Dissipative Particle Dynamics Simulation Of Single Droplet Deformation And Breakup In Shear Flow And Its Visualization

Droplet deformation,breakup and coalescence in an external flow field are the bases of describing and predicting the droplet size and its distribution in immiscible liquid-liquid multiphase fluid systems,which are common in process industry.So far,the deformation and breakup of single droplet in simple flow with negligible inertia have been relatively well documented.However,the effect of surfactants and flow with inertia on behaviors of the droplet needs further study.In this thesis,the deformation,breakup and coalescence of single droplet were investigated using Dissipative Particle Dynamics(DPD).For droplet deformation in shear flow with moderate Reynolds number(1?16),the droplet inclination angle,the deformation parameter and the surfactant distribution on the interface were investigated under different surfactant amounts and flow field intensities,from which the fitting correlation among the deformation parameter of droplet without surfactant,the Capillary number and the Weber number were obtained.When the droplet size in water in oil(W/O)system is close to the characteristic size of surfactant molecules,the distribution of surfactants at the phase interface is more non-uniform,the inclination angle is smaller and the deformation parameter is larger,compared with their counterparts in oil in water(O/W)system.On the basis of droplet deformation simulations,the critical breakup conditions of single droplet covered with different amounts of surfactant in shear flow were investigated.With the increase of surfactant amounts,both the critical Capillary number and the critical Reynolds number decrease,while the maximum deformation parameter before droplet breakup is almost the same.The head-on collision of two droplets with the same radius was simulated preliminarily,and effects of surfactant amount and hydrophilicity were investigated in both W/O and O/W systems.In order to facilitate the acquisition of simulation results information and prepare for larger simulations in the future,the in-situ visualization of the DPD simulation results and offline visualization of large scale particle-based simulation results were implemented based on the open source visualization program ParaView and its in-situ visualization tool Catalyst,and the usability of the simulation program was improved.