Morphological Study of Cavity and Worthington Jet Formations for Newtonian and Non-Newtonian Liquids

In this article a morphological study of the cavity formation and the liquid column formation of the Worthington jet with lapse of time for the Newtonian liquids of water and glycerine wt 70% solution and for non-Newtonian liquids of acrylic copolymer solution of ACA-wt1%, ACA-wt2%, and ACA-wt3% by a droplet falling to the free surface of the target liquid in the cylindrical container from a height of H = 100, 200, 300, 400, and 500 mm is described. The calculated results by the energy equation for the maximum cavity radius Rmax/d and for the morphological size D · h/d² of the Worthington jet are in agreement with the experimental results. In order to take photographs of the cavity formation and the Worthington jet formation with lapse of time, a CCD camera was used. The falling droplet and the target liquid are the same material. Here d is the mean diameter of the droplet and D and h are the mean diameter and maximum height of the liquid column of the Worthington jet.     

Granulation of ferrosilicon alloy by rotary multi-nozzles cup atomizer: Granulation behavior and model formation

Nowadays, ferroalloys are mainly produced by mold casting and crushing process in China which have obvious drawbacks like low efficiency and high energy consumption. In the present study, a novel process which was based on a rotary multi-nozzles cup atomizer (RMCA) was suggested on FeSi75 (alloy containing 75?wt.% Si). A circle of water curtain was set around the rotary multi-nozzles cup atomizer. According to the calculation results of atomization mechanism, the granulation process agreed with Rayleigh’s mechanism. During the breakup of the alloy ligament, the surface tension plays an important role on the formation of droplet, and the effect of centrifugal force on the diameter of the alloy droplets becomes obvious with the increasing of the rotating speed. In the current study, the models of the traveling trajectories and the heat transfer of the alloy droplet are established. It is found that the solidification time of droplet with different thickness of solidification layer increase with the increase the alloy droplets’ diameter. And the thickness of water curtain required for cooling the alloy increases with increasing the rotating speed.     

Morphological Study of Cavity and Worthington Jet Formations for Newtonian and Non-Newtonian Liquids

In this article a morphological study of the cavity formation and the liquid column formation of the Worthington jet with lapse of time for the Newtonian liquids of water and glycerine wt 70% solution and for non-Newtonian liquids of acrylic copolymer solution of ACA-wt1%, ACA-wt2%, and ACA-wt3% by a droplet falling to the free surface of the target liquid in the cylindrical container from a height of H = 100, 200, 300, 400, and 500 mm is described. The calculated results by the energy equation for the maximum cavity radius Rmax/d and for the morphological size D · h/d² of the Worthington jet are in agreement with the experimental results. In order to take photographs of the cavity formation and the Worthington jet formation with lapse of time, a CCD camera was used. The falling droplet and the target liquid are the same material. Here d is the mean diameter of the droplet and D and h are the mean diameter and maximum height of the liquid column of the Worthington jet.     

Understanding the formation of ultrafine maltodextrin particles under simultaneous convective drying and antisolvent vapour precipitation

Research on simultaneous antisolvent-vapour-induced precipitation and convective drying of a solute-containing droplet was extensively conducted since this technique was introduced. However, the internal droplet compositions, which were suggested to be related to the formation of particle morphologies, had not been explored. Herein, the ethanol-vapour-induced precipitation of multi-solvent droplets containing maltodextrin as the solute was used to analyse internal droplet compositions. The droplet mass and diameter profiles were obtained via an established single-droplet drying experiment, which mimicked the spray drying of droplets. Analysis revealed that the antisolvent concentration increased with time and was higher than solvent concentration towards the end of the process. It is interesting to find out that the final particle morphology was profoundly impacted by the ambient ethanol humidity and also how spontaneous the subsequent drying was during ethanol-vapour-induced precipitation of the solutes. The formation of the porous structure was favoured with the occurrence of spontaneous vaporization once the ethanol was present for precipitation. Therefore, low ethanol humidity (20% ERH in this study) was sufficient. In contrast, higher ethanol humidity (>70% ERH) was preferable to produce spherical particles. This study provides an insight into particle engineering to unveil the internal droplet conditions and physical phenomena during this unique process.     

Effects of spacing and arrangement of droplet on combustion characteristics of monodispersed suspended-droplet cluster model under microgravity

For bridging between knowledge on droplet combustion and spray combustion, an experimental study was performed on autoignition and combustion of multiple droplet clusters. The monodispersed suspended-droplet cluster (MSDC) model with which arrangement, spacing and initial diameter of the droplet are well controlled has been developed. The effects of spacing and arrangement of droplet on combustion characteristics of the MSDC model in a high-temperature air were examined using microgravity environment in a drop shaft. The ignition delay and the burning time increased with decreasing the droplet spacing, regardless of the droplet number and the model dimensions. Larger droplet number with three-dimensional (3D) hexagonal closest packing (HCP) structure model resulted in longer ignition delay and longer burning time. 3D cubic closest packing (CCP) structure model showed rather longer ignition delay and much shorter burning time than 2D model. For 3D HCP model, an individual flame which enveloped each droplet was formed whole in the combustion duration with larger droplet spacing, while the group flame was formed whole in the combustion duration with smaller droplet spacing. When the droplet spacing was in the intermediate range, each droplet was ignited to form the individual flame, and each flame merged into the group flame. The diameter of the burning sphere decreased at the beginning of combustion, and turned to increase afterward. The transition from the individual flame to the group flame occurred around the time when the burning sphere diameter reached its minimum. The burning sphere diameter relative to the model diameter increased with decreasing the droplet spacing in the middle stage of combustion.     

Mechanism of stabilization of location of a droplet cluster above the liquid-gas interface

We studied the influence of sizes of droplets, forming the ??droplet cluster?? dissipative structure, on their levitation height in the vapor-air flow, which appears when free surface of horizontal water layer is locally heated. A sharp decrease in the velocity of the vapor-air flow takes place at a distance from the surface comparable with the droplet diameter. Allowing for the aerodynamic nature of the droplet levitation, this peculiarity of the flow determines the high stability of location of the droplet cluster above the interface. Existence of droplets that are anomalously heavy in the slope of the Stokes levitation mechanism is described.     

Sessile droplet formation in the laser-induced forward transfer of liquids: A time-resolved imaging study

The formation process of sessile droplets in the laser-induced forward transfer of aqueous solutions was analyzed through time-resolved imaging. At the irradiation conditions which lead to the deposition of well-defined droplets, a cavitation bubble is generated in the laser irradiated area. Such bubble evolves into a high-speed liquid jet which propagates towards the receptor solid substrate. Once the jet impinges on the receptor substrate, liquid gently starts accumulating on the impact position, and the growth of a sessile droplet initiates. In a first stage, which only lasts a few microseconds, the forming droplet suffers a fast spreading process. Then, the jet continues feeding the forming droplet for some hundreds of microseconds, but the droplet diameter remains constant, and thus the contact angle increases. Finally, liquid feeding stops due to jet breakup, and the sessile droplet initiates a slow relaxation process in which its contact angle diminishes and its diameter increases. This deposition process results in the deposition of a single sessile droplet up to donor film-receptor substrate distances of the order of the millimeter. At higher separations, satellite droplets appear, and at even higher separations only randomly distributed small droplets are deposited.     

Evaluation of the splats properties and relation with droplets diameters in atomization process using a De Laval Nozzle

Properties of the powders developed during atomization process are essentially determined by process parameters. Experiments based on splat collection have been performed at different stages of the process evolution. Formation of splat formed as a result of impingement of the melted metallic droplets onto a substrate was studied. Splat characteristics have been determined from image analysis in function of process parameters and time progress. Droplet diameters were measured using laser Coulter analyzer. Direct relationships between splat diameter and droplet diameter were established. The atomization experiments point out the strong influence of two processing parameters (atomizing gas and melt nozzle diameter) on splat characteristics and particle size. It has been observed that increasing atomizing pressure leads to a decrease of mean splat diameter and width of the size distribution. Similar evolution was found for droplet diameter. Moreover, it is clearly shown that increasing melt nozzle diameter induces an increase of both splat diameters and droplet diameters. The results provide a better understanding of the influence of atomization parameters on the size distribution.     

Numerical simulation of gas-droplets mixing and spray evaporation in rotary spray desulfurization tower

Motion and evaporation of droplets significantly affect the semidry flue gas desulfurization efficiency and long-term operation. Both the flow field distribution and the heat and mass transfer in the spray towers are studied by numerical simulation, and the process of droplet motion and evaporation is analyzed in detail. Then, two indices, mixing variance and droplet mass-weighted life, are provided to quantify gas droplet mixing and the droplet group evaporation time. The simulation results show that the radial penetration distance of the droplets is longer with the diameter increase, and the appropriate swirl number improves the mixing between the flue gas and droplets. With the increase of droplet diameter and velocity, the droplet distribution in the tower is more widely, obtaining the optimum mixing variance. The droplet mass-weighted life is promoted linearly with the increase of average droplet diameter and the decrease of flue gas temperature. With flue gas temperature increase from 458 k to 488 K, the droplet mass-weighted life decreases linearly by 31%. In comparison, the initial droplet velocity and spray angle have a slight effect on the droplet mass-weighted life.     

Mixing of vaporizing droplets on liquid substrates caused by festoon instability

A new configuration for a microfluid mixer, in which a mixed volume in the form of a volatile liquid droplet rests on a layer of water, is proposed. The mixing occurs owing to the injection of festoons emerging in a droplet under the influence of evaporation themocapillary convection from the periphery of the droplet to its central part. A linear relationship between the injection rate and the injection layer temperature is established, and it is shown that a droplet has time to repeatedly mix during its lifetime.     

EHD喷印技术相关参数数值分析

目的对基于电-液耦合动力学原理(简称EHD)喷印技术的相关参数,进行锥射流和滴落模式下的数值分析研究。方法在锥射流模式中,对毛细凝结加热液体喷射的物理模型进行调整,以适用于EHD喷印;对滴落模式的液滴沉积过程,引入表面张力概念进行数值分析。运用数值法得到了锥射流的轮廓图,集中讨论了流量和净高度对射流直径的影响;重点研究了液滴直径与电压频率和液体表面张力之间的关系,并将理论结果与实验和经验数据进行了比较分析。结果锥射流模式在一定条件下,射流直径随着流量和净高度的增大而增加;在滴落模式中,得到的液滴直径随电压频率和流体表面张力的增大而减小,且数值分析得到的结果与实验结果相一致。结论对相关参数进行数值分析是对实验研究的补充,为EHD喷印技术研究提供了理论参考。     

Linear size gradient single layers of polymer-dispersed liquid crystal micrometer-sized droplets for diffractive optics

An experimental study of coherent light diffraction by wedge-formed single layers composed of liquid crystal (LC) micro-sized droplets dispersed in a transparent solid polymer matrix is reported. The micrometer-sized polymer-dispersed liquid crystal (PDLC) material contains prolate-ellipsoid-like LC droplets with a linear-gradient size distribution along the wedge slope. The droplet diameter in the films reaches several tens of micrometers, defined by the wedge. Such a droplet organization in a two-dimensional layer provides both spatial and electrical control of the coherent light diffraction by the LC/polymer interface.     

DVB泡沫微胶囊的制备方法

根据密度匹配乳液技术设计开发了一套用于微胶囊制备的三喷嘴乳粒发生器,利用该装置实现了空心泡沫微球的可控连续制备。以二乙烯基苯(DVB)的邻苯二甲酸二丁酯(DBP)溶液为油相(O),双蒸水与重水的混合液为内水相(W1),质量百分比为5%的聚乙烯醇(PVA)水溶液作为外水相(W2)制作出水/油/水(W1/O/W2)双重微乳液。以偶氮二异丁腈(AIBN)为引发剂,通过水平旋转水浴加热方式使DVB凝胶固化,采用CO2超临界法干燥,最终制得直径(1.0mm～4.0mm)和壁厚(90μm～360μm)可调的DVB微胶囊。利用扫描电镜对微胶囊的形貌进行了研究,并归纳出影响微胶囊的粒径大小及单分散性的因素。     

压电喷墨液滴撞击光滑壁面铺展行为的数值研究

目的 研究典型流体相关无量纲参数对墨滴在光滑承印物表面铺展行为的影响,确定各无量纲参数对铺展直径、铺展因子和稳定铺展时间的影响规律。方法 利用Ansys软件,建立墨滴撞击光滑壁面的数值计算模型,采用VOF模型追踪液滴形状,采用PISO算法计算压力速度耦合。引入韦伯数、雷诺数、奥内佐格数来分析墨滴撞击光滑承印物表面的铺展行为。结果 计算获得不同韦伯数、雷诺数、奥内佐格数下墨滴的最大铺展直径、最终平衡铺展直径、最大铺展因子和最终铺展时间。结论 韦伯数和雷诺数对墨滴最大铺展直径的影响较大,对最终平衡直径的影响较小。韦伯数或雷诺数越小,回缩阶段越短,越快达到平衡。韦伯数、雷诺数与最大铺展因子呈明显正相关。奥内佐格数对墨滴的最大铺展直径、最终平衡直径的影响都较小。奥内佐格数越小,回缩阶段越短,越快达到平衡,奥内佐格数与液滴最大铺展因子呈不明显的正相关性。     

Growth of InN and its effect on InGaN epilayer by metalorganic chemical vapor deposition

InN has been successfully grown on GaN with a thin InGaN intermediate layer by metalorganic chemical vapor deposition. A pyramid growth was observed for the InN with lateral size of about 270 nm and thickness of about 70-75 nm. This InN contributes to the green emission of the subsequently grown InGaN layer despite the V-pits formation on the surface. The InGaN intermediate layer serves to reduce the lattice mismatch between InN and GaN. Earlier attempt to grow InN directly in GaN resulted in indium droplet formation only.     

MALDI-TOF-MS analysis of droplets prepared in an electrodynamic balance: "wall-less" sample preparation

Methodology enabling mass spectral analysis of the composition of droplet(s) prepared in an electrodynamic balance (EDB) by matrix-assisted laser desorption/ionization (MALDI) is described. The dc field surrounding the electrodynamic balance was manipulated to eject single droplets at a time from the EDB thereby causing their deposition onto a MALDI sample plate precoated with matrix. When the laser was directed onto the droplet(s) and held stationary, marked gains in the signal-to-noise and signal-to-background ratios were realized with each subsequent mass spectrum due to the suppression of matrix cluster ion formation. Optical microscopy of the plate, after 1024 laser shots were fired at eight droplets that had been deposited one on top of the other, revealed a residual island of droplet matter (area approximately 3.1 x 10(-9) m2) inside the region where the crystalline matrix had been ablated away within the laser spot (area approximately 1.6 x 10(-8) m2). Removing the predried crystalline matrix layer and, instead, adding matrix into the starting solution was found to be a more effective means of suppressing matrix cluster ion formation. The chemical composition of the droplet(s) prepared in the EDB is discussed with regard to sample preconcentration, the images of the laser spot after MALDI, matrix cluster ion suppression, and the possibility for improved quantitation and detection limits by MALDI-TOF-MS.     

乳状液制备新工艺——膜乳化过程实验研究

用膜乳化系统制备了Ｏ／Ｗ型乳状液,考察了乳化时间、平均膜孔径、壁面剪应力、膜两侧压差和乳化剂等因素对乳化效果的影响．实验显示,分散相液滴平均直径不随乳化时间而变化;在此条件下,该直径约是膜平均孔径的５～１２倍．随着连续相一侧壁面剪应力的增大液滴平均直径减小,但当壁面剪应力大到一定值后,减小的幅度变得很小．增大膜平均孔径和膜两侧压差都将增加分散相透过膜的通量．此外,乳化剂分子的吸附速度越快,分散相液滴平均直径越小．     

高精度气体水雾含量测量方法的研究

研究了一种快速高精度测量气体中水雾含量的方法.当含有水雾的气体通过装有玻璃纤维的采样管时,多种过滤机制使水雾沉降到玻璃纤维表面,通过称量玻璃纤维滤筒的重量差,可计算出气体的水雾含量.分析结果表明:当玻璃纤维直径为5 μm时,其过滤层对水雾的收集效率大于99%;采用高纯度的玻璃纤维,可以减小其在烘箱中的失重.当玻璃纤维纯度为99.5%时,经7 h加热后,失重小于0.1 mg;玻璃纤维床层阻力和收集效率随液滴平均粒径增大而增加,对于平均粒径为1 μm 的水雾粒子,其收集效率大于99.5%.玻璃纤维过滤法比吸附法和光学法测量精度高,重复性和稳定性好,且测量结果不受环境和气体温度的影响.     

Preparation of TiO2 hollow microparticles by spraying water droplets into an organic solution of titanium tetraisopropoxide

Hollow, spherical TiO₂ microparticles several tens of micrometers in diameter were prepared by spraying water into an organic phase containing titanium tetraisopropoxide (TTIP) as a titanium source. The rapid hydrolysis of TTIP at the water-oil interface resulted in the formation of a TiO₂ shell covering the water droplet. Hexane and cyclohexane were better solvents than isopropanol for fabricating hollow spherical microparticles, suggesting the importance of immiscibility of the solvent with water in this synthesis method. The average particle size increased as the distance from the nozzle to the surface of the TTIP solution was increased. The shell thickness was reduced by the addition of ethanol to the sprayed water droplet. These results demonstrate the controllability of the structure of TiO₂ hollow microparticles, including the diameter and the shell thickness.     

Printing with Satellite Droplets

Despite their specific methodologies, all current noncontact printing techniques such as inkjet printing (IJP), involve the break‐up of a liquid meniscus during the separation of the ink droplet from the bulk ink reservoir. Often, the break‐up of a liquid meniscus results in the formation of one or more satellite droplet whose volumes are several orders of magnitude smaller than the primary droplet. Many attempts are directed to suppress or control the formation of satellite droplets because they blur the printing result. For the first time, a simple mechanism by which a single satellite droplet is exclusively formed and directed to the substrate by a gas stream while the primary droplet remains attached to a metal rod used for controlling the formation and break‐up of the meniscus is reported. High printing resolution is demonstrated by satellite droplets printing (SDP) without the need for small orifices which are prone to clogging. Furthermore, the droplet generation from a large orifice enables SDP to handle viscous inks which has remained challenging for traditional IJP.