螺带式搅拌器在假塑液中的混合及放大的研究

本文综合研究了螺带式搅拌器在假塑性液体中的混合特性及动力特性，测定了双螺带，内外螺带及螺带螺旋３种类型搅拌器的功率常数Ｋｐ和Ｍｅｔａｎｅｒ常数Ｋｓ，并得出混匀操作和传质工艺过程的放大准则。     

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。     

布风方式对流化床混合特性的影响

通过将离散单元法同计算流体力学相结合,对流化床内物料混合过程进行了研究。给出了水平布风板均匀布风、倾斜布风板非均匀布风2种情况下的示踪颗粒场历变过程。模拟结果表明:瞬时颗粒场组图能够较为直观表征床内混合现象;其中,在均匀布风情况下,床内气泡横向运动受到限制,颗粒整体横向运动能力较弱,混合方式以扩散混合为主;而对于非均匀布风流化床,床内存在较大的横向颗粒浓度梯度,对流混和起主要作用,且混合速度较为迅速。     

三维喷动床内异径干湿颗粒混合特性数值模拟

基于计算流体力学-离散单元法,建立了三维喷动床内气固两相流数学模型,采用Fortran语言编制了并行数值模拟程序。对三维喷动床内两种不同直径的干颗粒及湿颗粒的混合特性进行了数值模拟,并从颗粒角度分析了双组分颗粒的运动机制。利用Lacey混合指数对床内整体以及特定区域的混合程度进行了定量分析,并研究了液桥体积、颗粒密度比以及表观气速对异径颗粒混合的影响。结果表明：在单孔射流喷动床内,干湿两种颗粒流动方式相似,湿颗粒无明显的聚团现象;液桥力对小直径的颗粒影响较大,使不同直径湿颗粒速度差减小;环隙区内颗粒的混合是影响整床颗粒混合的关键因素;液桥体积对颗粒混合的影响较大,对颗粒密度比以及表观气速的影响有限。     

部分烧结陶瓷材料力学特性的DEM模拟

通过开展三维离散单元法数值模拟,考察了部分烧结陶瓷在单轴拉伸和压缩加载条件下的力学响应行为.模拟结果表明,拉伸加载下试样的破坏表现为裂纹\"成核\"效应,而压缩加载下则呈现为裂纹\"聚并\"效应;通过追踪固体键的断裂顺序和断裂模式发现,拉伸加载下固体键的破坏主要源于拉伸作用,而压缩加载下则为剪切作用.试样的宏观断裂强度与固体键...     

卧式螺带混合设备结构及设计时应注意的问题

前言 湿法薄形陶瓷砖工艺是一种新型的制造陶瓷砖的工艺技术,其中有一个工序是混料。混料设备有很多种,根据此技术的要求,我们对螺带式混合设备做了重点调研和分析。转子呈螺带状的混合设备称为螺带式混合设备。根据螺带的个数将螺带混合设备分为单螺带混合设备和多螺带混合设备;根据螺带的安装方式又可分为卧式螺带混合设备（见图1）、立式螺带混合设备（见图2）和斜式螺带混合设备（见图3）,通常以卧式为主。     

移动床内颗粒共振行为的DEM模拟

移动床在各种过程工业中普遍存在。从颗粒尺度出发刻画移动床内颗粒物料的复杂流动行为,对于大型移动床反应器的设计、放大和优化具有重要的意义。本工作基于三维离散单元法(Discrete Element Method, DEM)数值模拟,考察了漏斗流和半整体流卸料流型下移动床内颗粒物料的运动特性,重点探讨了两种卸料流型下颗粒运动脉动特性的异同。首先通过对比流动区轮廓及其特征宽度随时间演化的模拟预测结果和实验测量结果,检验了DEM模拟结果的可靠性。DEM模拟结果表明,两种卸料流型下,流动区上部区域不同位置处颗粒平均轴向速度随时间的变化都呈现出显著的非随机波动,表现为颗粒平均轴向速度时间序列的离散傅里叶变换频谱图都出现了明显的特征峰。空间相关性分析结果表明,在流动区上部区域,不同位置处颗粒轴向速度随时间的波动呈现强烈的空间相关性,两种卸料流型下体系内都形成了局部共振。不同轴向位置处颗粒轴向速度的延迟相关性分析结果表明,这种共振行为源自于床层底部出口上方。对颗粒轴向速度和颗粒间接触力之间延迟相关性的分析结果显示,两者之间存在显著的相关性,且后者的波动先于前者的波动,说明模拟得到的共振现象可能源于自由...     

螺旋输送器中颗粒混合过程的模拟

采用离散单元法（discrete element method,DEM）模拟了工业尺度螺旋输送器中两种不同密度与粒径的颗粒的流动状态与混合过程。采用Lacey混合指标的定量分析表明,该输送器的混合性能强烈地依赖于操作条件和结构尺寸,转速和物料的添加速率对混合效果影响最大,其次是混合段螺距和物料粒径。根据工业生产的具体要求,可参考上述发现合理地选择技术参数、提高混合效率、降低能耗。     

颗粒物料在半封闭式回转鼓内的混合特性

采用DEM离散单元法,对不同转速与倾角下半封闭式回转鼓内颗粒物料的混合过程进行了模拟。通过“颗粒接触数”定义的分离指数S,分析了不同转速和倾角对回转鼓内颗粒物料径向与轴向混合特性的影响。结果表明：转速与倾角对回转鼓内颗粒物料径向与轴向混合特性有显著的影响;倾角不变,转速分别为15r/min、30r/min、45r/min时,颗粒物料的径向与轴向混合速度随转速的增加而增加,当转速超过30r/min后,增加转速对径向与轴向混合速度的影响越来越小;转速不变,倾角分别为0°、17°、34°时,增大倾角能有效的增加轴向混合速度,但对径向混合速度没有促进作用,当倾角超过17°后,轴向混合速度的增幅随着倾角的增加而逐渐变小,而径向混合速度随着倾角的增大而减小,但增加转速可以减小径向混合速度下降幅度。     

柱状生物质颗粒与钢球颗粒在滚筒中的混合特性

采用离散单元法DEM（discrete element method）对圆柱形生物质颗粒和钢球颗粒在滚筒中的混合进行了数值模拟,分析了滚筒转速和颗粒数量比对混合质量的影响。结果表明：在本文设定的工况下,颗粒的混合模式为阶梯模式,并且颗粒在混合时可以分成3个区域,即左面的单层钢球颗粒区、中间的钢球颗粒和生物质颗粒混合区、右面的生物质颗粒堆积区。左右两边的颗粒混合效果较差,中间的颗粒混合效果较好。当滚筒转速相同时,钢球颗粒和生物质颗粒数量比为3000∶200时的颗粒混合效果比钢球颗粒和生物质颗粒数量比为3000∶100时的好,即当钢球颗粒数量远大于生物质颗粒数量时,增加生物质颗粒的数量可以提高混合效果。在钢球颗粒和生物质颗粒数量比相同的情况下,当滚筒转速在5~25r/min的范围内,滚筒转速越高,颗粒的混合质量越好,并且颗粒混合达到稳定的时间就越短。     

The effect of interparticle cohesion on powder mixing in a ribbon mixer

The effect of interparticle cohesion on powder mixing in a ribbon mixer was studied by means of the discrete element method. It is shown that with an increase in the cohesion, the mixing rate and uniformity of mixing deteriorate, the coordination number increases indicating the loss of the ability of particles to be engaged in free flowing motion, and a majority of particles have a stronger tangential velocity allowing bulk angular motion of particles. Conversely, with a decrease in the cohesion, more particles have larger axial velocities, which will increase convective motion in the axial direction. When the cohesion is reduced, the number of particles having large radial stresses increases, and normal stress in the axial direction remains mostly unchanged. The ribbon mixer can mix cohesive particles in a wide range of the Bond numbers without causing large stresses. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1023–1037, 2016     

基于离散元方法的差动自清洁混合器混合特性研究

采用离散元方法对LIST卧式差动双轴搅拌设备内高密度聚乙烯（PE?HD）填充碳酸钙复合材料的混合过程进行了仿真模拟,研究了不同加料速率及不同转速条件对该类自清洁混合器混合腔内物料充满度、物料停留时间分布及混合均匀程度的影响。结果表明,该类自清洁混合器的轴向输送能力主要由后续物料的推动作用实现,采用高速轴转速40 r/min,加料速率为10 kg/h的工艺参数可以获得最佳的混合均匀程度。     

不同初始相位角同步转子密炼机混炼流场的有限元模拟分析

基于粘弹性流体模拟软件POLYFLOW对不同初始相位角同步转子密炼机的混炼流场进行三维动态模拟,采用粒子轨迹示踪法并结合统计学后处理软件POLYSTAT对粒子运动轨迹进行统计分析,以粒子分布状态、粒子拉伸长度自然对数平均值和平均混合效率为特征参数对流场进行定量分析和对比。结果表明,采取0°初始相位角布置的同步转子密炼机的混炼分散效果最好。     

双工质塑料冷混机设计研讨

介绍了可提高塑料混合时冷却效率的双工质塑料冷混机，并简要叙述了立式，卧式和立式搅龙双工质冷混机却装置冷却物料的工序。     

Validating granular segregation rate models

One significant hindrance to the development of granular segregation rate models is the inherent difficulty of performing the dynamic experiments required for validation. Here, we seek to overcome this experimental hurdle by establishing an “equilibrium” between segregation and flow perturbation in free surface granular flows and use steady‐state—rather than dynamic—measurements for validation. That is, we combine the segregation rate expressions to be tested with a segregation control framework such that the perturbation rate enables us to infer the segregation rate by measuring simply the steady state extent of segregation. We use periodic flow inversions via an axially located baffle in a tumbler‐type mixer to provide the perturbations that ultimately alter the steady‐state distribution of particles. This work examines the efficacy of existing models for binary segregation driven by either size or density differences. For completeness, we test our model validation framework both computationally and experimentally. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3756–3763, 2017     

不同三维微通道中被动混合特性的研究

Based on the transport phenomena theory, the passive mixing of water and ethanol in different three-dimensional microchannels is simulated numerically. The average variance of water volume fraction is used to index the mixing efficiency in the cases with different Reynolds number and different fabricated mixers. The results show that the efficiency of liquid mixing is progressively dependent on the convective transport as the Reynolds number increases. The efficiency of serpentine microchannel decreases with the increasing Reynolds number in the laminar regime. Altering the aspect ratio of channel inlet section has no significant effect on the mixing efficiency. Increasing the area of channel inlet section will cause the decrease of the mixing efficiency. The mixing in serpentine channels is the most efficient among three different mixers because of the existence of second flow introduced by its special structure.     

A particle‐scale index in the quantification of mixing of particles

Discrete element method (DEM) is a useful tool for obtaining details of mixing processes at a particle scale. It has been shown to satisfactorily describe the flow structure developed in bladed mixers. Here, the advantage is taken of the microstructure gained from DEM to evaluate how best to quantify the microstructure created by mixing. A particle‐scale mixing index (PSMI) is defined based on coordination numbers to represent the structure of a particle mixture. The mixture quality is then analyzed qualitatively and quantitatively in three different ways: a macroscopic mixing index based on the conventional approach, coordination number, and PSMI. Their effectiveness is examined based on DEM data generated for different particle loading arrangements and binary mixtures of particles with various volume fractions, size ratios, and density ratios. Unlike the two other methods, PSMI reveals in a straightforward manner whether a binary mixture of different particles is mixing or segregating over time, while being able to detect particle‐scale structural changes accompanying the mixing or segregation processes in all the mixtures investigated. Moreover, PSMI is promising in that it is not influenced by the size and number of samples, which afflict conventional mixing indexes. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Numerical modeling of adhesive particle mixing

The discrete element method is used to investigate adhesive particle mixing in a system that includes large carrier particles and fine particle agglomerates in a Couette mixer. The simulation starts with 200 carriers and 10 agglomerates with 1000 fine particles each. During mixing, the agglomerates are broken, fractions adhere to the carriers, and there is continuous redistribution of fines between carriers. The focus is to obtain information on the quantity and quality of fine particles adhered to carriers by postprocessing the simulation data. Variation in the structure of agglomerates due to shearing is studied over mixing time. Findings indicate that major fraction of fine particles are dispersed evenly onto the surface of carriers and the rest are in form of free debris. A time‐dependent index is introduced to predict the degree of mixing. Finally, the adhesion force between carriers and coated layers is observed to have a peak at 1 nN. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2599–2609, 2017     

塑料混合机混合质量初探

提出了评定ＰＶＣ塑料混合机混合质量的三个指标,对其测试方式和效果判断进行了讨论,同时也论及了混合质量对制品质量的影响。