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Effects of rotational speed and fill level on particle mixing in a stirred tank with different impellers

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Chinese Journal of Chemical Engineering 2018年第6期26卷 1383-1391页

作者： yuyun bao Yu Lu Ziqi Cai Zhengming Gao State Key Laboratory of Chemical Resource Engineering School of Chemical EngineeringBeijing University of Chemical Technology

The particle mixing was studied in a cylindrical stirred tank with elliptical dished bottom by experiments and *** impeller types used were double helical ribbon(HR) + bottom HR,pitched blade ribbon + bottom HR,inner and outer HR + bottom HR,and pitched blade ribbon + Pfaudler + bottom HR labeled as impellers Ⅰ to Ⅳ,*** quantitative correlations among the rotational speed,fill level and power consumption for impeller Ⅰ and impeller Ⅱ were obtained by experiments to validate the discrete element method(DEM) *** particle mixing at different operating conditions was simulated via DEM simulations to calculate the mixing index using the Lacey method,which is a statistical method to provide a mathematical understanding of the mixing state in a binary *** simulation results reveal that as the rotational speed increases,the final mixing index increases,and as the fill level increases,the final mixing index *** the same operating conditions,impeller Ⅲ is the optimal combination,which provides the highest mixing index at the same revolutions.

关键词： Particle Mixing Discrete element method(DEM) Rotational speed Fill level Lacey index

Discrete element method study of effects of the impeller configuration and operating conditions on particle mixing in a cylindrical mixer

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Particuology 2020年第2期18卷 146-158页

作者： yuyun bao Tianchi Li Dengfei Wang Ziqi Cai Zhengming Gao State Key Laboratory of Chemical Resource Engineering School of Chemical EngineeringBeijing University of Chemical TechnologyBeijing 100029China Daqing Petrochemical Research Center Petrochemical Research InstituteChina National Petroleum CorporationDaqing 163714Heilongjiang ProvinceChina

We employed the discrete element method to study the effects of the impeller configuration(i.e.,blade diameter,inclination angle,and blade number),rotational speed,and fill level on the flow and mixing of particles in a cylindrical mixer equipped with flat and inclined *** coefficient of rolling friction,coefficient of static friction,and coefficient of restitution were experimentally determined before the simulation,and simulation results of the torque and surface particle distribution were validated in experiments,particularly when using a true Young's modulus in the discrete element *** performance of the mixer was assessed using the Lacey mixing *** input work per unit volume was used to represent the mixing *** circumferential velocity and axial diffusion coefficient of the particles were quantitatively analyzed to reveal the effect of particle flow on the *** was found that the mixing performance and efficiency of a three-blade mixer are better than those of two-and four-blade *** pitched blades,a three-fiat-blade mixer has better mixing performance than a three-45°-blade own-pumping or a three-45°-blade up-pumping mixer,but the mixing efficiency of the three-45°-blade up-pumping mixer is the best among these three *** the rotational speed increases,the mixing performance improves but the mixing efficiency hardly *** the fill level is 0.4 times the cylinder diameter,the 160D two-flat-blade mixer has good mixing performance with high mixing *** circumferential velocity has the greatest effect on mixing performance for side-by-side initial loading.

关键词： Cylindrical mixer Impeller configuration Discrete element method Particle Mixing behavior

Gas dispersion and solid suspension in a three-phase stirred tank with triple impellers

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Chinese Journal of Chemical Engineering 2020年第5期28卷 1195-1202页

作者： Hanbin Wang Zhengming Gao Bingjie Wang yuyun bao Ziqi Cai State Key Laboratory of Chemical Resource Engineering Beijing University of Chemical TechnologyBeijing 100029China

The hydrodynamics is still not fully understood in the three-phase stirred tank equipped with multi-impeller due to the intensive interaction between *** this work,the solid critical suspension speed(NJSG),relative power demand(RPD)and overall gas holdup(ε_G)were measured in an air–water–glass beads stirred tank equipped with multi-impeller,which consists of a parabolic blade disk turbine below two down-pumping *** show that either the NJSGor the specific power consumption increases when increasing the volumetric solid concentration or superficial gas *** changes less than 10%when solid volumetric concentration ranges from 0 to 15%.ε_G decreases with the increase of solid concentration,and increases with the increase of both superficial gas velocity and the total specific power *** quantitative correlations of NJSG,RPD andεGwere regressed as the function of superficial gas velocity,specific power consumption,Froude number and gas flow number,in order to provide the reference in the design of such three-phase stirred tank with similar multi-impellers.

关键词： Solid suspension Gas holdup Gas-liquid-solid system Stirred reactor

A review on single bubble gas–liquid mass transfer

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Chinese Journal of Chemical Engineering 2020年第11期28卷 2707-2722页

作者： yuyun bao Jinting Jia Shuaifei Tong Zhengming Gao Ziqi Cai State Key Laboratory of Chemical Resource Engineering Beijing University of Chemical TechnologyBeijing 100029China

It is common to empirically correlate volumetric mass transfer coefficient kLa for predicting gas–liquid mass transfer in industrial applications,and the investigation of single bubble mass transfer is crucial for a detailed understanding of mass transfer *** this work,experiments,models and simulations based on the experimental results were highlighted to elucidate the mass transfer between single bubbles and ambient *** experimental setups,measurement methods,the mass transfer of single bubbles in the Newtonian and the nonNewtonian liquid,models derived from the concept of eddy diffusion,the extension of Whitman’s,Higbie’s and Danckwerts’models,or dimensionless numbers,and simulation methods on turbulence,gas–liquid partition methods and mass transfer source term determination are introduced and commented *** people have a great knowledge on mass transfer between single bubbles and ambient liquid in single conditions,it is still insufficient when facing complex liquid conditions or some phenomena such as turbulence,contamination or non-Newtonian *** studies on single bubbles are required for experiments and models in various liquid conditions in future.

关键词： Gas-liguid mass transfer Single bubbles Mass transfer models Simulation Surfactant Non-Newtonian fluid

Mass transfer in gas–liquid stirred reactor with various triple-impeller combinations

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Chinese Journal of Chemical Engineering 2016年第6期24卷 703-710页

作者： Jinjin Zhang Zhengming Gao Yating Cai Ziqi Cai Jie Yang yuyun bao State Key Laboratory of Chemical Resource Engineering School of Chemical Engineering Beijing University of Chemical Technology Beijing 100029 China School of Chemical Engineering Shandong University of Technology Zibo 255000 China

The gassed power demand and volumetric mass transfer coefficient （kca） were investigated in a fully baffled, dished-base stirred vessel with a diameter of 0.30 m agitated by five triple-impeller combinations. Six types of impellers （six-half-elliptical-blade disk turbine （HEDT）, four-wide-blade hydrofoil impeller （WH） pumping down （D） and pumping up （U）, parabolic-blade disk turbine （PDT）, and CBY narrow blade （N） and wide blade （W）） were used to form five combinations identified by PDT ＋ 2CBYN, PDT ＋ 2CBYw, PDT ＋ 2WHD, HEDT ＋ 2WHD and HEDT ＋ 2WHo, respectively. The results show that the relative power demand of HEDT ＋ 2WHu is higher than that of other four impeller combinations under all operating conditions. At low superficial gas velocity （uc）, kLa differences among impeller combinations are not obvious. However when UG iS high, PDT ＋ 2WHD shows the best mass transfer performance and HEDT ＋ 2WHu shows the worst mass trans- fer performance under all operating conditions. At high uc and a given power input, the impeller combinations with high agitation speed and big projection cross-sectional area lead to relatively high values of kLa. Based on the experimental data, the regressed correlations of gassed power number with Froude number and gas flow number, and kLa with power consumption and superficial gas velocity are obtained for five different impeller combinations, which could be used as guidance for industrial design.

关键词： Stirred vesselGassed powerMass transferTriple-impeller combinationGas-liquid system

Torque and bending moment acting on a flexible shaft agitated by disk turbines in a gas–liquid stirred vessel

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Chinese Journal of Chemical Engineering 2019年第4期27卷 781-793页

作者： Yangyang Liang Zhengming Gao Dai'en Shi Haotian Li yuyun bao Ziqi Cai State Key Laboratory of Chemical Resource Engineering Beijing University of Chemical Technology Beijing 100029 China Mechanical Engineering School Yancheng Institute of Technology Yancheng 224051 China

The torque and bending moment acting on a flexible overhung shaft in a gas–liquid stirred vessel agitated by a Rushton turbine and three different curved-blade disk turbines(half circular blades disk turbine, half elliptical blades disk turbine, and parabolic blades disk turbine) were experimentally measured by a customized moment sensor. The results show that the amplitude distribution of torque can be fitted by a symmetric bimodal distribution for disk turbines, and generally the distribution is more dispersive as the blade curvature or the gas flow rate increases. The amplitude distribution of shaft bending moment can be fitted by an asymmetric Weibull distribution for disk turbines. The relative shaft bending moment manifests a "rising-falling-rising" trend over the gas flow number, which is a corporate contribution of the unstable gas–liquid flow around the impeller, the gas cavities behind the blades, and the direct impact of gas on the impeller. And the "falling" stage is greater and lasts wider over the gas flow number for Rushton turbine than for the curved-blade disk turbines.

关键词： Shaft bending moment Torque Disk turbines Gas–liquid flow Fluid structure interaction

Hydrodynamic Behavior of a Single Bubble Rising in Viscous Liquids

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Chinese Journal of Chemical Engineering 2010年第6期18卷 923-930页

作者： CAI Ziqi bao yuyun GAO Zhengming State Key Laboratory of Chemical Resource Engineering School of Chemical Engineering Beijing University ofChemical Technology Beijing 100029 China

The rising behavior of single bubbles has been investigated in six systems with different viscosity and Morton number(Mo) from 3.21×10-11 to 163. Bubbles with maximum equivalent diameter of up to 16 mm were investigated. The bubble Reynolds number(Re) ranged from 0.02 to 1200 covering 3 regimes in which two func-tions are obtained relating the drag coefficient,CD,with Re and Mo. It has been found that in the high Reynolds number regime the drag coefficient increases until the Reynolds number of about 1200. The classic expression of Jamialahmadi(1994) is improved and extended to high viscosity liquids. A new relationship for the aspect ratio of deformed bubbles in terms of Re,the Etvs number and Mo,applicable to a wide range of system properties,espe-cially in high viscosity liquids,is also suggested.

关键词： bubble rising velocity viscous liquid drag coefficient deformation

Effects of the Blade Shape on the Trailing Vortices in Liquid Flow Generated by Disc Turbines

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Chinese Journal of Chemical Engineering 2011年第2期19卷 232-242页

作者：赵静高正明包雨云 State Key Laboratory of Chemical Resource Engineering Beijing University of Chemical Technology Beijing 100029 China

Particle image velocimetry technique was used to analyze the trailing vortices and elucidate their rela-tionship with turbulence properties in a stirred tank of 0.48 m diameter,agitated by four different disc turbines,in-cluding Rushton turbine,concaved blade disk turbine,half elliptical blade disk turbine,and parabolic blade disk ***-averaged and phase-resolved flow fields near the impeller blades were measured and the structure of trailing vortices was studied in *** location,size and strength of vortices were determined by the simplified λ2-criterion and the results showed that the blade shape had great effect on the trailing vortex *** larger curvature resulted in longer residence time of the vortex at the impeller tip,bigger distance between the upper and lower vortices and longer vortex life,also leads to smaller and stronger *** addition,the turbulent ki-netic energy and turbulent energy dissipation in the discharge flow were determined and *** turbulent kinetic energy and turbulent energy dissipation regions were located between the upper and lower vortices and moved along with *** restricted to single phase flow,the presented results are essential for reliable de-sign and scale-up of stirred tank with disc turbines.

关键词： trailing vortices disc turbine particle image velocimetry blade shape

Void Fraction Distributions in Cold-gassed and Hot-sparged Three Phase Stirred Tanks with Multi-impeller

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Chinese Journal of Chemical Engineering 2009年第6期17卷 887-895页

作者：陈雷包雨云高正明 School of Chemical Engineering Beijing University of Chemical Technology Beijing 100029 China

Vertical distributions of void fraction in gas-liquid and gas-liquid-solid stirred tanks have been measured in a fully baffled dished base vessel of 0.48 m diameter, using a conductivity probe. The impeller configuration （a hollow half elliptical blade dispersing turbine below two up-pumping wide blade hydrofoils, identified as HEDT＋2WHu） recommended in previous work has been used in this work. The operating temperatures were 24℃ and 81℃, identified as cold and hot respectively. The effects of superficial gas velocity, agitator speed and the corresponding power input on the local void fraction in two-phase systems are .investigated and discussed. Results show thatth-e increasing of agitator speed or gas flow rate leads to an increase in local-void fraction at the majority of measurement points in both cold and hot systems. However, the unifo,rmity of gas dispersion does not always in crease as the raising of agitator speed and power input. In either cold or hot sparged conditions, the two- and three-phase *** similar vertical profiles for void fraction, with maxima in similar locations; however, the void fractions are significantly lower in hot sparging than with cold. In cold operation the presence of particles leads to a lower void fraction at most points, although the local void fractions increase a little with the addition of solid particles at high temperature, in good agreement with the global gas holdup results, and the possible reasons are discussed in this paper. This work can give a better understanding of the differences between cold-gassed and hot-sparged three phase＇stirred tanks.

关键词： void fraction conductivity probe hot sparged reactor dispersed gas distribution multi-impeller