Theoretical And Experimental Research On The Control Technology Of Film Coating On The Cylindrical Fiber

The film falling down a vertical fiber under the action of the gravity is an unstable and open flow.The coating flow involves multiple phenomena that often result in complex processes and complicated behaviors.The balance between all of these phenomena,and the manner in which they evolve,will strongly influence the quality of the coating process.The research on the flow characteristics of the film has great engineering application value and scientific research value.This paper uses the ordinary and self-rewetting fluids as research objects to study the flow characteristics of the flow of the film.The evolution equation of the interface of the film is established in the framework of a long-wave approximation theory.The effect of thermocapillarity?Marangoni effect?on the absolute/convective instability?AI/CI?is investigated.The effect of thermocapillarity on the Rayleigh-Plateau instability is investigated by examining the dispersion relation.The characteristics of film flow are considered for different Marangoni number?Ma?in different regions of absolute/convective instability using a spatio-temporal stability analysis.Numerical simulations of the nonlinear evolution in various regions of absolute/convective instability are also performed.The results of spatio-temporal stability analysis are in good agreement with the results of direct numerical simulation.The results show that when the research object is an ordinary fluid,the increase of Marangoni effect promotes the absolute instability with the increase of Ma;when the research object is a self-rewetting fluid,the effect of thermocapillarity on absolute and convective instability depends on the difference between the temperature at the interface?48?_i,and the temperature?48?₀ corresponding the minimum surface tensions₀.The results indicate that the thermocapillarity suppresses the absolute instability and enhances the convective instability as Ma increases when?48?_i is higher than?48?₀,and enhances the absolute instability as Ma increases when?48?_i is lower than?48?₀.The comparison of the effects of thermocapillarity on absolute convective instability of two fluids,the results shows that when the interface temperature is higher than ₀T,the use of self-rewetting fluids as coating fluid can help improve the coating process.This paper also designed an experimental device of the thin film and developed a set of non-contact experimental device for measuring the boundary shape of the thin film.The experimental device adopts a flexible split design,and the free combination of different components can be used to prepare the films with different film thicknesses and flow rates.The film prepared under different experimental conditions can be used to capture and record the process of the flow of the film through image acquisition equipment.In this paper,the image processing module in MATLAB is used to process the image,and the GUI interface for extracting the boundary shape of the film is developed based on the Canny algorithm.