Research On The Breakup Characteristics Of Viscoelastic Polymers Solution Droplet In Uniform Flow

The problem of droplet breakup is the research hotspot of atomization combustion,spray drying and coating.Especially when the mechanical response of droplet is viscoelastic,the viscosity changes with the change of shear rate,the motion includes deformation,and the stress-strain properties show nonlinear characteristics.This special performance makes the viscoelastic droplet breakup problem become the key breakthrough point of some emerging technologies.The current work mainly focuses on the effect of droplet viscous properties on the breakup process.However,due to the complex rheological properties of viscoelastic fluids,the research on droplet breakup has not yet formed a complete system.In this paper,the droplet breakup characteristics of viscoelastic polymer solutions are studied by experiment and numerical simulations.The specific research content is mainly divided into two aspects:Firstly,based on the continuous jet method and high-speed photography technology,an experimental platform for droplet breakup was built to capture the deformation and breakup process of polyethylene oxide(PEO)solution droplets with the characteristics of Boger fluid.After comparison,the experimental results show that the regime division of viscoelastic fluid droplet breakup is basically consistent with that of Newtonian fluid.The difference is that after the viscoelastic droplet is broken,the beads on a string phenomenon will occur,which affect the particle size and spatial distribution of the sub-droplets.The analysis of droplet breakup time,deformation and particle size distribution shows that,in certain extent,the elastic change has little effect on the breakup characteristic parameters.Based on the experimental data and the previous research results,the prediction formulas of time and some deformation parameters are established.And it is determined that the particle size distribution of the sub-droplets in the bag and bag-stamen breakup regime still satisfy the normal distribution.Second,based on the OpenFOAM platform,using the Volume of Fluid method and adaptive mesh refinement technology,the three-dimensional numerical simulation of the viscoelastic droplet breakup is carried out based on the Oldroyd-B model.Combined with the distribution of pressure and velocity in the flow,it is found that the uneven distribution of velocity in each area inside the droplet may lead to three breakup regimes of bag,bag-stamen and sheet;The breakup morphology of the viscoelastic droplet is,in certain extent,is less sensitive to elastic changes.And the first normal stress difference mainly acts on the surface of the droplet in the process of deformation and breakup,and presents the form of squeeze flow;The change of droplet drag coefficient is closely related to the radial deformation of droplets;The kinetic energy of the droplet increases with the increase of the We number,and the growth rate is also accelerating.