平板浸涂过程中的液膜排液影响因素

针对一端与活性剂溶液池相接的竖直平板浸涂液膜排液过程,基于润滑理论建立了液膜厚度、活性剂浓度及液膜表面速度的演化方程组,通过数值计算分析了Marangoni效应和表面黏度对液膜排液特征的影响。结果表明,Marangoni效应是影响液膜排液过程的重要因素,可导致液膜厚度增加,随Marangoni效应增强可得到更均匀的液膜。液膜表面速度随表面黏度增大而减小,较大的表面黏度将推迟表面速度逆流现象的发生,但其对膜厚均匀度几乎没有影响。     

滑移边界对含表面活性剂超薄液膜去湿特性的影响

针对预置在固体基底上含非溶性表面活性剂的超薄液膜去湿过程,基于滑移边界条件下的液膜厚度和表面活性剂浓度的非线性演化方程组,采用PDECOL程序对液膜去湿过程进行了数值模拟,分析了不同滑移尺度对含有内源和外源表面活性剂去湿特性的影响。研究表明,滑移边界对去湿过程的影响与表面活性剂初始分布密切相关,且不同平衡液膜厚度下滑移尺度的影响存在较大差异;总体上滑移边界促使超薄液膜趋于稳定,特别是当平衡液膜厚度较小时,滑移边界可有效控制去湿过程的发生;对于Spinodally稳定液膜,滑移边界对外源性情况的影响远大于内源性情况。     

电解质溶液的受热降膜传热与Marangoni效应

采用红外热成像技术研究了电解质Na2SO4-H2O溶液受热降膜传热过程中的Marangoni效应。实验结果表明,降膜表面的流向和径向上存在分别由温度和浓度分布不均引起的热和溶质Marangoni效应。降膜径向热Marangoni效应引起了液膜的收缩,使液膜厚度增加,增大了液膜热阻;流向热Marangoni效应加剧了液膜的湍动,减小了液膜滞流层厚度,降低了液膜热阻;径向溶质Marangoni效应则减弱了热Marangoni效应对液膜的收缩作用,促进了液膜的扩展。分析发现在本实验条件下,表征Marangoni效应大小的Marangoni数Ma不能准确地反映不同雷诺数Re下Marangoni效应对降膜流动的影响,为此引入判断Marangoni效应对降膜流动影响程度的Marangoni效应影响因子ε,ε与实验结果具有较好的一致性。     

Marangoni效应对降膜加热流动的影响

采用红外热像仪和智能化薄膜厚度测试仪研究了垂直板上受热降膜的流动特性, 得到液膜表面温度分布、液膜宽度、液膜厚度、局部液膜厚度随时间变化关系等参数 通过对这些参数的分析,可知降膜加热流动时,液膜表面出现轴向和径向的温度梯度,由此产生的表面张力梯度引起Marangoni效应对降膜流动有着很大的影响降膜加热流动过程中,Marangoni 效应使液膜产生较大的收缩,膜厚增加,表面波动加强.     

功能表面材料与流体界面相互作用对垂直降液膜流动特性的影响

通过调节水温度、添加表面活性剂以及铝合金壁面表面改性处理来改变降膜流体与固体表面之间的表面自由能差值,运用JDC-2000型精密测微仪测定垂直降液膜的厚度,研究固体表面和液体间相互作用对流体垂直降膜流动特性的影响;考察了液膜雷诺数、流体温度、添加表面活性剂、固体表面材料物理化学性质等因素对垂直壁面降液膜流动特性的影响规律。实验结果表明:改变固体表面与降液膜流体的物理化学特性,即改变固液界面的相互作用能够改变流体的降膜流动特性。降液膜平均厚度随液固表面自由能差的增大而减小。     

多相传质过程中的Marangoni效应

Marangoni效应广泛存在于液液、气液相际传质过程中,通常会对传质速率产生重要影响。对Marangoni效应的实验及理论研究有助于增进对微观传质机理的理解,是强化相间传质过程效率的重要因素。重点介绍了液液体系中单液滴萃取的实验和模拟研究,对液液体系中Marangoni效应不稳定性的判据,对气液体系有效传质面积的影响,以及两种体系中利用表面活性剂进行传质调控的研究等方面的进展进行了综述,还探讨了传质过程中Marangoni效应应用研究的方向。     

非平整倾斜表面上流动液膜的影响因素分析

基于流体体积函数法(VOF),分别从液体物性和液相入口流速等因素对非平整倾斜表面上的液膜流动特性进行数值模拟,得出流体黏度的增大可增大液膜厚度并降低液膜整体流动速度,但不影响液膜与壁面之间的相位角;流体表面张力影响液膜与壁面之间的相位差及液膜的均匀性;液相入口雷诺数的增大可以增大液膜厚度,当雷诺数增大到一定程度时,液膜厚度不再有明显的变化,且液膜表面趋于光滑。研究结果表明:液膜的流动形式由液体各项物性和液相入口流速共同决定。     

液膜夹带溶胀发生与消除

本文讨论了液膜夹带溶的发生机理与消除方法，证明在界面上表面活性剂分子吸附速度的大小是液膜夹带深胀大小的原因，吸附速度与所采用的表面活性剂有关，并提出了液膜夹带溶胀的常用消除方法。     

流体在固体表面超铺展特性的研究进展

对流体在固体表面超铺展特性的研究进展进行了综述,总结了具有超铺展特性的动态湿润体系、超铺展特性的影响因素、内在机理以及实验关联式建立和数值模拟方法。部分丙硅氧烷类和烷基乙氧基化物类以及少数离子型表面活性剂溶液具有超铺展特性,浓度和固体表面能是超铺展的重要影响因素。气液界面的浓度Marangoni效应被认为是超铺展过程的控制因素,表面活性剂在气液、固液和三相接触线前缘固气界面的输运和吸附对浓度Marangoni效应有重要影响。分析认为,实验方面未来应拓展实验体系,建立超铺展产生的判据;深入研究宏观影响因素以及微观输运和吸附机理,同时考虑外加物理场影响,为超铺展的实际应用奠定基础。理论方面需综合考虑表面活性剂向界面的输运、吸附对界面性质的作用规律以及浓度Marangoni效应的影响,借鉴相对成熟的牛顿流体动态湿润理论,建立描述超铺展特性的全过程理论模型。数值模拟方面应以分子动力学模拟为基础建立表面活性剂输运和界面吸附的微观物理模型,将其引入流体动力学模型,实现对超铺展过程精确定量化的描述。本文还给出了可能的超铺展体系铺展全过程的物理图景。     

流体在固体表面超铺展特性的研究进展

对流体在固体表面超铺展特性的研究进展进行了综述,总结了具有超铺展特性的动态湿润体系、超铺展特性的影响因素、内在机理以及实验关联式建立和数值模拟方法。部分丙硅氧烷类和烷基乙氧基化物类以及少数离子型表面活性剂溶液具有超铺展特性,浓度和固体表面能是超铺展的重要影响因素。气液界面的浓度Marangoni效应被认为是超铺展过程的控制因素,表面活性剂在气液、固液和三相接触线前缘固气界面的输运和吸附对浓度Marangoni效应有重要影响。分析认为,实验方面未来应拓展实验体系,建立超铺展产生的判据;深入研究宏观影响因素以及微观输运和吸附机理,同时考虑外加物理场影响,为超铺展的实际应用奠定基础。理论方面需综合考虑表面活性剂向界面的输运、吸附对界面性质的作用规律以及浓度Marangoni效应的影响,借鉴相对成熟的牛顿流体动态湿润理论,建立描述超铺展特性的全过程理论模型。数值模拟方面应以分子动力学模拟为基础建立表面活性剂输运和界面吸附的微观物理模型,将其引入流体动力学模型,实现对超铺展过程精确定量化的描述。本文还给出了可能的超铺展体系铺展全过程的物理图景。     

A description of phase inversion behaviour in agitated liquid-liquid dispersions under the influence of the Marangoni effect

The influence of the Marangoni effect on phase inversion behaviour is examined by integrating a microscopic study of the drop coalescence process, in which thin film drainage in the presence of insoluble surfactant occurs, into a macroscopic phase inversion model which has been developed previously using a Monte Carlo technique. This is achieved via an immobility factor, obtained from a comparison of the film drainage times for surfactant-laden systems and surfactant-free systems as a function of the drop approach velocity, surface Péclet number, initial surfactant concentration and the Hamaker constant, which is then used to modify the coalescence probability in the phase inversion model. On the one hand, the results indicate that the Marangoni effect removes any influence that the viscosity ratio has on phase inversion due to immobilisation of the interface, thus shielding the flow in the film from the effects of the flow in the dispersed phase; the point at which phase inversion occurs therefore tends towards equivolume holdups with the addition of surfactant. On the other hand, when comparisons are made with pure systems in which surfactant is absent, the system is seen to be either stabilised or de-stabilised from inversion depending on the viscosity ratio of the system. This is attributed to the influence of surfactant on the dispersion morphologies on either side of the inversion (i.e. water-in-oil dispersions and oil-in-water dispersions) and depends on the dispersed phase holdup; the Marangoni effect is felt stronger when the dispersed phase holdup is low.     

Effect of Electric Double Layer Repulsion on Oil Droplet Coalescence Process

Film drainage between two droplets approaching each other at constant velocity under the influence of electric double layer repulsion is studied systematically. Based on the lubrication equations, a mathematical model is given to govern the evolution of film drainage between two oil droplets. This model consists of three coupled fourth‐order nonlinear parabolic partial differential equations describing the dynamic evolution of the film thickness, film pressure and surfactant interfacial concentration. The numerical method used is the finite element method. The main objective of this research work is to modify the film pressure equation by considering the electric double layer repulsion. The effects of electric double layer repulsion and viscosity ratio on film drainage are investigated theoretically.     

The effect of surfactant on the flow of a thin liquid film over a spinning disc

We examine the flow of a thin liquid film over a spinning disc in the presence of dilute insoluble surfactant. We use the integral method to derive a coupled system of equations that govern the axisymmetric evolution of the film thickness, radial flow rate, angular momentum and surfactant surface concentration; a linear equation of state is used for closure. This system of equations is parameterized by a modified Weber number, a Marangoni parameter, M, and a surface Peclet number, Pe_s. Numerical solutions of these equations reveal that the presence of surfactant gives rise to Marangoni stresses which interfere with the mechanisms of wave growth. For M∼0.1, our results indicate that the formation of interfacial waves is suppressed.     

分离压/结合压作用下的活性剂液滴演化特征

当含活性剂液膜厚度小于100 nm时,分子间力表现出的分离压或结合压效应将对其演化特征及去润湿特性产生重要影响。针对可溶性活性剂液滴的铺展历程,采用润滑理论建立了液膜厚度、活性剂表面浓度和内部浓度的演化模型,模拟了正负体系中受分离压或结合压影响的液滴演化过程。结果表明,分离压可促进正体系下的液滴稳定铺展,并抑制去润湿现象的发生;而负体系下,分离压则加剧不稳定性,并改变Marangoni负效应对液滴演化的影响。正体系下液滴受结合压作用呈现不稳定特征,在极短时间内发生破断;结合压对负体系下的液滴演化影响与分离压作用相似,具有促进液滴不稳定演化的作用。     

温度和活性剂浓度梯度协同驱动的液滴铺展特性

引言液滴在固体表面上的铺展(spreading)过程是一个学科交叉的研究热点,在镀膜、印刷、采油、矿物浮选、胶片制造、磁流体材料制备以及医疗等领域有着广泛的应用,近些年来开展了大量理论和实验研究工作。     

The effects of surface viscosity on the axisymmetric drainage of planar liquid films

The Reynolds equation is extended to allow for the effects of shear and dilational surface viscosities on the axisymmetric drainage of planar films. It is shown that the number of immobile surfaces, n, may be expected to decrease with increasing film radius and bulk viscosity and with decreasing film thickness and surface viscosity, as observed experimentally. The predicted rate of film thinning agrees well with available experimental results.     

竖直流动皂膜中解吸导致的Marangoni对流观察

In gas-liquid mass transfer processes,Marangoni convection may occur due to the surface tension gradient produced by mass transfer near the interface.With a falling soap film tunnel and the Schlieren optical method,the Marangoni convection patterns along the film surface were observed directly in the desorption process of acetone from the falling soap film.The Schlieren images showed the regular roll convection in the thin falling soap film during the acetone desorption.The hydraulic characteristics were determined experimentally by measuring the variation of acetone concentration in the film and the surface tension of the soap liquid.The results show that the acetone concentration gradient vertical to the falling direction is very small because the thickness of the soap film is in the order of 10^-6 m.The variation of acetone concentration along the falling film is large,so there is a significant surface tension gradient,resulting in the Marangoni roll convection.The experimental results and a qualitative analysis may be helpful to understand the mechanism of Marangoni convection near the interface in the mass transfer.     

波纹状基底上含不溶性活性剂液滴的铺展过程

针对波纹状基底上含不溶性活性剂液滴的铺展过程,采用润滑理论建立了液膜厚度和浓度演化模型,通过PDECOL程序数值求解了演化方程组,得到了液滴的铺展特性及基底结构参数的影响规律。研究表明:当液滴铺展进入中后期,Marangoni效应减弱,此时基底的作用范围相应增大,基底对液滴铺展过程的影响逐渐显著。与平整基底相比,波纹状基底上的最小液膜厚度明显降低,而铺展前沿处的子波数显著增多,子波波峰高度呈单驼峰形的模态变化;而且,增加波纹状基底的高度或减小波数具有加剧液滴铺展不稳定性的作用。