Investigatation Of Flow Behavior Of Droples Impact On Stainless Steel Wire Mesh Units

Droplet impacting stainless steel wire mesh phenomenon is widespread in industry,agriculture and daily life.In the chemical process,the dispersion of droplets by the wire mesh determines the heat and mass transfer efficiency and the degree of macro mixing and micro mixing in various reactors.In this paper,the visualization technology is used.The picture information of the overall movement of the droplets is taken through the high-speed camera technology.The stainless steel wire mesh is split into different units for detailed study:single fiber unit,cross fiber unit and grid unit.We research the influence of droplet velocity,droplet size,mesh size and structures of units on flow characteristics,film spreading and surface area increase rate.In addition,we built up the boundary models of different dripping modes.The main results were as follows:(1)There are three dripping modes of droplet impacting on the units of the single fiber:one-drop,double-drop,and ligament.According to the force analysis of the droplet impact the straight single fiber,the conversion criteria of different dripping mode were established.Based on the criterion of straight single fiber,the transition criterion of droplet impact convex single fiber and concave single fiber were established.Furthermore,the spreading length of the liquid film after the droplets impact the single fiber was measured,and the correlation formula of the spreading length of the liquid film on the straight single fiber was fitted.Based on the correlation correction of the straight single fiber the spreading length of the convex single fiber and the concave single fiber could be obtained,having deviations generally within ± 10%.(2)There are two typical dripping modes for droplet impacting the crossing fibers:four-part and two-part.According to the force analysis of the droplet impacting the crossing fibers,the conversion criteria of different dripping mode were established.At the same time,because of the different positions of the fibers which make up the cross fiber unit,the maximum spreading length of liquid film L on the upper fiber and lower fiber are different.Based on the correlation formula of the spreading length of the liquid film on the straight single fiber,the correlation formula of the liquid film spreading length of the upper fiber and lower fiber in the crossing fibers were corrected,having deviations generally within ±10%.(3)According to the research of the droplet impact on the single fiber and the erossing fibers,after droplet impacting the mesh grid,there are four typical dripping modes:single hole without spilling,single hole with spilling,multihole without synechia,and multihole with synechia.In the multihole dripping mode,the phenomenon is similar to single fiber and cross fiber.In the single hole dripping modes,because of the small size of the droplet,the dripping is influenced by capillary force and surface tension.In addition,this paper compared the influence of cross fiber and mesh unit of the same size on the increase rate of droplet surface area.When the mesh size is moderate,the dispersion effect of the droplet is the best.While the mesh number is large,the dispersion effect of mesh grid is better.And when the mesh number is small,the dispersion effect of cross fiber is better.