Study On The Phenomenon Of Film Climbing And Film Drainage Instability On A Vertical Plate

The flow process of liquid film with surfactants on the solid substrate is complicated and interesting,which contains abundant dynamic behavior.This process is extremely common in daily life,and widely used in various industries such as petrochemicals,micro-electromechanical materials,food processing and medical treatment.Presently,it has become a research hotspot in the field of fluid mechanics and surface science.The flow processes of liquid film containing climbing and drainage on the substrate are studied thoroughly,combining the method of experiment and numerical simulation.An experiment of film climbing is designed,which is driven by the Marangoni force generated by the gradient of surfactant concentration.From the experimental phenomena,the one-dimensional model of liquid film climbing process and the two-dimensional model of drainage unstable phenomenon is established,and the influence of Marangoni effect on the flow is analyzed.The main contents are as follows:(1)The phenomenon of film climbing along the wall was studied experimentally.and the changes of liquid film morphology and contact line position were recorded.The development of liquid film morphology and contact line position are recorded by high-speed photography.The thickness of liquid film is measured by thickness meter,and the climbing distance under different surfactant concentration is analyzed.The results show that the film thickness increases with time at the characteristic position near the bottom of the plate,while the film thickness decreases at the characteristic position near the top.Strong Marangoni effect increases the climbing height of liquid film and the peak thickness of liquid film at the characteristic position at the bottom.(2)For the film climbing process,use lubrication theory to establish onedimensional liquid film flow model.The evolution characteristics of liquid film are simulated,and the influence of Marangoni force and gravity on the flow is analyzed.The results show that when the Marangoni force is stronger than the gravity,the liquid film climbs from the liquid pool,carries the surfactants upstream and drives the film thickness to increase.When the latter effect is higher than the former,the liquid film becomes thinner,showing the law of gravity drainage,but the existence of Marangoni makes the drainage process delayed.(3)For film drainage unstable phenomenon,use lubrication theory to establish two-dimensional evolution model describing surface velocity,film thickness and surfactant concentration.A disturbing function at meniscus position is introduced into initial conditions of film thickness and surfactant concentration,then the evolution of local disturbances on drainage is examined by numerical calculation,and the influence of Marangoni effect on stability of film drainage was further explored.The results show that the Marangoni effect enhances the disturbance characteristics of film surface with the spreading disturbance,when the film thickness is very thin in the late draining period.which is detrimental to the stability of film.