FAULT DETECTION OF THE FLUIDIZED BED DISTRIBUTOR BY PRESSURE FLUCTUATION SIGNAL

The feasibility and effectiveness of the sensing and correlating on-line differential pressure fluctuations across a fluidized bed as a diagnostic tool for malfunction of the distributor were experimentally tested by varying the extent and location of the blockage of the distributor openings. The results show that the direct observations or recordings of fluctuating signals and their statistical properties computed on-line, namely 80% fluctuating interval and standard deviation, are sensitive indicators of malfunction of the distributor.     

A MODEL OF MIXING IN A MOTIONLESS MIXER

This paper deals with the modelling of a Sulzer-Koch motionless mixer. A flow model involving convection and diffusion has been solved to characterize the dispersive mixing in one node of the network and this result was then complemented by a network analysis to obtain the flow distribution. Experimental data are in general agreement with the theory. The approach of this study is shown to provide valuable conclusions about the design of the mixer and to complement the more commonly used integral or statistical treatments. In particular, it has been shown that the ratio of internal resistances controls the distributive mixing in one mixer unit and that significant convective mass transport takes place within the node even when there is no net cross-flow.     

静态混合器的设置

介绍了由上海化工研究院研制开发的ＳＶ，ＳＸ，ＳＬ，ＳＨ和ＳＫ五种类型国内生产的静态混合器的特点和适用范围，对工程设计选用和设置要求进行了具体说明。为方便选用，附有标准产品的型号和规格。     

文氏管煤粉混合器的数值模拟

在煤粉工业锅炉系统中,煤粉混合器存在呼吸帽正压、风速偏低和供粉波动等问题.使用CFD软件FLUENT对煤粉工业锅炉文氏管煤粉混合器不同工况下的速度场、压力场、颗粒轨迹和供粉浓度等进行了模拟和分析,并通过实验对模拟结果进行了验证.结果表明,上述问题是由下游阻力过大、风机工作点偏差和文氏管负压区偏差等原因导致的.     

Kenics静态混合器的应用及研究进展

介绍了Kenics静态混合器的混合机理及其在流体混合和强化传热等操作过程中的应用,重点介绍了Kenics静态混合器的压力降计算方法以及拉伸混合和无序混合等方面的研究进展。     

PRESSURE DROP AND HOMOGENIZATION EFFICIENCY OF A MOTIONLESS MIXER

Pressure drop and homogenization efficiency of a motionless mixer of helical type have been studied experimentally. For evaluation of the drag coefficient the equation has been proposed which is valid within the range of Reynolds number from 10^?2 to 10⁴ The efficiency of the motionless mixer for mixing of two Newtonian liquids has been investigated by using a decolourization method. For the operating conditions studied in this work it appears that there is the worse performance of the mixer about the Reynolds number of 50. No influence of volume flow rate ratios (from 1 to 10) upon the performance of the mixer has been observed. A higher number of mixing elements must be applied for homogemzation of liquids with viscosity ratios above 100 as compared with that for viscosity ratio 1.     

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。     

Development of positron emission particle tracking for studying laminar mixing in Kenics static mixer

Positron emission particle tracking (PEPT) is a flow visualisation technique that has found application in a wide range of processes. In this work, PEPT has been used to study laminar flow of a high viscosity Newtonian and non-Newtonian fluid in a Kenics static mixer (KM). Through analysis of the trajectories of many hundreds of passes of the tracer particle through the mixer, it is possible to compute the overall flow field and to visualise how the fluid twists and folds as it passes along the mixer. Eulerian velocity maps plotted for the Newtonian and non-Newtonian fluids showed that the length required for the flow to develop is shorter for the non-Newtonian fluid than the Newtonian. The stretching and folding mechanism of mixing was observed by grouping the trajectories into clusters according to whether the trajectory passes to the left or right of the blade at the transition between elements. Those trajectories making the same L–R–L decision tended to remain in the same striation through two or three elements until that striation became stretched and folded back on itself, sandwiching other layers. It is clear that the PEPT data is rich and powerful. We are hopeful that the techniques we develop for the flow and mixing in the Kenics mixer will be applicable to studying more complex laminar flows.     

双转子连续混炼机混合工艺特点及影响因素

讨论了双转子连续混炼机的混合工艺特点及转子结构尺寸,转子螺杆顶部线速度,物料卸料门开启度大小对混合过程的影响,提出了以物料在混炼机中的转向混合循环次数,转子螺棱顶部线速度为基本参数控制混炼机的混合过程。     

双转子连续混炼机混炼段分散混合效率的研究

利用有限元分析软件Polyflow对自行设计的ECM30型双转子连续混炼机转子的混炼过程作了三维等温流场分析,借助于剪应力和混合指数对转子的分散混合效率进行了分析研究;讨论了不同的操作工艺对分散混合效率的影响。该数值模拟的结果将有助于针对不同的聚合物采用不同的混炼工艺,使得聚合物在转子中的混合达到最优化。     

球窝型动态混合器结构和机理的研究

介绍研制的题示混合器结构及其混合机理。在分析球窝流场各节点速度分布的基础上,用加权平均总应变和分流混合度作为评定指标,对球窝型混合器的混合行为进行分析。通过对比实验证明球窝型混合器对于高粘流体具有良好的混合功效。     

双转子连续混炼机混炼过程分析

分析了双转子连续混炼机工作原理和影响剪切速率、剪切应力大小的因素,提出最大剪切应力出现在转子混炼段螺棱的顶部,其大小与转子的结构、操作条件有关。适当降低转子混炼段螺棱宽度和转子与料筒的间隙,提高转子转速,可以有效地增强转子对物料的剪切作用。     

FULLY DEVELOPED FLOW IN TWISTED TAPES: A MODEL FOR MOTIONLESS MIXERS

The fully developed flow fields in twisted tapes for arbitrary aspect ratios were found via a transformation to a non-orthogonal coordinate system. A streamfunction formulation permitted the removal of the transverse pressure field. The method presented allows for non zero Reynolds numbers and offers some computational advantages over previous methods.

Results for aspect ratios between 0.1 to 6.4 and Re =0 show that the mixing action is not a strong function of the aspect ratio. Comparisons between Re =0 and Re = 2.5 at an aspect ratio of 1.6 show a small effect upon the transverse circulation. The equations were stable up to Re = 7.5 for aspect ratio 1.6. The aspect ratio strongly influenced the stability of the equations.

An optimal design for a motionless mixer was obtained by maximizing the percentage deformation obtained per unit pressure. Optimization parameters were aspect ratio and amount of twist per clement. The optimum mixer has an aspect ratio of 0.5 and 90 degrees of twist per element. The standard Kenics configuration has an aspect ratio of 1.6 and 180 degrees of twist. Efficiency is approximately doubled at the proposed optimum.

Tapes of finite thickness (t = 0.125 R) were also studied and show the same general behavior as the infinitely thin tape. The thickness of the tape decreases the cross sectional area for flow and gives a corresponding increase in pressure drop.     

RESIDENCE TIME DISTRIBUTION OF RHEOLOGICALLY COMPLEX FLUIDS PASSING THROUGH A SULZER SMX STATIC MIXER

Static mixers are widely used in continuous mixing, heat and mass transfer processes and chemical reactions. However, a proper understanding of the flow pattern is still missing when rheologically complex fluids are involved. This paper presents a study of the Residence Time Distribution (RTD) determination in a Sulzer SMX static mixer. A two-parameter RTD model, based on each mixing element, was proposed to describe the flow pattern of rheologically complex fluids in a such mixer. It was shown that in this model the flowrate fraction across the plug flow component increases with the generalized Reynolds number. However, the volumetric fraction of the plug flow component depends not only on the generalized Reynolds number, but also on the number of mixing elements, apparently due to memory effects of viscoelastic fluids.     

BULK POLYMERIZATION OF STYRENE IN A STATIC MIXER

An experimental investigation of thermal bulk polymerization of styrene in a pilot plant will be reported. The plant is composed of a recycle tubular reactor followed by a tubular reactor. The conversion of the pre-polymerization part is in the range of 0 to 60% and at the outlet of the pilot plant up to 96%. Studies on the residence time distribution show plug-flow behaviour for a variety of different conditions with respect to viscosity and density gradient. The polymers obtained are characterized by gel permeation chromatography and compared to commercial products.     

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。     

用流动可视化技术研究混合器内研究简报流场及混合效果

引　言不同流体的混合是化工、生物制品、食品工业等工艺过程中一道重要的工序 ,仅依靠流体在输送过程中的自然湍流扩散不能进行有效的混合 ,因此必须使用混合器 ,使液体在短时间内获得均匀的特性 ,达到满意的混合效果 ,并使损失的能量较小 .不同行业由于介质性能和混合要求不同 ,相应混合器的结构也不同 .通常国内外多采用经验类比法设计混合器 ,用取样分析法检验混合效果 .随着新技术的发展 ,深入研究流体混合机理对于高效节能混合器的设计具有重要意义 .尽管许多学者采用数值方法对混合器内部的流动和混合效果进行了研究[1,2 ],但由于数…     

化工搅拌器的参数优选

本文提出了确定化工用搅拌器搅拌时间的一种简单试验方法,并用正交表安排寻找最佳搅拌参数的试验和整理试验数据,得到了有实用价值的结果。     

Single and two-phase flows in a horizontal pipe with a Kenics static mixer: Effect of pressure drop on mixing

Single and two-phase flows pressure drops through a Kenics static mixer were investigated, for liquid and gas Reynolds numbers ranging from 8110 < Re_L < 18 940 to 1730 < Re_G < 8680, respectively. New friction factor correlations were established for single and two-phase flows, showing better agreement than those available in the literature. Dissipated energy and characteristic time constants were estimated from experimental data. For instance, a dissipated energy with a maximum value of 510 W/kg was calculated in two-phase flow with the drift-flux model. The dispersed phase reduced the characteristic mixing times and its influence was more important than the continuous phase for all the characteristic mixing time investigated. Furthermore, the macroscopic characteristic mixing time was shown to be the governing mixing process for almost all gas and liquid flow rates explored.