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.     

无挡板搅拌槽中液－固体系的分散特性

在内径0.3 m、高0.45 m的无挡板搅拌槽内,采用直径0.15 m的三叶70o下推斜叶透平桨(PBTD, Pitched Blade Turbine Downflow)进行水-二氧化硅两相体系液固分散特性的研究. 应用PC-6A粉体浓度测量仪对体系中颗粒局部浓度进行测定. 考察了颗粒平均相含率为0.005的条件下,不同搅拌转速、搅拌桨离底高度对颗粒局部浓度分布的影响. 结果表明,采用较高搅拌转速、较低的搅拌桨离底高度有利于固体颗粒的悬浮. 本实验中,在搅拌转速为173 r/min、搅拌桨离底高度为0.08 m的操作条件下,颗粒悬浮效果最好.     

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.     

改进型三斜叶-Rushton组合桨槽内流场特性研究

为将改进型三斜叶-Rushton组合桨高效应用于实际工程,通过计算流体动力学(CFD)对装配改进型三斜叶-Rushton组合桨搅拌槽内的流场进行了模拟研究,与三斜叶-Rushton组合桨进行了对比;并通过粒子图像测速(PIV)技术研究该组合桨槽内搅拌转速n、桨叶间距C2及离底距离C1的变化对流场产生的影响。结果表明当转速为100r×min~(-1)时能有效改善槽底和上桨叶区域的混合效果,槽内速度分布相对均匀,实验结果和模拟结果吻合效果较好;模拟结果表明改进型三斜叶桨的泵吸效果较三斜叶桨更强,能有效缩小搅拌槽底部和内壁附近的低速区域,槽内混合效果更好;实验结果表明当桨叶间距为0.25h时,槽内速度分布更合理;当离底距离为0.3h时,上桨叶区的较低速区域进一步缩小。     

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...     

搅拌槽中固液悬浮及其放大的研究

研究了具有盘管、碟形底和斜叶涡轮固液悬浮搅拌槽的放大规律。试验用槽径（外径）分别为０．２ｍ、０．５ｍ和１．０ｍ的三个有机玻璃搅拌槽。用激光法测定悬浮液浓度。得出离底悬浮及均匀悬浮时搅拌转速和比功率的经验关联式，与测定槽内轴向速度分布所导出的均匀悬浮方程相吻合，并表明槽径的放大指数主要由循环流数所决定。     

搅拌槽内桨叶安装高度的数值模拟

采用CFD软件对搅拌槽内的气、液、固三相流动状态进行了数值模拟,桨型采用的是六直叶圆盘涡轮桨,具体从桨叶安装高度进行细致的数值分析,得出能够获得槽内良好固液悬浮性能下的最优化结构,并和标准搅拌槽进行对比,本研究为工业中搅拌槽的结构优化和放大提供了理论基础。     

三轴搅拌釜不同桨径比下固-液悬浮特性的数值模拟

利用FLUENT软件对不同桨径比下立式三轴搅拌釜内单相和固-液两相混合过程分别进行三维数值模拟,对流场分析可知增大桨径比能改善立式三轴搅拌釜内流场的结构。利用修正速度判据得出不同桨径比下搅拌釜的临界悬浮转速,并通过计算临界悬浮转速下的搅拌功率,初步得出立式三轴搅拌釜桨径比的最佳取值范围在0.1～0.125之间。     

不同桨型组合淤浆聚合釜内固液悬浮特性研究

针对高密度聚乙烯搅拌式聚合釜物料体系,利用三叶后掠式搅拌桨HQ、抛物线圆盘涡轮式搅拌桨BTD、三宽叶旋桨式搅拌桨KHX、桨叶安放角δ分别为45°和75°的斜叶圆盘涡轮式搅拌桨ZY和平直叶圆盘涡轮式搅拌桨PY构成四种桨型组合,在直径T=480 mm的圆柱形有机玻璃搅拌槽内进行了固液悬浮实验。基于计算流体力学软件Ansys Fluent 2020R2,采用多重参考系法以及欧拉-欧拉多相流模型,研究了各桨型组合在30.71%固含率下的流场和固液悬浮状态。研究结果表明,转速小于250 r/min时,桨型组合2和3在搅拌槽内顶部会形成清液层;桨型组合1和4能在更低转速和更低功率的情况下达到物料的均匀混合状态,且桨型组合4比桨型组合1的功率消耗降低约30%,具有高效节能的效果。模拟获得的固含率分布趋势与实验所测数值吻合较好。模拟的流场表明桨型组合4和1的流型相似,可以有效避免桨型组合2和3在低转速下出现的清液层。     

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。     

具有双层桨结构的自吸式搅拌反应器的流体力学性能

在直径0.48 m的搅拌槽中以水?空气为介质,对具有双层桨结构的自吸式反应器的流体力学性能进行了实验研究,考察了自吸式桨浸没深度、底层桨结构和搅拌桨层间距对自吸式桨的临界吸气转速、吸气速率和气含率的影响。结果表明,临界吸气转速随自吸式桨浸没深度增加而增加,临界吸气转速几乎与下层桨的结构无关;吸气速率与气含率随浸没深度增加而减小,吸气速率与气含率受下层桨影响较大,层间距为自吸式桨直径(D)且采用上推式的四叶宽叶翼形轴流式桨作下层桨时,自吸式桨的吸气性能最佳。     

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 solid suspension behavior, i.e. smaller particles with lower density are more likely to be suspended evenly in the liquid with higher liquid viscosity. At a low impeller rotating speed (N), increase in N leads to an obvious improvement in the solid distribution homogeneity. Moreover, the proposed LSB impeller has obvious advantages in the uniform distribution of the solid particles compared with single Rushton turbine (RT), dual RT impellers or CBY hydrofoil impeller under the same power consumption.     

Numerical optimization for blades of Intermig impeller in solid–liquid stirred tank

The multiphase flow in the solid-liquid tank stirred with a new structure of Intermig impeller was analyzed by computational fluid dynamics(CFD).The Eulerian multiphase model and standard k-ε turbulence model were adopted to simulate the fluid flow,turbulent kinetic energy distribution,mixing performance and power consumption in a stirred tank.The simulation results were also verified by the water model experiments,and good agreement was achieved.The solid-liquid mixing performances of Intermig impeller with different blade structures were compared in detail.The results show that the improved Intermig impeller not only enhances the solid mixing and suspension,but also saves more than 20% power compared with the standard one.The inner blades have relatively little influence on power and the best angle of inner blades is 45°,while the outer blades affect greatly the power consumption and the optimized value is 45°.     

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

The critical impeller speed, NJS, for complete suspension of solid particles in the agitated solid-liquid two-phase system in baffled stirred tanks with a standard Rushton impeller is predicted using the computational procedure proposed in Part I. Three different numerical criteria are tested for determining the critical solid suspension. The predicted NJS is compared with those obtained from several empirical correlations. It is suggested the most reasonable criterion for determining the complete suspension of solid particles is the positive sign of simulated axial velocity of solid phase at the location where the solid particles are most difficult to be suspended.     

搅拌槽内液-固两相体系的数值研究(Ⅱ)临界搅拌转速的预测

The critical impeller speed, NJS, for complete suspension of solid particles in the agitated solid-liquid two-phase system in baffled stirred tanks with a standard Rushton impeller is predicted using the computational procedure proposed in Part Ⅰ. Three different numerical criteria are tested for determining the critical solid suspension. The predicted NJS is compared with those obtained from several empirical correlations. It is suggested the most reasonable criterion for determining the complete suspension of solid particles is the positive sign of simulated axial velocity of solid phase at the location where the solid particles are most difficult to be suspended.     

立式圆槽内多轴搅拌器固-液悬浮性能

在直径(T)为2 m、高(H)为0.8 m的圆形搅拌槽内,采用三桨搅拌,桨型为CBY III(桨径D=0.174 m),3个桨在槽内均匀分布,通过对临界悬浮叶端线速度、沉积面积的分析,研究了搅拌桨槽内最优安装位置. 结果表明,最优径向安装位置为距壁面0.285R(R为圆形搅拌槽半径,m)处;液位为0.3T时的搅拌效果优于0.2T和0.25T;但液位在一定(0.2T~0.3T)范围内对功率的影响微小. 对比分析实验结果与文献数据可知,达到相同完全悬浮状态,立式多轴搅拌的功率消耗为单轴情况下(D=0.731 m)的2.8倍,但立式多轴搅拌器的制造成本更低;与侧伸式搅拌相比,5%沉积面积时立式多轴搅拌节省20%能耗,且安装维护更简便,在大型储罐中具有广泛的工业应用前景.