旋转填充床内微观混合的数值模拟

旋转填充床作为新型的高效反应传质设备,广泛应用于快速反应过程,如制备纳米粉体材料.对旋转填充床内微观混合进行研究,有助于进一步认识旋转填充床内高度分散液体微元在填料丝网中的流动行为和分散混合机制,为旋转填充床内液液反应混合制备纳米材料提供理论基础.基于公开文献报道的实验观测结果,通过合理假设,建立了旋转填充床内微元流动的物理模型.在该物理模型的基础上,结合此前提出的湍流混合与反应模型,模拟计算了液体微元经过实验条件下50层丝网填料最终流出填料空间的浓度分布.由浓度分布得到的微观混合特征指数与实验值进行了对比,吻合良好.     

旋转填充床内微观混合化学反应计算数学模型

在层状扩散模型的基础上, 以1-萘酚与对氨基苯磺酸重氮盐在旋转填充床内发生的竞争串联偶氮化合反应为例，探讨了填充床内的微观混合情况.引进了两个调整反应物与生成物关系的参数，对整个反应过程建立了一个计算数学模型;并进行了计算，计算预测的结果与实验数据在规律上和数值上都较好符合.     

泡沫陶瓷填料旋转填充床微观混合性能

采用碘化物-碘酸盐平行竞争反应为工作体系,以离集指数(XS)表征微观混合性能,实验考察了物料体积流量、H+浓度、旋转填充床转速、物料体积流量比等对两种不同孔径的新型整体泡沫陶瓷填料旋转填充床的微观混合性能的影响。结果表明,孔径较小的泡沫陶瓷填料更利于微观混合;H+浓度、进料体积流量比的增加会导致XS增加;而旋转填充床转速、进料流量的增大都可使XS下降。在实验研究的基础上,利用团聚模型计算泡沫陶瓷填料旋转填充床微观混合时间(tm),得到tm范围为0.385~8.55 ms。与传统不锈钢丝网填料对比,泡沫陶瓷填料tm最小值(0.385 ms)低于不锈钢丝网填料的tm最小值(1.6 ms),表明泡沫陶瓷填料的微观混合性能优于传统不锈钢丝网填料。     

泡沫陶瓷填料旋转填充床微观混合性能

采用碘化物-碘酸盐平行竞争反应为工作体系,以离集指数（X_S）表征微观混合性能,实验考察了物料体积流量、H⁺浓度、旋转填充床转速、物料体积流量比等对两种不同孔径的新型整体泡沫陶瓷填料旋转填充床的微观混合性能的影响。结果表明,孔径较小的泡沫陶瓷填料更利于微观混合;H⁺浓度、进料体积流量比的增加会导致X_S增加;而旋转填充床转速、进料流量的增大都可使X_S下降。在实验研究的基础上,利用团聚模型计算泡沫陶瓷填料旋转填充床微观混合时间（t_m）,得到t_m范围为0.385～8.55 ms。与传统不锈钢丝网填料对比,泡沫陶瓷填料t_m最小值（0.385 ms）低于不锈钢丝网填料的t_m最小值（1.6 ms）,表明泡沫陶瓷填料的微观混合性能优于传统不锈钢丝网填料。     

旋转填充床中微观混合实验研究

采用 １萘酚与对氨基苯磺酸重氮盐偶合竞争串联反应体系,对旋转填充床内的微观混合进行了实验研究,得到了转速、浓度、流量、体积比等因素对离集指数影响规律,并对之进行了合理的解释和分析。结果表明,旋转填充床中微观混合能被极大地强化,可成为适合快速反应的新一代反应器     

旋转床内微观混合与反应过程的特性

对旋转床内微观混合的研究有助于建立其内部微观尺度上的混合与反应机制。在以往研究工作的基础上,依据数值模拟与实验结果的对比,间接确定了旋转床内的液膜厚度范围;对液膜速度模拟进行合理修正,通过流体流动、传质及反应过程的数值模拟,得到离集指数、湍流耗散率、停留时间以及微观混合时间的变化。实验结果和数值模拟表明：不同转速下的离集指数、混合时间、湍流动能耗散率等均表现出一定的多尺度现象。研究结果丰富了旋转床内微观混合与反应的认识,将为后续研究提供坚实的基础。     

旋转填充床中微观混合模型与实验验证

根据旋转填充床中液体流动和混合特征,建立了一个新的复合式微观混合模型,并对串联竞争反应的标准体系进行了模拟和实验验证。结果表明,在旋转填充床内,当体积比α较小时（如α＝2）,微观混合影响很小,过程处于化学反应控制区;当α较大时（如α＝20）,过程处于微观混合作用区,提高转速使离集指数降低,流量增加对离集指数影响很小;考虑液体初始宏观分布不均匀对混合的影响,模型计算结果与实验结果吻合良好。     

旋转填料床与盘管组合反应器中的流动特性

以饱和的NaCl水溶液为示踪剂,采用脉冲法考察了液体流量、转子转速对旋转填料床与盘管组合反应器停留时间分布(RTD)曲线的影响。用轴向扩散模型对流动状况和返混程度进行了表征。结果表明,组合反应器内的流体流动型态与盘管相同,接近活塞流,且流量越大,平均停留时间越短。旋转填料床转子转速对组合反应器停留时间分布影响很小。     

一种新型反应设备——旋转填料床技术及其应用

旋转填料床技术是一种突破性的过程强化新技术,在化工、能源、环保、材料、生物化工等工业领域中有广阔的商业化应用前景,笔者概要介绍了该新技术的特点,国内外研究开发和应用。     

提升管-下行床耦合反应器内颗粒混合行为

引　言循环流化床中气固两相的流动有两种不同的方式 :提升管中为气固并流上行的逆重力场运动 ,下行床中为气固并流下行的顺重力场运动 .其差异表现为提升管内颗粒浓度、速度以及气体速度在径向上严重的不均匀 ,颗粒浓度概率密度分布以及速度的瞬时信号都表明了颗粒团 -空穴两相结构的存在[1] ,一些研究[2 ,3] 还发现提升管中颗粒的停留时间分布 (ＲＴＤ)曲线存在较大的拖尾甚至出现双峰 ,研究者认为提升管内存在弥散颗粒和颗粒团两种不同的混合机理 ;下行床则比提升管大大改善 ,气固速度、颗粒浓度沿径向分布要均匀得多 ,颗粒的ＲＴＤ曲线…     

Characterization of Mixing and Size Segregation in a Rotating Drum by a Particle Tracking Method

The mechanisms of segregation in solids mixing, even in simple rotating drums, are not clearly understood. Although most past studies have focused on binary mixtures, this work investigates the effect of polydispersity on granular flow, mixing, and segregation in a rotating drum operated in rolling regime through particle trajectories obtained from the radioactive particle tracking technique. Velocity profiles, radial segregation, and axial dispersion coefficients for monodisperse and polydisperse systems of glass beads are analyzed with respect to rotational speed and particle size. A model is introduced to predict the residence times along streamlines and evaluate the rate at which the material renews at the free surface and within the inner layers of the bed. Our results reveal similar velocity profiles and residence times for monodisperse and polydisperse systems. They also indicate that the particles distribute along the radial direction of the drum, although not necessarily in a core/shell configuration. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1894–1905, 2013     

Hardwood fibre fractionation using rotating cone

Rotating cones were used to carry out fibre fractionation of a 100% hardwood pulp having a consistency of 0.93± 0.02%. The unique features of the rotating cone fractionator adopted in this study were that its surface was constructed from a sieve mesh, thereby introducing a “rough” surface, and the feed pipe was located at an off-centre position to the axis of rotation. In all earlier studies reported in the literature, the fibre fractions were collected at different radial locations. However, in the present study, collection of the various fractions was made either at different radial or at angular positions. Tests were conducted for 120 mm diameter cones having a cone angle of 30°. Visual observations, photographs and fibre length measurements suggested that fibre fractionation performance strongly depended on the flow characteristics formed on and surrounding the rotating cone. In turn, they were found to be strongly dependent on the surface roughness, rotational speed and feed flow rate. Results for fibre fractionation showed quite conclusively that rotating cones made from 20-mesh and 32-mesh screens were more effective for fibre fractionation than “smooth” surface rotating cones.     

高密度液固循环流化床流动特性研究及数值模拟

在φ80 mm×8000 mm的液固循环流化床提升管中,利用实心玻璃珠和常温水,采用实验和数值模拟相结合的方法对高密度液固循环流化床的流动特性进行了考察。实验发现,高密度液固提升管中,颗粒固含率和颗粒速度径向分布均为抛物线分布,轴向平均固含率分布总体上为下浓上稀的波动形式分布,颗粒在提升管中的流动表现出加速-减速-再加速直至充分发展的过程。这种分布特征与较高颗粒浓度、较高表观液速和颗粒循环速率及喷管式液体分布器的影响有关。液固提升管中固体颗粒的停留时间分布曲线均为尖而窄、较对称且没有明显拖尾的单峰分布,这表明颗粒基本是以弥散颗粒形式存在,颗粒停留时间分布较为均匀。通过将数值模拟结果与实验结果进行比较发现,模拟值与实验值吻合较好,说明所建立的数学模型较为合理,进一步通过数值模拟实验对颗粒密度和颗粒粒径对流动特性的影响规律进行了考察。     

Numerical Simulation of Macroscopic Mixing in a Rushton Impeller Stirred Tank

The macroscopic mixing in a stirred tank with different tracer injection locations, impeller speeds and impeller positions is simulated numerically by solving the transport equation of the tracer based on the whole flow field in the baffled tank with a Rushton disk turbine numerically resolved using the improved inner-outer iterative procedure. Predicted mixing time is compared well with the literature correlations. The predicted residence time distribution of the stirred tank is very close to the present experimental results. The effect of the installation of a draft tube on the mixing time and residence time distributions is addressed.     

折流式旋转床持液量的研究

将折流式旋转床分成若干液体流动区,计算流动区内动、静圈壁上液膜及动、静圈之间液滴的运动时间,在此基础上建立折流式旋转床持液量模型. 以空气-水为物系,在直径300 mm、高51 mm的折流式旋转床中进行实验,分别测得不通和通空气时转子的持液量,用实验数据拟合出持液量模型参数. 结果表明,转子持液量随液量和气量增加而增加,随转子转速增加而减小,高转速下气量对持液量的影响明显减弱. 折流式旋转床不通气持液量为2.35%~3.68%,是普通丝网旋转填料床不通气持液量的1.32~2.06倍.     

Investigating the dynamics of cylindrical particles in a rotating drum using multiple radioactive particle tracking

The behavior of granular flows inside rotating drums is an ongoing area of research. Only a few studies have investigated non‐spherical particles despite the fact that particle shape is known to have a significant impact on flow behavior. In addition, the experimental techniques limit the interpretation of the results of these studies. In this work, we compared the flow behavior of cylindrical and spherical particles using the multiple radioactive particle tracking technique to capture the positions and orientations of cylindrical particles simultaneously. We analyzed two important components of the transverse flow dynamics, that is, the boundary between the active and passive layers, and the velocity profile on the free surface. For the cylindrical particles, two general models are proposed to calculate the velocity profiles on the free surface and the effective particle sizes in the active and passive layers. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2622–2634, 2016     

搅拌釜中自浮颗粒三相体系的混合时间

液相混合时间是搅拌过程中的重要内容。在釜径３８６ｍｍ的搅拌釜内,采用热电偶温差法考察了搅拌桨型、挡板、等操作因素对自浮颗粒三相搅拌混合的液相混合时间的影响。     

齿形盘元件的局部停留时间分布

采用自制荧光检测装置在线测量含齿形盘元件（TME）的双螺杆挤出机的部分停留时间分布（PRTD），利用去卷积方法计算TME的局部停留时间分布（LRTD），并将PRTD转换成停留体积分布（RVD）和停留转数分布（RRD）。研究表明，直齿的LRTD曲线形状比斜齿更宽，其混合能力更强；喂料速率（Q）和螺杆转速（N）的提高均使LRTD曲线向短时间方向移动。等流量转速比（Q／N）的RRD和RVD曲线重合；提高Q／N，使RRD向低转数的方向移动，而RVD向高体积方向移动。对于特定螺杆构型，不同螺杆转速和喂料速率下的RVD曲线仅是体积坐标方向的平移，RVD曲线形状主要取决于螺杆构型。     

The movement of solids through flighted rotating drums. Part II solids-gas interaction and model validation

A residence time model for a rotating drum with lifting flights which includes axial displacement of airborne particles due to the drag of the gas stream has been developed in Part I of this study (Sherritt et al., 1993). Because the particles fall in curtains, the equations for single particle drag overestimated the effect of the gas stream on the displacement of the falling particles. In this paper, large scale wind tunnel experiments, which involved pouring a curtain of particles into a gas stream, indicated that the shielding effect of the curtain could be represented by a lower-than-average gas velocity within the curtain. The magnitude of the curtain shielding effect is related to the flight discharge rate, the fall distance and the flight length. Incorporating the results of the experiments into the residence time model provides a significant improvement on the effect of the gas velocity, and hence the best model available, especially for industrial-scale equipment.     

Mixing performance comparison of milliscale continuous high‐shear mixers

Mixing performance of two continuous flow millilitre‐scale reactors (volumes 9.5 mL and 2.5 mL) equipped with rotor‐stator mixers was studied. Cumulative residence time distributions (RTD) were determined experimentally using a step response method. Distributions were measured for both reactors by varying impeller speed and feed flow rate. The mixing effect was determined by measured RTDs. Computational fluid dynamics (CFD) were used to verify that the residence time distribution in the measurement outlet agreed with the outlet flow. The mixing power of both reactors was determined using a calorimetric method. The reactor inlet flow rate was found to affect mixing performance at 1–13 s residence times but the effect of impeller speed could not be noted. Both milliscale reactors are close to an ideal continuous stirred‐tank reactor (CSTR) at the studied impeller speed and flow rate ranges. The specific interfacial area was found to depend on the reactor inlet flow rate at constant impeller speed for the case of copper solvent extraction.