Dynamic Characteristic And Critical Criteria For Droplet Breakthrough Upon Impacting Mesh Screen

Mesh screen is widely used in gas-liquid separation device for energy and chemical industry.It has the advantages of high efficience,low pressure drop and low cost.When gas-liquid mixture flows across the screen,gas passes through the holes while droplets are intercepted by mesh,resulting in the separetion of two phase.Once the doplet velocity reaches to a critical value,subdroplets will be generated and passed through mesh screen,which would cause severe performance of the separation device.Impacting process of droplet on mesh screen is the key part of gas-liquid separation.Droplet dynamic characteristics are closely related to separation efficiency.An visualization experiment,based on high-speed camera system,was carried out to study the dynamic process of droplet impacting mesh screen in this paper.Main points of the research is the dynamic charactoristics and crirical breakthrough condition after the impact.The influence of droplet diam eter,impact velocity,tilt angle,mesh screen structure and surface wettability are careful discussed.The spreading and shrinking dynamic behaviour after collision could be characterized by dimensionless spreading factor.Topograpgy changes of the droplet are driven by the conversion between kinetic energy and surface energy,some of which is wasted by viscous dissipation.Increasement of droplet diameter and impact velocity both leads to larger inertia force,resulting in a wider spreading area.On hydrophilic surface,droplet is dragged by the viscous force,thus the spreading area is reduced.Structure parameters of mesh screen,which are relatively independent with those forces,do not appreciably affected the spreading process.The drop impacting process is governed by the dynamic pressure together with the additional water hammer pressure competed with the capillary pressure in the mesh pore.As liquid penetrating into the mesh pore,rapid declination of flow area yields significant liquid compression,which would cause additional water hammer pressure.Analysis shows that the value of water hammer pressure is related to dimension parameters of both droplet and mesh screen.Droplet is distributed after impacting inclined mesh screen,yielding normal and tangent direction of flow.However,inertia force is only determined by the normal one.Droplet interface curvature in the mesh pore is constrained by instinct advance angle.Capillary force could be calculated with known the curvature and pore diameter.Based on the balance of three forces,the paper derive a critical criterion formula,which contains the factors above and matches experiment results.Considering that the critical criterion formula is expressed in demensionless form,it could be generalize d to different situations,and guide the optimization design of gas-liquid sparator.