Bubble coalescence efficiency near multi-orifice plate

Bubble coalescence reduces specific area and weakens the work performance of bubble column. The bubble coalescence near gas sparger which is caused mainly by bubble growing is different from the ones occurring in major liquid. Bubble coalescence efficiency near gas sparger is influenced by many factors including sparger configuration, gas flow rate, bubble deformation, solution composition, etc. This work has conducted a set of visual experiments to study the coalescence characteristics near multi-orifice plate. The experiment parameters cover a wide range of conditions including large scope of gas flow rate,different kinds of solution and orifice configurations. The experimental results suggest that coalescence time is applicable to reflect the influence of the pitch of orifices and gas flow rate on bubble coalescence efficiency. As the number of orifices increases, bubble coalescence efficiency is reduced by the disturbance from the bubbles at adjacent orifices. A hindering coefficient is used to consider the hindering effect of additives on bubble coalescence efficiency. Finally a new calculation expression is established to predict bubble coalescence efficiency near multi-orifice plate whose fundamental form is based on the logistic curve of binary response. The calculated values that refer to this calculation expression are well consistent with the experimental results.

COALESCENCE BETWEEN SMALL BUBBLES:EFFECTS OF SURFACE TENSION GRADIENT

1 INTRODUCTIONThe rate of coalescence between bubbles is important to the stability of foams,the mo-bility control in tertiary oil recovery,and a broad class of operations in which gas orvapor is the dispersed phase.Therefore,it is very important that the mechanism of thecoalescence process be understood,so that the effects of the physical properties oncoalescence can be assessed.

CFD aided investigation of single droplet coalescence

This article describes the development of a coalescence model using various CFD work packages,and is validated using as toluene water model system.Numerical studies were performed to describe droplet interactions in liquid–liquid test systems.Current models use adjustable parameters to describe these phenomena.The research in the past decades led to different correlations to model coalescence and breakage depending on the chemical system and the apparatus geometry.Especially the complexity of droplet coalescence requires a detailed investigation of local phenomena during the droplet interaction.Computational fluid dynamics(CFD) studies of single droplet interactions were performed and validated with experimental results to improve the understanding of the local hydrodynamics and film drainage during coalescence.The CFD simulations were performed for the interaction of two differently sized droplets at industrial relevant impact velocities.The experimental verification and validation of the numerical results were done with standardized high-speed imaging studies by using a special test cell with a pendant and a free rising droplet.An experimental based algorithm was implemented in the open source code OpenF OAM to account for the contact time and the dimple formation.The standard European Federation of Chemical Engineering(EFCE) test system toluene/water was used for the numerical studies and the experimental investigations as well.The results of the CFD simulations are in good accordance with the observed coalescence behavior in the experimental studies.In addition,a detailed description of local phenomena,like film rupture,velocity gradients,pressures and micro-droplet entrainment could be obtained.

EFFECTS OF MASS TRANSFER ON THE THINNING AND RUPTURE OF A PLANE PARALLEL LIQUID FILM

The effects of mass transfer and physical properties upon the thinning and rupture of adraining plane parallel film are investigated.An equation is derived in which the thinning rate is afunction of bulk properties.surface properties(surface tension,surface viscosities,and the variationof surface tension with surface concentration),intermolecular forces(London-van der Waals forcesand electrostatic double layer forces),adsorption and surface diffusion coefficients,bubble size andfilm thickness.An estimation for the critical thickness at which a film rupture is carried out and thecoalescence time is obtained by integration to the critical thickness,The coalescence time is predictedas a function of bulk and surface properties,London-van der forces,adsorption and surfacediffusion coefficients,and bubble size.

水平均匀电场下盐水中氯气气泡的聚并特性

实验测量了电场条件下盐水中氯气气泡的大小、气泡间距离及其聚并时间。采用两相流和相场模型对电场条件下氯气聚并过程进行了数值模拟。结果表明,采用实验和数值模拟方法所得到的气泡聚并时间的偏差为11.0%,说明两者吻合较好。在此基础上,分析了不同电压下气泡的聚并过程,考察了气泡直径、液体表面张力和黏度对氯气气泡聚并过程的影响。结果表明:在电压为0~200 V范围内,电压、气泡直径和液体黏度越大,气泡间距越大,聚并时间越长;液体的表面张力越大,气泡间距越小,聚并时间越短。

气泡聚并机理模型

对气液二相体系中气泡间凸面状薄液膜内以及气液界面上动量和质量传递行为进行了分析,建立了气泡聚并时间模型,考虑了范德华作用力以及双电层作用力对液膜变薄过程产生的影响.模型值与文献实验值吻合较好.

界面流变性质对小液滴聚并过程的影响

对表面活性剂溶液中两个小液滴的聚并现象进行理论分析，并考虑相界面上质量传递对该过程的影响，得到聚并时间与界而张力和界面张力梯度、界面粘度、表面活性剂界面扩散系数、连续相和分散相的主体性质、范德华力及液滴半径的关系．

液滴在斜板层膜上聚结时间的计算

在对聚结过程和分离界面处液滴与层膜流体力学特性分析的基础上，建立了单个液滴在斜板层膜上聚结时间模型，模型计算值与BlassE等人报道的实验结果误差小于10％。

表面粘度对小气泡聚并的影响

对2个小气泡间的聚并过程进行了动力学分析,着重考虑界面粘度的影响,得到气泡聚并所需时间与气泡直径、流体主体和界面性质的关系。

两个液滴之间的聚并

对于系统中不含杂质时两个液滴在不互溶液体中的聚并过程进行理论分析，得到聚并所需时间与两相物理性质和范德华力的关系．该结果也适用于气泡在液体中的聚并．只要知道系统的物性数据和液滴半径，就可以计算聚并时间．理论预测与实验结果符合较好.

双气泡间的聚并时间测量及其影响因素

聚并时间是研究气泡聚并行为过程中的一个重要参数。在消除气泡生长速度对聚并时间影响的条件下,利用自行开发的光学测试技术对双气泡间的聚并时间进行了精确的测量。考察了气泡尺寸、靠近速度、有机溶质的扩散、电解质和表面活性剂的加入对气泡聚并行为的影响。实验结果表明,双气泡间的聚并时间随着气泡直径的增加、气泡老化时间的延长、靠近速度的减小和有机溶质浓度的增大而增加。

小气泡或小液滴之间的聚并

对2个小气泡或小液滴之间的聚并进行了动力学分析,并考虑范德华力的影响,得到了界面无切向运动时气泡或液滴聚并所需时间与气泡直径、流体主体和界面性质的关系。

成膜条件对乳胶漆耐洗刷性能的研究

成膜条件是影响乳胶漆成膜过程和涂膜性能的重要因素。成膜助剂可以改善乳胶漆的成膜过程,提高乳胶漆的涂膜性能。本文研究了成膜助剂、成膜温度和成膜时间对乳胶漆耐洗刷性能的影响。发现使用成膜助剂可以显著改善乳胶漆的耐洗刷性能;提高干燥温度和延长干燥时间可提高乳胶漆的耐洗刷性能。

单液膜气泡聚并和连接过程的移动粒子半隐式法数值模拟

为了研究单液膜气泡单层液膜包裹气体的特殊结构形式和内外壁面均受气液表面张力的特殊力学形式,在拉格朗日框架下采用无网格移动粒子半隐式法并基于表面自由能表面张力模型,建立了单液膜双气液界面表面张力模型,从而实现了单液膜气泡振荡变形过程中的复杂界面计算和捕捉。在此基础上对2个单液膜气泡的聚并和连接过程进行了模拟分析,获得了典型的流动现象和液膜变形特征与规律,发现减小表面张力系数或增大黏性系数均会减弱气泡变形过程中表面张力项的变形主导作用。为此,提出了凹点切线法用于计算连接型气泡的液膜夹角,明晰了连接型气泡的形状。计算结果可为工业消泡技术提供一定的理论依据。

Review on the deformable drop/bubble interaction-AFM study

The physicochemical properties of emulsions stabilized by surfactants depend on the film drainage and coalescence behavior between dispersed drops in a system.The combination of direct measurement of the interaction forces between soft matters by AFM and the prediction of the film drainage process by the SRYL model helps to explore the dynamic behavior of droplets in the emulsion system.In this review,novel experimental designs and recent advances in experimental methodologies for solving interaction forces,interfacial deformation and drop coalescence are presented,which show the advantage of using AFM as a tool for probing colloidal interactions.The effects of hydrodynamic forces,both DLVO and non-DLVO forces,on the emulsion stabilization mechanism are discussed.In addition,an outlook is presented to discuss the further development of the relevant technology and the problems that need to be solved.

掺He钛膜中He泡的演化研究

本文利用慢正电子束分析(SPBA)和透射电子显微镜(TEM)方法研究了钛膜内He相关缺陷的演化.实验结果表明:室温下,钛膜中的He主要形成均匀的小He泡.随着He浓度的增大,He泡的密度相应地增加.在973K高温退火后,在含高浓度He的钛膜样品中观测到大He泡的出现.实验结果表明迁移合并和较大He泡周围的级联融合共同作用导致了大He泡的形成.