Janus颗粒撞击气泡的行为特征

为更好地在相变传热中应用双亲性Janus颗粒,用铜球制备了亲水-超疏水Janus颗粒,其粒径为1.0 mm,气泡直径为3.0 mm.研究了不同高度下带小气泡的Janus颗粒撞击气泡的行为特征.结果表明:Janus颗粒不同润湿性表面撞击气泡时的行为特征存在明显差异,当超疏水侧接触气泡时,会沿着气泡表面无旋转地滑到气泡底部;当亲水侧接触气泡时,会先沿着气泡表面滑行一段距离,随后发生旋转,对气泡造成强烈扰动;而亲水-超疏水分界面接触气泡时,颗粒会在接触的瞬间开始旋转.当Janus颗粒具有一定的高度撞击气泡时,一般以亲水面首先与气泡接触,随高度的增加, Janus颗粒拉扯气泡变形的程度增加.基于受力分析发现:Janus颗粒发生旋转的主要原因是不同润湿性表面所受毛细力作用点和方向的不同,相应地产生旋转力矩.     

排烟增湿脱硫活化反应器内液滴──脱硫剂颗粒碰撞的数值模拟

排烟增湿脱硫活化反应器内液滴──脱硫剂颗粒碰撞的数值模拟唐庆，徐旭常（清华大学热能工程系北京１０００８４）关键词液滴－颗粒碰撞，脱硫，数值模拟要有效的控制ＳＯＺ的污染，降低燃煤电厂排烟中ＳＯＺ的浓度显得尤为重要。在众多的烟气脱硫技术中，排烟增湿活化脱...     

液滴碰撞不同接触角线缆表面的模拟

针对常见的液滴输电线缆搭建对应的计算模型, 通过Fluent内置的VOF对不同疏水性表面进行计算, 讨论液滴与线缆的接触时间、铺展半径与接触角度之间的关系, 并分析不同接触角下液滴的压力云图和速度矢量图。模拟计算结果显示: 液滴与壁面接触的运动状态受壁面接触角的影响, 液滴铺展面积和接触时间与壁面接触角呈反比关系; 提高壁面接触角会降低铺展面积、减少接触时间, 加快液滴的回缩、回弹, 运动液滴最终滑落离开壁面; 小接触角壁面铺展面积增大、接触时间增加, 液滴最终完全铺展停留于壁面上。研究结果对探究不同疏水性下液滴在线缆壁面结冰的原理及特性具有一定的指导和参考意义。     

甘油液滴与水平固壁面碰撞力的试验研究

本文通过搭建液滴碰撞试验台,研究了甘油液滴分别撞击干燥水平壁面和带液滴壁面时碰撞力随时间的变化规律.研究结果显示:液滴撞击干燥壁面时,碰撞力峰值随碰撞速度与液滴直径的增大而增大;不同液滴直径与碰撞速度下的无因次碰撞力-无因次时间曲线明显贴近,无因次碰撞力峰值随液滴雷诺数增大而具有下降趋势;撞击带液滴壁面会使碰撞力峰值减...     

液滴在不同润湿性表面上蒸发时的动力学特性

基于润滑理论,采用滑移边界条件建立了二维液滴厚度的演化模型和移动接触线动力学模型,利用数值计算方法模拟了均匀加热基底上固着液滴蒸发时的动力学特性,分析了液-气、固-气和液-固界面张力温度敏感性对壁面润湿性和液滴动态特性的影响.结果表明,液滴的运动过程受毛细力、重力、热毛细力和蒸发的影响,重力对液滴铺展起促进作用,而毛细力、热毛细力则起抑制作用;通过改变界面张力温度敏感性系数,可使液滴蒸发过程中的接触线呈现处于钉扎或部分钉扎模式,且接触线钉扎模式下的液滴存续时间低于部分钉扎模式;提高液-气与液-固界面张力温度敏感系数均可改善壁面润湿性能,加快液滴铺展速率;而增大固-气界面张力温度敏感系数则导致壁面润湿性能恶化、延缓液滴铺展过程;通过改变固-气界面张力温度敏感系数更有利于调控处于蒸发状态下的液滴运动.     

等直径微液滴碰撞过程的改进光滑粒子动力学模拟

运用一种改进光滑粒子动力学(SPH)方法模拟了相溶和不相溶两种情况下的等直径微液滴碰撞动力学过程. 为提高传统SPH方法的数值精度和稳定性, 采用一种不涉及核导数计算的核梯度改进形式; 为处理液滴界面张力采用修正的van der Waals表面张力模型. 通过模拟牛顿液滴碰撞聚并变形过程并与相关文献或试验结果进行对比, 验证了改进SPH 方法模拟微液滴碰撞过程的可靠性. 随后, 研究了基于van der Waals模型相溶聚合物微液滴碰撞聚并变形过程及不相溶微液滴碰撞后的反弹、分离过程, 讨论了碰撞过程中碰撞速度、碰撞角度、密度比等参数对碰撞变形过程的影响, 分析了流体桥、旋转角度等因素的变化情况.关键词：光滑粒子动力学微液滴聚合物液滴碰撞     

颗粒碰撞率的实验研究

本文采用一种新的研究思路,以高速摄像作为手段,结合各种新颖的PTV算法,在毫秒级时间尺度和毫米级空间尺度上(颗粒尺寸)来对颗粒碰撞率做实验研究,对长期以来一直沿用的描述颗粒碰撞率的关系进行检验与修正。通过对实际颗粒碰撞率与颗粒浓度、平均相对速度的关系进行测量研究,发现理论关系与实验存在较大的差别,理论关系较大地高估了碰撞率。指出了需要进一步深入和完善描述颗粒碰撞率的实验规律,这些规律可直接应用于气固两相流动的数值计算与理论分析中。     

气固两相流中颗粒-颗粒随机碰撞新模型

本文提出一种气固两相流中计算颗粒－颗粒碰撞新模型．该模型提出一种碰撞概率新概念,与已有模型相比,新模型对碰撞概率的思考另辟蹊径,由所得公式可以确定影响碰撞概率大小的因素．此外,该模型提出在所研究控制体中选择虚拟颗粒的方法,特别是对虚拟颗粒的粒径、速度和随机数之间提出相关性准则．它弥补了以往模型的缺陷．经过计算,验证了新模型的合理性．     

简单剪切流条件下液滴破碎和碰撞模拟

利用耗散粒子动力学(DPD)对简单剪切流条件下液滴的破碎和碰撞分离过程进行了模拟.液滴由多颗简单的DPD粒子构成,液滴与周围流体的不互溶性由提高它们之间的保守力系数获得.通道的上下壁面沿着相反方向运动从而使流体产生简单剪切流动.计算结果表明,在简单剪切流条件下,当界面张力数超过临界界面张力数后,液滴不稳定;液滴将被拉长并破碎成数个较小的稳定的液滴.当两个液滴相互碰撞并分离的现象发生时,两个液滴的质心在速度梯度方向上的距离与整个碰撞过程相关,碰撞之后的δz值比碰撞前的δz大.     

结构高度对纳米液滴碰撞壁面过程的影响

液滴与壁面的碰撞过程广泛存在于自然界以及各类生产生活中,探究其传热传质作用机理以及形态演变对发展表面自清洁、喷墨打印、强化滴状冷凝、抗结冰结霜等技术都具有重要意义。为了探究结构高度在碰撞过程中的作用,本文通过分子动力学模拟对纳米液滴与壁面的碰撞过程进行了研究。构建了具有方柱状结构的粗糙表面模型,研究了壁面上纳米柱状结构的高度对碰撞过程的影响,记录了液滴的变形过程,并对相关的动力学特征以及能量变化进行了分析。     

粒子束在气体系统中的碰撞频率和反应速率系数

利用统计的方法,系统研究了粒子束与气体系统中粒子的碰撞频率分布和总碰撞频率;分析了气体系统粒子间的碰撞频率以及反应速率系数与特征速率的关系.     

液滴冲击液膜问题的光滑粒子动力学模拟

本文对传统的光滑粒子动力学方法进行了改进．改进的光滑粒子动力学方法对传统粒子方法中的核梯度进行了修正,采用了一种新型的耦合边界条件,添加了表面张力和人工应力的计算程序．应用改进的光滑粒子动力学方法对液滴冲击液膜问题进行了数值模拟．得到了不同时刻液滴内部的压力变化特征,精细地捕捉了不同时刻的自由面,从机理上分析了液滴产生飞溅的条件,探讨了韦伯数,表面张力对液滴冲击液膜问题的影响．计算结果表明,改进光滑粒子动力学方法能够有效地描述液滴冲击液膜的动力学特性和自由表面变化特征,能够得到稳定精度的结果．     

Simulation solution for micro droplet impingementon a flat dry surface

This paper presents a computational fluid dynamics approach for micro droplet impacting on a flat dry surface. A two-phase flow approach is employed using FLUENT VOF multiphase model to calculate the flow distributions upon impact. The contact line velocity is tracked to calculate the dynamic contact angle through user defined function program. The study showed that the treatment of contact line velocity is crucial for the accurate prediction of droplet impacting on poor wettability surfaces. On the other hand, it has much less influence on the simulation of droplet impacting on good wettability surfaces. Good fit between simulation results and experimental data is obtained using this model.     

Binary collision of a burning droplet and a non-burning droplet of xylene: Outcome regimes and flame dynamics

The binary collisions of a burning droplet and a non-burning droplet of xylene are experimentally investigated. The experimental parameters span an extensive range of Weber number and impact parameter, covering the collision outcome regimes of coalescence, reflexive separation, and stretching separation. A high-speed camera captures the temporal details of the collision process, involving flame spread, visible radiation, and flame distributions around droplets. For reflexive separation and stretching separation, the flame from the droplet spreads to the ligament, surrounding it during the interaction process, and then spreads around separated droplets and satellite droplets. Highly-interactive flames are formed in-between the droplets, with very sooty flames generated for most collisions. For the coalescence case, a swirling flame forms around the rotating coalesced droplet. For similar Weber numbers, visible flame radiation is compared for different collision regimes. The visible flame radiation changes more significantly for the reflexive and stretching separation cases than it does for the coalescence case. The change of the averaged visible flame radiation for reflexive separation and stretching separation is more than two times higher than that for coalescence. The map of three different collision regimes is plotted in the Weber number versus impact parameter domain and compared with available theoretical model predictions. Although the different outcomes of collision with the presence of flame can be well predicted by the model, using fluid properties determined by the averaged properties of the two droplets, the dynamics of the detailed processes involved in the collisions are very interesting and have strong implications on overall combustion behavior that go well beyond the mapped regimes.     

再谈"小球与均质自由杆的碰撞"

讨论了小球在杆上任一点的碰撞问题,并指出《大学物理》2006年第5期《小球与均质自由杆的碰撞》一文中"完全非弹性碰撞后两物体不一定粘在一起共同运动"的说法是错误的.     

Charged particle fluctuation in Au+Au collision

In this paper,we present the centrality,transverse momentum region and rapidity window size dependence of charged particle fluctuation from Relativistic Quantum Molecular Dynamics (RQMD) model.D Q,Γ Q and Φ Q all depend on the rapidity windows we chosen.ν +-,dyn is a promising observable in experiments,it weakly depends on the acceptance.The beam energy dependence of ν +-,dyn has been studied to present baseline prediction for net charge fluctuations in experiments.     

Charged particle fluctuation in Au+Au collision

In this paper,we present the centrality,transverse momentum region and rapidity window size dependence of charged particle fluctuation from Relativistic Quantum Molecular Dynamics （RQMD） model.D Q,Γ Q and Φ Q all depend on the rapidity windows we chosen.ν ＋-,dyn is a promising observable in experiments,it weakly depends on the acceptance.The beam energy dependence of ν ＋-,dyn has been studied to present baseline prediction for net charge fluctuations in experiments.     

跟踪碰撞的图形描述

借碰撞的图形描述法,澄清了碰撞分类中的一些相关问题。     

A new method for determining hydrodynamic effects on the collision of two spheres

A sphere falling in a fluid may collide with another sphere falling more slowly if, when the spheres are far apart vertically, the horizontal distance between their centers is less than or equal to a critical radius. Accurate prediction of aerosol particle coagulation requires a good understanding of this process. Previously reported optical techniques for measuring hydrodynamic effects on this phenomenon have inherent difficulties detecting grazing collisions and hence in determining the critical radius. In this work, a novel detection technique is demonstrated and it is shown that the critical radius may be determined from the sound generated by the collision of two spheres in a viscous liquid. The technique is shown to provide a more precise and decisive indication of when hard spheres collide.