搅拌釜内流场三维数值模拟及功率预测

大型搅拌釜,尤其是涉及传热或两相介质搅拌的容器,其搅拌效果和功率往往难以预测。针对大型搅拌釜的搅拌器设计、流场结构模拟和功率预测等问题,采用CFD数值模拟技术,对搅拌釜内部的三维流场进行了数值计算。分析了搅拌釜内的流动结构,计算了不同曝气量时的搅拌功率,获得了详细的流场信息和各项特性参数。     

搅拌槽内固液两相流的数值模拟及功率计算

使用计算流体动力学的方法对搅拌槽中的流场进行模拟,得到搅拌槽中液体的流动状况和体积分数分布。对流场分布规律、固体颗粒体积分数特点加以分析,进而利用模拟出的数据计算搅拌轴的功率,为搅拌器的设计提供参考。     

Numerical Simulation of the Two‐Phase Fluid Field in a Gas‐Around‐Liquid Spray Nozzle

A new gas‐around‐liquid spray nozzle (GLSN) was designed, and the two‐phase flow fluid field in this nozzle was simulated numerically. Flow characteristics under different structural parameters were obtained by changing the L/D ratio of the premixing chamber, incident angle, and inlet pressures. Increasing the L/D ratio and incident angle improved flow characteristics such as atomization flow, outlet velocity, and turbulence intensity. The nozzle performed optimally at an L/D ratio of 0.5 and incident angle of 60°. The atomization flow decreased with higher gas pressure and increased with higher liquid pressure. The outlet velocity mainly depended on the inlet gas pressure, not on the inlet liquid pressure. These results provide an indication for optimum structures and parameters of the GLSN.     

Rushton桨搅拌槽中气液两相流动的全流场数值模拟

The gas-liquid flow field in a stirred tank with a Rushton disk turbine,including the impeller region,was numerically simulated using the improved inner-outer iterative procedure.The characteristic features of the strirred tank,such as gas cavity and accumulation of gas at the two sides of wall baffles,can be captured by the simulation.The simulated results agree well with available experimental data.Since the improved inner-outer iterative algorithm demands no empirical formula and experimental data for the impeller region,and the approach seems generally applicable for simulating gas-liquid stirred tanks.     

Numerical Study on Bubble Formation of a Gas‐Liquid Flow in a T‐Junction Microchannel

Bubble emergence in a gas‐liquid flow in a T‐junction microchannel of 100 μm diameter, operated under a squeezing regime, was simulated with the computational fluid dynamics method. In general, bubble formation in channels includes three stages: expansion, collapse and pinching off. After analyzing and comparing quantitatively the three forces of pressure, surface tension and shear stress acting on the gas thread in the whole process, their effects in the different stages were identified. The collapse stage was the most important for bubble formation and was investigated in detail. It was found that the collapse process was mostly influenced by the liquid superficial velocity, and the rate and time of collapse can be correlated with empirical equations including the liquid superficial velocity, the capillary number and the Reynolds number.     

Design and Numerical Simulation Analysis of an Integrative Gas‐Liquid‐Solid Separation Hydrocyclone

Normally, a gas‐liquid‐solid separation includes both degassing and desanding processes, which means a relatively higher facility investment and larger energy consumption. Based on an inner‐cone hydrocyclone developed before, an integrative degassing and desanding hydrocyclone was designed. Its design idea and process are described in detail. By means of a hollow inner cone (IC), the separated liquid enters into the cone through holes on it and then flows to the liquid‐phase outlet. Due to integrative separation and tangential solid outlet, the separator has a more compact size. Simulation analysis of the effect of IC diameter and IC height on separation performance was carried out. Results indicate that with a larger IC diameter the gas content in the solid outlet decreases, while as the IC height rises, the gas content in the liquid outlet increases.     

多层新型桨搅拌槽内气-液两相流动的实验与数值模拟

对三层新型组合桨气-液两相搅拌槽内的流体流动进行了实验研究,并采用计算流体力学(CFD)的方法对气-液两相搅拌槽的通气搅拌功率、流场、局部气含率及总体气含率进行了数值模拟,数值模拟采用了欧拉-欧拉方法,数值模拟结果与实验值吻合良好,同时考察了通气流量和搅拌转速对通气搅拌功率和气含率的影响规律. 研究结果表明,欧拉-欧拉方法能较好地模拟搅拌槽内气-液两相流的流动状况.     

Modeling of Slug Velocity and Pressure Drop in Gas‐Liquid‐Liquid Slug Flow

Gas‐liquid‐liquid slug flow in a capillary reactor is a promising new concept that allows one to incorporate gas‐liquid reaction, liquid‐liquid extraction, and facile catalyst separation in a single unit. In order to assess the performance of a gas‐liquid‐liquid slug flow reactor, it is necessary to predict the slug velocity and pressure drop to ascertain residence times and reaction rates. New empirical models for velocity and pressure drop were developed based on existing models for two‐phase gas‐liquid and liquid‐liquid slug flows, and these were validated experimentally.     

Free‐Surface Turbulent Flow in an Eccentric Stirred Tank

This work aims at a reliable prediction of the flow dynamics in stirred tanks. The focus is on the free‐surface turbulent flow in an eccentric stirred tank by using the combination of detached‐eddy simulation and volume of fluid model. The flow field, profiles of the free surface, mean velocities, and the macroinstability phenomenon were explored and compared with the available experimental data. A reasonable representation of the free‐surface hydrodynamics was achieved. The findings indicate that the model and simulation strategies presented here can be used with sufficient confidence to predict the free‐surface hydrodynamics in stirred tanks.     

Micromixing of Solid‐liquid Systems in a Stirred Tank with Double Impellers

The effect of solid particles on micromixing has been studied using the competitive iodide/iodate reaction system in stirred, multi‐impeller, solid‐liquid systems. The influences of particle size, impeller speed, solid holdup, feed position, and energy input have been investigated. The change of the segregation index with the power input was more distinguishable only for the 450–600 μm particles as compared with the large ones, at the same solid holdups. Also, for the small ones, cloud formation was observed at a particle concentration of 12.1 wt %. However, the influence of larger particles of 1–1.25 mm on micromixing was negligible, though both energy input and solid loading were increased. Besides, the optimal feed position was identified, and multiple feeds were also explored.     

Estimation of kLa Values in Bench‐Scale Stirred Tank Reactors with Self‐Inducing Impeller by Multiphase CFD Simulations

A multiphase computational fluid dynamics (CFD) simulation methodology is developed and proposed for the estimation of the spatial distribution of k_La values in a bench‐scale reactor equipped with a self‐inducing impeller. The importance of estimating an apparent drag coefficient, which considers the effect of turbulence on the gas bubble rising velocity, is also tackled by applying different correlations available in literature, namely, Brucato, modified Brucato, and Pinelli correlations. The spatial distribution of k_La values in the agitated vessel is found from the CFD results using Danckwert's surface renewal model. An analysis of the gas volume fraction distribution obtained from the simulations is performed in order to choose the most suitable drag model. The modified Brucato correction correlation for the drag force exhibits the best agreement with experimental data.     

乙烯利酯化搅拌反应器的改进与模拟优化

利用计算流体力学（CFD）技术对乙烯利酯化搅拌釜内流场进行了模拟研究,对比了工业酯化釜和新酯化釜的气体分散效果等反应器性能。结果表明,工业酯化釜因桨叶形式不当、桨间距过小等原因,气体分散效果很差;新改进的酯化釜依照工艺要求,调整了桨叶结构,增加了挡板,使气体分散效果得到明显改善,反应器液层空间得到有效利用。模拟研究结果可为工业酯化釜装置的技术改进提供一定的指导。     

螺旋桨搅拌槽内湍流运动测量及数据处理

螺旋桨搅拌槽内湍流运动测量及数据处理侯拴弟，王英琛，施力田（北京化工大学化学工程系，北京１０００２９）关键词搅拌槽，湍流运动，螺旋桨１前言轴流式搅拌槽常用于物料混匀、结晶、悬浮及催化反应等过程，是化工生产中重要的单元设备之一。纵观以往文献［１～３］，...     

橡胶沥青搅拌罐内混合过程的数值模拟

针对橡胶粉与基质沥青混合过程中出现的漂浮、沉底、粘壁及挂料现象,建立了橡胶沥青搅拌罐的几何模型,基于计算流体力学软件对罐内混合过程进行非定常固液两相流数值模拟,分析了影响混合均匀性的因素,如桨叶直径、桨叶位置、挡板及搅拌速度等. 结果表明,尺寸适宜的桨叶直径与合适的桨叶位置有利于形成循环的轴向流,并减少定常流现象,安装挡板有效减少了切向流,搅拌器转速不影响内部流场的基本形态,但适宜的搅拌转速提高了混合均匀性. 混合均匀度与模拟结果印证,且当搅拌器直径800 mm、桨叶距离罐底680 mm、桨叶宽100 mm、搅拌速度280 r/min时,优化后橡胶粉的分布较均匀,混合均匀度为0.24,处于完全离底悬浮状态,模拟结果与实验结果较吻合.     

Full‐Loop Simulation of Gas‐Solids Flow in a Pilot‐Scale Circulating Fluidized Bed

In order to study the system hydrodynamics in a circulating fluidized bed (CFB), a 3D full‐loop simulation was conducted for a pilot‐scale CFB. The Eulerian‐Eulerian two‐fluid model with the kinetic theory of granular theory helped to simulate the gas‐solids flow in the CFB. The system hydrodynamics including pressure balance, vectors of gas and solids, distribution of solids holdup, and instantaneous circulating rates were obtained to get a comprehensive understanding of the system. It was predicted that the main driving force was the pressure drop of the storage tank. The storage height and valve opening were critical operating factors to control the riser operation. The effects of operating conditions including solids circulating rates and superficial gas velocity on the hydrodynamics were investigated to provide guidance for the stable operation of the CFB system.     

涡轮桨搅拌槽内流动特性的大涡模拟

利用大涡模拟方法研究了涡轮桨搅拌槽内的流动特性,采用了三种亚格子模式:标准Smagorinsky-Lilly模式(SLM)、Smagorinsky-Lilly动力模式(DSLM)和亚格子动能动力模式(DKEM),并将模拟结果与标准k-ε模型及文献实验数据进行了详细的比较.结果表明:大涡模拟方法可获得搅拌槽内的瞬态流场;对桨叶区时均速度及湍流动能的预测与实验数据相吻合,比标准k-ε模型计算结果有明显改进,三种亚格子模型中DSLM和DKEM模拟结果更好.同时分析了大涡模拟中桨叶端部附近湍流动能估计偏差的原因,发现主要是由于对轴向湍流均方根速度的预测偏差造成的.大涡模拟方法为搅拌槽内非稳态、周期性的湍流流动和湍流特性的研究提供了强有力的工具.     

旋流燃烧室内冷态和热态流场的三维数值模拟分析

采用RNGk-ε湍流模型以及有限化学反应速率涡破碎模型(Eddy break up)对Allied Signal公司75 kW微型燃气轮机旋流燃烧室内冷态和热态时气流三维流动过程进行了模拟计算。结果表明,燃烧室火焰筒内热态时与冷态时的流场相似,烧室火焰筒内都有3个回流区,3个回流区的存在将有助于燃料的连续点火和火焰的稳定;燃烧室内热态三维流场的中心回流区长度小于冷态时的中心回流区长度,气流的轴向速度也大于相应的冷态轴向速度,而且掺冷孔空气射流对环向速度分布的影响小于冷态时的影响。     

翼形桨搅拌槽内混合过程的数值模拟

采用FLUENT软件的多重参考系(MRF)及标准k-ε模型,将速度场与浓度场方程分开进行求解,对单层轴流式三叶CBY翼形桨搅拌槽内的混合过程进行了数值模拟,所得的混合时间的模拟结果与实验值相吻合。同时采用数值模拟的方法研究了不同的示踪剂加料点、监测点位置及操作条件对混合时间的影响规律;模拟结果表明,混合过程主要由搅拌槽内的流体流动所控制,混合时间与示踪剂加料点及监测点位置密切相关。上述的研究结果对于工业搅拌反应器的优化具有一定的参考意义。     

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.