圆盘反应器流场数值模拟

以圆盘反应器的开发和应用为背景,根据反应器内气液两相的流动特点和接触方式,采用流体体积函数(VOF)模型研究圆盘表面液膜厚度、速度分布和槽内液相流型,得到反应器的流场特性。从轴功率、持液量两方面对反应器性能进行研究,并考察了流场和性能的关系。结果表明,圆盘表面液膜分为起始区、加速区和匀速区。起始区液膜厚,速度慢,部分液体回流;加速区液膜变薄,加速,表面更新快;匀速区膜厚和速度变化较小。液相主体以Stewartson流型为主,盘间距对液相流型影响明显。圆盘液膜与槽内液相通过"垂直涡"进行物质传递,当圆盘间距与圆盘直径之比(L/D)为0.2~0.4时,最有利于两者混合和物质传递。将数值模拟和量纲分析结合,得到功率数(NP)和平均膜厚表达式,并与文献进行比较,表明计算流体力学(CFD)方法能够较好的模拟圆盘反应器内流体力学特性,预测流场和性能。     

圆盘反应器的流动模型

剖析了圆盘反应器的流型及其影响因素,指出圆盘反应器的虚拟级数N应为盘数;讨论了反应器中熔体流动过程中存在多次的动量、能量的传递;由于反应器结构上存在死角和短路,其F(t),E(t)并非理想状态。对反应器气相流动作了简述。     

流体弹性对圆盘反应器功率特性的影响

以工业聚酯终缩聚圆盘反应器开发应用为研究背景 ,分别考察了圆盘反应器在黏性和黏弹性介质中的功率特性 ,通过对两种实验介质中功率特性的比较 ,得出弹性对圆盘反应器功率消耗的影响程度 ,并给出相应的功率消耗关联式 ,为聚酯终缩聚圆盘反应器国产化开发应用提供功率设计依据 .     

圆盘摩擦损失降阻新方法的实验研究

采用在封闭空腔间隙流场内插入一自由旋转圆盘的方法降低圆盘摩擦损失。在圆盘旋转雷诺数为２×１０５～９．５×１０５条件下，对空腔轴向间距比Ｓ／Ｄ２为０．０７８３～０．１０８７、插入盘的无量纲轴向位置Ｌ／Ｓ及其半径不同情况分别进行实验研究。结果表明，采用插入盘方法可以降低圆盘摩擦损失；插入盘半径减小使圆盘摩擦损失增大；随着轴向间距、圆盘旋转雷诺数增大，降阻效果增强；插入盘位于不同轴向位置对降阻效果有不同影响。最后，对减阻的机理进行初步分析。     

圆盘反应器中的PET缩聚过程

利用薄膜实验研究了PET缩聚过程反应和传质规律 ,建立了链增长、链降解反应动力学模型和泡沫脱挥时的传质速率方程 ;通过冷模实验研究了圆盘反应器中PET的混合、流动、成膜、膜表面更新以及传质规律 ;综合了反应和反应器研究结果 ,建立了圆盘反应器中的PET缩聚过程模型 ,对圆盘反应器中的PET缩聚过程进行了仿真分析 ,考察了温度、压力、停留时间、转速、催化剂浓度、负荷大小等各种因素的影响     

柱形涡发生器强化撞击流反应器流场特性的数值模拟

利用数值模拟方法分析设有柱形涡发生器的撞击流反应器的流场特性,优化了柱形涡发生器的尺寸与位置参数,考察了柱形涡发生器尺寸与位置参数对撞击流反应器流场结构、速度分布、湍流尺度和混合性能的影响。结果表明,柱形涡发生器直径D=10 mm时,反应器内旋涡数量最多,涡系影响范围最广;D<10 mm时,旋涡数量减少;D>10 mm时,涡系影响范围减小。柱形涡发生器横向间距的增加使反应器内旋涡数量减小,涡系影响范围增大。随着柱形涡发生器横向间距、纵向间距的增加,撞击流反应器径向流速、湍流尺度和混合强度均先增大后减小。当柱形涡发生器横向间距K=5 mm、纵向间距J=70 mm时,撞击流反应器混合效果最佳。     

弹性棒对仿生学柔性反应器的流体混合强化

在柔性反应器底部放置竖直的弹性硅胶棒（弹性棒），通过弹性棒运动对周围流体产生扰动，强化流体混合。基于酸碱中和脱色法和图像分析方法，研究了柔性反应器的混合过程和混合时间；通过混合时间定量评估了弹性棒的强化效果；并分别研究了弹性棒的位置和高度及柔性反应器系统的最大挤压深度和频率对流体混合行为的影响。结果表明：弹性棒的放置能够使柔性反应器内隔离区结构改变，混合时间减少。弹性棒位置靠近挤压头一侧时，对流体混合强化最明显。在弹性棒高度低于柔性反应器内液面时，弹性棒高度增加，强化效果增加。超过液面之后，继续增加弹性棒高度，强化效果没有进一步增加。当弹性棒靠近挤压头、高度超过液面且最大挤压深度为2.5cm，与没有弹性棒时相比混合时间减少了57%。在其他实验条件不变的前提下，最大挤压深度增加，强化效果增加。     

圆盘反应器减速器降速增扭作用及其各级轴向间隙计算的探讨

介绍了圆盘反应器减速器的内部结构及其安装、联接和支撑结构特点,STUWE胀盘的联接结构及其安装注意事项和减速器的降速增扭作用,减速器轴系各级轴向间隙的计算及其理论依据。     

终聚圆盘反应器的混合性能初析

通过实验研究了终聚圆盘反应器的混合、成膜与更新，以及功率特性，分析了工业反应器的设计和操作的原则、合理操作的液位、功率放大方法，以及强化表面更新应由粘度范围不同而采取不同的措施。     

撞击流反应器混合性能研究进展

按照撞击流反应器的研究发展进程,分析了撞击流反应器的混合过程。结合大量学者研究工作,回顾了反应空间、流体流动、喷嘴结构等因素对常见的开放式撞击流反应器、受限撞击流反应器、浸没循环撞击流反应器等反应器混合性能影响的研究。简述了外界激励和其他技术对撞击流反应器混合效果影响的研究进展,并总结了几类反应器的微观混合时间及关联式。同时介绍了一种新型水平三向撞击流反应器,该反应器产生的径向射流不同于两喷嘴径向射流,而为交叉状的伞状射流;通过进一步探究发现当量喷嘴间距L*=2 D~3 D时径向射流偏转角β出现峰值,而且此时的混合时间也最短。最后对撞击流反应器混合性能研究前景进行展望。     

非牛顿特性对偏心圆筒内流体混沌混合的影响

Effect of fluid elasticity and shear-thinning viscosity on the chaotic mixing between two alternately rotating cylinders has been studied. The h-p finite element method is used to obtain high accurate solutions of the steady flow. The unsteady, periodic flow is simulated using the piecewise-steady approximation. Characteristics of the chaotic mixing axe analyzed by examining the asymptotic coverage of a passive tracer and the lineal stretching ofthe fluid elements in the annulus. For the viscoelastic fluids modeled by the upper-convected Maxwell constitutive equation (UCM), our computation predicts little effect of the fluid elasticity on the mixing patterns. On the other hand, the shear-thinning viscosity, modeled by the Carreau equation, has a large impact on the advection of a passive tracer and the distribution of lineal stretching. We find that the zones of the lowest stretching match remarkably well with the regular zones in the tracer-coverage plotting. Our study reveals the vital importance of reducing the discretization errors of the velocity field in the numerical simulation of chaotic flows.     

Polyvinyl butyral-zirconia hybrid hollow fibers prepared by air gap spinning

In this study, an air gap spinning method was adopted to develop polyvinyl butyral (PVB)-zirconium (Zr) hybrid hollow fibers. With zirconium alkoxide, three kinds of PVB with different degree of acetalization were used as organic polymers. The morphologies, surface Zr content and relative bonding inside the hollow fibers were characterized by changing coagulation solution concentration, spinning dope viscosity and air gap distance. The effect of Zr on PVB structure were examined in terms of x-ray photoelectron spectroscopy, scanning electron microscopy, thermogravimetric analysis and Fourier transform infrared spectroscopy. Results indicate that PVB spinning solution experienced good mixing mechanism at room temperature and immediately develop structural hollow fiber when extruded into coagulation fluid of Zr alkoxide by 2.0 cm air gap distance. Among other prepared fibers, fiber contained 20 wt% PVB with 2 cm air gap confirms effective average diameter of about 1016 μm which strongly influenced by spinning solution viscosity. The variation of maximum Zr content (8.18%–14.36%) confirms the asymmetry of coordinate bonding occurred on internal and external surface. Moreover, changing of spinning solution viscosity, coagulation liquid concentration and air gap can only affect the surface roughness and fiber diameter whereas no micro pores were developed in the fiber sublayers.     

3‐D numerical simulations of nonisothermal flow in co‐rotating twin screw extruders

Three‐dimensional nonisothermal flow simulations in the kneading disc regions of co‐rotating twin screw extruders were performed using a finite element method. The standard Galerkin method and penalty function scheme were applied to the flow field. The streamline‐upwind/Petrov‐Galerkin scheme was used in the temperature field to reduce numerical oscillation. The simulations were carried out under the operational conditions of The Japan Steel Works TEX30 machine for various rotational speeds. The configuration was ten 2‐lobe kneading discs with a 90° stagger angle. Experimental observations were also performed to validate the numerical simulations under the same operational conditions. The pressure in front of the tip in the rotation direction was higher than behind the tip, and the region behind the tip sometimes had a negative value. Since variation of the pressure gradient in the axial direction causes forward and backward flows in the disc gap regions, the disc gap regions play an important role for mixing. The temperature becomes higher with increasing rotation speed due to high viscous dissipation. A high temperature was observed on the disc surface, in the disc gap, and in the intermeshing regions. The numerical results of pressure profiles with the rotation and the temperature in the axial direction were in good agreement with the experimental observations.     

Effects of Physical Property Differences on Blending

Within this study, the effects of viscosity differences between added and bulk liquids on mixing times were investigated. This was carried out in stirred tanks of diameter T = 0.31, 0.61, 1.83 m to study the effect of scale. Different impeller types (hydrofoils, disc turbines, and pitched blade turbines) and sizes (D = T/2 and T/3) were employed. Operating conditions for which mixing time correlations for similar property liquids could be used were identified at scales relevant to industrial applications. Recommendations are made for improving blending under operating conditions where these correlations are not applicable as the mixing times are too long.     

在轴向流搅拌桨发酵罐中进行PHB和结冷胶的发酵实验研究

在对轴向流搅拌桨的混合效果和传质效果进行考察的基础上用轴向流搅拌桨进行了ＰＨＢ和结冷胶发酵的实验研究,结果发现轴向流搅拌桨能更好地适用于高密度和高粘度的微生物发酵搅拌,高密度培养最终可使菌体浓度提高１２％,产物含量提高１０％;高粘度发酵可使生产强度提高２０％。     

INTERFACIAL AREA AND MASS TRANSFER WITH GAS-LIQUID SYSTEMS IN TURBINE-AGITATED VESSELS

Highly viscous, non-Newtonian Xanthan gum solutions and two transparent model fluids with similar Theological properties have been studied under aerated (up to 1 vvm) and unaerated conditions in a 0.29m diameter agitated vessel. Rushton disc turbines of size 1/3 and 1/2 of the tank diameter have been used alone and also in conjunction with 6-bladed, 45°-pitch axial flow turbines of the same size at speeds up lo 24 rev/s, enabling specific power inputs of up to 15 W/kg to be imparted.

Flow patterns were studied by flow visualisation and hot film anemometry. When the fluids have a yield stress, the fluid divides into a turbulent well-mixed cavern which increases in size with increasing speed with the remainder stagnant. A model for the size of the cavern fits the experimental data well for both aerated and unaerated mixing. Large diameter combinations produce good mixing at about 1 to 2 W/kg which is about 1/3 to 1/4 of that required with small diameter combinations. Single disc turbine impellers are unsatisfactory.     

LIQUID PHASE MIXING IN MECHANICALLY AGITATED VESSELS

Liquid phase mixing and power consumption have been studied in 0.3, 0.57, 1.0 and 1.5 m i.d. mechanically agitated contactors. Tap water was used as liquid phase. The impeller speed was varied in the range 2-13.33 r/s. Three types of impellers namely disc turbine (DT), pitched turbine downflow (PTD) and pitched turbine upflow (PTU) were employed. The impeller diameter to vessel diameter ratio was varied in the range of 0.25 to 0.58. The effect of impeller clearance from tank bottom was also studied. Mixing time was measured using the transient conductivity measurement.

The PTD impeller was found to be the most energy efficient for mixing in liquid phase alone. Further, PTD (T/3) was found to be most energy efficient as compared with other impeller diameters. The effect of clearance was found to be design dependent and it was found to be diameter dependent in the case of pitched turbines.

Flow patterns of different impellers have been studied by visual observations (using guide particles). These observations were supported by the measurements using Laser Doppler Velocimetry. A model has been developed for the prediction of mixing time. In the case of all the three impeller designs, a fairly good agreement was found between the predicted and experimental values of mixing time.     

Microstructure and rheologic development of polypropylene/nano‐CaCO3 composites along twin‐screw extruder

Polypropylene/nano‐calcium carbonate (PP/nano‐CaCO₃) composites were prepared by using an intermeshing, co‐rotating twin‐screw extruder. Two different screw configurations, denoted by screws A and B, respectively, were employed. The former provided high dispersive mixing and the later provided high dispersive and distributive mixing. Effect of mixing type on microstructure and rheologic development of nanocomposites was investigated by taking samples from four locations along screws A and B. Transmission electron microscopy results show that in the sample at the exit of extruder, the percentage of nano‐CaCO₃ particles with the equivalent diameter lower than 100 nm along screws A and B is 66.5 and 79.0%. respectively. Moreover, for screw B, the number‐averaged diameter at four sampling locations is smaller than that for screw A. This means that the distributive mixing, provided by screw B, favors the size decrease of nano‐CaCO₃ in the PP matrix. In addition, rheologic results show that the decrease of complex viscosity for the nanocomposites is deeply related to turbine mixing elements, which provides distributive mixing. The online melt shear viscosity of the nanocomposite at the exit of extruder prepared by screw B is lower than that of pure PP. This is related to the dispersion of nano‐CaCO₃ in PP matrix. Finally, the relationship between rheologic properties and microstructure was analyzed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

FLOW BEHAVIOR OF A THERMOTROPIC LIQUID CRYSTAL AROMATIC COPOLYESTER

The rheology of a thermotropic aromatic copolyester, especially the steady shear viscosity, has been studied and found to be very different and more complex than that of analogous conventional isotropic polymers. The viscosity has a power-law dependence on shear rate over a wide range. The temperature dependence is very high below 300°C, and is comparable to that of isotropic polyesters above that temperature. The end correction measured by capillary viscometry is large, which is normally indicative of high melt elasticity, but nevertheless the extrudate swell is very small. The melt viscosity is shear and temperature history dependent. Unexplained effects that have been observed include dependence of viscosity upon apparatus gap dimensions and upon shear history.     

HYDRODYNAMICS AND AXIAL MIXING OF LIQUIDSOLID SYSTEM IN OPEN TURBINE ROTATING DISC CONTACTOR

The open turbine rotating disc contactor (OTRDC) has been installed simply by adding three narrow strips to the lower surface of each rotating disc in the rotating disc contactor (RDC), so it can be used for the system with high solid particle content. Hydrodynamics and axial mixing have been investigated in a 0.152m diameter OTRDC of different compartment height for the system of tap water and quartz particles. A model has been developed to describe the flow of liquid and solid phases. The solid phase holdup can be calculated satisfactorily according to the model equations. Axial mixing data have been treated by the backflow model and the correlations for predicting backflow ratios of liquid and solid phases in OTRDC have been presented.