing time Slag layering

Impingement and mixing dynamics of micro-droplets on a solid surface

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Chinese Journal of Chemical Engineering 2022年第12期52卷 66-77页

作者： Guina Yi Ziqi Cai Zhengming Gao J.J.Derksen Beijing Advanced Innovation Center for Soft Matter Science and Engineering Beijing University of Chemical TechnologyBeijing 100029China State Key Laboratory of Chemical Resource Engineering School of Chemical EngineeringBeijing University of Chemical TechnologyBeijing 100029China School of Engineering University of AberdeenAberdeen AB243UEUK

The hydrodynamics and mixing during the nonaxisymmetry impingement of a micro-droplet and a sessile droplet of the same fluid are investigated by many-body dissipative particle dynamics(MDPD) *** this work,the range of the impingement angle(θ_(i)) between the impinging droplet and the sessile droplet is 0°-60° and the contact angle is set as 45° or 124°.The droplets impingement and mixing behavior is analyzed based on the droplet internal flow field,the concentration distribution and the time scale of the decay of the kinetic energy of the impinging *** dimensionless total mixing time(τ_(m)) is calculated by a modified mixing *** the Weber number(We) ranging from 5.65 to22.7 and the Ohnesorge number(Oh) ranging from 0.136 to 0.214,we find rm hardly changes with We and ***,θ_(i)and surface wettability are found to have a significant effect on τ_(m).We find that θ_(i)has no clear effect on τ_(m)on a hydrophobic surface,while on the hydrophilic surface,τ_(m)increase with the θ_(i).Thus,reducing the impinging angle is a valid method to shorten the τ_(m).

关键词： Droplets impingement mixing behavior mixing time Concentration distribution Many-body dissipative particle dynamics

Characterization on the hydrodynamics of a covering-plate Rushton impeller

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Chinese Journal of Chemical Engineering 2018年第6期26卷 1392-1400页

作者： Tenglong Su Fengling Yang Meiting Li Kanghui Wu School of Mechanical Engineering Shandong University Key Laboratory of High Efficiency and Clean Mechanical Manufacture(Shandong University) Ministry of EducationShandong University

A modified Rushton impeller with two circular covering-plates mounted on the upper and lower sides of the blades was *** are gaps between the plates and the *** turbulent hydrodynamics was analyzed by the computational fluid dynamics(CFD) ***,the reliability of the numerical model and simulation method was verified by comparing with the experimental results from ***,the power consumption,flow pattern,mean velocity and mixing time of the covering-plate Rushton impeller(RT-C) were studied and compared with the standard Rushton impeller(RT) operated under the same *** show that the power consumption can be decreased about 18%.Compared with the almost unchanged flow field in the lower stirred tank,the mean velocity was increased at the upper half of the stirred *** in the impeller region,the mean axial and radial velocities were increased,the mean tangential velocity was *** addition,the average mixing time of RT-C was shortened about 4.14% than the counterpart of *** conclusions obtained here indicated that RT-C has a more effective mixing performance and it can be used as an alternative of RT in the process industries.

关键词： Covering-plate Rushton impeller(RT-C) Power consumption Flow pattern Mean velocity mixing time Computational fluid dynamics(CFD)