旋转盘式混合器混合过程数值模拟

基于旋转盘式混合器的研制实践,采用Polyflow软件在分析其速度和剪切速率分布的基础上,研究了物料粒子的动态混合过程;并从物料停留时间和最大剪切应力分布角度分析了旋转盘式混合器的分布和分散混合性能。结果表明,旋转盘式混合器可提供强大的剪切、置换和压缩作用,随着动盘旋转体转速增加,分散混合性能增强,不利于轴向分布混合。     

聚氨酯低压混合器内流场的数值模拟

利用计算流体力学软件Fluent,对聚氨酯无卤阻燃墙体保温材料生产线上低压混合器内流场进行三维数值模拟,分析了混合器内流体的速度场、温度场、压力场分布。计算结果表明,混合器内混合段流体速度出现明显波动,有利于物料的混合。物料黏度不变时,随着转速增大混合区域不断减小;转速不变时,随着物料黏度增大混合位置区域不断增大。通过对温度场、速度场的分析,表明搅拌混合效果良好。     

PA6/PE共混纺丝中圆盘静态混合器的应用研究

采用聚己内酰胺/聚乙烯(PA6/PE)熔体共混纺丝,对纺丝组件中装有不同套数的圆盘静态混合器的应用效果进行了研究。结果表明:纺丝组件中装了圆盘静态混合器,与原组件相比,其PA6,PE共混的分布均匀性及细化程度较好;静态混合圆盘的数量越多,共混物料的分布均匀性与细化程度越好;装有3套(6块)静态混合圆盘的应用效果较好,所得PA6/PE共混纤维横截面及纵向表面规整,没有孔洞,纺丝时无断头,卷绕成形良好。     

转子相对旋转方向对双转子混合器混合性能的影响

在双转子混合器内将聚丙烯/红色色母粒进行共混,并利用数字图像处理方法计算共混物中红色度分布的均匀性,用以表征混合器的混合性能。分析了不同转子相对旋转方向下混合器内示踪粒子运动轨迹和物料的速度场分布。从示踪粒子轨迹角度揭示了粒子在混炼腔内不同的运动形式;从速度场分布角度揭示了不同转子相对旋转方向下混合器的混炼机理。研究发现两转子同向旋转模式下,由速度场分布引起的持续沿混炼腔轮廓交换形""运动更有利于促进混合器左右两腔中物料的相互交换,提高混合器的混合性能。     

物料无桨混合过程数值模拟

目前物料混合主要采用有桨混合方式,该方法容易使物料受到较大摩擦作用。为了解决这一问题,本文对无桨滚筒混合工艺过程进行探索研究。采用离散元软件EDEM模拟无桨滚筒对两种物料的混合过程,分析混合过程中物料的运动特征,通过定义颗粒混合均匀性指数来定量表征混合均匀程度,分析了不同填料（10000~20000个颗粒）和转速（7~22r/min）对混料均匀性的影响规律,并对物料受力情况进行了定量分析。研究结果表明：在无桨滚筒混料过程中,可以实现对两种物料的混合,且随着转速提高,物料能较快达到均匀。在混合过程中物料受力呈波动式变化,其中最大受力小于0.6N,稳定在0.1~0.35N;物料受力平均值小于0.015N,稳定在0.005~0.01N;最大受力是平均受力值的20~30倍;且随着填料和滚筒转速增加,物料的受力略有增加。     

聚氨酯低压混合器内液固两相流数值模拟

为了探究颗粒粒径、颗粒体积分数、流体黏度、混合头转速对混合器内液固两相流流场的影响以及对叶片尖端所受压力进行预测,运用计算流体力学(CFD)软件Fluent,对聚氨酯低压混合器内液固两相流进行三维数值模拟。结果表明,随着颗粒粒径、颗粒浓度、流体黏度的增加,混合头周向叶片间出现颗粒低速区,其范围不断扩大,不利于物料的混合,而提高转速并不能有效地消除颗粒低速区。混合头结构模拟的计算结果表明,优化过的混合头有效地消除了颗粒低速区,能够实现混合器内物料的充分混合。对叶片尖端所受压力进行拟合,得到不同工况下混合头叶片尖端处所受压力的预测公式,为混合头的冲蚀磨损及新型混合头的设计与研究提供参考。     

旋转式混合器内流场数值模拟及研究

通过对旋转式Kenics混合元件、间断螺纹混合元件和交错平板混合元件引入CFD数值模拟,比较了高黏度不可压缩流体在不同流量、转速、元件单元数、机筒间隙、长径比下三种旋转式混合器内的应变速率.结果表明,增大入口处流量和转动轴转速,增加元件单元数,减少混合元件与机筒间间隙以及长径比,都有利于提高混合器内的平均应变速率,增强混合效果,在相同条件下间断螺纹元件混合效果最好;不同结构的混合元件存在最优结构参数组合.     

恒压加料混合罐流场分析

现代工业要求搅拌设备具有混合均匀、混匀时间短、排量大的特点。本文确定了一种恒压加料混合罐结构及其叶轮结构,并利用CFD技术对该混合罐进行了流场分析。当叶轮转速为200～1000 rpm时发现该混合罐混匀时间约为5秒,排量在114～137 m3/h之间,叶轮中心产生负压区,满足恒压加料混合的使用要求。通过单因素法研究了叶轮转速r以及叶轮直径D对混合罐混合性能的影响,分析结果表明,叶轮转速越高,固液两相混合越均匀,但随着转速的增大,排出液平均密度呈小幅度下降趋势,叶轮转速取400～600 r/min时,排出液混合均匀程度比较理想,且轴功率较小;叶轮直径与排出液均匀程度总体上呈现正相关关系,叶轮直径取345 mm左右时排出液混合均匀程度较好,且平均密度与理想值最接近。     

Kenics混合器混合性能的模拟研究

利用Fluent有限元分析软件计算了流体流过Kenics混合器过程中的应变速率,进而分析混合元件转速与旋转式Kenics混合器混合效率的关系,以及混合元件与机筒间隙对静态和旋转式Kenics混合器对混合效率的影响。模拟分析结果表明:旋转式Kenics混合器混合效率随转速增加而提高;减小混合元件与机筒间间隙有利于增加静态Kenics混合器混合效率,但间隙的减小对旋转式Kenics混合器混合效率的影响却很小。     

无序环流混合器的流体力学特性和颗粒混合特性

在内径为Φ286 mm的无序环流混合器装置中,研究了无序环流混合器的流体力学特性和颗粒混合特性。以催化裂化(FCC)平衡剂为颗粒相,在中心区表观气速为0.3~0.5 m/s,边壁区表观气速为0.1 m/s,系统循环强度为0.25~1.00 kg/s的操作条件下,采用PV-6D型颗粒速度密度测量仪测量了混合器内床层各截面密度,并给出不同操作条件下的截面不均匀指数(RNI);采用热颗粒示踪技术给出了混合器内各测量截面的无因次温度分布,并引入混合指数用来定量描述不同操作条件下的颗粒混合程度,同时对比了传统环流混合器与无序环流混合器的混合能力。结果表明,无序环流混合器内部床层密度呈现中心低,边壁高的分布模式。随着循环强度的增加,RNI先减小后增大,随着表观气速的增加,RNI增大。预混合区混合指数为0.7~0.9,在高循环量,低中心区表观气速条件下(G_s为1.00 kg/s,u_(gd)为0.3 m/s),下料管进料影响区的截面混合指数低于其他操作条件。另外,无序环流混合器混合能力优于传统环流混合器。     

Influence of dispersant structure and mixing speed on concrete slump retention

The relationship between rate of dispersant depletion from the aqueous phase and concrete slump retention was investigated by varying polycarboxylate dispersant structure and mixing speed. The influence of dispersant structure on the rate of slump loss was determined by testing two polycarboxylate-polyether dispersants that differed in charge density. The influence of mixing rate on slump loss was determined by changing mixer rotation speed. The rate of dispersant depletion was influenced by dispersant structure and mixing speed. A higher rate of dispersant depletion was observed at higher mixing speed and with a polymer of higher charge density. In comparing the different mixing procedures, a good correlation was found between slump value and the number of drum revolutions, while a poor correlation was found between slump value and time. Concrete slump retention was influenced by the rate of dispersant depletion and the rate of dispersant depletion was influenced by dispersant structure and mixing speed.     

Effect of processing conditions on dimensions of sisal fibers in thermoplastic biodegradable composites

Biodegradable composites based on treated and untreated sisal fiber and mater Bi‐Z were processed using an internal batch mixer. The effect of processing conditions (temperature, speed of rotation, and time of mixing) and alkaline treatment on the dimensions of sisal fiber was studied. The length and diameter of the initial fibers were reduced during mixing and this effect was correlated to the magnitude of the shear stress developed in the mixer. An increase of the speed of rotation and/or a reduction of temperature produced fibers of smaller dimensions but with a higher aspect ratio l/d. Alkaline treatment increased the kinetics associated to the reduction of the fiber's dimensions. A semiempirical model was employed to predict the size of the fibers versus the time of mixing. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1084–1091, 2001     

A numerical study of mixing intensification for highly viscous fluids in multistage rotor–stator mixers

How to achieve uniform mixing of highly viscous fluids with low energy consumption is a major industry demand and one of the hot spots of mixing research. A typical multistage rotor-stator mixer (MRSM) equipped with a distributor was investigated to disclose the effects on the mixing performance and power consumption for highly viscous fluids via numerical simulation, considering the influence factors associated with different geometric parameters of both MRSM and the distributor. The mixing index and power consumption are used to evaluate the performance of the mixers. The dimensionless correlations for the mixing index and the power consumption are established considering the factors including the flow rate, rotor speed, the number of mixing units. Adopting the optimized mixer with the distributor (X1-T1), the mixing index increases to 0.85 (obviously higher than 0.46 for the mixer T1 without a distributor), meanwhile the corresponding power consumption is about 1/5 of that of T1 achieving the same mixing effect. It illustrates that the distributor can significantly improve the mixing of highly viscous fluids in the MRSM without the cost of large power consumption. These results would provide a guidance on the design and optimization of multistage rotor-stator mixers in industrial applications.     

多级磨盘式强剪切分散混炼器作用下PP/nano-CaCO3体系性能的研究

为了改善填充和共混体系的混炼和分散效果,自行研制了一套高性能混炼设备（多级磨盘式强剪切分散混炼器）,并利用此设备研究了PP／nano-CaCO3体系的稳态流变性、动态流变性和分散性的变化及其影响因素。实验结果表明,未加抗氧剂时,随着混炼器转速的提高,填充体系的MFR增加;nano-CaCO3的加入整体上改善了体系的流变性。当nano-CaCO3的质量分数为4％时,MFR出现最大值。加入抗氧剂之后,PP填充体系中不再有自由基引发的降解反应发生,混炼器转速的提高使填充体系的MFR增加的幅度很小;混炼器的作用导致填充体系的动态贮能模量、损耗模量和复数黏度都下降;经混炼器作用后的填充体系中纳米碳酸钙粒子的分散状态明显优于未经混炼器作用的体系。     

Production of commercial dyes via impingement-sheet mixing: Part I. Testing of a device suitable for industrial application

Impingement-sheet mixing is a proven technique for the rapid mixing of liquids on the laboratory scale. In this paper a practical mixer design for use on the industrial scale is presented. The industrial impingement-sheet mixer was tested at flow rate ratios typical of commercial applications and, compared with earlier laboratory results, only a slight loss in mixing speed was noted. At flow rates of the order of liters/minute and pressure drops up to 1.5 bar, the micromixing times of the industrial impingement-sheet mixer are of the order of tens of milliseconds for reactant stoichiometric ratios near 1.00. If one of the reactants is present in at least a 10% excess, then the micromixing time of the limiting reagent is reduced to several milliseconds.     

The effect of humidity on the trace mixing kinetics in fine powders

Humidity markedly affects the kinetics of mixing fine powders and has a strong interaction with the mixer speed. The effect observed appears to be related to the adsorption of water vapor on the powder. Contact electrostatic charging at low humidities and multilayer adsorption phenomena at high humidities seem to influence the mixing kinetics by changing the powder flow behavior of the mixer. The addition of hydrophobic agents, such as magnesium stearate or stearic acid, eliminate the effect of water vapor on mixing behavior.     

拉伸流动静态混合器混合性能的实验研究

设计了1种能够增强聚合物混合效果的拉伸流动静态混合器（EFM）,以高密度聚乙烯/聚苯乙烯（PE⁃HD/PS）作为混合体系,根据共混体系扫描电子显微镜（SEM）照片及分散相的平均粒径,研究了不同盘形结构和不同盘棱间隙（δ）（0.125~2.0 mm）下EFM的混合性能。结果表明,EFM的盘形入口结构对其混合性能影响较小,混合能力随盘棱顶端圆角半径的增大而有所提升,随δ的增大出现先降低再升高又降低的变化趋势。     

粉体混合过程及搅拌功率的DEM数值模拟和实验

采用数值模拟与功率测试相结合的方法,研究直叶桨式粉体混合机搅拌过程及搅拌功率、扭矩的变化规律。对粉体混合机内球形颗粒的混合过程进行离散单元法DEM数值模拟,研究直叶桨式粉体混合机内搅拌转速、搅拌桨直径、桨叶数目等特性参数对粉体混合时搅拌功率和扭矩的影响,并拟合得到功率计算公式。搭建粉体搅拌试验台,测试粉体搅拌功率并与模拟结果比较。结果表明,直叶桨式粉体混合机内功率消耗与搅拌桨转速、搅拌桨直径、桨叶数目等特性参数有密切关系。同时,扭矩值和功率值与搅拌桨转速、搅拌桨直径和桨叶数目都呈正相关。实验得到了与模拟类似的扭矩-转速关系以及功率-转速关系,模拟值与测试值具有较好的吻合性,验证了所推导公式的准确性。     

The effect of mixing shear rate on the properties of liquid crystalline polymer/polyethylene terephthalate blends

The effect of mixing speed of a batch mixer on the properties of liquid crystalline polymer/polyethylene terepthalate (LCP/PET) blends is investigated through two techniques: scanning electron micrographs to examine morphological changes, and tensile testing to determine the mechanical property dependence of the degree of mixing. The results of the two methodologies are well correlated, indicating that the increased degree of mixing of the blend, which is a function of the mixing speed, can be related directly to improved mechanical properties. The results are discussed in the light of existing theories on polymer mixing. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1783–1787, 2000