Axisymmetric wetting of a liquid droplet on a stretched elastic membrane

Wetting of a liquid droplet on another liquid substrate is governed by the well-known Neumann equations.The present work aims to develop an explicit modified version of the Neumann equations for axisymmetric wetting of a liquid droplet on a highly stretched elastic membrane of non-zero bending rigidity.An explicit modified form of the Neumann equations is derived to determine the two contact angles,which is reduced to Young's equation for a liquid droplet on a rigid membrane or to the Neumann equations for a liquid droplet on another liquid substrate.Further implications of the modified Neumann equations are examined by comparison with some previous results reported in the recent literature,particularly considering the ranges of material and geometrical parameters of the liquid droplet-membrane system which have not been recently addressed in the literature.

Study on Nonlinear Coupling Wave Model for Liquid Droplet-Solid Impact

In order to investigate the material corrosion by liquid droplet solid impact, a nonlinear coupling wave model adopted to analyze the impact between the spherical liquid droplet and an elastic solid plane has been developed. Many usable results such as the dimensionless pressure in the contact plane of liquid solid and inside the liquid droplet, the equivalent stress distribution inside the solid, the effect of solid elasticity on the impact, and the locations of the maximum equivalent stress in different...

Modeling of Coalescence and Separation of Liquid Droplets During Solidification of Immiscible Alloys

Directional solidification methods are being used f or in-situ production of metallic immiscible composites. A quantitative understa nding of the dynamic behavior and growth kinetics of the nucleated second phase during solidification is necessary to produce homogeneous dispersion in solidifi ed composites. This paper presents a mathematical model for describing the grow th of nucleated dispersed phase in the two-liquid phase region ahead of the sol idification front and the entrapment of these droplets by the moving solid-liqu id interface in vertical unidirectional solidification systems. The model has t wo components. A macro-heat transfer model for describing the temperature prof iles and the rate of advance of the solidification front. The dynamic behavior and coalescence and growth of nucleated droplets in the two-liquid phase region under the influence of effective gravity and thermocapillary forces were repres ented through the solution the droplet momentum and mass conservation equations in particle space. These two components of the models were coupled through a sp ecial algorithm for tracking the particle location and size with respect to movi ng solidification front in the solidification time scale. The model is used to study the particle size distribution in unidirectional solidified Zn-Bi hypermo notectic alloys at reduced gravity conditions. It has been found that the parti cle size and distribution in the solidified alloy depends on solidification rate and the ratio of effective gravity to thermocapillary forces. It was also foun d that uniform dispersion could only be obtained in a very narrow range of effec tive gravity values near zero gravity. The model predictions were compared agai nst experimental measurements obtained at different effective gravity conditions in a novel unidirectional solidification apparatus that uses electromagnetic fo rces to modulate gravitational forces. The model was found to reasonably predic t the experimentally measured particle size and distribution over the entire ran ge of effective gravity investigated as well as gravity conditions for settling and flotation of the second phase during solidification. The practical signific ance of these findings will be discussed.

Millimeter-Scale Liquid Droplet Migration on Solid Surface with Temperature Gradient: A Simulation Investigation

In this paper, we established a time-dependent model that investigates the migration behavior of a millimeter-scale liquid droplet on a solid surface with temperature gradient. Both fluid mechanics and heat transfer are incorporated in the model. The Navier-Stokes equation is employed both inside and outside the droplet. Size variation is observed in the transient simulation. Results show that the velocity of the migration is about 1.7 mm/s under a temperature gradient of 30 K/mm. The model is consistent with results with previous literatures.

Preparation of Microcapsules with Liquid Droplet Coalescence Method Followed by Phase Separation

Novel preparation method of microencapsules was developed on the basis of the liquid coalescence method followed by phase separation. Oil droplets of limonene dissolving expanded polystyrene as a shell material were forced to collide and coalesce with the Isopar oil droplets of core material in the continuous wates phase. When two kinds of oil droplets are collided and coalesced with each other, expanded polystyrene dissolved in the limonene oil may be phase-separated in the oil droplets newly formed to form the microcapsule shell, because the Isopar oil was a poor solvent for expanded polystyrene but a good solvent for the limonene oil. In the experiment, the diameter (or number) of limonene oil droplets dissolving expanded polystyrene was mainly changed, because the coalescence frequency between the droplets is strongly dependent on the number of droplets. Favorable core shell types of microcapsules with the shell thickness from 1.0 to 5.0 μm were able to be prepared under all the experimental conditions adopted here.

A New Model to Predict Average Pressure Difference of Liquid Droplet and Its Application in Gas Well

The distribution of droplet surface pressure is uneven?under the action of high velocity gas streams in gas wells, and there exists a pressure difference which leads to droplet deformation before and after the droplet. Moreover, it affects the critical liquid carrying rate. The pressure difference prediction model must be determined, because of the existing one lacking theoretical basis. Based on the droplet surface pressure distribution in high velocity gas streams, a new model is established to predict the average differential pressure of droplets. Compared with the new differential pressure prediction results, the existing pressure difference prediction results were overvalued by 46.0%. This article also improves four gas-well critical liquid carrying models using the proposed pressure difference prediction model, and compares with the original one. The result indicates that the critical velocity of the original models is undervalued by 10% or so, due to the overestimate to the pressuredifference. In addition, comparisons of the improved model with original models show that it is necessary to consider the adaptability, because the models have significant differences in results, and different suitability for different well conditions.

TRACKING METHODS FOR FREE SURFACE AND SIMULATION OF A LIQUID DROPLET IMPACTING ON A SOLID SURFACE BASED ON SPH

With some popular tracking methods for free surface, simulations of several typical examples are carried out under various flow field conditions. The results show that the Smoothed Particle Hydrodynamics （SPH） method is very suitable in simulating the flow problems with a free surface. A viscous liquid droplet with an initial velocity impacting on a solid surface is simulated based on the SPH method, and the surface tension is considered by searching the free surface particles, the initial impact effect is considered by using the artificial viscosity method, boundary virtual particles and image virtual particles are introduced to deal with the boundary problem, and the boundary defect can be identified quite well. The comparisons of simulated results and experimental photographs show that the SPH method can not only exactly simulate the spreading process and the rebound process of a liquid droplet impacting on a solid surface but also accurately track the free surface particles, simulate the free-surface flow and determine the shape of the free surface due to its particle nature.

A Review on Thermal Design of Liquid Droplet Radiator System

Liquid Droplet Radiator (LDR) system is regarded as a quite promising waste heat rejection system for aerospace engineering.A comprehensive review on the state-of-the-art of LDR system was carried out.The thermal design considerations of crucial components such as working fluid,droplet generator and collector,intermediate heat exchanger,circulating pump and return pipe were reviewed.The state-of-the-art of existing mathematical models of radiation and evaporation characteristics of droplet layer from literatures were summarized.Furthermore,thermal designs of three LDR systems were completed.The weight and required planform area between the rectangular and triangular LDR systems were respectively compared and the evaporation models for calculating the mass loss were evaluated.Based on the review,some prospective studies of LDR system were put forward in this paper.

A study of different fluid droplets impacting on a liquid film

Knowledge of droplet dynamics provides the basis of predicting pressure drops, holdups and corrosion inhibitor distribution in multiphase flow. Droplet size and its distribution also determine the separation efficiency between different phases. Experimental observations were conducted for droplet impingements with different fluids, droplet sizes and velocities, and film thicknesses. The observed transition boundaries were compared with the models developed by different authors. For impingement on a deep pool surface, the Marengo and Tropea correlation for splashing does not agree with the experimental results in this study. The Bai and Gosman critical Weber number for bouncing agrees with the water results but not the oil results. Three new correlations for transition boundaries between bouncing, coalescence, jetting and splashing were proposed and compared with the experimental observations.

Pre-concentration and determination of amitriptyline residues in waste water by ionic liquid based immersed droplet microextraction and HPLC

This paper describes a new approach for the determination of amitriptyline in wastewater by ionic liquid based immersed droplet microextraction （IL-IDME） prior to highperformance liquid chromatography with ultraviolet detection. 1-Hexyl-3-methylimidazolium hexafluorophosphate （[C6MIM][PF6]） was used as an ionic liquid. Various factors that affect extraction, such as volume of ionic liquid, stirring rate, extraction time, pH of the aqueous solution and salting effect, were optimized. The optimal conditions were as follows： microextraction time, 10 min; stirring rate, 720 rpm; pH, 11; ionic drop volume, 100 uL; and no sodium chloride addition. In quantitative experiments the method showed linearity in a range from 0.01 to 10 ug/mL, a limit of detection of 0.004 ug/mL and an excellent pre-concentration factor （PF） of 1100. Finally, the method was successfully applied to the determination of amitriptyline in the hospital wastewater samples.

Visual study on the characteristics of liquid and droplet in a novel rotor-stator reactor

Rotor–stator reactor(RSR), an efficient mass transfer enhancer, has been applied in many fields. However,the hydrodynamic characteristics of liquid flow in RSR are still a mystery despite they are fundamental for the mass transfer performance and processing capacity. In view of the above, this paper studies the liquid–liquid flow and liquid holdup in RSR under various conditions with a high-speed camera. The paper firstly demonstrates two flow patterns and liquid holdup patterns that we obtained from our experiment and then presents in succession a flow pattern and a liquid holdup criterion for the transition of film flow to filament flow and complete filling to incomplete filling. It is found that experimental parameters, including rotor–stator distance, rotational speed and volume flow rate exert great influence on the average droplet diameter and size distribution. Besides, by comparison and contrast, we also find that the experimental values match well with our previous predicted calculations of the average diameter, and the relation between the average diameter and the mean energy dissipation rate.

Sensitivity of the Grid-point Atmospheric Model of IAP LASG(GAMILI.I.0)Climate Simulations to Cloud Droplet Effective Radius and Liquid Water Path

This paper documents a study to examine the sensitivity to cloud droplet effective radius and liquid water path and the alleviation the energy imbalance at the top of the atmosphere and at the surface in the latest version of the Grid-point Atmospheric Model of the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics （LASG）, Institute of Atmospheric Physics （IAP） （GAMIL1.1.0）. Considerable negative biases in all flux components, and thus an energy imbalance, are found in GAMIL1.1.0. In order to alleviate the energy imbalance, two modifications, namely an increase in cloud droplet effective radius and a decrease in cloud liquid water path, have been made to the cloud properties used in GAMIL. With the increased cloud droplet effective radius, the single scattering albedo of clouds is reduced, and thus the reflection of solar radiation into space by clouds is reduced and the net solar radiation flux at the top of the atmosphere is increased. With the reduced cloud optical depth, the net surface shortwave radiation flux is increased, causing a net warming over the land surface. This results in an increase in both sensible and latent heat fluxes over the land regions, which is largely balanced by the increased terrestrial radiation fluxes. Consequently, the energy balance at the top of atmosphere and at the surface is achieved with energy flux components consistent with available satellite observations.

Manipulation of Colloidal Droplets in Space and the Instability of Thermocapillary Convection in Large Prandtl Number Liquid Bridge in Microgravity

In 2016 and 2017, SJ-10 and TG-2 satellites were launched. In this short paper, we report recent progress on the studies of manipulation of colloidal droplets and instability of thermocapillary convection in large Prandtl number liquid bridge that based on the space experiments boarding SJ-10 and TG-2 satellites,separately. It was shown that the colloidal droplets can be successfully formed and manipulated in microgravity through the patterned substrates. In another aspect, the coffee-ring effect was observed at the first time in space. For the studies of the instability of thermocapillary convection in large Prandtl number liquid bridge in microgravity, our experiments in TG-2 broadened the way of such kind of study and abundant experimental results are emerging.

Interaction of Surfactants and Polyelectrolyte-Coated Liquid Crystal Droplets

It is known that the adsorption of surfactants at the liquid crystal (LC)/aqueous interface can induce a bipolar-to-radial director configuration of LC droplets dispersed in aqueous solution. In this paper, we study the effect of charged polyelectrolyte-coating on the interaction of surfactants and LC droplet cores by observing the director configuration of the LC droplet cores as a function of surfactant concentrations. It is found that surfactants can penetrate into the polyelectrolyte coating and react with the LC droplet cores to induce the bipolar-to-radial transition of the LC inside the droplet cores. However, the concentration of charged surfactants required to induce the configuration transition of the LC droplet cores is affected by the charged polyelectrolyte coating. The effect is significantly enlarged with decreasing the alkyl chain length of charged surfactants. Our results highlight the possibility of engineering polyelectrolyte coatings to tune the interaction of LC droplets with analysts, which is critical towards designing LC droplet based sensors.

Interaction phenomena between liquid droplets and hot particles—Captured via high-speed camera

The interaction of evaporating droplets and hot catalyst particles plays a major role in heterogeneously catalysed reactions. The liquid feed is injected into a gas-solid flow and is mixed with the catalyst. The interaction phenomena determine the evaporation time which should be minimised to keep the reactor vessel small. First measurements with a bed of fixed hot FCC-particles （fluid catalytic cracking） and two model fluids have been conducted. The interactions of ethanol and water droplets with the hot bed surface were captured via a high-speed camera. While the ethanol droplet developed a stable steam cushion due to Leidenfrost phenomena, water showed intense interaction and steam explosions which induced repulsion and atomisation of the droplet.

颗粒击穿气泡时气泡的变形和破裂

通过高速摄像机拍摄研究了颗粒击穿半球气泡破碎的演变过程.观察并分析了气泡成型后边缘再生和对流情况、受到颗粒击穿时气泡破碎的概率、以及成孔后的气泡破碎行为.通过量纲分析以及实验研究发现,气泡破碎概率是雷诺数和韦伯数的函数,概率P=1.08(Re^(0.5)We^(0.25))^(0.664),且当Re^(0.5)We^(0.25)>1020时,概率升至100%,气泡破碎形成的不稳定性射流数量是奥内佐格数Oh的函数.气泡液膜的卷曲速度随溶液浓度提高而升高,气泡液厚度随浓度提高而减小.

黏性牛顿流体液滴撞击干燥或预湿网面的实验研究

液滴撞击网面现象广泛存在于自然界和一系列应用中,液滴撞网后会穿透破碎产生二次液滴或不破碎全部附着在网面上,两种情况下都会残留液体在网面而形成预湿,影响后续撞击结果,但前人研究集中于低黏性液滴撞击干燥网面,黏性牛顿流体液滴撞击干燥或预湿网面的演化与机理仍有待探索.文章采用高速阴影成像技术,研究了黏性液滴(甘油水溶液)撞击干燥和预湿网面形成液指和破碎的演化规律,考虑了网面结构尺寸、液滴黏性及撞击前网面上预湿液膜厚度对撞击结果的影响.实验结果表明,液滴撞击干燥网面后形成液指的最大长度随网孔宽度降低、液滴黏性增加而减小;液滴黏性增加、网孔宽度减小均会抑制液滴对干燥网面的完全穿透;预湿液膜高度的增加抑制液滴对网面的完全穿透,并使不完全穿透时形成液指的最大长度减小.建立了考虑液滴黏性、网孔宽度和网面预湿的液滴撞击网面后不完全穿透时形成液指的最大长度预测模型,以及出现完全穿透时的临界参数理论预测模型,模型预测结果均与实验结果吻合良好.

低温风洞中液氮液滴的破碎特性模拟研究

为探究低温风洞中液氮液滴的破碎特性并阐明其破碎机理,基于耦合水平集流体体积函数(CLSVOF)方法,采用自适应局部网格加密技术,构建了二维液氮液滴破碎模型,对比了液氮液滴与常温液滴的形态演变规律,计算分析了韦伯数(We)对液氮液滴形态、变形系数及时间特性的影响规律。模拟结果表明:液氮液滴的We高于常温液滴,且更容易发生变形和破碎;随着We的增大,液氮液滴依次发生袋状破碎、多模式破碎和剪切破碎;液滴迎风面和背风面的压差均随时间呈现先增大后减小的规律,发生转变的原因是袋状结构形成或边缘液滴颗粒脱落;不同液氮液滴破碎模式下,变形系数的变化规律差异明显;液氮液滴无量纲初始破碎时间随We的增大而减小,在0<We<100时,临界变形系数维持在2.6附近。研究结果可为低温风洞中液氮喷雾冷却系统的优化提供理论依据。

气田高含盐采出水旋转雾化影响因素数值模拟

雾化后的液滴粒径越集中,越容易控制雾化过程,调节雾化参数可达到降低气田采出水系统的运行成本,提升处理效果的目的。采用耦合气液两相湍流理论、离散相模型和TAB(Taylor Analogy Breakup)模型,建立了基于拉格朗日方法的旋转雾化模型,对气田高含盐采出水雾化过程进行了数值模拟研究,复现了不同时刻液滴破碎过程,得到连续相空气、离散相液滴的速度矢量分布。分析旋转雾化转速、转盘直径、进液量的影响作用规律。研究结果表明,转速越快、转盘直径越大、进液量越少,雾化效果越好。研究结果可为旋转雾化器的结构工艺参数优化提供理论参考。

Marangoni流动对液滴撞击过热液池影响的数值模拟

对液滴撞击过热液池的动态过程进行数值模拟,着重关注由液池表面不均匀温度引起的马兰戈尼效应(Marangoni effect)对液池内的流场和温度场演化过程的影响。当乙醇液滴落入过热油池后,液池表面温度随着液滴的靠近而迅速下降,从而在径向上产生很大的温度梯度。由此引发的沿径向向内的Marangoni力会与沿径向向外的蒸汽剪切应力相抗衡,进而在蒸汽层最薄的位置形成一个“热射流”结构。随着时间的推进,占据主导地位的Marangoni力逐渐将“热射流”向内推动,直至在液滴下方形成下沉羽流。此外,随着液池黏度的增加,液池内由表面蒸汽应力引起的流动将被抑制,进而导致界面附近的换热效率大幅下降。