皂膜解吸Marangoni对流观察及分析

利用竖直流动皂膜装置,使用纹影光学方法观察了由于丙酮从皂液中解吸,在微米级厚度皂膜上出现的滚筒状Marangoni对流结构;通过建立皂膜传质数学模型及求解,分析了丙酮从皂膜解吸过程中浓度及表面张力的变化。结果表明:由于微米级的皂膜厚度,在皂膜平面法向方向皂膜内皂液丙酮浓度变化很小,但浓度梯度较大,对应的表面张力梯度较大,此较大表面张力梯度是丙酮从皂膜解吸过程中出现Marangoni对流的主要成因。     

Marangoni对流的纹影实验分析

通过纹影系统对乙醇溶液解吸CO₂的过程进行了实验研究,液层自由界面的俯视纹影图记录了对流结构的演化过程,并捕捉到了Marangoni对流结构的初始形态。相应的胞型结构因发展空间的限制,由初始的近圆形逐渐变成了多边形结构。利用纹影图片的灰度分布信息,对单个胞型结构的出现、发展及分裂阶段进行了定性分析,发现界面非均匀传质所引发的界面对流在其胞型发展的过程中将会导致界面的变形。湍动的后期,液层表面将布满多边形结构,且胞型结构基本保持不变。相应纹影图片的颜色差异随解吸的进行逐渐减小,即随着传质推动力的减小,湍动强度也将减弱。     

气液传质过程中Marangoni对流的观测与定量分析

建立了一套气液传质装置和一套纹影系统对乙醇解吸CO₂过程中产生的Marangoni对流结构进行垂直界面方向上的观察,发现解吸过程中近界面处出现均匀分布的旋涡状的对流结构,并随时间聚合发展变大。此外还利用定量纹影法考察了传质过程中的浓度分布和界面张力梯度等信息。定量的结果表明较大的界面张力梯度位于对流胞型的边缘和中心处,驱动着界面流体的运动,并耦合浮力效应,形成了近界面环流的运动形式。这种环流运动造成了对流胞型边缘浓度较大、内部浓度小的分布,促进了相界面流体微元的更新,加强了传质过程。     

气液传质液滴界面的Marangoni对流

通过氮气吹扫双组分液滴,用激光投影法定性观察由于轻组分向气相扩散导致的Marangoni对流结构,结果表明Marangoni对流以小尺度涡流结构和大尺度对称循环流动的形式出现,其中乙醇-水体系首先出现小尺度涡流结构,涡流不断长大合并;丙酮-水体系则以大尺度对称循环对流结构为主,随后在近界面处形成小尺度涡流结构。采用氮气吹扫乙醇-水及丙酮-水静止悬垂单液滴的方法,通过比较实验测量传质系数与理论预测值,表明液滴近界面处Marangoni对流小尺度涡结构对传质促进作用较小,而液滴内大尺度循环对流结构对传质促进作用大。     

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.     

CO2在纳米流体解吸过程中的微对流现象

建立了一套水平气液界面传质模拟装置,利用粒子成像测速仪（PIV）对CO2从乙醇和乙醇纳米流体中解吸过程液相流场进行了观测和分析。传质发生时,在近界面处均观察到了由Marangoni效应造成的湍动。通过对平均速度的分析,发现在乙醇纳米流体中发生的湍动强度和湍动范围较乙醇溶液中大。纳米流体中的Marangoni效应加剧了纳米粒子的布朗运动,引发了纳米流体中的微对流,从而将界面处的湍动传递至液相主体中,导致液相主体的漩涡增多、流体混合加剧,促进了气液传质。     

界面传质中Rayleigh对流的定量分析

通过纹影光路观察了特定气液传质装置中乙醇吸收CO₂过程所引发的Rayleigh对流在垂直界面方向上的发展过程。随着溶质吸收的进行,液层的流体稳定性变弱,扰动加剧气液界面失稳并发生湍动,进而发展为羽状流并逐步向液相主体发展,在此过程中伴随着对流胞的融合与增长。液层的浓度分布可通过对相应液层纹影图像进行定量分析获得。液层浓度分布和瞬时传质系数变化表征了Rayleigh对流的引发与发展及其对传质过程的强化效果,界面浓度分布及临界Rayleigh数解释了非均匀传质对湍动的引发机理。羽状流将高浓度液体快速带入主体,加速了近界面液层与主体液层的混合,增强了气液传质。     

气液界面对流传质的观测与定量分析

采用光学纹影系统对乙醇和水双组分解吸传质过程的对流结构的界面湍动进行了定性观察和定量分析。建立了一套水平非稳态气液传质设备,试验观测了乙醇和水体系中液相组分向气相传质过程的Marangoni界面对流结构。还通过对传统纹影方法的改进,对乙醇解吸传质过程的浓度(本文用质量分数表示)梯度场进行了定量测量。定量分析表明乙醇和水系统解吸过程中,引发界面湍动的原因是局部较大的表面张力梯度。定量分析的结果很好的解释了伴随Marangoni效应的传质过程的混乱的对流结构,为进一步对界面湍动现象的分析提供了帮助。     

液体降膜中Marangoni效应的研究进展

降膜过程中的Marangoni效应是当前流体传递过程与非线性理论研究领域中的热点,对产品质量具有重要影响。回顾了近几年国内外关于Marangoni效应的最新研究进展,重点介绍了有关热Marangoni效应的实验及理论研究成果,并进行了比较和分析。结果发现,Marangoni效应与体系温度和浓度变化等有关,并会影响降膜稳定性。同时,针对目前研究中存在的一些不足,提出了今后研究工作的一些建议。     

原油与化学驱油体系界面Marangoni对流实验研究

利用微观显微摄像系统研究了新疆油田石油磺酸盐(KPS)、Na2CO3及其复合体系与新疆原油接触后的界面变化特征.结果表明:KPS,Na2CO3及其复合体系与新疆原油接触后可以发生Marangoni对流,产生剧烈的界面扰动;Na2CO3与KPS在产生Marangoni对流过程中具有协同作用,低界面张力条件下Marangoni对流产生的界面扰动能够使原油自发乳化;聚合物的加入抑制了Marangoni对流.     

Marangoni效应与降膜传递过程

M arangon i效应在降膜传热、传质过程中广泛存在,并对这些过程有着显著影响。人们对M arangon i效应进行过大量的理论和实验研究。初步总结了近年来关于M arangon i效应的研究工作,并对其中的热点问题进行分析,进而展望了未来关于M arangon i效应的研究趋势。     

Simulation of interfacial Marangoni convection in gas-liquid mass transfer by lattice Boltzmann method

Interfacial Marangoni convection has significant effect on gas-liquid and/or liquid-liquid mass transfer processes. In this paper, an approach based on lattice Boltzmann method is established and two perturbation models, fixed perturbation model and self-renewable interface model, are proposed for the simulation of interfacial Marangoni convection in gas-liquid mass transfer process. The simulation results show that the concentration contours are well consistent with the typical roll cell convection patterns obtained experimentally in previous studies.     

3D multiphase flow simulation of Marangoni convection on reactive absorption of CO2 by monoethanolamine in microchannel

A multiphase flow 3D numerical simulation method employing the coupled volume of fluid (VOF) and level set model is established to study the reactive absorption of CO₂ by the monoethanolamine (MEA) aqueous solution in a falling film microchannel. Based on the flow-reaction-mass transfer model of the MEA-CO₂ system in the falling film microchannel, the enhancement effect of the Marangoni convection in this reactive absorption process is analyzed. The enhancement factor of the Marangoni convection obtained in this work is in good agreement with experimental results in the literature. With consideration of the absorption ratio as well as the enhancement effect of the Marangoni convection, the influence of different MEA concentrations on absorption of CO₂ is investigated. Furthermore, the appropriate MEA concentration for absorption enhanced by the Marangoni convection is acquired.     

Local analysis of Marangoni effects during and after droplet formation

The influence on the mass transfer in liquid-liquid extraction was investigated during droplet formation in a quiescent aqueous continuous phase for the two transition components, acetone and acetonitrile, in toluene. Both transition components have similar characteristics. However, an approximately eight times slower mass transfer of a droplet hanging on a capillary in relation to a rising droplet could be observed. The droplet formation time and the initial solute concentration are decisive for the mass transfer behaviour. A lower volumetric flow leads to slower droplet formation and a higher specific mass transfer area enhancing mass transfer, which is visualized via laser induced fluorescence (LIF). Additionally, as expected, higher initial solute concentrations promote Marangoni turbulences and thus mass transfer, which is measured via confocal Raman spectroscopy inside a fixed hanging droplet.     

Mixed convection heat and Mass transfer in a vertical channel with film evaporation

Numerical results are presented for effects of latent heat transport associated with film vaporization on laminar mixed convection heat and mass transfer in a vertical channel with a half channel width b = 0.01 m. The influences of the inlet liquid mass flowrate and wall temperature on the film vaporization and the associated heat and mass transfer characteristics are examined for air-water and air-ethanol systems with gas Reynolds number Re_g = 2000. Predicted results obtained by including transport in the liquid film are contrasted with those where liquid film transport is neglected, showing that the assumption of an extremely thin film made in Lin et al. (1988) and Yan and Lin (1989) is only valid for systems having small liquid mass flow rates. Additionally, it is found that the interfacial heat flux is predominantly determined by latent heat transfer connected with film evaporation.     

双光路纹影仪观察气液传质界面湍动现象

建立了双光路纹影仪实验系统,并利用双光路纹影仪,同时从垂直和平行于界面两个方向对氯苯吸收、解吸CO₂的传质对流结构进行了观察,发现在氯苯吸收CO₂时,没有明显的对流结构,只是在垂直界面的纹影图像中观察到逐渐变粗的暗条纹。在氯苯解吸CO₂时,在垂直和平行于界面两个方向都观察到了明显的对流结构,在垂直界面的纹影图像中开始时出现分层现象,随着解吸的进行,对流加剧,分层现象被破坏;平行界面方向的对流结构发展较快,优先在平行界面的纹影图像中观察到明显的对流结构。由于传质的热效应,两个方向的对流结构都有向中心运动的趋势。实验表明,双光路纹影仪实验系统能观察界面传质对流过程的三维变化,可深化对界面传质对流过程的认识。