二维鼓泡床内气液流动特性实验与数值模拟

采用高速摄像法测量了0.20 m×0.02 m×2.00 m拟二维床内气泡尺寸分布和流型等变化规律,结果表明,随着表观气速的增大,鼓泡床内依次呈现均匀鼓泡区、过渡区和湍动区3种形式,以气泡个数概率表示的气泡尺寸分布呈对数正态分布。以计算流体力学软件ANSYS CFX 10.0为平台,采用k-ε湍流模型和GRACE曳力模型对气液鼓泡床内流体动力学行为展开了数值模拟,其结果与实验值比较吻合。研究表明,从多相流理论出发的计算流体力学模拟方法可以用来预报鼓泡床内流型过渡等流体动力学特性。     

静电效应对有无埋管气固鼓泡床内气泡特性的影响分析

采用基于双流体模型(TFM)耦合静电模型的方法,研究颗粒的静电对有无埋管气固鼓泡床内气固流动特性和气泡特性的影响。首先在无静电场存在的条件下,利用双流体模型对自由鼓泡床和埋管鼓泡床内的流动情况进行模拟并与实验结果进行对比;进一步耦合静电模型,考察静电对自由鼓泡床和埋管鼓泡床内床层的整体性质和气泡特性的影响。研究结果表明,在无静电场条件下采用双流体模型能较好地预测自由鼓泡床和埋管鼓泡床内的气固流动状况以及气泡的平均直径和气泡的上升速度。埋管的存在使鼓泡床内气固流动发生强烈扰动,并使气泡的平均直径和气泡的上升速度均呈振荡分布。静电的存在对自由鼓泡床和埋管鼓泡床内床层的平均固含率影响不大,但对气泡分布规律影响较大,使得自由鼓泡床内气泡数目减少,而埋管鼓泡床下部区域的气泡分布比较集中,上部有大气泡出现。     

不同黏度下气液体系流体力学行为的PBM模拟

基于Eulef-Euler双流体模型,分别采用均一气泡尺寸和PBM方法对鼓泡床内气液两相流体系中的流体力学行为进行了数值模拟,经与实验结果比较表明,采用PBM方法获得的模拟结果更为准确,表明了PBM方法的优越性.采用PBM模型模拟了不同黏度气液体系中的流体力学行为,获得了包括平均及局部气含率分布、气泡尺寸分布,循环液速和大小气泡的空间分布等流体力学信息,并将模拟结果与相应操作条件下的实验结果进行了比较,吻合较好,说明PBM方法不仅可以用于鼓泡床反应器内气液两相流体系的模拟研究,还能对不同液相黏度下气液体系中的流体力学行为作出正确的预测和描述,为多相流反应器的设计和放大提供了有益的参考.     

鼓泡床中的气泡尺寸分布

根据气泡聚并和破裂速率模型,提出一个描述鼓泡床中气泡尺寸分布的总体平衡(Population Balance)模型。该模型可预计鼓泡床中气泡尺寸分布随床高的变化。对空气-水体系的模拟结果与实测结果吻合较好。     

基于DEM模拟的气固鼓泡床内流场间歇性及颗粒相干结构的分析

采用计算流体力学和离散元方法(CFD-DEM)对气固鼓泡床流动行为进行模拟研究,并基于模拟结果分析鼓泡床内气泡和颗粒微观运动特性。对颗粒速度的脉动能谱进行分析,发现鼓泡床流场中存在间歇性。通过对比鼓泡床不同轴、径向位置的颗粒脉动速度的平坦因子,发现鼓泡床内不同位置的流场间歇性不同,随着床层高度的增加,流场的间歇性减弱;在径向上,过渡区的流场间歇性明显大于边壁区和中心区。进一步采用连续小波分析方法揭示了相干结构(颗粒涡团)的分布以及演化过程,并分析了不同尺度下相干结构(颗粒涡团)的分布与鼓泡床内颗粒与气泡运动的关系。     

气液两相流摆动特性实验的数值模拟

为了给鼓泡塔反应器设计提供依据,运用计算流体力学(CFD)软件模拟了鼓泡塔气液两相流动态行为。采用双欧拉法对鼓泡塔矩形反应器内不同曝气量下气液两相流的摆动特性进行了模拟考察,液相采用标准κ-ε紊流模型,气相采用分散相零方程模型,分析了网格尺寸、时间步长以及相间作用力对模拟结果的影响,模拟的曝气量为42.5~237 m L/s。结果表明,当相间作用力仅考虑阻力时,气液两相流呈现周期性摆动规律;随着气流量的增加,气泡羽流的摆动幅度和频率增大,同时液体的气含率也在增加;模拟的气液两相流摆动频率数据与实验值吻合较好,两者的相对误差为7.2%~12.9%。     

新型洗涤冷却室内气液两相的分布特性

采用双头电导探针法对新型洗涤冷却室环隙鼓泡床内气液两相的局部气含率、气泡直径等分布规律进行了实验研究,并用Fluent商业软件对床层内气含率分布进行了模拟计算,模拟结果与实验结果吻合较好。研究结果表明：新型洗涤冷却室内部构件对环隙鼓泡床内气液两相的分布特性影响显著,气相分布更加均匀,液面波动更趋平稳,有效地减少了气体带水问题,相比国外技术具有更好的操作弹性。     

CFD-PBM耦合模型模拟气液鼓泡床的通用性研究

通过对不同操作压力和不同液体性质气液鼓泡床的模拟值与实验数据进行对比,从而验证CFD-PBM耦合模型的通用性。结果表明,CFD-PBM耦合模型在加入了气泡破碎修正因子后,可以很好地预测压力对鼓泡床流体力学行为的影响趋势,当压力升高时,气含率显著升高。不同液体黏度和表面张力条件下CFD-PBM耦合模型的模拟结果与实验结果均吻合较好。随液体黏度增大,气泡破碎速率减小,气泡尺寸分布变宽,曳力显著下降,气含率随之降低。随表面张力减小,气泡破碎速率增大,气泡变小,气含率升高。CFD-PBM耦合模型具有很好的通用性,原因在于考虑了压力、液体黏度和表面张力对气泡聚并、破碎和气液相间作用力的影响。     

加压鼓泡塔反应器中气液两相流CFD数值模拟

对加压气液鼓泡塔反应器内的气液两相流进行了二维数值模拟,模拟的压力为0.5～2.0 MPa,表观气速为0.120～0.312 m/s;模拟采用了Euler-Euler模型,并耦合了气泡群平衡模型（PBM）预测气泡尺寸,该模型考虑了气泡聚并与破碎对气泡的影响。液相湍流采用标准k-ε模型,两相间的作用力只考虑曳力。模拟获得了局部气含率、局部气/液相时均轴向速度及其径向分布等数据,并与实验结果进行比较。结果表明,局部气含率、局部气相速度模拟结果与实验结果吻合较好,局部液相速度径向分布特征模拟结果与文献结果相符。     

CFD-PBM耦合模型模拟气液鼓泡床的通用性研究

通过对不同操作压力和不同液体性质气液鼓泡床的模拟值与实验数据进行对比，从而验证CFD-PBM耦合模型的通用性。结果表明，CFD-PBM耦合模型在加入了气泡破碎修正因子后，可以很好地预测压力对鼓泡床流体力学行为的影响趋势，当压力升高时，气含率显著升高。不同液体黏度和表面张力条件下CFD-PBM耦合模型的模拟结果与实验结果均吻合较好。随液体黏度增大，气泡破碎速率减小，气泡尺寸分布变宽，曳力显著下降，气含率随之降低。随表面张力减小，气泡破碎速率增大，气泡变小，气含率升高。CFD-PBM耦合模型具有很好的通用性，原因在于考虑了压力、液体黏度和表面张力对气泡聚并、破碎和气液相间作用力的影响。     

Coalescence efficiency of bubbles in bubble columns

Bubble size distribution was modelled by employing the population balance equation (PBE). All three bubble coalescence mechanisms (turbulence, buoyancy and laminar shear) and the main bubble breakup mechanism (breakup due to turbulent eddies) were considered in the model. Local bubble size distributions at the top and bottom of the column were obtained by solving this PBE. The results were compared with the experimental data for seven independent multiphase systems (water/air, isomax diesel/air, kerosene/air and four other liquid mixture/air) at two diverse gas velocities. The experimental adjustable constant in the coalescence efficiency function was determined by fitting the population balance to the experimental bubble size distributions. An empirical correlation was proposed for the coalescence efficiency by the dimensional analysis, which includes Reynolds and Weber numbers. © 2011 Canadian Society for Chemical Engineering     

鼓泡塔中气泡尺寸分布和局部气含率研究

在内径为0.38 m的鼓泡塔中采用双电导探针法对不同通气速率下的气泡尺寸分布和局部气含率进行了实验研究,分析了气泡尺寸的概率密度分布。结果表明:气泡尺寸随轴向高度的增加而增大,随径向距离增加而减小;鼓泡塔中气液流动可分为过渡流域和充分发展流域,在过渡流域气含率随轴向高度增加而增大,在充分发展流域气含率趋于均值,径向局部气含率分布呈抛物线型下降。高气速下气泡尺寸概率密度分布比低气速下宽,且随轴向高度的增加分布变宽。     

Local hydrodynamics modeling of a gas–liquid–solid three-phase bubble column

A three-dimensional (3D) transient model was developed to simulate the local hydrodynamics of a gas–liquid–solid three-phase bubble column using the computational fluid dynamic method, where the multiple size group model was adopted to determine the size distribution of the gas bubbles. Model simulation results, such as the local time-averaged gas holdups and axial liquid velocities, were validated by experimental measurements under varied operating conditions, e.g., superficial gas velocities and initial solid loadings at different locations in the three-phase bubble column. Furthermore, the local transient hydrodynamic characteristics, such as gas holdups, liquid velocities, and solid holdups, as well as gas bubble size distribution were predicted reasonably by the developed model for the dynamic behaviors of the three-phase bubble column. © 2007 American Institute of Chemical Engineers AIChE J, 2007     

Hydrodynamics and simulation of air–water homogeneous bubble column under elevated pressure

A gas–liquid Eulerian computational fluid dynamics (CFD) model coupled with a population balance equation (PBE) was presented to investigate hydrodynamics of an air–water bubble column (1.8 m in height and 0.1 m in inner diameter) under elevated pressure in terms of pressure drop, gas holdup, mean bubble size, and bubble surface area. The CFD-PBE model was modified with three pressure correction factors to predict both the total gas holdup and the mean bubble size in the homogeneous bubbly flow regime. The three correction factors were optimized compared to experimental data. Increasing the pressure led to increasing the density, reducing the bubble size, and increasing the gas holdup. The bubble size distribution moved toward a smaller bubble size, as the pressure increased. The modified CFD-PBE model validated with experimental data and empirical models represented well hydrodynamics of the bubble column at P = 0.1, 1.5, and 3.5 MPa.     

PDA measurements in a three‐phase bubble column

Phase Doppler anemometry was used to quantify the flow characteristic of a three phases (liquid, solid, and bubbles) cylindrical bubble column driven by a point air source made of a 30‐mm diameter perforated air stone centrally mounted at the bottom. The cylindrical bubble column had an inner diameter of 152 mm and was filled with liquid up to 1 m above the point source. Acrylic beads with a nominal diameter of 3 mm were used as the solid phase. To match the density of the solid phase which was 1.05 kg/m³, the liquid density was raised to about 1.0485 kg/m3 by added salt. The bubble diameters generated were within the range of 600–2400 µm. The detailed turbulent characteristics of the liquid‐phase velocity, bubble diameter, bubble velocity, and solid velocity were measured at three different air rates, namely 0.4, 0.8, and 1.2 L/min (corresponding to average gas volume fraction of 0.0084, 0.0168, and 0.0258, respectively) for the homogeneous bubble column regime. With the addition of the solid phase, the flow field was found to be relatively steady compared to the two‐phase column referencing the probability density functions for both the liquid and bubble velocities. An analysis based on the determination of the drag forces and transversal lift forces was performed to examine the flow stability in the three‐phase bubble column. The analysis illustrated that how the added solid phase effectively stabilized the flow field to achieve a steady circulation in the bubble column and a generalized criterion for the flow stability in the three‐phase bubble column was derived. Further investigation for the transition and the heterogeneous bubble column regime with air rates at 2.0 and 4.0 L/min shown that this criterion can also be used as a general prediction of flow stability in this three‐phase bubble column. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2286–2307, 2013     

鼓泡塔反应器气液两相流CFD数值模拟

对圆柱形鼓泡塔反应器内的气液两相流动进行了三维瞬态数值模拟,模拟的表观气速范围为0.02～0.30 m•s^-1; 模拟采用了双流体模型,并耦合了气泡界面密度单方程模型预测气泡尺寸,该模型考虑了气泡聚并与破碎对气泡尺寸的影响。液相湍流采用考虑气相影响的修正k-ε模型,两相间的动量传输仅考虑曳力作用。模拟获得了轴向气/液相速度分布、气含率分布、湍流动能分布以及气泡表面面积密度等,对部分模拟结果与实验值进行了定量比较,结果表明模拟结果与实验结果吻合较好。     

Bubble size distribution in bubble columns

The bubble size distributions are measured for the air-water system as a function of air velocity at room temperature in two bubble columns. High speed cinephotography and fiber optic probe techniques are used to measure the bubble size. Our limited measurements suggest that the bubble size may be independent of gas velocity in the range 3.6 to 9.2 cm/s and may be dependent on column diameter with smaller bubbles for narrower columns. The bubble size appears to be smaller at the column wall than at distances away from the wall.     

PX氧化鼓泡塔反应器内的TA浓度分布

利用新建的D476鼓泡塔冷模实验装置和沉降—扩散模型对工业鼓泡塔PX氧化反应器内的TA浓度分布进行了实验和数学模拟研究。结果表明,由于PX氧化气速较大,塔内TA浓度接近均匀分布。     

Prediction of hydrodynamic behaviour in bubble columns

A simple theoretical model is used to describe hydrodynamic behaviour in bubble columns. The model is based on an energy balance which takes into account the energy dissipation in the liquid motion and the energy dissipation at the gas–liquid interface. Gas hold-up, liquid velocity at the column axis and radial profile of liquid velocity are predicted in a wide range of operating conditions (J_G up to 1·452 m s⁻¹) and column sizes (D = 0·1–1 m and H = 1·22–9·5 m) with good accuracy. Predictions of liquid velocity are also compared with one of the most widely accepted models.