双层涡轮桨搅拌反应器内混合时间的大涡模拟

采用计算流体力学(CFD)方法对直径为0.476m双层涡轮桨搅拌反应器内的流动及混合进行了数值模拟,并实验测试了混合过程。利用大涡模拟(LES)及Smagorinsky-Lilly亚格子模型求解湍流流动与示踪剂传递过程,桨叶区域采用滑移网格技术。研究结果表明,大涡模拟得到的示踪剂响应曲线和混合时间与实验结果吻合良好,其预测精度明显优于基于雷诺平均(Reynolds-averaged Navier-Stokes,RANS)的标准k-ε模型的模拟结果。大涡模拟是研究搅拌反应器内非稳态及周期性湍流流动的有效方法。     

大涡模拟搅拌槽中的液相流动

采采用大涡模拟湍流模型对有档板的Rushton 桨搅拌槽进行了数值模拟研究。控制方程采用控制容积法进行离散,对流项用三阶QUICK格式,扩散项是二阶中心差分。压力 速度耦合方程在交错网格上采用SIMPLE算法进行求解。小尺度流动的模化采用动力学（dynamic）亚格子模型。搅拌桨与档板之间的相互作用采用改进的内外迭代法进行处理。计算结果和文献值吻合得很好。     

涡轮桨搅拌槽内单循环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单循环流动特性,采用Smagorinsky-Lilly动力亚格子模式,与文献实验及模拟数据进行了详细的比较. 结果表明,叶片后方的双尾涡偏向槽底运动,上尾涡在30o处已开始衰减. 800000个非均匀分布的计算网格和30个桨叶旋转周期的样本数据统计可获得准确的大涡模拟数据. 时均速度、均方根速度和湍流动能的大涡模拟值与实验数据一致,而k-e模型的模拟值与实验不符. 桨叶区呈现较强的各向异性,这是导致k-e模型预测不准确的主要原因. 对于搅拌槽内的复杂流动,大涡模拟方法是一个非常有效的工具.     

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.     

基于FLUENT软件的管式搅拌反应器流场的数值模拟

运用商业计算流体力学(CFD)软件FLUENT对一种新型管式搅拌反应器进行流场模拟,用GAMBIT建立流场实体模型,采用标准k-ε湍流模型以及多重参考系法(MRF)处理搅拌桨区.结果表明,计算所选模型能较准确地预测搅拌反应器的速度场、压力场及湍流动能分布,考察流量为1 m3/h时不同搅拌转速对反应器内部混合的影响,此时对应的最佳搅拌转速为50 rpm左右.模拟结果将为实验研究提供适当的操作参数,对搅拌反应器的优化和放大具有一定参考价值.     

偏心进气式鼓泡反应器内气液流动的大涡模拟

采用气液两相流动的欧拉-欧拉大涡模拟,研究了偏心进气式鼓泡塔内气液两相湍流流动。模拟结果表明：气泡流的运动与气含率的分布与试验结果吻合良好,得到了气液两相湍流瞬态结构形成和演变过程;增大气速使涡结构剧烈变化,液体粘度增高限制了旋涡尺度的发展,反应器高径比减小使涡数量减少。     

管式搅拌反应器停留时间分布的数值模拟

对一种新型管式搅拌反应器的停留时间分布(RTD)进行了实验研究,运用商业计算流体力学(CFD)软件FLUENT进行流场模拟及RTD计算,证实管式搅拌反应器的停留时间分布受搅拌转速及入口流量等因素影响,带搅拌装置的管式反应器适当增加转速能使RTD曲线变窄,改善流型和抑制返混;转速过大会使RTD曲线变宽,导致死区的产生,不利于反应器的混合.RTD曲线的数值模拟计算结果与实验结果基本稳合.     

搅拌反应器内计算流体力学模拟技术进展

综述了计算流体力学(CFD)技术应用在搅拌反应器的进展情况。重点对搅拌反应器内流动场模拟的各种处理方法,包括"黑箱"模型法、内外迭代法、多重参考系法和滑移网格法,进行了介绍与评价,指出了各种方法所具有的特点及存在的问题。阐述了搅拌反应器内CFD技术的发展方向,并就国内的研究现状进行了简单概述。     

用大涡模拟结合改进的内外迭代法数值模拟搅拌槽中的液相流动

1 INTRODUCTION Stirred tank reactors are widely encountered in the chemical, pharmaceutical, and hydrometallurgical proc- esses. The fluid motion in stirred tanks is three-dimensional, complex, and covers a wide range of spatial and temporal scales. In the area surrounding the impeller, the flow is highly turbulent and swirling. The numerical simulation of such reactor systems is helpful in quantifying the effects of the impeller type, geometry, and the operational conditions in order to …     

偏心搅拌槽内宏观不稳定性的分离涡模拟

为研究偏心搅拌槽内的宏观不稳定性,基于分离涡模型建立了偏心搅拌数值模拟方法。采用滑移网格法模拟搅拌桨的旋转,实现了偏心搅拌流场的非稳态模拟。对不同工况时的宏观不稳定性进行了频谱分析,讨论了偏心率、雷诺数和桨径比对宏观不稳定频率的影响,并进行了PIV实验验证。研究表明,偏心搅拌槽内存在明显的宏观不稳定现象,其变化周期约为桨叶通过周期的10倍;PIV实验结果与分离涡模拟结果吻合较好,都表明偏心搅拌槽内的宏观不稳定频率随雷诺数的升高而增大,随偏心率的增大而减小,随桨径比的增大而增大。     

Three-dimensional large eddy simulation of wave characteristics of liquid film flow in a spinning disk reactor

The waves of liquid film flow play an important role on the process intensification in spinning disk reactors (SDRs). However, the mechanism of wave formation was still unclear. In this work, a three-dimensional large eddy simulation was developed to investigate the mechanism, as well as the characteristics of waves in the SDR. Agreed with the imaging results, different wave patterns were identified as: smooth film, concentric, and spiral waves in spreading direction; sine-like and pulse-like waves in fluctuating direction. The radial and tangential relative movements among the layers of liquid film were found to dominate the formation of different wave patterns. Local average film thickness (h_avg) and local wave amplitude (Δh) ranged from 0 to 500 μm and 0 to 200 μm, respectively. The waves can improve the turbulent intensity and enlarge the specific surface area, resulting in the intensification of transfer processes.     

PIV experiments and large eddy simulations of single-loop flow fields in Rushton turbine stirred tanks

The single-loop flow fields in Rushton turbine stirred tanks with clearance C=0.15T (T is tank diameter) were investigated by using particle image velocimetry (PIV) experiments and large eddy simulation (LES) methods. The velocity and turbulent kinetic energy (TKE) were carefully measured and resolved with high resolution camera. The regions with high TKE are affected by the movement of the trailing vortices generated behind the impeller blades. The effects of both geometrical configuration and Reynolds number were discussed. It is found that the Reynolds number has little effect on the mean flow for the configuration of impeller diameter D=T/3, C=0.15T. However, the single-loop flow pattern is changed into a double-loop one if D is increased from T/3 to T/2. The LES results were compared with the PIV experiments and the laser Doppler anemometry (LDA) data in the literature. The effect of the grid was validated, and the levels of local anisotropy of turbulence near the impeller discharge regions were investigated. Both the phase-averaged and phase-resolved LES results are in good agreement with the PIV experimental data, and are better than the predictions of the k–ε model. The agreement shows that the LES method can be used to simulate the complex flow fields in stirred tanks.     

搅拌反应器气液两相流混合过程的涡旋效应数值模拟

为研究气液两相搅拌釜桨叶对釜内流动结构及气液混合性能的影响,本文以直叶片和推进叶片为研究对象,采用ICEM软件对搅拌釜流场进行六面体结构网格划分,基于SST-DDES湍流模型及欧拉-欧拉多相流模型对搅拌釜内部流场进行三维非定常计算,获得两种桨叶下搅拌釜内部涡结构及其演化过程,并分析搅拌釜内瞬态气相分布和瞬时流场的分布规律。研究结果表明：由于叶片旋转而产生的涡有撕裂、合并、衰减和耗散的演化过程;直叶片相较于推进叶片,其涡耗散速度较快,涡产生到消失的周期较短;由于叶片结构不同,主流的运动方向也随之改变,直叶片沿径向分布,推进叶片沿轴向分布。前者在釜内形成上下两层循环区,不利于气相扩散。后者在釜内形成一个大循环区,加剧釜内流动循环,造成后者的气相扩散能力大于前者。比较两者T_0.95分布,推进叶片要小于直叶片,推进叶片搅拌釜T_0.95近似为直叶片搅拌釜T_0.95的50%。     

Numerical simulation of liquid-solid two-phase flow in a tubular loop polymerization reactor

Understanding hydrodynamics of tubular loop reactors is crucial in proper scale-up and design of these reactors. Computational fluid dynamics (CFD) models have shown promise in gaining this understanding. In this paper, a three-dimensional (3D) CFD model, using a Eulerian-Eulerian two-fluid model incorporating the kinetic theory of granular flow, was developed to describe the steady-state liquid-solid two-phase flow in a tubular loop propylene polymerization reactor composing of loop and axial flow pump. Corresponding simulations were carried out in the commercial CFD code Fluent. The entire flow field in the loop reactor was calculated by the model. The predicted pressure gradient data were found to agree well with the classical calculated data. Furthermore, the model was used to investigate the influences of the circulation flow velocity and the sold particle size on the solid hold-up. The simulation results showed that the solid hold-up has a relatively uniform distribution in the loop reactor at small particles in volume and high-circulation flow velocities.     

CFD simulation of liquid-phase mixing in solid-liquid stirred reactor

A comprehensive CFD model was developed to gain an insight into solid suspension and its implications on the liquid-phase mixing process in a solid-liquid stirred reactor. The turbulent solid-liquid flow in a stirred reactor was simulated using a two-fluid model with the standard k-ε turbulence model with mixture properties. The multiple reference frames (MRFs) approach was used to simulate impeller rotation in a fully baffled reactor. The computational model with necessary sub-models was mapped on to a commercial solver FLUENT 6.2 (of Fluent Inc., USA). The predicted solid concentration distribution was compared with the experimental data of Yamazaki et al. [1986. Concentration profiles of solids suspended in a stirred tank. Powder Technology 48, 205-216]. The computational model was then further extended to simulate and understand the implications of the suspension quality on liquid-phase mixing process. The computational model and the predicted results discussed here will be useful for understanding the liquid-phase mixing process in stirred slurry reactors in various stages of solid suspension.     

Stereo‐PIV experiments and large eddy simulations of flow fields in stirred tanks with Rushton and curved‐Blade turbines

The flow characteristics in pilot‐scale stirred tanks with Rushton and curved‐blade turbines were investigated by using stereoscopic particle image velocimetry (SPIV) experiments and large eddy simulation (LES) methods. The velocity and turbulent kinetic energy (TKE) in the impeller discharge regions were carefully resolved with a high resolution SPIV system, and the detailed phase‐resolved velocity and TKE profiles were used to validate the LES results. The effects of Reynolds number and blade shape on the flow characteristics were discussed. The LES results of velocity, TKE, and the evolution of trailing vortices were compared with the SPIV experimental data, and good agreement was obtained at various phase angles. The effects of subgrid scale model and hybrid grid with different mesh resolutions on the LES results were investigated. LES is a computationally affordable method for the accurate predictions of the complex flow fields in pilot‐scale stirred tanks is presented. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3986–4003, 2013     

大涡模拟方法模拟鼓泡床内气固两相流动

采用大涡模拟（LES）方法模拟气相湍流,颗粒动理学方法考虑颗粒相碰撞产生的动量和能量传递和耗散,采用颗粒相大涡模拟方法（LESp）模拟颗粒脉动导致的能量耗散,同时考虑介观尺度对颗粒相压力的影响,建立了气体-颗粒LES-θ-LESp双流体模型,研究鼓泡流化床内气固两相流动的特性。数值模拟与文献实测颗粒速度和实测颗粒浓度结果具有相同的变化趋势。