Investigation Of The Dynamics Of A Coating Flow On A Vertical Fiber Immersed In Surrounding Liquid Phase

Under the influence of gravity,the coating flow of vertical fibers covered by liquid has important research value.Under the Rayleigh-Plateau mechanism,the liquid film breaks into liquid droplets or liquid beads,exhibiting a rich dynamic phenomenon of absolute instability and convective instability.It has important applications in industrial systems such as desalination of seawater,gas absorption,heat exchangers,and fast coating technology.In recent years,the study of coating flow in the air environment has received widespread attention.However,the study of coating flow films in the liquid phase has not been extensively researched.Therefore,this paper experimentally studied the flow of coating flow in the liquid phase,which exhibits rich dynamic characteristics.In this study,an immersed coating flow film experimental device was constructed,which mainly consists of an integral frame,liquid outlet unit,liquid phase unit,and image acquisition unit.The device was used to complete immersed coating flow experiments under different physical parameter conditions and collect experimental images.MATLAB software was used to process the images to extract the liquid film contour and determine the boundary coordinates.The study showed that the immersed coating flow exhibits regular flow,Bound structure flow,and irregular flow at different flow rates.Among them,regular bead flow and irregular bead flow correspond to absolute instability(AI)and convective instability(CI),respectively.Bound structure flow is at the boundary of absolute instability and convective instability.Through experiments,it was found that as the liquid viscosity increases with the same fiber diameter,the critical flow rate for absolute instability and convective instability gradually decreases,and the absolute instability of coating flow in low-viscosity liquid environments has a wider range of flow rates.In addition,the flow characteristics of the liquid film are reflected by spatiotemporal graphs.Furthermore,we quantitatively studied three important characteristic parameters of immersed coating flow: liquid droplet amplitude,droplet spacing,and wave speed.The results showed that as the flow rate increases,the droplet spacing gradually decreases,and the droplet amplitude and wave speed gradually increase.When the liquid phase environment has a higher viscosity,the liquid film on the fiber has a larger droplet amplitude,shorter droplet spacing,and lower wave speed.When the experimental fiber diameter increases,the droplet amplitude,droplet spacing,and wave speed all decrease.In addition,we also studied the dynamic characteristics of gas-liquid phase coating flow,which showed different experimental results from immersed coating flow.Furthermore,the regularities of the droplet amplitude,droplet spacing,and wave speed of gas-liquid phase coating flow are significantly different from those of immersed coating flow.Finally,this paper compared the characteristic parameters of two different liquid phase coating flow in different ways.