气液传质过程中界面对流的实验研究

发布时间：2018-05-30 17:38

本文选题：界面传质 + Marangoni效应　；参考：《天津大学》2015年硕士论文

【摘要】：相际传质过程产生的近界面处流体物性差异可能引发界面对流。根据驱动力的不同,界面对流可分为由界面张力梯度引发的Marangoni对流和由密度梯度引发的Rayleigh对流。界面对流的产生能够促进界面处流体微元的更新,从而加快传质过程,因此界面对流效应的深入研究对解吸、吸收、精馏和萃取等传质分离过程的意义非常重大。文中通过改进后的纹影观测系统和气液传质装置,对不同体系在传质过程中产生的Marangoni对流和Rayleigh对流进行了考察,得到了这些过程中界面对流结构的引发、演化和消退过程的纹影图片。从大量的纹影图像可以得出界面对流是由Marangoni效应与Rayleigh效应耦合叠加后的产物,而且还受到诸如实验流体物性差异和实验观察液层厚度等因素的影响,使得对流结构较为复杂。在界面对流引发之前,传质以扩散形式进行,界面保持静止,这个过程持续的时间随着实验条件不同而不同。Marangoni效应引起的界面对流结构是流体往四周扩张的结构,根据对流形成时间和物性不同界面对流结构会有一定差异。乙醇解吸CO_2体系中,对流刚刚形成时,界面对流结构呈圆形,之后多个对流结构相接触,因为空间限制转变为多边形对流结构。乙酸乙酯水溶液解吸过程中,较大的对流强度导致其对流结构尺寸较大且形状不太规则。Rayleigh不稳定的传质过程中,界面从平静转变为多边形结构,不同于Marangoni多边形对流结构,之后这些多边形破碎,对流结构变为无序混沌状。此外对导致界面对流产生的Marangoni效应进行了详细研究,包括对流的立体结构、引发过程和其导致的界面变形等。分别从俯视和主视方向对产生对流的液相进行观察,获得了Marangoni对流中流体微元的运动模式。以单个Marangoni对流结构作为分析对象,研究了其面积增长和半径比变化。根据大量的纹影图片,并结合表面变形详细地描述了Marangoni对流引发过程。还利用定量纹影原理考察了Marangoni对流刚刚形成时液层相对高度分布图,这些不同高度液面的形成是Marangoni对流与重力等抑制因素的共同结果。
[Abstract]:The physical properties of the fluid near the interface may lead to interfacial convection due to the interphase mass transfer process. According to the driving force, interfacial convection can be divided into Marangoni convection induced by interfacial tension gradient and Rayleigh convection caused by density gradient. The generation of interfacial convection can promote the renewal of fluid microelements at the interface, thus speeding up the mass transfer process. Therefore, the in-depth study of the interfacial convection effect is of great significance to the mass transfer separation processes such as desorption, absorption, distillation and extraction. Through the improved schlieren observation system and the gas-liquid mass transfer device, the Marangoni convection and Rayleigh convection produced by different systems in the mass transfer process are investigated, and the initiation of the interfacial convection structure in these processes is obtained. A picture of the evolution and extinction process. From a large number of schlieren images, it can be concluded that the interfacial convection is the product of the coupling superposition of the Marangoni effect and the Rayleigh effect, and is also affected by factors such as the physical property difference of the experimental fluid and the thickness of the liquid layer observed experimentally, which makes the convection structure more complicated. Prior to the initiation of interfacial convection, mass transfer takes place in the form of diffusion and the interface remains static. The duration of this process varies with the experimental conditions. The interfacial convection structure caused by the Marangoni effect is the structure of the fluid expanding around it. According to the time of formation of convection and physical properties, the convection structure of different interfaces will be different. In the ethanol desorption CO_2 system, the convection structure at the interface is circular when the convection is just formed, and then several convection structures contact each other, because the spatial limitation changes to polygonal convection structure. In the process of desorption of ethyl acetate solution, the larger convection intensity leads to the large size and irregular shape of the convection structure. The interface changes from calm to polygonal structure, which is different from the Marangoni polygonal convection structure. These polygons are then broken and the convective structure becomes chaotic. In addition, the Marangoni effect which leads to interfacial convection is studied in detail, including the three-dimensional structure of convection, the initiation process and the interface deformation caused by the convection. The motion patterns of the fluid elements in Marangoni convection were obtained by observing the liquid phase which produced convection from the subsurface direction and the principal apparent direction, respectively. The area growth and radius ratio change of a single Marangoni convection structure are studied. The Marangoni convection initiation process is described in detail according to a large number of schlieren images and surface deformation. Based on the principle of quantitative schlieren, the distribution of the relative height of the liquid layer at the beginning of Marangoni convection was investigated. The formation of these liquid surfaces at different altitudes is the result of the inhibition factors such as Marangoni convection and gravity.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ021.4

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