溶气气浮池气液两相流二维数值模拟

采用计算流体力学软件FLUENT对溶气气浮池进行了二维数值模拟,分别对液相单相流动和气液两相流动进行了研究。模拟采用了RNG k-ε湍流模型,气液两相流的模拟采用了欧拉模型。计算得到了溶气气浮池内液相流场情况和气相在溶气气浮池内的体积分数分布,模拟结果与实验结果符合。     

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.     

底吹气连铸中间包内气液两相流的数值模拟

以宝钢集团梅山钢厂1台连铸中间包为原型,进行底吹气中间包水模型研究. 实测结果表明,底吹气在中间包内形成"鼓泡流"形式的流动结构;"鼓泡流"的形成一方面能够破坏中间包内"层流"形式的短路流动,增强混合,另一方面能在中间包内形成"气幕挡墙",有利于夹杂物去除. 针对中间包内气-液两相"鼓泡流"特征,建立了底吹气中间包内气-液两相欧拉多流体模型,模型中考虑了气泡的存在对湍流增强的影响,考虑了相间滑移、气泡浮力及湍流分散力. 采用所建立的模型对底吹气中间包内气液两相流动和混合特性进行了模拟和分析,结果与水模型实测结果一致.     

分解炉内气固两相流动特性的数值模拟

采用Eulerian—Eulerian气固两相双流体模型、大涡模拟方法模拟气相湍流流动、颗粒动力学理论模拟颗粒相流动,数值模拟分解炉内气固两相流体的动力特性。用小波分析方法研究分解炉内气固两相湍流特性。在分解炉中心区域形成高浓度-高速度的上升颗粒流、在壁面区域形成高浓度、低速度的下降颗粒流,构成颗粒的内循环流动。     

柱式膜组件曝气过程的气液两相流模拟

采用欧拉模型与多孔介质模型对柱式膜组件的曝气过程中气液两相流进行了计算模拟,研究了曝气量、曝气孔数目以及相对位置对膜组件的气液两相分布、流体湍流黏度、液体速度场的影响,模拟数据与实验数据吻合良好。研究结果表明:随着曝气孔数目增加与相对位置均匀排布使得膜组件内气液两相分布更加均匀;湍流黏度随着曝气量增大而增大,当曝气量达到5 m~3×h~(-1)时,湍流黏度不再增加;随着曝气孔数目增加与相对位置的均匀排布使得液体形成较多涡流流动与循环流动。增加曝气孔数目与优化曝气孔相对位置能够有效提高组件内部流场的均匀分布,有利于膜丝的清洗。     

直接模拟蒙特卡罗方法研究循环流化床内颗粒聚团的流动

采用直接模拟蒙特卡罗方法(DSMC)模拟颗粒间的碰撞,用Lagrangian方法计算颗粒的运动.采用考虑颗粒脉动流动对气相湍流流动影响的大涡模拟(LES)研究气相湍流.数值模拟垂直管道内气固两相上升流动,对管内气相速度和颗粒相速度、浓度,以及聚团流动进行分析,得到气固两相上升流中颗粒流动的有关信息.     

渣油加氢沸腾床的多相流流动特性模拟

采用欧拉-欧拉-欧拉三相流模型,对STRONG沸腾床渣油加氢反应器进行了二维冷模多相流动过程模拟。其中液-固相间作用力采用Syamlal-O’Brien模型,气-液相间作用力采用Schiller-naumann模型,忽略气固之间的作用力。由气含率、液含率、固含率云图随时间的变化,可以看出催化剂在气液两相的作用下,逐渐实现了流化;在三相分离器的作用下,气相、液相、固相实现了分离,气相富集在三相分离器上端,液相从侧出口流出,固相在流化床内实现了循环利用。同时模拟结果表明,三相分离器分离效果理想,但是在局部截面积较小和结构复杂地方会出现局部湍流,不利于分离的进行。     

气液固三相湍流流动的E/E/L模型与模拟

采用基于双流体模型与粒子分散模型相结合的方法 ,建立了一个用于描述气液固三相湍流流动的Eulerian/Eulerian/Lagrangian模型 (简称E/E/L模型 ) .在Euler坐标系中考虑了气液两相 ,利用双流体模型来表述气液两相的相互关系 ;同时在Lagrange坐标系中考察了颗粒的运动 ,并把颗粒对气液两相的影响耦合于双流体模型中 .以流化床内气液固三相湍流流动为例进行的数值模拟结果与实验结果吻合良好 .所提出的模型及其模拟具有很好的准确性和可靠性 ,为研究气液固三相湍流流动提供了一种新的途径     

亚格子湍动能模型及循环流化床气固湍流特性分析

以气相大涡-颗粒相二阶矩双流体模型为框架,基于单相流亚格子湍动能推导方法,考虑固相影响推导气相亚格子湍动能方程,建立了适用于气固两相流动的气相亚格子湍动能模型;同时考虑气相亚格子湍动能与颗粒相速度脉动二阶矩之间的脉动能量传递,补充了气固相间脉动能量作用模型。模拟了循环流化床内气固两相湍流流动过程,模拟结果与实验数据吻合较好,并较未考虑湍流模型的模拟结果更接近实验值。比较了不同亚格子湍流模型对颗粒运动的影响,与Smagorinsky亚格子涡黏模型相比,亚格子湍动能模型能够更好地模拟两相流的湍流特性。分析了气体表观速度对湍流作用的影响。研究表明,随着气体表观速度的增加,气相亚格子湍动能和亚格子能量耗散逐渐增加,径向分布的非均匀性增强。     

气液逆流洗涤器内两相流场的实验研究与数值模拟

采用RNG k-ε湍流模型和欧拉双流体多相流模型模拟了气液逆流接触洗涤器内的两相流场,将计算结果用实验验证.通过考察两相流速、湍流强度、压降、气含率等参数验证了模型的可靠性,对不同喷嘴结构和操作条件下的泡沫区流场特性进行了模拟分析.结果表明,气液撞击形成的泡沫区湍流强度高,气液两相径向与切向速度较大,轴向速度较小,可用湍流强度大小表征泡沫区的大小.泡沫区占整个洗涤器的体积分数β随气液质量流量比增大先增大后减小,气液质量流量比为0.0096时达峰值;随进液轴/切流量比增大β先增大后减小,流量比为0.66时达峰值.喷口直径为8 mm、切向进液倾斜角为60°时气液传质效果最好.     

气泡大小对反应器内氧传递系数的影响

在气液反应过程中,气泡的大小对结果往往起了决定性的作用。通过减小气泡的尺寸,可以促进气液传递,加快反应的进程。在气液搅拌式反应器上安装了一种特殊的气体分布器,通过搅拌产生离心场,从而诱导生成泰勒涡柱,使大量进入反应器的空气气泡保持在泰勒涡柱的内部。由于减少了气泡间的凝并作用,气泡尺寸减小,与对照组相比,反应器中最小的气泡尺寸减小了近50%,气泡的比表面积增加近80%。通过对不同通气流量和搅拌速度下气液反应器内氧传递系数的测量,与对照实验比较,使用特殊气体分布器的反应器中,氧的传递系数增加了10%~40%,证明这种气体分布器确实可以增加气液间氧的传递。     

Model validation for low and high superficial gas velocity bubble column flows

In the present work, gas-liquid flow dynamics in a bubble column are simulated with CFDLib using an Eulerian-Eulerian ensemble-averaging method in a two-dimensional Cartesian system. The two-phase flow simulations are compared to experimental measurements of a rectangular bubble column performed by Mudde et al. [1997. Role of coherent structures on Reynolds stresses in a 2-D bubble column. A.I.Ch.E. Journal 43, 913-926] and a cylindrical bubble column performed by Rampure et al. [2003. Modeling of gas-liquid/gas-liquid-solid flows in bubble columns: experiments and CFD simulations. The Canadian Journal of Chemical Engineering 81, 692-706] for low and high superficial gas velocities, respectively. The objectives are to obtain grid-independent numerical solutions using CFDLib to reconcile unphysical results observed using FLUENT with increasing grid resolutions [Law, D., Battaglia, F., Heindel, T.J., 2006. Numerical simulations of gas-liquid flow dynamics in bubble columns. In: Proceedings of the ASME Fluids Engineering Division, IMECE2006-13544, Chicago, IL], and to validate computational fluid dynamics (CFD) simulations with experimental data to demonstrate the use of numerical simulations as a viable design tool for gas-liquid bubble column flows. Numerical predictions are presented for the local time-averaged liquid velocity and gas fraction at various axial heights as a function of horizontal or radial position. The effects of grid resolution, bubble pressure (BP) model, and drag coefficient models on the numerical predictions are examined. The BP model is hypothesized to account for bubble stability, thus providing physical solutions.     

分布器对鼓泡塔中气泡直径分布的影响

采用电导探针测定了冷态鼓泡塔中不同气速下的气泡直径及气含率的轴向分布,考察了分布板对鼓泡塔操作性能的影响.结果表明:随着开孔率的减小,从均匀鼓泡区到过渡区的转变提前;在均匀鼓泡区,开孔率对气泡直径影响较小;在过渡区,开孔率大的分布器形成的稳定气泡直径较小、气含率较大;分布板开孔直径越大,形成的初始气泡直径越大,但对轴向气泡直径分布的影响仅限于分布器区.包含分布器影响的气泡直径经验关联式为d/D=140.2Bo-0.5Ga-0.12Fr0.099(h/D)-0.15T-0.34(0.5 cm/s＜ug＜7 cm/s).     

气泡-液体闭式射流的大涡与二阶矩模拟

The Large-eddy simulation (LES) with two-way coupling is used to study bubble-liquid two-phase confined multiple jets discharged into a 2D channel.The LES results reveal the large-eddy vortex structures of both liquid flow and bubble motion,the shear-generated and bubble-induced liquid turbulence,and indicate much stronger bubble fluctuation than that of the liquid,the enhancement of liquid turbulence by bubbles.Both shear and bubble-liquid interaction are important for the liquid turbulence generation in the case studied.     

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。     

多级鼓泡塔内液体速度分布的实验研究

液体循环流动是多级鼓泡塔重要流体力学特征之一,文中在内径为282 mm,高2000 mm的鼓泡塔内,采用不同类型的筛板将普通鼓泡塔分割成双级气液鼓泡塔.采用Pavlov管测液速的方法考察了不同筛板、不同表观气速下该鼓泡塔中上下二侧的液体速度分布.根据实验结果得出了液体速度在塔中心处最大,且与表观气速有关,随着表观气速的...     

气液鼓泡床泡罩式气体分布器流场的CFD模拟

采用ANSYS FLUENT商用CFD软件对气液鼓泡床内泡罩式气体分布器单体进行了数值模拟。以Ug=12.34m/s的入口速度对计算模型进行单相三维稳态模拟。研究了泡罩内径、泡罩齿片和入口管开孔分别对塔内不均度和泡罩式气体分布器的压降影响规律。研究表明,随着泡罩内径的增加,塔内不均度和分布器压降减小;泡罩齿片加宽,齿片对气体的阻力增加;齿片间距增加,齿片对气体的阻力减小;入口管开孔数对塔内不均度没有任何影响。开孔数很少时,开孔数量的增加使分布器的压降减小,然而开孔数增加到一定数量时,开孔数对分布器的压降影响甚微。对泡罩式气体分布器进行了结构优化。     

Chemical absorption in a bubble column loading concentrated slurry

Carbon dioxide was absorbed into aqueous slurries of magnesium hydroxide or calcium hydroxide particles in a bubble column at 308 K and 0.1013 MPa. The volumetric mass transfer coefficient and the effective gas-liquid interfacial area were obtained separately by these absorption experiments. It was found that the liquid-side physical mass transfer coefficient as well as the effective gas-liquid interfacial area decrease with increasing the slurry concentration and that there is an optimal point of fine reactant particle concentration where the chemical absorption rate has its maximum value. The process of gas absorption into slurry in a bubble column was formulated by a film-theory model incorporating a finite dissolution rate of solid particles. The observed absorption rates of carbon dioxide into calcium hydroxide slurries in the bubble column were successfully predicted by the proposed model.     

Experimental investigation on flue gas purification and gas-liquid multiphase flow in a spraying column with perforated plate

The synergetic removal of sulphur dioxide and particulate matters (PM) in flue gas was investigated in a spraying column equipped with flow pattern controlling (FPC) internals. The performance of the novel column was compared with that of the traditional open column by monitoring the removal efficiency and system pressure drop. To understand the gas-liquid multiphase flow field and mass transfer process inside the column with different structures, image processing based on the Otsu method and particle image velocimetry (PIV) technology were used. It was found that the FPC column with a section size of 200 mm × 200 mm, hole diameter of 4 mm, and aperture ratio of 0.65 demonstrated the best performance. As clearly observed from the flow filed, bubble flow was formed in FPC column, while the dispersive and falling-film flow was developed in the open column. The liquid holdup in FPC unit was much more than in the open spraying column, which enhanced the mass transfer process. According to the PIV results, the reverse flow of the liquid, caused by the gas jet ascribed to the perforated plate and the confined space in the FPC unit, was the primary reason for bubble generation and the gas-liquid flow pattern in the column.     

Mathematical modeling of gas-liquid mass transfer rate in bubble columns operated in the heterogeneous regime

In this paper, a multi-scale approach is followed to study gas-liquid mass transfer in bubble columns. First, a single bubble of equivalent diameter d is considered. Its morphology and its gas to liquid relative velocity are related to the bubble diameter through the use of known correlations. Then, the gas-liquid mass transfer between the bubble and the surrounding liquid is studied theoretically. An equation describing the transport of the transferred species in the viscous boundary layer around the bubble is solved. In a second step, a bubble column of 6-10 m height is studied experimentally. The gas phase in the column is characterized experimentally by means of a gammametric technique. Finally, the two studies are linked, yielding a 1D mathematical model able to predict the gas-liquid mass transfer rate in a bubble column operated in the heterogeneous regime.