高固含搅拌槽内临界离底悬浮转速的数值模拟

使用计算流体软件CFX5.5.1对固液搅拌槽内颗粒的临界离底悬浮转速进行了数值模拟. 搅拌槽直径D=0.476 m,搅拌桨为三叶CBY螺旋桨. 桨叶安装高度h=D/3. 固液两相为玻璃珠-水,固体体积浓度为15%~50%. 对临界离底悬浮的速度判据进行了修正,并利用浓度判据与修正的速度判据得到颗粒临界离底悬浮转速Njs,模拟计算结果与实验数据的误差在工业允许的范围内. 同时,对临界离底悬浮状态槽底部不同浓度下的流体湍流动能的分布情况以及大小进行了预测,并对2种固体临界离底悬浮机理进行了验证.     

改进型INTER-MIG搅拌槽内固液悬浮特性的数值模拟

应用CFD软件Fluent 12.0和并行计算机工作站对双层改进型INTER-MIG桨式搅拌槽内的固液悬浮特性、临界离底悬浮转速及功率消耗进行数值模拟,分析了在固体体积分数as=30%下,转速n、桨叶离底距离C1和桨间距C2等因素对搅拌槽内颗粒悬浮特性的影响. 结果表明,在一定的转速和桨径下,改变C1和C2会改变流场的局部结构,选取适合的C1和C2可使固液混合更均匀,有利于颗粒悬浮和整个搅拌槽传质传热的进行. 最佳桨叶离底高度与槽径比为0.36,最佳桨叶间距与槽径比为0.44;在该最佳工况下临界离底悬浮转速Njs=118.3 r/min;得到既能达到完全离底悬浮、又能使搅拌功耗最小的最佳转速为n=124 r/min.     

聚丙烯N催化剂合成体系搅拌优化

通过冷模模拟搅拌研究,对聚丙烯N催化剂合成体系的搅拌形式进行优化。研究表明,采用双层d/D=0.5的45°四叶斜桨,下层桨离底高度为h/D=0.18,二桨的桨间距s/d=1时,体系的临界搅拌转速nc为最小,二层桨之间不良影响较小,适合固体在体系中的悬浮。催化剂合成热模实验表明,采用以上的搅拌形式,在一定的搅拌转速范围内,可以较好地控制催化剂的颗粒形态。     

种分槽改进Intermig桨搅拌性能的实验研究

为了研究改进的Intermig桨的搅拌性能,在无挡板的氧化铝种分搅拌槽内,采用PC6D颗粒浓度测量仪对水-玻璃珠液-固体系在不同条件下的颗粒轴向和径向局部浓度进行了测量与分析.结果表明,较高的搅拌转速和体系粘度更有利于固体颗粒的悬浮.粘度μ=3.50×10-3Pa·s、转速n=172 r/min时,实验浓度平均值是理论...     

不通气的沸腾汽-液-固三相搅拌槽中的汽液分散和固体悬浮

在直径为0.476 m的椭圆底搅拌槽中,采用直径为0.238 m的单层六叶深凹叶盘式涡轮桨(HEDT),在液位为0.5 m的全挡板条件下研究了沸腾状态下,蒸汽、去离子水和玻璃珠组成的汽-液-固体系中搅拌功率、气含率及固体颗粒完全离底悬浮特性,并与常温通空气三相体系进行对比.研究结果表明,沸腾条件下的流体动力学性能与常温通气体系相比存在较大差异.在沸腾条件下,搅拌功率消耗随着搅拌转速的增加有所下降,但HEDT桨具有较高的载气能力,即使在高叶端线速度下,相对功率消耗(RPD)仍能保持在较高的水平;沸腾体系的气含率随单位质量流体输入功率的增加表现出先增后减的规律,即存在气含率的极大值,蒸汽成核位置和固体颗粒悬浮特性随搅拌功率增加而改变是造成上述行为的主要原因;沸腾体系中的气含率远远低于常温通空气体系.临界悬浮搅拌转速(NJSG)随固相体积分率的增加略有增加;沸腾体系中蒸汽量的变化对NJSG影响远小于常温通气体系.研究结果对于工业沸腾态三相搅拌反应器的设计和操作具有一定的参考价值.     

磷酸陈化槽内桨叶高度对颗粒悬浮特性影响的数值模拟

以磷酸陈化槽为研究对象,使用计算流体力学软件FLUENT对陈化槽内的磷石膏固体颗粒的悬浮特性进行了数值模拟,模拟结果表明在高搅拌转速条件下,过大或过小的桨叶离底高度都不利于颗粒悬浮,搅拌功率随着桨叶的离底距离先增大,然后趋于稳定,但是离底距离对搅拌功率的影响较小,可以忽略不计,结合搅拌槽内固相的浓度分布情况,得出相对最好的桨叶离底距离为陈化槽直径的0.33倍。     

改进Intermig桨种分槽搅拌性能的数值模拟

利用商业CFD软件Fluent 12.0和并行计算系统图形工作站,对改进的Intermig桨种分槽内部流场进行了三维数值解析.采用Realizable κ-ω流模型和欧拉-欧拉多相流模型对槽内不同桨叶离底距离C、桨叶直径D下的氢氧化铝颗粒悬浮规律以及搅拌桨功率消耗进行了模拟.结果显示,搅拌转速一定的条件下,桨叶直径越大...     

侧伸式搅拌槽固液悬浮性能

采用f2 m′4.2 m侧伸式搅拌槽,研究了搅拌桨安装位置、通气速率、固体颗粒浓度和液位高度对侧伸式搅拌槽颗粒悬浮性能的影响. 结果表明,搅拌轴水平偏转角对功率准数的影响很小,均布式为侧伸式搅拌槽搅拌桨的最佳排布方式,最佳偏转角bopt=10o;临界转速NJS最小值出现在搅拌桨伸入长度/搅拌桨直径比L/d=1.44处;降低搅拌桨安装高度h为0.75d左右,相比于传统的h=1.5d可减少约30%能耗;液位高度/搅拌槽直径比H/T<0.5时,NJS随H的升高而迅速增大. 得到了通气量QV与NJS的关系式NJSG-NJS=1.46QV1.15和固相浓度w对NJS影响的关系式NJSμw0.27.     

刚柔组合桨强化粉煤灰酸浸搅拌槽内固液混沌混合

传统粉煤灰提铝工艺中酸浸搅拌槽均采用刚性搅拌桨。因刚性桨卷吸能力有限,导致固体颗粒易沉槽、流体混沌混合效率低。提出刚柔组合桨强化酸浸搅拌槽中固液混沌混合行为。实验基于固含率为30%的粉煤灰-自来水体系,研究了刚柔组合酸浸搅拌槽内混沌混合特性及能量耗散规律。采用扭矩传感器采集扭矩时间序列信号,借助Matlab软件编译计算混合过程中最大Lyapunov指数和多尺度熵等混沌特性参数,以单位体积功耗表征搅拌反应器的功率特性。实验考察了搅拌桨安装离底高度、柔性片长度、柔性片宽度等因素对酸浸槽内粉煤灰混沌混合的影响,对比了刚性桨与刚柔组合桨体系的能耗差异。研究结果表明:刚柔组合桨通过柔性片的作用,能增大搅拌桨的卷吸力,进而减少固体颗粒沉槽现象,促进全槽混沌混合;在最优化条件(120 r/min,搅拌桨安装离底高度为T/4,柔性片长度为1.2H1、柔性片宽度为D/8)下,体系最大Lyapunov指数达到最大值0.0645,各尺度下的MSE均比其他条件更大,表明刚柔组合桨能够通过柔性片的多体运动,强化体系混沌混合,均化体系能量分布;刚性桨与刚柔组合桨的单位体积功耗随着转速的增加呈现指数规律增长。     

刚柔组合桨强化粉煤灰酸浸搅拌槽内固液混沌混合

传统粉煤灰提铝工艺中酸浸搅拌槽均采用刚性搅拌桨。因刚性桨卷吸能力有限，导致固体颗粒易沉槽、流体混沌混合效率低。提出刚柔组合桨强化酸浸搅拌槽中固液混沌混合行为。实验基于固含率为30%的粉煤灰-自来水体系，研究了刚柔组合酸浸搅拌槽内混沌混合特性及能量耗散规律。采用扭矩传感器采集扭矩时间序列信号，借助Matlab软件编译计算混合过程中最大Lyapunov指数和多尺度熵等混沌特性参数，以单位体积功耗表征搅拌反应器的功率特性。实验考察了搅拌桨安装离底高度、柔性片长度、柔性片宽度等因素对酸浸槽内粉煤灰混沌混合的影响，对比了刚性桨与刚柔组合桨体系的能耗差异。研究结果表明：刚柔组合桨通过柔性片的作用，能增大搅拌桨的卷吸力，进而减少固体颗粒沉槽现象，促进全槽混沌混合；在最优化条件（120 r/min，搅拌桨安装离底高度为T/4，柔性片长度为1.2H ₁、柔性片宽度为D/8）下，体系最大Lyapunov指数达到最大值0.0645，各尺度下的MSE均比其他条件更大，表明刚柔组合桨能够通过柔性片的多体运动，强化体系混沌混合，均化体系能量分布；刚性桨与刚柔组合桨的单位体积功耗随着转速的增加呈现指数规律增长。     

Design factors affecting the dynamic performance of soil suspension in an agitated,baffled tank

The effects of particle size, impeller clearance and impel er speed are assessed to show how condition variations influence power consumption in the water-solid slurry suspension in an agitated tank. The energy efficiency of slurry height variation, impel er type and diameter, and solid movement speed has been investigated with six soil series stirred in a soil-water slurry. Coarser sand particles are observed to significantly increase power consumption, while finer particles, for instance clay, decrease the stirring power requirement. The 3-blade HR100 SUPERMIX? impeller manufactured by SATAKE general y performs more efficiently than a conventional 4-pitched blade turbine. The impeller's geometric design, including diameter and number of blades influences the impeller's energy efficiency, and HR100 impellers with greater diameters remarkably reduce power consumption. The tests demonstrated that the power required to provide off-bottom solid suspension and solid dispersion can be reduced dramatically by increasing the slurry height rather than by accelerating the impel er, if this option is possible.     

固-液导流筒搅拌槽内流体流动和颗粒悬浮特性

在直径0.8 m的导流筒搅拌槽内,对单相液体的三维速度分布、固-液两相的固体颗粒浓度分布和离底悬浮特性进行了系统的实验研究. 结果表明,导流筒内外的轴向液相速度远大于径向和切向速度,导流筒外壁附近存在一个与主体轴向流动方向相反的二次流区域;搅拌槽底部结构对固体颗粒的临界离底悬浮转速(NJS)有显著的影响,浅锥底的NJS比平底的低14%以上;NJS随固相浓度的增加而增加,但当浓度超过50%时,NJS略有降低;槽内固相浓度分布的均匀性随固相浓度的增加而得到改善. 本研究结果对导流筒搅拌槽的优化设计具有一定的指导意义.     

Study on the solid–liquid suspension behavior in a tank stirred by the long-short blades impeller

We investigated the solid–liquid suspension characteristics in the tank with a liquid height/tank diameter ratio of 1.5 stirred by a novel long-short blades(LSB) impeller by the Euler granular flow model coupled with the standard k–ε turbulence model. After validation of the local solid holdup by experiments,numerical predictions have been successfully used to explain the influences of impeller rotating speed,particle density, particle size, liquid viscosity and initial solid loading on the soli...     

新型自吸式多相搅拌槽临界悬浮特性的实验研究

在不通气的情况下,对新型多相搅拌槽进行实验,得出了其固相含量w、颗粒密度r、搅拌槽内径D与临界悬浮转速Nc的关系,在相同条件下,与给定结构尺寸的标准搅拌槽对比了临界悬浮转速. 结果表明,Nc随固相分率j增加和粒径dp增大而增大,不利于达到良好的悬浮效果;固相颗粒密度越大,临界悬浮转速随之增大;槽径增大使达到悬浮状态的临界转速降低. 该新型搅拌槽临界悬浮转速的关联式是Nc=6.3dp0.21(gDr/rL)0.45w0.19/D0.55;同一固相分率下,新型多相搅拌槽的临界悬浮转速比标准搅拌槽降低了30%,在较低转速下就能使颗粒悬浮.     

NUMERICAL SIMULATION OF LAMINAR SOLID-LIQUID TWO-PHASE FLOW IN STIRRED TANKS

Laminar flow of solid-liquid suspension has been rarely reported in the literature. In this article, the laminar solid-liquid two-phase flow in a lab-scale stirred tank is measured with digital particle image velocimetry (DPIV) and numerically simulated with the improved inner-outer iterative method. The simulation results show good agreement with the present data. In the range of low solid volume concentration under investigation, solid particles have minor impact on two-phase flow, and the simulated flow fields of both phases are similar to the counterpart of single-phase laminar liquid flow. The comparison of simulation with experiments of single-phase laminar flow shows reasonable agreement. These observations suggest that the numerical method employed in the present study is reliable for analysis of stirred tanks. The influence of impeller off-bottom clearance on velocities is found significant: the lower the impeller, the smaller the radial and axial velocities, and the higher the solid concentration.     

CRITICAL IMPELLER SPEED FOR SOLID SUSPENSION IN MULTI-IMPELLER AGITATED CONTACTORS: SOLID-LIQUID SYSTEM

The critical impeller speed for suspension of solid particles (N_js) has been measured in multi-impeller mechanically agitated contactors of 0.15 and 0.30m id and 1.0 m height. Three types of impellers, i.e. disk turbine (DT), pitched turbine downflow(PTD) and pitched turbine upflow(PTU) were used. The number of impellers used in the 0.3 m and 0.15 m id reactors were three and four, respectively. The distance maintained between two impellers was equivalent lo the tank diameter. The effect of impeller type and diameter, particle size and loading, and clearance of the bottom impeller from the reactor bottom was studied and results compared with those of single impeller agitated contactors. PTD impeller was found to be more efficient for solid suspension. The N_js values obtained in reactors with multiple impeller are essentially the same as those observed in single impeller reactor and the bottom impeller plays dominant role in determining the N_js, values. An empirical correlation has been proposed for estimation of N_js and an attempt has been made to explain the mechanism of suspension in multi-impeller agitated reactor.     

板式螺旋桨搅拌槽内的流场及其流动特性

以板式螺旋桨叶轮为例,采用相位多普勒粒子分析仪测量了直径为300 mm的平底圆筒搅拌槽内的流场;分析了时均速度、脉动速度及湍流动能的分布,以及叶轮离底间隙变化和挡板对流场的影响。结果表明:随离底间隙增大,叶轮区脉动速度和湍流动能增大,时均速度和脉动速度最大值位置向槽中心方向移动;主循环区轴向速度最大值随离底间隙增大而减小;叶轮区湍流动能较高,随离底间隙增大,湍流动能最大值增大,位置靠近叶轮端部;挡板阻碍槽内切向流动,影响湍流动能的分布,挡板前流场反映了叶轮区的湍流动能分布。     

Impeller design for mixing of suspensions

This paper deals with effect of impeller type on off-bottom particle suspension. On the basis of numerous suspension measurements correlations are proposed for calculation just suspended impeller speed for eleven impeller types and geometries in the wide range of concentrations and particle diameters. The suspension efficiency of tested impellers has been compared by means of the power consumption required for off-bottom suspension of solid particles.