基于EMMS方法的鼓泡塔反应器CFD及群平衡模拟

能量最小多尺度(energy-minimization multi-scale,EMMS)方法已经被应用于气液体系中群平衡(population balance model,PBM)模型的改进。EMMS模型可计算气泡破碎聚并过程的能量,进而获得聚并速率的修正因子。应用这一模型对高气速鼓泡塔进行了模拟计算,并进一步对比了均一尺径模型、CFD-PBM模型以及CFD-PBM-EMMS模型的模拟结果与实验数据。结果表明,在高表观气速条件下,基于EMMS方法的群平衡模型可以更加准确地预测鼓泡塔中不同高度的气泡尺径分布和轴向液速,同时提高了对整体气含率和局部气含率的模拟准确性。在表观气速为0.16 m·s~(-1)和0.25 m·s~(-1)时,CFD-PBM-EMMS模型对气泡尺径分布的预测精度更高,同时整体气含率模拟的相对误差下降为5%和15%,局部气含率模拟平均相对误差下降为8%和17%。     

基于气泡群相间作用力模型的加压鼓泡塔流体力学模拟

目前,多数文献报道了冷态加压湍动鼓泡塔内流动特征,并且通过实验数据回归相关经验关联式。然而,此类关联式适用范围有限,难以直接外推到工业鼓泡塔反应器条件。因此,在FLUENT平台上建立了基于气泡群相间作用力的、动态二维加压鼓泡塔计算流体力学模型。通过数值模拟考察了操作压力为0.5~2.0 MPa,表观气速为0.20~0.31 m·s^-1,内径0.3 m鼓泡塔内流场特性参数分布,并且与冷态实验数据进行比较。结果表明,采用修正后的气泡群曳力模型、径向力平衡模型以及壁面润滑力模型描述气泡群相间作用力,能够较为准确地反映平均气含率和气含率径向分布随操作压力和表观气速变化的规律。     

采用电阻层析成像技术测量气液加压鼓泡塔局部气泡参数

在内径0.3 m,高6.6 m的加压气液鼓泡塔反应器中,采用电阻层析成像技术(ERT)研究了空气-水体系中气泡群平均上升速度、局部气含率及其径向分布。在表观气速0.119~0.312 m s 1,压力0.5~2.0 MPa,考察了表观气速、压力对气泡群上升速度、局部气含率及其径向分布的影响。实验结果表明,鼓泡塔中局部气含率随着表观气速与压力的增大而增大,其径向分布呈现出中心高边壁低的分布特征,但整个截面的分布并非严格对称,在r/R=0~0.3,气含率变化较小,且极大值出现在该范围内;气泡群的局部上升速度随着表观气速的增大而增大,但是随着压力的增大而减小。     

加温加压下CFD-PBM耦合模型空气-水两相流数值模拟研究

计算流体力学与群体平衡模型（CFD-PBM）结合可有效地模拟鼓泡塔内流体行为,较准确地预测流场、相含率以及局部气泡尺寸分布。以直径100 mm、高1.3 m的加温加压鼓泡塔为模拟对象,在系统压力为1 MPa、表观气速为0.08~0.24 m/s、温度为30~160℃条件下系统地考察了空气-水体系的表观气速、温度以及固含率对平均气含率、大小气泡气含率、气泡直径和气泡尺寸分布等参数的影响。结果表明,平均气含率的模拟结果和实验值在10%的误差范围内吻合较好;温度的变化主要影响了塔内气泡的聚并和破碎,并用聚并破碎的机理解释了温度对其流体行为的影响。     

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。     

鼓泡塔中离子液体-空气两相流的CFD-PBM耦合模拟

针对咪唑类离子液体介质,采用Euler-Euler双流体模型与群平衡模型（PBM）耦合的方法,引入由实验结果拟合获得的适用于该介质的气液相间曳力系数模型,对内径0.203 m、高2 m的鼓泡塔中离子液体-空气两相流进行计算流体力学模拟,研究了不同表观气速下塔内气液两相速度场分布、气含率和气泡尺寸分布等流体动力学性质。与现有的相间曳力系数模型Schiller-Naumann模型模拟结果对比,采用本文模型得到的气含率与实验值吻合更好,气泡尺寸分布与实验结果一致。     

基于径向力平衡的鼓泡塔二维流体力学模型

提出了一种鼓泡塔二维轴对称流体力学模型,模型中将气泡所受的升力以及湍动扩散力作为形成塔内气含率稳定分布的主要机制.采用Fluent 6.3流体力学软件求解模型,能得到稳定的二维流场,气含率与液速分布与实验值吻合良好,模型能准确反映表观气速(0.12～0.62 m·s^-1)以及塔径(ø200 mm、ø500 mm、ø800 mm)对流型的影响.利用该模型对更大直径鼓泡塔的流动参数进行了预测,结果与文献给出的经验关联式相符.     

基于气泡群相间作用力模型的加压鼓泡塔流体力学模拟

目前,多数文献报道了冷态加压湍动鼓泡塔内流动特征,并且通过实验数据回归相关经验关联式。然而,此类关联式适用范围有限,难以直接外推到工业鼓泡塔反应器条件。因此,在FLUENT平台上建立了基于气泡群相间作用力的、动态二维加压鼓泡塔计算流体力学模型。通过数值模拟考察了操作压力为0.5~2.0 MPa,表观气速为0.20~0.31 m·s~(-1),内径0.3 m鼓泡塔内流场特性参数分布,并且与冷态实验数据进行比较。结果表明,采用修正后的气泡群曳力模型、径向力平衡模型以及壁面润滑力模型描述气泡群相间作用力,能够较为准确地反映平均气含率和气含率径向分布随操作压力和表观气速变化的规律。     

含垂直列管束内构件鼓泡塔的CFD模拟

针对含有密集垂直列管束内构件的气液鼓泡塔,在两相Euler二维轴对称k-ε模型中,分别考虑气相和液相受到的列管阻力。通过引入相应的动量源、湍动源以及耗散源建立带列管内构件的鼓泡塔二维CFD模型。模型能清晰、准确地描述带列管束鼓泡塔中气液流动的特征:"烟囱效应"以及分布器影响区延长。计算得到的气含率以及液速的二维分布在宽泛的表观气速(0.12～0.62 m·s^-1)范围内与实验值相符。     

喷淋散射塔鼓泡区域的气液两相流动特性

为了探究喷淋散射脱硫塔鼓泡区域的气液两相流动特性,搭建了鼓泡塔实验台,在不同表观气速和气体分布器浸没深度的条件下进行了实验。实验结果表明:气体分布器表面形成的气泡直径约12 mm;气泡溢出液面时有小气泡形成,并随着返混的液相运动,且液相的返混剧烈程度与表观气速和气体分布器浸没深度正相关;液相在散射管管壁和鼓泡池壁面间形成大尺度循环;随着表观气速增大,气泡直径和气泡运动速度均增大,使得气含率增大,气液两相湍动加剧;随着气体分布器浸没深度增大,鼓泡床床层气含率降低,表观气速对气含率的影响效果减弱。实验结果对喷淋散射脱硫塔的设计和运行有一定参考价值。     

Effects of Orifice Orientation and Gas-Liquid Flow Pattern on Initial Bubble Size

In many gasliquid processes, the initial bubble size is determined by a series of operation parameters along with the sparger design and gasliquid flow pattern. Bubble formation models for variant gasliquid flow pat terns have been developed based on force balance. The effects of the orientation of gasliquid flow, gas velocity, liquid velocity and orifice diameter on the initial bubble size have been clarified. In ambient airwater system, thesultable gasllquid flow pattern is important to obtain smaller bubbles under the low velocity liquid crossflow con ditions with stainless steel spargers. Among the four types of gasliquid flow patterns discussed, the horizontal orifice in a vertically upward liquid flow produces the smallest initial bubbles. However the orientation effects of gas and liquid flow are found tobe insgnifican whenliq.uid velocity is.higher than. 3.2 m;sa or theorifice diameter is small enough.     

顶部浸没竖直向下平口管口气泡膨胀脱离特性

利用高速摄像机拍摄顶部浸没竖直向下管口气泡膨胀及脱离演变过程,对比分析管径、平均气速对气泡尺寸、形成时间的影响规律。引入泡龄k表征管口气泡位置特性,用椭球形气泡长短轴比L表征气泡形状特征。研究发现,气泡生成机理有间歇生成气泡、含抽吸间歇生成气泡和连续生成气泡3种;气泡脱离直径随平均气速变化过程明显存在气泡脱离形态转变点;气泡膨胀脱离模式随平均气速变化分为单个气泡形成、气泡聚并形成两种。平均气速为3.1 m·s^-1时管口处存在抽吸现象,此时最大泡龄k_max最小;脱离阶段气泡长短轴比L随脱离时间变化过程明显存在时间分界点。在分界点前,L值在2.0附近波动,气泡主要以椭球形存在。分界点后,L值明显增加,气泡形状向扁椭球体发展。     

垂直惰性阳极铝电解槽内的析气行为

垂直惰性阳极铝电解槽内,析气行为会影响氧化铝浓度分布和电流效率。利用新设计的透明电解槽进行了电解试验,观察了大尺寸惰性阳极气泡的析出及逸出过程。试验结果表明：在阳极底掌下,气泡进行周期性的生长、长大、并聚和脱离,但大尺寸阳极上气泡的滑动和并聚过程与小尺寸阳极上的不同。阳极工作面上则形成了气泡群,新形成的气泡迅速脱离。紧贴着阳极的气泡运行速度慢,外层的气泡运动速度快。所有气泡最终都经液面逸出,大部分气泡到达液面时立即逸出,少部分未及时逸出的气泡随着电解质做一段水平运动后才逐步逸出。测量到的惰性阳极的气泡运动速度为0.006~0.445 m·s^-1,底部的气泡运动速度分布范围宽,然而,受电解质的限制,中上部的范围窄。     

Effects of internals on phase holdup and backmixing in a slightlyexpanded-bed reactor with gas-liquid concurrent upflow

Five different internals were designed, and their effects on phase holdup and backmixing were investigated in a gas-liquid concurrent upflow reactor where the spherical alumina packing particles of three diameters (3.0, 4.5 and 6.0 mm) were slightly expanded under the conditions of varied superficial gas velocities (6.77×10^-2-3.61×10^-1 m·s^-1) and superficial liquid velocities (9.47×10^-4-2.17×10^-3 m·s^-1). The experimental results show that the gas holdup increases with the superficial gas velocity and particle size, opposite to the variational trend of liquid holdup. When an internal component is installed amid the upflow reactor, a higher gas holdup, a less liquid holdup and a larger Peclet number characterizing the weaker backmixing are obtained compared to those in the bed without internals under the same operating conditions. Additionally, the minimal backmixing is observed in the reactor equipped with the internals with a novel multi-step design. Finally, empirical correlations were proposed for estimating gas holdup, liquid holdup and Peclet number with the relative deviations within 11%, 12% and 25%, respectively.     

Influence of impeller diameter on overall gas dispersion properties in a sparged multi-impeller stirred tank☆

The impeller configuration with a six parabolic blade disk turbine below two down-pumping hydrofoil propellers, identified as PDT + 2CBY, was used in this study. The effect of the impeller diameter D, ranging from 0.30T to 0.40T (T as the tank diameter), on gas dispersion in a stirred tank of 0.48 m diameter was investigated by experimental and CFD simulation methods. Power consumption and total gas holdup were measured for the same impeller configuration PDT + 2CBY with four different D/T. Results show that with D/T increases from 0.30 to 0.40, the relative power demand (RPD) in a gas–liquid system decreases slightly. At low superficial gas velocity V_S of 0.0078 m·s^-1, the gas holdup increases evidently with the increase of D/T. However, at high superficial gas velocity, the systemwith D/T=0.33 gets a good balance between the gas recirculation and liquid shearing rate, which resulted in the highest gas holdup among four different D/T. CFD simulation based on the two-fluid model along with the Population Balance Model (PBM) was used to investigate the effect of impeller diameter on the gas dispersion. The power consumption and total gas holdup predicted by CFD simulation were in reasonable agreement with the experimental data.     

Experimental and numerical investigations of scale-up effects on the hydrodynamics of slurry bubble columns

Experiments and simulations were conducted for bubble columns with diameter of 0.2 m(180 mm i.d.), 0.5 m(476 mm i.d.) and 0.8 m(760 mm i.d.) at high superficial gas velocities(0.12–0.62 m·s-1) and high solid concentrations(0–30 vol%). Radial profiles of time-averaged gas holdup, axial liquid velocity, and turbulent kinetic energy were measured by using in-house developed conductivity probes and Pavlov tubes. Effects of column diameter, superficial gas velocity, and solid concentration were investigated in a wide range of operating conditions. Experimental results indicated that the average gas holdup remarkably increases with superficial gas velocity, and the radial profiles of investigated flow properties become steeper at high superficial gas velocities. The axial liquid velocities significantly increase with the growth of the column size, whereas the gas holdup was slightly affected. The presence of solid in bubble columns would inhibit the breakage of bubbles, which results in an increase in bubble rise velocity and a decrease in gas holdup, but time-averaged axial liquid velocities remain almost the same as that of the hollow column. Furthermore, a 2-D axisymmetric k–ε model was used to simulate heterogeneous bubbly flow using commercial code FLUENT 6.2. The lateral lift force and the turbulent diffusion force were introduced for the determination of gas holdup profiles and the effects of solid concentration were considered as the variation of average bubble diameter in the model. Results predicted by the CFD simulation showed good agreement with experimental data.