球形气泡界面变化对尾涡性质和尺寸的影响

利用计算流体力学法研究了中等Reynolds数下(25≤Re≤500)气泡界面污染程度对其尾流的影响。借鉴圆球绕流和停滞帽模型,提出了一种模拟中等Reynolds数下受污染球形气泡尾流的三维模型,气泡界面污染程度取决于帽角(θ)的大小,帽角越大表示气泡表面污染程度越小。研究发现:Re=25~200时,污染程度的减小会减小尾涡长度(s)、分离角(φ)以及涡中心位置(l)和(h)的数值,但不会改变其与Reynolds数表征的关系;污染程度的减小会使Re=250~500时尾涡的三维特性减弱,使Re=350时有序脱落的尾涡的强度减小并最终使其不发生脱落,使Re=500时无规律脱落的尾涡的无序性减弱并最终使其不发生脱落。     

析气界面上的气泡生长速率

析气界面上的气泡生长速率李新海，陈新民，莫鼎成，刘今（中南工业大学化学系长沙４１００８３）关键词气泡，界面，气泡生长１前言液体中，可以由外界鼓入气体，在气体导管出口即喷咀上形成气泡，也可以由气体物质过饱和的溶液中自动成核，生成气泡。对这两种气泡的成泡...     

界面纳米气泡研究历史和展望

界面科学研究因其在工业、农业、环境和催化等领域的重要性一直是国内外科学工作者非常关注的领域.固液界面纳米气泡的发现和研究是近20年来科学界的一匹"黑马",它的存在颠覆了人们的认知,以超乎常人想象的效果在水处理、农业、矿物浮选、界面输运和清洗等领域表现出色,成为国内外相关领域的研究热点.该综述对界面纳米气泡的研究历史、产...     

析气界面上气泡滑移促进的传质模型探索

本文在充分研究析气界面上气泡行为的基础上，根据界面上析出气泡的动力学行为，结合界面附近流体及相间传质理论。导出了气泡滑移促进的传质模型     

流经突然扩张的微通道的单气泡界面形态演变的数值模拟

采用界面追踪方法(FTM)研究了狭窄通道内受浮力上升的单气泡经过突然扩张通道时的运动形态,考察了狭窄通道和宽阔通道的通道宽度比及Eotvos数(Eo)和Morton数(Mo)对气泡形态和上升速度的影响. 结果表明,在狭窄通道、扩张部位和宽阔通道内气泡形态呈不同特性,气泡在离开扩张处时高宽比最大. 随通道宽度比增大,气泡最大高宽比减小. Eo数较小时,减小Mo数,气泡高宽比减小,气泡上升速度增大;增大Eo数,气泡上升时形变更严重. 改变初始时刻气泡相对于狭窄通道的位置对气泡形态有影响,初始位置靠近单侧壁面时,气泡横向变形较严重,在两侧壁面之间摆动上升.     

界面活性二氧化硅纳米球稳定气泡性能研究

用辛基三甲氧基硅烷对SiO2纳米球(SN)表面进行功能化修饰,制得了具有界面活性的SiO2材料(SN-C8-n,n=0.3,0.6,0.9和1.2),并将其作为起泡剂稳定气泡。研究了硅烷偶联剂的嫁接量、SN-C8-0.6的用量、NaCl的质量浓度及温度对气泡的影响。结果表明,当硅烷嫁接量为0.6 mmol/g,且将0.2 g SN-C8-0.6加入到2 mL质量浓度为0.05 g/m L的Na Cl水溶液中时,起泡性能最好且在25℃气泡可稳定72 h以上。     

单个运动气泡近界面浓度场的研究

对单个气泡传质的近界面浓度场影响因素进行了实验和理论研究．实时激光全息干涉法测量结果表明,运动气泡近界面浓度是一个定态值,受流速、泡径、温度等因素影响显著;假设该传质过程达到局部平衡,进行热力学分析,得到的结论与实验结果一致．在实验测量结果的基础上,对单个O_2气泡在乙醇中吸收时的传质近界面浓度场进行了数值模拟,取得了良好的结果．     

运动气泡近界面湍流场的激光测量及其湍流结构特性

运用二维激光多普勒测速仪,测定了运动气泡近界面的动力学特性,其中包括时均特性及湍流场结构.实验表明,尾涡区的时均流速呈非均匀分布,湍流场由双结构组成,即由完全随机的湍流涡及规律性的相干涡构成,这种双结构现象在尾涡的中心及边缘部又有所变化,其相关函数、谱密度函数及统计尺度亦随不同的部位而变化.泡前区受尾涡区周期性Karman涡脱落的影响,呈现相同频率的周期波动.这种特性存在于切向及法向速度中.     

球形碳酸钙的界面合成及表面性质

以氯化钙、碳酸钠为反应物，在水／氯仿界面上，以十二烷基硫酸钠为添加剂合成了球形碳酸钙。用扫描电镜表征其形貌；以碳酸钙在二次蒸馏水中的润湿时间长度来表示该碳酸钙的亲疏水程度。结果表明，该碳酸钙为球形形貌，且比天然碳酸钙的疏水性较强。     

高活性氧化镍对搪瓷气泡结构的影响

本文研究了不同的烧成时间,添加活性氧化镍后搪瓷底釉的气泡结构所产生的变化,并对活性氧化镍作用机理作了一定的探讨,它有助于搪瓷均匀气泡结构的形成。     

Characteristics of a countercurrent reciprocating plate bubble column. I. Holdup,pressure drop and bubble diameter

The hydrodynamics of countercurrent air/water flow in a 5 cm diameter reciprocating plate bubble column have been studied; the plates contained 14 mm diameter perforations and had a fractional open area of 0.57. The ranges of superficial velocities of air and water were respectively 0-0.99 cm/s and 0-3.95 cm/s. The stroke was in most cases 4.5 cm and the reciprocation frequency was in the range 0–5 Hz. The pressure drops were measured in the absence of reciprocation for single phase and two phase flow conditions. Pressure fluctuations and time-averaged pressure drops were measured with plate reciprocation under single and two-phase conditions. The results were described in terms of the simple quasi-steady state model; the effective orifice coefficients of the perforations were within the range 0.4 to 0.97 depending on the reciprocation conditions. The Sauter mean diameters of the bubbles decreased with agitation; they were about twice the values predicted from an earlier correlation developed for liquid-liquid systems. The gas holdups were also substantially greater than predicted from correlations based on liquid-liquid systems. Both these effects were explained as due to the tendency for bubbles to cluster in the plate region.     

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。     

Gas holdup,bubble size distribution,and mass transfer in an airlift reactor with ceramic membrane and perforated plate distributor

The airlift reactor is one of the most commonly used gas–liquid two-phase reactors in chemical and biological processes. The objective of this study is to generate different-sized bubbles in an internal loop airlift reactor and characterize the behaviours of the bubbly flows. The bubble size, gas holdup, liquid circulation velocity, and the volumetric mass transfer coefficient of gas–liquid two-phase co-current flow in an internal loop airlift reactor equipped with a ceramic membrane module (CMM) and a perforated-plate distributor (PPD) are measured. Experimental results show that CMM can generate small bubbles with Sauter mean diameter d₃₂ less than 2.5 mm. As the liquid inlet velocity increases, the bubble size decreases and the gas holdup increases. In contrast, PPD can generate large bubbles with 4 mm < d₃₂ < 10 mm. The bubble size and liquid circulation velocity increase as the superficial gas velocity increases. Multiscale bubbles with 0.5 mm < d₃₂ < 10 mm can be generated by the CMM and PPD together. The volumetric mass transfer coefficient k_La of the multiscale bubbles is 0.033–0.062 s⁻¹, while that of small bubbles is 0.011–0.057 s⁻¹. Under the same flow rate of oxygen, the k_La of the multiscale bubbles increases by up to 160% in comparison to that of the small bubbles. Finally, empirical correlations for k_La are obtained.     

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。     

Simultaneous effect of particle size and solid concentration on the hydrodynamics of slurry bubble column reactors

The simultaneous effect of particle size and concentration on the total gas holdup of slurry bubble column reactors was investigated in this work. The total gas holdup was measured for air–water–glass beads systems. Three solid concentrations and three particle diameters were used. It was found that increasing particle size at high constant concentration decreases gas holdup. Moreover, increasing solid concentration decreases gas holdup and this decreasing effect is higher for larger particles. Also, solid particles have two effects on hydrodynamics, namely, changing the viscosity and density of the liquid phase as well as hindering the bubbles from rising within the column by the collision phenomenon. Therefore, a novel correcting factor was introduced to correct the gas holdup. The hindering factor considers both the collision efficiency affected by the particle size as well as the solid concentration. A novel correlation was developed to predict the experimental data of the three-phase gas holdup.     

低压沸腾管内汽泡尺寸的测量与研究

沸腾工况汽液两相流汽泡尺寸的研究对于深入理解两相流动特性以及相关模型的发展具有重要意义。文中采用双探头光学探针对受热上升管内汽液两相流汽泡尺寸的径向分布特性进行了测量与研究。此外,通过对汽泡尺寸概率密度数的分析,得出了对应工况的两相流流型,根据理论分析及实验结果,总结了汽泡尺寸径向分布与流型的关系。     

Bouncing of a bubble at a liquid–liquid interface

Significant industrial relevance of gas–liquid–liquid flows calls for understanding of their various aspects. This study focusing on one of the aspects, i.e., interaction of a single bubble with a liquid–liquid interface, is aimed at providing the experimental evidence of a hitherto unreported phenomenon of conditional bouncing of a bubble at the interface between two immiscible, initially quiescent liquids. Bouncing of the bubble is observed for two of the six pairs of the immiscible liquids used in the experiments. The data, obtained by conducting experiments with different pairs of the lighter and heavier liquid bubble diameters and rise heights, suggest that a bubble crossing a liquid–liquid interface is expected to bounce when its average velocity is less than a threshold value that depends on the interfacial tension between the two liquids and the viscosity of the heavier liquid. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3150–3157, 2017     

二维鼓泡床内气泡尺寸分布的实验与CFD模拟

在有机玻璃制成的二维鼓泡床(0.20m×0.02m×2.00m)内,采用摄像法对空气－自来水的气液两相体系的气泡尺寸分布进行了考察。以商业计算流体力学软件ANSYS CFX 10.0为平台,在双流体模型的基础上,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进行了多相流CFD数值模拟。结果表明 MUSIG(Multiple Size Group)模型实现了对多气泡体系内气泡尺寸分布特性的考察,气泡尺寸分布的模拟结果与实验结果吻合得较好,从而说明了考虑了气泡聚并破碎的MUSIG模型能很好地反映出鼓泡床内气泡尺寸分布特性。     

特征时间对剪切稀化流体气泡上浮特性的影响

非牛顿气液两相流广泛存在于工农业生产中,气泡和液相间的接触非常复杂,对相间的传递效率具有重要的影响。为了理解气泡在非牛顿流体中的运动特性,基于连续表面张力模型与Carreau本构模型,本文运用volume of fluid（VOF）法研究了单气泡在剪切稀化流体内自由上浮的运动特性。研究发现：气泡的动力学特性与液相的特征时间λ密切相关,液相的剪切稀化程度越强（流变指数n越小）或表面张力越小（Eo数越大）时,特征时间λ对气泡变形和尾涡的影响越大。在给定的剪切稀化程度和表面张力下,λ越大,气泡终端速度越大,其尾涡强度和尺度也越大,导致气泡周围液相高剪切速率区和低表观黏度区的范围越宽。此外,当液相的表面张力较小时,在气泡尾部出现了黏度盲区;并且随着λ的增大,黏度盲区逐渐脱离气泡尾部并破碎;黏度盲区的出现减小了气泡周围液相低表观黏度区的面积,增大了气泡上浮过程的摩擦阻力,降低了气泡的终端速度。     

Hydrodynamic studies with foaming and non-newtonian solutions in bubble columns

Experiments were conducted in 0.05 m ID and 0.23 m ID by 3 m tall bubble columns to study the effect of surfactants and viscosity of liquid medium on gas hold-up and Sauter mean bubble diameter. The addition of n-butanol (0.5 and 1 wt.%) to water leads to the formation of foam and consequently produces higher gas hold-ups. The foam could be eliminated completely with the addition of a sufficient quantity (0.5 wt.%) of carboxymethyl cellulose to the aqueous alcohol solution. In the absence of foam, gas hold-ups were similar to those obtained with pure liquids. Sauter mean bubble diameters, obtained using the dynamic gas disengagement technique, increase with viscosity of liquid medium.