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.     

Kenics型静态混合器内分散相液滴破碎和聚结过程的CFD-PBM数值模拟

采用CFD-PBM耦合方法对Kenics型静态混合器内分散相油滴破碎及聚并行为进行数值模拟研究,分析了雷诺数、混合元件数、元件长径比等参数对分散相液滴粒径的影响,揭示了分散相在Kenics静态混合器内流动过程中液滴粒径的演化规律.结果表明,随雷诺数增大,分散相液滴出口粒径不断减小,并出现临界趋势;静态混合器的前几个元件...     

Kenics型静态混合器的结构优化与数值模拟

基于三维有限元数值模拟方法,对应用于高黏聚酯熔体直纺工业丝过程中熔体管道输送的Kenics型静态混合器进行结构优化;对静态混合器内示踪粒子的流动轨迹进行统计学处理,通过停留时间分布、分离尺度、面积伸展率以及时间平均效率表征流动特性与混合性能。结果表明:相比传统静态混合器,当静态混合器的元件旋转角度为120°时,静态混合器的分离尺度降低,分散混合能力增强,拉伸作用增强,混合特性提高;相同管径下元件长径比为0.75时,静态混合器的混合能力较长径比为1.00或1.25时都有明显的提高;随元件长径比增加,混合效果逐渐变差,流动方式趋近于理想平推流动。     

数值模拟静态混合器结构对PS/CO_2熔体温度的影响

利用专用CFD软件Polyflow对SMX型和Kenics型静态混合器中PS/CO_2发泡溶液进行数值模拟计算,分析比较不同板厚在不同元件个数条件下两种静态混合器消耗的压力损失,以及不同CO_2浓度对静态混合器压力损失的影响;并引入"离散系数"分析比较两种静态混合器出口温度均匀性的变化.数值模拟的结果表明:SMX型静态混合器冷却效果优于Kenics型静态混合器,并且SMX型静态混合器出口温度均匀性高于Kenics型静态混合器.     

水平液固循环流化床换热器传热性能评价

对管内插入Kenics静态混合器的水平液固循环流化床换热器进行实验研究,实验考察了静态混合器扭率、静态混合器安装方式、液体流速、颗粒体积分数对传热性能和流阻性能的影响,并运用综合强化传热性能评价指标（PEC）对其进行分析。实验发现,传热性能和阻力系数均随扭率增加而减小。当雷诺数在10000~45000之间时,扭率为1.5、2、2.5、3.5的Kenics静态混合器的PEC指标均大于1,说明了水平流化床换热器插入Kenics静态混合器能够改善传热。在雷诺数达到25000左右、Kenics静态混合器扭率为2.5、颗粒体积分数为4%时,水平流化床换热器的PEC指标最高达到1.18。当两个扭率均为2.5的Kenics静态混合器安装间距为200mm时,水平流化床换热器的PEC指标最高。     

几种旋转式反应注射混合元件混合性能的实验研究

在深入分析旋转式Kenics混合元件混合机理基础上开发出两种新型混合元件,将这两种混合元件与Kenics混合元件的混合性能进行实验对比。结果表明,开发的螺纹元件能够取得与Kenics混合元件相近的混合效果,所得制件表面质量最好;而交错平板元件混合效果差,反应不均匀,反应速度慢;旋转式Kenics混合元件的螺旋结构产生的拉伸和剪切在混合过程中起主要作用,交错平板结构的分割作用是次要的。     

带有Kenics静态混合器的水平液固两相流化床换热管的压降研究

以饱和硫酸钙为介质,在安装Kenics静态混合器的水平液固两相流化床换热管上进行实验研究,考察介质流速、Kenics静态混合器扭率、颗粒体积分数及颗粒尺寸对压降的影响,并与冷态实验条件下的压降变化规律进行比较。结果表明：同等操作条件,安装Kenics静态混合器后压降比安装前提高20%～140%;压降随雷诺数的增大而增大,随Kenics静态混合器扭率的增大而减小;颗粒体积分数对压降也有影响。根据实验数据,得出了稳定操作条件下压降与上述影响因素之间的经验关联式,为带有Kenics静态混合器的水平液固两相流化床换热器的设计提供计算依据。     

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。     

Kenics静态混合器在水平液固循环流化床中的研究

为了解决水平液固循环流化床中颗粒分布不均匀问题,在内径29 mm、长4 m的水平有机玻璃管流化床内放入Kenics静态混合器,采用CCD图像测量与数据处理系统考察静态混合器的结构、个数、安装位置对液固二相流中颗粒分布的影响;同时,利用U型管压差计考察不同条件下静态混合器的压降。实验结果表明:Kenics静态混合器能明显地改善管内颗粒分布情况;单个扭率Y=3.5的Kenics静态混合器压降最小;2个扭率Y=3.5的Kenics静态混合器间距为40 mm时对颗粒分布影响长度是最长的。     

旋流静态混合器内瞬态流动特性研究进展

首先概括了静态混合的技术特色;其次,重点综述了近年来旋流静态混合器内脉动压力与速度波动的统计特征、多尺度分形和混沌混合特性等方面的研究进展;实验研究发现Kenics静态混合器各点压力最大波动幅值与进口流量呈二次函数关系,脉动功率谱随着频率的增加呈幂函数关系衰减;轴截面内壁面自由涡和主体区强制涡相互耦合诱导混沌流的产生,同时提高速度与温度梯度的场协同程度。最后,总结了静态混合器内螺旋元件的切割分流、改变流向和径向混合等功能在强化CO2水合物形成过程中的作用。指出将计算流体力学、映射法等方法同LIF、PIV、PFS有机结合可有效地分析静态混合器内多相流动混合机理。     

Performance of Kenics static mixer over a wide range of Reynolds number

The present study deals with the numerical simulation of flow patterns and mixing behaviour in Kenics static mixer over a wide range of Reynolds number. Three different sets of Kenics mixer (aspect ratio = 1.5) comprised of 3, 9 and 25 elements each have been characterized. The Reynolds number was varied in the range of 1 to 25,000 (i.e., from laminar to turbulent flow regime). The numerical approach takes into account the aspects of the fluid flow at higher Reynolds number values including circumferential velocity profiles at different cross-sections within the Kenics mixer, which were neglected in previous studies. It was observed that cross-sectional mixing in the turbulent flow regime takes place up to 30% of each element length at element-to-element transition; beyond that velocity profiles were uniform. The experiments were also carried out to measure the circumferential and axial velocity profiles and pressure drop in three different Kenics Mixers using air as fluid. The pressure drop per unit element (ΔP/η) was found to be independent of the number of Kenics mixing elements used in the system. The total pressure drop across Kenics mixer obtained by CFD simulations were compared with the experimental pressure drop values and correlations available in the literature. The numerical results were found in good agreement with the experimental as well as the results reported in the literature. A new pressure drop correlation in the Kenics static mixer has been developed.     

混合元件数对SK型静态混合器流场特性的影响

以SK型静态混合器为对象,运用激光多普勒测速仪对混合器内流场进行测量分析,研究混合元件数对混合器内速度分布和湍动性能影响。结果表明：在扭旋叶片作用下,流体在混合器内的速度会重新分布,湍动会被强化,这一过程主要在前3个混合元件中实现,且湍动逐渐增加,但增加速度逐渐减弱,第1个混合元件强化作用最为显著,进入第4个混合元件后基本达到稳定;当混合叶片数量超过3个以后,对流体湍动的强化基本达到混合器强化能力的极限,继续增加元件数量不能提高流体的湍动程度,但可以维持这种湍动。     

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。     

反应注射成型设备混合系统的类型与性能

介绍了反应注射成型设备的撞击混合式、旋转混合式以及旋转Kenics混合器等混合系统的结构特点,并对工作性能进行了分析     

Reactions and residence time distributions in motionless mixers

Motionless mixers are modeled as open, circular tubes with parabolic velocity distributions except at a few isolated planes where radial mixing occurs via an instantaneous coordinate transformation. Possible transformations are constrained by continuity of volumetric flow. Complete flow inversion appears the theoretically optimal transformation, being superior to complete mixing. A model consisting of intermediate planes of complete mixing approximates existing experimental data on the Kenics Static Mixer when four Kenics elements are made equivalent to a single plane of complete mixing. This model preserves the essential nature of a laminar flow residence time distribution while providing a relatively simple means of estimating mixer performance.     

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.     

Residence Time and Concentration Distribution in a Kenics Static Mixer

Static mixers, often referred to as motionless mixers, are in-line mixing devices that consist of mixing elements inserted into a length of pipe. Most of the experimental works in this field have concentrated on establishing design guidelines and pressure drop correlations. Due to experimental difficulties, few articles have been published on the investigation of the flow and mixing mechanisms. In this work, a Kenics KMX static mixer was utilized to study concentration and residence time distribution (RTD) and effect of Reynolds number on mixing. The static mixer had six mixing elements arranged in-line along the length of the tube, and the angle between two neighboring elements was 90°. The length of the mixer was 0.98 m with internal and external diameters of 5.0 cm and 6.0 cm, respectively. The main continuous fluid was water, and NaCl solution was used as a tracer. All experiments were conducted with three replications at three Reynolds numbers, Re = 1188.71, 1584.95, and 1981.19. A dispersion model was used to model the RTD data. The experimental results were compared with the model results and reasonable agreement was achieved.