Thesis Advisor何险峰
Degree Grantor中国科学院研究生院
Degree Name硕士
Degree Discipline化学工程

液滴在外加流场中的变形、破裂以及聚并是研究过程工业中广泛存在的液液不互溶体系的液滴尺寸及其分布的基础。目前对于单液滴在惯性力可忽略的简单流场中的变形与破裂已经有了较为充分的认识,而表面活性剂和惯性力对液滴行为的影响有待进一步研究。本文采用耗散粒子动力学方法,研究了表面活性剂和惯性力影响下的单液滴的变形、破裂与聚并。对于中等雷诺数(1~16)下剪切流场中单液滴的变形,在不同表面活性剂添加量和流场强度下,考察了液滴的倾斜角、变形度以及表面活性剂在相界面的分布状况,得到了无表面活性剂液滴的变形度与毛细数和韦伯数的拟合关联式;通过分别模拟油包水和水包油两种体系,发现当液滴尺寸与表面活性剂特征尺寸相近时,在相同的外加流场和表面活性剂添加量下,油包水体系中表面活性剂在相界面的分布更不均匀,液滴倾斜角更小,变形度更大。在液滴变形模拟的基础上,考察了不同表面活性剂添加量下液滴破裂的临界条件,发现随着表面活性剂添加量的增大,液滴破裂的临界毛细数和临界雷诺数均减小,而破裂前的最大变形度基本不变;对相同尺寸的两个液滴的对心碰撞进行了初步模拟,考察了油包水和水包油体系中不同表面活性剂添加量和表面活性剂极性端亲水性对液滴碰撞结果的影响。为方便模拟结果信息的获取,并为未来更大规模的模拟做准备,基于开源可视化软件ParaView及其原位可视化工具Catalyst实现了耗散粒子动力学模拟结果的原位可视化以及大规模离散模拟结果的离线可视化,提升了模拟软件的易用性。;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. 

Document Type学位论文
Recommended Citation
GB/T 7714
张驭洲. 剪切流场中单液滴变形与破裂的耗散粒子动力学模拟及可视化[D]. 中国科学院研究生院,2018.
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剪切流场中单液滴变形与破裂的耗散粒子动力(3863KB)学位论文 限制开放CC BY-NC-SAApplication Full Text
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