离子液体液滴在加热平板上的铺展特性研究

采用FLIR红外热像仪对离子液体及其水溶液液滴撞击加热平板后的表面温度分布进行研究,分析了液滴铺展直径随平板加热温度及加热时间的变化规律。结果表明:随着液滴与平板加热时间的增加,液滴表面温度分布均由凹状分布变化至均匀分布;随着平板温度的增加,液滴表面温度增加。随着加热时间的增加,水液滴直径缓慢减小,并在某一时刻急剧降低;而对于60wt%离子液体液滴及纯离子液体液滴,液滴直径反而缓慢增加并趋于稳定。随着加热温度的增加,水液滴直径急剧降低的时刻点前移,对于60wt%离子液体溶液液滴,液滴直径变化规律不明显,而对于纯离子液体液滴,液滴直径逐渐增加。     

应用光纤液滴传感器进行液体测试

光纤液滴传感器是利用测试液滴的形成过程与液体成份之间的关系而制成的一种液体测试传感器。主要利用光纤来监测液滴的增长过程,得到随液滴下降过程的光强变化情况,从中获得反映液体的物理、化学性质的“液滴指纹图”。通过对指纹图进行分析对比得到液体的特性参数,实现对各种液体的鉴别。     

图像处理技术用于计算液滴体积

液体的液滴体积大小包含了该液体的许多物理、化学特性,提出用图像处理技术测量液滴体积的方法。通过CCD摄像机实时采集液滴生长过程中的轮廓变化情况,通过图像处理系统存储图像并运用Sobel或Laplacian检测算子进行边缘提取,最后根据液滴的轮廓边缘积分计算出液滴的体积。给出了液滴生成过程的CCD图像记录和液滴体积变化曲线。     

垂直激励液体表面液滴的存活时间研究

液滴滴落在垂直激励的液体表面,有可能会在表面停留很长时间.本文对该现象进行了实验研究,分析了多种因素对液滴存活时间的影响.结果发现:当驱动频率、驱动振幅、液滴滴落高度处于适当的值时,可以使得液滴存活较长的时间,并且液滴的存活时间会随着液体浓度的改变而改变.     

基于Marangoni效应的液-液驱动铺展过程

液体表面的液滴运动在微流体和许多生物过程中具有广泛的应用前景.本文通过研究在液体基底上一种低表面张力液体对另一液体的驱动来理解Marangoni效应在自发驱动体系中的作用.为了研究液体驱动的液滴铺展过程,建立了以不易挥发性硅油作为驱动溶剂、正十六烷作为受驱动液滴,以及不同浓度的十二烷基硫酸钠溶液作为基底溶液的实验体系.通过对正十六烷液滴受驱动铺展动态过程的观察和研究,发现界面张力梯度对液体驱动的铺展起主导作用.实验结果表明:基底溶液浓度主要对正十六烷液滴的最大铺展半径存在影响.此外,用经典稳定性分析模型解释了正十六烷在受驱动铺展过程中由液柱破碎成小液滴的原因,同时得到了失稳特征参数最快不稳定波长与正十六烷液柱半径之间的关系.     

蘸粘式光纤液体分析仪的折射率传感特性研究

提出了一种测量液体折射率的光纤液体分析仪。利用液体表面张力的作用,在光纤探头端形成一个液滴。该液滴的作用相当于一个平凸透镜,发射光纤出射的光经液滴表面折射、未扰液面的反射和液滴表面的再次折射后进入接收光纤。根据菲涅耳公式,光线在各个界面的透射系数和反射系数与液体的折射率有关,且对于不同的液体,光线的传输路径不同。基于球面折射成像和反射式强度调制原理,分析了光线的传输路径,并建立了接收光纤接收到的光强与液体折射率的关系模型。对不同浓度的NaCl溶液进行了测量,实验结果符合理论预期,表明该方法可以用于液体折射率的测量。     

液体火箭有机凝胶喷雾液滴蒸发模型及仿真研究

凝胶推进剂虽然兼具有液体推进剂流量可控和固体推进剂长期可储存等优点, 但凝胶喷雾液滴蒸发燃烧问题却一直困扰着凝胶推进剂研制及燃烧室设计工作, 阻碍了凝胶推进剂实际工程应用.设计实现了凝胶单液滴蒸发燃烧实验系统, 通过某型有机凝胶偏二甲肼(UDMH)单液滴在四氧化二氮蒸气中的蒸发燃烧实验现象, 进一步深入分析了凝胶液滴蒸发燃烧机理.根据实验中凝胶单液滴在不同阶段的蒸发特性, 建立了有机凝胶喷雾液滴在胶凝剂膜形成、膨胀、破裂三个不同蒸发阶段的多组分蒸发模型, 采用初步选定的模型参数及物性参数对凝胶单液滴在高温气体环境中的蒸发全过程进行了仿真计算, 并与常规液体液滴的仿真结果进行了对比分析.结果表明,凝胶喷雾液滴表面胶凝剂含量在蒸发初期增加比较缓慢, 但在某临界时刻后的极短时间内迅速升高至形成胶凝剂膜的质量分数95%, 导致表面质量流率迅速下降至0,表面温度则快速上升至UDMH推进剂沸点.胶凝剂膜形成后, 液滴半径及表面UDMH蒸气质量分数出现了实验现象中凝胶液滴反复膨胀-破裂的震荡现象, 液滴表面温度维持在略高于沸点的某温度范围内,凝胶液滴内部的沸腾蒸发明显强于液体液滴表面稳态蒸发流率, 使得凝胶喷雾液滴生存时间小于常规液体液滴.     

微纳米结构超疏水表面低浓度乙醇液滴的合并弹跳

本文以去离子水、质量分数为8%和16%的低浓度乙醇溶液为工质,研究了液体表面张力对液滴在平超疏水和层级微槽超疏水表面合并弹跳的影响,揭示液体表面张力变化引起液滴合并过程中与表面结构相互作用的改变,为实现低表面张力工质的动力学行为调控研究提供前期探索。研究发现,在平超疏水表面,质量分数为8%和16%的乙醇液滴合并弹跳过程由惯性效应主导,合并弹跳速度遵循惯性毛细定律,无量纲速度为0.23～0.27,能量转化效率为5.6%～6%。液体表面张力的减小导致平超疏水表面液滴合并弹跳速度的减小,并未影响液滴合并过程中内部动量的传递机制。在层级微槽超疏水表面,槽道边缘增强的黏附作用改变了乙醇液滴合并过程的形态演变,影响了其内部动量的传递,导致液滴合并弹跳速度和能量转化效率降低。随着液体表面张力的减小,液滴间凸台结构对合并弹跳性能的强化作用减弱,而凹槽结构对合并弹跳性能的恶化作用增强。     

异性荷电液滴非聚合特性的实验研究

基于显微高数数码摄像技术对异性荷电液滴对撞行为的演变过程进行了实验研究。以不同离子浓度的盐酸水溶液为研究介质,精确捕捉了不同电压下异性荷电液滴的非聚合破碎形貌特征,探讨了介质电导率等对异性荷电液滴非聚合及破碎特性的影响规律。实验结果表明:低电导率液滴在较高电压下的动力学行为表现为非接触反弹。随着电导率的增加,液滴对撞过程的动力学行为表现为非接触破碎,液滴尖端的离子浓度在发生空气放电前达到瑞利极限。液滴破碎行为的剧烈程度与液体电导率成正比,高电导率液体在较低的电压区间便观察到液滴的破碎行为,且液滴拉伸速率及破碎体积对电场强度的变化更加敏感。     

高频感应等离子体炬内液体喷雾的运动与蒸发

本文建立了液体喷雾在高频感应等离子体内运动和蒸发的数学模型,在考虑喷雾液滴相互碰撞和喷雾与等离子体相互耦合效应的情况下,模拟了不同喷雾参数下液体喷雾在高频感应等离子内的运动和蒸发.单个液滴的计算结果和文献中的实验结果进行了比较,结果吻合良好.模拟表明,在通常情况下,喷雾液体的碰撞会导致更大尺寸液滴的形成,从而延缓喷雾的完全蒸发.结果还表明,液体喷雾蒸发对等离子体温度场的局部冷却效应明显,因此必须考虑两者的耦合效应.     

水平均质表面上液滴聚合过程的可视化实验研究

对水平均匀表面上液滴的聚合过程及特性进行了可视化实验研究,获得了液滴半径和液滴物性等参数对液滴聚合过程中液滴液桥半径和接触角变化特性的影响规律。实验结果表明:液滴聚合中液桥半径和接触角都呈衰减振荡变化; 聚合前液滴半径越小,液桥半径振荡频率越大,振幅越小,振荡时间越短;液滴的粘度越大,液桥半径的振荡频率越小, 振幅越小,振荡时间越短;液滴聚合前的接触角明显大于聚合液滴静止后的接触角,其差值与固体界面状况和气、固、液物性相关。     

倾斜均质表面上非等径液滴的聚合特性

对倾斜均匀表面上非等径液滴的聚合过程及特性进行了可视化实验研究,获得了液滴半径和表面倾角等参数对液滴聚合过程中液滴液桥半径、接触角和接触线变化特性的影响规律,进一步说明了倾斜表面上液滴聚合可以加快液滴的运动.     

倾斜均质表面上等径水滴聚合过程的可视化实验

对倾斜均匀表面上等直径水滴的聚合过程及特性进行了可视化实验研究,获得了水滴直径和表面倾角等参数对液滴聚合过程中液滴液桥半径、接触角和接触线变化特性的影响,分析了水滴聚合对其运动的影响.实验结果表明:表面倾角越大,下滑的临界半径越小;液滴的直径越大,液滴聚合后越容易下滑;液滴聚合可以加快液滴的运动,使下滑临界半径减小.     

Energy analysis of possible channels for decomposition of a charged drop into two parts

Based on numerical analysis of the mathematical expression for potential energy of an isolated charged spheroidal drop and two approximate spheroidal daughter drops, mechanisms for decomposition of a multiply charged drop in two nearly equal parts were studied taking into account the electrostatic interaction of the daughter drops. It was shown that, as the distance between the daughter drops increased, both the probability of spontaneous decomposition of a multiply charged drop in two daughter drops and the decomposition symmetry degree increase at the moment of breaking the connection between the daughter drops.     

Difference in the conditions and characteristics of evaporation of inhomogeneous water drops in a high-temperature gaseous medium

The evaporation of water drops of initial mass 5–15 mg on a stationary graphite substrate, as well as inhomogeneous drops with solitary solid inclusions, during heating by high-temperature combustion products has been investigated experimentally. Experiments have also been carried out with analogous inhomogeneous drops moving through combustion products. The possibility of two mechanisms of phase transformations of inhomogeneous liquid drops has been established. The scales of the effect of the area of the inclusion surface (up to 20%) and the initial mass of water (up to 90%) on the characteristics of the evaporation of inhomogeneous drops have been determined.     

利用折射光场分析液滴中光传播规律

为了保证液滴分析技术的重复性和可靠性,必须对光在液滴中的传播规律有更为深入的了解.设计并制作了三套不同方位的实验系统,以纯净水作为实验样品.分别拍摄了自液滴中向三个方向的折射光场分布.通过分析折射光线分布,并利用光纤出射光场的实验规律,进一步得出光在液滴中的传播轨迹,解释了光纤液滴指纹图中峰值形成过程.实验结果表明,光纤液滴指纹图中不同的特征峰值所对应的光在液滴中的传播模式是不同的.     

Simulations of coulombic fission of charged inviscid drops

We present boundary-integral simulations of the evolution of critically charged droplets. For such droplets, small perturbations are unstable and eventually lead to the formation of a lemon-shaped drop with very sharp tips. For perfectly conducting drops, the tip forms a self-similar cone shape with a subtended angle identical to that of a Taylor cone, and quantities such as pressure and velocity diverge in time with power-law scaling. In contrast, when charge transport is described by a finite conductivity, we find that small progeny drops are formed at the tips, whose size decreases as the conductivity is increased. These small progeny drops are of nearly critical charge, and are precursors to the emission of a sustained flow of liquid from the tips as observed in experiments of isolated charged drops.     

Theory of electroacoustic waves in cloudy atmosphere

A general system of equations of motion of a mixture of weakly charged gas and a dropwise liquid is obtained. Vapor condensation on the drops, electrization of the gas, as well as coagulation of drops are taken into account.     

Electro-hydrodynamic propulsion of counter-rotating Pickering drops

Insulating particles or drops suspended in carrier liquids may start to rotate with a constant frequency when subjected to a uniform DC electric field. This is known as the Quincke rotation electro-hydrodynamic instability. A single isolated rotating particle exhibit no translational motion at low Reynolds number, however interacting rotating particles may move relative to one another. Here we present a simple system consisting of two interacting and deformable Quincke rotating particle covered drops, i.e. deformable Pickering drops. The drops attract one another and spontaneously form a counter-rotating pair that exhibits electro-hydrodynamic driven propulsion at low Reynolds number flow.     

Detonation waves in bubble-drop media

Wave processes in chemically active multicomponent media: liquid — gas bubbles — liquid drops have been studied experimentally. Existence of detonation waves in multicomponent (bubble-drop) media has been proved. Structure of detonation waves in bubble-drop and bubble media is qualitatively identical: detonation waves are solitary waves with pulsation profile the pressure behind which is close in value to the one in unperturbed medium. Propagation velocity of detonation waves in bubble and bubble-drop media drops with the increase in medium gas phase concentration and with the decrease in carrier liquid viscosity. Presence of liquid drops decreases detonation wave velocity compared with bubble medium that does not contain liquid drops. Detonation wave propagation in multicomponent media causes gas bubbles fragmentation as well as fragmentation of individual liquid drops. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 04-03-33106).